Osteomyelitis

The bony skeleton is divided into two parts: the axial skeleton and the appendicular skeleton. The axial skeleton is the central core unit, consisting of the skull, vertebrae, ribs, and sternum; the appendicular skeleton comprises the bones of the extremities. The human skeleton consists of 213 bones, of which 126 are part of the appendicular skeleton, 74 are part of the axial skeleton, and six are part of the auditory ossicles.

Hematogenous osteomyelitis most commonly involves the vertebrae, but infection may also occur in the metaphysis of the long bones, pelvis, and clavicle. Vertebral osteomyelitis usually involves two adjacent vertebrae with the corresponding intervertebral disk. (See the image below.) The lumbar spine is most commonly affected, followed by the thoracic and cervical regions. A form of hematogenous osteomyelitis that is more common occurs in infants and children and develops in the metaphysis.

Posttraumatic osteomyelitis begins outside the bony cortex and works its way in toward the medullary canal; it is typically found in the tibia but can occur in any bone. Contiguous-focus osteomyelitis often occurs in the bones of the feet in patients with diabetes mellitus and vascular compromise.

For more information about the relevant anatomy, see Skeletal System Anatomy in Adults and Osteology (Bone Anatomy).

Bone is normally resistant to infection. However, when microorganisms are introduced into bone hematogenously from surrounding structures or from direct inoculation related to surgery or trauma, osteomyelitis can occur. Bone infection may result from the treatment of trauma, which allows pathogens to enter bone and proliferate in the traumatized tissue. When bone infection persists for months, the resulting infection is referred to as chronic osteomyelitis and may be polymicrobial. Although all bones are subject to infection, the lower extremity is most commonly involved.[1, 2]  Osteomyelitis can be acute, subacute, or chronic, depending on its duration.

Important factors in the pathogenesis of osteomyelitis include the following:

• Virulence of the infecting organism
• Underlying disease
• Immune status of the host
• Type, location, and vascularity of the bone

Bacteria may possess various factors that may contribute to the development of osteomyelitis. For example, factors promoted by S aureus may promote bacterial adherence, resistance to host defense mechanisms, and proteolytic activity.[3]

Hematogenous osteomyelitis

In adults, the vertebrae are the most common site of hematogenous osteomyelitis, but infection may also occur in the long bones, pelvis, and clavicle.[4]

Primary hematogenous osteomyelitis is more common in infants and children, usually occurring in the long-bone metaphysis. However, it may spread to the medullary canal or into the joint. When infection extends into soft tissue, sinus tracts eventually will form. Secondary hematogenous osteomyelitis is more common and can develop from any primary focus of infection or from reactivation of a previous infection in the presence of immunocompromised status. In adults, the location is also usually metaphyseal.[4]

The metaphysis is the region of a long bone between the epiphysis and the diaphysis. This part contains the growth plate and, because of its vascular characteristics, is the preferred region of hematogenous osteomyelitis. In particular, children younger than 5 years are susceptible to it due to the abundance of blood vessels with leaky endothelium that end in capillary loops.

In the long bones, the blood supply penetrates the bone at the midshaft but then splits into two segments traveling to each metaphyseal endplate. These vessels are terminal, and bacteria enter through the nutrient artery and lodge at the valveless capillary loops in the junction between the metaphysis and the physis. The blood flow through capillary loops and sinusoidal veins at the epiphyseal-metaphyseal junction is very slow, allowing the bacteria to establish and proliferate. This region does not permit good penetration of white blood cells and other immune mediators, thus serving to protect the bacteria.

As the bacteria continue to multiply, the scarce functioning phagocytes release enzymes that lyse the bone, thereby creating an inflammatory response. This results in formation of pus (a protein-rich exudate containing dead phagocytes, tissue debris, and microorganisms), increasing the intramedullary pressure in the area and thus further limiting the already compromised blood supply. The stasis and cytokine activity promote clot formation in the blood vessels, leading to bone ischemia and then necrosis.

Infection then spreads into the vortex through the Haversian system and Volkmann canals and finally into the subperiosteal space. The infection and the formation of pus in this region strip the periosteum from the shaft and stimulate an osteoblastic response. As a result, new bone is formed in response to the periosteal stripping. Part of the necrotic bone may separate; this is referred to as the sequestra.

In a severe infection, the entire shaft is encased in a sheath of new bone, which is referred to as the involucrum. Once this occurs, a major part of the shaft has been deprived of its blood supply.The involucrum can have openings called cloacae, which allow pus to escape from the bone, leading to fulminant disease.[5, 6, 7, 8]

In the 0- to 18-month age range, the epiphysis and the metaphysis have communicating vessels that result in direct extension of infection from metaphysis to epiphysis. Once the infection extends into the epiphysis, it leads to destruction of the epiphyseal cartilage and secondary ossification center, resulting in permanent growth impairment. The extension into the epiphysis also leads to a higher incidence of septic arthritis.[6]

S aureus is the pathogenic organism most commonly recovered from bone, followed by Pseudomonas and Enterobacteriaceae. Organisms less commonly involved include anaerobe gram-negative bacilli. Intravenous (IV) drug users may acquire pseudomonal infections. Gastrointestinal or genitourinary infections may lead to osteomyelitis involving gram-negative organisms. Dental extraction has been associated with viridans streptococcal infections. In adults, infections often recur and usually present with minimal constitutional symptoms and pain. Acutely, patients may present with fever, chills, swelling, and erythema over the affected area.[2, 9]

Contiguous-focus and posttraumatic osteomyelitis

The initiating factor in contiguous-focus osteomyelitis often consists of direct inoculation of bacteria via trauma, surgical reduction and internal fixation of fractures, prosthetic devices, spread from soft-tissue infection, spread from adjacent septic arthritis, or nosocomial contamination. Infection usually results approximately 1 month after inoculation.

Posttraumatic osteomyelitis more commonly affects adults and typically occurs in the tibia. The most commonly isolated organism is S aureus. At the same time, local soft-tissue vascularity may be compromised, leading to interference with healing. Compared with hematogenous infection, posttraumatic infection begins outside the bony cortex and works its way in toward the medullary canal. Low-grade fever, drainage, and pain may be present. Loss of bone stability, necrosis, and soft-tissue damage may lead to a greater risk of recurrence.[4, 9]

Septic arthritis may lead to osteomyelitis. Abnormalities at the joint margins or centrally, which may arise from overgrowth and hypertrophy of the synovial pannus and granulation tissue, may eventually extend into the underlying bone, leading to erosions and osteomyelitis. One study demonstrated that septic arthritis in elderly persons most commonly involves the knee and that, despite most of the patients having a history of surgery, 38% developed osteomyelitis.

Septic arthritis is more common in neonates than in older children and is often associated with metaphyseal osteomyelitis. Although rare, gonococcal osteomyelitis may arise in a bone adjacent to a chronically infected joint.[10, 11]  In children the intra-articular position of some metaphyses makes them prone to the development of secondary septic arthritis (eg, in the knee, hip, or shoulder).

Many patients with vascular compromise, as in diabetes mellitus, are predisposed to osteomyelitis owing to an inadequate local tissue response.[4]

Infection in neuropathic or vascular-compromised feet is most often caused by minor trauma to the feet with multiple organisms isolated from bone, including Streptococcus species, Enterococcus species, coagulase-positive and -negative staphylococci, gram-negative bacilli, and anaerobic organisms. Fungal infections are also known in neuropathic feet with osteomyelitis. Foot ulcers allow bacteria to reach the bone. Patients may not experience any resulting pain, because of peripheral neuropathy, and may present with a perforating foot ulcer, cellulitis, or an ingrown toenail.

Treatment of osteomyelitis in diabetic feet is multidisciplinary and prolonged, involving complex debridements, soft-tissue cover, and antimicrobial and antifungal treatments.

Vertebral osteomyelitis

The incidence of vertebral osteomyelitis generally increases progressively with age, with most affected patients being older than 50 years. Although devastating complications may result from a delay in diagnosis, vertebral osteomyelitis has rarely been fatal since the development of antibiotics. However, the elderly have higher rates of bacteremia and infective endocarditis at the time of diagnosis, and they have a higher mortality than younger patients with osteomyelitis do.[12]

The infection usually originates hematogenously and generally involves two adjacent vertebrae with the corresponding intervertebral disk. The lumbar spine is most commonly affected, followed by the thoracic and cervical regions.[4, 1]  

Potential sources of infection include skin, soft tissue, respiratory tract, genitourinary tract, infected intravenous (IV) sites, and dental infections. S aureus is the most commonly isolated organism. However, Pseudomonas aeruginosa is more common in IV drug users.

Most patients with vertebral osteomyelitis present with localized pain and tenderness of the involved vertebrae with a slow progression over 3 weeks to 3 months. Fever may be present in approximately 50% of patients. Some 15% of patients may have motor and sensory deficits. Laboratory studies may reveal peripheral leukocytosis and an elevated erythrocyte sedimentation rate (ESR). Extension of the infection may lead to abscess formation.[4]

Osteomyelitis in children

Acute hematogenous osteomyelitis usually occurs after an episode of bacteremia in which the organisms inoculate the bone. The organisms most commonly isolated in these cases include S aureus, Streptococcus pneumoniae, and Haemophilus influenza type b (less common since the use of vaccine for H influenza type b). The incidence of Kinsella kingae infection is increasing; such infection is a common cause of osteomyelitis in children younger than 4 years.[13]

Acute hematogenous S aureus osteomyelitis in children can lead to pathologic fractures. This can occur in about 5% of cases, with a 72-day mean time from disease onset to fracture.[14]

In children with subacute focal osteomyelitis (see the image below), S aureus is the most commonly isolated organism.

Gram-negative bacteria such as Pseudomonas species or Escherichia coli are common causes of infection after puncture wounds of the feet or open injuries to bone. Anaerobes can also cause bone infection after human or animal bites.

Osteomyelitis in the neonate results from hematogenous spread, especially in patients with indwelling central venous catheters. The common organisms in osteomyelitis of the neonate include those that frequently cause neonatal sepsis—namely, group B Streptococcus species—and E coli. Infections in the neonate can involve multiple osseous sites, and approximately half of the cases also involve eventual development of septic arthritis in the adjacent joint.

Children with sickle cell disease are at an increased risk for bacterial infections, and osteomyelitis is the second most common infection in these patients. The most common organisms involved in osteomyelitis in children with sickle cell anemia include Salmonella species, S aureus, Serratia species, and Proteus mirabilis.

The major causes of osteomyelitis include the following:

• Primary - Hematogenous
• Secondary - Secondary to trauma, surgery, or sepsis of any etiology

Approximately 20% of adult cases of osteomyelitis are hematogenous, which is more common in males for unknown reasons.[4]

The incidence of spinal osteomyelitis was estimated to be 1 in 450,000 in 2001. In subsequent years, however, the overall incidence of vertebral osteomyelitis is believed to have increased as a consequence of IV drug use, increasing age of the population, and higher rates of nosocomial infection due to intravascular devices and other instrumentation.[15, 16] The overall incidence of osteomyelitis is higher in developing countries.

Acute osteomyelitis is a surgical and medical emergency necessitating immediate antibiotic therapy, surgical drainage, and secondary procedures as needed. The prognosis of osteomyelitis depends on etiology, patient factors, and time to institution of suitable treatment, as well as a host of other factors (eg, location, organism, and antibiotic susceptibility and sensitivity).

Chronic osteomyelitis is prolonged in its course and can be extremely debilitating, with episodes of recurring infection interspersed with quiescent periods. The organisms become increasingly resistant, and local treatment carries more value than systemic therapy in the absence of acute exacerbation.

The complications of osteomyelitis, with all the comorbid factors and etiologic factors having been taken into account, can be extremely varied and may include sepsis and multiorgan dysfunction, stiffness, deformity, chronic discharging sinuses, limb-length discrepancies, chronic pain, loss of function, amputation, and even secondary cancers in sinus sites.

Patients who are diagnosed with bone and joint infection must be counseled specifically with reference to its short- and long-term consequences. Parents of children with osteomyelitis must be counseled regarding its possible effects on the growth plate and on adjacent joints and regarding the need for careful long-term follow-up until maturity. Patients with an implant must be counseled as to the possible nature of the infection, biofilms and their roles, the need for debridement or more radical measures (eg, implant removal), and the need for and effects of long-term antibiotic therapy. 

Acute osteomyelitis requires that the clinician maintain a high degree of suspicion so as to minimize delayed diagnosis and the consequences thereof. Osteomyelitis is often diagnosed clinically on the basis of nonspecific symptoms such as fever, chills, fatigue, lethargy, or irritability. The classic signs of inflammation, including local pain, swelling, or redness, may also occur and usually disappear within 5-7 days.[1]  

Chronic posttraumatic osteomyelitis requires a detailed history for diagnosis, including information regarding the initial injury and previous antibiotic and surgical treatment. Weightbearing and function of the involved extremity are typically disturbed. Local pain, swelling, erythema, and edema may also be reported.[2]

Before the introduction of penicillin in the 1940s, management of osteomyelitis was mainly surgical, consisting of extensive debridement, saucerization, and wound packing, after which the affected area is left to heal by secondary intention, resulting in high mortality from sepsis. Since the availability of antibiotics, mortality from osteomyelitis, including staphylococcal osteomyelitis, has improved significantly.[17]

 

On physical examination, scars or local disturbance of wound healing may be noted along with the cardinal signs of inflammation.[2] Range of motion ROM), deformity, and local signs of impaired vascularity are also sought in the involved extremity. If periosteal tissues are involved, point tenderness may be present.[9]

In children, the clinical presentation of osteomyelitis can be challenging for physicians because it can present with only nonspecific signs and symptoms and because the clinical findings are extremely variable. Children may present with decreased movement and pain in the affected limb and adjacent joint, as well as edema and erythema over the involved area. In addition, children may also present with fever, malaise, and irritability. Newborns with osteomyelitis may demonstrate decreased movement of a limb without any other signs or symptoms.

The most common complication in children with osteomyelitis is recurrence of bone infection. Complications as a result of acute hematogenous osteomyelitis due to methicillin-resistant S aureus (MRSA) is often attributed to more complicated illness, as compared with osteomyelitis caused by methicillin-sensitive S aureus (MSSA) or any other organism. Potential complications of osteomyelitis include the following:

• Septic pulmonary emboli
• Deep vein thrombosis in the region near the infected bone
• Intraosseous and subperiosteal abscess
• Pathologic fracture - This is a rare complication and can occur as a result of extreme bone destruction or thinning of the cortex
• Growth disturbance when epiphyseal plate is involved
• Bone deformity
• Disseminated infection with multiorgan failure resulting in sepsis

These complications contribute to longer median hospital stay and a higher likelihood that surgical intervention will be needed to drain deep abscesses. The severity of the disease can relate to S aureus virulence factor (also known as PVL), which is a cytotoxin that destroys leukocytes. In general, complications are more likely to arise when proper diagnosis and initiation of therapy are delayed. Such delay contributes to significant morbidity, which can include longitudinal bone growth and angular deformity, as well as sepsis and chronic infection. 

With a diagnosis of acute hematogenous osteomyelitis, it is crucial to establish a 2-week follow-up after discharge to reduce the likelihood of a complication and to ensure that there is continued clinical improvement. Children who developed osteomyelitis near the growth plate are at increased risk for bone deformities and growth impairment; therefore, they must be followed clinically and radiographically on a yearly basis until they reach skeletal maturity to ensure that no further interventions are required to address the potential sequelae.[18]

Patient must receive proper education about the duration of therapy and the importance of compliance with treatment recommendations to promote healing and to decrease the rate of recurrence.[5, 17]

Adverse outcomes are common with delayed treatment; however, even when appropriate treatment is provided, chronic infection may still develop in 5-10% of cases. Chronic osteomyelitis presents 6 weeks or longer after a bone infection, and its characteristics include bone destruction and formation of sequestra. Leading complications resulting from chronic osteomyelitis include sinus tracts and extension to adjacent structures, as well as abscess formation. One complication that must not be missed is malignant transformation (ie, Marjolin ulcer). This typically has a latency period of 27-30 years from the initial onset of osteomyelitis, and it involves aggressive squamous cell carcinoma (SCC).[19]

When centrally placed intravenous (IV) catheters are used in cases that require prolonged IV antibiotic treatment, catheter-associated complications can occur. However, the use of peripherally inserted central venous catheters (PICC lines) has reduced the frequency of these complications.

In a study of 17,238 Taiwanese patients newly diagnosed with chronic osteomyelitis from 2000 to 2008 who were identified on the basis of Taiwanese National Health Insurance (NHI) inpatient claims, Tseng et al found chronic osteomyelitis to be associated with an increased risk of dementia, particularly among the younger patients studied.[20]

A complete blood count (CBC) is useful for evaluating leukocytosis and anemia. Leukocytosis is common in acute osteomyelitis before therapy. The leukocyte count rarely exceeds 15,000/µL acutely and is usually normal in chronic osteomyelitis. The erythrocyte sedimentation rate (ESR) and the C-reactive protein (CRP) level are usually increased.[24, 2, 25] In metastatic and some metabolic bone disease, alkaline phosphatase (ALP), calcium, and phosphate are elevated, but they are within normal limits in osteomyelitis.[26]

Blood cultures are positive in only 50% of cases of osteomyelitis.[9] They should be obtained before or at least 48 hours after antibiotic treatment. Although sinus tract cultures do not predict the presence of gram-negative organisms, they are helpful for confirming S aureus.

The American College of Radiology (ACR) has published imaging guidelines for the diagnosis of suspected osteomyelitis, septic arthritis, and soft-tissue infections in cases not involving the spine or the diabetic foot.[27]  (See Guidelines.)

Radiography

Conventional radiography is the initial imaging study at presentation of acute osteomyelitis. It is helpful to interpret current and old radiographs together. (See the image below.)

Radiographic findings include periosteal thickening or elevation, as well as cortical thickening, sclerosis, and irregularity. Other changes include loss of trabecular architecture, osteolysis, and new bone formation. These changes may not be evident until 5-7 days in children and 10-14 days in adults. Plain films show lytic changes after at least 50-75% of the bone matrix is destroyed. Therefore, negative radiographic studies do not exclude the diagnosis of acute osteomyelitis.

Healing fractures, cancers, and benign tumors may appear similarly on plain film. Subtle changes may indicate contiguous-focus or chronic osteomyelitis.[4, 2, 9, 28]

Computed tomography

Computed tomography (CT) is useful for guiding needle biopsies in closed infections and for preoperative planning to detect osseous abnormalities, foreign bodies, or necrotic bone and soft tissue. It may assist in the assessment of bony integrity, cortical disruption, and soft-tissue involvement. It may also reveal edema. Intraosseous fistula and cortical defects that lead to soft tissue sinus tracts are also demonstrated on CT.

Although CT may play a role in diagnosis of osteomyelitis, the scatter phenomenon may result in significant loss of image resolution when metal is near the area of inflammation.[4, 2, 9]

Magnetic resonance imaging

Magnetic resonance imaging (MRI) is a very useful modality in detecting osteomyelitis and gauging the success of therapy because of its high sensitivity and excellent spatial resolution. The extent and location of osteomyelitis is demonstrated along with pathologic changes of bone marrow and soft tissue.[4] (See the image below.)

MRI shows a localized marrow abnormality in osteomyelitis. T1-weighted images typically show decreased signal intensity, whereas T2-weighted images produce increased signal intensity.[4] Increased intensity on T2-weighted images may indicate sinus tracts, which extend from marrow and bone to skin through soft tissue. A decreased intensity on T1-weighted images with no change on T2-weighted images may indicate surgical or posttraumatic scarring of bone marrow.

Ultrasonography

On ultrasonography (US), the presence of fluid collection adjacent to the bone without intervening soft tissue usually suggests osteomyelitis. Other findings on US include elevation and thickening of the periosteum. US may also be useful in cases with orthopedic hardware or in patients who are unable to undergo MRI.[29, 30, 31, 28]

Nuclear medicine imaging

Three-phase bone scanning is helpful in evaluating acute osteomyelitic and doubtful diskitis. However, the specificity of this procedure is decreased in secondary osteomyelitis. The bone scan may reveal increased metabolic activity in osteomyelitis, but this finding is indistinguishable from those seen with posttraumatic injury or following surgery or cancer.[4, 1] (See the image below.)

One approach makes use of white blood cells (WBCs) labeled with technetium-99m (99mTc) hexamethylpropylene amine oxime (99mTc-HMPAO) or indium-111 (111In) oxime. This method, when used in the combination of 111In-oxime WBC scanning with 99mTc-sulfur colloid bone marrow scanning, is helpful for evaluating infections of hip prostheses. Isotope accumulates in areas of increased blood flow and new bone formation in the 99mTc polyphosphate scan.

When the imaging is present on the labeled WBC scan but not on the 99mTc bone marrow scan, the test is positive for osteomyelitis. A negative test result may indicate an impaired blood supply to the affected area. When red marrow is present (ie, axial skeleton and spine), WBC scanning is less sensitive for imaging.[4, 1, 28]

Gallium citrate attaches to transferrin, which then leaks into inflamed areas from the bloodstream. Increased uptake may occur in infection, cancer, and sterile inflammatory conditions. Performing a 99mTc scan along with the gallium-67 (67Ga) citrate scan may help distinguish bone and soft-tissue inflammation and show bone detail.[4, 1] However, the scan is most useful in cases of spondylodiskitis.[28]

In the assessment of inflammation of spinal lesions, 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG) positron emission tomography (PET) may provide high-resolution tomographic images and may represent an alternative to 67Ga citrate scanning.[1] 18F-FDG PET scans have high sensitivity and specificity (97.5% and 86.3%, respectively) in detecting musculoskeletal infections. However, the specificity drops in cases of suspected knee prosthesis infections.[32]

Bone biopsy leads to a definitive diagnosis by isolation of pathogens directly from the bone lesion.[9]  Bone biopsy should be performed through uninfected tissue and either before the initiation of antibiotics or more than 48 hours after discontinuance.

Open or percutaneous needle bone biopsy with histopathologic examination and culture is the routine for the diagnosis of osteomyelitis. This procedure may not be necessary if blood cultures are positive with consistent radiologic findings.

When clinical suspicion is high but blood cultures and needle biopsy have yielded negative results, a repeat needle biopsy or an open biopsy should be performed. A bone sample can be collected at the time of debridement for histopathologic diagnosis in patients with compromised vasculature. To obtain accurate cultures, bone biopsy must be performed through uninvolved tissue. Cultures of the sinus tract may be useful if S aureus and Salmonella species are isolated.[33, 34]

Acute osteomyelitis presents with acute inflammatory cells, edema, vascular congestion, and small-vessel thrombosis. In early disease, infection extends into the surrounding soft tissue, which compromises the vascular supply to the bone, as well as host response, surgery, and/or antibiotic therapy.

Large areas of dead bone may form if both medullary and periosteal blood supplies are compromised. Necrotic bone shows extensive resorption and inflammatory exudates on bone biopsy and appears whiter than living bone owing to the loss of blood supply. The development of granulation tissue occurs at the surface of dead bone, which is broken down by proteolytic enzymes, including polymorphonuclear leukocytes, macrophages, and osteoclasts. This occurs most rapidly at the junction of living and necrotic bone. A sequestrum is formed when dead cortical bone is gradually detached from living bone.

Chronic osteomyelitis presents with pathologic findings of necrotic bone, formation of new bone, and polymorphonuclear leukocyte exudation, which is joined by large numbers of lymphocytes, histiocytes, and occasional plasma cells.

The formation of new bone occurs over weeks or months as a vascular reaction to the infection. New bone arises from the surviving fragments of periosteum, endosteum, and cortex in the region of infection along the intact periosteal and endosteal surfaces. It may also occur when periosteum forms an involucrum, which is dead bone surrounded by a sheath of living bone. Involucrum may lead to sinus tracts due to perforations that allow pus to enter surrounding soft tissues and ultimately skin surface. A new shaft forms as the density and thickness of involucrum increases.

As a result of inflammatory reaction and atrophy disuse during the active period of osteomyelitis, surviving bone in the area of infection usually becomes osteoporotic. Bone density increases partially from reuse as the infection subsides and extensive transformation of bone may occur to conform to areas of new mechanical stresses. Over time, old living bone and newly formed bone may appear similar and might be indistinguishable, especially in children.

Two classification systems are commonly used for osteomyelitis.

In 1970, Waldvogel et al classified bone infections on the basis of pathogenesis and proposed the original osteomyelitis staging system. This system classifies bone infections as either hematogenous or osteomyelitis secondary to a contiguous focus of infection. Contiguous-focus osteomyelitis is further classified according to the presence or absence of vascular insufficiency. Both hematogenous and contiguous-focus osteomyelitis may then be classified as either acute or chronic.[35]

In 2003, Cierny-Mader et al developed their staging system, which at present is more commonly used. This system considers host immunocompetence in addition to anatomic osseous involvement and histologic features of osteomyelitis.[36, 1]  The first part of the system specifies four stages, as follows:

• Stage 1 disease involves medullary bone and is usually caused by a single organism
• Stage 2 disease involves the surfaces of bones and may occur with deep soft-tissue wounds or ulcers
• Stage 3 disease is an advanced local infection of bone and soft tissue that often results from a polymicrobially infected intramedullary rod or open fracture; stage 3 osteomyelitis often responds well to limited surgical intervention that preserves bony stability
• Stage 4 osteomyelitis represents extensive disease involving multiple bony and soft tissue layers; stage 4 disease is complex and requires a combination of medical and surgical therapies, and postoperative stabilization may be needed if the infected bone is an essential weightbearing bone

The second part of the Cierny-Mader classification system describes the physiologic status of the host, as follows:

• Class A hosts have normal physiologic, metabolic, and immune functions
• Class B hosts are systemically (Bs) or locally (Bl) immunocompromised; individuals with local and systemic immune deficiencies are labeled as ‘‘Bls’’
• In class C hosts, treatment poses a greater risk of harm than osteomyelitis itself; the state of the host is the strongest predictor of osteomyelitis treatment failure, and thus the physiologic class of the infected individual is often more important than the anatomic stage ^[9]

Other classification systems have been proposed for long-bone osteomyelitis. The Gordon classification classifies long-bone osteomyelitis on the basis of osseous defects, using infected tibial nonunions and segmental defects, as follows[37] :

• Type A includes tibial defects and nonunions without significant segmental loss
• Type B includes tibial defects greater than 3 cm with an intact fibula
• Type C includes tibial defects of greater than 3 cm in patients without an intact fibula

The Ger classification is used to address the physiology of the wound in osteomyelitis, which is categorized as follows[38, 39] :

• Simple sinus
• Chronic superficial ulcer
• Multiple sinuses
• Multiple skin-lined sinuses

Bone infection persists if appropriate wound management is not undertaken. It is important to cover open tibial fractures with soft tissue early in the disease to prevent infection and ulceration.

The Weiland classification categorizes chronic osteomyelitis as a wound with exposed bone, positive bone culture results, and drainage for more than 6 months.[40] This system also considers soft tissue and location of affected bone. It does not recognize chronic infection if wound drainage lasts less than 6 months. Weiland et al specified the following three types:

• Type I osteomyelitis was defined as open exposed bone without evidence of osseous infection but with evidence of soft-tissue infection
• Type II osteomyelitis showed circumferential, cortical, and endosteal infection, demonstrated on radiographs as a diffuse inflammatory response, increased bone density, and spindle-shaped sclerotic thickening of the cortex; other radiographic findings included areas of bony resorption and often a sequestrum with a surrounding involucrum
• Type III osteomyelitis revealed cortical and endosteal infection associated with a segmental bone defect

The Kelly classification considers the following types of osteomyelitis in adults:

• Hematogenous osteomyelitis
• Osteomyelitis in a fracture with union
• Osteomyelitis in a fracture with nonunion
• Postoperative osteomyelitis without fracture

This system emphasizes the etiology of the infection along with its relation to fracture healing.[41, 38]

The principles of management of osteomyelitis necessitate a multipronged, multidisciplinary approach that may involve a team consisting of the following:

• Orthopedic surgeon
• Infectious disease consultant
• Plastic surgeon
• Microbiologist
• Others as needed

This approach should first determine whether the disease is acute, chronic, or an acute exacerbation of a chronic disease or (in some cases) a partially treated subacute osteomyelitis. Acute osteomyelitis must be treated surgically to drain pus and prevent bone necrosis. Antibiotics suited to the patient's age and the organism are given to control hematogenous spread and to treat the local infection. In other words, antibiotics save life, and surgery helps save bone.

Debridement of necrotic tissues, removal of foreign materials, and sometimes skin closure of chronic unhealed wounds are necessary in some cases.

Although vertebral osteomyelitis does not usually necessitate surgical treatment, indications include failure to respond to antimicrobial therapy, neural compression, spinal instability, or drainage of epidural or paravertebral abscesses.

The Infectious Diseases Society of America (IDSA) has published clinical practice guidelines for the diagnosis and treatment of native vertebral osteomyelitis in adults, including recommendations regarding antibiotic therapy and surgical intervention (see Guidelines).[42]

Antibiotic treatment should be based on the identification of pathogens from bone cultures at the time of bone biopsy or debridement.[1, 4] Bone cultures are obtained first, and suspected pathogens are then covered by initiation of a parenteral antimicrobial treatment. However, treatment may be modified once the organism is identified. Parenteral and oral antibiotics may be used alone or in combination, depending on microorganism sensitivity results, patient compliance, and infectious disease consultation.

Prophylactic treatment with the bead pouch technique has been suggested in open fractures to reduce the risk of infection. Systemic antibiotics supplemented with antibiotic beads are preferred to systemic antibiotics alone.

Local antibiotic therapy with gentamicin-impregnated Septopal beads, though available in Europe, has been controversial.[43]  Factors involved in the debate include the length of implantation, the need for removal, and the choice of nonabsorbable versus bioabsorbable delivery vehicles. Prolonged implantation of antibiotic beads and spacers remains controversial owing to the risk of secondary infection and development of resistant organisms. Secondary infection stems from the beads, which may serve as a foreign body upon complete elution of antibiotic.

Traditionally, antibiotic treatment of osteomyelitis has consisted of a 4- to 6-week course.[4] Animal studies and observations show that bone revascularization following debridement takes about 4 weeks. However, if all infected bone is removed, as in forefoot osteomyelitis, antibiotic therapy can be shortened to 10 days.[44]

Oral antibiotics that have been proved to be effective include clindamycin, rifampin, trimethoprim-sulfamethoxazole, and fluoroquinolones. Clindamycin is given orally after initial intravenous (IV) treatment for 1-2 weeks and has excellent bioavailability. It is active against most gram-positive bacteria, including staphylococci. Linezolid is active against methicillin-resistant staphylococci and vancomycin-resistant Enterococcus. It inhibits bacterial protein synthesis, has excellent bone penetration, and is administered IV or orally.

Oral quinolones are often used in adults for gram-negative organisms. Quinolones have excellent oral absorption and may be used as soon as patient is able to take them. Rifampin has an optimal intercellular concentration and a good sensitivity profile for methicillin-resistant staphylococci. It is used in combination with cell wall–active antibiotics to achieve synergistic killing and to avoid rapid emergence of resistant strains.

Empiric therapy is necessary when it is not possible to isolate organisms from the infection site.[1] Hospital-acquired infections are usually derived from methicillin-resistant staphylococci. Infections contracted outside the hospital are often polymicrobial with the presence of gram-negative bacteria.

Infection may fail to improve, owing to the ability of bacteria to resist antibiotics. Some bacteria, such as S epidermidis in prosthesis infections, adhere to a biofilm that protects the organism from phagocytosis and impedes delivery of the antibiotic. The use of rifampin in combination with other antibiotics has been found to be more effective than monotherapy for treating infection associated with surgical hardware.[1, 45]

Suppressive antibiotic therapy should also be directed by bone culture and is given orally when surgery is contraindicated.[4] Good bioavailability, low toxicity, and adequate bone penetration are important factors in treatment. If the infection recurs after 6 months of suppressive antibiotic treatment, a new lifelong regimen of suppressive therapy may be tried.

Extensive studies of suppressive therapy with administration of rifampin, ofloxacin, fusidic acid, and trimethoprim-sulfamethoxazole for 6-9 months have been performed in patients with infected orthopedic implants. Studies have shown that, after discontinuance of antibiotics, no recurrence of infection occurred in 67% of patients treated with trimethoprim-sulfamethoxazole, 55% of patients treated with rifampin and fusidic acid, and 50% of patients treated with rifampin and ofloxacin.[4]

The Ilizarov technique is usually well tolerated by the patient, with little associated pain. A few complications that have been reported include pin-tract infections and cellulitis, flexion contractures above and below the frame, limb edema, and bone-fragment rotation with malunion.[46]

During the course of treatment with the Ilizarov technique, patients have a high emotional and physical burdens. However, these symptoms improve, and patients are similar to the general population postoperatively. Appropriate patient counseling regarding the psychological impact of this treatment is needed.[47]

The complication rate may be decreased by future efforts to improve the Ilizarov method.[48]  Some goals include improving the technique to prevent pin-track infections and osteomyelitis, premature or delayed consolidation of bone, angular or axial deviation of the new bone, joint contracture or instability, neurovascular compromise, and psychological adjustment reactions.

Preoperative planning

The Cierny-Mader classification system (see Workup) plays an important role in guiding treatment. As noted, stage 1 and 2 disease usually do not require surgical treatment, whereas stage 3 and 4 respond well to surgical treatment. In Cierny-Mader class C hosts, treatment may be more harmful than the osteomyelitis itself.[9]

Operative treatment consists of the following[4] :

• Adequate drainage
• Extensive debridement of necrotic tissue
• Management of dead space
• Adequate soft-tissue coverage
• Restoration of blood supply

When a fracture and stable hardware are involved, surgery is used to treat a residual infection after suppressing the infection until the fracture heals. Techniques involve second-stage hardware removal followed by treatment of an infected nonunion, often with an external fixator. External fixators, plates, screws, and rods may be used to restore skeletal stability at the infection site.[4] Because hardware tends to become secondarily infected, external fixation is preferred to internal fixation.

Remission or cure is most likely with extensive debridement, obliteration of dead space, removal of any hardware, and appropriate antibiotic therapy.

Debridement of all nonviable or infected tissue is critical because retained necrotic or infected debris can result in osteomyelitis recurrence. Bone debridement is performed until punctuate bleeding is noted.[4] The remaining tissue is still considered contaminated even after adequate debridement of necrotic tissue. Studies have shown that marginal resection may be sufficient in normal hosts. However, in compromised hosts, extensive resection seems to be much more important.

The term dead space refers to the soft-tissue and bony defect left behind after debridement.[4] Appropriate management of this space is necessary to reduce the risk of persistent infection from poor vascularization of the area and to maintain the integrity of the skeletal part.

Dead space must be filled with durable vascularized tissue, sometimes from the fibula or ilium. Antibiotic-impregnated beads may be used for temporary sterilization of dead space. Vancomycin, tobramycin, and gentamicin are some of the common antibiotics used in these beads. Within 2-4 weeks, the beads may be replaced with cancellous bone graft.

Because two major aims of surgical treatment are resection of necrotic bone and thorough debridement of intraosseous and soft-tissue fistula, computed tomography (CT) is sometimes performed for the purpose of planning a surgical intervention and guiding surgery. Preoperatively, CT is helpful for characterizing bone quality, demonstrating intraosseous fistula, and detecting devitalized bone areas or cortical defects that lead to soft-tissue sinus tracts.[2]

When osteomyelitis involves a fracture, it is also important to include a workup to be sure the fracture has healed. Antibiotic-impregnated beads may be used as an effective measure to maintain sterile dead space until a definitive surgical procedure can be performed.

In order to apply the Ilizarov method successfully and to prevent damage to vital nerves and blood vessels, preoperative planning is helpful, with careful attention to "safe zones" during wire insertion. It is important to adjust the skin to prevent tension on the skin-wire interface. Correction of the deformity or lengthening is better achieved by appropriately constructing the Ilizarov frame.[49]

Antibiotic-impregnated ceramics

Given that a central tenet in surgical management of osteomyelitis involves filling in the dead space with viable vascularized tissue, it is not surprising that various ways of filling the defect and maximizing local antibiotic delivery have been engineered (eg, use of antibiotic-impregnated cements). Antibiotic-impregnated polymethylmethacrylate (PMMA) cement can provide sustained therapeutic concentrations of antibiotics locally in treatment and prophylaxis of osteomyelitis and has been widely used in clinical practice for 40 years.[50] This method relies on local diffusion and depends on the surface area of the cement and the concentration gradient between the cement and the local tissues.[51]

A retrospective cohort study of 501 shoulders showed that antibiotic-impregnated PMMA cement was effective in reducing deep infection for primary reverse total shoulder arthroplasty.[52] Nevertheless, PMMA cement has several drawbacks: it undergoes a thermogenic reaction that can degrade impregnated antibiotics, it loses structural integrity with high concentrations of antibiotic, and the dose of locally administered antibiotic is high in the first 24-72 hours but falls steeply to lower levels thereafter. Furthermore, PMMA is not biodegradable, and a second surgical procedure must be performed to remove to remove the implants once the infection has been treated.  

To address this issue, exploration into biodegradable inorganic ceramic materials has yielded developments in ceramic antibiotic carriers—principally, calcium phosphate cement (CPC) materials and calcium sulfate–based materials. These biomaterials, which have chemical and crystal properties similar to those of bone, may promote osteoconduction and osteogenesis and have been used to repair bone defects.[50, 53]  In addition, they are biodegradable and thus do not have to be removed with a second surgical procedure after placement.

CPC impregnated with antibiotics can release locally therapeutic amounts of antibiotics over long periods.[54, 55, 56]  Studies comparing the release efficacy of vancomycin from CPC with that from PMMA have demonstrated that CPC can release more antibiotics than PMMA because it does not undergo a thermogenic reaction, which can cause the molecule to undergo thermal degradation.[57, 58]

The most commonly used commercially available antibiotic ceramic carriers are the following[59] :

• Osteoset T - α-Hemihydrate calcium sulphate pellets, with tobramycin
• Herafill G - Calcium sulphate and carbonate pellets, with gentamicin
• Cerament G and Cerament V - Biphasic paste mix of calcium sulphate and nanocrystalline hydroxyapatite, with gentamicin (G) or vancomycin (V)

To date, there have been few high-powered studies investigating the outcomes in humans treated for osteomyelitis with these compounds. In a prospective study of 100 patients with chronic osteomyelitis who were treated with standard care plus a gentamicin-loaded calcium sulfate–hydroxyapatite biocomposite into the dead space, 96 patients were successfully treated with a single surgical procedure; the other four were successfully treated with a subsequent surgical procedure.[60, 61]

Bone transport (Ilizarov method)

The Ilizarov method, developed by Ilizarov in 1951, promotes bone growth through distraction osteogenesis using a specialized device and systematic approach. This technique has facilitated limb-lengthening, reduced the incidence of many complications, and decreased the level of surgical intervention necessary.

The Ilizarov method involves the use of a tissue-sparing cortical osteotomy-osteoclasis technique that preserves the osteogenic elements in the limb. To create a preliminary callus that can be lengthened, Ilizarov advocated a delay of several days before distraction is initiated. A high-frequency, small-step distraction rhythm permits regeneration of good-quality bone and leads to fewer soft-tissue complications (eg, nerve and vessel injury). It utilizes the concept of "tension stress," in which gradual distraction stimulates bone production and neogenesis.

The Ilizarov device is attached to the distal or proximal portion of the affected bone. Bone regenerates as the screw and wire mechanism moves the healthy bone fragment at a maximal rate of approximately 0.25 mm four times per day for an overall rate of 1 mm/day. An advantage of using this procedure is that it minimizes the prevalence of nonunion and thus further bone grafting by producing good-quality bone formation.

The risk of repeat osteotomy and osteoclasis is also decreased, owing to less premature consolidation of the lengthened segment.[48] However, Ilizarov techniques are often not tolerated well by patients, and other options, including amputation, may be preferred.

The Ilizarov external fixator is a popular device that is composed of wires, fixation bolts, rings, threaded rods, hinges, and plates, together allowing customized assemblies. Although this apparatus is stiff for bending and torsion, it is less stiff for axial loading. This feature is thought to help promote osteogenesis.[49]

Nonunions, malunions, or defects of any length can be treated and may also be corrected by using the Ilizarov method. At the same time, the Ilizarov technique is labor-intensive and may require at least 8 months of treatment. In addition, the fixator pins can be uncomfortable and often become infected. Amputation is an option if reconstruction is not suitable.

After a corticotomy is made for bone lengthening, a latency period is required before distraction. Once distraction has begun, new bone should be apparent within 3-4 weeks. After the appropriate length is obtained or the angular deformity corrected, the apparatus remains in place until completion of the consolidation phase. During the postoperative period, it is necessary to adjust or modify the assembly, and the apparatus is removed when the goal is achieved.[49]

Because the apparatus may be in place for an extended period, even as long as 1 year, special postoperative considerations are important.[49]  Pain management may be a challenge because of the duration of mild-to-moderate postoperative pain. For preventing flexion contractures of the surrounding joints, intensive physical therapy and splinting techniques are key elements. Successful treatment also requires psychological support and family counseling.

Problems to be particularly watchful for during the postoperative period include pin-track infections, premature or delayed consolidation, joint contractures, and pin breakage that may require replacement.

Imaging studies in the follow-up period are most useful in patients who have equivocal or worse clinical status at the end of therapy.

Management of critical bone defect

Debridement of all nonviable or infected tissue is critical because retained necrotic or infected debris can result in recurrence of osteomyelitis. Bone debridement is typically performed until punctuate bleeding is noted.[4]  In this process, a bone defect is often left to be dealt with. A so-called critical bone defect is one that will not heal without additional surgical intervention. Typically, a segmental bone deficit of a length exceeding 2 to 2.5 times the diameter of the affected bone is considered a critical bone defect.[62]

Induced membrane (Masquelet) technique

The induced membrane technique (Masquelet technique) is a two-stage procedure that requires a robust preoperative assessment of the patient and planning of the surgical procedures. The steps of the method along with the specific technical details have been well described.[63]  Although retrospective in nature, all of the studies on the use of this technique have reported favorable outcomes.[64, 65, 66]

The only prospective study to date, by Cho et al,[67]  included 21 patients who were treated with the Masquelet technique. The patients had critical-size defects located at the metadiaphyseal area of 11 tibias, eight femurs, and two humeri, averaging  8.9 cm in length and 65.2 cm3 in volume. Eighteen patients (86%) were healed radiographically at an average of 9.1 months.

Nonvascularized bone graft

Nonvascularized bone grafts can be used for reconstruction of large segmental defects but require at least 4 to 8 weeks for revascularization. Most cells in autogenous grafts do not survive the transplantation and must be replaced and repaired by using new bone in a process called creeping substitution. It is likely that the graft is never completely replaced by healthy bone; the result is a mixture of necrotic and viable bone. Accordingly, autogenous nonvascularized bone graft is indicated only for filling bone defects smaller than 6 cm, in the setting of adequate soft-tissue coverage.

The disadvantages are infection of the wire site, docking-site nonunion, and prolonged use of the external fixator.

Vascularized bone graft

Vascularized bone grafts are indicated when the skeletal defect is longer than 6 cm.[68]  They combine the viability of cancellous grafts with the stability of cortical analogues while leaving their nutrient blood supplies intact. Their use can achieve the following goals:

• Obliterate the dead space
• Bridge the large bone defect
• Enhance bone healing
• Resist infection (with increased blood supply)
• Allow early rehabilitation
• Ensure better clinical outcomes

The reported success rates for microsurgical flap transfer for osteomyelitis treatment has ranged from 80% to 95%.[68]

Suction irrigation system

The Lautenbach system, using a closed double-lumen tube delivering antibiotic locally, followed by suction, has previously been used in the treatment of infected hip replacements.[69]

Hashmi et al[70] described a series of 17 patients with posttraumatic osteomyelitis who were treated by this method and achieved a 94.4% infection clearance rate after a mean follow-up of 75 months. All patients remained infection-free for the duration of the study.

Wound closure

To arrest infection, it is necessary to provide adequate soft-tissue coverage.[4] Over small soft-tissue defects, a split-thickness skin graft may be placed, whereas large soft-tissue defects may be covered with local muscle flaps and free vascularized muscle flaps. Rotation of a local muscle with its neurovascular supply must be possible anatomically for that procedure to be successful.

These flaps bring in a blood supply, which is important for host defense mechanisms, new bone regeneration, delivery of antibiotics, and healing. They also may be used in combination with antibiotics and surgical debridement of necrotic and infected tissues. The fibula and iliac crest are common donor sites for free flaps.

Hydrocolloid wound dressings

Hydrocolloid dressings form an occlusive barrier over the wound while maintaining a moist wound environment and preventing bacterial contamination. A gel is formed when wound exudate comes in contact with the dressing. This gel can have fibrillolytic properties that enhance wound healing, protect against secondary infection, and insulate the wound from contaminants. Hydrocolloids help prevent friction and shear and may be used in stage 1, 2, 3, and some stage 4 pressure injuries with minimal exudate and no necrotic tissue.[71]

Negative-pressure wound therapy

Negative-pressure wound therapy (NPWT) has increasingly become a popular treatment for the management of both acute and chronic wounds. Its use in orthopedics is diverse and includes the acute traumatic setting, as well as chronic wounds associated with pressure injuries and diabetic foot surgery.

The theoretical basis for the use of NPWT is that the local factors at the wound bed can have a negative effect on the wound-healing process. The presence of infection, local edema, high-flowing exudates, and ischemia can delay the healing process. NPWT is thought to reduce these negative effects via the following mechanisms[72] :

• Promoting a lower bacterial count
• Increasing vascularity and cell proliferation
• Promoting removal of exudate from the wound
• Promoting granulation tissue and encouraging the wound edges to come together

In the case of acute open traumatic wounds, NPWT may be used to facilitate delayed primary closure, promote secondary healing by granulation, or prepare for subsequent placement of a graft or flap.

Lee et al reported on the use of NPWT in 16 patients with severe open traumatic wounds of the foot and ankle.[73] Before applying NPWT, the authors irrigated and debrided necrotic and contaminated tissue and fixated fractures, if present. Negative pressure was applied continuously at 100-125 mm Hg. The mean reduction in wound size was 24%. In 15 patients, the wound bed granulated sufficiently to allow application of a split-thickness skin graft for closure; one patient required a free flap. There were no major complications and only two minor complications of skin-graft contracture.

NPWT may preserve limbs in patients with diabetic or neuropathic foot ulcers by diminishing their size to allow subsequent coverage procedures. In a meta-analysis (eight studies; N = 669) aimed at determining the efficacy and safety of NPWT for diabetic foot ulcers,[74] Zhang et al found that NPWT, compared with treatment without NPWT, had a relative risk (RR) of 1.52 for healing, a greater reduction in the area of the ulcer, and a shorter time to healing (mean difference, −1.1 months). NPWT resulted in significantly fewer major amputations, but there was no significant difference in the rate of minor amputations.

Adjunctive hyperbaric oxygen therapy

Adjunctive hyperbaric oxygen therapy (HBOT) can promote collagen production, angiogenesis, and healing in an ischemic or infected wound.[4]

Adults 

In patients without retained hardware, a course of IV antibiotics for at least 6 weeks is recommended, with weekly blood chemistries and inflammatory markers (including erythrocyte sedimentation rate [ESR] and C-reactive protein [CRP]) at the beginning and end of antibiotic therapy to monitor for recurrence.[75]

For patients with retained hardware, an extended course of antibiotics is recommended for at least 6 weeks. Follow-up involves monitoring of blood chemistries weekly and inflammatory markers (including ESR and CRP) at the beginning and end of therapy and during the transition from IV to oral antibiotics. For patients with retained hardware or necrotic bone not amenable to debridement, oral antibiotics should be administered for an extended period for suppression. While the patient is on oral antibiotics, blood chemistries and inflammatory markers are checked at 2, 4, 8, and 12 weeks and 6 and 12 months.[76, 77, 78]

Children 

Follow-up for children with osteomyelitis is similar to that for adults. Antimicrobial therapy is initiated for a minimum of 4 weeks, typically starting with IV antibiotics and then bridging to oral antibiotics as systemic symptoms (eg, fever and leukocytosis) resolve. Before therapy has been completed, ESR and CRP are checked, and antimicrobial therapy is maintained if there are any elevations. Radiographs are commonly obtained as well to evaluate for bony lesions.

In chronic osteomyelitis, IV therapy for 2-6 weeks, followed by oral antibiotics for a total of 4-8 weeks, may be required. Prolonged courses may be required in neonates, immunocompromised or malnourished patients, patients with sickle cell disease, and patients with distant foci of infection (eg, endocarditis).[75, 79, 80, 81, 82]

The American College of Radiology (ACR) has published clinical practice guidelines for the diagnosis of suspected musculoskeletal infections (with the spine and diabetic foot excluded).[27] These recommendations are summarized below.

First study in suspected osteomyelitis, septic arthritis, or soft-tissue infection (excluding the spine and diabetic foot):

• The initial study should be a radiograph

Additional imaging after radiography with soft-tissue or juxta-articular swelling and suspected soft-tissue infections:

• Magnetic resonance imaging (MRI) is favored over computed tomography (CT) to determine the extent of soft-tissue infection
• MRI with and without intravenous (IV) contrast is preferred, but MRI without IV contrast is an alternative if contrast is contraindicated
• Ultrasonography (US) has decreased visualization of deep structures but may be more useful in young children or in cases of foreign bodies, joint effusions, or soft-tissue fluid collections

Soft-tissue or juxta-articular swelling with a history of puncture wound with suspected foreign body and negative radiographs:

• US is recommended for visualization of radiolucent foreign bodies
• CT without IV contrast is preferred for radiopaque foreign bodies

Additional imaging after radiography in soft-tissue or juxta-articular swelling and a skin lesion, injury, wound, ulcer, or blister in suspected osteomyelitis:

• MRI with and without IV contrast is preferred in cases of acute osteomyelitis
• MRI without IV contrast is an alternative if contrast is contraindicated
• CT with IV contrast may be used if MRI is contraindicated
• A labeled leukocyte scan with technetium-99m ( ^99mTc) three-phase bone scan or ^99mTc sulfur colloid has greater specificity in infections

Additional imaging after radiography in soft-tissue swelling or juxta-articular swelling with a history of prior surgery:

• If septic arthritis is suspected, aspiration of the area is recommended
• MRI with and without IV contrast is also recommended to evaluate for osteomyelitis and to determine the degree of infection; MRI without IV contrast is appropriate if contrast is contraindicated; CT with IV contrast is appropriate if MRI is contraindicated

Additional imaging after radiography in pain and swelling or cellulitis associated with a site of previous nonarthroplasty hardware and suspected osteomyelitis or septic arthritis:

• If septic arthritis is suspected, aspiration of the area is recommended
• MRI with and without IV contrast is also recommended to evaluate for osteomyelitis and to determine the degree of infection; MRI without IV contrast is appropriate if contrast is contraindicated; CT with IV contrast is appropriate if MRI is contraindicated
• A labeled leukocyte scan with  ^99mTc sulfur colloid marrow scan has greater specificity for infection and is usually appropriate, especially if extensive hardware is present

Additional imaging after radiography in draining sinus (not associated with a joint prosthesis) in suspected osteomyelitis:

• MRI with and without IV contrast is recommended; MRI without IV contrast is appropriate if contrast is contraindicated; CT with IV contrast is appropriate if MRI is contraindicated

First study in the clinical examination suggesting crepitus and suspected soft-tissue gas:

• Radiographs are recommended as the initial study, but they are less able to detect deep fascial gas
• CT with IV contrast, if not contraindicated, has the highest sensitivity in detecting soft-tissue gas

Initial radiographs showing soft-tissue gas in the absence of a puncture wound:

• CT without IV contrast is recommended as the initial study because it has a high sensitivity for detecting soft-tissue gas and can be completed quickly

The Infectious Diseases Society of America (IDSA) has published clinical practice guidelines for the diagnosis and treatment of native vertebral osteomyelitis (NVO) in adults, including recommendations regarding antibiotic therapy and surgical intervention.[42]  These recommendations are structured on the basis of answers to 13 clinical questions, as follows.

Clinical diagnostics

When should the diagnosis of NVO be considered?

• In patients with new or worsening back or neck pain and fever
• In patients with new or worsening back or neck pain and elevated erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP)
• In patients with new or worsening back or neck pain and bloodstream infection (BSI) or infective endocarditis
• Potentially, in patients who present with fever and new neurologic symptoms with or without back pain
• Potentially, in patients who present with new localized neck or back pain, following a recent episode of Staphylococcus aureus bloodstream infection

What is the appropriate diagnostic evaluation for suspected NVO?

• Recommended: a pertinent medical and motor/sensory neurologic examination in patients with suspected NVO
• Recommended: bacterial (aerobic and anaerobic) blood cultures (two sets) and baseline ESR and CRP in all patients with suspected NVO
• Recommended: MRI of the spine in patients with suspected NVO
• Suggested: a combination spine gallium/ ^99mTc bone scan or CT or positron emission tomography (PET) in patients with suspected NVO when MRI cannot be obtained (eg, implantable cardiac devices, cochlear implants, claustrophobia, or unavailability)
• Recommended: blood cultures and serologic tests for Brucella sp. in patients with subacute NVO residing in endemic areas for brucellosis
• Suggested: fungal blood cultures in patients with suspected NVO and at risk for fungal infection (epidemiologic risk or host risk factors)
• Suggested: purified protein derivative (PPD) test or obtaining an interferon gamma release assay in patients with subacute NVO and at risk for Mycobacterium tuberculosis NVO (ie, originating or residing in endemic regions or having risk factors)
• May be considered: in patients with suspected NVO, evaluation by an infectious disease specialist and a spine surgeon

When should an image-guided aspiration biopsy or additional workup be performed?

• Recommended: image-guided aspiration biopsy in patients with suspected NVO (on the basis of clinical, laboratory, and imaging studies) when a microbiologic diagnosis for a known associated organism ( S aureus, Staphylococcus lugdunensis, and Brucella sp.) has not been established by blood cultures or serologic tests
• Not advised: image-guided aspiration biopsy in patients with S aureus, S lugdunensis, or Brucella sp. BSI suspected of having NVO on the basis of clinical, laboratory, and imaging studies
• Not advised: image-guided aspiration biopsy in patients with suspected subacute NVO (high endemic setting) and strongly positive Brucella serology (strong, low).

How long should antimicrobial therapy be withheld before image-guided diagnostic aspiration biopsy in suspected NVO?

• Recommended: immediate surgical intervention and initiation of empiric antimicrobial therapy in patients with neurologic compromise with or without impending sepsis or hemodynamic instability

When is it appropriate to send fungal/mycobacterial/brucellar cultures or other specialized testing after image-guided aspiration biopsy in suspected NVO?

• Suggested: addition of fungal, mycobacterial, or brucellar cultures on image-guided biopsy and aspiration specimens in patients with suspected NVO if epidemiologic, host risk factors, or characteristic radiologic clues are present
• Suggested: addition of fungal and mycobacterial cultures and bacterial nucleic acid amplification testing (NAAT) to appropriately stored specimens if aerobic and anaerobic bacterial cultures reveal no growth in patients with suspected NVO

When is it appropriate to send specimens for pathologic examination after image-guided aspiration biopsy in suspected NVO?

• Recommended: from all patients (if adequate tissue can be safely obtained) to help confirm NVO and guide further diagnostic testing, especially in the setting of negative cultures

What is the preferred next step with nondiagnostic image-guided aspiration biopsy and suspected NVO?

• Recommended: in the absence of concomitant BSI, a second aspiration biopsy if the original image-guided aspiration biopsy specimen grew a skin contaminant (coagulase-negative staphylococci [except S lugdunensis], Propionibacterium sp., or diphtheroids)
• Recommended: with a nondiagnostic first image-guided aspiration biopsy and suspected NVO, further testing to exclude difficult-to-grow organisms (eg, anaerobes, fungi, Brucella sp., or mycobacteria)
• Suggested: with suspected NVO and a nondiagnostic image-guided aspiration biopsy and laboratory workup, either repeating a second image-guided aspiration biopsy, performing percutaneous endoscopic diskectomy and drainage (PEDD), or proceeding with an open excisional biopsy

Clinical therapy

When should empiric antimicrobial therapy be started?

• Suggested: in patients with normal and stable neurologic examination and stable hemodynamics, hold empiric antimicrobial therapy until a microbiologic diagnosis is established
• Suggested: in patients with hemodynamic instability, sepsis, septic shock, or severe or progressive neurologic symptoms, initiate empiric antimicrobial therapy in conjunction with an attempt at establishing a microbiologic diagnosis

What is the optimal duration of antimicrobial therapy?

• Recommended: total duration of 6 weeks of parenteral or highly bioavailable oral antimicrobial therapy for most patients with bacterial NVO
• Recommended: total duration of 3 months of antimicrobial therapy for most patients with NVO due to Brucella sp.

What are the indications for surgical intervention?

• Recommended: surgical intervention in patients with progressive neurologic deficits, progressive deformity, and spinal instability with or without pain despite adequate antimicrobial therapy
• Suggested: surgical debridement with or without stabilization in patients with persistent or recurrent BSI (without an alternative source) or worsening pain despite appropriate medical therapy
• Not advised: surgical debridement and/or stabilization in patients who have worsening bony imaging findings at 4-6 weeks in the setting of improvement in clinical symptoms, physical examination, and inflammatory markers

Clinical follow-up

How should failure of therapy be defined in treated patients?

• Suggested: persistent pain, residual neurologic deficits, elevated markers of systemic inflammation, or radiographic findings alone do not necessarily signify treatment failure in treated patients 

What roles do systemic inflammatory markers and MRI play in follow-up after treatment?

• Suggested: monitoring ESR, CRP, or both after approximately 4 weeks of antimicrobial therapy, in conjunction with a clinical assessment
• Not recommended: routinely ordering a follow-up MRI in patients who exhibit a favorable clinical and laboratory response to antimicrobial therapy
• Suggested: performing a follow-up MRI to assess evolutionary changes of the epidural and paraspinal soft tissues in patients who are judged to have a poor clinical response to therapy

How should suspected treatment failure be approached?

• Suggested: obtaining ESR and CRP values; unchanged or increasing values after 4 weeks of treatment should increase suspicion for treatment failure
• Recommended: obtaining a follow-up MRI with emphasis on evolutionary changes in the paraspinal and epidural soft-tissue findings
• Suggested: in patients with clinical and radiographic evidence of treatment failure, obtaining additional tissue samples for microbiologic (bacteria, fungal, and mycobacterial) and histopathologic examination, either by image-guided aspiration biopsy or through surgical sampling
• Suggested: in patients with clinical and radiographic evidence of treatment failure, consultation with a spine surgeon and an infectious disease physician