eMedicine Specialties > Radiology > Musculoskeletal

Osteomyelitis, Chronic

Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia
Coauthor(s): Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute
Contributor Information and Disclosures

Updated: Feb 10, 2009

Introduction

Background

Osteomyelitis is an infection of bone and bone marrow. It may be subdivided into acute, subacute, and chronic stages. Chronic osteomyelitis may appear as such at the initial presentation; not all patients show progression through the 3 phases. Rarely, a sclerotic nonpurulent form of osteomyelitis occurs; this is termed Garrès sclerosing osteomyelitis. Other related disorders are chronic recurrent multifocal osteomyelitis, tuberculous osteomyelitis, synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome.^1,2,3

Pathophysiology

Infective process

Osteomyelitis is an infective process involving all osseous components, including bone marrow. Chronic osteomyelitis results when the inflammatory process continues over time, leading to bone sclerosis and deformity.

The ends of long bones are the most common locus of infection, and Staphylococcus aureus is the most common infective organism involved. Traumatic fractures or previous surgery may be responsible by providing access for infection; hematogenous osteomyelitis may originate from sepsis.

Infection at the bone locus creates an increase of intramedullary pressure as a result of inflammatory exudate stripping the periosteum; this leads to vascular thrombosis, followed by bone necrosis and the formation of sequestra. Usually, necrosis of the large segments of bone leads to sequestrum formation. These sequestra with infected material are surrounded by sclerotic bone that is relatively avascular. The haversian canals are blocked with scar tissue, and the bone is surrounded by thickened periosteum and scarred muscle. Antibiotics cannot penetrate these relatively avascular tissues and are hence ineffective in clearing the infection.

New bone formation occurs at the same time (involucrum). Multiple openings appear in this involucrum, through which exudates and debris from the sequestrum pass via the sinuses. A periosteal reaction acts to circumscribe the sequestrum, producing a thick sheet of new bone or involucrum.

Specific forms of chronic osteomyelitis

Forms of chronic osteomyelitis include a Brodie abscess, tuberculous osteomyelitis, congenital syphilis, and acquired syphilis.

A Brodie abscess is a form of chronic osteomyelitis that occurs in the absence of a preceding episode of acute osteomyelitis. The lesion causes a localized abscess within the bone, often close to metaphysis.

Tuberculous osteomyelitis of the bone is secondary to the spread of infection from a primary source in the lung or GI tract. It most commonly occurs in the vertebrae (body) and long bones. Once established, the bacilli provoke a chronic inflammatory reaction. Small patches of caseous necrosis occur; these coalesce to form larger abscesses. The infection spreads across the epiphysis into the joints. The infection may track along soft tissue to appear as a cold abscess at a distant site (eg, psoas abscess in case of spinal tuberculosis).

The transplacental spread of spirochetes from mother to the fetus results in congenital syphilis. Long bones, such as the tibia, are mainly affected. Congenital syphilis has 2 forms: periosteitis and metaphysitis. In periosteitis, the periosteum is lifted off the diaphysis of long bone with subperiosteal new-bone formation. This process gives a characteristic appearance known as sabre tibia. In metaphysitis, the juxtaepiphyseal metaphysis is involved with increased bone resorption. Absent osteoblastic activity results in separation of the epiphyseal from the metaphysis.

Regarding acquired syphilis, bone lesions are manifestations of tertiary syphilis. Gummatous lesions appear as discrete punched-out radiolucent lesions in medulla or destructive lesions within the cortex. The surrounding bone is sclerotic; no discharge is present.

Frequency

United States

The prevalence of chronic osteomyelitis is 5-25% after an episode of acute osteomyelitis. The prevalence of tuberculous osteomyelitis is 1-5% of the population affected by tuberculosis. The incidence in developed countries is low.

International

The incidence of chronic osteomyelitis in developing countries is higher than in other countries, although the exact incidence is not known.

Mortality/Morbidity

• Mortality from osteomyelitis was 5-25% in the preantibiotic era. Currently, the mortality rate approaches 0%.
• Complications of osteomyelitis include (1) septic arthritis, (2) destruction of the adjacent soft tissues, (3) malignant transformation (eg, Marjolin ulcer [squamous cell carcinoma], epidermoid carcinoma of the sinus tract), (4) secondary amyloidoses, and (5) pathologic fractures.

Anatomy

Sharp nonanastomosing loops are present at the capillary ends of nutrient artery and enter into large venous sinusoids. This anatomy results in a slowing of circulation and a reduction in oxygen tension. The capillaries do not communicate because columns of calcified cartilage separate them from each other.

Children younger than 2 years have transphyseal vessels, which cross from metaphysis to epiphysis. This causes the spread of infection into the joint. In children older than 2 years, the transphyseal vessels are absent; hence, the epiphyseal plate acts as a barrier to the spread of infection into the joint.

Cierny and Mader proposed an anatomic classification of chronic osteomyelitis:

1. Type 1 — Endosteal or medullary lesion
2. Type 2 — Superficial osteomyelitis limited to the surface
3. Type 3 — Localized, well-marked legion with sequestration and cavity formation
4. Type 4 — Diffuse osteomyelitis lesions

Presentation

Unlike acute osteomyelitis, chronic osteomyelitis causes no acute constitutional symptoms. The presenting features may be those of a long-standing, discharging sinus or chronic bone pain that persists despite treatment. Patients may also present with acute exacerbations and usually have a history of acute osteomyelitis, sometimes dating back to childhood. Other symptoms include deep boring pain, especially in cases of a Brodie abscess. In osteomyelitis that occurs after joint replacement, the main symptom is the recurrence of pain.

Findings in tuberculosis include the following:

• History of tuberculosis elsewhere
• Attacks of fever and lassitude
• Night cries
• Intense episodes of pain in the affected bones
• Muscle wasting, synovial thickening, and restriction of joint movement in all directions
• Kyphosis, back pain, and symptoms and signs of spinal cord compression in spinal tuberculosis

Findings in syphilis include the following:

• Pain, refusal to move the affected limb
• Restriction of movement in an adjacent joint
• Pain in the bone
• Local swelling, redness, and warmth
• Fever
• Nausea
• General discomfort, uneasiness, or ill feeling (malaise)
• Drainage of pus through the skin (in chronic osteomyelitis)

Additional symptoms that may be associated with chronic osteomyelitis include the following:

• Excessive sweating
• Chills
• Low back pain
• Swelling of the ankles, feet, and legs

Physical examination shows bone tenderness and, possibly, swelling and redness.

During laboratory testing, a full blood count may show leukocytosis. The erythrocyte sedimentation rate (ESR) is elevated. Blood cultures may help identify the causative organism.

Results of bone lesion biopsy and cultures may be positive for the organism. A skin lesion with a sinus tract (ie, the lesion tunnels under the tissues) may yield pus for culturing.

Preferred Examination

Radiologic assessment of chronic osteomyelitis is performed for the following reasons: (1) to evaluate bone involvement (eg, the extent of active intramedullary infection or abscess superimposed on areas of necrosis, sequestrum and fibrosis) and (2) to identify soft tissue involvement (areas of cellulitis, abscess, and sinus tracts).

Plain radiographs are usually obtained initially. Ultrasonography may readily depict soft tissue involvement, but it provides only limited information about bone changes.^{4,5,6,7,8,9,10}

Because of its high sensitivity in the detection of bone marrow changes, MRI may provide detailed information regarding the extent and activity of the process by allowing the detection of the intramedullary site of infection and its complications. MRI may also be used to distinguish soft tissue involvement, allowing differential diagnosis. With scintigraphy, other conditions not involving bone marrow, such as cellulitis and myositis, may cause errors; scintigraphy may be indicated for the assessment of local disturbances in vascular perfusion that are common in cases of chronic osteomyelitis.^{11,12,13,14,15,16,17,18}

Limitations of Techniques

Although plain radiographs may provide important clues for diagnosis (eg, demonstration of bone remodeling, sclerosis, and thickening), the radiographic impression is often equivocal and relies heavily on clinical findings.

CT may depict intramedullary and soft tissue gas, sequestra, sinus tracts, and foreign bodies. However, CT scanning is insufficient for the assessment of the activity of the process.

MRI has limited availability, it is relatively expensive, and it is contraindicated in patients with certain implant devices and metallic clips. In addition, MRI is not tolerated by all patients with claustrophobia or morbid obesity, and young children may require sedation. Good MRIs require patient cooperation because patient motion degrades the images.

Differential Diagnoses

Other Problems to Be Considered

Septic arthritis
Other causes of periosteitis
Fungal infections of the bone
Hydatid disease
SAPHO syndrome (synovitis, acne, palmoplantar pustulosis, hyperostosis, osteitis)

SAPHO syndrome may be triggered by an infectious state involving P. acnes. Its ability to persist in bone lesions in a form that is incompatible with culturing suggests the possibility of arthritis that is secondary to a "persistent" infection.^2,3
 

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