eMedicine Specialties > Orthopedic Surgery > Spine

Spinal Infections

Author: Federico C Vinas, MD, Consulting Neurosurgeon, Department of Neurological Surgery, Halifax Medical Center
Coauthor(s): J Richard Rhodes, MD, Orthopedic Surgeon, Atlantic Orthopaedics, PA, and Coastal Medical Research; Amy L Stumpf, MPH, PA-C, Clinical Director, Assistant Professor, Physician Assistant Program, Nova Southeastern University
Contributor Information and Disclosures

Updated: Nov 3, 2008

Introduction

Pyogenic vertebral osteomyelitis is the most commonly encountered form of vertebral infection. It can develop from direct open spinal trauma, from infections in adjacent structures, from hematogenous spread of bacteria to a vertebra, or postoperatively. Left untreated, it can lead to permanent neurologic deficits, significant spinal deformity, or death.^1,2,3,4,5,6

History of the Procedure

Evidence of vertebral osteomyelitis has been found in Egyptian mummies. Hippocrates first described the infection of the vertebral column. Later on, Galen related this infectious process to spinal deformity.

Prior to the development of antibiotics and bacteriology, little knowledge was added to the basic understandings of the Hippocratic school until Servino and Potts characterized and described the pathology of tuberculosis infection of the spine. In 1879, Lannelonge described bacterial osteomyelitis as we recognize it today.

Although successful treatment of spinal abscess with surgical drainage was reported early on, the high complication rate from secondary infection caused this surgery to remain in poor favor. Following the introduction of antisepsis, surgical intervention for spinal infections became feasible.

The initial procedure introduced for the surgical treatment of spinal infections was a laminectomy. However, this procedure did not allow access to anterior abscesses and contributed to spinal instability, which often resulted in progressive deformity. Ito et al first described the anterior approach to the spine. Later, Hodgson and Stock extensively reported this procedure in the treatment of tuberculosis of the spine. Late spinal deformity was prevented with spinal fusion and instrumentation. While Hodgson and Stock performed fusions from the anterior approach, Hibbs and Albee independently presented techniques for posterior spinal fusion in the treatment of tuberculosis of the spine. Currently, the advancement of bacteriology and the development of modern chemotherapeutic agents have changed the characteristics of spinal osteomyelitis.

Problem

Vertebral osteomyelitis, if untreated, can lead to permanent paralysis, significant spinal deformity, or death. It can result on severe compression of the neural stuctures due to formation of an epidural abscess or due to a pathological fracture resulting from bone softening.

Frequency

Vertebral osteomyelitis is considered uncommon, with an incidence of 1 case per 100,000-250,000 population per year. However, some reviews suggest that the incidence of spinal infections is now increasing. This increase may be secondary to increased use of vascular devices and other forms of instrumentation and to increasing rates of intravenous drug abuse. Because of its rarity and vague initial signs and symptoms, diagnosis is often delayed.

No specific predilection for a particular race has been noted. Osteomyelitis has a predilection for males. A bimodal age distribution occurs in diskitis. Diskitis and osteomyelitis peak in pediatric patients; the incidence of spinal infections then decreases until middle age, when a second peak in incidence is observed at approximately age 50 years.⁷ Some authors argue that childhood diskitis is a separate disease entity and should be considered independently.

In developed nations, incidence of spinal osteomyelitis is similar to that in the United States. However, in less developed nations, infectious osteomyelitis is more common. In some areas of Africa, a reported 11% of all patients seen for back pain were diagnosed with diskitis and osteomyelitis.

Etiology

Presumably, a distant focus of infection provides an infective nidus from which bacteria spread by the bloodstream to the spinal column. The skin and the genitourinary tract are common antecedent sites, but a review of the literature reveals multiple foci, such as septic arthritis, sinusitis, subacute bacterial endocarditis, and respiratory, oral, or gastrointestinal infection.^8,9 Approximately 30-70% of patients with vertebral osteomyelitis have no obvious prior infection.

Risk factors for developing osteomyelitis include conditions that compromise the immune system, such as the following:

• Advanced age¹⁰
• Intravenous drug use¹¹
• Congenital immunodepression
• Long-term systemic administration of steroids
• Diabetes mellitus¹²
• Organ transplantation
• Malnutrition
• Cancer

Intravenous drug abuse

Intravenous drug abuse is a growing cause of spinal infections. Typically, the organism most likely to infect the spine is Staphylococcus aureus; however, in intravenous drug users, Pseudomonas species are also a common cause.¹³ Nonpyogenic osteomyelitis can be caused by tuberculosis, fungus, yeast, or parasitic organisms.^{14,15,16,17,18}

Surgical site infection

Surgical site infection can result as an adverse event after a spinal procedure. Timing of preoperative antibiotic prophylaxis as well as careful aseptic technique can reduce the incidence of surgical infections during spinal procedures.^19,20

Fungal infection

Fungal infections of the spine are rare and generally occur in patients who are debilitated or have diabetes or a compromised immune system. Patients with acute leukemia, alcoholics, patients with lymphoma, recipients of organ transplants, and those receiving chemotherapy are particularly susceptible to fungal infections.

Infection location

Most vertebral body infections occur in the lumbar spine because of the blood flow to this region of the spine. Tuberculosis infections have a predilection for the thoracic spine, and intravenous drug abusers are more likely to contract an infection of the cervical spine.

Pathophysiology

Approximately 95% of pyogenic spinal infections involve the vertebral body, and only 5% involve the posterior elements of the spine. This disparity has been attributed in part to the voluminous blood supply to the vertebral body and its rich, cellular marrow.

Bacteria circulating through the blood may enter a vertebra or a disk space via its arterial blood supply or via the venous system. In the typical case, bacteria enter the vertebral body through small metaphyseal arteries arising from larger primary periosteal arteries that, in turn, branch from the spinal arteries. In adults, blockage of metaphyseal arteries by septic thrombi may infarct relatively large amounts of bone. Subsequently, bacteria can readily colonize a large bony sequestrum adjacent to the disk. In the adult, after bacterial colonization of the metaphyseal region, the avascular disk is secondarily invaded by bacteria from the endplate region. Intermetaphyseal communicating arteries allow the spread of septic thrombi from one metaphysis to the other in a single vertebral body without involvement of the mid portion of the vertebra.

Although the arterial route is the usual route of bacterial spread to a vertebra, another proposed route of infection is the retrograde seeding of venous blood via the Batson plexus. During periods of increased intra-abdominal pressure, venous blood is shunted toward the vertebral venous plexus. Some authors have proposed that the venous system may be the route of bacterial spread from genitourinary tract infections.

Another possible means of infection is by the spread of contiguous infection into the vertebrae and disk (eg, from a retropharyngeal abscess or a retroperitoneal abscess), resulting in osteomyelitis and diskitis.²¹

Presentation

The onset is usually insidious. Back pain is the most common symptom. Most patients have a history of several weeks or months of gradually progressing neck or back pain that increases with movement. The pain is initially localized at the level of the involved area, and gradually increases in intensity. Thereafter, the pain eventually becomes so severe that it is not relieved by analgesics or even complete bedrest. Usually, neurologic signs are not present until late in the disease course and may be associated with destruction and collapse of the vertebral body.²²

In the typical case with mild symptoms, physical examination reveals only mild tenderness over the spinous process of the involved vertebra, and minimal spasm may be present in nearby paravertebral muscles. A decreased range of motion is also common. Only about half of patients are febrile. Later, neurologic compromise is caused by bony collapse, spread of the infection underneath the posterior longitudinal ligament, or frank epidural abscess with compression of the spinal cord or nerve roots. A progression to radicular signs followed by weakness and paralysis suggests the formation of an epidural abscess. Spinal epidural abscess occurs in 5-18% of cases and is most commonly located anteriorly in the epidural space. Cervical vertebral osteomyelitis is associated with paralysis more commonly than either thoracic or lumbar infection.¹

Children with vertebral osteomyelitis and associated diskitis usually present with an abrupt onset of malaise, fever, and back pain. They commonly demonstrate back stiffness, restricted motion, guarded walking, and spine tenderness. Some patients can also present acutely with fever, night sweats, elevated leukocyte counts, and signs and symptoms of shock.

In patients with neurologic compromise, a detailed motor and sensory examination should be performed. Muscle strength and weakness are graded ranging from a strength of 5/5, considered normal, to a strength of 0/5, or paralysis, as follows:

• 0 - No contraction
• 1 - Flicker of movement
• 2 - Can move when gravity is eliminated
• 3 - Can elevate against gravity
• 4 - Can move against resistance (-4, slight resistance; 4, moderate resistance; +4, strong resistance)
• 5 - Normal strength

The sensory examination should include detection of a sensory level, posterior column function, normal and abnormal reflexes, and examination of rectal tone and perianal sensation. The presence of a Babinski sign should also be noted and documented. The neurologic examination should be repeated and documented at regular intervals to serve as a reference for improvement or deterioration of the patient's neurologic status over time.

Indications

The combination of mechanical compression of the spinal cord by pus or granulation tissue can result in ischemia with spinal cord infarction, which accounts for the rapid neurologic progression of this disease. Patients with a spinal epidural abscess may progress to complete paralysis within minutes to hours, even while receiving optimal antibiotic therapy. In addition, patients with vertebral osteomyelitis can develop pathological fractures, caused by the softening of the bone, and present with acute spinal cord compression.

Indications for surgery include significant osseous involvement, neurologic deficits, septic course with clinical toxicity from an abscess not responding to antibiotics, failure of needle biopsy to obtain necessary cultures, and failure of intravenous antibiotics alone to eradicate the infection.

Relevant Anatomy

The anatomy of the spine includes the vertebral bodies, intervertebral disks, and associated joints, muscles, tendons, ligaments, and neural elements.

The intervertebral disk is a fibrocartilaginous remnant of the embryonic notochord, which provides the spine with strength, mobility, and resistance to strain. It consists of 3 parts: the annulus fibrosus, the nucleus pulposus, and the cartilaginous endplates. The annulus fibrosus, is made up of type I collagen fibrils, which are arranged in 15-20 concentric lamellae brought together into parallel bundles. These bundles are firmly attached to the vertebral bodies and are arranged in layers to provide strength and limit vertebral movement when the disk is compressed. The nucleus pulposus is composed of type II collagen and represents 30-60% of the disk volume. The nucleus pulposus is supplied with blood vessels through small perforations in the central cartilaginous endplates.

The cervical spine consists of the first 7 vertebrae in the spinal column. Typically these vertebrae are small and possess a foramen on the transverse process for the vertebral artery. The thoracic spine consists of the next 12 vertebrae and is stabilized by the attached rib cage and intercostal musculature. The lumbar spine consists of a mobile segment of 5 vertebrae, located between the relatively immobile segments of the thoracic and sacral segments. The lumbar vertebrae are particularly large and heavy in comparison with the cervical and thoracic vertebrae. The bodies are wider and have shorter and heavier pedicles, and the transverse processes project somewhat more laterally and ventrally than the other spinal segments. The laminae are shorter vertically than the bodies and are bridged by strong ligaments. The spinal processes are broader and stronger than those in the thoracic and cervical spine.

Contraindications

Most patients with pyogenic vertebral osteomyelitis respond to medical management. However, surgery may be required if medical management is unsuccessful. Indications for surgery include significant osseous involvement, neurologic deficits, septic course with clinical toxicity from an abscess not responding to antibiotics, failure of needle biopsy to obtain necessary cultures, and failure of intravenous antibiotics alone to eradicate the infection.

• Search for CME/CE on This Topic »

• Spinal Infections: Evolving Concepts