Chapter 120. Osteomyelitis (Part 2)

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Vertebral Osteomyelitis The vertebrae are the most common sites of hematogenous osteomyelitis in adults. Organisms reach the well-perfused vertebral body via spinal arteries and quickly spread from the end plate into the disk space and then to the adjacent vertebral body. Sources of bacteremia include the urinary tract (especially among men over age 50), dental abscesses, soft tissue infections, and contaminated IV lines, but the source of bacteremia is not evident in more than half of patients. Diabetes mellitus requiring insulin injection, a recent invasive medical procedure, hemodialysis, and injection drug use carry an increased risk of spinal infection. Many...

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Chapter 120. Osteomyelitis (Part 2) Vertebral Osteomyelitis The vertebrae are the most common sites of hematogenous osteomyelitis in adults. Organisms reach the well-perfused vertebral body via spinal arteries and quickly spread from the end plate into the disk space and then to the adjacent vertebral body. Sources of bacteremia include the urinary tract (especially among men over age 50), dental abscesses, soft tissue infections, and contaminated IV lines, but the source of bacteremia is not evident in more than half of patients. Diabetes mellitus requiring insulin injection, a recent invasive medical procedure, hemodialysis, and injection drug use carry an increased risk of spinal infection. Many patients have a history of degenerative joint disease involving the spine, and some report an episode of trauma preceding the onset of infection. Penetrating
injuries and surgical procedures involving the spine may cause nonhematogenous vertebral osteomyelitis or infection localized to a disk. Most patients with vertebral osteomyelitis report neck or back pain; patients may describe atypical pain in the chest, the abdomen, or an extremity that is due to irritation of nerve roots. Symptoms are localized to the lumbar spine more often than to the thoracic spine (>50% vs. 35% of cases) or the cervical spine in pyogenic infections, but the thoracic spine is involved most commonly in tuberculous spondylitis (Pott's disease). More than 50% of patients experience a subacute illness in which a vague, dull pain gradually intensifies over 2–3 months. Fever is usually low-grade or absent, but some patients recall having had an episode of fever and chills prior to or at the onset of pain. An acute presentation with high fever and toxicity is less common and suggests ongoing bacteremia. Percussion over the involved vertebra elicits tenderness, and physical examination may reveal spasm of the paraspinal muscles and limitation of motion. Laboratory findings at the time of presentation include a normal or modestly elevated white blood cell count, anemia, and, almost invariably, an increased erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level. Blood cultures are positive only 20–50% of the time. By the time the patient seeks medical attention, plain radiographs often show irregular erosions in the end plates of adjacent vertebral bodies and
narrowing of the intervening disk space. This radiographic pattern is virtually diagnostic of bacterial infection because tumors and other diseases of the spine rarely cross the disk space. CT or MRI may demonstrate epidural, paraspinal, retropharyngeal, mediastinal, retroperitoneal, or psoas abscesses that originate in the spine. A spinal epidural abscess may evolve suddenly or over several weeks; the classic clinical presentation is spinal pain progressing to radicular pain and/or weakness. Irreversible paralysis may result from failure to recognize epidural abscess before the development of neurologic deficits. MRI is the best procedure for detection of epidural abscess and should be performed in all cases of vertebral osteomyelitis accompanied by subjective weakness or objective neurologic abnormalities. Microbiology More than 95% of cases of hematogenous osteomyelitis are caused by a single organism, with Staphylococcus aureus accounting for 50% of cases. Other common pathogens in children are group A streptococci and, during the neonatal period, group B streptococci and Escherichia coli. In adults, vertebral osteomyelitis is caused by E. coli and other enteric bacilli in ~25% of cases. S. aureus, Pseudomonas aeruginosa, Serratia, and Candida albicans infections are associated with injection drug use and may involve the sacroiliac, sternoclavicular,
or pubic joints as well as the spine. Salmonella spp. and S. aureus are the major causes of long-bone osteomyelitis complicating sickle cell anemia and other hemoglobinopathies. Tuberculosis and brucellosis affect the spine more often than other bones. Other common sites of tuberculous osteomyelitis include the small bones of the hands and feet, the metaphyses of long bones, the ribs, and the sternum. Unusual causes of hematogenous osteomyelitis include disseminated histoplasmosis, coccidioidomycosis, and blastomycosis in endemic areas. Immunocompromised persons may rarely develop osteomyelitis due to atypical mycobacteria, Bartonella henselae, or opportunistic fungi. Hematogenous osteomyelitis with Mycobacterium bovis has been reported following intravesicular instillation of bacille Calmette-Guérin (BCG) for cancer of the bladder. The etiology of chronic relapsing multifocal osteomyelitis, an inflammatory condition of children that is characterized by recurrent episodes of painful lytic lesions in multiple bones, has not been identified. Osteomyelitis Secondary to a Contiguous Focus of Infection Clinical Features This broad category of osteomyelitis accounts for ~80% of all cases and occurs most commonly in adults. It includes infections introduced by penetrating injuries, such as bites, puncture wounds, and open fractures; by surgical
procedures; and by direct extension of infection from adjacent soft tissues. Generalized vascular insufficiency and the presence of a foreign body are important predisposing factors and also make infection more difficult to cure. Frequently, the diagnosis of this type of osteomyelitis is not made until the infection has already become chronic. The pain, fever, and inflammatory signs due to bony infection may be attributed to the original injury, to underlying bone or joint disease (such as degenerative arthritis), or to overlying soft tissue infection. Osteomyelitis may become apparent only weeks or months later, when a sinus tract develops, a surgical wound breaks down, or a fracture fails to heal. It may be impossible to distinguish radiographic abnormalities due to osteomyelitis from those due to the precipitating condition. A special type of contiguous-focus osteomyelitis occurs in the setting of peripheral vascular disease and nearly always involves the small bones of the feet of adults with diabetes. This type of infection is a major cause of morbidity for patients with diabetes and results in many thousands of amputations per year. Diabetic neuropathy exposes the foot to frequent trauma and pressure sores, and the patient may be unaware of infection as it spreads into bone. Poor tissue perfusion impairs normal inflammatory responses and wound healing and creates a milieu that is conducive to anaerobic infections. It is often during the evaluation of a nonhealing ulcer, a swollen toe, or acute cellulitis that a radiograph provides the
first evidence of osteomyelitis. If bone is palpable during examination of the base of an ulcer with a blunt surgical probe, osteomyelitis is likely.