In 5% to 25% of cases, acute osteomyelitis fails to resolve and persists as chronic infection. Chronic infections may develop when there is delay in diagnosis, extensive bone necrosis, inadequate antibiotic therapy or surgical debridement, or weakened host defenses. The course of chronic infections may be punctuated by acute flare-ups; these are usually spontaneous and may occur after years of dormancy. Other complications of chronic osteomyelitis include pathologic fracture, secondary amyloidosis, endocarditis, sepsis, and the development of squamous cell carcinoma in the draining sinus tracts and sarcoma in the infected bone.
Fig.21.14Resectedfemurinapersonwithdrainingosteomyelitis.Thedrainagetractinthesubperiostealshellofviablenewbone(involucrum)showstheinnernativenecroticcortex(sequestrum).
Mycobacterial osteomyelitis, historically a problem in developing countries, has increased in incidence in the developed world because of immigration patterns and immunocompromised patients. Overall, approximately 1% to 3% of individuals with pulmonary or extrapulmonary tuberculosis exhibit osseous infection.
The organisms are usually blood borne and originate from a focus of active visceral disease during the initial stages of primary infection. Direct extension (e.g., from a pulmonary focus into a rib or from tracheobronchial nodes into adjacent vertebrae) also may occur. The bone infection may persist for years before being recognized. Typically, affected individuals present with localized pain, low-grade fevers, chills, and weight loss. Infection is usually solitary except in immunocompromised individuals. The histologic findings, namely caseous necrosis and granulomas, are typical of tuberculosis. Mycobacterial osteomyelitis tends to be more destructive and resistant to control than pyogenic osteomyelitis.
Tuberculous spondylitis (Pott disease) is a destructive infection of vertebrae. The spine is involved in 40% of cases of mycobacterial osteomyelitis. The infection breaks through intervertebral discs to affect multiple vertebrae and extends into the soft tissues. Destruction of discs and vertebrae frequently results in permanent compression fractures that produce scoliosis or kyphosis and neurologic deficits secondary to spinal cord and nerve compression.
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The rarity of primary bone tumors and the often-disfiguring surgery required to treat a bone malignancy make this group of disorders especially challenging. About 2400 primary bone sarcomas are diagnosed annually in the United States. Therapy aims to optimize survival while maintaining the function of affected body parts. The predilection of specific types of tumors for certain age groups and particular anatomic sites provides important diagnostic clues. For example, osteosarcoma peaks during adolescence and most frequently involves the knee, whereas chondrosarcoma affects older adults and involves the pelvis and proximal extremities.
Bone tumors may present in a number of ways. The more common benign lesions are often asymptomatic incidental findings. Many tumors, however, produce pain or a slow-growing mass. In some circumstances the first hint of a tumor’s presence is a pathologic fracture. Radiographic imaging studies have an important role in diagnosing these lesions. In addition to providing the exact location and extent of the tumor, imaging studies can detect features that narrow the diagnostic possibilities. In almost all instances biopsy is necessary for definitive diagnosis.
When possible, bone tumors are classified according to the normal cell or matrix they produce. Lesions that do not have normal tissue counterparts are grouped according to their clinicopathologic features (
Table 21.1 ). Benign tumors greatly outnumber their malignant counterparts and occur with