Infections of Bones

Direct microbial contamination of bones results from open fracture, surgical procedures, gunshot wounds, diagnostic needle aspirations, and therapeutic or self-administered drug injections.

Indirect or secondary infections are first noticed in other areas of the body and extend to bones by hematogenous routes.

Acute Pyogenic Osteomyelitis

Essentials of Diagnosis

Fever and chills associated with pain and tenderness of involved bone.

Aspiration of involved bone is usually diagnostic.

Culture of blood or lesion tissue is essential for precise diagnosis.

Radiographs early in the course are typically negative.

General Considerations

Initial bone infections are indirectly seeded by a single strain of pyogenic bacteria about 95% of the time. About 75% of hematogenous acute infections of bone are due to staphylococci; group A hemolytic streptococci are the next most common pathogens. Vertebral osteomyelitis, due to more indolent organisms, is being encountered with increasing frequency in elderly patients. Infections of bone due to trauma are often polymicrobial.

Salmonellae cause many cases of bacteremia associated with sickle cell disease. Among patients with hemoglobinopathies, osteomyelitis is caused by salmonellae almost 10 times as often as by other pyogenic bacteria. In otherwise healthy patients with salmonellosis, bone lesions are likely to be solitary. In typhoid fever, however, infections of bones occur as a complication in less than 1% of cases.

Bone infection is an uncommon complication of brucellosis, but the clinical picture when it does occur is characteristic. Bone lesions most commonly occur in the lumbar spine or sacroiliac joints.

Clinical Findings

A. Symptoms and Signs : The onset of acute osteomyelitis in adults is less likely to be striking than the sudden and alarming presentation often seen in children. Generalized toxic symptoms of bacteremia may be absent, and vague or evanescent local pain may be the earliest manifestation. Tenderness may be present or absent, depending upon the extent and duration of bone involvement.

B. Laboratory Findings : Aspiration of bone and periosteum to recover organisms for culture is necessary for accurate diagnosis. Blood cultures are frequently positive, particularly when systemic symptoms are prominent, in which case the white count and sedimentation rate are often elevated.

With infections due to Salmonella or Brucella, significant rising serologic agglutination titers support a tentative diagnosis during the acute stage. Culture of material from the osteoid focus is specific.

C. Imaging : Early findings may include soft tissue swelling, loss of tissue planes, and periarticular demineralization of bone. About 2 weeks after onset of symptoms, erosion of bone and alteration of cancellous bone appear, followed by periostitis. Xeroradiography and radionuclide imaging may localize occult lesions several days before conventional radiographic studies are suggestive. When osteomyelitis involves the vertebrae, it commonly traverses the disk space-a find that is not observed in tumor.

Differential Diagnosis

Acute hematogenous osteomyelitis should be dis-tinguished from suppurative arthritis, rheumatic fever, and cellulitis. More subacute forms must be differentiated from tuberculous or mycotic infections of bone and Ewing's sarcoma or from metastatic tumor (vertebral osteomyelitis).

Complications

Inadequate treatment of bone infections results in chronicity of infection, and this possibility is increased by delay in diagnosis and treatment. Extension to adjacent bone or joints may complicate acute osteomyelitis. Recurrence of bone infections often results in anemia, weight loss, weakness, and rarely amyloidosis. Pseudoepitheliomatous hyperplasia, squamous cell carcinoma, or fibrosarcoma may occasionally arise in persistently infected tissues.

Treatment

Cultures and antibiotic sensitivity studies should determine the choice of antibiotic agents; the initial selection of drug is based on clinical assessment of the most probable cause. Open or closed drainage of the local lesion is important when prompt clinical response to initial treatment does not occur. Parenteral antibiotic therapy should be continued for a total of 6 weeks. Analgesics, rest, immobilization, and eleva-tion of the part should be used from the beginning of treatment.

Prognosis

If sterility of the lesion is achieved within 2-4 days, a good result can be expected in most cases if there is no compromise of the patient's immune system. However, progression of the disease to a chronic form may occur. It is especially common in the lower extremities and in patients in whom circulation is impaired (eg, diabetics). Surgical saucerization, excision of bone, and debridement of healthy tissues are often necessary.

Mycotic Infections of Bones & Joints

Fungal infections of the skeletal system are usually secondary to a primary infection in another organ, frequently the lungs. Although skeletal lesions have a predilection for the cancellous extremities of long bones and the bodies of vertebrae, the predominant lesion - a granuloma with varying degrees of necrosis and abscess formation - does not produce a characteristic clinical picture.

Differentiation from other chronic focal infections depends upon culture studies of synovial fluid or tissue obtained from the local lesion. Serologic tests and skin tests provide presumptive support of the diagnosis.

1. Coccidioidomycosis

Coccidioidomycosis of bones and joints is usually secondary to primary pulmonary infection. Early arthralgia with periarticular swelling, especially in the knees and ankles, should be differentiated from organic bone and joint involvement. Osseous lesions commonly occur in cancellous bone of the vertebrae or near the ends of long bones. These lesions are initially osteolytic and thus may mimic metastatic tumor or myeloma.

The precise diagnosis depends upon recovery of Coccidioides immitis from the lesion or histologic examination of tissue obtained by open biopsy. Rising titers of IgA complement-fixing antibodies provide further evidence of the disseminated nature of the disease.

Systemic treatment with amphotericin B should be tried for bone and joint infections. Treatment with miconazole may be effective, but the results remain unproved. Chronic infection may require operative excision of infected bone and soft tissue; amputation may be the only solution for stubbornly progressive infections. Immobilization of joints by plaster casts and avoidance of weight bearing provide benefit. Synovectomy, joint debridement, and arthrodesis are reserved for more advanced joint infections.

2. Histoplasmosis

Focal skeletal or joint involvement in histoplasmosis is rare and generally represents dissemination from a primary focus in the lungs. Skeletal lesions may be single or multiple and are not characteristic.

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