Porth's Essentials of Pathophysiology, 4e

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Musculoskeletal Function

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sensitivity to antibiotic therapy. 31–33 Initial antibiotic therapy is often followed by surgery to remove foreign bodies (e.g., metal plates, screws) or sequestra and by long-term antibiotic therapy. Immobilization of the affected part usually is necessary, with restriction of weight bearing on a lower extremity. External fixation devices are sometimes used. Direct Penetration and Contiguous Spread Osteomyelitis. Direct penetration or extension of bac- teria from an outside (exogenous) source is now the most common cause of osteomyelitis in the United States. 19 Bacteria may be introduced directly into the bone by a penetrating wound, an open fracture, or surgery. In persons with vascular insufficiency or poorly controlled diabetes, osteomyelitis may develop from a skin lesion. Iatrogenic bone infections are those inadvertently brought about by surgery or other treatments. These complications include pin tract infection in skeletal trac- tion, septic (infected) joints in joint replacement sur- gery, and wound infections after surgery. Risk factors for the development of a surgical site infection include both host factors and those related to the procedure. 34 Delays in wound healing, infection and failure of surgi- cal implants cause greater morbidity and possibly the need for subsequent revision surgery. Osteomyelitis after trauma or bone surgery usually is associated with persistent or recurrent fever, increased pain at the operative or trauma site, and poor incisional healing, which often is accompanied by continued wound drainage and wound separation. Prosthetic joint infections often present with joint pain, fever, and cuta- neous drainage. Treatment includes the use of antibiotics and selective use of surgical interventions. The choice of agents and method of administration depend on the microorganisms causing the infection. In acute osteomyelitis that does not respond to antibiotic therapy, surgical decompression is used to release intramedullary pressure and remove drainage from the periosteal area. Prosthesis removal may be necessary in cases of an infected prosthetic joint. The joint is left out while a 2- to 6-week course of ther- apy is given, after which another joint is implanted. 32 Tuberculosis Osteomyelitis A resurgence of tuberculosis osteomyelitis is occurring in industrializedcountries of theworld, attributed to the influx of immigrants from developing countries and the greater numbers of immunocompromised people. 19 Tuberculosis can spread from one part of the body, such as the lungs or the lymph nodes, to the musculoskeletal system. Any bone, joint, or bursa may be affected, but the spine is the most common site, followed by the knees and hips. 18,19,35 Tubercular osteomyelitis tends to be more destructive and difficult to control than pyogenic osteomyelitis. The infec- tion spreads through large areas of the medullary cavity and causes extensive necrosis. In tuberculosis of the spine, also known as Pott disease, the infection spreads through the intervertebral disks to involve multiple vertebrae and extends into the soft tissue, forming abscesses.

to form devascularized fragments, called sequestra. 18,19 Eventually, the purulent drainage may penetrate the periosteum and skin to form a draining sinus. In children 1 year of age and younger, the adjacent joint is often involved because the periosteum is not firmly attached to the cortex. 18,19 From 1 year of age to puberty, subperi- osteal abscesses are more common. As the process con- tinues, periosteal new bone formation and reactive bone formation in the marrow tend to wall off the infection. In adults, the long bone microvasculature no lon- ger favors seeding, and hematogenous infection rarely affects the appendicular skeleton. Instead, vertebrae, sternoclavicular and sacroiliac joints, and the symphy- sis pubis are involved. Infection typically first involves subchondral bone, then spreads to the joint space. With vertebral osteomyelitis, this causes sequential destruc- tion of the endplate, adjoining disk, and contiguous ver- tebral body. Infection less commonly begins in the joint and spreads to the adjacent bone. The signs and symptoms of acute hematogenous osteomyelitis are those of bacteremia accompanied by symptoms referable to the site of the bone lesion. Bacteremia is characterized by chills, fever, and malaise. There often is pain on movement of the affected extrem- ity, loss of movement, and local tenderness followed by redness and swelling. X-ray studies may appear normal initially, but they show evidence of periosteal elevation and increased osteoclast activity after an abscess has formed. Radiographic bone scans and MRI can usually detect subtle changes at an earlier stage. The treatment of hematogenous osteomyelitis begins with identification of the causative organism through blood and bone aspiration cultures. Antimicrobial agents are given first parenterally and then orally. The length of time the affected limb needs to be rested and the pain con- trol measures used are based on the person’s symptoms. Débridement and surgical drainage also may be necessary. Chronic Osteomyelitis. Chronic osteomyelitis usually occurs in adults and is secondary to an open wound, most often to the bone or surrounding tissue. It may be the result of delayed or inadequate treatment of acute hematogenous osteomyelitis or osteomyelitis caused by direct contamination of bone by exogenous organ- isms. Chronic osteomyelitis can persist for years; it may appear spontaneously following a minor trauma, or when resistance is lowered. The hallmark feature of chronic osteomyelitis is the presence of infected dead bone, a sequestrum, that has separated from the living bone. 8,18,19 A sheath of new bone, called the involucrum, forms around the dead bone. Radiologic techniques such as x-ray films, bone scans, and sinograms are used to identify the infected site. Chronic osteomyelitis or infection around a total joint prosthesis can be difficult to diagnose because the classic signs of infection are not apparent and the blood leukocyte count may not be elevated. A subclinical infec- tion may exist for years. Bone scans are used with bone biopsy for a definitive diagnosis. The treatment of chronic bone infections begins with wound cultures to identify the microorganism and its