Porth's Essentials of Pathophysiology, 4e

1094

Musculoskeletal Function

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The calcium and free fatty acids form lesions composed of an insoluble “soap.” Because bone lacks mechanisms for resolving the infarct, the lesions remain for life. The symptoms associated with osteonecrosis are varied and depend on the site and extent of infarction. Typically, subchondral infarcts cause chronic pain that is initially associated with activity but that gradually becomes more progressive until it is experienced at rest. Subchondral infarcts often collapse and predispose the patient to severe secondary osteoarthritis. Diagnosis of osteonecrosis is based on history, physical findings, radiographic findings, and the results of special imaging studies, including CT scans and technetium-99m bone scans. Treatment depends on the underlying patho- logic process. In some cases, only short-term immobili- zation, nonsteroidal anti-inflammatory drugs, exercises, and limitation in weight bearing are used. Osteonecrosis of the hip is particularly difficult to treat. In persons with early disease, limitation of weight bearing through the use of a walker may allow the condition to stabilize. Although several surgical approaches have been used, the most definitive treatment of advanced osteonecrosis of the knee or hip is total joint replacement. ■■ Osteomyelitis, or infection of the bone and marrow, may be caused by a wide variety of microorganisms introduced during injury, operative procedures, or from the bloodstream. Acute osteomyelitis is seen most often as a result of direct contamination of bone by a foreign object. Chronic osteomyelitis represents an infection that continues beyond 6 to 8 weeks and may persist for years. Tuberculosis osteomyelitis, which is characterized by bone destruction and abscess formation, is caused by spread of infection from the lungs or lymph nodes. ■■ Bone infections are difficult to treat and eradicate. Measures to prevent infection include careful cleaning and debridement of skeletal injuries and strict operating room procedures. ■■ Osteonecrosis, or death of a segment of bone, is due to an interruption in blood flow rather than an infection.The mechanisms are varied and include mechanical interruption such as occurs with a fracture, vessel injury, increased intraosseous pressure with vascular compression, and corticosteroid therapy. Sites with poor collateral circulation, such as the femoral head, are most commonly affected. Symptoms include pain that varies in severity, depending on the extent of infarction.Total joint replacement is the most frequently used treatment for advanced osteonecrosis. SUMMARY CONCEPTS

Neoplasms Neoplasms of the skeletal system, often referred to as bone tumors , may be benign or malignant, and in the case of malignant neoplasms, may represent a primary tumor or secondary metastatic lesion. 5,8,18,19,41 Benign tumors greatly outnumber their malignant counterparts and occur with the greatest frequency in the first three decades of life, whereas in the elderly a bone tumor is more likely to be malignant. Both benign and malignant tumors can develop from the cartilage (chondrogenic), bone (osteogenic), and sup- porting (fibrogenic) elements of bone, and bone tumors are generally classified according to their tissue coun- terpart. As a group, these tumors affect all age groups and arise in virtually every bone. Most develop during the first several decades of life and have a propensity to originate in the long bones of the extremities; however, certain types of tumors target specific age groups and anatomic sites. Thus, the location of the tumor provides important diagnostic information. There are three major manifestations of bone tumors: pain, presence of a mass, and impairment of function. 5,8 Although benign tumors are frequently asymptomatic and are detected as an incidental finding, malignant tumors are associated with constant, deep aching pain that does not go away with rest and is present at night. However, certain benign tumors also cause night pain. A mass or hard lump may be the first sign of a bone tumor. A malignant tumor is suspected when a painful mass exists that is enlarging or eroding the cortex of the bone. The ease of discovery of a mass depends on the location of the tumor; a small lump arising on the surface of the tibia is easy to detect, whereas a tumor that is deep in the medial portion of the femur may grow to a considerable size before it is noticed. Benign and malignant tumors may cause the bone to erode to the point where it cannot withstand the strain of ordi- nary use. A sudden increase in pain followed by trivial trauma that is preceded by a history of mild, dull aching pain is suggestive of a pathologic fracture. A tumor also may produce pressure on a peripheral nerve, causing a decreased sensation, numbness, a limp, or limitation in movement. The diagnosis of bone tumors relies on the history and physical examination, as well radiography, computed tomography, andMRI. Radiographs give themost general diagnostic information, such as malignant versus benign and primary versus metastatic status. The radiograph demonstrates the region of bone involvement, extent of destruction, and amount of reactive bone formed. CT scans further aid diagnosis and anatomic localization and can identify small pulmonary metastases not seen by conventional radiographs. Magnetic resonance imaging is the most accurate method of evaluating the intramed- ullary extent of bone tumor and can demarcate the soft structures in relation to neurovascular structures with- out the use of contrast media. It is best used in conjunc- tion with a CT scan. Radionuclide bone scans are used to assess for metastasis. A biopsy may be done to determine the histologic characteristics of the tumor.