Disturbances in the structure and function of the skeletal system. The musculoskeletal system provides a rigid structural frame that permits locomotion through muscle action and aids in the functioning of the other organ systems. It also houses blood-forming marrow tissue and stores calcium, phosphorus, magnesium, and a variety of other ionic species. Bone is unique among the tissues of the body in that it responds to injury by re-forming itself identically over time, without scarring.
Trauma
Trauma to the musculoskeletal system can produce a closed or open fracture, a joint dislocation, or a sprain. Fractures are manifested clinically by significant pain, swelling, and false motion, and in long-bone injuries by crepitation. Dislocation occurs more commonly in the shoulder and fingers than in any other joints. Injuries to the ligaments that maintain joint alignment are known as sprains and occur most frequently at the ankle.
Bone healing begins with cellular proliferation and the formation of new blood vessels, which provide provisional stabilization through the formation of a cartilaginous matrix. Calcification of this matrix produces a disorganized bony architecture (callus) that provides mechanical stability at the fracture site until final internal remodeling takes place. The extent and speed of this process depend on both mechanical stress and the age of the individual. See also Bone.
Neoplasms
Primary neoplasms of bone and connective tissue are relatively uncommon compared with other musculoskeletal conditions. The most frequently occurring malignant neoplasms are multiple myeloma, osteosarcoma, chondrosarcoma, and Ewing's tumor. In young individuals the most common site of a neoplasm is the tibia or femur in the vicinity of the knee, while in older individuals the flat bones, such as the ilium and those of the axial skeleton, are frequently affected.
Benign lesions have many names and are also classified according to the type of tissue primarily affected (bone, cartilage, fibrous tissue). The enchondroma is a lesion of cartilage within the bone; an exostosis is a lesion of cartilage that grows away from bone on a bony pedicle, usually near a joint. Bony lesions include the osteoblastoma and the osteoid osteoma; both of these have the histologic appearance of bone and are benign. Fibrocystic lesions include unicameral bone cysts, fibrous cortical defects, fibrous dysplasia, and giant-cell tumors. Fibrous dysplasia is a developmental lesion that often is characterized by multiply involved bones and is associated with café-au-lait spots on the skin. Unicameral bone cysts occur preferentially on the proximal humerus in adolescent children. They cause thinning of the bone and, occasionally, pathologic fractures. See also Oncology; Tumor.
Metabolic bone disease
Metabolic bone disease is an alteration in the normal bone metabolism. In various metabolic bone diseases, there are disturbances in the balance between osteoblastic and osteoclastic activity that alter the stability of skeletal structures. Vitamin D deficiency results in an inability to mineralize the osteoid, the consequences of which are rickets in children and osteomalacia in adults. Rickets is characterized by shortness of stature and angular deformities of the weight-bearing bones. Osteomalacia is rare but can result when vitamin D is not absorbed through the gastrointestinal tract. It is associated with significant and widespread pain and tenderness of the bones and deformity of the spine and limbs. See also Vitamin D.
Osteoporosis, the most common metabolic bone disease, occurs in a variety of diseases. In older persons, it can lead to fracture; thoracic vertebral bodies, the hip, and the wrist are the sites most commonly affected. While postmenopausal and senile osteoporosis results from insufficient bone production (decreased osteoblastic activity) and excessive bone destruction (increased osteoclastic activity), the precise etiology of this disorder is unknown. See also Calcium metabolism; Osteoporosis.
Osteomyelitis
Osteomyelitis is an infection of bone that is the result of either the blood-borne spread of an infectious agent or the secondary contamination of a fracture that has penetrated the skin. The bacterium Staphylococcus aureus is the most common causative agent. Acute osteomyelitis is characterized by severe bone tenderness and an unwillingness to use the limb, accompanied by loss of appetite and a fever.
Septic arthritis
Although infection of a joint can result from direct inoculation with an infectious agent, septic arthritis is most often a blood-borne condition. As with osteomyelitis, S. aureus is most often responsible. An individual with an infected joint usually experiences muscle spasm, severe tenderness and pain with the slightest movement, elevated temperature, and swelling of the joint.
Osteoarthrosis
Osteoarthrosis is a premature or excessive deterioration of the cartilage surface of a joint. The local deterioration of the cartilage surface is associated with remodeling of the contiguous bone and subsequent secondary inflammation of the membrane lining the joint. When it reaches this stage, it is referred to as osteoarthritis.
Rheumatoid arthritis
Rheumatoid arthritis is one of a family of inflammatory polyarthritides. The condition is thought to be caused by an abnormality in the immune system in which the body produces antibodies against its own tissues. In addition to the joints, other organ systems are often involved. See also Arthritis; Skeletal system.
