joint disease

Introduction

      any of the diseases or injuries that affect human joints (joint). arthritis is no doubt the best-known joint disease, but there are also many others. Diseases of the joints may be variously short-lived or exceedingly chronic, agonizingly painful or merely nagging and uncomfortable; they may be confined to one joint or may affect many parts of the skeleton. For the purposes of this article, two principal categories are distinguished: joint diseases in which inflammation is the principal set of signs or symptoms and joint diseases, called noninflammatory in this article, in which inflammation may be present to some degree (as after an injury) but is not the essential feature.

Inflammatory (inflammation) joint diseases: types of arthritis

       arthritis is a generic term for inflammatory joint disease. Regardless of the cause, inflammation of the joints may cause pain, stiffness, swelling, and some redness of the skin about the joint. Effusion of fluid into the joint cavity is common, and examination of this fluid is often a valuable procedure for determining the nature of the disease. The inflammation may be of such a nature and of such severity as to destroy the joint cartilage and underlying bone and cause irreparable deformities. Adhesions between the articulating members are frequent in such cases, and the resulting fusion with loss of mobility is called ankylosis. Inflammation restricted to the lining of a joint (the synovial membrane) is referred to as synovitis. Arthralgias simply are pains in the joints; as ordinarily used, the word implies that there is no other accompanying evidence of arthritis. rheumatism, which is not synonymous with these, does not necessarily imply an inflammatory state but refers to all manners of discomfort of the articular apparatus including the joints and also the bursas, ligaments, tendons, and tendon sheaths. Inflammation of the spine and joints is called spondylitis.

bursitis

      Inflammation of a synovial bursa, the lubricating sac located over a joint or between tendons and muscles or bones, is called bursitis (or bursal synovitis). Bursas sometimes are affected along with the joints and tendon sheaths in rheumatoid arthritis and gout. Infectious agents introduced by penetrating wounds or borne by the bloodstream also may result in bursitis, but this is unusual. The prepatellar bursa, located on the lower part of the kneecap, is especially subject to involvement in brucellosis (undulant fever).

      The cause of most cases of bursitis appears to be local mechanical irritation. Often the irritation is of occupational origin and occurs in the shoulder region, at the knee, or near the hip. The inflammatory reaction may or may not include deposition of calcium salts. The border between bursitis and other painful rheumatic conditions of the soft tissues is indistinct in many instances.

      The most common form of bursitis affects the subdeltoid bursa, which lies above the shoulder joint. Bursitis in this circumstance is not the primary abnormality but results from degeneration and calcification of the adjacent rotator tendon. Direct injury is not usually the cause of calcium deposits and inflammation in the tendon; indeed, heavy labourers are less frequently affected than persons employed in less-strenuous occupations. The bursa proper is affected only when debris from the tendon extends into it, this intrusion being the principal cause of an acutely painful shoulder. The condition occurs most often in middle age and is infrequent among young children. Women are twice as likely to have the condition as men. The onset may be sudden and unprovoked. Pain and tenderness are great, and there is difficulty in raising the arm. Resting the arm and use of analgesics tend to lessen the discomfort; corticosteroids may reduce inflammation; and carefully graduated exercises may be used to lessen the possibility of lasting stiffness of the shoulder. Many months may pass before complete recovery is attained. Chronic inflammation of the bursa at the side of the hip joint—trochanteric bursitis—has a similar course.

      The more clearly traumatic forms of bursitis are exemplified by “beat knee,” a bursitis that develops below the kneecap because of severe or prolonged pressure on the knee. Bloody fluid distends the bursa and, unless removed early, may cause the walls of the bursa to become thickened permanently. Treatment, which involves protection from further irritation to the extent that this is possible, is otherwise similar to that for subdeltoid bursitis. A fair proportion of these lesions become infected as a consequence of injury to the overlying skin.

Infectious (infectious disease) arthritis

      Joints may be infected by many types of microorganisms (bacteria, fungi, viruses) and occasionally by animal parasites. There are three routes of infection: by direct contamination, by way of the bloodstream, and by extension from adjacent bony infections ( osteomyelitis). Direct contamination usually arises from penetrating wounds but may also occur during surgery on joints. Blood-borne infections may enter the joints through the synovial blood vessels. Commonly, however, foci of osteomyelitis occur first in the long bones near the end of the shaft or next to the joint. The infection then extends into the joint through natural openings or pathological breaches in the outside layer, or cortex, of the bone. Characteristically, hematogenous (blood-borne) infectious arthritis affects one joint (monarthritis) or a very few joints (oligoarthritis) rather than many of them (polyarthritis) and usually affects large joints (knee and hip) rather than small ones. Infections of the joints, like infections elsewhere in the body, often cause fever and other systemic indications of inflammation.

      Joint cartilage may be damaged rapidly by formation of pus in infections by such bacteria as staphylococci, hemolytic streptococci, and pneumococci. tuberculosis of the joint can result in extensive destruction of the adjacent bone and open pathways to the skin. Tuberculous spondylitis (Pott disease), also known as Pott disease, is the most common form of this infection. It occurs mostly in young children. Treatment is with the antibiotic streptomycin and with antituberculous medications such as isoniazid and rifampin. A frequent fungal infection in the United States is caused by Coccidioides immitis, an organism indigenous to the arid regions of the southwestern United States. As in tuberculosis, seeding from the lung to the bone usually precedes involvement of a joint. brucellosis, like tuberculosis, has a particular affinity for the spine. Brucella suis is the most likely brucellar organism to cause skeletal disease. Deformities and destructive changes in the joints in leprosy (Hansen disease) arise from infection of the nerves by the leprosy bacillus or from infection by other bacteria.

      Among the better-recognized viral infections that can cause joint discomforts are rubella (German measles) and serum hepatitis, both of which usually are of short duration and have no permanent effect. Several tropical forms of synovitis are also viral. Dranunculiasis (Guinea worm disease) is an infection caused by the guinea worm, a parasitic nematode that affects persons in tropical countries, and may involve the joints.

      Infectious arthritis complicates several sexually transmitted diseases (sexually transmitted disease), including gonorrhea. Early treatment with penicillin may provide a prompt cure and may prevent the marked destruction of the joint that could otherwise ensue. Reactive arthritis (Reiter disease (Reiter syndrome)), which may occur after food poisoning or infection with some sexually transmitted diseases, usually improves spontaneously over the course of several months. Characteristically, reactive arthritis involves inflammation of the joints, the urethra, and the conjunctiva of the eyes. syphilis appears not to infect the joints directly except in the most advanced stage of the disease and in congenital syphilis. The latter frequently causes destructive inflammation in the growing cartilaginous ends of the bones of newborn infants. Untreated, it leads to deformity and restriction of growth of the involved part, but early treatment with penicillin may result in complete recovery. Clutton joint is another type of congenital syphilitic lesion. It is a true inflammation of the synovial membrane that occurs in children between ages 6 and 16; although it causes swelling of the knees, it is a relatively benign condition. Lesions characteristic of tertiary syphilis sometimes occur in the joints of children who have congenital syphilis. yaws, a nonvenereal infection by an organism closely related to that causing syphilis, leads to similar skeletal lesions. The condition has largely been eradicated but still affects persons in tropical areas.

rheumatoid arthritis and allied disorders

      In several types of arthritis that resemble infectious joint disease, no causative agent has been isolated. Principal among these is rheumatoid arthritis. This disorder may appear at any age but is most usual in the fourth and fifth decades. A type that affects children is called juvenile rheumatoid arthritis. Rheumatoid arthritis typically affects the same joints on both sides of the body. Almost any movable joint can be involved, but the fingers, wrists, and knees are particularly susceptible. The joints are especially stiff when the affected person awakes. Rheumatoid arthritis is not only a disease of the joints; fatigue and anemia indicate that there is a more generalized systemic involvement. A slight fever may sometimes be present. Lesions also occur in sites outside the joints. Involvement of bursas, tendons, and tendon sheaths is an integral part of the disease. Approximately one of five affected persons has nodules in the subcutaneous tissue at the point of the elbow or elsewhere. Inflammatory changes also are found sometimes in small arteries and the pericardium—the membrane enclosing the heart.

      The course of the disease varies greatly from person to person and is characterized by a striking tendency toward spontaneous remission and exacerbation. With continuing inflammation of the joints, there is destruction of the joint cartilage. The degree of articular (joint) disability present in rheumatoid arthritis depends in large measure upon the amount of damage done to this cartilage. If the injury is severe, large areas of bone may be denuded of cartilage, so that adhesions form between the articular surfaces. Subsequent transformation of these adhesions into mature fibrous or bony connective tissue leads to firm union between the bony surfaces (ankylosis), which interferes with motion of the joint and may render it totally immobile. In other instances, the loss of cartilage and bone, coupled with the weakening of tendons, ligaments, and other supporting structures, results in instability and partial dislocation of the joint. In a small minority of cases, the disease pursues a rapidly progressive course marked by relentless joint destruction and evidence of diffuse vasculitis (inflammation of blood vessels). Many affected persons are benefited over the course of several months by rest, analgesic medications, and therapeutic exercises. In approximately one-third of the instances of the disease, it progresses and causes serious incapacity. In the absence of proper physical therapy, the joints may become greatly deformed and ankylosed.

      There is now convincing evidence that immunologic reactions play an important role in the causation of rheumatoid arthritis. The blood of approximately 80 to 90 percent of persons with rheumatoid arthritis contains an immunoglobulin called rheumatoid factor that behaves as an antibody and reacts with another class of immunoglobulin. This immunoglobulin is produced by plasma cells that are present in sites of tissue injury. There is evidence that suggests that this agent may be one or more viruses or viral antigens that persist in the joint tissues.

      Although there is no cure, corticosteroid medications and nonsteroidal anti-inflammatory drugs (NSAIDs) may be helpful in reducing pain and inflammation. The effectiveness of corticosteroids generally diminishes with time, and there are definite disadvantages in their use, such as a greater susceptibility to infection and peptic ulcers (peptic ulcer). Disease-modifying antirheumatic drugs (DMARDs) may slow the progression of the disease by inhibiting further joint damage. Surgery is often of value in correcting established deformities. A mild dry climate seems to be beneficial in some cases, but the improvement is generally not sufficient to justify a move that would disrupt the affected person's life.

      There is at times a close association between rheumatoid arthritis and seemingly unrelated disorders. In about one-third of the cases of Sjögren syndrome (Sjögren's syndrome), there is also rheumatoid arthritis, and high levels of rheumatoid factors are usually present in the bloodstream. In Felty syndrome, rheumatoid arthritis coexists with enlargement of the spleen and diminution in the number of circulating blood cells, particularly the white blood cells. Removal of the spleen restores the number of blood cells to normal but has no effect on the arthritis.

      Several other types of polyarthritis resemble rheumatoid arthritis but characteristically lack the rheumatoid factors in the bloodstream. Psoriatic arthritis, associated with the skin disease psoriasis, differs from rheumatoid arthritis insofar as it has a predilection for the outer rather than the inner joints of the fingers and toes; furthermore, it results in more destruction of bone. Another type of arthritis is associated with chronic intestinal diseases— ulcerative colitis, regional enteritis, inflammatory bowel disease, cirrhosis, and Whipple disease. Ankylosing spondylitis, also known as Marie-Strümpell disease or Bechterew disease, affects some of the peripheral joints, such as the hip; but its principal location is in the spine and sacroiliac joints. In the spine the small synovial joints and the margins of the intervertebral disks are both involved. These structures become bridged by bone, and the spine becomes rigid. Ankylosing spondylitis affects approximately eight times as many men as women. The age of onset is lower than that of rheumatoid arthritis. The general management of the two disorders is much the same, but phenylbutazone is more effective in ankylosing spondylitis than in rheumatoid arthritis.

collagen diseases

      The collagen diseases are so called because in all of them abnormalities develop in the collagen-containing connective tissue. These diseases are primarily systemic and are frequently accompanied by joint problems. One of these diseases, systemic lupus erythematosus (lupus erythematosus) (SLE), may affect any structure or organ of the body. An association with rheumatoid arthritis is suggested by the fact that one-quarter of those with SLE have positive serological tests for rheumatoid factor, and perhaps as many patients with rheumatoid arthritis have positive lupus erythematosus tests. In another collagen disease, generalized scleroderma, the skin becomes thickened and tight. Similar changes occur in other organs, particularly the gastrointestinal tract.

       rheumatic fever often is classified with the collagen diseases. It has certain similarities to rheumatoid arthritis, as the name suggests, but the differences are more notable. In both conditions, arthritis and subcutaneous nodules occur, and inflammation of the pericardium is frequent. Nevertheless, the joint manifestations of rheumatic fever typically are transient, while those of rheumatoid arthritis are more persistent. The reverse is true of cardiac involvement in the two disorders. There is no compelling evidence that streptococcal infection is an important causative factor in rheumatoid arthritis, but it appears well established in rheumatic fever.

      Arthritis more or less resembling rheumatoid arthritis occurs in roughly one-fourth of children who lack gamma globulins in the blood. In this circumstance there is a deficit in the body's mechanisms for forming antibodies.

Miscellaneous arthritides

      Several types of arthritis appear to be related to a hypersensitivity reaction. Erythema nodosum is a skin disease characterized by the formation of reddened nodules usually on the front of the legs. In the majority of cases, pain may arise in various joints, and sometimes swelling appears. Lymph nodes at the hilus of the lung (the site of entrance of bronchus, blood vessels, and nerves) are enlarged. The synovitis disappears in the course of several weeks or months. Many cases of erythema nodosum are associated with drug hypersensitivity, with infections such as tuberculosis, coccidioidomycosis, and leprosy, and with sarcoidosis, a systemic disease in which nodules form in the lymph nodes and other organs and structures of the body. Synovitis of this sort occurs in 10 to 15 percent of patients with sarcoidosis.

      Palindromic rheumatism is a disease of unknown cause that is characterized by attacks that last one or two days but leave no permanent effects. Nevertheless, palindromic rheumatism rarely remits completely, and approximately one-third of cases result in rheumatoid arthritis. Polymyalgia rheumatica, a relatively frequent condition occurring in older people, is characterized by aching and stiffness in the muscles in the region of the hips and shoulders, but the joints proper do not seem to be involved. There does seem to be some relationship to a type of arterial inflammation called giant cell arteritis. Polymyalgia rheumatica is not usually accompanied by serious systemic abnormalities and is treated with corticosteroids or NSAIDs.

Noninflammatory joint diseases: injury and degenerative disorders

Traumatic joint diseases

      Blunt injuries to joints vary in severity from mild sprains (sprain) to overt fractures and dislocations. A sprain is ligament, tendon, or muscle damage that follows a sudden wrench and momentary incomplete dislocation (subluxation) of a joint. There is some slight hemorrhage into these tissues, and healing usually takes place in several days. More-violent stresses may cause tears in ligaments and tendons. Because the ligaments and tendons are so strong, they frequently are torn from their bony attachments rather than ripped into segments. Ligamentous, tendinous, and capsular tears are able to heal by fibrous union, provided that the edges are not totally separated from each other. Internal derangements of the knee most often arise from tears in the semilunar cartilages (menisci). Usually it is the medial meniscus that is disrupted. These tears are particularly frequent in athletes and develop as the knee is twisted while the foot remains fixed on the ground. Locking of the knee is a characteristic symptom. Because the semilunar cartilages have little capacity for repair, they must be removed surgically. Bleeding into the joint, called hemarthrosis, may also result from injuries.

      Most traumatic dislocations are treated by prolonged immobilization to permit the capsular and other tears to heal. In some instances, surgical repairs are required. Fractures of bone in the vicinity of joints may or may not extend into the joint space. Whether they do or not, the normal contour of the joint must be restored or arthritic complications are likely to develop.

Degenerative joint disease

       osteoarthritis is a ubiquitous disorder affecting all adults to a greater or lesser degree by the time they have reached middle age. The name osteoarthritis is a misnomer insofar as its suffix implies that the condition has an inherently inflammatory nature. For this reason it frequently is called degenerative joint disease, osteoarthrosis, or arthrosis deformans. When the spine is involved, the corresponding term is spondylosis. Unlike rheumatoid arthritis, osteoarthritis is not a systemic disease and rarely causes crippling deformities. In the majority of instances, the milder anatomical changes are not accompanied by appreciable symptoms. The changes are characterized by abrasive wearing away of the articular cartilage concurrent with a reshaping of adjacent ends of the bones. As a result, masses of newly proliferated bone (osteophytes) protrude from the margins of the joints.

      The clinical manifestations of osteoarthritis vary with the location and severity of the lesions. The most disabling form of the disorder occurs in the hip joint, where it is known as malum coxae senilis. Osteoarthritis of the hip, like that of other joints, is classified as primary or secondary. In secondary osteoarthritis the changes occur as a consequence of some antecedent structural or postural abnormality of the joint. In about half the cases, however, even rigorous examination fails to disclose such an abnormality; in these instances the osteoarthritis is called primary.

      Probably the most frequent cause of osteoarthritis of the hip is congenital dysplasia (dislocation or subluxation of the hip). This term refers to a poor fit of the head of the femur, the long bone of the thigh, with its socket in the pelvis, the acetabulum. There is evidence that many cases arise in infancy as a consequence of swaddling infants or carrying them in headboards, procedures that keep the thighs in an extended position. Before the child is able to walk, the hip joint has frequently not yet fully developed, and the head of the femur is forced out of its normal position by this extension.

      Osteoarthritis of the hip occurring in relatively young persons—in their 30s or 40s—frequently follows a progressive course and requires surgical treatment. Two rather different strategies of surgery are employed: one, an osteotomy, involves reshaping the upper end of the femur so that the load borne by the joint is distributed more efficiently; the other requires removal of the diseased tissue and replacement by an artificial joint.

      Aside from the rapidly developing forms, osteoarthritis of the hips also appears frequently in elderly persons. Aging is an important factor in the development of other forms of degenerative joint disease as well, since the lesions increase in frequency and severity as time passes.

      Considerations like these have led to the view that the principal causative factors in degenerative arthritis are faulty mechanical loading and senescent deterioration of joint tissue. Single injuries, unless they leave a joint permanently deformed, rarely result in osteoarthritis. Recurrent small athletic and occupational injuries, such as those arising from heavy pneumatic drill vibrations, apparently are more likely to do so. Lifting heavy weights has been implicated in some studies of spinal involvement.

      Aside from surgery of the sort noted in the hip and sometimes the knee, treatment includes rest and proper exercise, avoidance of injury, the use of analgesics, NSAIDs, and corticosteroids to relieve pain, and several types of physical therapy.

      Chondromalacia patellae is a common and distinctive softening of the articular cartilage of the kneecap in young persons, particularly young athletes. It results in “catching” and discomfort in the region of the patella, or kneecap, as the knee is bent and straightened out. Pathologically, the changes are indistinguishable from changes that occur early in osteoarthritis. Treatment includes rest, NSAIDs, and physical therapy. More-serious cases of chrondromalacia patellae may require surgery.

      Degeneration of the intervertebral disks between the vertebrae of the spine is a frequent and in some ways analogous disorder. Often this occurs acutely in young and middle-aged adults. The pulpy centre of the disk pushes out through tears in the fibrous outer ring, resulting in a slipped disk (herniated disk). When this takes place in the lumbosacral region, the displaced centre (the nucleus pulposus) impinges on the adjacent nerve roots and causes shooting pains in the distribution of the sciatic nerve—hence the name sciatica. Pain in the small of the back may be associated not only with degeneration of the intervertebral disk and spondylosis but also with structural abnormalities of the region. Principal among these is spondylolisthesis, in which there is an anterior displacement of one lumbosacral vertebral body on another. The episodes respond to bed rest and mechanical support from wearing an abdominal brace. Muscle relaxants and muscle-strengthening exercises also may be of value. Recurrences are prevented by avoidance of back strains. The protruding tissue is removed by surgery only in cases in which pain and neurological defects are severe and fail to improve after less drastic measures.

Congenital (congenital disorder) and hereditary abnormalities

      Congenital abnormalities are not necessarily transmitted from generation to generation but can be acquired during fetal life or soon after delivery. The latter abnormalities usually are structural; the inherited defects may be structural or appear later in life as the consequence of a systemic metabolic defect present from conception. Mention has already been made of congenital dysplasia of the hip. The joint proper may be initially normal in this condition and in several other congenital disorders; only after other supporting tissues have altered the proper relationships does the contour of the bone and joint become distorted. In arthrogryposis multiplex congenita (multiple congenital crooked joints), many joints are deformed at birth, particularly the hip. The deformities are the consequence of muscle weakness that in turn sometimes results from spinal cord disease. clubfoot (talipes equinovarus) is a congenital deformity in which the foot is twisted downward and inward because the ligaments and tendons are too short. Only infrequently are the muscles at fault. Idiopathic scoliosis (lateral curvature of the spine) usually makes its appearance during early adolescence. There is considerable plasticity of the tissues with latitude for correction of these deformities and for preventing their progression. For this reason the application of splints and other mechanical supports as soon as the condition is recognized is the major part of treatment. Surgery is resorted to when other measures have failed.

      Structural variations in the lumbosacral spine are common and often harmless. Incompletely ossified interarticular portions of the neural arches of a vertebra constitute a congenital anomaly referred to as spondylolysis (spondylosis); it predisposes to forward slipping of the vertebra later in life and so to the congenital type of spondylolisthesis described above. By contrast, when the failure of bony fusion exists between the right and left halves of the neural arch, the condition is called spina bifida occulta.

      Several genetically influenced metabolic diseases (metabolic disease) have articular manifestations. gout is the most frequent of these. Chalklike masses of sodium acid urate crystals are deposited in and about the joints. Acute episodes of gouty arthritis are extremely painful. There is a tendency toward involvement of the big toe, a condition known as podagra.

      Ochronotic arthropathy results from another, rarer inborn error of metabolism. It is characterized by pigmentation and degeneration of hyaline cartilage and by defective breakdown of the amino acids tyrosine and phenylalanine, causing large amounts of homogentisic acid to accumulate in body fluids and the urine. The urine turns black when exposed to air, a phenomenon called alkaptonuria. After many years, severe degenerative changes occur in the peripheral joints and in the spine.

      In yet another metabolic disease, chondrocalcinosis, or pseudogout, crystals of calcium pyrophosphate are deposited in joint cartilages. There are several forms of the disease. Sometimes there are no symptoms; in other cases, symptoms are sufficiently severe to cause confusion with rheumatoid arthritis. Some cases run in families.

      Joints also are affected by several relatively rare hereditary diseases collectively called the mucopolysaccharidoses, which result from defects in the metabolism of connective tissue matrices. In Hurler syndrome (Hurler's syndrome), for example, manifestations include mental retardation and heart failure, although skeletal growth also is abnormal. Most affected persons do not survive adolescence. Morquio disease (Morquio syndrome), by contrast, is a recessively inherited form of severe dwarfism that is not associated with mental deficiency or cardiac insufficiency. X-rays of the spine reveal a characteristic misshapen flattened appearance of the vertebral bodies. Premature and severe degenerative changes in the peripheral and spinal joints are common. Polyepiphyseal dysplasias (abnormal development in childhood of a number of epiphyses—the ends or outlying portions of bones separated from the main body of the bone by cartilage) are a vaguely similar, though much milder, group of conditions in which precocious osteoarthritis and spondylosis are the first abnormalities to appear. Preexisting changes in the skeleton, resembling a milder form of Morquio disease, may then be discovered upon X-ray examination. The hip joint is most severely affected. In some cases the inheritance is dominant, in others recessive. Abnormalities in the fibrous components of connective tissue matrices are characteristic of Marfan syndrome. Many organs are affected by this condition, and the articular manifestations are less important. The joints are excessively loose, however, and painful complications develop in about half of affected individuals.

Secondary joint diseases

Hemorrhagic joint diseases

      Hemarthrosis (bleeding into the joints) is a major complication of hemorrhagic disorders. Aside from the life-threatening episodes of bleeding, it constitutes the principal disability arising from the hemophilias (hemophilia). Most persons with these clotting defects are affected and usually within the first years of life. Bleeding into the joints is usually caused by relatively minor injury but may leave several residual deformities and loss of mobility of the part. Recurrent hemorrhage into an isolated joint, in the absence of a systemic tendency to bleed, is characteristic of pigmented villonodular synovitis, a tumour characterized by abnormal thickening and coloration of the synovial membrane. This is not a primary inflammatory disease of joints, despite the name. Large joints, usually of the lower extremity, are affected.

Aseptic necrosis

      Because joint cartilages are without blood vessels, they are not destroyed by failures in the blood supply. Nevertheless, several joint diseases arise in association with aseptic necrosis—tissue death not caused by infection—of bone next to the joints. The precise nature of the failure of the blood supply is not always known. Fractures are one obvious cause. In decompression sickness (caisson disease) the obstructive elements are minute gas bubbles formed in the circulating blood from excessively rapid decompression. Decompression syndromes occur principally in divers and tunnel workers. Acute cases take the form of the “bends” and frequently are fatal. However, in a large proportion of workers in these occupations, even those who have not experienced the bends, extensive infarcts (areas of dead tissue) of bones and secondary osteoarthritis develop after many years. Analogous changes in sickle cell anemia presumably result from blood clotting related to the abnormality of the red blood cells. There is no entirely persuasive explanation for other types of aseptic necrosis that occur in adults. In each instance the hip is the joint most affected. Osteochondritis dissecans is a similar disorder in which a piece of joint cartilage and of underlying bone breaks off and lodges in the joint cavity. Usually the person affected can remember having injured the joint. The knee is the most frequent site. The condition usually occurs during the second and third decades of life. The displaced fragment causes a creaking sound when the joint is moved and must be removed by surgery.

      Two different patterns of aseptic necrosis with joint involvement occur in growing children. One type (slipped epiphysis) is characterized by partial or complete tearing away of an epiphysis, usually as the result of injury. The epiphysis at the upper end of the thighbone (femur) is particularly susceptible. Osgood-Schlatter disease is an analogous lesion, but it affects a growth centre (anterior tibial tubercle) at a slight distance from the joint rather than in its immediate vicinity. In the second type of aseptic necrosis in children, the necrosis is not the consequence of mechanical tearing away of the part. The most frequent site is in the head of the thighbone; necrosis at this site is known as Legg-Calvé-Perthes disease. It occurs in children between ages 3 and 13 and is much more frequent in boys than in girls. Persistent pain is the most prominent symptom. Uncorrected severe lesions lead to arrest of growth, deformity, and arthritic changes in the hip joint.

Endocrine (endocrine system, human) factors

      The only joint lesion clearly related to a malfunctioning of the ductless (endocrine) glands is acromegaly. This disease results from excessive secretion of growth hormone by a tumour of the anterior pituitary gland. The hormone stimulates the proliferation of several skeletal soft tissues and bone including the joint cartilage. This causes the enlargement of the fingers that is characteristic of the disease. The enlarged joints are particularly prone to undergo osteoarthritic degeneration. Cretinism, which is related to hypothyroidism, causes dwarfism and abnormally developed bony epiphyses but apparently does not lead to joint disease. Severe diabetes mellitus, however, may result in Charcot joint (see below) arising from the effect of diabetes on the nervous system.

neurogenic arthropathy

      Neurogenic arthropathy, also known as Charcot joint, is a severe degenerative disease related to nerve lesions that develops when the sensory mechanisms of joints are impaired. The current view is that these joints become excessively strained because the ability to receive stimuli from bodily structures and organs necessary for normal limitation of motion is lacking. As a result, the supporting tissues are torn, and there is extreme disintegration of the structure. Neurogenic arthropathy is most often associated with diabetes mellitus, tabes dorsalis (a late form of syphilis affecting the posterior columns of the spinal cord), syringomyelia (a disease in which cavities develop in the gray substance of the spinal cord), pernicious anemia, and leprosy. The disease usually is localized to one joint or one group of joints, depending on the location of the nerve defect. Pain is frequently mild considering the massive distortion of the joint. Treatment is difficult and is based primarily on immobilization and restriction of weight bearing.

Hypertrophic osteoarthropathy

      In approximately 5 to 10 percent of persons who have primary tumours within the chest, the ends of the bones near the joints become enlarged and painful. New bone is formed in the periosteum, and only occasionally do abnormalities develop within the joints themselves. Just how the chest abnormality leads to hypertrophic osteoarthropathy (disease of bones and joints with abnormal growth of bone) is somewhat of a mystery, but there is reason to believe that the vagus nerve is involved, since the condition is usually relieved promptly by cutting the vagus. It is also relieved by removal of the tumour. In this disorder the tips of the fingers become club-shaped, a painless lesion that occurs in many other circumstances as well.

Reflex sympathetic dystrophy

      Reflex sympathetic dystrophy—also called shoulder-hand syndrome because pain in the shoulder is associated with pain, swelling, and stiffness of the hand—only rarely develops in the wake of external injury. Most often it follows a heart attack (myocardial infarction) or is associated with disease in the neck vertebrae; frequently there is no apparent cause. Most often the syndrome begins with pain and stiffness of a shoulder, followed shortly by pain and swelling of the hand, with vascular (blood vessel) changes in the skin of the hand. Over the course of several months, the swelling and vascular changes subside, but the skin and soft tissues become tightened. These changes sometimes disappear completely, but in other cases they leave permanent contractures—i.e., flexion and loss of mobility due to the tightening of the fingers. Loss of mineral occurs in the bones of the shoulder, wrist, and fingers. Blocking (interruption of functioning) of sympathetic nerves serving the area, administration of corticosteroids, and therapeutic exercises are used in the management of the condition.

Tumours (tumour) of joints

      Tumours (tumour) of joints are uncommon. In synovial chondromatosis, a benign condition, numerous cartilaginous nodules form in the soft tissues of the joint. The lesion is usually confined to one joint, particularly the knee, and occurs in young or middle-aged adults. It may or may not cause pain or swelling and usually is cured by excision of a portion of the synovial membrane. The tumour rarely becomes malignant. The cartilaginous nodules sometimes also contain islands of bone; in this circumstance the lesion is called synovial osteochondromatosis. Like synovial chondromatosis, synovial osteochondromatosis is often a spontaneous or primary disorder of unknown cause. In many cases, however, it is a development secondary to other diseases of the synovium, such as rheumatoid arthritis and even osteoarthritis.

      Synoviomas, or synovial sarcomas, are malignant tumours that arise in the tissues around the joints—the capsule, the tendon sheaths, the bursas, the fasciae, and the intermuscular septa, or divisions—and only rarely within the joint proper. Although they may occur at any age, they are most frequent in adolescents and young adults. The legs are more often involved than the arms. The tumours spread locally and also to regional lymph nodes and lungs. Synoviomas are not particularly sensitive to X-rays, and treatment with drugs has been ineffective. If distant spread has not occurred at the time the condition is identified, radical excision, which may include amputation of the part, is the recommended treatment.

Leon Sokoloff

Additional Reading

Joint diseases are described in the following advanced textbooks: W.S.C. Copeman, Copeman's Textbook of the Rheumatic Diseases, 6th ed., edited by J.T. Scott, 2 vol. (1986); Daniel J. McCarty and William J. Koopman (eds.), Arthritis and Allied Conditions: A Textbook of Rheumatology, 12th ed. (1993); and Emanuel Rubin and John L. Farber, Pathology, 3rd ed. (1999).

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