Loose Joint

LOOSE JOINT, a term referring only to so-called true joints, or diarthroses. The area of contact between two or more bones forming a joint depends mainly on the geometric shape of the articular ends. The strength of this contact in the ball-and-socket hip joint is ensured, in addition to other forces common to all joints, by air pressure, which sucks the head into the acetabulum. The usual fastenings of a joint are the articular capsule and the ligaments fused to it with great strength and little elasticity. The location of these ligaments corresponds to the mechanics of joint movement and aims to properly direct movement and limit it within certain bounds. The living muscular force, adapting to different positions of the articular ends in different phases of movement, is also an energetic obstacle to the separation of the articular ends. The range of movement in various joints thus depends on the shape of the articular ends, the elasticity of the capsule, the location of the ligaments, and the relationship of the muscles to the joint. Excess surface area in a joint, extending beyond certain limits, gives rise to the term loose joint. Among the causes of this phenomenon, conditions that disrupt the integrity of the joint skeleton are foremost. Severe trauma (whether it is a gunshot wound with comminution of one or both epiphyses, extensive resection of both joint ends) leads to a defect causing joint laxity. Significant changes in the shape of the articular ends, depending also on trauma or chronic deforming arthritis, by disrupting proper contact between the articular ends, can weaken the strength of the capsule and ligamentous apparatus, especially when statics of the lower limbs are disturbed. A rare example of this type is the loose knee (jambe de Polichinelle) in tabetic joint destruction. Improper statics alone can cause knee laxity in genu valgum. Muscle insufficiency in paralysis of the corresponding muscle group, especially when developed from childhood on the basis of poliomyelitis, leads to severe forms of loose joint. The effect of gravity on the upper extremity particularly increases the stretching of the capsule and ligaments of the shoulder joint; similar laxity is observed in the joints of the lower extremities, especially the ankle. A loose joint can also result from extensive, long-lasting effusion in the joint. A loose joint manifests as severe functional impairment. Severe defects of the bony apparatus, with intact muscles, disrupt the mechanics in the former joint due to the destruction of fixed axes of rotation. Laxity of a large joint can affect more peripheral joints due to the inability to fix the origin points of muscles necessary for developing motor force. Thus, one large loose joint severely impairs the function of the entire limb. Treatment measures for loose joints may have limited success. In view of this, prevention is particularly important. Resections of joints should be, as much as possible, conservative; in some cases, the defect resulting from surgery has been compensated for by a transplanted (homo- or heteroplastic) joint. With prolonged effusions, stretching of the capsule is prevented by punctures. To prevent joint laxity in childhood paralysis, measures are taken to maintain muscle vitality (for example, electrization, massage, mud therapy). In hopeless cases of loose joint, it is fixed by an orthopedic apparatus, which makes the joint immobile or allows limited movement within desired limits. More complex "fixation apparatuses" for the loose knee can be equipped with a lock that prevents knee flexion during walking and opens for knee flexion when sitting. A severe but radical and inexpensive method of fixing a loose joint is artificial fusion of the articular surfaces—arthrodesis, performed by removal of the articular cartilage. Such operations are most frequently applied to the shoulder, knee, ankle, and other joints of the foot. In some cases of joint lesions of the lower extremity (in the knee or foot), amputation and an artificial limb provide a more favorable solution. G. Turner.