Abnormalities of Joint Position

There are five different clinical situations that are consistently associated with joint subluxation and/or dislocation: (a) trauma; (b) inflammatory joint diseases; (c) disorders with muscular imbalance; (d) disorders with joint laxity; and (e) disorders with defective development of the osseous components of the joint. A discussion of the clinical and radiographic manifestations of joint subluxation/dislocation related to trauma and inflammatory disorders is beyond the scope of this book. Among the latter, only rheumatoid arthritis is mentioned here, because of its frequency and relevance in the clinical practice (Fig. 8.7).

The broad designation of 'muscular imbalance' is meant to include several unrelated disorders, all of which are characterized by incompetence of the muscular function at a given joint. Muscular incompetence, that is, absence, atrophy, fibrosis, flaccidity, or spasticity of a muscle from any cause, results in mal-positioning and impaired development of the bony components of that joint (Dunne and Clarren 1986; Bunch 1977; Baratta et al. 1988; Fidler and Jowett 1976). However, normal growth of the osseous structures at a given joint depends not only on adequacy of the muscular forces applied, but also on proper anatomical positioning and maintenance of the joint activity; hence, absence or loss of one of these requirements affects bone growth, resulting in various bone deformities. Deformed bones lead, in turn, to anatomical incongruities at their articulation, further compromising correct bone positioning (Fer-rone 1976). An example of this complex interaction of events is offered by hip subluxation/dislocation occurring in association with neuromuscular disorders, in which both absence of hip extensor and abductors - in the presence of functioning hip flexors and adductors - and valgus deformity of the femoral neck act in concert to facilitate lateral migration of the femoral head (Goldman et al. 1988). Additional examples include glenoid dysplasia and shoulder in-

Joint Anomalies

Fig. 8.7. Rheumatoid arthritis in a 75-year-old woman. Multiple metacarpophalangeal joint subluxations with severe ulnar deviation of fingers. The simultaneous radial deviation at the radiocarpal joint of the wrist gives rise to the zigzag deformity typical of the disease. Note osteoporosis and extensive carpal bone involvement, with progressive loss of articular space and sclerosis in all compartments (the widespread nature of wrist involvement is characteristic of rheumatoid arthritis and allows differentiation from other disorders with selective com-partmental distribution)

Fig. 8.7. Rheumatoid arthritis in a 75-year-old woman. Multiple metacarpophalangeal joint subluxations with severe ulnar deviation of fingers. The simultaneous radial deviation at the radiocarpal joint of the wrist gives rise to the zigzag deformity typical of the disease. Note osteoporosis and extensive carpal bone involvement, with progressive loss of articular space and sclerosis in all compartments (the widespread nature of wrist involvement is characteristic of rheumatoid arthritis and allows differentiation from other disorders with selective com-partmental distribution)

stability developing in patients with paralysis of the upper arm caused by obstetric trauma to the brachial plexus or dislocation of an abnormally small patella, as seen in the nail-patella syndrome. In this context, it is not surprising that individuals who have suffered from intrauterine faulty positioning of the bone components in their joints, such as those with disorders loosely labeled arthrogryposis, can be affected by multiple joint subluxation or dislocations at birth (Akazawa et al. 1998; Sodergard and Ryoppy 1990; Houston et al. 1981). Similarly, it is not surprising that patients with primary disorders of bone formation and growth, such as those with dysostoses and skeletal dysplasias with prominent epiphyseal involvement, have an increased likelihood of developing joint dislocation at one or several anatomical sites. The arthrogrypotic syndromes have been discussed above in the section entitled "Joint Contracture, Joint Stiffness." The adverse effects of ligamen-tous laxity on joint mechanics and stability have been discussed in the section headed "Joint Laxity, Joint hypermobility" along with the disorders in which joint laxity is prominent, such as the Ehlers-Danlos syndromes, Marfan syndrome, and spondy-loepimetaphyseal dysplasia with joint laxity (Giunta et al. 1999).

In this section, some relevant instances of congenital single joint dislocation are presented, followed by examples of disorders that commonly manifest with multiple joint dislocations.

Arthritis Relief and Prevention

Arthritis Relief and Prevention

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