The unstable metacarpophalangeal joint in rheumatoid arthritis: anatomy, pathomechanics, and physical rehabilitation considerations

Abstract

The metacarpophalangeal (MCP) joints bestow important strength to the longitudinal and transverse arch systems of the hand. In addition, these joints guide active movements of the fingers in 2 degrees of freedom, while allowing sufficient laxity for passive accessory motions. Both stability and mobility functions are attained in the healthy hand by a complex interaction among the muscles and the joints' periarticular connective tissues. Rheumatoid arthritis (RA) often causes destruction of the MCP joints' connective tissues, which leads to weakness of the tissues and an imbalance of active and passive forces, and subsequently, instability, pain, and deformity. The 2 most common deformities of the MCP joints associated with RA and instability are palmar subluxation and ulnar "drift." Therapists and physicians often collaborate to treat these conditions through a combination of surgical and nonsurgical interventions. Two of the more conservative nonsurgical interventions typically involve a combination of splinting and education on joint protection. Additional nonsurgical treatment may include the judicious use of exercise and methods for relieving pain and reducing inflammation. Surgical intervention is often indicated when the more conservative treatments fail to arrest the progression of the pain or deformity. Regardless of the specific approach, effective intervention for instability of the MCP joint requires that the clinician possess a sound knowledge of the anatomy and the pathomechanical influences that predispose or cause the instability. This clinical commentary is intended to provide this information, as well as offer treatment guidelines based on our clinical experience. Whenever possible, research will be cited to support clinical interventions. This paper is especially geared to the therapist who may not currently specialize in the treatment of instability of the MCP joint but may require basic information on this important topic.