THUMB CARPOMETACARPAL JOINT OSTEOARTHRITIS
Another condition commonly associated with OA of the wrist and hand is thumb CMC joint OA. An overview is provided, followed by discussion of conservative medical management, surgical management, and appropriate therapeutic interventions. The carpometacarpal (CMC) joint of the thumb is the second most likely joint of the hand to develop OA, with the proximal interphalangeal (PIP) joints the third. A client experiencing OA of the CMC thumb joint typically reports pinching and swelling at the base of the thumb just distal to the wrist. As the disease progresses, instability, impaired motion, and diminished strength are also reported and are increased significantly by repeated pinching, wringing motions, and grasping (Arthritis Foundation, n.d.). With radiographic examination, lesions most commonly observed in OA of the CMC joint are at the trapezio-metacarpal (TM) joint, but lesions can also be observed at other joints, including the trapezium and scaphoid. Radiographs for CMC OA show typical narrowing of the joint with sclerotic changes, spur formation, and lateral subluxation of the base of the first metacarpal. Joint changes might have existed for a long period until an acute injury or repeated minor trauma occurred and irritated the joint tissues. As a result of the degree of pain experienced during strong pinching or abduction, a client typically avoids these motions and therefore experiences difficulty completing daily tasks. When limitation of motion at the TM joint occurs, compensatory movement takes place in the distal joint to give the thumb the necessary function. These compensatory movements eventually lead to thumb deformity. The two primary deformities of an arthritic thumb and fingers are the boutonniere and swan-neck deformities (Figure 18). Although these deformities occur rarely in OA of the fingers, CMC OA of the thumb leads to these patterns of deformity (Figure 19; Hauser et al.,2012). Boutonniere deformity results from arthritic involvement of the metacarpophalangeal (MCP) joint, which becomes enlarged (Figure 18). This enlarged joint causes elongation or erosion of the attachment of the extensor pollicis brevis muscle to the base of the proximal phalanx, leading to flexion deformity. As a result, the extensor pollicis longus tendon and adductor expansions become displaced ulnarly, and lateral thenar expansions are displaced radially. This leads to further decreases in active MCP extension. When attempting extension of the MCP joint, there is hyperextension of the interphalangeal joint, which eventually creates a pattern of function leading to joint contracture (Hauser et al., 2012; Figure 18). Swan-neck deformity occurs when the MCP joint is held in hyperextension and the TM joint is forced into a subluxed position with the interphalangeal joint in flexion. If there is marked swelling of the CMC joint, the capsule becomes overstretched and the joint enlarges. This eventually leads to subluxation of the base of the metacarpal. With both boutonniere and swan-neck deformities, continuous avoidance of abduction secondary to pain gradually leads to development of an adduction contracture (Figure 18). A compensatory pattern of hyperextension of the thumb MCP follows, called a Z-deformity (Badia, 2011). Conservative management Clients might first seek the advice of a physician when experiencing an acute exacerbation of the CMC OA that leads to pain and swelling. Pain might be brought on by pinching or gross use of the hand, and might be present at rest and when engaging in activity. Pain might come on suddenly due to engagement in a particularly stressful activity, or gradually when the thumb is used frequently with or without stress. Conservative medical treatment of CMC OA may include anti- inflammatory medications, wear of orthoses, or corticosteroid injections to aid in pain relief (Badia, 2011). It is prudent for the
For ease of identification, all thumb deformities can be identified using the Nalebuff classification system, which includes six deformities and their respective pathological mechanics (Hauser et al., 2012): ● Type I : Boutonniere with CMC unaffected; passively correctable; MCP joint flexion and interphalangeal (IP) joint hyperextension. ● Type II : Boutonniere with CMC affected; adduction deformity. ● Type III : Swan-neck with MCP joint hyperextension and IP joint flexion. ● Type IV : Gamekeeper with injury to the ulnar collateral ligament. ● Type V : Swan-neck alone. ● Type VI : Skeletal collapse with bone loss; arthritis mutilans (i.e., severe derangement of the joints). Figure 18: Swan-Neck Deformities of Fingers; Boutonniere and Adduction Contracture of Thumb
Note: “Swan neck deformity” by Phoenix 119, used under Creative Commons license BY-SA 3.0. Figure 19: Mild Swan-Neck Deformity of the Thumb
Source: Erin Peterson
physician to recommend therapy to provide any appropriate orthoses, education and adaptations to items used in daily life, education in joint protection techniques, and suggestions for home-based treatment methods such as paraffin baths and ice packs (Hunter & Lo, 2008). The physician also should explain to the client the pathophysiology of the disease, the likely sequelae of the condition, and the potential for future invasive procedures such as joint replacement surgery.
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