A Review on CMC Joint Arthritis
Osteoarthritis of the carpometacarpal joint is a common cause of thumb pain in patients with degenerative joint disease and/or overuse injuries. With the increasing popularity of cell phone use, there is a corresponding increase in thumb-related pathology. Osteoarthritis represents one such overuse syndrome. The second most common location in the hand where patients develop osteoarthritis is their thumb trapeziometacarpal joint (Glyka Martou, 2004). Unfortunately for those suffering, the CMC joint is involved with flexion, extension, adduction, abduction, and opposition of the thumb (David Melville, 2015).
Etiology. Upwards of 25% of women over the age of 50 will develop thumb carpometacarpal joint arthritis (Frank Yuan, 20178). The CMC joint is a bicon-cavoconvex joint (reciprocal saddle) that relies on capsular ligaments, intrinsic, and extrinsic hand muscles as the primary joint restraints (Glyka Martou, 2004; SW Song, 2019). This differs from most joints that typically have more bony constraint. In 1994 Pellegrini, et. al hypothesized that ligamentous laxity leads to the development of shearing forces in the joint leading to degeneration of the articular cartilage (Glyka Martou, 2004). The main culprit is weakness of the anterior oblique ligament of the joint (Marie-Lyne Grenier, 2016). Patient’s with Ehler-Danlos were found to have arthritic changes in their CMC joint as early as age 15 (Ann Van Heest, 2008).
Physical Exam. A patient with pain at the base of the thumb that is worsened with pinching will clue a physician in on the CMC joint (SW Song, 2019). Other common complaints are pain with opening jars, weakness in pinch strength, and cramping in the hand (Kristofer Matullo, 2007). On examination, the physician may find soft tissue swelling on inspection of the joint and patients typically have pain with palpation over the joint (SW Song, 2019). Pain at the CMC can also be exacerbated with the grind test (Kristofer Matullo, 2007).
Imaging. The primary target when imaging for CMC arthritis is the trapeziometacarpal joint (David Melville, 2015). Radiographs of the carpometacarpal joint include a true AP, lateral, and oblique view (David Melville, 2015). A true AP of the CMC joint is known as the Robert’s view and the patient’s forearm is positioned in max pronation for the xray (David Melville, 2015). One specialty view to better visualize the trapezial articulation is the basal joint stress view (Figure 1), which has the patient press both thumbs together. This image allows for a better view of the trapeziometacarpal articulation (David Melville, 2015). Classification of the stage of arthritis is known as the Eaton-Little staging (David Melville, 2015). Stage I involves widening of the joint without any joint space narrowing, stage II has mild joint space narrowing and osteophyte formation, stage III has pronounced narrowing of the joint, subchondral sclerosis and cyst formation and osteophytes, and Stage IV is similar to stage III but with even more narrowing and sclerosis/cyst formation (David Melville, 2015).
Figure 1. Trapeial articulation is the basal joint stress view (Melvill 2015)
Treatment. Nonsurgical treatment is first line for patients with thumb carpometacarpal arthritis. Orthoses are typically used as part of a nonsurgical treatment. A study in 2016 looked at three thumb orthoses and looked at their effect on pinch strength since the decrease in pinch strength is one of the biggest functional limitations of CMC arthritis (Marie-Lyne Grenier, 2016). Another purpose of an orthotic is to decrease motion at the CMC joint with the aim that this will decrease pain by decreasing further cartilage wearing (Marie-Lyne Grenier, 2016). The studied found improvements in pinch strength in all groups wearing an orthotic (Marie-Lyne Grenier, 2016).
Figure 2. Example of carpometacarpal (CMC) joint injection (courtesy of dorsethandsurgery.co.uk)
Conclusion. The main take away from this article is that CMC arthritis is a common condition in our patient population over the age of 50 and that physicians should attempt a gradual step up from conservative measures to a myriad of surgical options. When evaluating surgical options, there is no trial or study that places one surgery in favor over all the others (SW Song, 2019). However, amongst a recent survey for physicians in the American Society for Surgery of the Hand, a trapeziectomy with LRTI is the most commonly done (SW Song, 2019).