Arthroscopy Basal Joint or Carpometacarpal Joint – CMC
Turning a key, twisting the lid off a jar and grasping a door handle appear to be such simple tasks. In each movement, the thumb plays an integral part. Without cooperation from this key digit, squeezing and gripping motions would be virtually impossible.
Over time, though, even the thumb can reach its limits. The basal joint or carpometacarpal joint (CMC)–located at the base of the thumb–allows these crucial swiveling and pivoting motions. But because sophisticated movements depend on this joint, it’s susceptible to wear-and-tear from normal use. And when the CMC joint wears down, arthritis can develop and hinder even the easiest functions.
For patients, a well-structured program of hand therapy may restore previous levels of function. But if that doesn’t work or the CMC joint disorder is too severe, surgery may be the only option. One such procedure–arthroscopy–can help identify the stage of the problem and give patients a minimally invasive solution to a common problem.
Arthritis at the CMC joint is a common, painful condition that occurs more frequently in middle-aged women. It also occurs with men, although it tends to begin at a later age and causes less disability. The condition progresses gradually and, eventually, the joint is destroyed, which causes pain, disability and pinch weakness.
Early symptoms of CMC joint disorder are often ignored, as patients heed the advice of physicians who often provide a myriad of diagnoses to explain subtle pain at the base of the thumb or along the radial side of the wrist. Swelling and tenderness are noted at the base of the thumb with a painful grinding that can be illicited with passive compression and motion of the CMC joint by the examiner. Pain often radiates up the arm and can lead to carpal tunnel syndrome, which is often the first sign of a problem.
When a patient begins to complain of even subtle pain at the base of the thumb, obtain an X-ray to determine the radiographic stage of potential arthritis. Although X-rays are frequently normal in this early stage, it’s the best time to initiate treatment because patients will respond well to simple conservative measures. Those measures include splinting to immobilize the thumb by using a hand-based or wrist-extended spica splint. In addition, nonsteroidal anti-inflammatory drugs can help alleviate symptoms. Clinicians should also begin hand therapy to strengthen surrounding muscles, reduce inflammation, and promote good motion flexibility and pinch strength.
However, because most osteoarthritic conditions tend to be progressive, the pain never really resolves and patients start looking for other options beyond therapy. Corticosteroid injections offer relief from painful joint arthritis, but that respite is only temporary. In fact, it can lead to progressive cartilage wear. Multiple catabolic steroid injections in the hand joint can lead to weakening of the joint capsule and surrounding ligaments, and even cause further breakdown to articular cartilage.
In severe cases of dysfunction, surgery may be the only choice, even though reconstruction can alter normal anatomy; a prolonged, painful postoperative recovery process ensues.
The classic surgical procedure for more advanced basal joint arthritis consists of a complete excision of the arthritic trapezium bone, with a ligament reconstruction using either the flexor carpi radialis or the long thumb abductor in the first compartment. The remainder of the tendon is then stuffed into the space between the metacarpal base and trapezium to serve as an “anchovy spacer.” The anchovy represents a rolled up tendon graft that then acts as a biological cushion to avoid contact between the two arthritic surfaces and minimizes collapse.
When X-rays show obvious signs of advanced degenerative changes, patients are usually offered the classical open reconstruction. Although this procedure remains the gold standard in basal joint reconstruction, recovery time is often lengthy. This reconstruction carries another risk: A patient has few salvage alternatives if it doesn’t provide expected relief. For instance, the basal joint exerts a great deal of force, and the ligament reconstruction often has complications, such as loosening.
Total joint arthroplasty offers a better solution, especially in the late stages of basal joint arthritis. This procedure provides an excellent alternative with extremely rapid recovery of function and complete pain relief. It’s used predominantly in much older, low-demand patients. This is because a total joint replacement with metal and plastic components can wear out or loosen as in any other joint arthroplasty. This risk is minimized when patients place less strenuous demands on the joint and have a shorter life span remaining.
An arthroscopic procedure allows for synovectomy and debridement, which provides pain relief. With an arthroscope, a hand surgeon can also inspect the articular cartilage for early degeneration. If the cartilage is still intact, then the patient may undergo a capsular shrinkage procedure to minimize the laxity that often accompanies these joints during arthritic stages. This step may halt the progress of arthritis and provide pain relief without the obvious drawbacks of corticosteroids.
X-rays will show subtle changes, but an arthroscopy determines the true level of arthritis based on cartilage loss. This allows clinicians to either choose osteotomy in the early stages, or an arthroscopic interposition arthroplasty for advanced stages. If cartilage damage is focal, patients can benefit from arthroscopic debridement and a shrinkage procedure to stabilize the joint.
A hand surgeon can then perform a limited incision metacarpal osteotomy to alter joint biomechanics. The metacarpal can be centralized on the trapezium, avoiding subluxation and, perhaps, terminating the vicious cycle of osteoarthritis in the unstable joint.
If the cartilage damage seems to be advanced, then the surgeon conducts a burring of the trapezium’s articular surface to increase joint space. This minimizes direct contact between the metacarpal base and trapezium. It also causes bleeding of the subchondral bone, producing clotting that adheres to the tendon graft. This tendon graft, such as the palmaris longus tendon, is inserted through one of the arthroscopic portals,. When this graft is introduced into the joint through one of the portals, the blood clot from trapezial debridement acts as a cushion between the opposing bony surfaces. This leads to good pain relief across the joint with minimal contact. This is minimally invasive and hence is less painful postoperatively.
Following arthroscopy, patients are treated for a three- or four-week period of thumb spica cast immobilization so the capsule can heal, and the new joint is stabilized. With postop therapy, patients can regain good opposition and supple range of motion, while regaining pinch strength that was lost from thenar muscle atrophy.
