CMC Basal Joint Arthritis: The Full Breakdown | Form & Function MD
ORTHO / UPPER EXTREMITY

CMC Basal Joint Arthritis: The Full Breakdown

Form & Function MD · Dr. Ben, MD

Dr. Ben, MD · Orthopaedic Hand & Upper Extremity Surgeon

The carpometacarpal (CMC) joint at the base of the thumb is one of the most common sites of hand arthritis — and one of the most functionally significant, because nearly every pinch, grip, and twisting motion loads this single joint. This is also the topic of the first episode of the YouTube channel, where I walk through the mechanism, imaging, and full treatment ladder in more depth than a written post allows.

Why this joint wears out

The CMC joint is a saddle joint, built for a wide range of motion to allow the thumb's opposition — the movement that makes the human hand functionally unique. That mobility comes at a cost: less inherent bony stability than most joints, which shifts more of the stabilizing work onto ligaments that loosen with age, repetitive loading, and in some patients, genetic predisposition. It disproportionately affects women after age 50, likely from a combination of ligamentous laxity and hormonal factors affecting cartilage.

This is a joint asked to do more range of motion with less inherent stability than almost anywhere else in the body. Eventually, for many people, that trade catches up.

How it presents

Early symptoms are activity-related pain at the base of the thumb — opening jars, turning keys, pinching to write. As it progresses, patients often notice the joint looking more prominent, sometimes described as "squared off," from a combination of bone spurring and subluxation. Grip and pinch strength both decline measurably as the disease advances.

The treatment ladder
  • First line: activity modification, a thumb spica splint (particularly helpful at night and during aggravating activities), and NSAIDs for flares
  • Second line: corticosteroid injection into the joint — effective for symptom control, though benefit duration varies and diminishes with repeated injections
  • Surgical: reserved for patients with persistent pain limiting daily function despite adequate conservative treatment — not for X-ray severity alone, since imaging findings correlate poorly with symptoms

What surgery actually involves

The most common procedure, trapeziectomy with ligament reconstruction and tendon interposition (LRTI), removes the arthritic trapezium bone and reconstructs stability using a local tendon. Recovery involves a period of immobilization followed by progressive hand therapy, with most patients returning to full activity by three to four months, though grip strength gains continue to improve for up to a year. Thumb CMC joint replacement is a newer alternative gaining traction for appropriately selected patients wanting faster return of strength.

The honest odds
Most patients I see with CMC arthritis never need surgery — splinting, activity modification, and occasional injections manage the majority of cases indefinitely. The patients who do go on to surgery are almost always glad they didn't wait longer once they've healed on the other side.
  • Wolf JM, et al. Prevalence of thumb carpometacarpal osteoarthritis. J Hand Surg Am. 2014.
  • Vermeulen GM, et al. Surgical management of primary thumb carpometacarpal osteoarthritis: a systematic review. J Hand Surg Am. 2011.