Is thumb carpometacarpal instability assessed in young patients with thumb base symptoms? A multicenter study.

Thumb base complaints in younger patients are diagnostically challenging, and symptoms are commonly attributed to either carpometacarpal (CMC) osteoarthritis or ligamentous instability. These conditions require fundamentally different treatment strategies, making accurate diagnosis essential. The reported frequency of CMC instability varies considerably across clinical practices, possibly reflecting differences in diagnostic awareness rather than true differences in prevalence. This study therefore aimed to describe the diagnostic workup of younger patients with nontraumatic thumb base complaints, with a focus on the use and findings of instability testing. In this retrospective multicenter study of 85 patients younger than 45 years, instability testing was performed in only 39%, yet was positive in 75% when assessed. Patient characteristics were similar between tested and untested patients, suggesting that testing reflected variation in diagnostic practice rather than clinical suspicion. Positive instability tests were also observed in patients labeled as osteoarthritis, often without radiographic signs of degeneration. These findings suggest that CMC instability may be underrecognized in younger patients, and that variation in diagnostic practice likely contributes to its inconsistent recognition. Failure to recognize instability may lead to osteoarthritis-directed surgery in patients who could have been treated with joint-preserving approaches. Systematic assessment of CMC instability is therefore essential to ensure accurate diagnosis and guide optimal treatment in this population. Level of evidence: Level IV.