Isolated Fourth Carpometacarpal Joint Injury in High-Level Baseball Players: A Case Series.

Background: We present a case series of high-level baseball players having sustained a rare, isolated injury to the fourth carpometacarpal joint of the nondominant or bottom hand during a jammed swing.

Methods: Ten patients were evaluated for ulnar-sided wrist pain and were subsequently diagnosed with fourth carpometacarpal joint synovitis based on physical examination and magnetic resonance imaging revealing increased signal intensity within the joint.

Results: Conservative treatment modalities including rest, nonsteroidal anti-inflammatory medications, splinting, and corticosteroid injections resulted in return to play within 4 weeks for all patients.

Conclusions: We propose a mechanism of injury involving the bottom hand in relative pronation receiving a dorsally directed force from bat during a jammed swing resulting in isolated injury to the fourth carpometacarpal joint. This report serves to highlight this rare injury in high-level baseball players and recommend a treatment algorithm for early return to play.