Middle Finger Metacarpophalangeal Joint Locked in Flexion Caused by Entrapped Ulnar Collateral Ligament

Type 1 finger metacarpophalangeal (MCP) joint locking is characterized by maintained flexion of the MCP, with a lack of active and passive extension. Metacarpophalangeal joint locking is rare but has several identified causes, most commonly involving a radial-sided osteophyte. We report a case of right middle finger ulnar collateral ligament (UCL) entrapment characterized as type 1 MCP joint locking. The physical examination demonstrated that the right middle finger was locked in flexion at 60° at the MCP joint. Magnetic resonance imaging (MRI) demonstrated a possible tear of the distal attachment of the UCL at the MCP joint. Closed manipulation was unsuccessful in the office, and the patient underwent MCP ulnar osteophyte excision with full postoperative recovery. Although diagnosing the cause of UCL locking may be complicated by the lack of evidence in imaging studies, patients can return to full function by restoring the integrity of the joint with surgical treatment.