Causes / typical injury mechanism: Ulnocarpal abutment syndrome, also known as ulnar impaction syndrome and ulnar abutment syndrome, is a chronic degenerative process secondary to compressive overload and shear forces at the articular surface of the ulnocarpal joint.

Classic history and presentation: Patients typically present with ulnar-sided wrist pain. Pain occurs with active and passive ulnar deviation of the wrist as well as with axial loading of the wrist.

Risk factors:

• History of trauma
• Distal radius fracture
• Radial head fracture with resulting shortening of radius
• Scapholunate dislocation
• Triangular fibrocartilage complex (TFCC) tears
• Lunotriquetral (LT) ligament tears

Pathophysiology: Ulnocarpal abutment syndrome is secondary to excessive stress between the ulna and the carpus. The relationship between the radius and ulna at the distal radial ulnar joint (DRUJ) is such that there can be ulnar variance from -2 mm to +2 mm when compared to the radius in the typical wrist. In patients with ulnar neutral or ulnar negative variance, 80% of the carpal load is transferred to the radius and 20% is transferred to the ulna. In a patient with ulnar positive variance (+2 mm or greater), that ratio shifts and 60% of the load lies with the radius while 40% lies with the ulna. This increased load over time leads to degenerative changes in the ulnocarpal joint that cause the symptoms seen in ulnocarpal abutment syndrome.