Translating Carpal Biomechanics to Triangular Fibrocartilage Complex Injury: Significance of Ulnar Variance in Predicting TFCC Lesions

Abstract

Ulnar variance (UV) describes the cranio‐caudal position of the distal ulna in relation to the distal radius at the wrist. Neutral ulnar variance (ulna and radius articulating at the carpus at exactly the same level) transmits 20% of the compressive load across the wrist to the distal ulna and 80% to the distal radius. A +2.5mm positive UV has been shown to increase the ulnocarpal load to 40%. The triangular fibrocartilage complex (TFCC) acts as a cushion for the ulnar carpus and transmits axial loads from the wrist to the ulna in a longitudinal direction across the ulnar column of the wrist. Consequently, a positive ulnar variance implicates a greater risk of TFCC injury. This study sought to calculate the prevalence of traumatic TFCC injury in those with a positive UV versus those with a negative UV. 20 cadaveric wrists aged 50 – 90 were assessed for TFCC damage via gross examination and classified according to Palmer's schema. A plain film PA radiograph of each wrist was then taken to measure the degree of UV. Results showed that all wrists had degenerative Class II lesions of the TFCC, while traumatic Class I lesions of the TFCC were found in 69% of wrists with positive UV as compared to 0% of wrists with negative UV (p<0.05). Our investigation prompts further research exploring a “dose‐response” relationship between UV and TFCC damage as well as between the degree of TFCC damage and clinical symptoms or diminished quality of life.Grant Funding Source: SUNY Downstate College of Medicine Alumni Association