Ulnar collateral ligament injuries of the thumb: phalangeal translation during valgus stress in human cadavera

The ulnar collateral ligament is the primary static stabilizer against valgus stress at the metacarpophalangeal joint of the thumb. Disruption of the ligament, if untreated, can result in chronic joint instability, functional limitation in pinch, and persistent pain1. Previous clinical and cadaveric studies have suggested that, when a sufficient valgus force is applied to the thumb, the proper ulnar collateral ligament ruptures first, followed by rupture of the accessory ulnar collateral ligament2-4. While injuries of the proper ulnar collateral ligament alone are amenable to nonoperative treatment, disruption of both the proper and the accessory ulnar collateral ligament may lead to a Stener lesion, with marked displacement of the ulnar collateral ligament superficial to the adductor pollicis aponeurosis, requiring operative repair for satisfactory clinical outcomes5. Ulnar collateral ligament disruption is a common injury, incurring substantial health-care costs as well as indirect societal costs. The annual incidence of ulnar collateral ligament injuries has been estimated to be fifty per 100,000 individuals6. In one ten-year experience, 66% of these injuries were in working adults, and the average time off from work was eighty-eight days, leading to substantial lost productivity. However, the diagnosis of a complete ulnar collateral ligament injury was definitively established clinically in only 38% of the cases; 62% required costly advanced imaging6. Complete tears of the ulnar collateral ligament at the metacarpophalangeal joint involve both the proper ulnar collateral ligament and the accessory ulnar collateral ligament. The proper ulnar collateral ligament courses from the dorsal third of the metacarpal head to the proximal volar aspect of the proximal phalanx7. The accessory ulnar collateral ligament is positioned volar to the proper collateral ligament, spanning from the volar surface of the metacarpal head to the ulnar border of the volar plate (Fig. 1)8. A complete ulnar collateral ligament tear (i.e., disruption of both the proper ulnar collateral ligament and the accessory ulnar collateral ligament) is the minimum injury necessary to allow sufficient displacement of the ligament to produce the Stener lesion, which requires operative repair5. Previous studies have demonstrated that the volar plate and dorsal capsule of the metacarpophalangeal joint provide minimal contributions to varus and valgus stability9. Fig. 1 Diagram of a normal ulnar collateral ligament complex (view of the thumb metacarpophalangeal joint from the ulnar side). pUCL = proper ulnar collateral ligament and aUCL = accessory ulnar collateral ligament. While magnetic resonance imaging (MRI) and ultrasound have been used to diagnose complete ulnar collateral ligament injuries, there are no universally accepted techniques for conclusively establishing the diagnosis of these injuries in the clinical setting. Given the recent concern over health-care expenditures, improving diagnostic accuracy without the use of advanced imaging is advantageous. The goal of this cadaveric study was to evaluate a novel, quantifiable measurement that differentiates partial from complete ulnar collateral ligament tears in the clinical setting. Our hypothesis was that the magnitude of radial translation of the proximal phalanx on the head of the thumb metacarpal could predict complete ulnar collateral ligament tears more accurately than could metacarpophalangeal joint angulation during valgus-stress fluoroscopic imaging.