A biomechanical study of the collateral ligaments of the proximal interphalangeal joint.

Collateral ligament injuries of the proximal interphalangeal joint are common. A significant number of these injuries result in complete rupture of the ligament. The forces that damage the ligaments are abduction and adduction stresses. Previous studies have investigated laxity, angulation, and patterns of failure, but detailed biomechanical rupture studies are scant. Sixty-eight proximal interphalangeal joints from fresh human cadaver fingers (average age, 67 years) were stressed at velocities of 1 mm/sec, 4 mm/sec, and 10 mm/sec. Sectioning studies were also done. Four distinct rupture patterns were noted: midsubstance tear, proximal detachment, distal detachment, and distal avulsion fracture. The prevalence of these patterns differed with the rate at which the ligaments were stressed. Lower speeds tended to produce midsubstance tears, while higher speeds yielded distal damage. The study confirmed that the lateral collateral ligament is the primary restraint against medial-lateral stress and that other supporting structures (the extensor hood and the palmar plate) did not contribute significantly to side-to-side stability.