Avulsion of the flexor digitorum profundus: anatomic and biomechanical considerations.

Avulsion of the profundus insertion occurs most commonly in the ring finger. The exact reason for this predilection is unknown. Clinical observation of patients with this injury reveals that a common finding is that the ring fingertip is usually more prominent or "longer" than any other fingertip during grip. A laboratory investigation shows that during grip the ring fingertip becomes 5 mm more prominent than any other digit in 90% of subjects and that it absorbs more force than any other finger during pull-away testing. These factors contribute to the susceptibility of the ring finger to the profundus avulsion injury.