Quantifying the effect of the distal intrinsic release procedure on proximal interphalangeal joint flexion: a cadaveric study.

Purpose: The distal intrinsic release procedure is a popular treatment for intrinsic hand tightness. The literature remains ambiguous regarding the optimal amount of extensor hood to excise. Our goals were to quantify the mathematic relationship between the amount of extensor hood excised and proximal interphalangeal (PIP) joint flexion and to determine the minimum amount of extensor hood excision required to significantly change PIP joint flexion capability (the ability to achieve a change from the initial PIP joint angle).

Methods: We simulated the distal intrinsic release procedure by sequentially excising 5-mm strips (perpendicular to the long axis of the finger) of the extensor hood of cadaveric fingers beginning 5 mm proximal to the PIP joint center. We tensioned the intrinsic muscles to each digit to produce an intrinsically tight state and tensioned the flexor digitorum superficialis to produce an antagonist force and simulate the intrinsic tightness test. We measured PIP joint angle (the angle of the long axis of the middle phalanx relative to the proximal phalanx) in response to greater portions of excised extensor hood to quantify its contribution to intrinsic tightness.

Results: The relationship between the amount of extensor hood excised and the PIP joint flexion capability appeared quadratic, not linear. For the index, ring, and small fingers significant changes in PIP joint flexion were detected after resection of 59%, 26%, and 33%, respectively, of the extensor hood length. Although our results did not show statistical significance for the middle finger we project the critical amount to be at least 65%.

Conclusions: We show PIP joint flexion changes after the distal intrinsic release procedure. We recommend excising a finger-dependent minimum amount of tissue before expecting a significant increase in PIP joint flexion capability.