Effect of finger ulnar deviation on gliding resistance of the flexor digitorum profundus tendon within the A1 and A2 pulley complex

Purpose: To evaluate the effect of ulnar deviation of the finger on gliding resistance of the flexor digitorum profundus tendon within the A1 and A2 pulley complex. Methods: Thirty-two human cadaveric fingers (index through small fingers) were used. The gliding resistance was measured at 5 different angles of ulnar deviation (0°, 15°, 30°, 45°, 60°). Results: There was a significant increase in gliding resistance with increased ulnar deviation. The gliding resistances at 0°, 15°, 30°, 45°, and 60°of ulnar deviation were 0.40 ± 0.13 N, 0.44 ± 0.13 N, 0.55 ± 0.17 N, 0.74 ± 0.21 N, and 1.02 ± 0.30 N, respectively. The gliding resistance at 60°was significantly greater than at all other angles; 45°ulnar deviation had significantly higher gliding resistance than 0°, 15°, and 30°; and 30°ulnar deviation had significantly higher gliding resistance than 0°. Conclusions: A greater angle of ulnar deviation causes higher gliding resistance during motion of the flexor digitorum profundus tendon within the A1 and A2 pulley complex. The gliding resistance increases significantly at angles greater than 30°of ulnar deviation. The increased tendon loading needed to overcome increased gliding resistance caused by ulnar deviation could result in a vicious cycle of progressive ulnar deviation. Although mild degrees of ulnar deviation may be well tolerated mechanically a reasonable therapeutic guideline might be to prevent deviation from exceeding 30°.