Wrist and digital joint motion produce unique flexor tendon force and excursion in the canine forelimb

The force and excursion within the canine digital flexor tendons were measu red during passive joint manipulations that simulate those used during reha bilitation after flexor tendon repair and during active muscle contraction, simulating the active rehabilitation protocol. Tendon force was measured u sing a small buckle placed upon the tendon while excursion was measured usi ng a suture marker and video analysis method. Passive finger motion imposed with the wrist flexed resulted in dramatically lower tendon force (similar to 5 N) compared to passive motion imposed with the wrist extended (simila r to 17 N). Lower excursions were seen at the level of the proximal interph alangeal joint with the wrist flexed (similar to 1.5 mm) while high excursi on was observed when the wrist was extended or when synergistic finger and wrist motion were imposed (similar to 3.5 mm). Bivariate discriminant analy sis of both force and excursion data revealed a natural clustering of the d ata into three general mechanical paradigms. With the wrist extended and wi th either one finger or four fingers manipulated, tendons experienced high loads of similar to 1500 g and high excursions of similar to 3.5 mm. In con trast, the same manipulations performed with the wrist flexed resulted in l ow tendon forces (4-8 N) and low tendon excursions of similar to 1.5 mm. Sy nergistic wrist and finger manipulation provided the third paradigm where t endon force was relatively low (similar to 4 N) but excursion was as high a s those seen in the groups which were manipulated with the wrist extended. Active muscle contraction produced a modest tendon excursion(similar to 1 m m) and high or low tendon force with the wrist extended or flexed, respecti vely. These data provide the basis for experimentally testable hypotheses w ith regard to the factors that most significantly affect functional recover y after digital flexor tendon injury and define the normal mechanical opera ting characteristics of these tendons. (C) 1999 Elsever Science Ltd. All ri ghts reserved.