RELATIONSHIP BETWEEN JOINT MOTION AND FLEXOR TENDON FORCE IN THE CANINE FORELIMB

To increase in vivo tendon force and gliding after flexor tendon repai r, a variety of modifications to the methods by which protective passi ve motion is administered have been advocated. To determine the relati onship between the prime variables, wrist and digital position, muscle activation, and in vivo tendon force, a clinically relevant canine mo del was developed. Force was measured in the flexor tendon during seve ral joint manipulation paradigms: single-finger flexion-extension with the wrist flexed (group 1F), single-finger flexion-extension with the wrist extended (group 1E), four-finger flexion-extension with the wri st flexed (group 4F), four-finger flexion-extension with the wrist ext ended (group 4E), and synergistic wrist and finger motion where wrist extension and finger flexion were performed simultaneously, followed b y wrist flexion and finger extension (group SYN). In addition, tendon force was measured during electric stimulation of the proximal flexor muscle mass. Passive tendon force with the wrist extended (groups 1E a nd 4E) was two to three times greater than that measured with the wris t flexed, independent of the number of digits moved. With the wrist ex tended, peak tendon force reached 1,977 g +/- 194 g during single-digi t manipulation (group 1E), compared to only 853 g +/- 104 g with the w rist flexed dur ing the same maneuver (group 1 Fl. Statistical compari son between means revealed that groups 1E and 4E were significantly di fferent from groups 1F, 4F, and SYN (p < .005). There were no signific ant differences between groups 1E and 4E or between groups 1F, 4F, and SYN (p > .200). Active muscle force elicited by electrical stimulatio n and passive force varied dramatically as the wrist was flexed from f ull extension 3460 g +/- 766 g to full flexion 427 g +/- 239 g (p < .0 01). Simultaneously, passive tension decreased from 940 g +/- 143 g wi th wrist extended to 76 g +/- 37 g with the wrist flexed. These data i ndicate that wrist position has the greatest effect on flexor tendon f orce during motions that are commonly used to rehabilitate flexor tend on repairs. Thus, if force is to be controlled during passive motion, wrist-joint angle will have the dominant effect, while the number of d igits manipulated will have much less of an effect. If the clinical go al is to minimize tendon force, rehabilitation could be carried out wi th the wrist flexed, whereas if the goal is to increase tendon force, rehabilitation could include exercise programs that use a greater degr ee of wrist extension.