Comparative flexor tendon excursion after passive mobilization: an in vitro study

Cyclic stress testing after in vivo healing of canine flexor tendon lacerations

This study evaluated the effects of cyclic tension applied to lacerated and repaired canine flexor tendons after various periods of in vivo healing for up to 30 days. Final gaps obtained after cyclic stress testing were found to increase from a baseline of 0.75 +/- 0.17 mm (zero time controls) to a maximum of 1.14 +/- 0.24 mm at 3 days after repair, before returning to baseline at 10 days (0.63 +/- 0.27 mm). Gap formation at 30 days after repair (0.65 +/- 0.27 mm) was similar to that of control tendons. This canine study suggests that continued protection of flexor tendons from strong repetitive tensile, stress should extend at least through 30 days after repair.

Passive properties of the forearm musculature with reference to hand and finger postures

OBJECTIVE: To quantify individual forearm muscle passive forces and evaluate their impact on hand function. DESIGN: The passive force-length properties of the 24 extrinsic hand and wrist muscles were determined in five fresh frozen cadaver arms. BACKGROUND: Muscle force production is a summation of the active and passive force components. The passive properties of the extrinsic finger musculature and wrist musculature appear to strongly affect both hand posture and hand movement. METHODS: The passive force-length properties of extrinsic hand and wrist muscles were determined by applying a slow, continuous extension to each muscle and recording the resulting tension. Each force-length curve was fit using exponential regression and were related to specific joint rotations and seven hand postures by calculating the muscle excursions for those postures. RESULTS: The exponential passive force-length relationship explained over 97% of the experimental variance. The largest passive forces were elicited in the digital extensors in grips involving large flexion angles such as tip pinch, key pinch, and a briefcase grip. CONCLUSIONS: The passive properties of the extrinsic finger musculature and wrist musculature affect both hand posture and movement especially in postures with flexed wrist and fingers.

Flexor tendon-pulley interaction after tendon repair. A biomechanical study

Ten normal ring fingers from ten donors were used to determine the effect of flexor tendon repair on the gliding resistance between the tendon and the A2 pulley. Gliding resistance was measured for the intact FDP tendon and for the same tendon after it was cut transversely and repaired with a 4/0 Ticron core suture and a 6/0 running epitendinous nylon suture. After repair, the gliding pattern of the tendon through the A2 pulley changed significantly. The resistance and the friction coefficient were approximately doubled (P < 0.005).

Method for the measurement of friction between tendon and pulley

An experimental system was developed that allows direct measurement of friction at the tendon-pulley interface, and the results were interpreted by use of a theoretical model for friction of a cable around a fixed pulley. Validation experiments were conducted with a nylon cable around a nylon rod. One end of the cable was connected to an actuator via a load cell, and the other end was connected to a 4.9 N load via a similar load cell. The cable was passed around the nylon rod and then pulled toward the actuator. Tests were performed at five different arcs of contact. The friction forces, as measured by the difference between two load transducers, were compared with those determined for a theoretical model and were used for calculation of the friction coefficient. The measurement system then was used to study the friction force between the flexor digitorum profundus tendon and the A2 pulley on nine fresh frozen index digits. The method allows us to measure the direct interaction between the tendon and pulley and could be used to evaluate and compare procedures for tendon-pulley and pulley repair and reconstruction, as well as for the study of tendon-pulley friction in various pathological conditions.