The Effect of Gelatin Molecular Weight on Tendon Lubrication Utilizing an Extrasynovialized Turkey Flexor Tendon Model

Abstract

Introduction: Flexor tendon injuries are common hand injuries among the military population often resulting in functional impairment. Flexor tendon gliding friction has been linked to adhesion formation, especially with the use of extrasynovial grafts. Carbodiimide-derivatized hyaluronic acid with gelatin (cd-HA-gelatin) can reduce gliding friction of the tendon graft; however, the effects of gelatin molecular weight (MW) have not been studied. The turkey model has been shown to better match humans, but extrasynovial tendons are unavailable. The purpose of this study was to (1) manually roughen turkey flexor digitorum profundus (FDP) tendons to simulate extrasynovial tendons and (2) investigate the effects of gelatin MW on tendon friction.

Materials and methods: The third digit of (n = 48) turkeys were dissected with the proximal pulley, and FDP tendon and the flexor superficialis tendon were preserved. Digits were randomly assigned into four groups: one saline control and three cd-HA-gelatin-treated groups of varying gelatin MW. Flexor digitorum profundus tendon friction was measured at its original condition, serving as a baseline. Tendons were roughened using a custom rig, and tendon friction was measured again. All four groups received treatment and gliding friction was measured every 100 cycles to a total of 1,000 cycles.

Results: Tendon friction significantly increased (P < 0.05) after roughening. Friction in the saline control group increased steadily over repeated cycles, whereas friction of all gelatin-treated tendons decreased significantly compared with the saline control group (P < 0.05), maintaining low friction to 1,000 cycles representing human tendons. There was no significant difference found between gelatin-treated groups.

Conclusions: We have developed a method to roughen synovial FDP tendons to create extrasynovial-like tendons for lubrication material evaluations. Cd-HA-gelatin effectively reduces tendon friction in this model. Our data suggest medium or low MW gelatin may provide a better reduction in friction compared with high MW gelatin.

FIGURE 1.

(A) Lateral and top view of custom roughening apparatus. Flexor digitorum profundus (FDP) tendons were placed 55 mm from the plane of the pulleys (Time 1) and naturally moved to the plane of the pulleys (Time 2) over repeated cycles to encourage anisotropic roughening. (B) Lateral view of testing apparatus for measurement of gliding resistance between the FDP tendon and its proximal pulley. F1 is the distal force transducer and F2 is the proximal force transducer. PIP, proximal interphalangeal; K-wire,  Kirschner wire.

FIGURE 2.

Average gliding friction is shown from the original, extrasynovialized (roughened) and from 100 to 1,000 cycles. “Original” data point represents friction before any modification, “Extrasynovialized” data point represents friction after roughening, and “Cycle” measurements represent the number of repetitive cycles under constant load.

FIGURE 3.

The comparison of average gliding friction at (A) original, (B) extrasynovialized, (C) 100 cycles, (D) 1,000 cycles between all groups. Significant difference found between saline and treatment groups at 100, 1,000 cycles (P < 0.05).

FIGURE 4.

Scanning electron microscopy imaging of saline group at 20× (A) and 100× (C) magnification and medium molecular weight group at 20× (B) and 100× (D) magnification after roughening, treatment and 1,000 repetitive cycles.