Lubricin surface modification improves extrasynovial tendon gliding in a canine model in vitro

Background: Lubricin is the principal lubricant in synovial fluid. Although lubricin has been identified in tendons, especially on the surface of intrasynovial tendons such as the flexor digitorum profundus tendon, its ability to improve tendon gliding is unknown. The purpose of this study was to investigate the effects of exogenously applied lubricin on the gliding of extrasynovial tendons in a canine model in vitro. Methods: Forty peroneus longus tendons, along with the proximal pulley in the ipsilateral hind paw, were harvested from adult mongrel dogs. After the gliding resistance of the normal tendons was measured, the tendons were treated with one of the following solutions: saline solution, lubricin, carbodiimide derivatized gelatin (cd-gelatin), carbodiimide derivatized gelatin with hyaluronic acid (cd-HA-gelatin), or carbodiimide derivatized gelatin to which lubricin had been added in a second step (cd-gelatin plus lubricin). Tendon gliding resistance was measured for 1000 cycles of simulated flexion-extension motion of the tendon. Transverse sections of the tendons were examined qualitatively at 100x magnification to estimate surface smoothness after 1000 cycles. Results: There was no significant difference in the gliding resistance between the tendons treated with saline solution and those treated with lubricin alone, or between the tendons treated with cd-HA-gelatin and those treated with cd-gelatin plus lubricin; however, the gliding resistance of the tendons treated with cd-gelatin plus lubricin was significantly lower than that of the tendons treated with saline solution, lubricin alone, or cd-gelatin alone (p < 0.05). After 1000 cycles of tendon motion, the gliding resistance of the tendons treated with cd-gelatin plus lubricin decreased 18.7% compared with the resistance before treatment, whereas the gliding resistance of the saline-solution-treated controls increased >400%. The tendon surfaces treated with cd-gelatin plus lubricin or with cd-HA-gelatin appeared smooth even after 1000 cycles of tendon motion, whereas the other surfaces appeared roughened. Conclusions: While the addition of lubricin alone did not affect friction in this tendon gliding model, the results indicate that lubricin may preferentially adhere to a tendon surface pretreated with cd-gelatin and, when so fixed in place, lubricin does have an important effect on tendon lubrication. Clinical Relevance: This in vitro canine study suggests that modification of a tendon surface with lubricin can improve the tendon's gliding ability, potentially improving clinical outcomes of extrasynovial tendon grafting.