Biomechanics and Motion Analysis

Strength of Suture-tendon Interface Increased by Eyelet Modification

Principal Investigator: Chunfeng Zhao, M.D.
Project Coordinator: Chunfeng Zhao, M.D. — zhao.chunfeng@mayo.edu
Funding Source: Musculoskeletal Transplant Foundation (MTF)

Recently, we have investigated the effects of treating tendon graft surfaces with a carbodiimide derivatized HA (cd-HA) gelatin mixture, which has been shown to improve tendon gliding ability and digit function after autografting extrasynovial tendons. The effects of such a treatment on the results of tendon allograft are not known. The purpose of this study is to investigate the role of surface treatment, a form of tissue engineering, on the results of flexor tendon allograft surgery in an animal model. To accomplish this purpose, we proposed two specific aims:

• Aim 1: To characterize the gliding ability and mechanical properties of allograft intrasynovial tendon treated with cd-HA-gelatin compared with autograft tendons in vitro;
• Aim 2: To test the results in vivo, in a canine model.

Figure 1: Gliding resistance

In Aim 1, a total of 36 flexor digitorum profundus (FDP) tendons from the 2nd and 5th digits of canine hind paws were harvested and randomly assigned for three groups. 12 tendons were immediately assessed both mechanically and morphologically, and served as the autograft control group. The other 24 FDP tendons were stored at -80 C for two weeks after freeze thaw cycling and lyophilization. These lyophilized tendons were randomly assigned to two groups, one treated with cd-HA-gelatin and the other not treated, to serve as the allograft control group. The frictional force was measured over 1000 simulated flexion/extension motion cycles using an established method. The tendons were then observed morphologically using scanning electron microscopy (SEM). The gliding resistance of the FDP tendons immediately following lyophilization was significantly increased compared to the normal FDP tendons (p < 0.05). However, the gliding resistance of the lyophilized FDP tendons after surface modification with cd-HA gelatin was significantly decreased compared to the lyophilized tendon without surface treatment (p < 0.05). There was no significant difference between normal FDP tendons and lyophilized FDP tendons treated with cd-HA gelatin. After 1000 cycles of motion, the relationship among three groups remained the same (Figure 1). In addition, the morphological results showed that the tendon surface treated with cd-HA-gelatin was well covered with a thin layer of cd-HA-gelatin even after 1000 cycles of tendon excursion, and scanning electron microscopy also demonstrated a smooth surface (Figure 2).

Figure 2: Tendon surface under scanning electron microscope (upper row with low magnification and bottom row with high magnification)

Lyophilization alters tendon surface morphology and increases tendon friction. Surface modification with cd-HA gelatin reverses this adverse effect, and restores the graft to its normal gliding properties. When tendon allografts are used in a situation where gliding of the allograft is important to subsequent clinical function, treatment of the surface with cd HA gelatin may be beneficial. Aim 2 of this study is ongoing.