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Orthopedic and Rehabilitation Engineering

Orthopedic and Rehabilitation Engineering - Poster Session E

Poster K19 - The Effects of Achilles Tenectomy or Replacement on the Tibialis Cranialis and Lateral Gastrocnemius

Saturday, October 26, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Permanent artificial tendons would be valuable alternatives to tendon grafts because they could reduce the risk of rejection and disease transmission (allografts) and eliminate donor site morbidity (autografts). Our previous studies tested artificial tendons composed of braided strands of polyester suture coated in silicone (PET-SI) [1, 2]. In a New Zealand White rabbit model, the insertion tendons of either the tibialis cranialis (TC) or triceps surae (Achilles tendon) muscles were surgically replaced with a PET-SI tendon. The PET-SI group demonstrated more similar kinematics to the pre-surgery baseline than a group that underwent tenectomy (TE) only [1, 2]. We hypothesize that the biomechanical function of rabbits with a PET-SI tendon partly depends on the extent to which the tendon preserves the structure and function of the attached and surrounding muscles. The goal of this study was to measure the effect of Achilles tendon replacement with a PET-SI tendon on the cross-sectional areas (CSAs) of the tibialis cranialis and lateral gastrocnemius (LG) muscles, compared to rabbits with Achilles tenectomy.

Materials and

Methods:  New Zealand White Rabbits were split into two groups, PET-SI (n=5) and TE (n=5). The rabbits in the PET-SI group underwent surgery to excise and replace the left Achilles tendon with a PET-SI tendon, while the rabbits in the TE group underwent surgical tenectomy of the left Achilles tendon. One rabbit in the TE group died during surgery due to anesthesia complications. For the remaining rabbits, approximately 8 cross-sectional images for the left TC and LG muscles of each rabbit, were recorded using ultrasound at 4 days pre-surgery and 12, 28, and 56 days post-surgery. We used image processing software (ImageJ) to measure the muscle CSAs from three of the eight clearest image samples for each muscle, rabbit, and timepoint. The data were averaged across samples, then normalized by the rabbit’s body mass measured at each respective timepoint. We used statistical analysis software (SPSS, SAS Inc.) to perform a 3-way ANOVA test comparing group, muscle, and time point. Post-hoc Student’s t-tests compared the means between groups and timepoints with values of p< 0.05 considered significant.

Results, Conclusions, and Discussions: ANOVA revealed no significant difference between groups, but based on post-hoc t-tests, LG CSA was significantly larger in the PET-SI group than the TE group at 56 days post-surgery (p=0.006). Additionally, ANOVA found a significant effect of timepoint and muscle (p < 0.05). For the PET-SI group, compared to 4 days pre-surgery, LG CSA was significantly less at 14 days, 28 days, and 56 days post-surgery (p < 0.05). The TE group’s CSA significantly decreased from 4 days pre-surgery to 14 days, 28 days, and 56 days post-surgery as well as 14 days post-surgery to 56 days post-surgery (p < 0.05). Qualitatively, the PET-SI group LG CSAs declined slower than the TE group. For the TC muscle, there was no significant difference in CSAs between the TE and PET-SI groups at any timepoint as ANOVA indicated. The TC CSAs for the TE group significantly decreased over time, specifically from 4 days pre-surgery to 56 days post-surgery and 14 days post-surgery to 56 days post-surgery (p < 0.05), while TC CSAs for the PET-SI group demonstrated no significant differences at any time point (p>0.05).
The PET-SI tendon preserved the size of the LG muscle compared to the TE group, suggesting that the PET-SI tendon can at least partly perform the load-transmission function of a biological tendon. A muscle's force-generating capacity is proportional to its physiologic cross-sectional area [3]. Our comparisons of geometric cross-sectional area assume that muscle fiber pennation angles and fiber lengths were comparable between groups; we will measure these values directly from the muscle tissues to determine if the assumption is reasonable. The TC CSA in the TE group decreased over time, which could have been expected since the force from a major antagonist muscle was removed allowing a lower exerted force by the TC to create motion. Conversely, the endpoint and baseline of the PET-SI group’s CSA suggests that the artificial tendon helped maintain the agonist-antagonist muscle relationship. While our preliminary results are promising, future studies should make more comprehensive measurements of musculoskeletal structure and function over a longer duration before clinical translation of PET-SI tendons.

Acknowledgements (Optional):  This study was supported by the NIH (Award #R61AR078096 and R33AR078096). Thank you to the University of Tennessee Office of Laboratory Animal Care for veterinary care of the rabbits during the study.
[1] Easton et al., J Ortho Res, 2024. [2] Hall et al., J Biomechanics, 2023. [3] Zajac, Crit Rev Biomed Eng, 1989.