Evaluation of a novel strap fixation method for biomechanical testing of sheep Achilles tendons

Reliable fixation of tendon specimens is a major challenge in biomechanical testing, as slippage and tissue damage can reduce accuracy and reproducibility. Although various clamp- and suture-based fixation methods have been reported, there is still no widely accepted, practical, low-cost technique that preserves tendon integrity during testing. This study aimed to compare commonly used fixation techniques and to evaluate whether a novel strap-based fixation method provides a more stable and tissue-preserving alternative for biomechanical testing of sheep Achilles tendons.

Forty fresh-frozen cadaveric sheep Achilles tendons obtained from a local butcher were used, and the specimens were stored at - 20 °C until testing. After controlled thawing at room temperature, all tendons were repaired using the Bunnell suture technique with No. 0 Vicryl. Four different proximal fixation methods were evaluated: (1) sutured fixation with strap, (2) direct clamp fixation, (3) Kocher clamp fixation, and (4) Krackow suture fixation. All specimens were mounted on a universal testing machine and subjected to a load-to-failure protocol at a constant loading rate of 10 mm/s. Maximum force (N), displacement at failure (mm), and mechanical failure mechanisms were recorded for each sample. Data were analyzed using the Kruskal-Wallis test with Bonferroni-corrected Mann-Whitney U tests for pairwise comparisons (p < 0.0083).

The strap method demonstrated the highest numerical load-carrying capacity [114.58 N (73.59-135.00)] with relatively controlled displacement [16.96 mm (8.79-26.52)]. Its maximum load was significantly higher than that of the direct clamp and Kocher clamp methods; however, the difference compared with the Krackow suture method did not remain statistically significant after Bonferroni correction. Tendons fixed directly by clamp (Group 2) exhibited tissue damage due to clamp pressure and showed lower load capacity [75.41 N (58.28-110.78)] with greater displacement [28.01 mm (17.63-51.93)]. The Kocher clamp method (Group 3) provided the lowest mechanical strength, and most specimens slipped at the onset of loading [38.35 N (26.41-49.53); 15.55 mm (10.92-17.54)]. The Krackow suture method (Group 4) showed intermediate performance [82.95 N (65.62-148.50); 27.00 mm (19.49-30.75)].

The strap fixation method provided stable fixation, no visible slippage, and the highest numerical load-to-failure values among the tested techniques. It was significantly stronger than the direct clamp and Kocher clamp methods; however, it was not statistically superior to the Krackow suture method after Bonferroni correction. The strap method may therefore be considered a practical and tissue-preserving alternative for further biomechanical tendon testing.