Biomechanical comparison of innovative suture techniques for repair of Achilles tendon rupture in a porcine flexor tendon model

INTRODUCTION: In recent years, evidence-based progressive rehabilitation protocols following the surgical treatment of Achilles tendon rupture have been shown to be safe and appear superior to more restrictive treatment regimens. These protocols mainly rely on early mobilization and weight bearing. To enable this during postoperative rehabilitation, a biomechanically stable surgical treatment must be ensured. Different solutions for suturing ruptured Achilles tendons are currently favored by orthopedic surgeons and have been investigated in the past, including promising further developments of traditional approaches such as the combination of pretension and the Bunnell technique, as well as minimally invasive or percutaneous techniques using systems like the Arthrex PARS. However, the best solution in this regard remains unclear. METHODS: We analyzed the biomechanical stability of four different suture techniques using porcine deep flexor tendons as a biomechanical model for human Achilles tendons. The tendons were harvested, prepared and sutured according to their respective group (A: Bunnell, B: Bunnell + pretension, C: PARS-to-PARS, D: PARS + anchor). The four groups (n = 12) underwent progressive, cyclic, uniaxial tensile loading in the biomechanical testing machine (ZwickRoell Z020). RESULTS: Group D (PARS + anchor) showed the highest maximum force at ultimate failure, resisting statistically significant higher loads compared to all the other groups. Pretension led to a non-significant increase in maximum force in the Bunnell groups. This was the case for the force necessary to create a 5 mm gap as well, while the force necessary to create the initial gap was equal in the PARS-to-PARS and pretensioned Bunnell group, both proving superior to the Bunnell group without pretension. Group D consistently resisted statistically significant higher forces in comparison to the PARS-to-PARS group for the initial gap, the 5 mm gap and until failure. This was generally valid for the number of cycles necessary to reach the initial gap, the 5 mm gap and the point of failure, as well. CONCLUSIONS: Considering the superiority over both Bunnell techniques during the biomechanical testing in this experimental model despite its limitations in transferability, using the PARS-to-PARS technique in suturing ruptured Achilles tendons seems to be a valid alternative from a biomechanical point of view. We hypothesize that its higher resistance to tension forces found in this study could provide the potential to facilitate more progressive postoperative treatment protocols reflected by earlier weight bearing, which could enable improved rehabilitation outcomes and should be investigated in future studies. While forces acting on the human Achilles tendon during walking in an ankle foot orthosis (AFO) with a lifted heel are estimated at approximately 200 N, our results indicate resistance within a similar force range for the PARS technique. We hypothesize that this technique may contribute to a reduced risk of rerupture, which should be investigated further. Using suture anchors increases the stress resistance of this system further, which makes it a viable alternative not only in distal ruptures. When an open approach is desired, applying pretension can improve the stress resistance of a traditional approach like the Bunnell method, so surgeons should consider this adaptation in such cases.