Biomechanical Comparison of Krackow Repair and Percutaneous Achilles Repair System for Achilles Tendon Rupture Fixation: A Cadaveric and Finite Element Analysis Study

Abstract

Background: Open and percutaneous repair surgeries are widely used for the Achilles tendon rupture. However, prior biomechanic studies of these 2 approaches have mixed conclusions; therefore, we designed a cadaver and finite element (FE) model biomechanical study to compare the mechanical differences between the percutaneous Achilles repair system (PARS) and Krackow open repair under tensile load and rotation. Methods: Sixteen Achilles tendons were extracted from fresh-frozen cadaver ankles and the calcaneums were fixed in mortar. A force control dynamic tensile mechanical test was performed at 1 Hz with 30- and 100-N cyclic loads. Initial intact baseline testing was followed by an incision on all Achilles tendons, 4 cm from the calcaneus insertion, which were then repaired using the PARS (n = 8) or Krackow (n = 8) method. Recorded force-displacement values were used to calculate mechanical parameters, and statistical significance of differences was determined by unpaired (between repair techniques) and paired (intact vs repaired) t tests. Material properties of the Achilles tendon in the FE model were modified and a 10-Nm flexion was simulated for intact and surgical groups. Results: No differences were found between intact tendons assigned to PARS or Krackow repairs in Young’s modulus ( P = .582) and stiffness ( P = .323). Pre- and postoperative Young’s modulus was significantly decreased for both groups (Intact 230.60±100.76 MPa vs PARS 142.44±37.37 MPa, P < .012; Intact 207.46±81.12 MPa vs Krackow109.43±27.63 MPa, P < .002). Stiffness decreased significantly after surgery for both groups (Intact 25.33±10.89 N/mm vs PARS 6.51±1.68 N/mm, P < .003; Intact 20.30±8.65 N/mm vs Krackow 5.97±1.30 N/mm, P < .003). PARS ultimate tensile strength was significantly higher than the Krackow (PARS 280.29±47.32 N vs Krackow 196.97±54.28 N, P < .003) but not significantly different in the ultimate tensile strain. PARS had a significantly lower postoperative gap compared to Krackow (PARS 9.75±5.87 mm vs Krackow 25.19±7.72 mm, P < .001). FE analysis predicted an increased talocalcaneal contact pressure, maximum principal stress, and rotation in the Krackow vs PARS models, respectively. Conclusion: Biomechanical parameters observed in this study through mechanical testing and FE analysis favor the selection of PARS over the Krackow repair based on better strength, higher failure force, and lower gap generation. Clinical Relevance: The study has analyzed two Achilles tendon repair methods using cadaver and numerical estimation and may help clinicians gain insight into selection of tendon repair approaches to generate better clinical outcomes.