Optimization of the knot configuration for early accelerated rehabilitation after Achilles tendon rupture

Highlights

• Panda Rope Bridge Technique is suitable for early rehabilitation after Achilles tendon rupture.

• The knots used for Panda Rope Bridge Technique should not be less than five half hitches.

• Ultrabraid™ #2 suture with optimal knot is better than Ethibond™ #5 suture.

• Ultrabraid™ #2 suture is suitable for Panda Rope Bridge Technique.

Abstract

Background Panda Rope Bridge Technique (PRBT) was an new minimally invasive technique consisted of two bridge anchors (proximal anchors at calcaneus and distal anchors at myotendinous junction) and strong ropes (threads of the suture anchors) stretched between them, which was suitable for early accelerated rehabilitation of Achilles tendon rupture. However, the optimal knot configuration with PRBT was unknow. The purpose of this study was identify minimum number of half hitches necessary to maintain knot security for PRBT.

Methods Using an Instron device we tested the effect of different knot configuration in two kinds of suture threads (Ethibond™ #5 and Ultrabraid™ #2). According to the result of it, we put the optimal knot configuration into Part 1 with PRBT test model and Part 2 with modified PRBT test model, to evaluate whether the optimal knot configuration could complete the cyclic loading test simulated early rehabilitation.

Findings In the first part of the study, the optimal knot configuration of Ethibond™ #5 suture thread was the combination of three half hitches and one double throw half knot, and the optimal knot configuration of Ultrabraid™ #2 suture thread was the combination of five half hitches and one double throw half knot. In the second part of the study, only Ultrabraid™ #2 suture thread with optimal knot configuration had finished all test in Part 1.

Interpretation The Ultrabraid™ #2 suture thread with optimal knot configuration was suitable for PRBT with early accelerated rehabilitation after Achilles tendon repair.

Introduction

Knotting is a crucial part of suture, whether a surgery can achieve a good outcome is closely related to the knot security. Knot security, defined as the ability to resist slippage and breakage as load was applied.(Burkhart et al., 2000)The knot security depended on suture material, suture thickness and configuration of knots (Tidwell et al., 2012). And the configuration of knot included tying technique and number of throws or hitches. As for the number of throws, it has been stated that tying with too few throws could result in knot failure, whereas too many throws than required offered no mechanical advantage but brought more foreign bodies in the wound which damaged host defenses and resistance to infection (Silver et al., 2016). Therefore, the purpose of the study with knot configuration is to provide good biomechanical stability with fewer hitches.

Despite being the largest and strongest tendon in the human body, the Achilles tendon ruptures has been found to be the most commonly ruptured tendon (Yin et al., 2018). Moreover, treatment delay leads to poorer outcomes, as a discontinuous or lengthened tendon can cause weak plantar flexion, fatigue, limp, and inability to run, heel rise, play sports, and climb stairs (Singh, 2015). Akizuki et al. reported that the healing tendon needed at least 400 N load bearing capacity during gait to avoid the detrimental effects of cyclic loading (Akizuki et al., 2001). Therefore, most techniques needed protection by immobilisation and without weight-bearing after Achilles tendon repair in the past. However, it was reported that the combination of minimally invasive surgery and early rehabilitation resulted in good postoperative function and the lowest risk of serious complications in patients with Achilles tendon rupture (Wu et al., 2019). Thus, there was no consensus on the postoperative rehabilitation of Achilles tendon rupture (Akizuki et al., 2001; Groetelaers et al., 2014; Mark-Christensen et al., 2016; Singh, 2015; Speck and Klaue, 1998). PRBT (Panda Rope Bridge Technique) was a new minimally invasive technique which provided a simple and effective treatment for acute Achilles tendon rupture, and met the requirements of early rehabilitation, and obtained good outcomes (Yin et al., 2018). Early rehabilitation required high safety of the knot, but there was no related biomechanical study of PRBT. It was reported that knot configurations of conventional Achilles tendon repair techniques were three to six throws or half hitches (Carmont and Maffulli, 2008; Clanton et al., 2015; Ilahi et al., 2008; Lee et al., 2009; Ma and Griffith, 1977; Ortiz et al., 2012; Watson et al., 1995). In order to prevent knot slippage during early rehabilitation, the knot configuration of PRBT was a combination of six half hitches and one double throw half knot (Yin et al., 2018). Until now, there was no study to determine whether three to six half hitches were sufficient for PRBT with early rehabilitation, or how many half hitches at least could provide the optimum knot security.

The objectives of the study were (1) to identify minimum number of half hitches necessary to maintain knot security for PRBT; (2) to evaluate whether PRBT composed of the optimal knot configuration could complete the cyclic loading test simulated early rehabilitation. Our hypothesis was that the lowest number of half hitches of optimal knot configuration was three, and PRBT with the knot configuration could complete the cyclic loading test simulated early rehabilitation.