Recovery from Achilles Tendon Repair: A Combination of Postsurgery Outcomes and Insufficient Remodeling of Muscle and Tendon

Abstract

Introduction: Achilles tendon rupture (ATR) patients have persistent functional deficits in the triceps surae muscle-tendon unit (MTU). The complex remodeling of the MTU accompanying these deficits remains poorly understood. The purpose of the present study was to associate in vivo and in silico data to investigate the relations between changes in MTU properties and strength deficits in ATR patients.Methods: Eleven male subjects who had undergone surgical repair of complete unilateral ATR were examined 4.6 ± 2.0 (mean ± SD) years after rupture. Gastrocnemius medialis (GM) tendon stiffness, morphology, and muscle architecture were determined using ultrasonography. The forcelength relation of the plantar flexor muscles was assessed at five ankle joint angles. In addition, simulations (OpenSim) of the GM MTU force-length properties were performed with various iterations of MTU properties found between the unaffected and the affected side. Results:The affected side of the patients displayed a longer, larger, and stiffer GM tendon (13 ± 10%, 105 ± 28% and 54 ± 24%, respectively) compared with the unaffected side. The GM muscle fascicles of the affected side were shorter (32 ± 12%) and with greater pennation angles (31 ± 26%). A mean deficit in plantarflexion moment of 31 ± 10% was measured. Simulations indicate that pairing an intact muscle with a longer tendon shifts the optimal angular range of peak force outside physiological angular ranges, whereas the shorter muscle fascicles and tendon stiffening seen in the affected side decrease this shift, albeit incompletely.Conclusions: These results suggest that the substantial changes in MTU properties found in ATR patients may partly result from compensatory remodeling, although this process appears insufficient to fully restore muscle function.

Muscle-tendon morphomechanical properties of non-surgically treated Achilles tendon 1-year post-rupture

“…After rupture, MG muscle probably adapts by resetting fascicle length (dictated by serial sarcomere number) and pennation angle to a new optimum for force production at a joint angle at which the force requirement during normal locomotion is largest. This still leads to reductions in the range of motion at which force can be produced (40) and the ability of the plantar flexors to perform work (35). We found that the reduction in MG fascicle length was inversely correlated with increased pennation angle, as shown previously (12).…”

“…As TS muscles operate mostly on the ascending limb of the force-length relationship (37), a higher AT stiffness helps to preserve favourable sarcomere lengths during force generation by reducing muscle shortening. Higher tendon stiffness may also help to minimize the impairments in force production caused by the increased AT resting length, albeit incompletely (40). AT stiffness is also positively correlated with TS rate of force development (13,44,45).…”

Altered Gastrocnemius Contractile Behavior in Former Achilles Tendon Rupture Patients During Walking

“…This study is part of a comprehensive investigation on ATR patients’ functional deficits. For this purpose, sample size calculations were based on ATR patients’ strength deficits, as described previously ( Stäudle et al, 2021 ). The a priori power analysis suggested a minimum sample size of 10 subjects.…”

“…Long after recovery and regardless of treatment strategy, the MTU of ATR patients is characterized by a longer tendon ( Silbernagel et al, 2012 ; Peng et al, 2019 ; Svensson et al, 2019 ). Recent studies suggest that the increased tendon stiffness ( Agres et al, 2015 ; Stäudle et al, 2021 ) and shorter gastrocnemius medialis (GM) muscle fascicles ( Baxter et al, 2018 ; Peng et al, 2019 ; Svensson et al, 2019 ) typically seen in ATR patients may compensate for their longer tendons, albeit incompletely ( Stäudle et al, 2021 ). Using a musculoskeletal model to simulate maximum isometric contractions at various joint angles, we have shown that the shorter GM fascicles in the affected leg enables sarcomeres to operate close to their optimal length, but at the expense of a narrowed range for active force generation ( Stäudle et al, 2021 ).…”

“…Recent studies suggest that the increased tendon stiffness ( Agres et al, 2015 ; Stäudle et al, 2021 ) and shorter gastrocnemius medialis (GM) muscle fascicles ( Baxter et al, 2018 ; Peng et al, 2019 ; Svensson et al, 2019 ) typically seen in ATR patients may compensate for their longer tendons, albeit incompletely ( Stäudle et al, 2021 ). Using a musculoskeletal model to simulate maximum isometric contractions at various joint angles, we have shown that the shorter GM fascicles in the affected leg enables sarcomeres to operate close to their optimal length, but at the expense of a narrowed range for active force generation ( Stäudle et al, 2021 ). The insights gained from these findings are, however, insufficient for predicting triceps surae mechanics in dynamic situations, where force-velocity conditions may set additional constraints.…”