Medial gastrocnemius muscle remodeling correlates with reduced plantarflexor kinetics 14 weeks following Achilles tendon rupture

Abstract

Deficits in plantarflexor kinetics are associated with poor outcomes in patients following Achilles tendon rupture. In this longitudinal study, we analyzed the fascicle length and pennation angle of the medial gastrocnemius muscle and the length of the Achilles tendon using ultrasound imaging. To determine the relationship between muscle remodeling and deficits in plantarflexor kinetics measured at 14 wk after injury, we correlated the reduction in fascicle length and increase in pennation angle with peak torque measured during isometric and isokinetic plantarflexor contractions. We found that the medial gastrocnemius underwent an immediate change in structure, characterized by decreased length and increased pennation of the muscle fascicles. This decrease in fascicle length was coupled with an increase in tendon length. These changes in muscle-tendon structure persisted throughout the first 14 wk following rupture. Deficits in peak plantarflexor torque were moderately correlated with decreased fascicle length at 120 degrees per second ( R2 = 0.424, P = 0.057) and strongly correlated with decreased fascicle length at 210 degrees per second ( R2 = 0.737, P = 0.003). However, increases in pennation angle did not explain functional deficits. These findings suggest that muscle-tendon structure is detrimentally affected following Achilles tendon rupture. Plantarflexor power deficits are positively correlated with the magnitude of reductions in fascicle length. Preserving muscle structure following Achilles tendon rupture should be a clinical priority to maintain plantarflexor kinetics. NEW & NOTEWORTHY In our study, we found that when the Achilles tendon ruptures due to excessive biomechanical loading, the neighboring skeletal muscle undergoes rapid changes in its configuration. The magnitude of this muscle remodeling explains the amount of ankle power loss demonstrated by these patients once their Achilles tendons are fully healed. These findings highlight the interconnected relationship between muscle and tendon. Isolated injuries to the tendon stimulate detrimental changes to the muscle, thereby limiting joint-level function.

Muscle structure governs joint function: linking natural variation in medial gastrocnemius structure with isokinetic plantar flexor function

“…We decided to measure the structure of the medial gastrocnemius due to previous observations linking structural changes in that muscle following Achilles tendon rupture to functional deficits (Baxter et al, 2018; Hullfish et al, 2019b) coupled with similar observations with other studies (Peng et al, 2017, 2019). Prior studies have linked plantar flexor torque measurements with medial gastrocnemius structure without accounting for the other two triceps surae muscles (Hauraix et al, 2015; Thom et al, 2007).…”

“…These links between gastrocnemius structure and plantar flexor function translate to patient populations as well. For example, the magnitude of plantar flexor power deficits in patients recovering from Achilles tendon ruptures is strongly correlated with the magnitude of remodeling of the medial gastrocnemius muscle, characterized by shorter resting fascicles in the injured limb (Hullfish et al, 2019b). The importance of fascicle geometry on plantar flexor function has also been demonstrated in silico .…”

“…While longer medial gastrocnemius fascicles are correlated with increased muscle shortening speed (Hauraix et al, 2015; Thom et al, 2007), these findings have not been translated to voluntary plantar flexor kinetics measured in vivo using isokinetic dynamometry. Given that variation in gastrocnemius muscle structure is well documented (Kawakami et al, 2000) and is modified by injury, (Hullfish et al, 2019b), training (Salzano et al, 2018), and aging (Morse et al, 2005); determining if natural variations in fascicle length and pennation angle impacts voluntary function has important implications.…”

Functional Ankle Range of Motion but Not Peak Achilles Tendon Force Diminished With Heel-Rise and Jumping Tasks After Achilles Tendon Repair

“…To compensate for an elongated tendon and adequately preload the muscle, the ankle moves into additional dorsiflexion (DF), decreasing the functional ankle range of motion (ROM) and shifting it toward dorsiflexion. This conceptual framework is supported by literature linking kinetic ankle deficits during concentric angle tasks with structural deficits in both patients 19 and computational models. Lower limb kinematics and kinetics were calculated by means of a constrained kinematic model using a previously described approach.…”

Novel instrumented insole algorithm accurately approximates plantar flexor loading

“…Plantar flexor loading is critical for ambulatory function throughout the lifespan [1,2] and in injured populations [3][4][5]. While inverse dynamics is the 'gold standard' for assessing joint moments, there are few wearable solutions to continuously monitor plantar flexor loading [6].…”