Functional deficits may be explained by plantarflexor remodeling following Achilles tendon rupture repair: Preliminary findings

Abstract

Achilles tendon ruptures are common injuries that often lead to long-term functional deficits. Despite the prevalence of these injuries, the mechanism responsible for limited function has not yet been established. Therefore, the purpose of this study was to present preliminary findings that support a hypothesis that skeletal muscle remodeling is the driving factor of poor outcomes in some patients. Biomechanical and ultrasonography assessments were performed on a patient that presented with poor functional outcomes 2.5 years after a surgically-repaired acute Achilles tendon rupture. Single-leg heel raise height was decreased by 75% in the affected limb (3.0 cm compared to 11.9 cm) while walking mechanics showed no deficits. Ultrasonography revealed that the affected medial gastrocnemius muscle was less thick and had shorter, more pennate fascicles compared to the unaffected limb. A simple computational model of a maximal-effort plantarflexion contraction was employed to test the implications of changes in muscle architecture on single-leg heel raise function. Subject-specific measurements of fascicle length and pennation were input into the model, which supported these architectural parameters as being drivers of heel raise function. These preliminary findings support the hypothesis that an Achilles tendon rupture elicits changes in skeletal muscle architecture, which reduces the amount of work and power the joint can generate. This multidisciplinary framework of biomechanical, imaging, and computational modeling provides a unique platform for studying the complex interactions between structure and function in patients recovering from Achilles tendon injuries.

Persistent functional loss following ruptured Achilles tendon is associated with reduced gastrocnemius muscle fascicle length, elongated gastrocnemius and soleus tendon, and reduced muscle cross‐sectional area

“…It has been suggested that this deficit reflects an increase in tendon length, which is supported by the present data. As previously mentioned, it may also represent reduced muscle excursion, and this study shows for the first time that the fascicle length of the gastrocnemius muscle is shorter on the injured side. The relationship between deficit in heel‐rise height and gastrocnemius tendon elongation, but not soleus tendon elongation, may indicate that the accompanying change in gastrocnemius fiber length/muscle length ratio has a greater influence on excursion than that of the soleus …”

Gastrocnemius muscle remodeling explains functional deficits three months following Achilles tendon rupture

“…[23][24][25] Plantarflexor functional deficits measured at three months following Achilles tendon rupture were explained by gastrocnemius remodeling. Based on our previous computer simulations that show the isolated effects of shorter gastrocnemius fascicle length on plantarflexor function, 9,14 these experimental findings confirm the link between changes in muscle structure and function. A previous report correlated fascicle length with heel raise height and found that patient reported outcomes were strongly correlated with the amount of fascicle remodeling in patients following surgical repair.…”

Gastrocnemius fascicles are shorter and more pennate throughout the first month following acute Achilles tendon rupture

“…Long-term functional deficits have been linked to tendon elongation (30), which occurs within the first month following the initial injury (16). Preliminary reports suggest that plantarflexor muscle structure is the primary determinant of function following Achilles tendon ruptures (1,2). Sudden changes in muscletendon tension, whether imposed by immobilization (32) or tendon repairs (18), elicit rapid remodeling of skeletal muscle.…”

“…We are closely monitoring muscle and tendon structure at each clinical visit. Once cleared for activity, we will test plantarflexor strength and power in these patients using dynamometry and single-leg heel raises (2,3). Prior research also suggests that these structural changes in muscle are permanent(2) and the magnitude of these changes may be predictive of long-term functional deficits (1,30).…”

“…Targeted training can increase muscle fascicle length (28), effectively increasing power potential. Although muscle structure has been linked to function in many populations, shorter muscle fascicles have only been reported in a single case report of a patient with poor outcomes following an Achilles tendon rupture (2). Sudden changes in muscle-tendon tension, either induced through joint immobilization (32,33) or changes in muscle leverage (7,17), stimulate changes in muscle fascicle length within weeks.…”