Recovery of the medial gastrocnemius muscle after calcaneus fracture differs between contractile and elastic components.

Background: Calcaneal fractures result in severe functional impairments and walking restrictions. Postoperative evaluation mainly focusses on the restoration of calcaneal anatomy while ankle plantar flexor insufficiency remains largely neglected. This study aims to investigate biomechanical and morphologic adaptions of elastic and contractile components of the gastrocnemius medialis after unilateral calcaneal fracture. Methods: 20 Patients (BMI: 27.6 +/- 3.1 kgm(-2), Age: 50 +/- 12 years) were measured using gait analysis and portable ultrasound over a follow-up of three, six and twelve months after surgery. Data comparison was performed using 20 matched healthy controls (BMI: 26.2 +/- 2.9 kgm(-2), Age: 48 +/- 11 years). Static and dynamic behavior of the gastrocnemius muscle tendon unit, muscle fascicle and the serial-elastic element as well ankle joint kinematics and kinetics were analyzed. Findings: Within patients, a significant (p < 0.05) increase in fascicle length (by 67%) during single support and a decrease of serial elastic element shortening (by 20%) during push off was found between three and twelve months follow-up comparisons. Patients showed differences for fascicle lengthening and pennation angle increase during single support after three and six months compared to healthy controls. A smaller shortening of the serial-elastic element (by 29%) and muscle-tendon unit (by 16%) persisted even for the twelve month comparisons. Interpretation: Patients with calcaneal fracture showed an incomplete restoration of the medial gastrocnemius dynamic morphological behavior. While muscle fascicle contraction almost recovered, the serial elastic component still showed restrictions regarding its shortening behavior. Limited foot mobility and plantarflexor strength as well as lowered responsiveness of elastic tissues to mechanical loading are regarded as key mechanisms.

Automated summary

This study investigated the biomechanical and morphological adaptations of the gastrocnemius muscle after unilateral calcaneal fracture. The results showed that patients had an increase in muscle fascicle length and a decrease in the shortening of the serial elastic element. Compared to healthy controls, patients had differences in fascicle lengthening and pennation angle increase. Even at twelve months after surgery, there were still restrictions in the shortening behavior of the serial elastic element and muscle-tendon unit. This suggests that the dynamic morphological behavior of the medial gastrocnemius is not fully restored in patients with calcaneal fracture.