Exploring persisting plantar flexor deficits during hopping 12 months after an Achilles tendon rupture: No correlation to Achilles tendon elongation.

Background: Following Achilles tendon rupture, previous studies have reported significant short- and long-term deficits in ankle joint function as a consequence of post-rupture tendon elongation. The present explorative study aimed to investigate the association between tendon elongation and biomechanical variables measured during hopping 12 months post-injury, including differences between the injured and non-injured leg.
Materials and methods: Participants (n=59) were recruited from the cohort of an ongoing randomized controlled trial. Tendon length was measured at baseline and at 6- and 12-months post-injury to calculate tendon elongation, while biomechanical variables; moment (Mpeak), concentric and eccentric power (respectively CPpeak and EPpeak) and relative concentric and eccentric ankle joint work (respectively RCWankle and REWankle) were measured during unilateral hopping 6- and 12-months post-injury.
Results: 12-months post injury no significant association was found between tendon elongation and biomechanical variables. Although improvements were observed between 6 and 12 months, statistically significant deficits in ankle joint function during hopping persisted 12 months post-injury. Specifically, Mpeak was 11% lower (p<0.01), CPpeak and EPpeak were 36% (p<0.01) and 28% lower (p=0.03), respectively, and RCWankle and REWankle were 15% (p<0.01) and 17% lower (p<0.01), respectively, in the injured leg compared to the non-injured leg. Additionally, a compensatory strategy with increased work from the knee- and hip joint was observed.
Conclusions: The present results suggest that tendon elongation may not solely explain deficits of ankle joint function following Achilles tendon rupture, but the observed deficits of function and compensatory strategy, indicate that patients are not fully recovered 12 months post-injury.