Exploring plantar flexor function 12 months after an Achilles tendon rupture

BackgroundAchilles tendon rupture (ATR) is associated with significant short- and long-term functional deficits, likely in consequence of rupture induced tendon elongation and associated changes in muscle contractile properties. PurposeTo investigate the association between tendon elongation and plantar flexor functional performance during unilateral hopping 12 months post-ATR. Further, the study examined side-to-side performance differences (injured vs. non-injured leg) 6 and 12 months post-ATR. Study DesignExplorative cross-sectional study. MethodsParticipants (n=59) were recruited from the cohort of a larger randomized controlled trial. Tendon length was measured using ultrasonography at baseline and at 6 and 12 month post-ATR to determine tendon elongation. Heel-rise height deficit (injured minus non-injured side) and biomechanical variables of unilateral hopping (peak moment (Mpeak), peak concentric and eccentric power (CPpeak and EPpeak) and relative concentric and eccentric ankle joint work (RCWankle and REWankle)) were measured on both sides at 6 and 12 months post injury. ResultsAbsolute and relative 12 months post-ATR tendon elongation was 19.3% (CI: 15.8-22.8mm) and 11.2% (CI: 9.2-13.2%) respectively. No significant associations were found between tendon elongation and biomechanical variables or heel-rise height deficit. Although functional improvements were observed between 6 and 12 months, significant deficits in plantar flexor function during hopping persisted at 12 months post-ATR for the injured vs. non-injured leg. Specifically, Mpeak was 11% lower (p < 0.001), CPpeak and EPpeak were 36% (p < 0.001) and 28% lower (p = 0.001), respectively, and RCWankle and REWankle were 15% (p < 0.001) and 17% lower (p < 0.001), respectively, in the injured leg compared to the non-injured leg. ConclusionNo significant associations were shown between absolute Achilles tendon elongation and plantar flexor functional performance. Furthermore, side-to-side differences were shown to persist at 12 months. Level of Evidence: 3O_ST_ABSClinical RelevanceC_ST_ABSOur study shows that deficits in plantar flexor contractile function persist at 12 months post-ATR and is compensated during hopping by work of muscles that span the knee- and hip-joint. The altered pattern of activation should be taken into consideration during rehabilitation and in return to sport decisions. Further, the present study indicates that heel-rise height has limited value as a proxy for injury induced tendon elongation. What is known about the subjectLarge functional differences between the injured and non-injured leg have been observed both in the short- and long-term following ATR. Functional deficits are more pronounced when examined in more demanding tasks such as jogging and jumping. What this study adds to existing knowledgeThis study shows functional deficits of the injured leg 12 months post-ATR and thereby confirms what other studies has found. Additionally, the findings indicate that tendon elongation alone does not explain the deficits in plantar flexor function. Further, the findings underline the importance of selecting a test that specifically measures ankle joint function.