Passive stiffness of the ankle and plantar flexor muscle performance after Achilles tendon repair: a cross-sectional study

BACKGROUND Deficits in ankle muscle strength and ankle stiffness may be present in those subjects who underwent surgical treatment for an Achilles tendon rupture. The presence of these long-term deficits may contribute to a lower performance during daily activities and may be linked to future injuries. OBJECTIVE To compare the ankle passive stiffness and the plantar flexor muscle performance in patients who underwent unilateral surgical treatment of Achilles tendon rupture with nonsurgical subjects. METHOD Twenty patients who underwent unilateral surgical treatment of Achilles tendon rupture [surgical (SU) group], and twenty nonsurgical subjects [non-surgical (NS) group] participated in this study. The ankle passive stiffness was evaluated using a clinical test. The concentric and eccentric plantar flexors performance (i.e. peak torque and work) was evaluated using an isokinetic dynamometer at 30°/s. RESULTS The surgical ankle of the surgical group presented lower stiffness compared to the non-surgical ankle (mean difference=3.790; 95%CI=1.23-6.35) and to the non-dominant ankle of the non-surgical group (mean difference=-3.860; 95%CI=-7.38 to -0.33). The surgical group had greater absolute asymmetry of ankle stiffness (mean difference=-2.630; 95%CI=-4.61 to -0.65) and greater absolute asymmetry of concentric (mean difference=-8.3%; 95%CI=-13.79 to -2.81) and eccentric (mean difference=-6.9%; 95%CI=-12.1 to -1.7) plantar flexor work compared to non-surgical group. There was no other difference in stiffness and plantar flexor performance. CONCLUSION Patients who underwent surgical repair of the Achilles tendon presented with long-term (1 year or more) deficits of ankle stiffness and asymmetries of ankle stiffness and plantar flexor work in the affected ankle compared to the uninjured side in the surgical group and both sides on the nonsurgical group.