Persistence of long term isokinetic strength deficits in subjects with lateral ankle sprain as measured with a protocol including maximal preloading

•We assessed the strength of the ankle muscles in persons with a lateral ankle sprain using a maximum preloading procedure.•Evertor and plantarflexor strength deficits measured at discharge from physiotherapy were negligeable after 6 months.•Weakness of the plantarflexors persisted at 6 months post-injury in persons with a grade II sprain.•Persons with an ankle sprain should keep doing strengthening after physiotherapy to accelerate and ensure full recovery.

BackgroundThe assessment of muscle function is a cornerstone in the management of subjects who have sustained a lateral ankle sprain. The ankle range of motion being relatively small, the use of preloading allows to measure maximal strength throughout the whole amplitude and therefore to better characterize ankle muscles weaknesses. This study aimed to assess muscle strength of the injured and uninjured ankles in subjects with a lateral ankle sprain, to document the timeline of strength recovery, and to determine the influence of sprain grade on strength loss.MethodsMaximal torque of the periarticular muscles of the ankle in a concentric mode using a protocol with maximal preloading was tested in 32 male soldiers at 8 weeks and 6 months post-injury.FindingsThe evertor muscles of the injured ankles were weaker than the uninjured ones at 8 weeks and 6 months post-injury (P < 0.0001, effect size = 0.31-0.42). Muscle weaknesses also persisted in the plantarflexors of the injured ankles at 8 weeks (P = 0.0014, effect size = 0.52-0.58) while at 6 months, only the subjects with a grade II sprain displayed such weaknesses (P < 0.0001, effect size 0.27-0.31). The strength of the invertor and dorsiflexor muscles did not differ between sides.InterpretationThe use of an isokinetic protocol with preloading demonstrates significant but small strength deficits in the evertor and plantarflexor muscles. These impairments may contribute to the high incidence of recurrence of lateral ankle sprain in very active individuals.