This prospective longitudinal observational cohort study will characterize recovery of donor-ankle sensorimotor function in adults who have undergone primary anterior cruciate ligament reconstruction using a peroneus longus tendon autograft. Twenty participants aged 18 to 55 years will be evaluated at postoperative 6-8 weeks, 3 months, and 6 months. The donor limb and the contralateral non-donor limb will be compared using surface electromyography of the peroneus longus, force-platform measures of postural control, inertial-sensor gait analysis, active ankle joint-position sense testing, and clinical and patient-reported foot and ankle function measures. The study does not assign the surgical procedure or rehabilitation treatment.