Objective To investigate the effect of reconstruction of anterior cruciate ligament (ACL) with modified peroneus longus tendon (PLT) on foot function.

Methods The clinical data of 45 patients with modified PLT for reconstruction of ACL were analyzed retrospectively. Lysholm score was used to evaluate knee joint function, and the American Orthopedic Foot and Ankle Association (AOFAS) score was used to evaluate ankle joint function. Lysholm and AOFAS scores before operation and at the last follow-up, the bilateral ankle muscle strength at one year after operation and foot arch angles two years after operation were compared.

Results Lysholm at the last follow-up was significantly higher than that before surgery (P < 0.05); there was no significant difference in the AOFAS score before operation and at the last follow-up (P>0.05). One year after operation, there were no significant differences in foot valgus and plantar flexor strength between the affected side and the healthy side (P>0.05). Two years after operation, there were no significant differences in the medial longitudinal arch, lateral longitudinal arch, anterior arch angle of transverse arch and posterior arch angle of transverse arch between the affected side and healthy side (P>0.05). Two years after operation, there were no significant differences in the average pace time, speed, acceleration, deceleration, foot angle, long metatarsal angle and transverse metatarsal angle between the affected side and healthy side (P>0.05).

Conclusion Reconstruction of ACL with modified PLT can effectively improve the patient's knee joint and will not affect the stability of ankle joint.