Three dimensional knee kinematics and kinetics in ACL-deficient patients with and without medial meniscus posterior horn tear during level walking

•MMPHT did not significantly affect gait patterns in stance in ACLD knees.•ACLD + MMPHT knees adapted a combination of “stiffening gait” and “pivot shift gait”.•ACLD + MMPHT knees showed extension deficiency and lower extension moments.•ACLD + MMPHT knees showed lower internal rotation moments during TSP.•ACLD + MMPHT knees showed increased external tibial rotation during PSP. The location of the meniscus tear has been reported to influence kinematics in anterior cruciate ligament deficient (ACLD) knees. Medial meniscus posterior horn tear (MMPHT) often occurred after ACL rupture. Whether MMPHT influences the kinematics and kinetics in ACLD knees has not been reported yet. The purpose of this study was to investigate three-dimensional (3D) kinematics and kinetics in ACLD knees with and without MMPHT (ACLD + MMPHT, ACLDs) during level walking. Fifteen patients with isolated unilateral ACLD, ten with unilateral ACLD + MMPHT, and twenty-two healthy controls underwent gait testing between January 2014 and December 2016. Participant characteristics, as well as gait parameters, were compared among control, ACLDs and ACLD + MMPHT knees. Compared to the healthy controls, the ACLD knees with and without MMPHT showed significant extension deficiency at maximum extension (flexion: ACLDs: 7.83 ± 4.3°, ACLD + MMPHT: 11.09 ± 7.8°, control: 3.12 ± 4.6°, p = 0.005) and lower extension moments during terminal stance phase of gait. Compared with the healthy controls, significantly increased external tibial rotation during pre-swing phase and lower rotation moments at terminal stance phase were observed in the ACLD + MMPHT knees, but not in the ACLDs knees. No significant differences in gait parameters were observed between ACLDs and ACLD + MMPHT knees during stance phase of walking. The ACLD knees with medial meniscus posterior horn tear exhibited extension deficiency, increased external tibial rotation, lower extension and internal rotation moments during the terminal stance phase compared to healthy control knees, presenting a combination of “stiffening gait” and “pivot shift gait” pattern. The ACLDs knees only presented extension deficiency and lower extension moments compared with healthy control knees, presenting a “stiffening gait”. Medial meniscus posterior horn tear did not significantly affect gait patterns during stance of walking in ACLD knees.