ObjectiveTo investigate effect of posterior oblique ligament (POL) repair on the rotational stability of the knee joint for the medial collateral ligament (MCL) combined with anterior cruciate ligament (ACL) ruptures.MethodsThe clinical data of 50 patients (50 knees) with grade-3 MCL-ACL combined injuries who met the selection criteria between January 2013 and December 2015 were retrospectively analyzed. All ACLs were reconstructed with autogenous tendon and the superficial and deep layers of MCLs were sutured; then, POLs were also sutured in 25 patients of repair group and only received conservation treatment postoperatively in 25 patients of conservation group. There was no significant difference in gender, age, disease duration, and preoperative KT-1000 measuring, medial joint space opening, International Knee Documentation Committee (IKDC) score, visual analogue scale (VAS) score, and knee range of motion between the two groups (P>0.05).ResultsAll incisions of the two groups healed by first intention, no surgical related complications occurred. All patients were followed up, with follow-up time of 28-56 months (mean, 38.1 months) in repair group and 26-55 months (mean, 29.1 months) in conservation group. At last follow-up, the IKDC score, VAS score, KT-1000 measuring, medial joint space opening, and knee range of motion significantly improved in the two groups when compared with preoperative ones (P<0.05); but there was no significant difference between the two groups (P>0.05). The Slocum test showed that there was no instability of the anterior medial rotation in the two groups.ConclusionThe POL repair can’t obtain more medial stability after ACL reconstruction and MCL repair (superficial and deep layers) for patients who have MCL-ACL combined injuries.