The aim of this study was to determine whether primary repair for intraoperative injury of the medial collateral ligament (MCL) can achieve satisfactory clinical results when compared to the clinical results of patients with no MCL injury. Simultaneously, we sought to determine the differences between 2 methods of primary repair (anchor suture and staple) in terms of their clinical outcomes.In our institute, 3897 total-knee arthroplasties (TKAs) were performed between 2003 and 2014. Sixty-five patients who suffered an MCL injury during the TKA procedure and in whom the injury was repaired with a suture anchor or staple (suture anchor: 36 vs staple: 29) were studied. A matched group of 65 patients without an MCL injury was selected to serve as the control group. Subjective feelings of instability and functional outcomes were assessed using the knee society (KS) score and the Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC). Objective stability was evaluated by the measurement of opening angles in extension and at 30° of knee flexion on valgus stress radiographs. The clinical outcomes and stability results were compared between the suture anchor and staple methods.The KS and WOMAC scores in patients who received primary repair of MCL injury during TKA improved from 50.6 ± 13.1 to 87.3 ± 7.3 (P < .001) and 65.9 ± 14.4 to 17.7 ± 6.6 (P < .001), respectively. However, there were no statistically significant differences in the KS (P = .84) and WOMAC (P = .71) scores when comparing the group that received primary repair to the control group. Radiographic stability also showed no differences between the repair and control groups in extension and at 30° of flexion (P = .48 and P = .11, respectively). In the subgroups, there were no significant differences between the suture anchor and staple repair methods in terms of stability and clinical outcomes.Primary repair of an MCL injury during TKA may have clinical outcomes comparable to that in the no MCL injury group. Both staple and suture anchor repair methods could provide excellent clinical and stability outcomes in these types of cases, although a further cohort study is required to validate our results.