To retrospectively analyse the correlations between sagittal position of the femoral prothesis and patellofemoral pain as well as joint function after total knee arthroplasty(TKA).

A total of 99 patients with end-stage knee osteoarthritis who failed to respond to conservative treatment and underwent total knee arthroplasty in the Sixth Affiliated Hospital of Guangzhou Medical University were enrolled. Patients with infectious, inflammatory arthritis and spinal, hip or ankle joint lesions were excluded, and the follow-up time was one year after surgery. In this study, patient-reported outcome measures (PROMs) included Knee Society score (KSS), the Western Ontario and McMaster (WOMAC), forgotten knee score (FKS)and patient satisfaction scores, clinician-reported outcome measures (CROMs), including range of motion (ROM), anterior condylar offset (ACO) and the angle between the flange of the femoral component (FC) and the distal femur anterior cortex line (α angle). According to the α angle, the patients were divided into two groups, the FC flexion group (α angle>0°) and the FC extension group (α angle<0°). The correlations between PROMs and CROMS were analyzed by t test and secondary regression.

Postoperative PROMs in the FC flexion group were better than those in the FC extension group (KSS joint score t=2.764, functional score t=2.215, FKS t=4.012, satisfaction scores t=2.492, P<0.05), while the incidence of postoperative anterior knee pain in the FC flexion group (10.0%) was significantly lower than that in the FC extension group (28.6%)(χ²=5.504, P=0.019), secondary regression analysis indicated that there was a convex upward correlation between the α angle and the postoperative ACO ratio. The α angle at the vertex was 2.411°, corresponding to the ACO ratio was 20.5% (P=0.006).

Compared with patients with FC extension, patients with FC flexion have a lower incidence of anterior knee pain and better recovery of joint function, which may be associated with the reduction of postoperative ACO having less effect on the sagittal plane position of FC.