RESTORATION OF TIBIAL SLOPE IN PRIMARY TOTAL KNEE ARTHROPLASTY: RELATIONSHIP WITH POSTOPERATIVE OUTCOMES

The posterior slope of the proximal tibial articular surface is a biomechanically important parameter in native knee kinematics and varies substantially between individuals. The purpose of this study was to investigate whether recreating the native tibial slope during a primary total knee arthroplasty improves post-operative patient function. A single-centre retrospective review was conducted of patients undergoing primary total knee arthroplasty between 1998 and 2022. A prospectively collected database for arthroplasty patients at our institution captures all patients undergoing hip and knee arthroplasty secondary to osteoarthritis, and includes patient demographics, implant characteristics, and Knee Society Scores (KSS) and Oxford Knee Scores (OKS). Scores are collected within three months prior to surgery, six weeks post-surgery, and either six months or one year post-surgery. Pre- and post-operative lateral knee radiographs were reviewed using a picture archiving and communication system. Tibial slope was measured from each radiograph using a previously validated method. A delta slope was calculated for each patient as the difference in measured tibial slope from pre- to post-surgery. Two trainees worked independently to perform the measurements, with thirty radiographs reviewed in duplicate. Inter-rater reliability was determined through calculation of the inter-rater correlation coefficient (ICC). Patients were classified as having a decrease in tibial slope (Group 1, Δ slope 3). A one-way analysis of variance (ANOVA) and Tukey's HSD post hoc test were conducted to determine if patient functional outcome scores differed between groups. Analysis was performed using custom Python scripts and calculated using SciPy, Pinguin, and statistical modules. A value of P < 0.05 was considered statistically significant. Of 9569 patients who underwent either a posterior-cruciate retaining (CR) or posterior-stabilized (PS) primary total knee arthroplasty for a diagnosis of osteoarthritis captured in the database between 1998 and 2022, 612 were eligible for inclusion in the current study. The present study included 231 males (38%) and 381 females (62%) with a mean age at surgery of 67 years (SD 8.2) and mean BMI 30.0 (12.4). The ICC for preoperative and postoperative slope measurements were 0.92 and 0.93, respectively, indicating excellent inter-rater reliability. Tibial slope was decreased in 279 (46%, Group 1), re-created in 259 (41%, Group 2), and increased in 82 (13%, Group 3) patients. Both KSS and OKS improved from pre- to post-surgery. Patients in Group 2 demonstrated a 4.4-point higher mean KSS at 6-weeks post TKA than patients in Group 1 (p=0.01, 95% CI: 0.94-7.89). Knee Society Scores at other time points and OKS at all time points did not differ between groups. In this large retrospective review of patients undergoing primary total knee arthroplasty, recreation of native pre-operative tibial slope was not associated with a clinically important difference in patient functional outcome scores.