Summary

Our current findings highlight that implantation with both computer navigated guides and traditional mechanical techniques will allow clinicians to achieve tibial and femoral biomechanical alignment close to standard targets for patients; If clinically desirable, computer navigated guides can achieve significantly closer total mean tibial varus angles and tibial slope angles to standard goals.

Abstract

Introduction

With increasing rates of total knee arthroplasties (TKA), it is important to evaluate the impact of the implantation method. The purpose of this study was to compare the ability of computer navigated guides and traditional mechanical instrumentation in achieving the intraoperative goals for knee biomechanical alignment.

Methods

We retrospectively analyzed the preoperative and postoperative (14-day follow-up) radiographs of 469 TKA cases (Cohort: 265 females, 204 males) conducted by the senior surgeon (MS) between November 2019 and March 2021 at our multi-physician orthopaedic private practice in Southwest, Ohio. 7 Stryker implant cases were excluded before analysis. The tibial axis, tibial slope, and femoral valgus angles were measured from the radiographs using Medstrat Joints software. The computer navigated systems (369 cases; Conformis, DePuy, Smith&Nephew) and mechanical instrumentation (100 cases) were evaluated for how closely the implant achieved our standard targets of 0° tibial varus, implant specific tibial slope, and 5° femoral valgus. T-tests were conducted to determine statistical significance (p<0.05). This study obtained informed consent from participants and was IRB approved (WIRB study: 20120963).

Results

SECTION: Computer navigated guides achieved a total mean tibial varus of 2.07° from the standard goal (Conformis: 2.41°; DePuy: 1.90°; Smith&Nephew: 1.85°), which was significantly closer than mechanical instrumentation (2.49°; p<0.05). For implant specific tibial slope targets, computer navigated guides (Total: 0.83°; Conformis: 0.74°; DePuy: 0.87°; Smith&Nephew: 0.88°) significantly cut closer than mechanical implantation (1.41°; p<0.05). Mechanical instrumentation achieved a total mean femoral valgus of 0.03° from the target, which was significantly closer than the total mean for computer navigated guides (Total: 0.67°; Conformis:0.02°; DePuy:1.56°; Smith&Nephew:1.6°).

Discussion

Regardless of manufacturer and instrumentation technique, most implants achieved tibial and femoral alignments close to our standard targets. Variations in postoperative alignment between implants may be the result of differing implant engineering. With respect to alignment goals, computer navigated guides achieved significantly closer total mean tibial varus and tibial slope angles, but significantly farther total mean femoral valgus angles compared to mechanical instrumentation.