Do Standard Surgical Guides Produce Accurate and Precise Femoral Bone Resections During Total Knee Arthroplasty?

Purpose: Accurate alignment and balanced flexion and extension gaps are critical elements in achieving a successful outcome following total knee arthroplasty (TKA). The ability to make accurate and precise bone cuts is essential in the creation of balanced gaps. We sought to determine if one type of modern-day standard surgical instrument using an intramedullary rod and posterior referencing produces accurate and precise distal and posterior femoral bone resections.

Materials And Methods: Seventy-five consecutive patients undergoing TKA were divided into three groups, with 25 patients in each group receiving one of three implant designs: 25 Stryker Triathlon® CR (Stryker, Mahwah, NJ), 25 Zimmer NexGen® Flex CR (Zimmer, Warsaw, IN), and 25 StelKast Proven Gen-FlexTM CR (StelKast, Pittsburgh, PA). Flexion-extension gap matching was determined using only the medial flexion and extension gaps. Accuracy was determined by comparing actual resection thickness to desired resection thickness. "Optimal" accuracy was considered to be within 1.0mm of desired, and "near-optimal" accuracy was considered to be within 2.0mm of the desired resection thickness. Precision was determined by the variability of resection thicknesses within each system.

Results: Data demonstrated a lack of accuracy and precision across all three tested systems, with each system resulting in certain unique tendencies. Only one out of 75 cases resulted in optimal resection accuracy with all three cuts (Zimmer). When lowering the threshold to include both optimal and near-optimal (within 2 mm of error) with all three cuts, only one third of Stryker and Zimmer cases and two thirds of StelKast cases achieved this threshold, representing 44% of cases (33/75).

Conclusions: Improvements in instrumentation to increase accuracy and precision may be warranted. Errors in fixation may be due to the instrumentation itself, and altering instrumentation to include less modularity, provide more stable fixation, and more reliably seal the implant on the femur may be of benefit.