Clinical Report: Impact of Mediolateral Implant Oversizing on TKA Outcomes

Overview

This study evaluated the effects of femoral and tibial component oversizing in total knee arthroplasty (TKA) on postoperative pain, function, and knee flexion. Analysis of 114 knees showed that implant oversizing relative to bone contours is associated with worse clinical outcomes at one year post-surgery.

Background

Anatomical variability in femoral and tibial dimensions, especially between sexes, has led manufacturers to expand TKA implant size ranges and introduce narrower femoral components to improve fit and reduce overhang. Oversizing implants may increase capsular and ligamentous tension, potentially compromising clinical results. Prior studies have linked femoral component overhang with residual pain, but the benefits of narrower implants remain debated. This study aimed to quantify the relationship between mediolateral implant sizing and clinical outcomes including pain, function, and range of motion.

Data Highlights

Key Findings

• Implant oversizing was defined as any mediolateral dimension of the prosthesis exceeding the corresponding bone measurement.
• Oversizing was assessed at three femoral zones and one tibial zone based on CT scans aligned with surgical bone cuts.
• Patients with implant oversizing showed increased residual knee pain and reduced function as measured by KOOS scores at 1 year.
• Maximum passive flexion was negatively impacted in cases of component oversizing, indicating reduced joint range of motion.
• There appears to be a threshold of oversizing beyond which clinical outcomes deteriorate significantly.
• Use of narrower femoral implants does not always guarantee improved outcomes, highlighting the complexity of implant sizing decisions.

Clinical Implications

Careful preoperative assessment of femoral and tibial bone dimensions using CT imaging can guide optimal implant sizing to avoid oversizing. Avoiding mediolateral implant overhang may reduce postoperative pain and improve functional outcomes and knee flexion after TKA. Surgeons should consider individual anatomical variability rather than relying solely on standard implant sizes or narrower designs.

Conclusion

Mediolateral implant oversizing in TKA is associated with worse pain, function, and flexion outcomes at one year postoperatively. Tailoring implant size to patient-specific bone anatomy is critical to optimize clinical results.

References

1. Mahoney et al. 2011 -- Femoral component overhang increases residual pain after TKA
2. Study Authors 2024 -- The Impact of Mediolateral Implant Oversizing on Pain, Functionality, and Flexion Post-TKA