Summary

The next generation knee system has both less overhang and underhang with its standard size, more likely due to surgical technique improvements, rather than component sizing modifications.

Abstract

Introduction

In spite of gender marketing, little evidence supports that gender-based changes to the femoral component lead to better sizing or clinical outcomes. The purpose of this study is to prospectively evaluate whether a single company's gender-based femoral component or their updated version with a modified surgical technique leads to better femoral component fit.

Methods

Between 2009 and 2018, 2508 consecutive primary total knee replacements in females were performed by a single surgeon. One knee system had gender-based femoral components available. The second knee system, the manufacturer's updated version, had standard and narrow sizes, but importantly a modified surgical technique for component placement.

Results

When the first knee system was used, over 49% of the time the gender component was selected for better fit (894/1820). Component overhang was less with the gender component compared to its standard counterpart (1% vs 18%, p< 0.001). However, occurrence of underhang was also greater (67% vs 30% (p< 0.02)). With the newer knee system, the narrower option was selected only 9.3% of the time (64/688). Overhang was rare with both the standard and narrow components (1% and 2%, p>0.4). Underhang was also less with use of either component (8% vs 12%, p>0.3).

Discussion

While a gender-specific component may provide more sizing options to provide better femoral fit options compared to its own standard size counterpart, it may only be addressing its own system's sizing limitations. The next generation knee system has both less overhang and underhang with its standard size, more likely due to surgical technique improvements, rather than component sizing modifications. Furthermore, the need for a narrower component option appears to be less since the newer design was used only one-fifth of the frequency that the gender component
was used relative to its standard option.