Upsizing the femoral component increases patellofemoral contact force in total knee replacement

Abstract

In posterior stabilised total knee replacement (TKR) a larger femoral component is sometimes selected to manage the increased flexion gap caused by resection of the posterior cruciate ligament. However, concerns remain regarding the adverse effect of the increased anteroposterior dimensions of the femoral component on the patellofemoral (PF) joint. Meanwhile, the gender-specific femoral component has a narrower and thinner anterior flange and is expected to reduce the PF contact force. PF contact forces were measured at 90°, 120°, 130° and 140° of flexion using the NexGen Legacy Posterior Stabilized (LPS)-Flex Fixed Bearing Knee system using Standard, Upsized and Gender femoral components during TKR. Increasing the size of the femoral component significantly increased mean PF forces at 120°, 130° and 140° of flexion (p = 0.005, p < 0.001 and p < 0.001, respectively). No difference was found in contact force between the Gender and the Standard components. Among the patients who had overhang of the Standard component, mean contact forces with the Gender component were slightly lower than those of the Standard component, but no statistical difference was found at 90°, 120°, 130° or 140° of flexion (p = 0.689, 0.615, 0.253 and 0.248, respectively). Upsized femoral components would increase PF forces in deep knee flexion. Gender-specific implants would not reduce PF forces.

Sagittal placement of the femoral component in total knee arthroplasty predicts knee flexion contracture at one-year follow-up

“…Studies have shown that using a larger femoral component could increase the patellofemoral contact force in TKA and possibly restrict knee range of motion including introducing a flexion contracture [27,28]. However, the results of this study do not show any correlation between implant size and flexion contracture 12 months postoperatively.…”

Anterior knee pain after a total knee arthroplasty: What can cause this pain?

“…The PFJ loading is influenced both by changes in the joint line height and by selecting a femoral component that is too large [39,53] . Tibia-femoral instability, due to inappropriate placement or other causes, leads to increased pressure on the PFJ, especially in flexion [54] .…”

Anterior knee pain following primary total knee arthroplasty

“…It has been demonstrated that women, on average, have smaller distal femurs as well as clinically significant variation in distal femur morphology compared to their male counterparts. One morphological variation in particular is a much larger aspect ratio (anterior/posterior to medial/lateral measurement) which places this patient population at a higher risk for medial/lateral femoral component overhang [35,[37][38][39][40][41] . Different body morphologic types have a significant correlation with distal femoral morphology.…”

“…Previous studies have considered various modifications of the anterior flange of the femoral component in order to reduce anterior impingement and pain following TKA. A femoral component with a wider and thicker anterior flange can lead to stuffing of the patello-femoral joint leading to increased patellar ligament tension and thus increased patellofemoral contact forces [35] . This will eventually cause accelerated polyethylene wear and an overall higher risk of patellar complications [35] .…”