Pain and Patellofemoral Functionality in Total Knee Arthroplasty

A Comparative Cohort Study of Two Prosthesis Designs

Luis Miguel Cely, MD; Cesar Hernando Rocha, MD

Disclosures

Curr Orthop Pract. 2021;32(1):53-57. 

In This Article

Abstract and Introduction

Abstract

Background: Total knee arthroplasty designs have changed from the original design, with the goal of becoming as close to normal knee biomechanics and anatomy as possible. Since 2009, Optetrak® Logic incorporated modifications to the previous product Optetrak® PS (Exactech, Gainsville, FL), with a change of the anterior surface of the tibial post of the polyethylene insert and the surface that articulates with the femoral component box. Also, the sagittal geometry of the femoral trochlea was changed, which decreased rates of anterior knee pain and "patellar clunk." The purpose of this study was to determine if there are differences in terms of pain and patellofemoral functionality between Optetrak PS and Optetrak Logic.

Methods: A prospective follow-up was performed comparing the results of the Kujala pain and patellofemoral functionality scale. Clinical and functional follow-up was performed in 132 knees (66 from the Optetrak Logic group and 66 from the Optetrak PS group) that underwent total knee arthroplasty from January 2015 to August 2019.

Results: Global results of the functional tests were: Oxford postoperative 50; Knee Society Score postoperative 85; Kujala postoperative 76. In comparing the two groups the Kujala score for Optetrak PS was 71 and the Kujala score for Optetrak Logic was 81.

Conclusions: Patellofemoral knee pain and functionality before and after total knee arthroplasty must be analyzed with functional scales. The new prosthetic designs are gentler to the patellofemoral joint, and this has been verified by objective analysis with functional scales such as the Kujala scale.

Level of Evidence: Level III.

Introduction

The Optetrak® PS prosthesis (Exactech, Inc., Gainesville, FL) was designed in 1995 as an evolution of the Insall-Burstein Posterior Stabilized knee system (Zimmer, Warsaw, IN). The congruence between the tibial and femoral components was modified to reduce stress at the polyethylene post,[1] the trochlea of the femoral component was deepened and lengthened to improve tracking and reduce patellar clunk. The survival rate of this implant has been excellent, from 94% to 98% in 10 yr (Figure 1).[2,3]

Figure 1.

Anteroposterior view (A) and lateral view (B) of the Optetrack® PS knee prosthesis.

In 2009, Optetrak® Logic (Exactech, Inc., Gainesville, FL) appeared on the market, incorporating modifications to the Optetrak PS. The geometry of the intercondylar box of the femoral component was modified to preserve more bone by changing the angle of the box cut and rounding its corners. In turn, the maximum flexion angle increased from 120 degrees to 145 degrees.[4–13]

In addition, the articulation between the anterior face of the polyethylene post and the corresponding articular surface of the femoral component was redesigned to decrease the contact stress of the polyethylene post at full extension. The anterior face of the tibial post changed from a flat surface to a saddle shape. A coupled saddle joint was incorporated into the anterior case of the femoral component.

Joint congruence and patellar tracking were unchanged; however, the trochlear profile of the femoral component is higher in the Optetrak PS than the Optetrak Logic; the sagittal geometry of the trochlea in the Optetrak Logic is more compatible with the patella because it has a flattened anterior rim and the patella is hemispherical, which provides greater patellofemoral congruence (Figure 2).[3,14–21]

Figure 2.

Anteroposterior view (A) and lateral view (B) of the Optetrack® Logic knee prosthesis.

We hypothesized that in patients with the Optetrak Logic, the incidence of patellar clunk would be reduced, and they would have less pain and better patellofemoral functionality than patients who had the Optetrak PS.

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