Elsevier

The Knee

Volume 12, Issue 1, January 2005, Pages 9-12
The Knee

Retropatellar contact characteristics before and after total knee arthroplasty

https://doi.org/10.1016/S0968-0160(02)00045-5Get rights and content

Abstract

Purpose: Qualitative analysis of the retropatellar contact characteristics after total knee arthroplasty. Material and Methods: Six cadaveric knees were investigated before and after implantation of a Genesis I knee prosthesis without and with patellar resurfacing in different positions. Joint contact characteristics were evaluated with Fuji Prescale film type ‘Super Low’ and analyzed qualitatively in nine quadrants. The pressure was determined from a 5-s loading duration in four different knee positions between 45° and 120° of flexion. The femoral component of the prosthesis was implanted in neutral as well as in internal and external rotation. A quadriceps force of 280 N with either a predominant medial or lateral pulling direction was applied. Results: Without prosthesis the largest contact area is between 60° and 90° of flexion. A lateral muscle force direction as well as an external rotation increased the frequency of loading in the medial quadrants. After implantation of the prosthesis the central and superior quadrants were predominantly contacted irrespective of the flexion angle. No marked differences between the flexion angles were found. Implantation of the patellar resurfacing led to contact in the three central quadrants. Conclusion: Implantation of the endoprosthesis leads to increased contact in slight and extreme flexion angles. Especially the central areas are increasingly loaded. No predominant influence of the rotation of the femoral component or the direction of the muscle pull was found. An improved distribution of the contact area could not be demonstrated after patellar resurfacing.

Introduction

A general problem in total knee arthroplasty, should the patella surface be replaced or not, has been discussed for quite some time. Even though the causes for patellar problems are not conclusively determined, high retropatellar pressures in an unfavorable position appear to be a main contributory factor [2], [4], [5]. Potential solutions are an external rotation of the femoral component, an implantation of a patellar replacement in different positions and a lateral release of the patella in combination with strengthening exercises of the vastus medialis muscle.

Lee et al. [11] investigated the influence of femoral rotation with Fuji film and demonstrated that an internal rotation of the femur caused an increased lateral contact stress of the patella, an external rotation increased the medial contact stress. Rhoads et al. [13] found a medialization of the patella between 20 and 80° of knee flexion with a 10° internal rotation of the femoral component. In flexion angles beyond 80° this effect vanished. Anouchi et al. [1] found comparable values for 5° of rotation. McLain et al. [12] demonstrated that patellar resurfacing reduced the contact area. Hsu et al. [6] revealed that patellar designs with improved conformity increased the contact area. Hsu et al. [7] and Jiang et al. [9] showed that the contact area decreased between 15 and 90° in comparison to a healthy knee joint.

Wackerhagen et al. [16] evaluated the influence of a splitting of the retinaculum and saw a significant decrease of the local force in the lateral and proximal quadrant that depended on the flexion angle, the direction of muscle force and the prosthetic design. A good congruence between patella and femur resulted in a marked reduction of joint contact forces. Takahashi et al. [15] demonstrated with Fuji film that a lateral retinaculum splitting does not cause major changes. Hsu et al. [8] revealed that a reduction of the contact force with retinaculum splitting could only be achieved in more extreme flexion angles. Between 30 and 75° they even found an increased contact force. The contact area moved to the lateral and proximal part of the patella.

The review of literature did not show an investigation which compared the situation with and without prosthesis or an evaluation of the effects of femoral rotation, muscle force direction and placement of the patellar resurfacing in a single prosthetic design. The present investigation will try to fill this gap.

Section snippets

Material and methods

Six cadaveric specimens with a mean age of 71.6 years (range 60–86 years) were investigated before and after implantation of a knee prosthesis. The cadavers were embalmed in a modified Thiel fixation that largely preserves bone and soft tissue characteristics and does not cause functional deficits.

A prosthesis model Genesis I (Smith & Nephew, Schenefeld, Germany) and the ‘onlay’ version of the patellar resurfacing in size ‘small’ and ‘medium’ were used. We used the size ‘large’ cemented

Results

The results before prosthesis implantation (Fig. 2) demonstrated signs of contact less frequently in 45° and 120° of flexion as compared to 60° and 90°. In the inferior quadrants imprints were rarely seen. A comparison of the muscle pull directions indicates that with a laterally dominant muscle force the superior medial and central medial quadrant often had contact. With a medial force the lateral central quadrant had the most frequent contact. An external rotation of the femur caused large

Discussion

Contrary to the situation without prosthesis, contact was measured also at 45° and 120° of flexion after implantation of the prosthesis. In accordance with Benjamin et al. [3] no marked difference between various flexion angles was found. Generally, a slight proximal shift of the contact areas was found after implantation. With respect to the goal to achieve a centralized patellar guidance the present results appear favorable indicating a most frequent contact in the central middle and superior

References (16)

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