Summary

This study showed that a greater reduction in the anterior condyle (ACH) of the distal femur and preoperative knee flexion were independently associated with improved flexion after TKA and the change in ACH did not worsen any clinical outcomes (2011 Knee Society Score); as a mechanism, changes in patellofemoral contact force was demonstrated using computer simulation.

Abstract

Introduction

The shape of the anterior condyle of the distal femur varies widely in patients with knee osteoarthritis. However, the effect of a change in the anterior condylar height (ACH) on knee function and clinical outcome after total knee arthroplasty (TKA) is unknown. The purpose of this study was to evaluate the effect of ACH change on (1) postoperative knee flexion angle, (2) patient reported outcome measures (PROMs), and (3) patellofemoral contact force using computer simulation.

Methods

The study included 101 knees undergoing cruciate-substituting TKA. Using pre- and postoperative computed tomography (CT), the height of the medial anterior condyle, trochlea sulcus, or lateral anterior condyle from the anterior cortex of the distal femur was defined as medial, central, or lateral ACH, respectively. The Pearson correlation coefficient between the change in ACH and knee flexion was calculated. The determinant of the change in flexion was evaluated using a multivariable linear regression model, with ACH and other anatomic and patient characteristics included as independent predictors. The association between ACH and the 2011 Knee Society Score (KSS) was assessed using simple linear regression. Finally, using the cases with the 3 highest and 3 lowest preoperative medial ACH, computer simulation analysis was performed to detect the change in patellofemoral contact force.

Results

A postoperative reduction in ACH correlated with increased flexion at 1 year (decrease in medial ACH: R = 0.58, p < 0.001; central ACH: R = 0.51, p < 0.001; lateral ACH: R = 0.48, p < 0.001). In the multivariable linear regression model (R2 = 0.45), a reduction in medial ACH (ß = 1.66, p < 0.001), and preoperative flexion (ß = -0.31, p < 0.001) were independently associated with increased flexion. ACH decrease was associated with improvement in advanced activities (medial: R2 = 0.06, p = 0.027, lateral: R2 = 0.08, p = 0.007) in 2011 KSS, and was not correlated with symptoms (medial: R2 = 0.02, p = 0.228, lateral: R2 = 0.00, p = 0.564). In computer simulation, the 3 cases with reduced medial ACH (-11.6 mm, -9.0 mm, -8.2 mm, respectively) showed decreased patellofemoral contact force (-42 N, -642 N, -101 N, respectively), whereas the 3 cases with increased medial ACH (+11.1 mm, +8.8 mm, +8.4 mm, respectively) showed increased patellofemoral contact force (+497 N, +288 N, +326 N, respectively). The increase of flexion strongly correlated with the decrease of patellofemoral contact force (R = 0.96, p = 0.002).

Conclusions

This study examined the clinical significance of a change in ACH, in which a greater reduction in ACH was associated with improved flexion after TKA. The reduction of ACH was associated with improvement in activity, and did not worsen clinical symptoms. As a mechanism, a change in patellofemoral contact force was demonstrated according to a change in ACH on computer simulation. Although greater reduction of ACH is related to increased postoperative flexion, an increase in postoperative ACH may be a risk factor for flexion loss.