2025 ISAKOS Congress in Munich, Germany

2025 ISAKOS Biennial Congress Paper


The Anti-Maquet Effect: High Grade Trochlear Dysplasia Increases Joint Pressure and Decreases the Knee Extension Torque and Tibial Tubercle Anteriorisation Does not Correct These Effects: Biomechanical Study in Vitro

Michael J. Dan, Mbbs, PhD, MSc(res), FRACS(oath), Merewether AUSTRALIA
Maria Moralidou, PhD, London UNITED KINGDOM
Andrew A. Amis, FREng, DSc, PhD, London UNITED KINGDOM
isabelle kuder, PhD, London UNITED KINGDOM
Richard Can Arkel, PhD, London UNITED KINGDOM
Nicolas Cance, MD, Lyon, Rhône-Alpes FRANCE
David H. Dejour, MD, Lyon FRANCE

Imperial College of London, London, London, UNITED KINGDOM

FDA Status Not Applicable

Summary

An anteriorised trochlea, which represented high grade trochlear dysplasia (Dejour grades B&D) caused elevated PFJ pressures and led to decreased mid-range knee extension torque leading theoretically to pain, cartilage damage and further patellofemoral arthritis, these effects were not offset by anteriorising the tibial tubercle, meaning this should be addressed at the trochlea.

Abstract

Introduction

High grade trochlear dysplasia involves changes in both the axial and sagittal planes, so that it is both flattened (or convex) transversely and more anteriorised, resulting in a lateral dislocation pattern. However the isolated influence of an anteriorised trochlea on patellofemoral joint reaction forces has not been investigated biomechanically, but it is postulated that it will increase patellofemoral joint reaction forces. In PFJ arthroplasty success is influenced by the ability to reduce the trochlear offset with respect to the anterior femoral cortex. However, recessing the trochlea may detrimentally alter extensor mechanism torque by decreasing the moment arm. Therefore, the sagittal position of the trochlea warrants further biomechanical analysis. Clinically there is increasing literature highlighting that differences in the position of the trochlea relative to the tibial tubercle in the sagittal plane are associated with PF instability, pain and cartilage damage. The aim of this biomechanical study was to document the changes to the PFJ mechanics caused by changes in the sagittal plane at the trochlea, reflecting the trochlear anteriorisation seen in high grade dysplasia, Dejour grades B and D. It was hypothesised that an anteriorised trochlea would increase PFJ contact pressure and alter the PFJ kinematics and Knee Extension Torque (KET). It was also hypothesised that the increased PFJ contact pressure could be reduced by anteriorising the tibial tubercle.

Methods

Seven fresh-frozen Caucasian cadaveric knees (mean age: 64 years, range 54-76, 4M:3F, 4L:3R) with no history of knee surgery or disease were sourced from an accredited tissue bank. This work measured changes in the PFJ mechanics – patellar tracking, joint contact pressure and knee extension torque - caused by simulated bony procedures in-vitro: anteriorisation/recession of the anterior trochlea and anteriorisation of the tibial tubercle, both isolated and combined.This allowed for 4 conditions to be tested
1) Native state;
2) Anteriorised trochlea;
3) Anteriorised trochlea plus anteriorised tibial tubercle;
4) Anteriorised tibial tubercle.

Results

Anteriorisation of the trochlea caused a significant increase of the average PFJ contact pressure above that of the native knee at 0º and 15º knee flexion (p=0.024; p=0.029). Conversely, anteriorisation of the tibial tubercle had a negligible effect on the average contact pressure.
An anteriorised trochlea resulted in less KET compared to the native state at 40º and 50º of knee flexion, (p=0.001, p=0.009). Adding an anteriorisation of the tibial tubercle to the knee with an anteriorised trochlea resulted in a small but statistically significant increase of mean KET compared to the anteriorised trochlea state (p=0.027)
The overall picture is that the kinematic changes were almost entirely caused by trochlear anteriorisation. Tibial tubercle anteriorisation, either in isolation or combined with trochlear anteriorisation, had only small effects (all <2mm or <2o) across the arc of knee flexion.

Conclusion

An anteriorised trochlea which represented high grade trochlear dysplasia (Dejour grades B&D) caused elevated PFJ pressures and led to decreased mid-range knee extension torque leading theoretically to pain, cartilage damage and further patellofemoral arthritis. These effects were not offset by anteriorising the tibial tubercle. This suggests that high grade trochlear dysplasia is best addressed biomechanically at the trochlea with a trochleoplasty, and not the tibial tubercle.