Patellofemoral instability in trochleodysplastic knee joints and the quantitative influence of simulated trochleoplasty – A finite element simulation

Abstract

Background: Patellofemoral instability is a debilitating condition mainly affecting young patients and has been correlated with trochlear dysplasia. It can occur when the patella is insufficiently guided through its range of motion. Currently, there is no literature describing patellofemoral stability in trochleodysplastic knees and the effect of isolated trochleoplasty on patellofemoral stability. Methods: The effect of isolated trochleoplasty in trochleodysplastic knees of patients with symptomatic patellofemoral instability was investigated using a quasi-static finite element model. MRI data of five healthy knees were segmented, meshed and a finite element analysis was performed in order to validate the model. A second validation was performed by comparing simulated patellofemoral kinematics to in-vivo values obtained from upright-weight bearing CT scans. Subsequently, five trochleodysplastic knees were modelled before and after simulated trochleoplasty. The force necessary to dislocate the patella by 10 mm and to fully dislocate the patella was calculated in various knee flexion angles between 0 and 45 •. Findings: The developed models successfully predicted outcome values within the range of reference values from literature. Lateral stability was significantly lower in trochleodysplastic knees compared to healthy knees. Trochleoplasty was determined to significantly increase the force necessary to dislocate the patella in trochleodysplastic knees to comparable values as in healthy knees. Interpretation: This is the first study to investigate lateral patellofemoral stability in patients with symptomatic patellofemoral instability and dysplasia of the trochlear groove. We confirm that patellofemoral stability is significantly lower in trochleodysplastic knees than in healthy knees. Trochleoplasty increases patellofemoral stability to levels similar to healthy.

The quantitative influence of current treatment options on patellofemoral stability in patients with trochlear dysplasia and symptomatic patellofemoral instability - a finite element simulation

“…The combination of MPFL reconstruction and trochleoplasty further increased the force necessary to lateralize the patella by 10 mm and to fully dislocate the patella especially from 20 • -45 • . At 45 • of flexion the force necessary to lateralize the patella was significantly greater than for isolated MPFL reconstruction as well isolated trochleoplasty (P = 0.04/ 0.02) (Kaiser et al, 2021). The force necessary to lateralize the patella by 10 mm and fully dislocate the patella over all investigated flexion angles was significantly greater compared to trochleodysplastic knees (P = 0.01), healthy knees (P = 0.01) as well as isolated trochleoplasty (P = 0.01-0.02).…”

“…The FE model used for this study has been successfully validated in a previous study (Kaiser et al, 2021). MR image data of five healthy adult knee joints were selected to have a comparable cohort to the six fresh frozen cadaver knees used in the literature (Amis et al, 2008;Farahmand et al, 2004).…”

“…The quadriceps muscle (red), MPFL (green), MPML (yellow), lateral retinaculum (blue) and patellar tendon (orange) are visualized. (Kaiser et al, 2021). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)…”

“…MPFL reconstruction as described in chapter 3.4 was performed in combination with trochleoplasty as described in a previous study (Kaiser et al, 2021). The force necessary to lateralize the patella 10 mm and the peak force to fully dislocate the patella were calculated.…”

“…The goal of this current study is to exploit a range of previously validated FE models (Kaiser et al, 2021) to investigate the quantitative effect of VMO strengthening, MPFL reconstruction and the combination of MPFL reconstruction and trochleoplasty on lateral patellofemoral stability in different flexion angles.…”