# Contact stress in dysplastic hips before and after periacetabular osteotomy

Ariane Lavoie-Hudon, Victor Grenier, Xavier Robert-Lachaîne, Ebrétchè Renaud V.I. Amoakon, Étienne L. Belzile, Philippe Corbeil

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Ariane Lavoie-Hudon, Victor Grenier, Xavier Robert-Lachaîne, Ebrétchè Renaud V.I. Amoakon, Étienne L. Belzile, et al.. Contact stress in dysplastic hips before and after periacetabular osteotomy. Multidisciplinary Biomechanics Journal, 2025, 50th congress of the.., 10.46298/mbj.16155. hal-05191707v2

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# Contact stress in dysplastic hips before and after periacetabular osteotomy

Ariane Lavoie-Hudon<sup>a, b*</sup>, Victor Grenier<sup>c</sup>,

Xavier Robert-Lachaîne<sup>a</sup>, Ebrétchè Renaud V.I. Amoakon<sup>a</sup>,

Étienne L. Belzile<sup>c</sup>, Philippe Corbeil<sup>a, b</sup>

Received date: 06/04/2025

Accepted date: 27/06/2025

Publication date: 27/10/2025

**Keywords:** acetabular dysplasia, functional tasks, gait analysis, squat, discrete element simulation

© 2025 The Authors

Licence CC-BY 4.0

Published by Société de Biomécanique

## 1. Introduction

The acetabulum of patients with dysplasia is shallow, resulting in a reduced contact surface with the femoral head. The acetabular cartilage can become overloaded, causing pain during activities of daily living. Without treatment, these patients would be at high risk of early osteoarthritis (Mavcic et al., 2008). Periacetabular osteotomy (PAO) is a surgical procedure indicated to treat dysplasia when the pathology is detected before cartilage degeneration occurs. Surgery aims to reorient the acetabular fragment in relation to the femoral head, thereby increasing the contact surface between the cartilages and helping to reduce high pressure points. There is limited data exist on the joint contact pressure profiles generated in dysplastic hips and how these profiles change following corrective surgery. A better understanding of the effects of PAO is needed to improve surgical planning and maximise joint longevity. The aim of this study is to analyze the contact mechanics in the dysplastic hip joint during functional tasks such as squatting and walking, before and after PAO.

## 2. Methods

### 2.1 Data collection

CT-derived images were obtained before and after PAO for six participants with acetabular dysplasia (2 ♂ and 4 ♀, 18-43 years). These patients performed squatting and walking tasks in the laboratory before and 10.1 ± 4.6 months after their surgery. Squat depth

was controlled to the height of the tibial plateau, and a comfortable walking speed was selected for each patient. An optoelectronic system (Vicon) recorded three-dimensional displacement of the pelvis and lower limbs during the tasks. Ground reaction forces were measured using force platforms (AMTI).

### 2.2 Data Processing

The CT-scans of the pelvis and femur were segmented, meshed and smoothed. The patient-specific hip joint centers were extracted from these scans using a custom Matlab script, which fit spheres to the femoral heads and calculated their position relative to a reference plane. This plane was defined as orthogonal to the line connecting the femoral heads and passing through the L5 vertebra midpoint. Cartilage surfaces were mathematically generated to cover the femoral head with a uniform thickness of 2mm and the acetabulum lunate with a thickness of 1 to 3mm, based on Nishii's method for dysplastic hips (Nishii, 2004).

From the kinetic and kinematic data collected, joint angles and joint reaction forces were calculated using musculoskeletal models in OpenSim. The models were personalized with each patient's own hip joint centers.

These variables and patient-specific bone geometries were used as input in a discrete element simulation model (Grenier et al., 2025). Measurements of the joint contact area and pressures at each instant of the movement cycle were extracted to characterize

<footnote><sup>a</sup> Groupe de Recherche en Analyse du Mouvement et Ergonomie (GRAME), Département de Kinésiologie, Université Laval, Québec, Canada</footnote>

<footnote><sup>b</sup> Centre Interdisciplinaire de Recherche en Réadaptation et Intégration Sociale (CIRRIS), Québec, Canada</footnote>

<footnote><sup>c</sup> CHU de Québec-Université Laval, Québec, Canada</footnote>

<footnote>* Corresponding author: ariane.lavoie-hudon.1@ulaval.ca</footnote>
the pressure profiles at the hip. Mean contact surface, peak and mean pressure were also computed. Due to the limited sample size, statistical analyses were not performed at this stage.

**3. Results and discussion**

Preliminary results showed that during walking, particularly at push-off, the mean joint contact area tended to increase (5.7 ± 1.3 → 7.2 ± 2.0 cm²) and maximum and mean pressures tended to decrease (17.2 ± 2.3 → 15.5 ± 3.9; 5.4 ± 0.7 → 4.5 ± 1.2 MPa) after PAO. Intra-articular pressures were lower and more evenly distributed after surgery (Fig.1). For the squat, the joint contact area did not meaningfully change in the deep part of the squat (6.1 ± 1.4 → 6.5 ± 1.1 cm²), while the maximum and mean pressure remained unchanged (13.9 ± 5.6 → 13.6 ± 2.6 MPa; 4.4 ± 1.1 → 3.9 ± 0.6 MPa).

The improvement in postoperative joint mechanics seems to be more evident in walking than in squatting. PAO often includes an anteversion of the acetabular fragment, which may reduce posterior coverage of the acetabulum in favor of anterior coverage. This repositioning seems to be more favorable for reducing anteriorly directed forces, such as those that occur during gait. Furthermore, the increase in lateral coverage would compensate for the loss of posterior coverage in the squat when the hip is in deep flexion and provide an adequate contact area to stabilize the hip laterally. The gait analysis results are consistent with those of Goetz et al. (2021), who reported modest improvements in intra-articular pressure distribution after surgery. However, while our study revealed improvements at push-off, Goetz et al. observed more significant changes at heel-strike. This discrepancy may be due to the lower degree of severity of the patients in our cohort or to the orthopaedic surgeon's choice for the acetabular fragment repositioning.

**4. Conclusions**

Periacetabular osteotomy could improve the mechanics of the joint when performing certain tasks that are typically repeated on a daily basis. This could help slow the development of osteoarthritis in dysplastic patients by reducing the high-pressure points that can accelerate acetabular cartilage wear. Patients can expect to see greater improvements in their walking tolerance than in high-flexion activities such as squatting.

<figure><img src="image_2.png" /><figcaption>**Figure 1.** (a) Example of joint contact pressure distribution in the acetabulum of a subject before surgery, at push-off (b) The same subject after surgery</figcaption></figure>

Credit: Victor Grenier & Ariane Lavoie-Hudon.

**Acknowledgements**

We thank Sylvie Turmel and Simon Laurendeau for their help with data collection and scheduling.

**Conflict of interest statement**

The authors have no conflicts to declare.

**Contributors Roles**

ALH: Methodology, Formal analysis, Writing original draft; VG: Methodology, Data curation; XRL:
Supervision; ERA: Formal analysis, Validation; ELB:
Conceptualization, Funding acquisition, Resources;
PC: Conceptualization, Supervision, Writing-review
& editing.

References

Mavcic, B., Iglic, A., Kralj-Iglic, V., Brand, R. A., & Vengust, R. (2008). Cumulative hip contact stress predicts osteoarthritis in DDH. *Clin Orthop Relat Res*, 466(4), 884-891. https://doi.org/10.1007/s11999-008-0145-3

Nishii, T., Sugano, N., Sato, Y., Tanaka, H., Miki, H., & Yoshikawa, H. (2004). Three-dimensional distribution of acetabular cartilage thickness in patients with hip dysplasia: A fully automated computational analysis of MR imaging. *Osteoarthritis and Cartilage*, 12(8), 650-657. https://doi.org/10.1016/j.joca.2004.04.009

Grenier, V., Ruel, C., Ruel, J., Sercia, Q., Rioux, M., Corbeil, P., & Belzile, E. (2025). Multivariate quantitative outcomes of periacetabular osteotomy using discrete element analysis. *Advances in Orthopedics*, 1479343. https://doi.org/10.1155/aort/1479343

Goetz, J. E., Thomas-Aitken, H. D., Sitton, S. E., Westermann, R. W., & Willey, M. C. (2023). Joint contact stress improves in dysplastic hips after periacetabular osteotomy but remains higher than in normal hips. *HIP International*, 33(2), 298-305. https://doi.org/10.1177/11207000211036414