# Effects of periacetabular osteotomy on the reaction forces within the dysplastic hip joint

Ariane Lavoie-Hudon, Victor Grenier, Xavier Robert-Lachaîne, Étienne L.

Belzile, Philippe Corbeil

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Ariane Lavoie-Hudon, Victor Grenier, Xavier Robert-Lachaîne, Étienne L. Belzile, Philippe Corbeil. Effects of periacetabular osteotomy on the reaction forces within the dysplastic hip joint. Multidisciplinary Biomechanics Journal, 2025, 50th congress of the.., 10.46298/mbj.16157. hal-05191709v2

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Submitted on 23 Oct 2025

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# Effects of periacetabular osteotomy on the reaction forces within the dysplastic hip joint

Ariane Lavoie-Hudon<sup>a, b*</sup>, Victor Grenier<sup>c</sup>, Xavier Robert-Lachaîne<sup>a</sup>, Étienne L. Belzile<sup>c</sup>, Philippe Corbeil<sup>a, b</sup>

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

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

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

* Corresponding author: ariane.lavoie-hudon.1@ulaval.ca

Received date: 06/04/2025

Accepted date: 27/06/2025

Publication date: 27/10/2025

**Keywords:** acetabular dysplasia, functional tasks, gait analysis, squat biomechanics, musculoskeletal modelling

© 2025 The Authors
Licence CC-BY 4.0
Published by Société de Biomécanique

## 1. Introduction

Hip dysplasia is a congenital condition characterized by a shallow acetabulum. This can reduce the contact surface with the femoral head, overloading the cartilage and causing pain during activities of daily living that mobilize the hip joint. This coverage deficiency increases pressure on the acetabular rim and labrum (Henak 2011), which accelerates the wear of articular cartilage and predispose patients to early osteoarthritis. Periacetabular osteotomy (PAO) is a surgical procedure indicated to treat acetabular dysplasia. The procedure has been shown to improve quality of life and ability to participate in activities. In the long term however, a majority of treated hips will require further treatment, such as a total hip arthroplasty (Lerch et al. 2017). Joint force analysis is necessary to understand the level of joint loading and the associated risk. Few data exist on the reaction forces generated at dysplastic hips due to their particular anatomy. The aim is to assess the effect of PAO on hip reaction forces during walking and squatting.

## 2. Methods

### 2.1 Data collection

Ten participants (4 ♂ and 6 ♀, 18-43 years) with unilateral acetabular dysplasia were tested before and 10.1 ± 4.6 months after PAO. An optoelectronic system (Vicon) recorded three-dimensional displacement of the pelvis and lower limbs during walking and squatting.

Ground reaction forces were measured using force platforms (AMTI). Patients were instructed to walk at a comfortable speed, and their squatting depth was controlled to the height of their tibial plateau. Lateral coverage angle (LCEA) and Tönnis angle, indicators of dysplasia severity, were measured from patients' medical imaging.

### 2.2 Data processing and statistics

Joint angles and hip reaction forces were calculated from customized musculoskeletal models in OpenSim through inverse kinematics, static optimization and joint reaction forces analysis. Radiographic measurements were compared pre- and post-surgery with a paired t-test. Time series of hip joint angles and reaction forces were analyzed using the parametric statistical mapping method (Pataky 2012) involving a repeated measures ANOVA: healthy side vs. treated side and pre- vs. post-surgery (p < 0.05).

## 3. Results and discussion

LCEA and Tönnis angle returned to normal values after surgery (LCEA: 16 ± 10 → 28 ± 6°, Tönnis: 13 ± 10 → 4 ± 6°; p < 0.001). A significant interaction between pre-post and healthy-affected factors was detected in hip rotation angle in the deep portion of the squat (p<0.05), indicating a reduction in internal rotation on the affected side (2.3 ± 5.1 → -2.4 ± 6.4°) and an increase on the healthy side (-2.0 ± 6.4 → 1.0 ± 6.2)
after surgery only. Symmetry in posterior hip reaction force profile was noted after surgery (Interaction: $p < 0.05$), the result of an increase on the healthy side ($2.3 \pm 0.4 \rightarrow 2.6 \pm 0.4$N/kg) and a reduction on the affected side ($2.8 \pm 0.6 \rightarrow 2.6 \pm 0.7$N/kg). Post-surgical improvements in lower-limb symmetry during the squat were also observed on other variables (pelvic rotation, medio-lateral and vertical forces). Regarding walking, posterior reaction forces were reduced after surgery ($1.0 \pm 0.1 \rightarrow 0.7 \pm 0.2$N/kg; $p < 0.05$). There was also an increase in mean hip flexion ($6.6 \pm 0.5 \rightarrow 11.7 \pm 1.1$; $p < 0.05$) and a reduction in adduction angle ($0.6 \pm 1.1 \rightarrow -0.9 \pm 0.6^\circ$; $p < 0.05$) on loading bilaterally after PAO.

All patients had a radiologically successful surgery, with Tönnis angle and LCEA normalizing to expected values (Novais et al. 2017). The improvement in symmetry for the squat may indicate that patients were more willing to load their affected hips after corrective surgery. A change in movement strategy was noted with a change in hip rotation and adduction; this could be due to a protective posture that shifted to a more natural movement after surgery. Both squats and gait were marked by a reduced posteriorly directed reaction force (Fig. 1); a likely explanation is that surgery shifted posterior coverage of the acetabulum to a more anterior coverage. Patients were likely to compensate for the limited anterior coverage by anteverting their pelvis, which allowed them to utilize their posterior coverage to a greater extent.

There are few studies to compare these results to. Socato et al. (2010) studied the joint reaction forces of teens before, 6-months and 12-months after surgery. They noted improvements in abductor impulses at 12-months, with residual deficit compared to controls. This is consistent with the reduced adduction angle we noted after surgery.

## 4. Conclusions

The surgery, which corrected the anatomy characteristic of dysplastic patients, seems to have had a positive functional impact observed during walking and squat movements. Reduced reaction forces and improved symmetry between the lower limbs were desired to reduce the level of joint loading. These changes brought about by PAO could help curb the development of osteoarthritis in this population.

<figure><img src="image_3.png" /><figcaption>**Figure 1.** (a) Mean antero-posterior contact forces for the squats (b) Mean antero-posterior contact forces for the stance phases of gait.</figcaption></figure>

Credit: 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; ELB: Conceptualization, Funding acquisition, Resources; PC: Conceptualization, Supervision, Writing-review & editing.

## References

Henak, C. R., Ellis, B. J., Harris, M. D., Anderson, A. E., Peters, C. L., & Weiss, J. A. (2011). Role of the acetabular labrum in load support across the hip joint. *J Biomech, 44*(12), 2201–2206. https://doi.org/10.1016/j.jbiomech.2011.06.011

Lerch, T. D., Steppacher, S. D., Liechti, E. F., Tannast, M., & Siebenrock, K. A. (2017). One-third of hips after periacetabular osteotomy survive 30 years with good clinical results, no progression of arthritis, or conversion to THA. *Clin Orthop Relat Res, 475*(4), 1154–1168. https://doi.org/10.1007/s11999-016-5169-5

Pataky, T. C. (2012). One-dimensional statistical parametric mapping in Python. *Computer methods in bio-mechanics and biomedical engineering, 15*(3), 295–301. https://doi.org/10.1080/10255842.2010.527837

Novais, E. N., Duncan, S., Nepple, J., Pashos, G., Schoenecker, P. L., & Clohisy, J. C. (2017). Do radiographic parameters of dysplasia improve to normal ranges after bernese periacetabular osteotomy? *Clin Orthop Relat Res, 475*(4), 1120–1127. https://doi.org/10.1007/s11999-016-5077-8

Sucato, D. J., Tulchin, K., Shrader, M. W., DeLaRocha, A., Gist, T., & Sheu, G. (2010). Gait, hip strength and functional outcomes after a Ganz periacetabular osteotomy for adolescent hip dysplasia. *J Pediatr Orthop, 30*(4), 344–350. https://doi.org/10.1097/bpo.0b013e3181d9bfa2