# Evaluating Accident Reconstruction Method for Mountain biking Spinal Injuries: From Accident Data to Biomechanical Modeling of the Injury Mechanism

Sophie Bonte, A. Thouzé, W. Wei, P-J. Arnoux, E. Marcaggi, L. Thollon, N. Bailly

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## To cite this version:

Sophie Bonte, A. Thouzé, W. Wei, P-J. Arnoux, E. Marcaggi, et al.. Evaluating Accident Recon-struction Method for Mountain biking Spinal Injuries: From Accident Data to Biomechanical Mod-eling of the Injury Mechanism. Multidisciplinary Biomechanics Journal, 2025, 50th congress of the., 10.46298/mbj.16211. hal-05191764v2

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Submitted on 23 Oct 2025

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# Evaluating Accident Reconstruction Method for Mountain biking Spinal Injuries: From Accident Data to Biomechanical Modeling of the Injury Mechanism

Sophie Bonte<sup>a, b*</sup>, Arsène Thouzé<sup>b</sup>, Wei Wei<sup>a</sup>, Pierre-Jean Arnoux<sup>a</sup>, Emmanuel Marcaggi<sup>c</sup>, Lionel Thollon<sup>a</sup>, Nicolas Bailly<sup>a</sup>

<sup>a</sup> Aix Marseille Univ, Univ Gustave Eiffel, LBA Marseille, Marseille, France

<sup>b</sup> Decathlon SporstLab, Lille, France

<sup>c</sup> Grenoble Alpes Univ, CHU Grenoble Alpes, Grenoble, France

* Corresponding author: sophie.bonte@univ-eiffel.fr

Received date: 06/04/2025

Accepted date: 27/06/2025

Publication date: 27/10/2025

**Keywords:** spinal injury, compression fracture, mountain biking, numerical models, video analysis

© 2025 The Authors

Licence CC-BY 4.0

Published by Société de Biomécanique

## 1. Introduction

Mountain biking (MTB) is growing in popularity but carries a high injury risk, with 16.8 injuries per 1,000 hours of practice (Carmont, 2008). Although spinal injuries are relatively rare, they account for 30–40% of severe trauma cases (Kim et al., 2006) and often result from over-the-handlebars (OTB) falls (Dodwell et al., 2010). Despite their severity, the specific back impact conditions—such as impact area, velocity components, and loading patterns—leading to thoracolumbar fractures remain poorly understood. Bridging this knowledge gap is essential for improving MTB rider safety, particularly by informing the development and evaluation of protective back equipment. Combining video analysis, epidemiology, MTB simulation, and finite element (FE) simulation has been successfully used to understand injury mechanisms in traffic accidents. We aimed to evaluate whether this approach could also be effective in understanding spinal injury mechanisms in mountain bike (MTB) accidents. The objective of this work is to develop a methodology and to evaluate its ability to reproduce real injury cases.

## 2. Methods

### 2.1 Accident Data Collection

Two complementary datasets were analyzed using a standardized questionnaire to collect injury details and crash circumstances.

1. **Video Dataset:** 534 crash videos were collected from the social media platform Pinkbike, all involving traumatic injuries. Among them, 25 cases with confirmed spinal injury were identified.

2. **Clinical Dataset:** Hospital records from CHU Grenoble documented 74 severe MTB crashes with 11 spinal injury cases.

Both datasets analysis offered a more comprehensive understanding of the crash scenarios and injury mechanisms associated with thoracolumbar spinal trauma.

<figure><img src="image_3.png" /><figcaption>**Figure 1.** (a) Identification of the main scenario leading to thoracolumbar injury (b) Impact conditions of the back using multibody simulation (c) Injury Mechanism using Biomechanical Modelling.</figcaption></figure>

Credit: Sophie Bonte.

### 2.2 Multibody Crash Reconstruction

A multibody model of a MTB forward falls was developed using a Human Facet Model (figure 1b) and used to reconstruct 288 falls with various speeds, slopes, bike inclinations, handlebar forces, and fall heights. Back
impact conditions that may lead to thoracolumbar
injuries were analyzed, focusing on impact area, angle,
and velocities (normal, tangential, and rotational).

**2.3 Biomechanical Finite Element Modelling**

Representative severe back impact conditions (at the
3rd quartile for Vn, Vt, and Vrot) were used to simulate
spinal loading using the THUMS V4 human FE model.
The vertebral strain distributions and flexion moments
were analyzed to identify risk of injury (compression
fractures, flexion, or torsional failure modes).

The capability of the entire methodology to repro-
duce the correct injury mechanism was evaluated by
comparing the injury predicted by the FE model to the
injury patterns observed in real cases.

3. Results and discussion

**3.1 Scenarios Leading to Thoracolumbar Injuries**

Forward fall, over-the-handlebars were the leading cause of spinal injuries (81%), mostly after poor jump landings (64%). Thoracolumbar injuries primarily resulted from rolling impacts (70%), either head-first then back (36%) or overflip back impacts (34%). One type of vertebral fractures was mainly observed compression fractures in the thoracic (T6-T12) and lumbar (L1-L3) regions.

**3.2 Back impact conditions in realistic crashes**

Among all simulations, 58.3% resulted in an over-the-
bars crash, with rolling impacts in 57% of cases. Among
these crashes, we distinguished upper back impact first
from lower back or rear pelvis. Severe back impacts
(Q3 values) had normal velocities of 5–9 m/s, tangential
7–7.5 m/s, and rotational 5–7.5 rad/s, varying by sce-
nario and impact area. A key factor was the significant
rotational component in impact speed and angle.

**3.3 Finite Element Simulations of Injury Mechanisms**

To confirm that the impact conditions obtained in 3.2,
could produce the injury observed in 3.1 we reproduced
one impact corresponding to the third quartile of 3.2
results (Vt: 7.3m/s; Vn: -9.2 m/s; Vrot: 5.3 rad/s).
The combination of rotational, tangential and normal
impact velocities resulted in significant compression
loading in the vertebral body of the thoracolumbar
spine of the FE model.

The computed loading and predicted injury by the
FE model correspond well with the main type of ver-
tebral fracture observed in 3.1: compression fracture

of the vertebral body suggesting that the methodology
is relevant to this type of crash.

4. Conclusion

The proposed multidisciplinary methodology, was able
to identified and replicate a biomechanical injury sig-
nature associated with thoracolumbar spinal trauma in
MTB : a compression fracture of the vertebral body
provoked by an other the bar crash scenario.

By quantitatively characterizing these conditions
and confirming their effects through FE modeling, the
study lays the groundwork for more relevant protec-
tive gear testing protocols. The initial findings suggest
that future protective equipment should be evaluated
under multi-axial dynamic conditions to account for
the complex impact profiles observed in MTB crashes.

Acknowledgements

We thank Outside Inc. for granting us access to video
resources on the Pinkbike.com platform used in our study.
We also appreciate the CRPH Committee for reviewing
our protocol and providing a favorable opinion. Finally,
we extend our gratitude to Grenoble University Hospital
(CHU) for their valuable partnership.

Conflict of Interest Statement

Arsène Thouzé and Sophie Bonte are employed by
the company Decathlon, which manufacture bikes and
protective equipment.

References

Carmont, M. R. (2008). Mountain biking injuries: A review. *British Medical Bulletin*, 85(1), 101–112, https://doi.org/10.1093/bmb/1dn009

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Kim, P. T. W., Jangra, D., Ritchie, A. H., Lower, M. E.,
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