Validation of a simplified modeling approach to predict strain in the cartilage and labrum of the hip with application to femoroacetabular impingement syndrome.
Hudson L, Schuring L, et al. • Journal of biomechanics • 2026
While STO modeling provides qualitative insight into strain patterns and contact locations, its ability to quantify strain magnitude, particularly under higher loading conditions and in the labrum, is limited.
Key Findings
Results
Soft tissue overlap (STO) models captured the general spatial patterns and locations of peak strain in both acetabular cartilage and labrum compared to subject-specific finite element models.
Eight individuals with radiographically normal hips and eight patients with cam-type femoroacetabular impingement syndrome were evaluated.
Subject-specific anatomy, kinematics, and joint reaction forces were used for all models.
Comparisons were made at heel-strike and heel-off using correspondence-based Network Analysis and Bland-Altman analyses.
STO models replicated qualitative spatial patterns of strain distribution in both tissue types.
Results
Significant differences between STO and FE strain predictions were present across 1% to 75% of the gait cycle, particularly during higher magnitudes of joint loading.
Discrepancies were especially pronounced during periods of higher joint loading.
The range of the gait cycle showing significant differences spanned from 1% to 75%.
Both cartilage and labrum showed disagreement between STO and FE predictions.
Bland-Altman analyses were used to quantify agreement between the two modeling approaches.
Results
STO models systematically underpredicted strain at higher magnitudes, with disagreement increasing as strain magnitude increased.
The systematic underprediction was identified through Bland-Altman analysis.
The relationship between disagreement and strain magnitude was monotonically increasing.
This systematic bias was most apparent under higher loading conditions.
The underprediction pattern was consistent across the pooled cohort of 16 subjects.
Results
Discrepancies between STO and FE models were most pronounced in the anterosuperior cartilage and labrum near heel-off, where FE models predicted higher, more localized strains.
The anterosuperior region is clinically relevant as it is a common site of pathology in femoroacetabular impingement syndrome.
FE models predicted strains that were both higher in magnitude and more spatially localized in this region near heel-off.
STO models failed to capture the localized concentration of strain in the anterosuperior labrum.
Heel-off represents a phase of relatively higher joint loading during simulated walking.
Results
No group-dependent differences in agreement between STO and FE models were observed between the normal hip and cam-type femoroacetabular impingement syndrome cohorts.
Eight individuals with radiographically normal hips were compared to eight patients with cam-type femoroacetabular impingement syndrome.
Because no group-dependent differences were found, results for the two cohorts were pooled for final analyses.
This finding suggests the limitations of STO modeling are not specific to hip pathology type.
The absence of group differences was assessed prior to pooling the cohorts.
Background
Subject-specific finite element modeling is computationally demanding, limiting its use in large cohorts, which motivated evaluation of the simplified STO approach.
STO modeling estimates strain from geometric overlap between articulating surfaces rather than full mechanical simulation.
The computational demands of subject-specific FE modeling restrict its application to large-scale studies.
STO modeling was proposed as a simplified alternative to enable analysis of larger cohorts.
Prior to this study, the predictive accuracy of STO models relative to FE models remained unclear.
What This Means
This research compared two different computer modeling approaches for predicting stress and strain in the cartilage and labrum (a ring of soft tissue) inside the hip joint during walking. The more detailed approach, called finite element (FE) modeling, simulates the actual mechanical behavior of tissues but requires significant computing time and resources. The simpler approach, called soft tissue overlap (STO) modeling, estimates strain by measuring how much the hip joint surfaces geometrically overlap during movement. The study tested both methods on 16 people — 8 with healthy hips and 8 with a condition called femoroacetabular impingement syndrome (FAIS), where abnormal bone shape causes pain and damage in the hip.
The study found that STO models did a reasonable job of showing where in the hip the highest strains generally occurred, but they consistently underestimated how large those strains were, especially when the hip was under greater load — such as during the push-off phase of walking. The biggest discrepancies appeared in the front-upper part of the hip joint, which is also the region most commonly damaged in people with hip impingement. Importantly, these limitations were similar regardless of whether the hip was healthy or had impingement, suggesting STO modeling has the same weaknesses in both populations.
This research suggests that STO modeling can be a useful screening tool for identifying which parts of the hip are at risk for injury, but it should not be relied upon for precise measurements of how much strain the cartilage or labrum actually experiences. Clinicians and researchers using STO models to study large groups of patients should be aware that this method may underestimate tissue strain, particularly in the labrum and during demanding activities, which could affect conclusions about injury risk or treatment effectiveness.
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Hudson L, Schuring L, Vargas B, Lisonbee R, Kussow S, Weiss J, et al.. (2026). Validation of a simplified modeling approach to predict strain in the cartilage and labrum of the hip with application to femoroacetabular impingement syndrome.. Journal of biomechanics. https://doi.org/10.1016/j.jbiomech.2026.113384