Purpose: - To investigate the association between hip-contact force (HCF) during walking and cartilage defect severity in football players with hip and groin (hip/groin) pain - To investigate the relationship between HCF and size of cam morphology in football players with hip/groin pain
Methods: 121 football players (26 women) with hip/groin pain participated. Players were eligible if aged 18 to 50 years, undertaking ≥ 2 sessions of football per week (training/games) and > 6-month history of insidious onset hip/groin pain with a positive flexion-adduction-internal rotation test. Exclusion criteria included a history of significant hip/groin injury or surgery, presence of hip osteoarthritis (OA), or previous intra-articular injection in the past 3 months. All participants underwent a Dunn 45° radiograph, and 3 tesla MRI of each hip. The alpha angle was used to determine the size of cam morphology on the Dunn 45° radiographs using statistical shape modelling software. The Scoring Hip Osteoarthritis with MRI (SHOMRI) method was used to quantify the severity of cartilage damage. For each hip, specific cartilage scores (severity of damage) were calculated (0-20). Biomechanical data collection was conducted at the La Trobe Gait Laboratory. Participants completed walking trials while full-body motion analysis and ground force data were recorded. HCF for an entire stride cycle was calculated using a musculoskeletal modelling approach in OpenSim. We considered the HCF as its three components (posterior-anterior (PA)), inferior-superior (IS), lateral-medial (LM)). HCF was normalised to each participant's body weight. Our outcome measure for the primary aim was the HCF impulse, with time-normalised data used for the secondary aim. Cartilage defects and subsequent severity was characterised as: absent (SHOMRI=0), mild (SHOMRI= 1 to 3), or moderate/severe (SHOMRI>4). Differences in HCF based on cartilage deficit severity were assessed using linear models, controlling for sex, age and contralateral hip status (painful or not). Significant main effects of cartilage severity were followed up with pairwise comparisons via the estimate marginal means package in R. The relationship between alpha angle size and HCF was explored using linear models via statistical parametric mapping.
Results: Impulse magnitude of HCF in AP and SI directions decreased with more severe cartilage defects (Table 1).
|Linear models and follow up comparisons for the differences in HCF between cartilage defect severity|
|Linear Model Result||Follow Up Comparisons|
|Component||F Statistic, P-value||Comparison||Adjusted MD||95% CI||P-value|
|Posterior-Anterior||F = 4.88, P=0.01*||Absent vs Mild||0.04BW||0.01 to 0.07BW||0.02|
|Absent vs Mod/severe||0.07BW||0.02 to 0.12BW||0.01|
|Inferior-Superior||F = 4.83, P=0.01*||Mild vs Mod/severe||0.03BW||-0.02 to 0.07BW||0.31|
|.||Absent vs Mild||0.10BW||<-0.01 to 0.21BW||0.06|
|Absent vs Mod/severe||0.23BW||0.08 to 0.38BW||<0.01|
|Mild vs Mod/severe||0.13BW||-0.03 to 0.28BW||0.10|
|Lateral-Medial||F = 4.83, P=0.01*||Absent vs Mild||-||-||-|
|Absent vs Mod/severe||-||-||-|
|Mild vs Mod/severe||-||-||-|
* significant cartilage main effect (<0.05);
† significant follow-up comparison; "BW" bodyweight, "MD" mean difference, "CI" confidence interval, "Mod" moderate, "-"not calculated.
A significant negative relationship was observed between AP HCF and alpha angle size at toe-off (∼58% to 60% of stride, P=0.040). In addition, significant negative relationships were also between alpha angle size and HCF in the SI direction (∼77% to 83% of stride, P=0.009) and ML direction (∼75% to 81% of stride, P=0.005) (Figure 1).
Conclusions: This study revealed that football players with hip/groin pain and greater cartilage defect severity display lower hip joint loads during walking. Optimal loading is integral to joint health, with hip OA progression thought to be related to increased joint loading. Our results challenge this paradigm. Whilst we cannot decipher cause and effect, it is possible that lower joint loading may play a role in the development and progression of OA features in young football players with hip/groin pain. Cam morphology is thought to influence joint forces during daily activities, with negative effects on articular cartilage and increasing hip OA risk. Football players with hip/groin pain and a larger cam walked with less HCF in the IS and LM direction at approximately 80% of stride, the time point corresponding to peak hip flexion during walking. Positions of hip flexion are often described as painful for people with hip/groin pain, and this reduction may be a compensatory mechanism to reduce discomfort and/or load in this position.
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