Purpose: To verify the relationship between muscle volumelateral centre-edge angle (LCEA)alpha angle (AA)body mass index (BMI) and Beighton score with stiffness coefficient (SC). To analyse the difference of traction force at different physical states of hip joint capsule.

Methods: Thirty-six patients who underwent hip arthroscopy operation were included. The volumes of some related muscles were measured in MRI images by 3D Slicer. We recorded and tested differences in traction force of five joint capsule physical statesincluding before (State 1) and after joint capsule puncture (State 2)after the establishment of anterolateral and mid-anterior approaches (State 3) and after incision of the joint capsule through these two approaches (States 45). The correlation between muscle volumeBMILCEAAA and SC was verified by Spearman test. Poisson regression was used to explain confounding variables.

Results: The average force at State 1 was 531.8 N. There were significant differences in traction force between these five states (p < 0.001). There was a significant positive correlation between muscle volumes and SC (p < 0.001). BMI had no correlation with SC (n.s.). The preoperative LCEA of the affected side was correlated with SC (p = 0.043). AA and SC were not correlated (n.s.).

Conclusion: The physical states of the hip joint capsule affected traction force. Muscle volume rather than BMI is an ideal index to estimate preoperative traction force. LCEA affected traction forcewhilst AA and Beighton score did not. Measuring the muscle volume can help estimate the most suitable traction force for the patient.

Levels of evidence: IV.