Relationship between piriformis distal insertion and femoral torsion angle

Abstract

Objectives: Biomechanical models commonly describe the piriformis muscle as reversing function from a hip external rotator to an internal rotator with increasing hip flexion. These models often assume a uniform distal tendon attachment, despite growing anatomical evidence of variability. Femoral torsion is a clinically measurable parameter that may influence piriformis tendon orientation and function. Methods: The piriformis muscle was examined in 63 femora from 38 embalmed donor bodies. The position of the piriformis distal tendon attachment on the superior surface of the greater trochanter was measured relative to its midpoint and classified as anterior or posterior. Femoral angle of torsion was measured using direct anatomical methods with a goniometer. The relationship between femoral torsion and piriformis tendon position was analyzed using Pearson’s correlation. Results: Across the full sample, no significant relationship was identified between femoral torsion and piriformis tendon position (r=0.13, p=0.31). Right femora demonstrated no meaningful association, whereas left femora showed a statistically significant moderate positive correlation, with increasing femoral torsion associated with a more posterior tendon position (r=0.38, p=0.04). No consistent or statistically significant patterns were observed when analyses were stratified by sex. Conclusion: These findings demonstrate that the relationship between femoral torsion and piriformis tendon position is inconsistent and not bilaterally uniform. When considered alongside documented variability in piriformis distal attachment, these results call into question simplified biomechanical models that assume a predictable reversal of piriformis function with hip flexion and support a more cautious interpretation of piriformis biomechanics.

Keywords

• femur
• hip torsion
• piriformis

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