Effect of Hip Rotation Stretch on Piriformis Tendon Thickness: A Diagnostic Ultrasound Study

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Objectives: The objective of the current study was to examine, using diagnostic ultrasound (US), the effect of stretching the piriformis muscle into medial and lateral rotation in varying degrees of hip flexion on the thickness at the muscle tendon unit of the piriformis muscle.

Background: Passive stretch is commonly used to assess piriformis muscle length and as a treatment to alter piriformis muscle tightness. However, current literature and practice suggests that the piriformis’ function may reverse from a hip lateral rotator to a hip medial rotator when the hip is flexed beyond 90 degrees. Anatomical studies suggest that there may be cases where the tendon’s distal attachment position on the femoral greater trochanter does not permit a reversal of function.

Methods and Measures: Twenty- six subjects’ left hips were placed in increasing flexion positions (0, 60, 90, 100, 110, and 120 degrees) and maximal lateral and medial rotation. Thickness at the muscle tendon unit of the piriformis muscle was visualized and measured using diagnostic ultrasound at each hip flexion and each rotation position.

Results: The data were analyzed using two-factor analysis of variance. The results demonstrated that the interaction effect, the difference between thickness during lateral or medial rotation, was not influenced by hip flexion position.

Conclusion: Considering that a muscle is stretched in a position opposite of its function, the current study showed no consistent change in piriformis muscle tendon unit thickness in medial or lateral rotation with increasing hip flexion. The current findings may call into question the clinical thought of the piriformis reversing function with increased degrees of hip flexion.

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Journal of Student Physical Therapy Research





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This article was published in The Journal of Student Physical Therapy Research, Volume 8, Issue 4, pages 110-122.

The published version is available at http://www.ptstudentjournal.org/volume-8-4.html.

Copyright © 2015.

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