Presentation
The effect of hip position on hip rotator strength and action of the piriformis using dynamic ultrasound imaging and dynamometry.
World Congress of Physiotherapy Meeting 2019
(2019)
Abstract
Background
The primary actions of the piriformis are hip external rotation and abduction; however studies have reported that the line of force changes over different degrees of hip flexion causing a reversal of action. Several studies have used string models to determine findings and assumed universal tendinous attachment sites despite some evidence to the contrary. More recently a cadaveric study reported that the piriformis was maximally lengthened by 105° of hip flexion and 10° adduction and relaxed by hip extension and abduction with peak strength by extension and abduction at 60° to 90° of hip flexion positions where as another cadaveric reported that the piriformis lengthens with the hip and knee flexed to 90 degrees with the addition of adduction or external rotation with the former providing the most lengthening of the muscle. Consequently, hip position may affect hip rotator strength and efficacy of interventions.
Purpose
This study dynamically assessed the effect of hip position on the action of the piriformis in real time with ultrasound imaging in addition to the effect on strength of the external (ER) and internal (IR) hip rotators as a group in healthy young adults.
Number of Subjects
25 (8 males,17 females) adults.
Methods
The experimental limb was randomly selected and assessed under 4 randomly assigned testing conditions: hip ER and IR performed in prone (HE) with knee flexed to 90° and in a seated 90/90 position (HF). Ultrasound (US) data were acquired using a curvilinear transducer initially orientated in the transverse plane lateral to the sacrum and moved caudally in the direction of the PSIS and SIJ until the piriformis was visualized exiting the greater sciatic foramen. The transducer was then oriented parallel to the muscle fibers and passive motion of the hip differentiated it from the gluteals. Subjects were prompted to perform 3 IRs and 3 ERs at a rate which was standardized with a metronome while US cineloops were recorded while the thigh was stabilized by an examiner. A concentric contraction was defined as a shortening of the piriformis muscle observed from its distal towards its proximal attachment while an eccentric contraction was defined as a lengthening from its proximal towards its distal attachment. A hand-held dynamometer was used to assess strength across all testing positions.
Results
US showed the piriformis shortened during ER and lengthened during IR regardless of hip position. A significant interaction effect was noted between hip position (HF, HE) and strength (IR, ER) (p<.001). Post hoc analysis revealed hip IRs (p<.001) and hip ERs (p=.01) were significantly stronger in the seated 90/90 position (HF) versus prone (HE) position. Furthermore, effect size (Cohen’s d) values were small (d=.2) and large (d=.9) for ER and IR respectively.
Conclusions
While strength of the ER as a group was stronger in HF when compared to HE, the effect was small and the piriformis muscle function did not appear to change its action per US imaging. IR was significantly stronger in HF, however this does not appear to be due to a reversal of action of the piriformis. Furthermore, recent anatomical studies have shown variability in the dimensions and attachment of the distal tendon which prevents a reversal of action.
Implications
Stretches for the piriformis are based on the belief that the piriformis becomes an IR when the hip is flexed at or above 90°, however these findings are primarily based on cadaveric studies or more recent static CT and 3D computational modeling studies. The results of this study are clinically significant in that they provide a functional dynamic visual record of the piriformis in vivo: the piriformis functioned as an ER in the HF position despite the effect of hip position on rotator strength. This finding may merely reflect a change in moment arm length and/or length tension relationships and not a reversal of muscle action as previously thought. Further imaging studies across a variety of hip positions may provide a true representation of piriformis muscle function.
References
- Gulledge BM, Marcellin-Little DJ, Levine D, et al. Comparison of two stretching methods and optimization of stretching protocol for the piriformis muscle. Med Eng Phys.2014;36(2):212-218.
- Waldner A, Monsrud J, Franklin M, Bernath D, Clemente R, Fabrizio PA. Effect of Hip Rotation Stretch on the Piriformis Muscle: A Pilot Study. JSPTR. 2015; 8(4)
- Bloom N, Cornbleet SL. Hip rotator strength in healthy young adults measured in hip flexion and extension by using a hand-held dynamometer. PM&R. 2014;6(12):1137-1142.
- Fabrizio P, Myers M, Rasicci D. The anatomy of the distal attachment of the piriformis muscle:a pilot study. JOSPT. 2011;41(1):A84.
- Neumann, D. Kinesiology of the Hip: A Focus on Muscular Actions. JOSPT. 2010;40(2):82-94
- McGovern RP, Kivlan BR, Martin RL. Length change of the short external rotators of the hip in common stretch positions: A Cadaveric study. Int J Sports Phys Ther. 2017;12(7):1068-1077.
- Battaglia, Patrick J. et al. Dynamic Ultrasonography of the Deep External Rotator Musculature of the Hip: A Descriptive Study. PM&R, 2017; 8 (7): 640 – 650.
Disciplines
Publication Date
Summer May 12, 2019
Location
Geneva, Switzerland
Comments
Platform presentation in Orthopedics section
Citation Information
Ruth M Maher, Cara Morrison and Y Zang. "The effect of hip position on hip rotator strength and action of the piriformis using dynamic ultrasound imaging and dynamometry." World Congress of Physiotherapy Meeting 2019 (2019) Available at: http://works.bepress.com/ruth-maher/19/