The number and organization of sarcomeres within a muscle (referred to as muscle architecture) can be used to predict functional capability. The six deep external rotator muscles of the hip (piriformis (PI), quadratus femoris (QF), obturator internus (OI), obturator externus (OE), superior gemellus (SG), and inferior gemellus (IG)) play a role in both hip stabilization and rotation and are damaged and relocated during total hip arthroplasty surgery. Understanding the architectural details of these muscles could lead to improved clinical understanding of their function. Therefore, muscles were excised from 12 embalmed cadavers (6 male, 6 female aged 56-88 years) to measure muscle mass, fascicle length, and sarcomere length. These variables were used to calculate the architectural parameters physiological cross-sectional area (PCSA) and normalized fascicle length (LFn). Results demonstrated that in the measured neutral cadaveric posture all six muscles had mean sarcomere lengths (2.40 to 2.57 μm) that placed them on the ascending limb of the force-length relationship where they could theoretically generate more than 90 percent of their maximum capable force. The OI had the largest PCSA, and thus largest force-generating capability, while the PI had the longest normalized fascicle length, and thus largest excursion and shortening velocity capabilities. SG and IG were the smallest in both regards. These data provide valuable insight into the force-generating capability of the hip deep external rotator muscles and can be used as inputs to biomechanical models to predict function in healthy movement or within a variety of clinical conditions.
Ian A. Scagnetti, Lorraine C. Jadeski, Stephen H.M. Brown
Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada
Eur. J. Anat.