Deep External Rotator Muscles of the Hip: An Anatomical and Architectural Study
Authors: Scagnetti Ian A. , Jadeski Lorraine C. , Brown Stephen HM. 
Published: June 2021

The arrangement of sarcomeres within a muscle (referred to as the muscle architecture) can be used to predict a muscle's functional capability. Parameters that are measured when studying muscle architecture are muscle fascicle length, sarcomere length, and the mass of the contractile tissue. Using these measured values, physiological cross‐Sectional Area (PCSA, representative of sarcomeres arranged in‐parallel) and normalized fascicle length (LFn, representative of sarcomeres arranged in‐series) can be calculated. PCSA is currently the best predictor of the relative force production capability of a muscle, and LFn is the best predictor of the excursion potential of a muscle. Additionally, based on the well‐known force‐length relationship for human muscle, sarcomere length at a given posture can be used to predict the percentage of maximal force generating capability that the muscle can produce.

In this study, the architectural parameters of six deep external rotator muscles of the hip (Piriformis, Quadratus Femoris, Obturator Internus, Obturator Externus, Gemellus Superior and Gemellus Inferior) were measured, and each muscle's anatomical pathway was photographed using high quality digital imaging. These muscles are primarily external rotators and stabilizers of the hip joint, and may be affected during hip surgery if the anatomical attachments or pathways are altered. Previously, there had been no detailed architectural data measured for these six deep hip external rotator muscles. The six muscles were removed from 12 embalmed cadavers on one side of the body (n=12, 6 male and 6 female, age 56–88 years). Each muscle was carefully removed from the cadaver using dissection hand tools and had all external fat, fascia and tendon removed. Muscle mass was measured using a digital scale. Three fascicles were isolated from different locations on the muscle and fascicle length was measured using a digital caliper. Three small biopsies were taken from each fascicle and were subjected to laser diffraction to measure sarcomere length. Table 1 shows all measured and calculated results. Obturator Internus is predicted to have the highest force generating capability (based on PCSA), and Piriformis is predicted to have the highest excursion potential (based on LFn). All of the six deep hip external rotator muscles have an average sarcomere length, measured in the neutral cadaveric posture, ranging between 2.41 um – 2.54 um. This suggests an ability for the muscles to produce 91 – 95% of their maximal force, on the ascending limb of the force‐length curve, in this posture. These data, in conjunction with modelling software, can be used to predict force generating capabilities throughout the hip range of motion, and will be valuable to predict changes in the muscles' behavior after being displaced from their respective anatomical attachments during hip surgery.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.