title: Primary functions of the quadratus femoris and obturator externus muscles indicated from lengths and moment arms measured in mobilized cadavers.
abstract: BACKGROUND
  The small muscles of the pelvis and hip are often implicated in painful conditions. Although the quadratus femoris and obturator externus are usually described as external rotators of the hip, little is known about how they change their lengths and moment arms during human movement. Therefore, more precise measurements defining the positions and directions for their maximal strength and stretch are needed to better describe their functions and guide the clinical approach to pain.
  
  
  METHODS
  Repeated measurements of the muscle lengths and range of motion were obtained using wires simulating dissected muscles on human cadaver hips. The lengths were measured at every 15° of flexion with and without maximal range of ab/adduction, rotation, and combinations of the two motions. Measurements were obtained from normal hips (n=3), and movement-lengthening relations were later differentiated into movement-moment arm relations.
  
  
  RESULTS
  The quadratus femoris showed maximum lengthening by flexion, adduction or abduction, and internal rotation, with the largest moment arms observed for extension in the deduced force-length efficient range of 60-90° flexion. The obturator externus showed maximum lengthening by extension, abduction, and internal rotation, with the largest moment arms observed for flexion and adduction in the deduced force-length efficient range around the hip's neutral position.
  
  
  CONCLUSIONS
  Our findings indicate that maximal strength of the quadratus femoris muscle will be delivered in a flexed position towards extension, while maximal strength of the obturator externus muscle will be delivered in an extended position towards flexion and adduction.
authors.affiliation: Department of Orthopaedics, Oslo University Hospital, PO Box 4956 Nydalen, N-0424 Oslo, Norway. Electronic address: kjartan.varbakken@yahoo.no.
authors.forename: Kjartan
authors.initials: K
authors.lastname: Vaarbakken
authors.affiliation: Department of Orthopaedics, Oslo University Hospital, PO Box 4956 Nydalen, N-0424 Oslo, Norway. Electronic address: harald.steen@ous-hf.no.
authors.forename: Harald
authors.initials: H
authors.lastname: Steen
authors.affiliation: Ullevål and Tåsen Physical Therapy and Exercise Inc., Tåsen Senter, PO Box 22, Tåsen, N-0801 Oslo, Norway. Electronic address: gsamuels@broadpark.no.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Samuelsen
authors.affiliation: Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, PO Box 1105, Blindern, N-0317 Oslo, Norway. Electronic address: h.a.dahl@medisin.uio.no.
authors.forename: Hans A
authors.initials: HA
authors.lastname: Dahl
authors.affiliation: Department of Anatomy, Institute of Basic Medical Sciences, University of Oslo, PO Box 1105, Blindern, N-0317 Oslo, Norway. Electronic address: t.b.leergaard@medisin.uio.no.
authors.forename: Trygve B
authors.initials: TB
authors.lastname: Leergaard
authors.affiliation: Department of Orthopaedics, Oslo University Hospital, PO Box 4956 Nydalen, N-0424 Oslo, Norway. Electronic address: britt.stuge@medisin.uio.no.
authors.forename: Britt
authors.initials: B
authors.lastname: Stuge
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006615:Hip / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D010388:Pelvis / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D013848:Thigh / Q000502:physiology*
keywords: External hip rotators; Function; Human cadaver; Length measurements; Moment arm; Range of motion; Strength; Stretch