title: Variability of ischiofemoral space dimensions with changes in hip flexion: an MRI study.
abstract: OBJECTIVE
  The primary aim of this study was to determine if ischiofemoral space (IFS) dimensions vary with changes in hip flexion as a result of placing a bolster behind the knees during magnetic resonance imaging (MRI). A secondary aim was to determine if IFS dimensions vary between supine and prone hip neutral positions.
  
  
  METHODS
  The study employed a prospective design.
  
  
  METHODS
  Sports medicine center within a tertiary care institution.
  
  
  METHODS
  Five male and five female adult subjects (age mean = 29.2, range = 23-35; body mass index [BMI] mean = 23.5, range = 19.5-26.6) were recruited to participate in the study.
  
  
  METHODS
  An axial, T1-weighted MRI sequence of the pelvis was obtained of each subject in a supine position with their hips in neutral and flexed positions, and in a prone position with their hips in neutral position. Supine hip flexion was induced by placing a standard, 9-cm-diameter MRI knee bolster under the subject's knees. The order of image acquisition (supine hip neutral, supine hip flexed, prone hip neutral) was randomized. The IFS dimensions were then measured on a separate workstation. The investigator performing the IFS measurements was blinded to the subject position for each image.
  
  
  METHODS
  The main outcome measurements were the IFS dimensions acquired with MRI.
  
  
  RESULTS
  The mean IFS dimensions in the prone position were 28.25 mm (SD 5.91 mm, standard error mean 1.32 mm). In the supine hip neutral position, the IFS dimensions were 25.1 (SD 5.6) mm. The mean difference between the two positions of 3.15 (3.6) mm was statistically significant (95 % CI of the difference = 1.4 to 4.8 mm, t19= 3.911, p = .001). The mean IFS dimensions in the hip flexed position were 36.9 (SD 5.7) mm. The mean difference between the two supine positions of 11.8 (4.1) mm was statistically significant (95 % CI of the difference = 9.9 to 13.7 mm, t19= 12.716, p < .001).
  
  
  CONCLUSIONS
  Our findings demonstrate that the IFS measurements obtained with MRI are dependent upon patient positioning with respect to hip flexion and supine versus prone positions. This finding has implications when evaluating for ischiofemoral impingement, an entity resulting in hip and/or buttock pain secondary to impingement of the quadratus femoris muscle within a pathologically narrowed IFS. One will need to account for patient hip flexion and supine versus prone positioning when evaluating individuals with suspected ischiofemoral impingement.
authors.affiliation: Department of Radiology, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN, 55905, USA. Johnson.adam@mayo.edu.
authors.forename: Adam C
authors.initials: AC
authors.lastname: Johnson
authors.affiliation: Department of Physical Medicine and Rehabilitation, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN, 55905, USA.
authors.forename: John H
authors.initials: JH
authors.lastname: Hollman
authors.affiliation: Department of Radiology, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN, 55905, USA.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Howe
authors.affiliation: Department of Physical Medicine and Rehabilitation, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN, 55905, USA.
authors.forename: Jonathan T
authors.initials: JT
authors.lastname: Finnoff
mesh_terms: D000328:Adult; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000502:physiology*; D006801:Humans; D007512:Ischium / Q000000981:diagnostic imaging* / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D056888:Patient Positioning; D016684:Prone Position; D011446:Prospective Studies; D016683:Supine Position
keywords: Buttock pain; Hip pain; Ischiofemoral impingement; Ischiofemoral space; Magnetic resonance imaging