title: Effect of angular deformities of the proximal femur on impingement-free hip range of motion in a three-dimensional rigid body model.
abstract: BACKGROUND
  Abnormalities in hip morphology can reduce range of motion (ROM) through femoroacetabular impingement (FAI). Structural issues, such as asphericity of the head-neck junction and regional or global acetabular over-coverage, have been extensively discussed in the literature. The effect of varying femoral neck-shaft angle or torsion on native hip range of motion, however, has been poorly studied. Our hypothesis was that varying neck-shaft angles or femoral torsion affect the impingement-free ROM of the hip and can be treated by femoral osteochondroplasty or acetabular rim resection.
  
  
  METHODS
  A computer-aided design tool and a 3-D model of the hip were used to simulate incremental deformation of the proximal femur. Neck-shaft angles ranging from 90-160°, and femoral torsions ranging from -15-50°, were created. Femoroacetabular impingement was defined as bone-to-bone contact within physiological hip ROM, as described in the literature.
  
  
  CONCLUSIONS
  With decreasing neck-shaft angles (≤110°) or femoral torsion (≤10°), impingement occurred at the anterosuperior rim area. With increasing neck-shaft angles (≥135°) and femoral torsion (≥25°) posteroinferior or ischiofemoral impingement occurred. Acetabular rim trimming could compensate for neck-shaft angles ≥90° and femoral torsion ≥-5°, without creating acetabular dysplasia. Femoral impingement zones in low neck-shaft and low femoral torsion angles were found to be distal to the head-neck junction at the mid-cervical region. The cross-sectional area at this neck region was the smallest, and thus osteochondroplasty at this location may prove potentially dangerous.
authors.affiliation: Balgrist University Hospital, Zürich - Switzerland.
authors.forename: Faustine
authors.initials: F
authors.lastname: Vallon
authors.affiliation: Balgrist University Hospital, Zürich - Switzerland.
authors.forename: Amélie
authors.initials: A
authors.lastname: Reymond
authors.affiliation: Balgrist University Hospital, Zürich - Switzerland.
authors.forename: Philipp
authors.initials: P
authors.lastname: Fürnstahl
authors.affiliation: Balgrist University Hospital, Zürich - Switzerland.
authors.forename: Patrick O
authors.initials: PO
authors.lastname: Zingg
authors.affiliation: Hospital of the University of Pennsylvania, Philadelphia - USA.
authors.forename: Atul F
authors.initials: AF
authors.lastname: Kamath
authors.affiliation: Balgrist University Hospital, Zürich - Switzerland.
authors.forename: Jess
authors.initials: J
authors.lastname: Snedeker
authors.affiliation: Balgrist University Hospital, Zürich - Switzerland.
authors.forename: Claudio
authors.initials: C
authors.lastname: Dora
mesh_terms: D000328:Adult; D002102:Cadaver; D057925:Femoracetabular Impingement / Q000209:etiology* / Q000503:physiopathology*; D005269:Femur; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D066230:Patient-Specific Modeling; D016059:Range of Motion, Articular / Q000502:physiology*