title: Relationships Between Severity of Deformity and Impingement in Slipped Capital Femoral Epiphysis.
abstract: BACKGROUND
  In situ pinning, a low-risk treatment for slipped capital femoral epiphysis (SCFE), leaves the slipped femoral head in place and may reduce range of motion (ROM) and cause impingement. It is unclear when a more complex surgery should be considered, because the relationships between severity, slip stability, remodeling, impingement, and ROM are unknown.
  
  
  OBJECTIVE
  (1) Do more severe acute SCFE deformities (no bony remodeling) result in a greater loss of flexion ROM?(2) Does the presence or location of impingement on the pelvis vary with severity of acute SCFE deformity?
  
  
  METHODS
  We developed a 3D geometric model of acute SCFE deformity from 1 computed tomography scan of a normal adolescent hip. Ethics board approval was obtained from our institution. Bone models were created from the segmented pelvis, epiphysis, and subphyseal femur.In total, 3721 SCFE deformities were simulated by combining posterior and inferior slips in the axial and coronal planes, respectively. Southwick angles were estimated from a frog-leg lateral projection. Deformities were divided into mild (0 to 30 degrees), moderate (30 to 60 degrees), and severe (≥60 degrees) Southwick groups. Each joint was flexed in combination with internal/external rotation until contact occurred. A total of 121 ROM trials, with different degrees of internal/external rotation (0 to 90 degrees at 1.5-degree steps) were performed for each deformity.
  
  
  RESULTS
  In total, 3355 simulated SCFE deformities (363 could not be rotated out of impingement) were analyzed.Increasing slip severity reduced flexion ROM across the range of internal/external rotation. Contact occurred for most mild deformities, and for all moderate and severe deformities in at least 1 ROM trial. Impingement was observed mainly on the anterosuperior aspect of the acetabulum.
  
  
  CONCLUSIONS
  Increasing slip severity in acute SCFE reduced flexion and increased incidence of impingement, primarily occurring on the anterosuperior aspect of the acetabulum. The impingement patterns observed are consistent with damaged cartilage locations seen in clinical literature.
  
  
  CONCLUSIONS
  In this experimental model, moderate and severe acute slips in SCFE lead to reduced ROM and impingement with the acetabulum. This suggests that in situ pinning may result in impingement of moderate and severe acute SCFE slips.
authors.affiliation: *Centre for Hip Health and Mobility Departments of †Engineering Physics §Orthopaedics ∥Mechanical Engineering, University of British Columbia ‡BC Children's Hospital, Vancouver, BC, Canada.
authors.forename: Carly E
authors.initials: CE
authors.lastname: Jones
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Cooper
authors.forename: Jonathan
authors.initials: J
authors.lastname: Doucette
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Buchan
authors.forename: David R
authors.initials: DR
authors.lastname: Wilson
authors.forename: Kishore
authors.initials: K
authors.lastname: Mulpuri
authors.forename: Agnes G
authors.initials: AG
authors.lastname: d'Entremont
mesh_terms: D000293:Adolescent; D003198:Computer Simulation; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008953:Models, Anatomic; D016059:Range of Motion, Articular; D012720:Severity of Illness Index; D060048:Slipped Capital Femoral Epiphyses / Q000150:complications / Q000503:physiopathology*; D014057:Tomography, X-Ray Computed