title: Factors affecting hip range of motion in surface replacement arthroplasty.
abstract: BACKGROUND
  Surface replacement arthroplasty aims to re-create normal hip biomechanics; however the pathoanathomy of the hip, prosthetic component design, surgical technique and other factors may have a significant impact on the range of motion restoration attained following surface replacement arthroplasty. However, there is paucity of information on the effect of such factors.
  
  
  METHODS
  A computerized three-dimensional hip model was created from preoperative computerized tomography images of a patient who was scheduled for a surface replacement arthroplasty. The effects of the femoral component size, translation and orientation on the range of motion were analysed as was the effect of increasing the seating depth and modification of the version of the acetabular component.
  
  
  RESULTS
  Increasing the femoral component size led to global improvement in range of motion while translation increased range of motion in one direction but reduced it in the opposite direction. Change in the femoral component orientation had minimal effects on range of motion in comparison to the effect of changes in the version of the acetabular component. Increasing the seating depth of the acetabulum only caused reduced range of motion in internal rotation in 90 degrees flexion.
  
  
  CONCLUSIONS
  To restore hip range of motion, surgeons performing surface replacement arthroplasty should aim to reproduce the natural femoral head-neck offset. Although increasing the femoral component size may achieve this, more acetabular bone will be resected. Knowing the specific zones of impingement of each arc of movement, selective translation of the femoral component or femoral neck osteoplasty can restore femoral neck offset in more critical areas without affecting acetabular bone stock. Over deepening of the acetabulum or leaving rim osteophytes should also be avoided to prevent impingement.
authors.affiliation: Department of Surgery, Montreal University, Maisonneuve-Rosemont Hospital, Montreal, Quebec, Canada H1T 2M4.
authors.forename: Pascal-André
authors.initials: PA
authors.lastname: Vendittoli
authors.forename: Muthu
authors.initials: M
authors.lastname: Ganapathi
authors.forename: Natalia
authors.initials: N
authors.lastname: Nuño
authors.forename: Dominic
authors.initials: D
authors.lastname: Plamondon
authors.forename: Martin
authors.initials: M
authors.lastname: Lavigne
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods*; D003198:Computer Simulation; D006621:Hip Joint / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D007593:Joint Instability / Q000209:etiology* / Q000503:physiopathology* / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011379:Prognosis; D016059:Range of Motion, Articular; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D013499:Surface Properties; D025321:Surgery, Computer-Assisted / Q000379:methods