title: Imageless navigation in hip resurfacing: avoiding component malposition during the surgeon learning curve.
abstract: BACKGROUND
  Studies suggest that hip arthroplasty procedures performed in specialty hospitals or by physicians in practices with a high surgical volume are associated with a decreased rate of adverse outcomes related to component malpositioning. Little is known, however, about the influence of imageless computer navigation systems on the procedural experience of the surgeon and the subsequent alignment of implants in the setting of hip resurfacing arthroplasty.
  
  
  METHODS
  Seventy-one consecutive hip resurfacing arthroplasties in which the components were placed with use of computer-assisted navigation were reviewed retrospectively. Intraoperative femoral and acetabular component parameters were compared with postoperative radiographic alignment values. Within this single surgeon series, operative time, intraoperative cup inclination and femoral stem-shaft angles, and postoperative cup inclination and femoral stem-shaft angles were measured and compared over the course of three discrete, sequential operative time periods. Patient demographic data and surgical parameters, including blood loss, surgical approach, and anesthesia time, were recorded.
  
  
  RESULTS
  No significant difference was seen between the intraoperative and postoperative cup inclination angles. A significant difference was noted between the intraoperative and postoperative femoral stem-shaft angles; however, the mean angles in all groups had a valgus orientation when compared with the mean native neck angles. Over three sequential operative time periods, computer-assisted navigation produced consistent values with regard to intraoperative cup inclination (43 degrees , 44 degrees , and 40 degrees ) and postoperative radiographic alignment of the cup (46 degrees , 44 degrees , and 43 degrees ) and femoral stem (148 degrees , 147 degrees , and 144 degrees ), despite different levels of surgeon experience. Operative times significantly decreased with surgeon experience, showing the largest decrease after the first sequence interval (110, ninety-eight, and ninety-five minutes, respectively). There was a significant difference with evolving surgeon experience concerning intraoperative stem placement (144 degrees , 142 degrees , and 138 degrees , respectively) despite the mean values remaining well-clustered. No femoral notching occurred throughout the series.
  
  
  CONCLUSIONS
  Computer-assisted navigation is a dependable and accurate method of positioning hip resurfacing components during arthroplasty, as measured by cup inclination, and a reliable technique for valgus stem placement and avoidance of notching. Furthermore, computer navigation allows for consistency of component alignment independent of procedural experience.
authors.affiliation: Department of Orthopaedic Surgery, University of Cincinnati, 224 Leather Leaf Lane, Lebanon, OH 45036, USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Romanowski
authors.forename: Michael L
authors.initials: ML
authors.lastname: Swank
mesh_terms: D000328:Adult; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D002983:Clinical Competence; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D011446:Prospective Studies; D012189:Retrospective Studies; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013997:Time Factors