title: Improving cup positioning using a mechanical navigation instrument.
abstract: BACKGROUND
  Although surgical navigation reduces the rate of malpositioned acetabular cups in total hip arthroplasty (THA), its use has not been widely adopted. As a result of our perceived need for simple and efficient methods of navigation, we developed a mechanical navigation device for acetabular cup orientation.
  
  
  OBJECTIVE
  We assessed accuracy of cup orientation (mean error of cup inclination and anteversion) of a novel mechanical navigation device, percentage of outliers, length of operation, and compared the results with a series of CT-based computer-assisted THAs.
  
  
  METHODS
  Cup orientation of 70 THAs performed using the mechanical navigation device was compared with a historical control group of 146 THAs performed using CT-based computer navigation. Postoperative cup orientation was measured using a validated two-dimensional/three-dimensional matching method. An outlier was defined outside a range of ± 10° from the planned inclination and/or anteversion.
  
  
  RESULTS
  Using the mechanical navigation device, we observed a decrease in the errors of inclination (1.3° ± 3.4° [range, -6.6° to 8.2°] versus 3.5° ± 4.2° [-12.7° to 6.9°]), errors of anteversion (1.0° ± 4.1° [-8.8° to 9.5°] versus 3.0° ± 5.8° [-11.8° to 19.6°]), percentages of outliers (0% versus 9.6%), and length of operation (112 ± 22 [78-184] minutes versus 132 ± 18 [90-197] minutes) compared with CT-based navigation.
  
  
  CONCLUSIONS
  Compared with CT-based surgical navigation, navigation of acetabular cup orientation using a mechanical device can be performed in less time, lower mean errors, and minimal equipment.
authors.affiliation: Center for Computer Assisted and Reconstructive Surgery, New England Baptist Hospital, Tufts University School of Medicine, 125 Parker Hill Avenue, Suite 545, Boston, MA 02120, USA.
authors.forename: Simon D
authors.initials: SD
authors.lastname: Steppacher
authors.forename: Jens H
authors.initials: JH
authors.lastname: Kowal
authors.forename: Stephen Barry
authors.initials: SB
authors.lastname: Murphy
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D007593:Joint Instability / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000209:etiology / Q000517:prevention & control*; D011475:Prosthesis Failure; D015203:Reproducibility of Results; D012189:Retrospective Studies; D025321:Surgery, Computer-Assisted / Q000379:methods; D055815:Young Adult