title: Soft tissue dissection in placement of reference markers during computer aided total hip arthroplasty.
abstract: OBJECTIVE
  During computer navigated hip arthroplasty, impingement of soft tissues on reference markers (RMs) may cause errors in the navigation process. The aim of this study was to investigate the effect of such soft tissue impingement during limb movement on the stability of different RMs.
  
  
  METHODS
  The stability of one- and two-screw RM systems inserted using three different levels of soft tissue dissection was analyzed in fresh cadaver lower limbs. All tests were done with RMs inserted in both the distal-anterior femur and the distal-lateral femur.
  
  
  RESULTS
  Rotations of less than 0.15 degrees and translations of less than 0.4 mm occurred in most test combinations. The combination that showed the greatest instability was when a stab incision was used to insert a screw in the distal-lateral femur (translation: 0.73 +/- 0.05 mm; rotation: 0.25 +/- 0.05 degrees ) (p < 0.001). This instability occurred in both single- and double-screw RMs (p = 0.21).
  
  
  CONCLUSIONS
  Reference markers can be placed in the anterior distal femur through stab incisions without resulting in significant impingement during limb movement. When RMs are placed in the lateral distal femur, impingement may occur from the fascia lata. Release of the fascia lata 1 cm either side of the screw prevents significant impingement. Wide skin incision is unnecessary in any location.
authors.affiliation: Wrightington Hospital, Wigan, and University of Manchester, Manchester, United Kingdom. tim@timboard.co.uk
authors.forename: T N
authors.initials: TN
authors.lastname: Board
authors.forename: D
authors.initials: D
authors.lastname: Kendoff
authors.forename: M
authors.initials: M
authors.lastname: Citak
authors.forename: C
authors.initials: C
authors.lastname: Krettek
authors.forename: T
authors.initials: T
authors.lastname: Hüfner
mesh_terms: D019644:Arthroplasty, Replacement, Hip; D001863:Bone Screws; D002102:Cadaver; D006621:Hip Joint / Q000601:surgery*; D006801:Humans; D016059:Range of Motion, Articular; D012399:Rotation; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*