title: A novel non-invasive mechanical technique of cup and stem placement and leg length adjustment in total hip arthroplasty for dysplastic hips.
abstract: OBJECTIVE
  This study assessed the accuracy of cup and stem positioning and limb length adjustment for developmental dysplasia of the hip (DDH) using our new mechanical technique compared with imageless navigation or a computed tomography (CT)-based navigation system.
  
  
  METHODS
  One hundred thirteen primary total hip arthroplasties (THAs) for DDH were evaluated. At pre-operative positioning, patients were placed in a precise lateral decubitus position by tilting the surgical table using simple ready-made devices (two shot pipe, metal chain, level gauge and goniometer). During surgery, cups were intentionally placed at 45° inclination and 15° anteversion on radiograph by using a level gauge and goniometer.
  
  
  RESULTS
  Cup inclination was 44.2° ± 3.4° (range, 32.0-51.2°), cup anteversion was 19.6° ± 6.1° (range, 3.0-33.1°), stem alignment was 0.04° ± 0.8° valgus (range, 2.1° varus to 1.9° valgus), and leg length discrepancy was -0.37 ± 3.7 mm (range, -12.8 to 8.8 mm) in postoperative radiographs. Outliers (outside ±10° from intentional position) occurred in 15 cases (13.3 %) in inclination or anteversion. Postoperative dislocation did not occur in any cases.
  
  
  CONCLUSIONS
  Cup and stem positioning in THAs with our new mechanical technique yielded satisfactory results compared with previously reported imageless navigation or CT-based navigation. Our results were superior with regard to being non-invasive and low cost and involving minimum radiation exposure.
authors.affiliation: Orthopaedic Surgery, Makiyama Central Hospital, 13-13 Hatsunechou, Tobata-ku, Kitakyushu, 804-0066, Japan, muraya-t@clnc.uoeh-u.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Murayama
authors.forename: Hideo
authors.initials: H
authors.lastname: Ohnishi
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Mori
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Okazaki
authors.forename: Kenji
authors.initials: K
authors.lastname: Sujita
authors.forename: Akinori
authors.initials: A
authors.lastname: Sakai
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D005260:Female; D006618:Hip Dislocation, Congenital / Q000601:surgery*; D006621:Hip Joint / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D007870:Leg Length Inequality / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D056888:Patient Positioning; D011184:Postoperative Period; D011446:Prospective Studies; D025321:Surgery, Computer-Assisted / Q000379:methods; D014057:Tomography, X-Ray Computed