title: The contributing factors of tapered wedge stem alignment during mini-invasive total hip arthroplasty.
abstract: BACKGROUND
  Minimally invasive surgical approaches are widely used for total hip arthroplasty (THA). However, potential problems related to a reduced visual field during surgery, such as implant malposition, neurovascular injury, and poor implant fixation, have been reported. In these situations, a shorter stem is easier to insert in the femoral canal. To evaluate the accuracy of shorter stem orientation, we focused on the accuracy of stem orientation especially in short tapered wedge stems and evaluated the contribution factors of stem malalignment during mini-invasive total hip arthroplasty.
  
  
  METHODS
  One hundred ten hips that underwent THA with a Summit stem (58 hips) (DePuy, Warsaw, IN) as straight stem and TriLock stem (52 hips) (DePuy) as tapered wedge stem were enrolled in this study. For preoperative and postoperative evaluation, a CT scan of the pelvis and knee joint was obtained and was transferred to 3D template software. We compared the alignment of preoperative plan for stem anteversion/valgus/anterior tilt angles and postoperative stem alignment, and the absolute error was defined as the surgical error. To clarify the factors contributing to the malalignment or surgical error, we evaluated postoperative stem alignment and several associated factors. Further, we compared the clinical parameters between two types of stems for analysis of the influence of stem type differences.
  
  
  RESULTS
  The mean absolute value of the alignment error (postoperative stem alignment-preoperative planning alignment) was not changed in the short tapered wedge and straight stems. Sex, age at operation, or original canal anteversion did not affect the accuracy of stem alignment. However, high body mass index (BMI) affected the accuracy of stem alignment. Clinical outcomes were not changed by the difference of stem types.
  
  
  CONCLUSIONS
  The postoperative alignment of short tapered wedge stem was accurate, same as the straight stem during mini-invasive THA, but we need to pay attention when using this in obese patients.
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan. shayashi@med.kobe-u.ac.jp.
authors.forename: Shinya
authors.initials: S
authors.lastname: Hayashi
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan. taka2446@yg8.so-net.ne.jp.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Fujishiro
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan. hashis@med.kobe-u.ac.jp.
authors.forename: Shingo
authors.initials: S
authors.lastname: Hashimoto
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan. kanzaki@med.kobe-u.ac.jp.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kanzaki
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan. kurodar@med.kobe-u.ac.jp.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Kuroda
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan. kurosaka@med.kobe-u.ac.jp.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kurosaka
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D019060:Minimally Invasive Surgical Procedures / Q000295:instrumentation / Q000379:methods*; D011182:Postoperative Care / Q000379:methods; D011474:Prosthesis Design / Q000379:methods*; D016059:Range of Motion, Articular; D016896:Treatment Outcome