title: The influence of stem offset and neck shaft angles on the range of motion in total hip arthroplasty.
abstract: OBJECTIVE
  To evaluate the influence of stem offset and neck shaft angles on the range of motion before component impingement (ROMCI) and bony impingement (ROMBI), and the types of impingement in total hip arthroplasty (THA).
  
  
  METHODS
  Using the computed tomography data of 101 patients who underwent THA, three-dimensional dynamic motion analysis was performed using a modular implant (Kinectiv(®) stem) that enabled adjustment of offset and leg length independently. We defined offset as horizontal offset (HO) and leg length as vertical offset (VO), and measured the ROMCI and ROMBI in flexion (Flex), internal rotation (Int-R) and external rotation (Ext-R) with the configuration of each horizontal/vertical offset.
  
  
  RESULTS
  We found that HO lengthening increased the ROMCI and ROMBI in Flex and Int-R by delaying bony impingement, although excessive lengthening had minimal effect. On the contrary, VO lengthening decreased the ROMCI and ROMBI in Flex and ROMCI in Int-R. As for Ext-R, VO lengthening had positive effects on the ROMCI and ROMBI, whereas lengthening of HO had negative effects on the ROMCI and ROMBI.
  
  
  CONCLUSIONS
  We demonstrated that the appropriate long offset with a low shaft angle increased the ROM in Flex and Int-R, and a high neck shaft angle increased the ROM in Ext-R. We should use implants properly in accordance with the types of impingement for avoiding dislocations in THA.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551, Japan. readymade_jpn@yahoo.co.jp.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Shoji
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551, Japan.
authors.forename: Takuma
authors.initials: T
authors.lastname: Yamasaki
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551, Japan.
authors.forename: Soutarou
authors.initials: S
authors.lastname: Izumi
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Hachisuka
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551, Japan.
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Ochi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation* / Q000379:methods; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000503:physiopathology / Q000601:surgery; D010020:Osteonecrosis / Q000503:physiopathology / Q000601:surgery; D016059:Range of Motion, Articular / Q000502:physiology*; D014057:Tomography, X-Ray Computed
keywords: Dislocation; Impingement; Neck shaft angle; Offset; Three-dimensional motion analysis; Total hip arthroplasty