title: Characteristic loosening of the distally straight cylindrical femoral stem.
abstract: BACKGROUND
  The cemented femoral stem with a distally straight cylindrical shape was designed to fill the distal femoral canal to facilitate higher cement pressurization and stability. We examined the mid-term outcomes of a stem made of titanium alloy and the efficacy of this shape.
  
  
  METHODS
  Four hundred and twenty-nine consecutive patients (505 hips), who underwent a total hip arthroplasty with the distally straight cylindrical stem made of titanium alloy as their primary hip arthroplasty at two institutes, were followed for a minimum 2 years. Loosening was defined as subsidence of over 3 mm, tilting of the femoral component, or fracture of the cement or the stem. A continuous radiolucent line along the entire interface was considered to indicate loosening, too. We examined the interface stresses on the distally straight cylindrical stem compared with a newly manufactured femoral prosthesis with a double-taper design using a finite element model study.
  
  
  RESULTS
  The mean follow-up was 101.3 months after surgery. Thirty patients (30 hips) had aseptic loosening of the stems. Of these 30 hips, 18 had osteolysis, 17 showed subsidence, and 11 had cement fractures at the tip of the stem. These 11 hips had osteolysis and ectasia in the same place: the stem tip. The stem survival rate with stem loosening as the end-point was 94.4 % at 10 years and 66.9 % at 15 years. A finite element model study revealed higher stress around the tip of the cylindrical stem compared with that in the double-taper stem.
  
  
  CONCLUSIONS
  The straight cylindrical stem is potentially subject to early failure because of high stress around the tip of the stem, and showed a characteristic loosening with osteolysis and ectasia at the tip of the stem.
authors: Department of Orthopedic Surgery, Kobe City Medical Center General Hospital, 2-1-1 Minatojima-Minamimachi, Chuo-ku, Kobe, 650-0047, Japan.
authors: Gota
authors: G
authors: Kimura
authors: Eijiro
authors: E
authors: Onishi
authors: Keiichi
authors: K
authors: Kawanabe
authors: So
authors: S
authors: Kazutaka
authors: Masako
authors: M
authors: Tsukanaka
authors: Haruhiko
authors: H
authors: Akiyama
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D001843:Bone Cements / Q000009:adverse effects; D005260:Female; D005269:Femur / Q000601:surgery*; D020342:Finite Element Analysis; D005500:Follow-Up Studies; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D011475:Prosthesis Failure; D014025:Titanium
chemical_list: D001843:Bone Cements; D014025:Titanium