title: Total hip arthroplasty with an HPF stem: the radiological findings around the cementless anatomical-shape stem for developmental dysplasia of the hip.
abstract: BACKGROUND
  We developed the HPF stem to suit the Japanese femoral bone marrow canal in developmental dysplasia of the hip. This anatomical-shape cementless stem improves canal occupation by the lateral and anterior flares. We report the clinical performance of the stem and details of the change in the X-rays, especially of the femoral side.
  
  
  METHODS
  We investigated 53 joints of total hip arthroplasty using the stem in 48 cases. The follow-up period was 8 years on average. We checked the Harris hip score (HHS) for clinical assessment. Existence of postoperative thigh pain was also investigated. For radiological assessment, the direction of stem insertion and initial fixation mode immediately after surgery were estimated. At the latest follow-up, we estimated the radiological findings of bone atrophy, spot welds, radiolucent zone, osteolysis, and sinking of the stem over 2 mm. Biological fixation was classified into four types: bone ingrowth, ingrowth suspected, suboptimum, and unstable fixation.
  
  
  RESULTS
  HHS was improved from 44 points before surgery to 92 points at the final follow-up. Light thigh pain appeared temporarily in three joints after surgery. Press-fit was achieved in femurs including total fit in 12 femurs, proximal fit in 4, middle fit in 25, and distal fit in 2. First degree stress shielding was seen in 25 femurs and second degree in 28. Forty-eight joints showed bone-ingrowth fixation, and five joints were ingrowth-suspected.
  
  
  CONCLUSIONS
  The clinical performance was excellent. Total or proximal fit was seen in only 30%. In these joints, cortical hypertrophy at the middle part of the stem and slight proximal bone atrophy appeared frequently, suggesting the stress transmission to the stem middle or distal portion, and there is a limit to the stress shielding evasion by the anatomical-shape stem.
authors.affiliation: Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori, 036-8562, Japan. yoshi-n@cc.hirosaki-u.ac.jp
authors.forename: Yoshihide
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Ohishi
authors.forename: Masaki
authors.initials: M
authors.lastname: Kishiya
authors.forename: Satoshi
authors.initials: S
authors.lastname: Toh
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D001848:Bone Diseases, Developmental / Q000000981:diagnostic imaging* / Q000601:surgery*; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D008875:Middle Aged; D011474:Prosthesis Design; D011859:Radiography