title: Periacetabular bone changes after uncemented total hip arthroplasty evaluated by quantitative computed tomography.
abstract: BACKGROUND
  There are few dual X-ray absorptiometry (DXA) studies on periacetabular bone density changes after cup implantation. This study was designed to analyze the load-transfer mechanism and stress pattern of periacetabular cortical and cancellous bone after implantation of a ihemispherical titanium alloy press-fit cup with alumina-alumina pairing in vivo. We introduced a novel method of computed tomography (CT)-assisted osteodensitometry.
  
  
  METHODS
  We investigated 26 hips (26 patients) with osteoarthritis using conventional sequential CT examinations performed within the first 10 days after implantation, and after a mean period of 1.1 years postoperatively. Bone density of full, cancellous and cortical bone (mgCaHA/mL) was measured.
  
  
  RESULTS
  At the time of follow-up, the mean bone density values of the cortical bone cranial to the cup increased by 3.6% (p = 0.03) while the cancellous bone density decreased by 18%. Cancellous bone loss was greater in the region ventral to the cup (-35%) than in the dorsal region (-30%). Cortical bone density decreased ventral to the cup (-6.4%). All these changes were statistically significant. The bone density changes in the dorsal cortical region were not significant.
  
  
  CONCLUSIONS
  The method presented is an excellent tool for detailed measurement of bone density changes around the cup after total hip arthroplasty, and allows a thorough assessment of stress shielding phenomena in vivo. The hemispherical titanium alloy press-fit cup is a rigid implant which stress shields cancellous bone and enhances load transfer to the cranial cortical bone. Further investigations will demonstrate the impact these factors have on the long-term results of the implant, and may allow a type-related predictable prognosis of the longevity of the prosthesis.
authors.affiliation: Department of Orthopaedic Surgery, University of Erlangen-Nuremberg, Erlangen, Germany. ltzmll@aol.com
authors.forename: Lutz Arne
authors.initials: LA
authors.lastname: Mueller
authors.forename: Alexander
authors.initials: A
authors.lastname: Kress
authors.forename: Tobias
authors.initials: T
authors.lastname: Nowak
authors.forename: David
authors.initials: D
authors.lastname: Pfander
authors.forename: Rocco Paolo
authors.initials: RP
authors.lastname: Pitto
authors.forename: Raimund
authors.initials: R
authors.lastname: Forst
authors.forename: Rainer
authors.initials: R
authors.lastname: Schmidt
mesh_terms: D015502:Absorptiometry, Photon; D000077:Acetabulum / Q000000981:diagnostic imaging / Q000473:pathology*; D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D015519:Bone Density; D005260:Female; D005500:Follow-Up Studies; D006622:Hip Prosthesis / Q000009:adverse effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D011379:Prognosis; D011446:Prospective Studies; D011474:Prosthesis Design; D014057:Tomography, X-Ray Computed / Q000379:methods