title: CT-based quantification of bone stock in large head metal-on-metal unilateral total hip replacements.
abstract: OBJECTIVE
  To explore ipsilateral and contralateral acetabular roof bone stock density in unilateral large head MoM THA whether there is a significant lower acetabular bone stock in the hip with a metal-on-metal (MoM) total hip replacement compared to the contralateral side. Second part of this study is to examine if there are any associates with regard to potential bone stock density difference.
  
  
  METHODS
  A database of 317 patients with unilateral metal-on-metal (MoM) total hip replacements was set up retrospectively for this study. On computed tomography scans, conducted after a relative short in situ time period averaging 2.8 years, regions-of-interests were drawn in the trabecular bone of the acetabulum to measure average Hounsfield Units (HU). HU differences were calculated and tested by Wilcoxon signed-rank test. Univariate analysis was conducted to examine associates of potential bone loss.
  
  
  RESULTS
  In a population of 317 patients (156 male, 161 female) with an average age of 61.9 ± 7.8, the median HU on the side of the MoM replacement was 123.3 (7.6-375.4). On the contralateral side, median HU was 144.7 (-0.4 to 332.8). The median HU difference was 21.4 after a mean post-operative in situ time of 2.8 years. The Wilcoxon signed-rank test proved a significant difference (p<0.001). Univariate analyses show that the in situ time of the MoM THA has a significant correlation with the bone density difference.
  
  
  CONCLUSIONS
  Results show a significant lower bone density at the acetabular roof at the side of the prosthesis compared with the contralateral side after short in situ time of the MoM THA in patients with unilateral MoM total hip replacements. In our patient population, the in situ time showed a significant association with the acetabular bone density difference. As acetabular roof bone stock measurements are feasible and show temporal decline this could become an important parameter to be used in orthopedic decision making for revision surgery.
authors.affiliation: Department of Radiology, Isala, Dokter van Heesweg 2, 8025 AB Zwolle, The Netherlands. Electronic address: m.f.boomsma@isala.nl.
authors.forename: Martijn F
authors.initials: MF
authors.lastname: Boomsma
authors.affiliation: Department of Radiology, Isala, Dokter van Heesweg 2, 8025 AB Zwolle, The Netherlands. Electronic address: i.slouwerhof@isala.nl.
authors.forename: Inge
authors.initials: I
authors.lastname: Slouwerhof
authors.affiliation: Department of Orthopedic surgery and Traumatology, Isala, Dokter van Heesweg 2, 8025 AB Zwolle, The Netherlands. Electronic address: c.van.lingen@isala.nl.
authors.forename: Christiaan
authors.initials: C
authors.lastname: van Lingen
authors.affiliation: Orthopedic Centre OCON, Geerdinksweg 141 7555 DL, Almelo/Hengelo, The Netherlands. Electronic address: d.pakvis@ocon.nl.
authors.forename: Dean F M
authors.initials: DF
authors.lastname: Pakvis
authors.affiliation: Department of Radiology, Isala, Dokter van Heesweg 2, 8025 AB Zwolle, The Netherlands. Electronic address: j.a.van.dalen@isala.nl.
authors.forename: Jorn A
authors.initials: JA
authors.lastname: van Dalen
authors.affiliation: Department of Innovation and Science, Isala, Dokter van Deenweg 1, 8025 BP Zwolle, The Netherlands. Electronic address: m.a.edens@isala.nl.
authors.forename: Mireille A
authors.initials: MA
authors.lastname: Edens
authors.affiliation: Department of Orthopedic surgery and Traumatology, Isala, Dokter van Heesweg 2, 8025 AB Zwolle, The Netherlands. Electronic address: h.b.ettema@isala.nl.
authors.forename: Harmen B
authors.initials: HB
authors.lastname: Ettema
authors.affiliation: Department of Orthopedic surgery and Traumatology, Isala, Dokter van Heesweg 2, 8025 AB Zwolle, The Netherlands. Electronic address: c.c.p.m.verheyen@isala.nl.
authors.forename: Cees C P M
authors.initials: CC
authors.lastname: Verheyen
authors.affiliation: Department of Radiology, AMC, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Electronic address: m.maas@amc.uva.nl.
authors.forename: Mario
authors.initials: M
authors.lastname: Maas
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging*; D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000379:methods; D015519:Bone Density / Q000502:physiology*; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006622:Hip Prosthesis; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D008670:Metals / Q000737:chemistry; D008875:Middle Aged; D011474:Prosthesis Design; D012086:Reoperation; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D008670:Metals
keywords: Acetabular bone stock; BMD; CT; MoM; Pseudotumor