Clinical Orthopaedics and Related Research®

, Volume 469, Issue 9, pp 2590–2597

Insufficient Acetabular Version Increases Blood Metal Ion Levels after Metal-on-metal Hip Resurfacing

  • Alister J. Hart
  • John A. Skinner
  • Johann Henckel
  • Barry Sampson
  • Fabiana Gordon
Clinical Research

DOI: 10.1007/s11999-011-1930-y

Cite this article as:
Hart, A.J., Skinner, J.A., Henckel, J. et al. Clin Orthop Relat Res (2011) 469: 2590. doi:10.1007/s11999-011-1930-y

Abstract

Background

Many factors affect the blood metal ion levels after metal-on-metal (MOM) hip arthroplasty. The main surgically adjustable variable is the amount of coverage of the head provided by the cup which is a function of the inclination and version angles. However, most studies have used plain radiographs which have questionable precision and accuracy, particularly for version and large diameter metal heads; further, these studies do not simultaneously assess version and inclination. Thus the relationship between version and blood metal ions levels has not been resolved.

Questions/purposes

We determined whether cup inclination and version influence blood metal ion levels while adjusting for age at assessment, gender, body mass index, horizontal femoral offset, head size, manufacturer hip type, and Oxford hip score.

Patients and Methods

We prospectively followed 100 individuals (51 females, 49 males) with unilateral MOM hip resurfacing who underwent clinical assessment, CT scanning, and blood metal ion measurement. Multiple regression analysis was used to determine which variables were predictors of blood metal ion levels and to model the effect of these variables.

Results

Only cup inclination, version angles, and gender influenced blood cobalt or chromium levels. Cobalt and chromium levels positively correlated with inclination angle and negatively correlated with version angle. The effect of changes in version angle was less than for inclination angle. Based on our observations, we developed a formula to predict the effect of these parameters on metal ion levels.

Conclusions

Our data suggest insufficient cup version can cause high blood metal ions after MOM hip arthroplasty. We were unable to show that excessive version caused high levels.

Level of Evidence

Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Copyright information

© The Association of Bone and Joint Surgeons® 2011

Authors and Affiliations

  • Alister J. Hart
    • 1
  • John A. Skinner
    • 2
  • Johann Henckel
    • 1
  • Barry Sampson
    • 3
  • Fabiana Gordon
    • 4
  1. 1.Department of Orthopaedic SurgeryImperial College, Charing Cross Hospital CampusLondonUK
  2. 2.Department of Orthopaedic SurgeryRoyal National Orthopaedic Hospital, University College LondonLondonUK
  3. 3.Department of Clinical ChemistryImperial College and Imperial College Healthcare NHS Trust, Charing Cross Hospital CampusLondonUK
  4. 4.Statistical Advisory ServiceImperial College, South Kensington CampusLondonUK