Resurfacing hip arthroplasty: High chromium concentrations observed at 24 months .
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OrthoEvidence Journal (OE Journal) - ACE Report
OE Journal. 2013;1(8):3 Acta Orthop. 2011 Oct;82(5):559-66Exclusive Author Interview
Dr. Van Susante discusses metal ion concentrations following hip resurfacing and conventional metal-on-metal arthroplasty
82 patients requiring a total hip replacement were randomized to receive a resurfacing hip arthroplasty or a conventional uncemented metal-on-metal total hip arthroplasty. The objective of this trial was to compare both functional outcomes and cobalt and chromium blood levels. The results indicate that patients who underwent resurfacing arthroplasty had higher chromium concentrations for up to 24 months post-surgery. Additionally, cobalt concentrations were higher in the blood for 6 months. Both groups demonstrated improvements in functional outcome measurements 24 month postoperatively.
Was the allocation sequence adequately generated?
Was allocation adequately concealed?
Blinding Treatment Providers: Was knowledge of the allocated interventions adequately prevented?
Blinding Outcome Assessors: Was knowledge of the allocated interventions adequately prevented?
Blinding Patients: Was knowledge of the allocated interventions adequately prevented?
Was loss to follow-up (missing outcome data) infrequent?
Are reports of the study free of suggestion of selective outcome reporting?
Were outcomes objective, patient-important and assessed in a manner to limit bias (ie. duplicate assessors, Independent assessors)?
Was the sample size sufficiently large to assure a balance of prognosis and sufficiently large number of outcome events?
Was investigator expertise/experience with both treatment and control techniques likely the same (ie.were criteria for surgeon participation/expertise provided)?
Yes = 1
Uncertain = 0.5
Not Relevant = 0
No = 0
The Reporting Criteria Assessment evaluates the transparency with which authors report the methodological and trial characteristics of the trial within the publication. The assessment is divided into five categories which are presented below.
3/4
Randomization
2/4
Outcome Measurements
4/4
Inclusion / Exclusion
4/4
Therapy Description
3/4
Statistics
Detsky AS, Naylor CD, O'Rourke K, McGeer AJ, L'Abbé KA. J Clin Epidemiol. 1992;45:255-65
The Fragility Index is a tool that aids in the interpretation of significant findings, providing a measure of strength for a result. The Fragility Index represents the number of consecutive events that need to be added to a dichotomous outcome to make the finding no longer significant. A small number represents a weaker finding and a large number represents a stronger finding.
Why was this study needed now?
In the treatment of advanced hip osteoarthritis, hip resurfacing arthroplasty is considered the best option. Although this procedure is hypothesized to have several advantages in comparison to conventional total hip arthroplasty; these benefits have not been confirmed by scientific evidence. Only one RCT evaluated the clinical outcomes observed with resurfacing arthroplasty compared to metal-on-metal hip arthroplasty. Results from this study demonstrate improvements in functional outcomes with the resurfacing procedure; however, confounding factors may be affecting the result. In addition, there is also concern regarding toxic effects from increased metal ions (cobalt and chromium) in the blood. The previous RCT only examined functional outcomes; therefore, a trial evaluating blood levels of cobalt and chromium was merited.
What was the principal research question?
What are the effects of a resurfacing total hip arthroplasty on functional outcomes and cobalt and chromium blood levels when compared to a conventional uncemented metal-on-metal total hip arthroplasty, measured over a 24 month period?
- All functional outcome measures (HHS, OHS, UCLA, SF-12) improved following surgery and was maintained up until 24 months, in both treatment groups (p<0.001).
- At 12 and 24 months, those in the resurfacing group had a median UCLA activity score of 8, compared to a score of 7 in the conventional group (p<0.05). Despite the randomization, patients in the resurfacing group had higher UCLA scores at baseline.
- At 24 months, the OHS was a median 13 in resurfacing patients compared to 16 in the conventional group (p<0.05).
- There was no statistically significant difference in patient satisfaction between the groups, at the 24 month follow up. However, patients in the resurfacing group were more satisfied than those in the conventional group, at 12 months (p=0.01, r=-0.30).
- Cobalt concentrations were higher in the patients undergoing resurfacing arthroplasty compared to those in the conventional arthroplasty group at both 3 months (p<0.001, r=-0.50) and 6 months (p=0.006, r=-0.35).
- Chromium concentrations were significantly higher in the resurfacing arthroplasty group, and this trend was observed for all time points up until 24 months (p<0.001, r=-0.50).
- Two patients in the conventional arthroplasty group had an insert exchange for recurrent dislocation. One patient in the resurfacing group had a femoral component revision due to early aseptic loosening. No pseudotumors were encountered in either group.
What should I remember most?
The levels of chromium and cobalt in the blood were greater in the resurfacing group at the 6 month follow-up, The increase concentration of chromium was maintained for all follow-ups, where as the increase concentration of cobalt diminished. Patients in the resurfacing group had superior UCLA, OHS scores, and satisfaction at some follow-up periods.
How will this affect the care of my patients?
Studies with longer follow-up periods are required to more accurately determine the benefits and risks associated with the resurfacing arthroplasty compared to the conventional arthroplasty.
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