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Subsidence and retroversion of femoral stem not affected by tobramycin-laden bone cement
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August 2013
Subsidence and retroversion of femoral stem not affected by tobramycin-laden bone cement
Study Type:Therapy
OE Level Evidence:1
Journal Level of Evidence:N/A
The effect of adding tobramycin to Simplex P cement on femoral stem micromotion as measured by radiostereometric analysis: a 2-year randomized controlled trial
Acta Orthop. 2012 Apr;83(2):115-20. doi: 10.3109/17453674.2011.652885. Epub 2012 Jan 17Did you know you're eligible to earn 0.5 CME credits for reading this report? Click Here
Synopsis
28 patients scheduled for total hip arthroplasty were randomized to receive cementing of components with simplex P cement or simplex T cement (which is simplex P cement with 1g tobramycin added by the manufacturer), to determine the effect of the antibiotic on aseptic component loosening. Radiostereometric analysis (RSA) of migration and rotation of the femoral stem component and clinical outcomes of Harris Hip and Western Ontario and McMaster Universities Arthritis Index (WOMAC) scores were examined over 2 years. The results indicated that there were no significant differences between groups at any time and demonstrated that simplex T cement did not adversely affect component loosening and functional outcomes in total hip arthroplasty over 2 years.
Publication Funding Details
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Funding:
Industry funded
Sponsor:
Stryker Orthopaedics
Conflicts:
None disclosed
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.
4/4
Randomization
4/4
Outcome Measurements
3/4
Inclusion / Exclusion
3/4
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?
Since the introduction of antibiotic-laden bone cement, laboratory testing has shown that a 1 gram to 20 gram ratio of antibiotic to bone cement powder has a negligible effect on the mechanical strength and fixation properties of bone cement. However, the appropriateness of the laboratory testing has been questioned, since regulatory standards require testing after 24 hours, which does not necessarily translate into long-term clinical success. Furthermore, no study has directly examined antibiotic additives to bone cement with the risk of aseptic loosening of components, indicating the need for this trial.
What was the principal research question?
Does Simplex T bone cement increase the risk of aseptic component loosening when measured after 2 years?
Study Characteristics
-
Population:
28 patients (30 hips) scheduled for primary total hip arthroplasty with Exeter femoral stems coupled with Trident acetabular cups (Stryker Orthopaedics). Direct lateral or posterior surgical approaches were performed. Tantalum markers were injected into greater trochanter, lesser trochanter, and femoral shaft for detection of migration using RSA (n=25 hips completed follow-up)
Intervention:
Simplex T Group: Patients received cementing of components with tobramycin-laden Simplex P bone cement. (n=14)
Comparison:
Simplex P Group: Patients received cementing of components with Simplex P bone cement, with no antibiotic added by the manufacturer. (n=11)
Outcomes:
Primary outcome was stem subsidence measured with RSA. Secondary outcomes were stem rotation/retroversion (assessed with RSA) and functional scores (assessed with Harris Hip Score and Western Ontario and McMaster Universities Arthritis Index (WOMAC))
Methods:
RCT, Triple blind
Time:
Follow-up was conducted at 6 weeks (RSA exclusive), 6 months, 1, and 2 years.
What were the important findings?
- Mean subsidence after 2 years did not significantly differ between groups, with translation of 0.71mm (SD 0.30) in the control group (Simplex P) and 0.77mm (SD 0.36) in tobramycin-laden group (Simplex T) (Difference 0.06, 95%CI -0.21 to 0.34, p=0.6). Component translation did not significantly differ between groups at the 6 month (p=0.9) or 1 year (p=0.7) follow-up periods, either.
- The two groups did not significantly differ in mean retroversion of component after 2 years: 0.60 degrees (SD 0.72) for Simplex P group versus 0.84 degrees (0.93) for Simplex T group (Difference -0.24, 95%CI -0.94 to 0.47, p=0.5). Progression of retroversion at 6 months (p=0.6) and 1 year (p=0.6) follow-up were not significantly different between groups.
- Differences were not significant between groups in functional outcomes of Harris Hip Scores and WOMAC Scores at any point in the study. (all p-values>0.2).
- Cumulative migrations in the second year indicated substantial distal and moderate posterior migration of the stem, which was similar in both groups.
What should I remember most?
The addition of tobramycin to Simplex P bone cement had no effect on the subsidence and retroversion of the femoral stem, as well Harris hip and WOMAC functional scores, when compared to bone cement without antibiotic after 2 years.
How will this affect the care of my patients?
The results of this trial indicated that antibiotic-laden bone cement is a safe method of cementing in total hip arthroplasty as it did not affect the subsidence and retroversion of the femoral stem component after 2 years. However, further studies with longer follow-up and larger sample sizes are necessary to assess the long-term results.
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