Radiostereometric analysis: no additional benefit of Unique femoral stem compared to AGB-I
Small and similar amounts of micromotion in an anatomical stem and a customized cementless femoral stem in regular-shaped femurs. A 5-year follow-up randomized RSA studyActa Orthop. 2014 Apr;85(2):152-8
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100 patients with primary or secondary osteoarthritis were randomized to investigate any additional benefits associated with the use of the Unique customized stem compared with the conventional ABG-I stem. Patients were evaluated over 5 years using radiostereometric (RSA). The evidence presented in this study revealed no improvement in long-term mechanical stability associated with the Unique stem. It is important to note that no included patients presented with abnormal geometry of the upper femur for which the custom stems are developed.
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.
Inclusion / Exclusion
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?
Micromovements along the implant-bone interface are associated with loosening of uncemented femoral stem implants. Generally speaking, a 40 micrometer interfacial motion contributes to partial bone ingrowth, and those exceeding 150 micrometers completely disrupts ingrowth. Mechanical stability of the implant is influenced by patient- and implant-specific factors, and uncemented customized femoral stems are hypothesized to promote superior mechanical fixation compared to standard implants. This study was needed to conduct radiostereometric (RSA) follow-up on a 5 year RCT that evaluated the Unique customized stem (Scandinavian Customized Prosthesis [SCP]), against a conventional ABG-I stem.
What was the principal research question?
What is the comparative migration between the use of the Unique customized stem, and the conventional ABG-I stem, as evaluated using radiostereometric (RSA) over 5 years?
What were the important findings?
- Motion between the 2 types of stems were comparable (all p>0.05): The median subsidence was -0.03mm for the ABG-I stem compared to -0.13mm for the Unique stem (p=0.15). Mean retroversion was 0.15 degrees compared to -0.08 degrees in the ABG-I and Unique stems respectively (p=0.41).
- Time was noted as a factor that was significantly related to: translation along the y (p=0.02) and z (p<0.01) axes and rotation around the x (p=0.03) and z (p=0.01) axes.
- A single Unique stem subsided 5.3mm within the first year and then stabilized. Further analysis revealed no loosening.
- Mean preoperative Merle d’Aubigne score was 11 in the ABG-I group compared to 10 in the Unique groups. At final follow-up of 5 years, mean scores in both groups was 17.
- Preoperative pain decreased from 6.5 to 1.1 in the ABG-I group and from 6.5 to 1.0 in the Unique group. Satisfaction was 1.1 and 0.7 respectively at 5 years.
- No hips were revised over the 5 years; there were, however, 5 complications: ABG –I group had 2 instances of DVT and 2 early dislocations. The Unique group had 1 common peroneal nerve dysfunction.
What should I remember most?
Radiostereometric analysis (RSA) between the use of the Unique customized stem ((Scandinavian Customized Prosthesis (SCP)), and the conventional ABG-I stem revealed no improvement in long-term mechanical stability associated with the Unique stem.
How will this affect the care of my patients?
The evidence presented in this study indicated no additional benefits associated with the use of the Unique customized stem ((Scandinavian Customized Prosthesis (SCP)). It is important to note that none of the included patients presented with abnormal geometry of the upper femur for which the custom stems were developed.
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