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Smaller migration with monoblock versus modular tibial component in uncemented TKA
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August 2017
Smaller migration with monoblock versus modular tibial component in uncemented TKA
Study Type:Therapy
OE Level Evidence:2
Journal Level of Evidence:N/A
Monoblock versus modular polyethylene insert in uncemented total knee arthroplasty
Acta Orthop. 2016 Dec;87(6):607-614Did you know you're eligible to earn 0.5 CME credits for reading this report? Click Here
Synopsis
67 patients scheduled for total knee arthroplasty were randomized to receive either a monoblock or modular tibial component. Patients were assessed for component migration over the first 24 months postoperatively, as well as clinical scores in the same time frame. Results demonstrated significantly lower maximum total point motion in the monoblock group compared to the modular group after 24 months. As well, single dimension migration demonstrated significantly lower subsidence in the monoblock group compared to the modular group. Clinical scores did not significantly differ between groups.
Publication Funding Details
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Funding:
Industry funded
Sponsor:
Zimmer; Gentofte Hospital, Copenhagen (non-industry)
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
3/4
Outcome Measurements
3/4
Inclusion / Exclusion
2/4
Therapy Description
4/4
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?
Aseptic loosening of tibial components remains a primary concern regarding the overall survivorship of total knee arthroplasty implants. Polyethylene wear has been identified as a potential contributor to aseptic loosening. Recently, there has been debate whether tibial component designs, specifically monoblock versus modular polyethylene components, may differ in their respective wear and migration profiles.
What was the principal research question?
In total knee arthroplasty, does the use of a monoblock tibial component result in significantly lower component migration within the first 2 years postoperatively when compared to a modular polyethylene component?
Study Characteristics
-
Population:
67 patients, under the age of 70, scheduled for total knee arthroplasty due to osteoarthritis were included. All cases were performed using an uncemented, cruciate-retaining NexGen total knee system (Zimmer) with a cemented, all-poly patellar component.
Intervention:
Monoblock group: Patients received the monoblock NexGen Trabecular Metal technology tibial component. Tantalum markers were inserted in the tibial bone and polyethylene portion of the tibial component to facilitate radiostereometric analysis (RSA) during follow-up. (33 randomized; 26 analyzed) (Mean age: 62 [47-70])
Comparison:
Modular group: Patients received the modular NexGen Trabecular Metal technology tibial component. Tantalum markers were inserted in the tibial bone and polyethylene portion of the tibial component to facilitate RSA during follow-up. (n=34 randomized; 27 analyzed) (Mean age: 61 [44-70])
Outcomes:
The primary outcome was tibial component migration measured via maximum total point motion on RSA. Secondary outcomes included tibial component translation and rotation individually in the x-, y- and z-axes, and clinical outcome via the Knee Society Score and EuroQoL 5-dimension questionnaire (EQ-5D).
Methods:
RCT
Time:
Follow-up was scheduled for 3, 6, 12, and 24 months postoperatively.
What were the important findings?
- There was no significant difference in MTPM between the monoblock group and the modular group after 3 months (0.58mm [95%CI 0.43-0.72] vs. 0.85mm [0.65-1.09]; p=0.2) or 6 months (0.66mm [0.44-0.77] vs. 0.98mm [0.74-1.26];p=0.1); MTPM was significantly lower in the monoblock group compared to the modular group at 12 months (0.65mm [0.46-0.78] vs. 1.01mm [0.81-1.28]; p=0.02) and 24 months (0.72mm [0.53-0.82 vs. 1.15mm [0.90-1.37]; p=0.02).
- In individual axes for translation, no significant differences between groups in anterior-posterior translation or lateral-medial translation of the tibial component were noted at any follow-up. In contrast, beginning at 6 months, significantly smaller superior-inferior translation of the tibial component was observed in the monoblock group compared to the modular group, and significance was maintained after 24 months (-0.18mm [-0.24, -0.07] vs. -0.38mm [-0.54, -0.23]; p=0.02).
- In individual axes for rotation, no significant differences between groups were observed in either anterior-posterior tilt, varus-valgus tilt, or internal-external rotation of the component at any follow-up time point (all p>0.05).
- No significant differences between groups were observed in Knee Society Knee scores, Knee Society Function scores, or EQ-5D scores at any follow-up time point (all p>0.05).
What should I remember most?
In uncemented total knee arthroplasty, the use of a monoblock tibial component was associated with significantly smaller maximum total point motion after 24 months, and, specifically, significantly lower superior-inferior translation of the tibial component after 24 months when compared to a modular polyethylene tibial component. No significant between-group differences were noted in x- and z-axis translation of the component, x-, y, and z-axis rotation of the component, or clinical scores after 24 months.
How will this affect the care of my patients?
The results of this study suggest that monoblock tibial components may result in a statistically significantly smaller degree of migration, as assessed via maximum total point motion, from 12 to 24 months after uncemented total knee arthroplasty when compared to modular polyethylene tibial components. Nonetheless, there did not appear to be any clinical impact of the difference observed between groups within this time frame. Follow-up studies are needed to determine if the observed difference in migration has any implication on the incidence of aseptic loosening and component survivorship in the long-term.
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