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Similar long-term clinical and radiological outcomes with mobile- or fixed-bearings in TKA
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March 2014
Similar long-term clinical and radiological outcomes with mobile- or fixed-bearings in TKA
Study Type:Therapy
OE Level Evidence:2
Journal Level of Evidence:N/A
Mobile vs fixed-bearing total knee arthroplasty performed by a single surgeon: a 4- to 6.5-year randomized, prospective, controlled, double-blinded study
J Arthroplasty. 2013 Dec;28(10):1712-6. doi: 10.1016/j.arth.2013.01.003. Epub 2013 Mar 23.Did you know you're eligible to earn 0.5 CME credits for reading this report? Click Here
Synopsis
56 patients undergoing unilateral total knee arthroplasty (TKA) were randomized to compare the clinical and radiological outcomes, as well as the safety, of two types of bearing systems. Patients underwent TKA using either a mobile- or fixed-bearing system (Scorpio + Single Axis and Duracon systems, respectively). Results at a final follow-up of 4-6.5 years indicated that most of the clinical outcomes were similar when TKA was performed using either a mobile- or fixed-bearing system, with the exception of range of motion, which favoured the mobile-bearing group. Radiological outcomes, patient satisfaction and the incidence of complications were also statistically similar between groups. Furthermore, the survival rate was 100% using both techniques.
Publication Funding Details
+
Funding:
Non-funded
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.
2/4
Randomization
3/4
Outcome Measurements
4/4
Inclusion / Exclusion
4/4
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?
Total knee arthroplasty (TKA) procedures have traditionally used prostheses comprised of fixed bearings. With the hopes of improving knee kinematics post-surgery, researchers have proposed the use of mobile bearings as an alternative in these procedures. Many studies comparing this relationship (i.e. mobile vs. fixed bearings) have found no significant differences in the clinical and radiological outcomes following TKA. Furthermore, there are no follow-up studies comparing the Scorpio + Single Axis system for mobile-bearing knee prostheses to the Duracon system for fixed-bearing knee prostheses (both Stryker Howmedica Osteonics, Allendale, New Jersey). This study compared mid-term clinical and radiological results obtained using the Duracon versus the Scorpio + Single Axis system.
What was the principal research question?
Does a mobile-bearing system (Scorpio + Single Axis system) yield better clinical and radiological outcomes, when compared to a fixed-bearing system (Duracon system), in patients undergoing total knee arthroplasty, at a 4- to 6.5-year follow-up?
Study Characteristics
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Population:
56 patients undergoing unilateral total knee arthroplasty. Components were cemented in all procedures.
Intervention:
Mobile-bearing (MB) group: Patients in this group (n=29) underwent cemented total knee arthroplasty (TKA) using a mobile-bearing system (Scorpio + Single Axis system (Stryker Howmedica Osteonics, Allendale, New Jersey)). The femoral component used in this system has a single anteroposterior (AP) radius and single axis of knee flexion in the epicondylar axis. The axis of flexion was placed more posteriorly in hopes of increasing the efficiency of the quadriceps. The tibial component had a symmetrical base plate, and was fabricated such that it required minimal bone removal. This mobile-bearing system allowed for unlimited internal and external rotation; however AP translation was not possible. (Mean age: 60.0 +/- 7.1 years; 24 females; 5 males).
Comparison:
Fixed-bearing (FB) group: Patients in this group (n=27) underwent cemented total knee arthroplasty (TKA) using a fixed-bearing system (Duracon system (Stryker Howmedica Osteonics, Allendale, New Jersey)). The femoral component used in this system is characterized by a traditional round-on-flat conformation. The tibial insert used in this group was fixed to the base plate with a snap-fit mechanism. (Mean age: 54.6 +/- 7.9 years; 23 females; 4 males).
Outcomes:
Outcomes assessed included Oxford Knee Scores (OKS), Knee Society Scores (KSS) (with Knee Society Knee Scores (KSKS) and Knee Society Functional Scores (KSFS) as subsets), radiological outcomes (alignment of the knee and positions of the femoral and tibial components), patient satisfaction, and the incidence of complications.
Methods:
RCT; Double-blinded (patients & assessors); Single-Center
Time:
Follow-up assessments took place at 3, 6, and 12 months postoperatively. A final follow up also took place at a mean of 67.3 and 66.4 months in the mobile- and fixed-bearing groups, respectively.
What were the important findings?
- At final follow-up, there were no significant between-group differences in OKS scores (MB group: 16.6 +/- 1.0 points; FB group: 17.9 +/- 1.4 points; p=0.312) or pain scores (MB group: 44.1 +/- 3.4 points; FB group: 46.4 +/- 3.3 points; p=0.296).
- KSS scores were also statistically similar in the mobile-bearing (173.9 +/- 10.5 points) and fixed-bearing (161.2 +/- 8.7 points) groups at final follow-up (p=0.059). Similar results were observed for the KSFS (p=0.060) and KSKS (p=0.365) subsets of the KSS assessment tool.
- Range of motion (ROM) at final follow-up was 125.3 and 110.4 degrees in the mobile- and fixed-bearing group, respectively. This was a statistically significant difference (p=0.016).
- In the mobile-bearing group, 72% of patients could sit cross legged, 48% could sit on the floor, and 17% could squat, while in the fixed-bearing group, these percentages were 19%, 7% and 0%, respectively.
- All radiological outcomes (knee alignment, position of the femoral and tibial components in the sagittal and coronal planes, and the shift in joint line) were similar between groups (p>0.05). There were no radiolucent lines seen in any knee throughout the study.
- All patients who received TKA with the fixed-bearing system were satisfied with the procedure, whereas 2 patients in the mobile-bearing group reported dissatisfaction with the procedure (stating it was due to their inability to squat). The difference in patient satisfaction was not significant (p=0.14).
- 3 patients in the mobile-bearing group and 4 patients in the fixed-bearing group reported anterior knee pain when rising from a chair or climbing stairs (p=0.49). In addition, 5 patients in the mobile-bearing group and 0 patients in the fixed-bearing group reported an asymptomatic clicking sensation in the knees.
- No complications were reported in either group. Furthermore, the Kaplan-Meier survival rate was 100% in both groups at final follow-up.
What should I remember most?
Most of the clinical outcomes were similar at final follow-up when total knee arthroplasty (TKA) was performed using either a mobile- or fixed-bearing system, with the exception of range of motion, which was greater in the mobile-bearing group. Radiological outcomes, patient satisfaction and the incidence of complications were also statistically similar between groups. Furthermore, survivorship at a follow-up between 4 and 6.5 years was 100% using both techniques.
How will this affect the care of my patients?
Although the use of a mobile-bearing system in total knee arthroplasty (TKA) provides some clinical benefits over a fixed-bearing system, most clinical outcomes are comparable between the two. The use of mobile- and fixed-bearing systems also yields similar safety and radiological outcomes. Additional long-term studies are needed, however, to compare these two systems in terms of polyethylene wear and periprosthetic osteolysis.
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