Abstract
Introduction
The number of revisions of total knee replacements (TKR) increases annually. Because of reduced bone stock, stable fixation of the implant is important. The femoral and tibial components are usually cemented whereas stems can be placed either cemented or press-fit (hybrid construct). To assess the stability of revision TKR with either cemented or hybrid places implants a randomized controlled trial (RCT) was executed, by using radiostereometric analysis (RSA). The short-term results of this RCT showed no differences between the two groups in stability and clinical outcomes. Although there were no clinical or radiological signs of loosening, both groups showed implants micromotion > 1 mm or degree. These findings might indicate the possibility of loosening later in time; therefore, the current study investigated the stability of cemented versus hybrid-placed revision TKR 6.5 years after surgery. Additionally, clinical results were evaluated.
Methods
Of the 32 patients in the original RCT, 23 (12 cement, 11 press-fit) were available for mid-term follow-up measures. RSA images taken at baseline, 6 weeks, 3, 6, 12 and 24 months postoperatively were used from the previous study. New RSA images were taken at median 6.5 years (range 5.4–7.3) postoperatively. Stability of the femoral and tibial implants was assessed by using model-based RSA software (RSAcore, Leiden, The Netherlands) to determine micromotion. Clinical results were evaluated using the Knee Society Score (KSS), the Knee injury and Osteoarthritis Outcome Score (KOOS), active flexion, and VAS pain and satisfaction. Stability and clinical outcome were compared between the two groups using independent t-tests or Mann-Whitney U tests when applicable.
Results
The median total translation at 6.5 years was 0.37 (0.13–1.96) mm and median total rotation 0.62 (0.11 – 2.81)° for the femoral component. For the tibia component the median total translation was 0.41 (0.10 – 1.04) mm and the median total rotation 0.61 (0.09 – 1.99)°. There were no differences in total translation and total rotation of the femoral and tibial component between the two groups. Additionally, none of the clinical scores differed between the groups. Interestingly, in the group with cemented stems five tibia implants showed > 1 mm or degree migration compared to zero in the hybrid group (p=0.02; Figure 1).
Conclusion
There was no difference in stability and clinical outcome between fully cemented and hybrid-placed revision TKR 6.5 years postoperatively. Until now micromotion >1 mm or degree in the tibial components of the cemented group has not yet resulted in re- revisions. The patients will be followed to examine the consequences of these amounts of micromotion in this type of implant in the long-term.
Figure 1. Scatter plot of total translation (x-axis) and total rotation (y-axis) for the tibia component at 6.5 years follow-up for fully cemented and hybrid-placed revision TKA.
