No Difference in Implant Micromotion Between Hybrid Fixation and Fully Cemented Revision Total Knee Arthroplasty: A Randomized Controlled Trial with Radiostereometric Analysis of Patients with Mild-to-Moderate Bone Loss.

BACKGROUND In revision total knee arthroplasty (TKA), the femoral component and tibial baseplate are usually cemented. However, stems can be fixed either with cement or with a press-fit technique, with the latter resulting in hybrid fixation. There is no consensus on the preferred stem fixation technique. Therefore, we compared the stability of cemented TKA implants with the stability of TKA implants fixed with the hybrid technique in a prospective randomized trial using radiostereometric analysis (RSA). METHODS Thirty-two patients with a Type-I or II bone defect who needed revision TKA and were randomly allocated at the time of surgery into either the cemented or hybrid-fixation group were included in the study. The radiographs for the RSA were obtained during hospitalization (baseline); at 6 weeks; and at 3, 6, 12, and 24 months. Migration of the femoral and tibial implants was measured using model-based RSA and expressed along or around the 3 orthogonal axes and as total translation (TT) and total rotation (TR). Clinical results were evaluated using the Knee Society Score (KSS), the Knee injury and Osteoarthritis Outcome Score (KOOS), active flexion, and visual analog scale (VAS) scores for pain and satisfaction. Mann-Whitney and chi-square tests were used to compare migration and clinical outcomes between the cement and hybrid techniques. RESULTS At 24 months, no difference in median migration or the number of migrating components was found between the cemented and hybrid-fixation groups. In each group, approximately one-third of the tibial components had total rotation of >1°. The clinical scores did not differ between the techniques. CONCLUSIONS At 24 months after revision TKAs, cemented and hybrid-fixation replacements were equally stable. Unexpectedly, both groups had implants with >1 mm or >1° of micromotion although there were no clinical or radiographic signs of loosening. Whether these findings indicate the possibility of loosening with longer follow-up remains to be investigated. LEVEL OF EVIDENCE Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.