Unsatisfactory clinical outcomes of second-generation mobile bearing floating platform total knee arthroplasty: comparing outcomes with fixed bearing after five years minimum.

BACKGROUND: The purpose of this retrospective study was to analyze and compare the clinical and radiologic outcomes of fixed bearing ultracongruent (UC) insert total knee arthroplasty (TKA) and mobile bearing (MB) floating platform TKA using the navigation-assisted gap balancing technique with a minimum follow-up of five years.

METHODS: The study retrospectively enrolled 105 patients who received the UC type fixed bearing insert (group 1) and 95 patients who received the floating platform MB insert (group 2) during the period from August 2009 to June 2012. All surgery was performed using the navigation-assisted gap balancing technique. For strict assessment of gap measurements, the offset-type-force-controlled-spreader-system was used. Radiologic and clinical outcomes were assessed before operation and at the most recent follow-up using the Knee Society Score (KSS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score. For statistical analysis, paired sample t tests were used. A p value less than 0.05 was considered significant.

RESULTS: Although the radiologic alignments were satisfactory for both groups (99/105 [94%] cases were neutral for group 1 and 90/95 [94%] for group 2), the functional and total WOMAC scores were inferior in group 2 (p < 0.05). There were two cases of insert breakage in group 2 that required bearing exchange. The Kaplan-Meier survivorship rates for groups 1 and 2 at 77 months were 100.0 and 97.9%, respectively.

CONCLUSION: Second-generation MB floating platform TKA cases did not have satisfactory outcomes. There were two cases of insert breakage, which required bearing exchange. Other patients who underwent surgery with second-generation MB floating platform were encouraged to avoid high knee flexion activities, resulting in lower clinical performance.