No reduced patellar loading with latest-generation cruciate-retaining total knee arthroplasty—a comparative study of Attune and Press-Fit Condylar®

PURPOSE: To investigate if the latest-generation cruciate-retaining total knee arthroplasty (CR-TKA) systems through more patella-friendly femoral trochlea reduce the patellar bone loading. METHODS: Twenty patients who underwent Attune CR-TKA were matched with twenty-one patients who underwent Press-Fit Condylar® (PFC) CR-TKA. The patella was always preserved. The in vivo patellar loading was measured twice by two blinded observers and localised on an 8-quadrant grid on 1-year post-operatively SPECT/CT images. The position of the TKA components, patella height, thickness, tilt, and tibial tuberosity-trochlear groove index were measured in 3D CT. Knee function was assessed pre-operatively, at 12 and 24 months post-operatively with the knee society score (KSS). All data were compared between groups with the Mann-Whitney U test and within groups with Spearman’s correlation. RESULTS: A significantly higher bone tracer uptake (BTU) was seen in the Attune group in the lateral non-articular patellar quadrants. No other significant differences of the BTU were seen. The post-operative KSS did not differ significantly. Spearman’s correlation showed no correlations between the significantly higher BTU of the lateral non-articular patellar quadrants and the position of the TKA and patellar measurements. All patellar measurements did not correlate with bone stress in SPECT/CT. CONCLUSION: No significant improvement in terms of in vivo patellar bone stress was seen with the latest-generation CR-TKA system. The increased bone stress at the non-articular lateral patellar quadrants of the Attune could be due to higher stabilising quadriceps forces.