Patellofemoral in-Vivo Loading after Total Knee Arthroplasty in Resurfaced and Unresurfaced Patellae

Purpose: The primary purpose of the study was to investigate if and how patellar bone tracer uptake (BTU) distribution in SPECT/CT is influenced by patellar resurfacing and the position of femoral and tibial TKA component position .The secondary purpose of the study was if patellar height, patellar thickness, patellar tilt, as well as TT-TG distance influence postoperative BTU pattern and if outcome correlates with BTU pattern.

Methods: A total of 104 knees of 103 consecutive patients who underwent primary TKA were prospectively investigated. Primary patellar resurfacing was done in 40 knees while 64 had a TKA without patellar resurfacing. All patients underwent clinical assessment using the knee society score (KSS) and radiological examination including standardised radiographs and Tc-99m-HDP-SPECT/CT before and 12 and 24 months after TKA. Measurements of BTU including intensity and anatomical distribution pattern in eight different patellar regions were performed. Tibial and femoral TKA component position was assessed from 3D reconstructed CT data. Univariate analysis was performed to identify differences between the two groups (p<0.05).

Results: Significantly higher BTU was found in the anterior, non-articular, areas of the patella in patients who underwent patellar resurfacing. The BTU pattern was similar between the groups, as the maximal uptake in both groups was seen in the superior posterior parts and the minimal uptake was seen in the inferior anterior parts. The mean postoperative KSS was significantly higher in the unresurfaced group after 12 months, but with no significant difference after 24 months.

Conclusions: Based on the findings of the present study patellar resurfacing is related with significantly higher BTU in the anterior parts of the patella and lower clinical outcomes. In light of these results, routine patellar resurfacing as part of a primary TKA cannot be supported. SPECT\CT enables a precise localization of the BTU and might be considered as the ideal imaging modality for evaluation and investigate of patellofemoral disorders after TKA.