Standard radiographic views for patellofemoral joint assessment do not reflect loading at which TKA patients may describe post-operative anterior symptoms. A novel weight bearing (WB) Merchant view has been described and demonstrated a number of tracking changes that correlated with clinical outcomes. In this study, we aim to validate the WB Merchant view and assess relationships with patient outcome scores.
Patients were randomly allocated to receive one of the three commonly used patellar implants with a single TKA prosthesis. Patients were evaluated at six months post-operatively using both NWB and WB Merchant views. Indicators of patellar tracking were correlated with improvement in KOOS, WOMAC and Kujala scores. For reliability assessment, radiographs were assessed twice by two readers.
The WB Merchant view showed a reduction in the percentage of outliers of tracking indices in comparison to the NWB view (Congruence angle: NWB = 37%, WB = 24%; Displacement: NWB = 2%, WB = 0%; Tilt angle: NWB = 60%, WB = 56%). There was an increase in the lateral contact state with the WB Merchant view (Type I: NWB = 19%, WB = 28%; Type II: NWB = 3%, WB = 4%). The state of lateral contact had a consistent and statistically significant correlation with the improvement in KOOS, WOMAC and Kujala scores (p value = 0.01, 0.01 and 0.03, respectively). All radiographic indices had good reliability with accepted variability.
The WB Merchant radiograph is an easy to perform and reliable view for the evaluation of patellar tracking and may provide additional information to the routinely used NWB view.