Lateral patellar maltracking and patellar alta in the absence of increased TT-TGdynamic distance in isolated patellofemoral pain: a dynamic kinematic CT study.

BACKGROUND: Patellar tracking in isolated patellofemoral pain needs further confirmation under dynamic conditions. The present study aimed to analyze the characteristics of patellar tracking and tibial tubercle-trochlear groove (TT-TGdynamic) distance during active knee motion in patients with isolated patellofemoral pain (PFP) via dynamic kinematic computed tomography (DKCT), and clarify whether the abnormal patellar tracking and TT-TGdynamic distance are associated with isolated PFP. METHODS: A total of 47 knees with isolated PFP and 47 control knees were scanned with DKCT. The TT-TGdynamic distance, bisect offset (BO) index, lateral patellar tilt (LPT), and patellotrochlear index (PTI) were evaluated. All parameters were analyzed by two-factor repeated measures ANOVA. RESULTS: In the two groups, the TT-TGdynamic distance, BO index, LPT, and PTI varied with the knee flexion angle (all p<0.001). Between the two groups, the variation trends of TT-TGdynamic distance and BO index were consistent (p = 0.131, 0.284, respectively), while those of LPT and PTI were significantly different (p = 0.001, <0.001, respectively). The BO index and LPT were significantly higher in the PFP group than those in the control group (p = 0.002, <0.001, respectively), and the PTI was significantly lower in the PFP group than that in the control group (p<0.001), whereas the TT-TGdynamic distance showed no significant difference between the two groups (p = 0.631). CONCLUSIONS: Abnormal lateral patellar displacement, tilt and patellar alta occurred in the absence of increased TT-TGdynamic distance in isolated PFP without trochlear dysplasia. Etiologic analysis of isolated PFP should emphasize lateral patellar tracking and patellar height.