Standing Weight-Bearing CT Measurement Differences in Patellofemoral Instability Patients
E.S. Mameri, L.F.M. Ambra, M.D.S.L. Júnior, V.T.F. Leitão, M.S. Kubota, C.E.D.S. FrancioziObjective:
Explore differences between patellofemoral (PF) alignment measurements between supine CT (nWBCT) and standing weight-bearing CT (WBCT) in a clinically-relevant sample of patients with PF instability.
Methods:
Ours was a trans-sectional diagnostic study of 10 patients (13 knees), previously diagnosed with PF instability (≥2 episodes of dislocation). Patients underwent both supine nWBCT and standing WBCT. Data collection included clinical examination (J-sign classification), radiographic (Dejour classification, CD index) and CT (TT-TG, Patellar tilt, Patelar Shift, Merchant Angle, PF distance, Sagittal PF Engagement Index, TF rotation) imaging. Measurements between groups were compared as our primary outcome.
Results:
Thirteen knees were assessed, with a mean age of 28.5 years (SD ± 6.93; range: 21-44 years), 80% female. Compared to nWBCT, standing WBCT revealed significantly decreased TT-TG (-2.59mm, p<.001), Patellar Tilt (-10.6º, p=.002), Patellar Shift (-9.11%, p=.043), and Merchant Angle (-27.9º, p=.031), as well as significant shift from internal rotation to external rotation (-8.92º, p<.001). No differences were found for PF distance or PF engagement. Clinically, a pathological J-sign was associated with higher TT-TG distances in nWBCT (p=.023) and WBCT (p=.036), and lateral shift in nWBCT (p=.028). Higher J-sign classification was associated with higher radiographical trochlear dysplasia (p=.004), PF engagement in WBCT (p=.041), TF rotation in nWBCT (p=.026). No significant correlations were found elsewhere.
Conclusion:
WBCT reveals significant differences relative to supine nWBCT in patients with PF instability. Loading and muscle activation leads to external tibial rotation and decreased PF malalignment (decreased TT-TG, tilt, shift, Merchant angle).