Magnetic Resonance Imaging Evaluation of Patellofemoral Instability with Emphasis on Tibial Tuberosity-Trochlear Groove Ratio: A Case Series.
Madhuri Panigrahi, Santosh Kumar Panda, Birajman Lakra
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Case in brief
Three patients with clinically suspected patellar dislocation underwent MRI assessment of trochlear morphology, patellar height and alignment, extensor mechanism alignment, and soft tissues. Two had recurrent dislocations after minor trauma; one had an acute dislocation after significant trauma. MRI showed lateral patellar maltracking in all three, borderline trochlear morphology in two, and patella alta by Insall-Salvati ratio in one. TT-TG distances were 13 to 19.5 mm, ranging from normal to borderline, while TT-TG ratios were 0.20 to 0.26; one case showed abnormal lateralization. Higher ratios corresponded with greater bisect offset and lateral patellar displacement.
What made this case unusual
The case series highlights discordance between normal-to-borderline absolute TT-TG distances and the TT-TG ratio, which corresponded more closely with lateral maltracking, including one case of abnormal lateralization.
Diagnostic / clinical pearl
When MRI shows patellar maltracking despite a normal-to-borderline TT-TG distance, consider interpreting the TT-TG ratio alongside other anatomical and alignment measures.