The Sagittal Tibial Tubercle Trochlear-Groove Distance Is Not Equivalent on Magnetic Resonance Imaging and Computed Tomography Measurements in Patients With Patellar Instability.

Abstract

Purpose: To analyze the difference of the sagittal tibial tubercle trochlear-groove (sTTTG) on magnetic resonance imaging (MRI) and computed tomography (CT) and to assess the influence of the knee flexion angle (KFA) and tibiofemoral (TF) rotation on the sTTTG.

Methods: All patients who underwent patellar-stabilizing surgery for patellar instability between January 2019 and July 2023 at a single institution were included in the current study. Patients were included when a preoperative MRI of the assessed knee and standardized CT imaging in full knee extension of the lower extremity was available. Two independent reviewers assessed KFA, TF rotation, and sTTTG distance on MRI and CT scans. The sTTTG distance was measured between both the osseous (MRI and CT) and chondral nadir of the trochlea (MRI only) and the bony apex of the tibial tubercle. A positive value indicated a posteriorly located tibial tubercle in relation to the trochlea. Differences between MRI and CT measurements as well as the influence of KFA and TF rotation on sTTTG were assessed.

Results: In the included knees (n = 77), the osseous sTTTG on MRI (4.8 mm, 95% confidence interval [CI] 3.7-5.8 mm) was significantly lower than both the chondral sTTTG on MRI (8.3 mm, 95% CI 7.2-9.3 mm) and the sTTTG on CT (6.6 mm, 95% CI 5.4-7.7 mm) (both P < .001). TF rotation was significantly correlated with sTTTG both on MRI and CT (r = 0.468; P < .001 and r = 0.634; P < .001). KFA was not correlated with sTTTG either on MRI or CT (nonsignificant). Neither the difference of TF rotation nor KFA between both modalities was associated with the difference seen in sTTTG between MRI (osseous) and CT (nonsignificant).

Conclusions: The sTTTG shows smaller values when measured on MRI compared with CT, but its clinical significance is yet to be determined. Although TF rotation is correlated with the sTTTG on MRI and CT, KFA does not influence the sTTTG in patients with patellar instability within the limits of range of motion during image acquisition.

Level of evidence: Level IV, retrospective case comparative study.