Objective assessment of patellar maltracking with 3 Tesla Dynamic MR Imaging: feasibility of a robust and reliable measuring technique

Objectives Patellofemoral (PF) maltracking predisposes the patellofemoral joint (PFJ) to instability. To evaluate patellar tracking, kinematic imaging protocols have been proposed, however, most are sequential static images or simply impractical for clinical day-to-day use.

Hypothesis/Purpose

The purpose of this study was to provide a feasible, reproducible and clinically relevant dynamic MRI measuring technique for PF maltracking and to investigate the influence of known anatomical risk factors on patellar maltracking and instability. We hypothesize, that with the presented technique PF maltracking can be clearly distinguished from physiological PF tracking in healthy volunteers.

Methods Ten patients with a clinically diagnosed maltracking and 20 healthy volunteers were examined with a dynamic, multi-slice gradient echo MRI sequence in transverse and sagittal plane orientation, during a repetitive cycle of flexion (30-40°) to full extension. The patellotrochlear distance and the patellar tilt were measured in multiple and defined patellar positions by two independent examiners and in relation to the size of the joint. Common radiological parameters, such as tibial tubercle to trochlear groove (TT-TG) and tibial tubercle to posterior cruciate ligament (TT-PCL) distances, patella height (CDI), trochlear depth, sulcus and lateral inclination angles were measured on transverse slices.

Results and Conclusion Ten patients (2 male, 8 female, &#61638;19y) and 20 volunteers (10 male, 10 female, &#61638;28y) were included. A time frame of 30 seconds was used for the acquisition of the three transverse slices. During the range of motion, the mediolateral patellar shift was significantly greater in the patient group (12.4±6.9mm vs. -0.1±2.3mm, p < 0.001) and the patella was positioned significantly more lateral (17.5±6.9mm vs. 3.1±2.4mm, p < 0.001). Further, the patella tilted 16.3±13.1° laterally in the patient group and 1.9±4.3° medially in the control group (p < 0.002). In the patient group, the mean TT-TG, CDI and trochlear sulcus angle were pathologically increased and strongly correlated with the extent of lateral patellar tracking and patellar tilt. Interrater correlation was excellent (0.971 and 0.976, 95%-confidence-intervals 0.939-0.986 and 0.950-0.988).

Conclusion

With the presented technique, dynamic MRI is a reliable, reproducible and feasible way to identify patellar maltracking in the clinical routine. Patellar tracking strongly correlates with common radiological parameters, which reinforces their clinical use and validates the presented technique.

Stichwörter patella, tracking, dynamic MRI, magnetic resonance imaging, patella instability, maltracking, patellofemoral, knee

Publication History

Article published online:
15 October 2020