Clinical Utility of Continuous Radial Magnetic Resonance Imaging Acquisition at 3 T in Real-time Patellofemoral Kinematic Assessment: A Feasibility Study

Abstract

Purpose: To compare patellar instability with magnetic resonance imaging analysis using continuous real-time radial gradient-echo (GRE) imaging in the assessment of symptomatic patients and asymptomatic subjects.

Methods: Symptomatic patients with suspected patellofemoral maltracking and asymptomatic volunteers were scanned in real time by a radial 2-dimensional GRE sequence at 3 T in axial orientation at the patella level through a range of flexion-extension. The degree of lateral maltracking, as well as the associated tibial tubercle-trochlear groove distance and trochlea depth, was measured. Patellar lateralization was categorized as normal (≤2 mm), mild (>2 to ≤5 mm), moderate (>5 to ≤10 mm), or severe (>10 mm). The patellofemoral cartilage was also assessed according to the modified Outerbridge grading system.

Results: The study included 20 symptomatic patients (13 women and 7 men; mean age, 36 ± 12.8 years) and 10 asymptomatic subjects (3 women and 7 men; mean age, 33.1 years). The mean time to perform the dynamic component ranged from 3 to 7 minutes. Lateralization in the symptomatic group was normal in 10 patients, mild in 1, moderate in 8, and severe in 1. There was no lateral tracking greater than 3 mm in the volunteer group. Lateral maltracking was significantly higher in symptomatic patients than in asymptomatic subjects (4.4 ± 3.7 mm vs 1.5 ± 0.71 mm, P = .007). Lateral tracking significantly correlated with tibial tubercle-trochlear groove distance (r = 0.48, P = .006). There was excellent agreement on lateral tracking between the 2 reviewers (intraclass correlation coefficient, 0.979; 95% confidence interval, 0.956-0.990).

Conclusions: The inclusion of a dynamic radial 2-dimensional GRE sequence is a rapid and easily performed addition to the standard magnetic resonance imaging protocol and allows dynamic quantitative assessment of patellar instability and lateral maltracking in symptomatic patients. With a paucity of reported data using this technique confirming that these results reach clinical significance, future work is required to determine how much lateral tracking is clinically significant.

Level of evidence: Level III, case control.

Fig 1

(A) Body coil in situ for dynamic examination. The body coil is strapped in place with the knee held in flexion by a pillow and support to ensure stability. The patient is instructed to extend from 30° of knee flexion to full extension. (B) Magnetic resonance workstation showing multiplanar alignment of the knee during real-time image acquisition with an 8-mm-thick axial slice selected at the level of the patella.

Fig 2

(A-I) Sequential images from the continuous dynamic gradient-echo sequence in a 26-year-old asymptomatic male volunteer. The acquisition was performed in real time with the patella centered within the axial plane (Video 1, available at www.arthroscopyjournal.org). There was no significant abnormal lateral excursion of the patella margin between 0° and 30° of flexion, measuring 1 mm.

Fig 3

(A-I) A 27-year-old male patient with anterior knee pain, chondromalacia (grade 2 patella and grade 3 trochlea scores according to modified Outerbridge system), and patellofemoral maltracking on clinical examination. Sequential images are shown from the continuous dynamic gradient-echo sequence obtained in the axial plane, showing the calculation of maximal lateral excursion of the patella margin between 0° and 30° of flexion, measuring 8 mm in this case (Video 2, available at www.arthroscopyjournal.org).