Objective: To determine the patterns of patellar motion in subjects without knee symptoms using dynamic magnetic resonance imaging (MRI).
Design: Patellar tracking MR examinations were performed on 50 asymptomatic volunteers. The presence and degree of lateral subluxation and tilt of the patella was assessed independently by three radiologists, and discrepancies resolved by consensus. Using the same criteria, the tracking pattern in 50 consecutive patients, recently referred for imaging assessment of anterior knee pain, was studied.
Patients: Fifty volunteers (22 male, mean age 37 years) and 50 unmatched patients (15 male, mean age 25.5 years) were examined.
Results and conclusions: Forty-one per cent of a total of 97 knees in the volunteer group showed evidence of lateral subluxation, which was either minimal (grade 1, 32%) or minor (grade 2, 9%). No volunteer demonstrated major (grade 3) subluxation; lateral tilt without translation of the patella was also seen (2%). In the patient group, higher grades of lateral subluxation were more common. Minimal (grade 1) lateralization is a common movement pattern of the patella on knee extension, and should be regarded as normal.