Best Practice Case Studies-Patellar Subluxation

Video Transcription

This is Barry Belosis, one of the musculoskeletal radiology fellows at Stanford University.  19 year old male with right thigh weakness and difficulty walking two years following patellar dislocation.  Concerned for patellar subluxation.  This is a different patient who presented after a twisting injury.  MRI knee without contrast was performed. Here on our left hand side, we can see an axial proton density fat set imaging  demonstrating bone contusion here at the medial patellar facet and in the lateral femoral condyle  characterized by this increased signal or edema in both the medial patellar facet and the lateral femoral condyle. These are typical findings of kissing contusion seen on patellar  dislocation. Additionally, we looked at the medial patellar retinaculum for any kind of edema to suggest sprain and here we have low-grade sprain.  Here on our coronal T1 imaging, we can see region of T1 hypo intensity in the lateral femoral condyle  correlating to the edema seen on our axial PD fat set imaging.  One of the risk factors for patellar dislocation or subluxation is a trochlear dysplasia.  Measurement of trochlear dysplasia is very challenging to assess because of differences in positioning of this patient.  But the general concept is to determine if the trochlea is relatively shallow  which could be seen on this patient. The other thing that we evaluate in patients with patellar dislocation or subluxation is the tibial tuberosity to trochlear groove distance.  We do this by drawing a line  along the posterior femoral condyle as we see here and a perpendicular line  bisecting the trochlear groove. And then we draw a perpendicular line  bisecting the expected location of the tibial tuberosity.  We do this by marking and going all the way to the tibial tuberosity right here  and we go up all the way to the level of the trochlear groove  right here. From here, we measure the distance between these two parallel lines and that determines the tibial tuberosity  to trochlear groove distance.

Video Summary

A 19-year-old male is evaluated for right thigh weakness and walking difficulty, two years post-patellar dislocation, with concern for patellar subluxation. MRI of the knee shows a bone contusion at the medial patellar facet and lateral femoral condyle, typical of "kissing contusion" from dislocation. A mild sprain in the medial patellar retinaculum is noted. Trochlear dysplasia, a risk factor for dislocation, is discussed alongside its assessment challenges due to positioning. The tibial tuberosity to trochlear groove distance is measured to evaluate the displacement, using specific imaging lines to calculate this crucial parameter.

Meta Tag

Edition 2nd Edition

Related Case 2nd Edition, CASE 26

Topic Knee

Keywords

2nd Edition, CASE 26

2nd Edition

Knee

patellar dislocation

kissing contusion

trochlear dysplasia

tibial tuberosity

MRI knee