Dynamic Mri exam is crucial in many situations; in a previous post I have shown a dynamic Mri study of patellofemoral impingement with patella alta.
Take a look at this patient in which the suspected patella baja is well studied during flexion-extension active movements.
The Insall-Salvati Index (ISI) and its modified version are used the same way on Mri studies as on plain radiographs.
Rember that in case of true patella baja, the patella remains engaged within the trochlear groove in full knee extension. The dynamic examination allows to appreciate the direct visualization of patellar and trochlear allignment for a more objective measurement, together with the others modalities. In this patient the dynamic examination shows a correct patellar positioning during active extension.
The knee has a particular anatomy with regard to the capsular-synovial relationship and contains several interposed fat pads. There is a limited amount of literature on suprapatellar fat pad anatomy of the knee and its pathology is likely underestimated due to underdiagnosis. Fat pad edema can be used as an indirect sign of synovial proliferation in patients with joint effusions. The most important symptom is chronic anterior knee pain proximal to the superior pole of the patella.
Axial T2w and Sagittal Ge-Stir (o.3 tesla) of a 20 years old patient with anterior knee pain. A clear picture of patellofemoral impingement is evident-
Prefemoral fat pad impingement may result from alterations in joint mechanics with repeated microtrauma between the patella and the anterior surface of the distal femur, especially on the lateral side of the fat pad. Mri examination is crucial for a correct diagnosis.
Sagittal Ge-Stir and T1w Mri scans (0.3 Tesla); high degree femoro-patellar chondropathy with patella alta and suspected fat pad impingement
I really like the dynamic Mri exam because in my daily practice gives a further completion of the diagnosis, showing the effective amount of impingement during flexion-extension movements.
Dynamic Mri exam of the same patient