Vastus lateralis fibrosis in habitual patella dislocation - An MRI study in 28 patients

We studied 28 patients with habitual or recurrent dislocation of the patell a with MRI of both thighs. Apart from the 2 patients whose dislocation coul d be related to trauma, we found signs of fibrosis of the vastus lateralis muscle in all the affected limbs of the 26 patients with an insidious onset of dislocation, This was seen as low signal intensity cords in the muscles in the T2 weighted image. Muscle degeneration was seen as high intensity s ignals in the T1 weighted image. In patients with unilateral disease, the v astus lateralis muscle of the affected side was hypotrophic, compared to th at of the normal side. 2 patients underwent a biopsy of the affected muscle area. Histopathological examination revealed inflammatory cell infiltratio n, fibrosis, and muscle fiber degeneration. Fibrosis of the vastus laterali s muscle appears to be common in patients with habitual patella dislocation in our population, and may be the cause of the dislocation. Since release of such a contracture may be of value, MRI study of the thigh muscles is he lpful in the evaluation of patients with this disorder.