Traumatic Dislocation of the Patella

The large majority of patellar dislocations are secondary to trochlear dysplasia (more than 80% of cases). The injury usually occurs after a valgus-external rotation traumatic mechanism (90% of cases). This entity is different from the injury entitled “knee dislocation” which is discussed separately. The patient may present with the patella in dislocated position or after the patella has been reduced in which case, the diagnosis can be missed in emergency. Appropriate radiographs are mandatory as well as MRI to diagnose associated lesions. Surgical treatment is argued for recurrent episodes of dislocation.