Empty Sunrise Sign: An Arthroscopic Finding in Recurrent Patellar Dislocation.

Patellar dislocation is a relatively common knee injury and can be challenging to diagnose. We describe an arthroscopic finding we noted in recurrent patellar dislocation. Arthroscopic photos were evaluated from 50 knees with a history patellar dislocation and 100 control patients. We quantified the amount of patellar subluxation seen on a single arthroscopic view and coined it Empty Sunrise Sign if the patella did not overlap the trochlea. Empty Sunrise Sign was found in 82% of 50 cases with recurrent patellar dislocation and none of the 100 control cases. The finding was 100% specific for identifying a recurrent patellar dislocator. High interobserver agreement was noted. Empty Sunrise Sign suggests significant capsular laxity. This may need to be considered in the surgical treatment of recurrent patellar dislocation.