Sonographic appearances of medial retinacular complex injury in transient patellar dislocation

To describe the sonographic appearances of the medial retinacular (MPFR) complex of the knee in patients with acute and recurrent patellar dislocation.

Thirty patients were scanned within 2-4 weeks of an acute episode of lateral patellar dislocation. Eleven gave a history of recurrent patellar dislocation. Ten patients had examination under anaesthesia with arthroscopy and repair of the injury. The sonographic and operative results were compared.

The normal sonographic appearance of the MPFR is described. Of the 10 patients who underwent examination under anaesthesia, four patients had complete avulsion of the MPFR from the patella, two patients had avulsion of the MPFR from the adductor tubercle and four patients had avulsion of the MPFR from both the patella and adductor tubercle. There was complete correlation between the sonographic and operative findings for injuries of the MPFR. Other findings included partial retinacular tears, injury to the medial collateral ligament, haematoma within vastus medialis obliquus (VMO) and bony avulsions from the patella and adductor tubercle

Sonography gives reliable information regarding the site of the injury and its extent thus helping to decide whether conservative or operative treatment is the most appropriate approach to management of the injury.