Aims: Acute lateral dislocation of the patella has been associated with disruption of the medial restraints of the patella and following non-operative management, a redislocation rate of up to 44%. Methods: Ten patients who presented to the Accident and Emergency dept. following acute patella dislocation had an ultrasound scan (USS) performed by an experienced musculoskel-etal radiologist. Each patient had an arthroscopy and washout of the knee and repair of ruptured structures. The ultrasound reports have now been compared to the surgical findings to determine the effectiveness of this investigation. Results: The ultrasound scans identified deficiencies in the ligamentous attachments to the medial border of the patella in eight patients and these were confirmed at operation in the same eight. The USS diagnosis of haematoma or torn fibres in the vastus medialis obliquus (VMO) (5 patients) corresponded with tearing of this muscle at operation; however the degree of muscle injury was underestimated in two. The USS finding of free fluid around the medial collateral ligament (MCL) at the adductor tubercle in three patients was associated with the operative finding of disruption of the femoral origin of the medial patellofemoral ligament (MPFL). Haematomata detected on USS along the adductor longus in two patients proved to have disruption of the VMO attachment. Conclusions: We recommend the use of ultrasound for assessment of all patella dislocations to accurately locate tears of the retinaculum and help clinicians to understand the severity of injury to the soft tissue restraints of the patella.

Acute lateral dislocation of the patella has been associated with disruption of the medial restraints of the patella. Following non-operative management there is a redislocation rate of up to 44%. This is an observational study testing whether sonography is a reliable method of assessing the medial retinaculum after acute dislocation of the patella.

Ten patients following acute patellar dislocation had an ultrasound scan (USS) performed by an experienced musculoskeletal radiologist. Each patient subsequently had an examination under anaesthetic, arthroscopy, and repair of the ruptured structures. The ultrasound reports were compared to the surgical findings to determine the accuracy of this investigation.

USS located deficiencies in the ligamentous attachments to the medial border of the patella and the presence of avulsed bony fragments, all of which were confirmed at operation. The sonographic diagnosis of haematoma or torn fibres in the vastus medialis obliquus corresponded with our operative findings.

The most significant findings were the correlation of free fluid around the medial collateral ligament (MCL) with avulsion of the femoral attachment of the medial patellofemoral ligament (MPFL) and the presence of avulsed fragments of bone from the medial border of the patella.

Sonography, in cadaveric studies consistently identifies the retinacula and like MRI offers a distinctive constellation of findings that can be used in diagnosis and therefore play a significant role in directing surgical management of these patients. We have found Sonography to be readily available and accurate.

This report does not include surgical outcome since the follow up is short and incomplete. We do, however, feel that ultrasound shows the state of the soft tissue restraints of the patella following lateral dislocation.