Ultrasound for suspected Baker's cyst: A test of limited clinical value?

Patients with posterior knee swellings are commonly encountered in clinical practice with the vast majority referred for an ultrasound scan to assess for a clinically suspected Baker's cyst.

Our aim was to determine the incidence of different pathologies in patients investigated for a posterior knee swelling of a clinically suspected Baker's cyst using ultrasound. We also wanted to investigate the incidence of significant pathologies in the popliteal fossa to assess whether the ultrasound scan findings influenced patient management.

Retrospective analysis was performed on all patients who underwent an ultrasound scan for a suspected Baker's cyst or posterior knee swelling at our institution, between January 2017 and December 2018. Patient demographics, ultrasound findings, further imaging investigations and histopathology were recorded. Patient records were followed up for a minimum period of 3 years after ultrasound.

A total of 680 patients had a posterior knee ultrasound scan. Of that, 51% (347/680) had a Baker's cyst and 40% (273/680) had a normal ultrasound scan. Sixty (9%) patients had other abnormalities identified within the popliteal fossa. Four patients had significant findings on ultrasound that required a change of management. No malignancies identified.

This study confirms the high incidence of Baker's cysts in patients presenting with a posterior knee swelling. In the absence of red flag symptoms, ultrasound of the posterior knee for a clinically suspected Baker's cyst is of limited clinical value.