Raincheck for Baker’s cyst? Umpteenth note on knee ultrasound

Dear Editor,

We read with great interest the recently published article ‘Ultrasound for suspected Baker’s cyst: A test of limited clinical value?’ by Charnock et al. ¹ We would like to congratulate the authors for aiming to determine the incidence of different pathologies in patients investigated with posterior knee swelling. However, we have an objection to raise regarding their conclusion that ultrasound of the posterior knee for a suspected Baker’s cyst is of limited clinical value.

First and foremost, with an incidence ranging from up to 58%, Baker’s cysts are considered as the most common mass in the popliteal fossa. ² Ultrasound has largely replaced all imaging modalities and become as the first-line assessment modality for Baker’s cysts. ³ The differential diagnosis includes popliteal artery aneurysm, soft tissue tumours, meniscal cyst, haematoma, thromboemboli and seroma. ² In the concurrent study, ¹ around 10% of patients had one of the alternative differential diagnosis, and hence with a small sample size and no follow-up of the patients, we find it unfair to conclude about its limited clinical value.

Second, we underscore the convenient role of ultrasound in substantial examination of the knee joint, ³ not only for simple detection of a mass lesion but also to better understand the clinical correlation between the exact anatomic/pathologic findings and the patient’s real-life complaints/scenario. In this context, imaging all aspects (not just the posterior part) of the knee would be more appropriate to understand the adherent pathologies. Needless to say, it not only serves for the diagnosis but also provides immediate guidance for a likely interventional. Also, since ultrasound examination is really patient and physician friendly; immediate reassurance of the patient as regards the diagnosis and treatment can easily be done throughout the examination and has already been shown to favourably impact the treatment outcome by providing real-time feedback. ⁴

Finally, the posterior lateral corner of the knee is a frequently overlooked area in routine ultrasound examinations, despite its susceptibility to sports injuries. ⁵ A comprehensive understanding of the regional anatomy helps clinicians detect potential sources of pain, where systematic ultrasound examination can be invaluable for uncovering common pathologies including ligamentous sprains and tears. Moreover, dynamic examination and sono-palpation can readily be useful in the differential diagnosis. In short, we remind the readers that ultrasound is a superior and interactive wholistic examination, not a static image alone.