A recent interesting case presented with lateral knee pain and no response to Physiotherapy. No prior history of trauma, but continued discomfort particularly on knee extension. On examination, there was no effusion and as reported subjectively there was a slight restriction on extension with a hard end feel. Knee flexion was full and pain free.

On office based ultrasound, a cystic,non-compressible, non-vascular, anechoic lesion on the lateral joint line, that appeared to communicate with the lateral meniscus and joint line. The initial hypothesis was that this represented a lateral meniscal cyst.

A meniscal cyst is a well-defined cystic lesion located along the peripheral margin of the meniscus, and is often associated with horizontal meniscal tears. The patient may present with local swelling and discomfort on the joint line, and potentially reduced range of movement. Meniscal cysts can be managed with the use of guided aspiration, but there is likely to be associated meniscal pathology which should be considered. In this instance the patient was subsequently referred to Orthopaedics for further input. An MRI was requested and the report read..

‘There is high signal in the anterior horn and the body of the lateral meniscus extending to a lobular area of fluid signal anteriorly and laterally consistent with a meniscal tear and a cyst. Several septae are seen within this. The medial meninscus, the medial and lateral collateral ligaments, anterior and posterior cruciate ligaments are normal. The quadriceps and patellar tendons are normal. The patellofemoral articulations and patellar retinacula are normal. No abnormality is seen in within the marrow.’

Musculoskeletal ultrasound helped facilitate the diagnosis for this patient. The patient presented with primarily a restriction of knee extension, and may have continued within Physiotherapy for a further number of sessions. The identification of the meniscal cyst on ultrasound increased the likelihood of a meniscal tear and led to the request of an MRI. It is worth commenting, that ultrasound is not the investigation of choice for meniscal tears, but it can assist with highlighting related pathology to enhance the detail of clinical assessment findings and facilitate appropriate management.

A review article looks at management of meniscal cysts, and aspiration. Rutten et al (1998) also discussed the sonographic appearance of meniscal cysts. There are also many other full text, free musculoskeletal ultrasound articles to be read here.