6 month history of pain and intermittent swelling of the left knee. On examination there was swelling and tenderness over the medial aspect of the knee joint.
The patient presented with a 6 month history of pain and intermittent swelling of his left knee. On examination there was swelling and tenderness over the medial aspect of the knee joint. A radiograph showed soft tissue swelling over the medial aspect of the knee and a large, associated erosion of the proximal tibia. MR imaging confirmed a large, lobualted cystic lesion which was displacing the medial collateral ligament and causing erosion of the adjacent tibia. A horizontal tear of the posterior horn of the medial meniscus was also shown. Arthroscopy confirmed the imaging findings and a partial meniscectomy and cyst decompression were performed.
Meniscal cysts(also known as ganglion cysts or juxta-articular myxomas) are multiloculated collections of mucinous material occuring at the periphery of a meniscus[1]. They usually affect young adults but are being increasingly diagnosed on MR imaging in other age groups. They are commoner on the lateral side where they often present with swelling and pain at the joint line. When they occur on the medial side they are often large and commonly asymptomatic. Although their cause is unknown the majority are associated with horizontal tears of the adjacent meniscus and it has ben postulated that there is an influx of synovial fluid through the tear into the parameniscal region forming a cystic lesion. Fluid within the cyst is identical to synovial fluid[2]. However, in the absence of a tear, meniscal cysts may develop from a compression injury to the periphery of an already degenerate meniscus. Complications may arise due to the size and location of the cyst. Meniscal cysts usually extend laterally and large cysts may dissect through the joint capsule and collateral ligaments to form mobile masses. They may dissect for considerable distances in the soft tissues. Cysts arising from posterior meniscal horn tears may extend centrally to lie in close proximity to the posterior cruciate ligament(PCL), mimicking a PCL ganglion cyst. Postero-medial extension from the lateral meniscus causing pressure effects on the popliteal artery has also been reported[3]. Diagnosis is usually made clinically and imaging performed to further evaluate the lesion. Occasionally gas formation and bone erosion may be seen on radiographs. MR imaging demonstrates the mucinous contents, the lobulated nature and the precise anatomical location of the cyst to periarticular and intra-articular structures.
Medial meniscal cyst causing tibial erosion
Based on the provided left knee X-ray and MRI images, the following main features are noted:
Considering the patient’s clinical history (65-year-old male, long-term left knee pain, intermittent swelling, with a palpable mass and tenderness over the medial joint space) and the imaging findings, the following potential diagnoses are suggested:
Based on the typical location surrounding the medial meniscus, the cystic, multilocular high-signal appearance on imaging, and possible horizontal tear signs, combined with the patient’s symptoms and age, the most likely diagnosis is:
Medial Meniscal Cyst (Meniscal Cyst).
If further confirmation is needed, arthroscopic examination or more detailed MRI sequences can be performed to assess the extent of any meniscal tear.
Rehabilitation should follow a gradual and individualized approach. During periods of significant inflammation and pain, excessive stress on the affected knee should be minimized. As symptoms improve, activity levels and intensity can be progressively increased. Below is an example plan:
During the above exercise prescription, follow the FITT-VP principle (Frequency, Intensity, Type, Time, and Progression) by gradually increasing the volume of training and closely monitoring the knee’s response. If significant pain or swelling occurs, rest and seek medical evaluation promptly.
Disclaimer: This report is a reference-based analysis drawn from existing imaging and clinical information, and does not replace in-person consultation or professional medical advice. Actual diagnosis and treatment options should be determined by integrating the patient’s full medical history, physical examination, and additional diagnostic results.
Medial meniscal cyst causing tibial erosion
