A 27-year-old male visited our hospital because of severe pain in the popliteal area that occurred when the knee was flexed actively beyond 100° during squatting or flexed passively beyond 120° in the crossed leg position. He had struck the lateral side of his left knee against the fence alongside a ski slope while snowboarding 8 weeks earlier, and the symptoms aggravated despite conservative management. He had no history of trauma prior to that event. On physical examination, the anterior drawer test was grade 1 (4 mm) and the Lachman test result was a firm end point. The pivot shift, posterior drawer and valgus stress tests were negative. The patient complained of tenderness around the medial femoral condyle (MFC).
Plain radiographs of the knee were normal. However, magnetic resonance imaging (MRI) of the left knee showed a bone marrow contusion on the lateral tibial plateau, sprains of the anterior cruciate ligament (ACL) and medial collateral ligament (MCL). In addition, MRI demonstrated a rounded and well-demarcated soft mass anterior to the PCL, and the ligament was slightly deformed due to the mass. The cystic lesion was seen originating from the deep recess between the posterior root of the MM and the PCL that bulged into the posteromedial joint space with a signal change in the posterior root of MM and the PCL adjacent to the cyst ().
Fig. 1 (A) Axial fat-suppressed T2-weighted MR image and (B) sagittal turbo spin echo T2-weighted MR image showing an intervening lobulated cystic lesion (asterisk) located in the deep recess between the posterior root of the medial meniscus (black arrow) and (more ...)
Arthroscopy revealed a cystic lesion, about 7 mm in diameter, originating from the anterior aspect of the PCL between the posterior root of the (MM) and the PCL (). During knee flexion, the cystic lesion enlarged as it was compressed between the posterior root of the MM and the PCL, and it impinged on the articular cartilage of the posterior MFC, the posterior root of the MM, and the PCL (). In addition, a dimple was found on the articular cartilage of the posterior MFC adjacent to the cystic lesion (). When the cyst was punctured, a jelly-like viscous fluid was extruded, and some degenerative soft tissue attached to the PCL was identified. We removed the cystic lesion completely along with some fibers from the PCL adjacent to the cystic lesion where the signal change was seen on MRI () and the specimen was sent to the pathology department. We did not find any significant instability related to the ACL, PCL, or MCL, and no other intra-articular pathology. The histologic examination of the cystic tissue showed proliferation of synovial cells with mild chronic inflammation and cystic space lined by fibrous connective tissue with focal myxoid degeneration, confirming the diagnosis of ganglion.
Fig. 2 Arthroscopic finding of the posteromedial compartment of the knee joint. (A) The ganglion cyst originated from the anterior aspect of the posterior cruciate ligament (PCL) in the deep recess between the posterior root of medial meniscus (MM) and the PCL. (more ...)
The symptoms improved immediately after the operation. At 12 months postoperatively, the patient was able to perform all activities of daily living, including squatting and sitting in the crossed leg position, and had full range of motion (ROM). No instability of the knee joint was detected. The Visual Analogue Scale had decreased from 9 preoperatively to 1.