Anterior Cruciate Ligament Cyst in a Powerlifter: A Case Report

Case Diagnosis: A 26-year-old female weightlifter with anterior cruciate ligament cyst.

Case Description or Program Description: The patient presented with deep right knee pain exacerbated by squatting and lunging. Two years ago, the patient suffered a right tibial plateau fracture after dropping a barbell during a Power Snatch. Pain had kept her from returning to weightlifting.

Physical exam revealed no erythema or effusion of either knee. The distal musculature, joint lines, and patellar facets were nontender. The right knee showed decreased range of motion compared to the left, with a 10° deficit in flexion and a 5° lag in extension. Strength testing was 5/5 bilaterally. Anterior drawer testing of the right knee showed increased laxity. Both knees were neurovascularly intact. Ultrasound showed an anechoic, well-circumscribed, non-compressible mass deep to the infrapatellar fat pad. The mass measured 2.02 cm x 1.08 cm x 1.72 cm and did not display color Doppler flow.

Treatment proceeded with cyst aspiration and a Toradol injection.

Setting: Outpatient Musculoskeletal Clinic

Assessment/Results: The patient reported 80% relief after the procedure. Patient resumed rehabilitation and continued working on a return to sport.

Discussion (relevance): Literature reports that anterior cruciate ligament (ACL) cysts are rare with a prevalence of 1.3% on MRI. They may develop within the intra-synovial or extra-synovial space, with the latter affecting the infrapatellar fat pad and cruciate ligaments. The literature hypothesizes that trauma and repetitive mechanical stress contribute to the development of intraarticular cysts. MRI is considered the gold standard in diagnosing ACL cysts due to its ability to differentiate cystic or infiltrative origin. However, cysts may also be visualized on ultrasound as anechoic and unilocular or multilocular structures. Ultrasound-guided aspiration may be used to treat ACL cysts in a more accessible and less invasive manner than surgery.

Conclusions: ACL cysts are a rare condition that may be diagnosed with ultrasound and treated with ultrasound-guided aspiration.