Right Knee Pain - Runner

Abstract

HISTORY: A 60 year old male runner with a history of right common peroneal nerve entrapment status post-surgical decompression presented for evaluation of right lateral knee pain that had been present for 1 year. He described dull, lateral, aching knee pain, worsened by impact activity (e.g., running). He denied mechanical symptoms or effusion. Knee MRI demonstrated popliteus tendinopathy with partial-thickness intrasubstance tearing and a 10x5mm peritendinous cyst. Ultrasound (US)-guidance was used to drain and fenestrate the cyst, and fenestrate and inject the popliteus tendon with leukocyte rich platelet rich plasma (PRP). The procedure was performed without complication. The patient used crutches for 5 days post-procedure, but on day 6 he walked 6 blocks without crutches. That evening, he developed pain and swelling with erythema in the suprapatellar region. No fever, chills, or knee drainage was present. Due to the symptoms, he returned to clinic for evaluation. PHYSICAL EXAMINATION: Healthy appearing male in no acute distress. Mildly antalgic gait pattern. Grade 2 right knee effusion with erythema around the superolateral aspect of the knee. Well-healed injection site without erythema. Mild tenderness to palpation over the popliteus tendon insertion. Normal ligamentous and meniscal tests. DIFFERENTIAL DIAGNOSIS: 1. Acute knee effusion secondary to overuse after recent PRP injection 2. Septic arthritis 3. Post-injection flare TEST AND RESULTS: Right knee limited ultrasound - moderate effusion within suprapatellar recess Right knee aspiration - Appearance: straw colored - Cell count: 1283 - Neutrophils: 60 - Gram stain: negative - Culture: no growth - Crystals: intracellular CPPD crystals FINAL WORKING DIAGNOSIS: Acute right knee pseudogout flair in a patient with no history of pseudogout, status post popliteus tendon PRP injection with peritendinous cyst aspiration and fenestration. TREATMENT AND OUTCOMES: The patient was successfully treated with crutches, ice, compression, elevation, and NSAIDs.