patient comes in with right knee in severe pain. cannot walk. needs wheelchair.

Possible causes of severe right knee pain with intermittent locking and inability to walk, especially in a patient playing social tennis weekly, include osteoarthritis with meniscal tear and mechanical joint symptoms.

Osteoarthritis of the knee is a common condition, particularly in middle-aged or older individuals who engage in knee-loading activities, such as tennis NICE CKS. The presence of anteromedial or anterolateral pain on walking and intermittent locking suggests meniscal injury, as locking (inability to fully straighten the knee) often indicates loose meniscal cartilage NICE CKS. Previous knee pain history supports chronic joint pathology such as osteoarthritis or meniscal degeneration NICE CKS,NICE CKS.

Associated clinical features in osteoarthritis include joint line tenderness, crepitus, quadriceps weakness (which contributes to episodes of giving way), swelling, and restricted flexion/extension NICE CKS. Severe pain and inability to walk requiring a wheelchair may indicate an acute meniscal tear superimposed on osteoarthritis or advanced disease NICE CKS,NICE CKS.

Other differential diagnoses include ligamentous injuries, inflammatory conditions, infection, tumours, referred pain, and bursitis NICE CKS. However, the history of intermittent locking and previous pain makes meniscal tear and osteoarthritis the most likely causes.

Participation in social tennis once or twice weekly increases cumulative load on the knee and risk of degenerative meniscal and cartilage injury NICE CKS,NICE CKS. Sporting activity is a recognized risk factor for osteoarthritic knee changes and meniscal tears NICE CKS.

Urgent assessment and possible imaging (knee MRI) are indicated to evaluate for meniscal tears and other intra-articular pathology given mechanical symptoms and severe functional impairment. Referral to musculoskeletal services for persistent symptoms or unclear diagnosis may be needed NICE CKS.