A 22-year-old woman with one week of left knee pain after a basketball game 8 days ago, knee effusion, and tenderness over the medial joint line. Most likely diagnosis?

• A. Chondromalacia patella
• B. Medial meniscus tear
• C. ACL tear
• D. Prepatellar bursitis

Answer: (B)

Pain along the joint line after a twisting knee injury points to a meniscal tear, and the medial meniscus is the one most commonly injured. The menisci sit between the femur and tibia and help distribute load; when the knee twists with the foot planted during basketball, the medial meniscus can be torn, producing tenderness specifically at the medial joint line and a developing effusion as the inflammatory fluid accumulates.

In contrast, chondromalacia patella typically causes anterior knee pain around the patella with possible crepitus and pain with kneeling or bending, not isolated medial joint line tenderness. An ACL tear often presents with immediate swelling and instability after a pivot or hyperextension; prepatellar bursitis shows swelling over the kneecap in the front, with tenderness there rather than along the medial joint line.

So the pattern of medial joint line tenderness after a twisting knee injury with subsequent effusion best fits a medial meniscal tear.