In evaluating a patient with knee swelling, which test helps differentiate intra-articular from extra-articular swelling?

• A. Anterior drawer test
• B. Patellar ballottement test and joint line palpation
• C. McMurray test
• D. Varus stress test

Answer: (B)

Differentiating where knee swelling sits hinges on detecting intra-articular fluid. The patellar ballottement test assesses intra-articular effusion by compressing the suprapatellar pouch and tapping the patella; a positive finding—patellar rebound or a fluid wave—indicates fluid inside the joint. Pairing this with joint line palpation helps confirm the source: true intra-articular effusion typically distends the joint line and yields a fluctuating swelling along the line of the joint, whereas extra-articular swelling from surrounding soft tissues does not produce a true joint effusion or distend the joint line.

Other maneuvers examine ligamentous stability or meniscal pathology rather than where the swelling originates, so they don’t directly differentiate intra- versus extra-articular swelling.