When using the lateral approach for knee arthrocentesis, an assistant may help direct synovial fluid towards the aspiration site by (A) gently applying pressure to the patella to displace it laterally from its natural position and (B) depressing the medial border of the patella towards the floor to tilt the lateral border upwards and open a larger window for aspiration. The needle is inserted approximately one finger breadth below the patellar edge; deep insertion should be avoided as the needle may encounter the periosteum and cause pain. Manipulation of the patella may be painful if the patient has patellofemoral cartilage loss.
