Magnetic resonance imaging of markedly obese patient with mistaken clinical diagnosis of joint effusion

False clinical impression of joint effusion in a markedly obese patient with rheumatoid arthritis. Axial T1-weighted image through the mid-patella shows no significant joint effusion. The normal collapsed medial recess of the knee joint is denoted by arrow heads. As can be seen by the hypothetical needle tract (arrow), a 1.5-inch needle could not reach this patient's joint via a medial approach. However, a lateral approach could be successful.