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 (long arrow), a 1.5-inch needle could not reach this patient's joint via a medial approach. However, a lateral approach could be successful.