Fluid in normal and abnormal ankle joints: amount and distribution as seen on MR images

The appearance of fluid in tendon sheaths of the ankle joint and in ankle articulations seems to vary. To determine the degree of this variability and to see if fluid occurs in normal ankles, we evaluated the presence, amount, and distribution of joint fluid as seen on MR images of normal and abnormal ankles. The study included 40 normal ankles of volunteers, 15 ankles of patients with disorders of the posterior tibial tendon, 73 ankles of patients with disorders not involving tendons studied (occult fractures, osteochondritis dissecans, and Achilles tendon disorders), and 46 asymptomatic ankles of patients with disorders of the opposite ankle. We analyzed the MR images of these ankles to determine the volume of fluid in the ankle and subtalar joints. We also analyzed the relative volumes of fluid in tendon sheaths. We then compared the results in patients who had symptoms with those in asymptomatic subjects and developed an algorithm of fluid interrelationships. Most patients had fluid in the ankle (77%) and subtalar joints (72%). Fluid was common around all tendons except the extensor tendons. Large amounts of fluid were particularly common around the flexor hallucis longus tendon (14%). No statistically significant difference in the prevalence or relative volumes of fluid in the subtalar or ankle joints or tendon sheaths was found between normal and abnormal ankles. A close relationship was found between volumes of fluid between tendons, usually those in close proximity to each other. We found no correlation between fluid in the subtalar and ankle joints. Our results show that fluid in the articulations and tendon sheaths of the ankle is common in asymptomatic patients, and the amounts of fluid are not significantly different from the amounts in patients with symptoms. There also appear to be complex interrelationships between fluid seen in the joint and in tendon sheaths.