Synovial fluid in the hindfoot and ankle: detection of amount and distribution with US.

PURPOSE: To determine the amount and distribution of synovial fluid detectable with ultrasonography (US) of the hindfoot and ankle in asymptomatic volunteers.

MATERIALS AND METHODS: US was performed with a 7.5- or 10-MHz linear transducer of 60 hindfeet and ankles in 30 volunteers. Presence and amount of fluid were assessed in the ankle joint recesses, adjacent bursae, and tendon sheaths. Symmetry of bilateral fluid was evaluated.

RESULTS: Fluid was detected in the anterior recess in 20 ankles (bilaterally in eight volunteers), retrocalcaneal bursa in 30 ankles (bilaterally in 12 volunteers), posterior tibial tendon sheath in 46 ankles (bilaterally in 19 volunteers), and common peroneal tendon sheath in seven ankles (bilaterally in three volunteers). No fluid was seen in the posterior recess. On average, symmetry was present for only the retrocalcaneal bursal and peroneal tendon sheath fluid.

CONCLUSION: US of the hindfoot and ankle commonly depicts articular, bursal, and tendon sheath fluid in asymptomatic volunteers. The presence of fluid in these locations, even when unilateral or asymmetric, does not necessarily imply underlying abnormality.