On the Cover: Os trigonum and posterior facet calcaneus subtalar bipolar arthritis. Photographs taken during subtalar joint arthroscopy. The patient was a 39-year-old woman who had experienced right foot and ankle pain for over a year. She was no longer able to run or wear high heels and she complained of constant pain. A preoperative MRI of her hindfoot was notable for chronic moderategrade sprains of the lateral ligaments, some sinus tarsi fluid collection, edema in the os trigonum, and synovitis. Given her chronic ankle pain and advanced imaging findings, she was scheduled for ankle/subtalar arthroscopy. These images show the os trigonum while viewing from the central portal and instrumenting from the posterolateral portal. We were impressed to find a loose, arthritic os trigonum that articulated with the posterior facet of the calcaneus. Instead of a normal synchondrosis, there was a groove in the os trigonum and a corresponding groove in the calcaneus. The articulation had developed significant arthritis to the point of bone-on-bone changes. (Left) The os trigonum and subtalar joint as we saw it on starting the diagnostic exam. (Center) Removal of the os trigonum with a pituitary rongeur. (Right) After excision, showing the size of the os trigonum. See accompanying video at www.arthroscopyjournal.org.. Courtesy of Randy Clark, M.D., and Richard D. Ferkel, M.D.
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