Morphological analysis of subchondral talar cysts on microCT.

PURPOSE: Osteochondral talar defects often present in conjunction with subchondral bone cysts. The exact aetiology of these cysts is unknown. Recently was shown in a computational bone model that pressurized fluid and osteocyte death could lead to cyst growth, through mechanoregulated bone adaptation. However, a difference in cyst morphology was present between the mechanisms. The purpose of this study was to evaluate and compare the cyst morphology of human cadaveric tali by using microCT with the morphological simulation results previously reported.
MATERIALS AND METHODS: Sixty-six fresh-frozen human cadaveric tali were screened in a regular CT for subchondral bone cysts, radiologically defined as unexpected rounded radiolucent area. Subsequently, the tali with a cyst were scanned in a microCT. The shape of the cysts, the presence of an opening through the subchondral bone plate, and the bone volume fraction around and next to the cyst were analysed.
RESULTS: In total, six tali were found to have a single cyst. Four cysts had an irregular shape, and two cysts were rounded. A clear opening from the cyst through the subchondral bone plate was found (diameter 0.5-1.7 mm) in four cysts. The bone volume fraction was higher (p = 0.025) around the cyst then next to the cyst.
CONCLUSIONS: The morphological findings that we found are only compatible with the previously reported simulation results of cyst growth in response to pressurized fluid, or pressurized fluid in combination with osteocyte death. It is therefore most likely that pressurized fluid plays a role in the pathoaetiology of cyst growth. A better understanding of cyst growth may improve treatment and prevent further cyst formation.