SLR - December 2020 - Steven B. Georgian

Possible Pathogenesis of Calcaneal Bone Cyst

References: Hoshi, M., Oebisu, N., Iwai, T. et al. Possible pathogenesis of calcaneal bone cysts. Arch Orthop Trauma Surg 140, 1303–1310 (2020). https://doi.org/10.1007/s00402-019-03299-0

Scientific Literature Review

Reviewed By: Steven B. Georgian, DPM
Residency Program: West Penn Hospital Foot and Ankle Surgery – Pittsburgh, PA

Podiatric Relevance: Despite the foot being an uncommon location to find a primary osseous tumor, bone cysts can be commonly encountered in the calcaneus. Many times, bone cysts are discovered incidentally on radiographic imaging as a result of trauma. There are limited studies of the pathogenesis of calcaneal bone cysts; therefore, this study gives us some insight into the radiologic and pathological findings of calcaneal bone cysts.  

Methods: Twenty-four patients (18 male and 6 female) were diagnosed with calcaneal bone cyst between the ages of 10 in 16 years of age. Inclusion criteria consisted of patients who were diagnosed with having a calcaneal bone cyst and who underwent surgery. Different imaging modalities such as CT scan, MRI, cystography, and bone scintigraphy were used to better analyze each calcaneal bone cyst. Bone cyst location and area of occupancy was described using Diard’s classification.

Results: In all 24 cases, each calcaneal bone cyst was located in the central triangular area of rarefacted bone. Six of the calcaneal bone cyst had extensions posteriorly and two extended anteriorly. Bone cysts laterality was examined using MRI with 21 cases located centrally, two medially and one laterally. A foramen structure was identified in 15/20 cases which allowed for communication between the subtalar joint (STJ) and the calcaneal cyst. This foramen structure was located at the anterior margin of posterior facet of the STJ. Throughout surgical intervention, cystic fluid was encountered in each case. In 18 patients, the aspirated fluid was hemorrhagic with six cases being straw-colored.

Conclusions: The sinus tarsi artery expands radially throughout the calcaneus to supply the calcaneus by means of the nutrient foramen, which is located at the anterior aspect of the posterior facet of the STJ. In instances where circulation collapse of the sinus tarsi artery occurs, chronic hemorrhage can result and accumulate in the biomechanically stress free zone of the central triangle of calcaneus, ultimately resulting in the formation of a calcaneal bone cyst. This study has given us a deeper understanding of  the pathogenesis of calcaneal bone cyst formation.

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