Calcaneal Trabecular Bone Architecture

Familiarity with the normal trabecular architecture of the calcaneus is important for detecting subtle fractures on radiographs and avoiding mistaking a pseudo-cyst of the calcaneus (more below) for a true lesion.

Five trabecular groups have been defined in the calcaneus. These may be lumped into compressive and tensile trabeculae.

Compressive

• Thalamic (yellow): Greek for room or chamber. These are the primary compressive trabeculae and extend from the articular surface of the subtalar joint to the cortex of the posterior tuberosity in a concave anteroinferior curve.
• Anterior apophyseal (red): These are the secondary compressive trabeculae. Curved trabeculations fan out from the region of the sinus tarsi anteroinferiorly to the anterior tuberosity.

Tensile

• Inferior plantar (cyan): These are the primary tensile trabeculae. Curved trabeculations extend from the inferior cortex to the cortex of the posterior tuberosity.
• Anterior plantar (green): These are the secondary tensile trabeculae. Trabeculations extend from the anterior part of the inferior cortex anterosuperiorly to the anterior tuberosity.
• Posterior achillean (purple): Also known as the tendotuberosity group, these tensile trabeculae run parallel to the posterior tuberosity.

Subtle disruptions in these trabecular patterns can alert you to the possibility of a fracture. Keats has also described a prominent trabeculation along the inferior aspect of the calcaneus on the lateral view that can simulate a stress fracture.

A relatively lucent triangular window bounded superiorly by the primary and secondary compressive trabeculae and inferiorly by the tensile trabeculae is referred to as the foramen calcaneus or Ward's triangle. When prominent, it can be mistaken for a lesion, and is referred to as the pseudocyst or pseudolesion of the calcaneus.

References

• Aggarwal ND, Singh GD, Aggarwal R, Kaur RP, Thapar SP. A survey of osteoporosis using the calcaneum as an index. Int Orthop. 1986;10(2):147-53.
• Diard F, Hauger O, Moinard M, Brunot S, Marcet B. Pseudo-cysts, lipomas, infarcts and simple cysts of the calcaneus: are there different or related lesions? JBR-BTR. 2007 Sep-Oct;90(5):315-24.
• Keats TE and Anderson MW. Atlas of Normal Roentgen Variants That May Simulate Disease. 8th edition, page 886; Mosby (2004).