Age / Sex : 73 / F

Chief complaint: ankle pain, swelling, mild heating sense

PHx: antidepressant medication

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Multifocal insufficiency fractures of the ankle

Discussion

Findings:

1. multifocal intraosseous irregular lines perpendicular to the main orientation of the trabecular bone in the posteromedial distal tibia, calcaneal tuberosity, talus body and head, and subchondral bone of the cuboid


2. diffuse bone marrow edema and periosteal reaction with enhancement

Differential Diagnosis: osteomyelitis, inflammatory arthritis, osteonecrosis

Diagnosis: insufficiency fractures due to osteoporosis

Discussion:

Metabolic bone disorders preferentially affect cancellous bone, which has a 10-fold higher proportion of surface area to mass than cortical bone, exposing large amounts of this surface to metabolic stimuli and regional blood flow. The bone loss seen in the cancellous trabeculae is nonuniform, with preferential loss of the secondary trabeculae rather than the primary longitudinally oriented weight-bearing trabeculae, leading to disordered bone architecture that fails easily with even physiologic loading. The ability of the unsupported primary longitudinal trabeculae to absorb compressive loading is severely diminished due to the loss of supporting secondary trabeculae, resulting in buckling failure as predicted by Euler law. Buckling failure of contiguous primary trabeculae accounts for the typical orientation of insufficiency fractures, which propagate perpendicular to the axis of the primary trabeculae.

Insufficiency fractures typically affect those regions of bone where there is a high cancellous fraction, such as the vertebral bodies, the flat bones of the pelvis (particularly the regions of the sacral ala), the subchondral regions of the long tubular bones, and the small irregular bones of the foot (such as the calcaneus). Collapse of the subchondral bone leads to an imaging appearance that simulates that of osteonecrosis. As an example of this, overloading of the subchondral bone about the knee, typically accompanied by adjacent meniscal and chondral abnormalities, results in collapse at the subchondral bone plate of the femur or tibia, a condition previously and erroneously designated spontaneous osteonecrosis

Use of antidepressant medications that act on the serotonin system has been linked to detrimental impacts on bone mineral density (BMD), and to osteoporosis.

References:

Mini NP, Christine BC, Donald LR. Acute and stress-related injuries of bone and cartilage: pertinent anatomy, basic biomechanics, and imaging perspective. Radiology 2016;280(1):21-38.

Rizzoli R, Cooper C, Reginster JY, et al. Antidepressant medications and osteoporosis. Bone 2012;51(3):606-13.