A 71-year-old woman is brought to the clinic because of sudden mid-back pain that began when she bent over to lift a light grocery bag. She denies trauma, fever, weight loss, or night sweats. She has a history of osteoporosis and has not taken her prescribed bisphosphonate for the past year. Vital signs are normal. Examination shows focal tenderness over the mid-thoracic spine and increased kyphosis. Neurologic examination of the lower extremities is normal. A lateral radiograph of the thoracic spine shows anterior wedging of the T8 vertebral body with loss of anterior height; the posterior vertebral body wall is intact.

Which structure is most likely damaged, leading to this patient’s vertebral deformity?