A 54-year-old woman comes to the clinic because of progressive, diffuse bone pain and difficulty climbing stairs for the past 8 months. She reports proximal muscle weakness and fatigue. She underwent a Roux-en-Y gastric bypass 3 years ago and has had chronic diarrhea and unintentional weight loss since then. Medications include a multivitamin taken inconsistently. She rarely goes outdoors. Physical examination shows tenderness over the ribs and tibias and 4/5 strength in hip flexion and shoulder abduction. Laboratory studies show:
X-ray of the pelvis shows diffuse osteopenia and thin transverse radiolucent lines perpendicular to the cortex in the femoral neck and pubic rami.
Which of the following best describes the underlying bone pathology responsible for this patient’s condition?
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