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Chapter Summary
• Context: The vertebral column possesses heightened vulnerability to bone metabolic disturbances due to its high proportion of trabecular bone and active remodeling. These characteristics make vertebrae primary target sites for osteoporosis and diverse metabolic bone disorders. Vertebral fractures can be clinically silent and frequently go unrecognized, despite signaling a markedly elevated risk for subsequent fractures and substantial functional impairment. Diagnostic evaluation does not end with confirming osteoporosis: secondary causes significantly alter management and must be systematically investigated. This chapter covers primary osteoporosis, glucocorticoid-induced osteoporosis, primary hyperparathyroidism, rickets and osteomalacia, and Paget disease of bone. It further addresses the critical interpretation of dual-energy X-ray absorptiometry (DXA), morphometric assessment of vertebral compression fractures, and fracture risk calculation tools. For spine surgeons, understanding these disorders is essential because bone mineral quality, deformity, frailty, and calcium-phosphate metabolism directly impact fracture risk, implant purchase, and spinal reconstruction outcomes.
• Chapter Objective: Understand why the spine is uniquely sensitive to metabolic bone diseases; recognize primary osteoporosis and diagnose secondary etiologies; critically interpret DXA scans and identify morphometric vertebral fractures; understand the mechanisms and fracture risks of glucocorticoid therapy; and differentiate primary hyperparathyroidism, osteomalacia, rickets, and Paget disease based on clinical, biochemical, and imaging profiles.
• The spine as a metabolically active organThe preponderance of trabecular bone renders the spine highly responsive to shifts in bone turnover. This biological property explains why systemic bone loss associated with aging, estrogen deficiency, or pharmacological exposure manifests early and prominently in the vertebral bodies.
• Osteoporosis and vertebral fracturesOsteoporosis represents compromised bone strength predisposing to an increased risk of fracture. It is diagnosed by bone mineral density (T-score ≤ -2.5) or the occurrence of a low-trauma fragility fracture. Figure 60.1 demonstrates how technical acquisition errors, positioning artifacts, and incorrect vertebral labeling on DXA distort diagnostic interpretation. Vertebral fractures exhibit various morphological patterns (wedge, biconcave, crush), summarized in Figure 60.2, and many remain asymptomatic. Identifying an existing vertebral fracture alters risk stratification and mandates active secondary etiology workup.
• Glucocorticoid-induced osteoporosisGlucocorticoids rapidly suppress osteoblastogenesis and osteocyte viability while transiently stimulating osteoclastic resorption, in addition to impairing muscle function and intestinal calcium absorption. Fracture risk rises rapidly within months of exposure and is disproportionate to DXA BMD measurements. Clinical risk calculators must be adjusted for glucocorticoid dosage and duration.
• Primary hyperparathyroidismPrimary hyperparathyroidism is frequently uncovered during secondary osteoporosis workup. Unlike states of generalized high turnover, cortical bone resorption (e.g., distal radius) is often more pronounced than trabecular loss; thus, seemingly preserved spine BMD does not exclude severe disease. Table 60.1 details criteria for surgical parathyroidectomy.
• Rickets and osteomalaciaMineralization defects result from abnormalities in calcium, vitamin D, or phosphate homeostasis. The chapter distinguishes calcipenic and phosphopenic disorders. Figures 60.3 and 60.4 illustrate how X-linked hypophosphatemic rickets can lead to severe enthesopathy, spinal canal narrowing, and DXA findings that do not simply reflect low bone mass.
• Paget disease of bonePaget disease arises from disordered, focal osteoclastic hyperactivity followed by chaotic bone formation, commonly involving the spine. Most patients are asymptomatic, with diagnosis triggered by elevated alkaline phosphatase or characteristic radiographic features (picture frame vertebra, cotton wool appearance). Figure 60.5 exemplifies multilevel spinal involvement.
• Clinical Application: For the spine surgeon, poor bone quality should never be accepted as a simple, monolithic diagnosis. A fragility fracture, low T-score, or impending instrumentation failure requires determining whether primary postmenopausal/senile osteoporosis or a treatable secondary disorder is present. DXA scans require rigorous visual verification: degenerative osteophytes, aortic calcifications, or vertebral collapse falsely elevate lumbar BMD. Clinically silent vertebral compression fractures must be actively searched for on sagittal radiographs or vertebral fracture assessment (VFA). In patients taking glucocorticoids, moderate BMD T-scores can conceal high fracture risk, warranting aggressive bone-protective treatment. Hypercalcemia, hypophosphatemia, diffuse bone pain, and proximal muscle weakness point toward specific endocrinopathies or mineralization defects requiring metabolic co-management before elective spinal reconstructions.
