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FOUNDATION OVERVIEW

Osteoporosis is characterized by bone loss, reduced bone strength, and deterioration of skeletal microarchitecture resulting in fragile bones. Due to decreased bone strength and quality, fracture risk is increased, particularly of the hip, spine, and wrist. Osteoporosis-related fractures are described as a fracture in adulthood that occurs with trauma less than or equal to a fall from standing height, excluding the fingers, toes, face, and skull. In the United States, women have a higher osteoporotic fracture risk compared to men, likely due to postmenopausal bone loss and lower peak bone mass. Adult peak bone mass is primarily regulated by physical activity, reproductive endocrine status, and calcium intake, with peak bone mass attainment generally occurring in the third decade of life.

Bone remodeling, continuous breakdown and replacement of bone tissue, is controlled by osteoblasts and osteoclasts. Osteoblasts are responsible for the formation and mineralization of bone. Osteoclasts break down bone to form cavities within the tissue (ie, resorption). As bone formation exceeds resorption, the overall increase in bone mass is achieved. In a young adult, bone remodeling is stable as new bone is generated, replacing damaged bone. As a person ages, there is an imbalance in the remodeling process—driven by osteoclasts and their resorptive properties. This increased rate of bone loss that begins during perimenopause may last up to 8 years postmenopause. Throughout this time, up to 2% of bone loss may occur annually. The remodeling process also leaves small bone deficits each cycle that accumulate over the life span. Another important mediator in the remodeling process involves receptor activator of nuclear factor-kappa-B ligand (RANK-L). RANK-L is secreted by osteoblasts and binds to the RANK receptor on osteoclasts, thereby promoting development and activation of osteoclasts inducing bone resorption.

Patients with osteoporosis are frequently asymptomatic, but experience localized pain with fractures described as sharp, nagging, or dull as well as immobility. Patients may also experience depression from physical limitations after fractures. Baseline laboratory tests include complete blood count, basic metabolic panel, thyroid stimulating hormone, 25-hydroxy vitamin D, serum creatinine, calcium, phosphorus, and alkaline phosphatase. In men, total testosterone is also assessed. Patients should be assessed for osteoporosis risk factors, in addition to fall risk (Tables 49-1 and 49-2).

TABLE 49-1Risk Factors for Osteoporosis

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