Osteoporosis

Osteoporosis is a decrease in bone strength. The strength of the bone depends on mineral density and bone quality (Figure 1).

Osteoporotic bone is at risk of fracture at the hip, wrist and spine.

If fracture of the vertebral spine occurs, the patient will have a five-fold increased risk for having a second vertebral fracture or hip fracture. A second vertebral fracture means the patient may have more spine compression fractures in the future.

With one hip fracture, there will be a tenfold increase of another hip fracture occurring. Men with hip fractures have a higher mortality rate than women (Figure 2). Lifetime risk of fractures of the hip, spine and wrist is 40%. The decrease of bone strength and bone mass clearly predicts a fracture risk.

Osteoporosis affects 45% of women aged 50 or older. There is some correlation between osteoporotic fracture and risk of death. This is logical since 25% of patients with hip fracture die within one year. The lifetime risk is high with senile osteoporosis. There are about one million osteoporosis related fractures that occur per year.

Men and women both begin to start “spending” or losing bone at a certain point in their lives. Banking or building up of bone during youth has benefits during the later years. Most individuals obtain their peak bone mass between ages of 16 and 25 years. Men begin to lose bone mass after the age of 25 years at a rate of 0.3% per year. Women begin to lose bone at a rate of 0.5% per year. After menopause there is an accelerated rate of bone loss at the rate of 2-3% of total bone loss per year for about 10 years (Figure 3).

There are two types of osteoporosis:

1. Type I: postmenopausal which occurs 15-20 years after menopause. It has an increased risk of vertebral and wrist fractures. It is due to estrogen deficiency. This affects the trabecular bone.

2. Type II: senile which occurs in men and women over the age of 70 years. Vertebral and hip fractures are a risk. It occurs more in females than males with a ratio 2:1. It is due to aging and long term calcium deficiency. This affects the cortical and trabecular bone equally.

20-25% of elderly patients could die within one year suffering of a hip fracture (Figure 4).

Risk factors for osteoporosis include: thin, north European descent, people who live sedentary lifestyles, smoker and drinkers, and anti-seizure medications as phenytoin (Dilantin) and phenobarbital.

The bone mineral density is measured by the T- score which is relative to normal age, young, matched control (25 year old women) and the Z-score which is relative to similar aged patients.

How is osteoporosis measured? It is measured by DEXA scan at the hip through the T –score (Figure 5). DEXA scan is important in predicting fracture risk.

Lab findings such as albumin, calcium, phosphate, vitamin D, parathyroid hormone and bone specific alkaline phosphatase are usually normal.

Vitamin D levels are low in about 70% of patients with fracture. Vitamin D absorbs calcium from the intestines. With aging, the stomach acidity decreases and the calcium absorption decreases and vitamin D requirements increase. Elderly need more vitamins D to absorb the same amount of calcium.

Treatment of osteoporosis include: bisphosphonates, Denosumab and calcitonin. Bone stimulation can be achieved by parathyroid hormone, calcium and vitamin D. Bisphosphonates inhibit osteoclast membrane ruffled border and could incorporate into the bone. Avoid bisphosphonates in renal failure. It can cause osteonecrosis of the jaw. Denosumab inhibits the binding of RANKL to RANK. Calcitonin inhibits osteoclasts activity.

When to initiate therapy? If T-score is less than -2 with no risk factors, if T-score is less than -1.5 with at least one risk factor as prior vertebral fracture or hip fracture.

What decides if you develop osteoporosis or not? Your savings: you can control this by adding more bone when you are young before the age of 25 years by living a healthy life with proper diet and some exercises. You begin spending your bone after 25 years.

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