Osteoporosis is a condition of bones, where the bone density and the bone mass gradually decrease and leads to various complications – mainly increased risk of having fractures.
The name osteoporosis is derived from two Greek words, ‘ostoun’ meaning “bone” and ‘poros’ meaning “pore”, so osteoporosis literally means the condition of having porous bone. Under microscope a healthy bone shows a honeycomb like structure but in the case of osteoporosis the holes and spaces in the honeycomb get increased. The image of a healthy bone and a bone with osteoporosis are given below :
Normal healthy bone
Bone with osteoporosis
Women are more prone (especially past menopause) to osteoporosis than men.
Symptoms of osteoporosis :
- Back pain or lower back pain due to vertebral collapse.
- Stooped posture
- Gradual loss of height
- Prone to bone fracture
- Sometime osteoporosis may also be asymptomatic
Pathogenesis : Osteoporosis happens due to the imbalance in the rate between the bone resorption or breakdown of bone and the bone formation. This imbalance may cause by various reasons, that are discussed later.
The remodeling of the matrix of bones is a continuous process. First the bone is resorped by osteoclast cells and then replaced by osteoblast cells, if the rate of bone resorption became higher than the rate of bone formation then osteoporosis happens.
Causes of osteoporosis : The main cause of osteoporosis for both men and women is advanced age. The women are more prone osteoporosis because of the oestrogen deficiency due to menopause or oophorectomy.
Other causes are as follows:-
- Vitamin D deficiency is a major cause of osteoporosis, it is seen that some association exists between 1,25-dihydroxycholecalciferol levels in blood serum and bone mineral density.
- Tobacco smoking generally detoriates bone health but the underlying mechanism is not yet clear, it is proposed that tobacco smoking may have some inhibition action upon the activity of osteoblast cells. The associated complications of tobacco smoking like lower body weight, earlier menopause are also increase the risk of osteoporosis.
- Excessive alcohol intake also increase fracture risk.
- Malnutrition is an important case of osteoporosis. Defeciency of calcium with or without phosphorus, zinc, boron, iron and various vitamins like vitamin A, D, E, K and C also the causes behind osteoporosis. Imbalance of omega-6 to omega-3 fatty acid ratio may also increase the risk.
- Underweight, inactive and short stature may also an indication of the increased risk of having osteoporosis.
- Exposure to the heavy metals like cadmium and lead may also increase the fracture risk.
- It is seen that prolonged immobilization may leads to osteoporosis. Immobilization of fractured limbs may sometime causes localized osteoporosis . Prolonged space flight may also leads to bone loss.
- Endocrine disorders like hyperparathyroidism, hypothyroidism, thyrotoxicosis, Cushing’s syndrome, diabetes mellitus type 1 and 2, acromegaly, and adrenal insufficiency may induce osteoporosis. Reversible bone loss can happen in the time of pregnancy and lactation due to the change in hormonal level.
- People with rheumatoid arthritis, ankylosing spondylitis are at increased risk of osteoporosis.
- The association of osteoporosis is seen with various inherited diseases like osteogenesis imperfecta, Marfan syndrome, hypophosphatasia, glycogen storage diseases, hemochromatosis, homocystinuria, porphyria, epidermolysis bullosa, Ehlers–Danlos syndrome, Menkes’ syndrome and Gaucher’s disease.
- Some medications like use of steroid drugs, anticoagulants, proton pump inhibitors, thiazolidinediones may increase the risk of osteoporosis.
Conventional radiography : Conventional radiography is used (with or without CT or MRI) for detecting reduced bone mass or preosteoporosis. The main feature of this diagnosis is the increased radiolucency of the bones due to the cortical thinning.
Dual-energy X-ray absorptiometry : It is the most widely used means of measuring bone mineral density. In this procedure two X-ray beams with different energy levels are aimed at the patient’s bones. Some of the X-rays are absorbed by the soft tissues of the patient and is subtracted out to get the bone mineral density from the degree of absorption of each X-ray beam by the bones. The radiation received by the patient during the scan is negligible.
When the measured bone mineral density is less than or equal to 2.5 standard deviations then it is diagnosed as osteoporosis. This measured standard deviation is termed as T-score. The following diagnostic guidelines has established by World Health Organization :
|Normal||T-score ≥ −1.0|
|Osteopenia*||−2.5 < T-score < −1.0|
|Osteoporosis||T-score ≤ −2.5|
|Severe osteoporosis||T-score ≤ −2.5 with fragility fracture|
Osteopenia* : When the bone mineral density is lower than normal then the condition is termed as osteopenia. It is sometimes considered as to be a precursor to osteoporosis.
Bio markers : The degree of bone degradation may also be detected by using chemical bio markers
A chart containing the comparison of bone pathology is given below :
|Condition||Calcium||Phosphate||Alkaline phosphatase||Parathyroid hormone||Comments|
|Osteoporosis||unaffected||unaffected||normal||unaffected||decreased bone mass|
|Osteopetrosis||unaffected||unaffected||elevated||unaffected||thick dense bones also known as marble bone|
|Osteomalacia and rickets||decreased||decreased||elevated||elevated||soft bones|
|Osteitis fibrosa cystica||elevated||decreased||elevated||elevated||brown tumors|
|Paget’s disease of bone||unaffected||unaffected||variable (depending on stage of disease)||unaffected||abnormal bone architecture|
As stated earlier excess alcohol intake and tobacco smoking increase the risk of osteoporosis, so moderation of alcohol intake and cessation of smoking are recommended.
Diet rich in calcium and vitamin D may help to decrease the risk of having osteoporosis. External Calcium and vitamin D supplements may also be given.
Hormones are very important in the treatment of osteoporosis. Estradiol has been shown to decrease bone resorption, and testosterone has been shown to build bone.
Drugs like Bisphosphonates, Teriparatide, Raloxifene have also been used and may be effective for the treatment of osteoporosis.