Wednesday, August 14, 2013

Bone Mineral Density

 A common myth among patients is that all bone related or orthopaedic problems are related to a lack of calcium. Daily, I see patients who are taking calcium supplements on their own accord. People especially women feel that they need to take calcium beyond a certain age, or taking calcium will prevent orthopaedic problems in the future. Usually it is a friend or family member that has scared a person into taking calcium supplements. 

It is wrong to attribute all bone problems to calcium. Often the source of musculoskeletal pain is a joint! There are many joints in the body. Everyone is familiar with the large joints like the hip or knee and small joints like the ones found in the hand and foot. There are also lesser known joints like the facet joints found in the spine (neck and back). Inflammation of the joint is known as arthritis. Arthritis has little to do with the lack of calcium. Therefore taking calcium will not reduce joint pain! 

So if lack of calcium does not cause joint pain, then what does a lack of calcium do? A decrease in the calcium content of bones is typically called osteoporosis (different from osteo-arthritis) There are other disorders of calcium like osteomalacia and rickets but these are rare. Osteoporosis affects women after menopause. It is the lack of female hormones (estrogen and progesterone) that leads to osteoporosis. Osteoporosis also affects men but at a later age and less commonly. Osteoporosis is a silent disease. That means that it causes very few or no symptoms. Many patients of osteoporosis will not know that they are suffering from it! This is similar to medical illnesses like diabetes and hypertension (high BP). Time and again the first symptom of osteoporosis is a fracture of the hip or a vertebra (spine fracture). Rarely osteoporosis may cause bone or muscle pain or tenderness (pain on pressing the bone). 

If osteoporosis is a silent disease, how do doctors and patients diagnose it? Like diabetes early diagnosis of osteoporosis is critical as treatment can reduce fracture risk. Earlier it was difficult to diagnose osteoporosis. Doctors would get some idea of bone strength by looking at x-rays of the patient. However x-rays are a crude test as they show osteoporosis only in the advanced stages. By then it is too late! Measuring the blood calcium levels gives no indication of the strength of bones or the level of calcium in the bones. Nowadays technology has improved. A DEXA scan is currently the gold standard for measuring bone mineral density (BMD). DEXA scan checks the density in the lower back and hip which are the critical areas. DEXA scan is a computerised X-ray based test. Ultrasound of the wrist or heel can also be done. Ultrasound is popular as it is portable (used frequently in patient camps) and cheaper. But ultrasound is less accurate and the wrist and heel density may differ from the density in the back and hip. I do not recommend treatment decisions to be made on ultrasound based bone density results. Does everybody need to do a DEXA scan? The answer is NO! The World Health Organisation (WHO) recommends BMD testing in all postmenopausal women above 65 years of age. In post menopausal women less than 65 and premenopausal women, density testing is required only if they have certain medical risk factors (ask your doctor). There is no need for healthy premenopausal women to do a DEXA scan or other BMD testing. BMD testing is also not recommended for healthy men with no risk factors. 
To conclude, I advice my readers to be smart about calcium supplements. Taking unnecessary supplements in the hope of reducing pain is a waste of money. At the same time one should be alert about osteoporosis. Timely BMD testing by DEXA scan is the key. If osteoporosis is diagnosed by a DEXA scan, then treatment with supplements is imperative.
BMD measurements have today become essential for fracture prevention and osteoporosis treatment, but due care is needed in utilising this asset.

Hip Replacement

Arthritis affects the hip joint just as it affects the knee. Hip arthritis is less common in Indians and Asians. One disease that we commonly see is avascular necrosis (AVN). In AVN the blood supply to the head of the femur (thigh bone) is cut off due to some pathology. The most common reasons for AVN are alcohol intake and steroid medication. The dead femoral head loses its round shape and becomes flat and deformed. This leads to destruction of the hip joint and arthritis. Patients have severe pain in the hip. Movements become restricted and very painful.   In advance stages patients have difficulty in walking. They walk slowly with a limp usually with support of a stick or walker.
There are many non surgical and surgical treatments of AVN in the early stages. However in the late stages the only solution is total hip replacement (THR). Similarly end stage arthritis of the hip due to any cause can be successfully treated by hip replacement alone. Hip replacement has been around for more than 60 years. In this time hip replacement has seen a tremendous evolution. Hip replacement can be partial or total. In partial hip replacement, only the ball (head of femur) is replaced. The original cup of the patient is retained. This surgery is typically done for older patients who fracture the neck of femur (hip fracture).
In total hip replacement, both the ball and socket is replaced. This surgery is done for hip arthritis where both ball and socket are damaged. Originally in total hip replacement both components (stem and cup) were fixed to bone with bone cement (cemented hip). The cemented stem (which holds the ball) works very well and has a long life. However the cemented cup lasts only 10 to 12 years. The need to improve life of the prosthesis led to the evolution of uncemented hips. In uncemented design, the cup and the stem are fitted into the bone without using cement. The surface of the stem and cup is made very rough or porous. This allows the bone to grow into the surface. As a result of this bone growth, the life of the prosthesis improves tremendously.  
Originally in total hip replacement, the ball was made ofmetal and the cup was made of high density plastic (metal onplastic). The problem with plastic is that it wears out over time. There has been a big improvement in these materials over the years. The original plastic has undergone a series of changes (highly cross linked) which has improved the durability of the plastic. The biggest change has been the introduction of ceramic. Early ceramic was brittle and had issues of breakage. With later generations of ceramic, the breakage problem was solved. By using ceramic heads instead of metal ones, the wear of the plastic cups is reduced (ceramic on plastic). Then came the ceramic cups. By using a ceramic cup and ceramic ball (ceramic on ceramic), there is very little wear of the cup and the life of the prosthesis is improved drastically. Ceramic on ceramic THR is ideal for the younger patient as it is very durable and lasts a long time. However it is a technically sensitive surgery and has to be done perfectly. It is also very expensive.
Total hip replacement is a life altering surgery. After the initial couple of months which are required to recover from the surgery, the patient starts experiencing dramatic relief of pain. Pain literally and magically disappears. In most arthritic conditions of the hip, the leg becomes short and thisshortening is corrected immediately after surgery. Movements become free and painless. Patient is able to walk normally without a limp or pain. Some patients even manage to run after surgery. In short patients become normal after hip replacement surgery and are cured of their arthritis. With modern surgical techniques and newer prosthetic materials and designs, these patients are able to enjoy their hip replacements for a long, long time.