But unlike the frame of a building, bones are never finished.
They always have “workers” on them—some cells that remove bone tissue (osteoclasts) and other cells that construct new bone (osteoblasts). Working together, these cells remodel a person’s bones throughout her lifetime.
When people are young, the bone-builders do more work than the removers. But as people age, the balance shifts. Bones no longer grow larger and denser. Instead, the builders and removers work at an even pace—or the removers begin to outpace the builders.
When bone removal outpaces construction, bones are left with fewer and fewer supports. The spaces between these supports grow bigger and bigger, and the internal architecture of the bones changes. This is one of the hallmarks of osteoporosis. As you might imagine, bones with osteoporosis are weak and brittle.
One big risk factor for osteoporosis is female sex: Women are about four times as likely as men to have the condition.
Another major risk factor is increasing age: Osteoporosis becomes more common after the age of 50.
As life expectancy continues to increase, this common disorder presents a problem for an increasing number of Americans.
And it presents a problem for neurosurgeons. Many spine surgeries are available today because neurosurgeons can rely on bone fusion to provide long-term spinal stability. In a fusion procedure, neurosurgeons use small pieces of transplanted bone called grafts to bridge the span between separate bones.
The bone-building cells do their work where the grafts and the existing bones meet, fusing them together into one strong, solid structure. Instruments like screws and rods scaffold the bones, holding them motionless while the bone-builders fuse them. Various biologic or synthetic materials can encourage this fusion.
Except, however, in patients with osteoporosis, fusion doesn’t always work out. The scaffolding can pull out of weakened bones more easily. And since bone removal already outpaces bone growth, the growth of new bone at the fusion site can be slow or nonexistent.
As part of the planning for surgery, neurosurgeons at NewYork-Presbyterian/Columbia University Irving Medical Center’s Spine Hospital evaluate their patients’ bone health. Special X-rays and blood tests can be used to reveal osteoporosis or its precursor, osteopenia.
The results of these tests inform the surgeons’ treatment decisions. According to Spine Hospital neurosurgeon Dr. Michael Kaiser, in some patients with osteoporosis, fusion surgery would likely do more harm than good. For these patients, non-surgical options are the best choice.
But in cases where the bones are stronger, surgery may be an option. In such cases, neurosurgeons like Dr. Kaiser, Dr. Peter Angevine, and Dr. Christopher Mandigo work as part of a multidisciplinary care team to help patients keep their bones as healthy as possible.
Patients may be prescribed medications that increase the activity and longevity of the bone-building cells. Other medications may decrease the lifespan of the bone-removing cells and make them less active.
Lifestyle factors also have an impact on the condition of the bones. Getting enough vitamin D and calcium, participating in weight-bearing exercise and avoiding nicotine are important ways patients can influence their bone health.
Another part of Dr. Kaiser’s, Dr. Angevine’s, and Dr. Mandigo’s jobs are performing spine surgery when it can be expected to provide benefit to a patient. They have a few options when bone health is a concern. For example, they may choose to use bigger and longer screws in the scaffolding, which may stay put better in weakened bone.
Or they may use materials such as bone cement to strengthen the interface between the bone and scaffolding. If possible, they may implant the screws in areas of bone that are especially strong. And they may select from a range of biologic and synthetic materials that may help fusion proceed.
Unfortunately, spinal fusion is not always possible in the presence of osteoporosis. New research on the issue is always being conducted, however, and a third part of Dr. Kaiser’s, Dr. Angevine’s, and Dr. Mandigo’s jobs are keeping up to date on tools and techniques that may benefit their patients.
Image credit: Building: (c) [Grand Canyon National Park] / Flickr
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