What Is Worse Than a Loose Screw? A Broken One in Your Back!Sometimes the spine needs a little extra help staying in place. This may call for a device that screws into the bones on either side of a weak spot, or internal fixation device. Doctors use this device for spine fractures, abnormal spine curves, and for injured or degenerated discs.
It's important to start moving again as soon as possible after any surgery. Physical therapy often begins within the first few days after spine surgery. Exercises are prescribed to improve muscle strength without putting too much load on the healing bone. With spinal fixation devices, there's always the worry that a screw will break under a heavy load. This happens in less than 10 percent of all cases, but when it happens, it is a serious complication.
How much load is too much? How much movement is safe? One group of researchers has done many studies to measure the spinal loads for different activities. Load can be accurately measured by using an implant that records and transmits signals. Load has been measured for such common activities as sitting, lying down, standing, walking, lifting one leg, lifting one arm, rising up on tiptoes, and turning over in bed.
The strength of spinal screws has also been tested. The manufacturer has given doctors and researchers the amount of force implants can handle without breaking. This amount is 110 percent of the maximum load on the spine while standing. This means the screws can withstand 10 percent more than the maximum force put on the spine when standing. Any activity that loads the spine less than this is considered safe. At this level, spine fracture or screw breakage is not likely.
Movements that exceed this load include walking, and bending forward or backward in the standing position. For example, bending forward in the standing position increases the pressure on the spine more than twice as much as standing. The risk of screws breaking is greater if these movements are done often. Placing the screws farther apart during surgery can also put the spine at greater risk.
Getting people up and moving after surgery that fixes the spine in place with screws may be risky. The forces placed on the screws while standing are safe, but walking appears to place a higher load on the screws. Other activities such as sitting, rolling, or crawling on hands and knees appear to have much lower loads than walking. More information of this kind will help physical therapists plan safe and effective rehabilitation programs following spinal surgery with fixation devices.
Antonius Rohlmann, Dr-Ing, et al. Loads On An Internal Spinal Fixation Device During Physical Therapy. In Physical Therapy. January 2002. Vol. 82. No. 1. Pp. 44-52.
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