My 69-year-old mother just had spinal surgery that included a fixation device to hold the healing bones in place. When the physical therapist came in to work with her, my mother was not allowed to walk a lot or sit up straight. Why is that?

Screws inserted to support the bones of the spine break in a small percentage of patients. The manufacturer has identified how much force or load the screws can handle. Some movements and positions exceed that load and place patients at risk for screw breakage.

Researchers have been able to test various body positions and movements to see how much load they put on the spine. Actively straightening the back to sit up puts more stress on the healing bone. In the early phases of recovery from this surgery, a more relaxed sitting position is better.

Other movements to be avoided include bending forward or backward in the standing position and walking long distances. The load on the spine varies from person to person depending on how long ago the surgery took place, how weak the muscles were before surgery, and how much pain is present after surgery.