What is a skylight sign? When the surgeon showed me Dad's hip X-rays, she said a skylight sign tipped her off to avoid a hip fracture during Dad's hip replacement operation.
Thinning of the bone allows light coming from the other side to stream through the thin section. This light stream through the bone is called the skylight sign. It can only be seen from the side. The surgeon must use a lateral (from the side) approach to see the skylight sign.

From this angle, the bone is exposed as the muscles are cut away. Using other methods, won't allow the surgeon to check for the skylight sign. Patients with a positive skylight sign are at increased risk for fracture. Fracture can be prevented by changing the surgical technique or size of the implant.

Sometimes reinforcing the bone with wire cables can help prevent fracture during the operation. The cables are placed around the bone. If a fracture occurs during the surgery, the cables can be left in place to help stabilize the bone during recovery and rehab.