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Risk of Fracture with Skylight Sign

Fracture during or after an uncemented total hip replacement (THR) is a serious complication. There may be a new way to prevent this from happening. In this study, Dr. S. F. Harwin from the Albert Einstein College of Medicine in New York reports on using the skylight sign to prevent fractures.

The skylight sign is a thinning of the bone seen by light coming through the bone. Thinning of the bone from bone loss can occur as a result of a natural defect in the bone or from other causes such as osteoporosis and arthritis. If this sign is present, the surgeon must be careful to avoid reaming (removing) bone from this area.

Bone is usually removed from inside the shaft of the femur (thigh bone) during the THR operation. This makes room for the stem of the implant to fit down into the femur. By checking for the skylight sign, Dr. Harwin was able to reduce the number of fractures in his THR patients.

In a study of 420 hips, 23 percent of the patients had the skylight sign. Wire cables were used around the femur before the bone was prepared. The cables were left in place when fractures or defects were observed. The cables gave stability to the bone and protected it during rehab. The surgeon can also change the size, shape, and type of implant used when the skylight sign is seen.

Even with these steps taken, eight per cent of the patients with skylight sign fractured during the operation. The authors conclude it isn't always possible to prevent femoral fractures during THR. This complication can be reduced by screening for skylight sign and making necessary adjustments during the operation.

References: Steven F. Harwin, MD. Recognizing Anterior Metaphyseal Femoral Bone Loss During Uncemented Total Hip Arthroplasty: The Skylight Sign. In Orthopedics. March 2007. Vol. 30. No. 3. Pp. 218-221.

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