Femoral neck notching reduces femoral head blood supply

Introduction of a low-wear bearing surface may lead avascular necrosis to a bigger role in femoral failure.

Notching the femoral neck during total hip replacement can lead to significantly reduced blood flow to the femoral head, a new study shows.

Paul E. Beaulé, MD, FRCSC, and colleagues at the Joint Replacement Institute of the University of California, Los Angeles’ Orthopedic Hospital, measured the changes in femoral head blood flow caused by simulated femoral neck notching. The study included 14 hips of 12 patients — eight men and four women — who underwent conventional THR at a mean age of 63 years.

Surgeons performed all THR procedures using a modified lateral approach. To measure blood flow, the researchers used a DRT laser Doppler flowmeter (Moor Instruments), which uses a 20 mW laser and a 780 nm wavelength fiberoptic probe, and can measure blood flow within 1 mm³ of surrounding bone, according to the study.

After exposing part of the extra-articular femoral head with the leg in a neutral position, surgeons inserted the probe through a 3.5-mm drill hole made through the femoral neck and into the anterolateral quadrant of the femoral head.

They made two more similar drill holes on the femoral head articular surface — one anterolateral and one centromedial — after dislocating the hip anteriorly. Blood flow measurements were again taken before and after femoral neck notching, simulated using a 0.75-inch osteotome aimed at the retinacular vessels, according to the study.

Before notching, femoral head blood flow averaged 60.4 flux units at the anterolateral sites and 82.4 flux units at the centromedial sites. Following simulated notching, mean blood flow significantly decreased an average of 54.9% to 21.4 flux units at the anterolateral sites and decreased an average 47.8% to 39.6 flux units at the centromedial sites (P=.001), according to the study.

Only four hips (28.6%) had a less-than-50% decrease in blood flow in both hips, the authors noted.

In clinical practice, femoral neck notching most likely occurs when the cylindrical reamer moves across the femoral head and neck junction, damaging the retinacular vessels. Such damage may impair the femoral head blood supply enough to increase the risk of an avascular event, which in turn can lead to femoral failure, the authors said in the study.

“Our data provide evidence to support this mechanism, as the majority of the arthritic femoral heads (10 of 14) demonstrated a significant decrease (at least 50%) in blood flow after simulated notching,” they said.

“With the introduction of a low-wear bearing surface, such as metal-on-metal, avascular necrosis and its subsequent reparative phase may become a more important mechanism of femoral failure. Careful attention should be paid to the blood vessels when performing resurfacing arthroplasty of the hip, and notching of the femoral neck and/or extensive dissection should be avoided,” they added.

For more information:
Beaulé PE, Campbell PA, Hoke R, Dorey F. Notching of the femoral neck during resurfacing arthroplasty of the hip. J Bone Joint Surg Br. 2006;88-B:35-39.