Does the extent of osteonecrosis affect the survival of hip resurfacing?

Abstract

Background: The effect of the extent of osteonecrosis on the survival of hip resurfacing for osteonecrosis of the femoral head (ONFH) has not been well documented, but is a potentially important variable in the decision to perform resurfacing.

Questions/purposes: We examined (1) the relationship between the volume of osteonecrosis in the femoral head before surgery and the extent of the residual necrotic bone after femoral head machining, (2) how the extent of the residual necrotic bone relative to the resurfaced femoral head (after femoral head machining) affected the survival of total hip resurfacing for patients with ONFH, and (3) how the extent of the necrotic bone relative to the entire femoral head (before femoral head machining) affected the survival and clinical outcome scores of patients who underwent total hip resurfacing.

Methods: Thirty-three patients (39 hips) who underwent hip resurfacing were reviewed after a mean followup of 8 years. The extent of osteonecrosis in the femoral head and residual osteonecrosis in the implant bony bed after femoral head machining were estimated using a three-dimensional MRI-based templating system.

Results: There was a statistically significant difference in the extent of osteonecrosis before and after femoral head machining, although the two were well correlated (r = 0.97). The mean percentage of osteonecrosis in the implant bony bed after femoral head machining was 5% smaller than that relative to the entire femoral head (range, -9% to 15%). There were no significant differences in implant survival between groups with small and large osteonecrosis classified by either the total amount of osteonecrosis before surgery or residual osteonecrosis after femoral head machining.

Conclusion: The extent of osteonecrosis in the femoral head significantly decreased after femoral head machining. Neither the residual osteonecrosis volume in the implant bony bed after femoral head machining nor the total amount of osteonecrosis before femoral head machining had significant influence on the survival of hip resurfacing.

Fig. 1A–B

The center of the femoral head was defined by fitting the sphere to the size of the subchondral bone of the noncollapsed part of the femoral head (thin white circle). Next, the center of the femoral neck was defined by fitting the two concentric spheres to the AP and superoinferior inner cortexes of the femoral neck at its isthmus (dashed circles). The line passing through the center of the femoral neck, and the femoral head center was defined as the femoral neck axis (white line). The center of the proximal femur was defined as the center of the femoral medullary canal at 15 cm distal from the tip of the greater trochanter (thick white circle). (A) The plane consisting of the femoral neck axis and the center of the proximal femur was defined as the oblique coronal plane of the femoral neck. (B) The plane perpendicular to the oblique coronal plane though the neck axis was defined as the oblique sagittal plane of the femoral neck.

Fig. 2A–C

(A) The areas of residual osteonecrosis were measured by segmenting areas of low-intensity band. (B) The areas of the resurfaced femoral head were measured by the bony area in the femoral component. (C) The residual osteonecrosis volumes and the resurfaced femoral head volume were calculated by the summation of their areas on serial coronal planes.

Fig. 3

This scattergraph shows the volume percentage of osteonecrosis relative to the entire femoral head, which is highly correlated to the volume percentage of residual osteonecrosis in the machined femoral head (Pearson’s correlation coefficient, r = 0.97, p < 0.001).