Focal osteonecrosis in the femoral head following stable anatomic fixation of displaced femoral neck fractures.
INTRODUCTION
Femoral head (FH) osteonecrosis (ON) and subsequent segmental collapse is a major concern following displaced femoral neck fractures (FNF). We aimed to quantify residual perfusion to the FH following FNF and evaluate the viability of the FH overtime after surgical fixation.


MATERIALS AND METHODS
Twenty-three patients with FNF underwent dynamic contrast-enhanced (DCE)-MRI to estimate bone perfusion in the FH, using the contralateral side as control. Following open anatomic reduction and a length/angle-stable fixation, a special MRI sequence evaluated the FH for ON changes over time at 3 and 12 months after surgery.


RESULTS
We found significant compromise of both arterial inflow [83.1%-initial area under the curve (IAUC) and 73.8%-peak) and venous outflow (243.2%-elimination rate (K el)] in the FH of the fractured side. The supero-medial quadrant suffered the greatest decrease in arterial inflow with a significant decrease of 71.6% (IAUC) and 68.5% (peak). Post-operative MRI revealed a high rate (87%-20/23) of small ON segments within the FH, and all developed in the anterior aspect of the supero-medial quadrants. Fracture characteristics, including subcapital FNF, varus deformity, posterior roll-off ≥20° and Pauwel's angle of 30°-50° demonstrated a greater decrease in perfusion compared to contralateral controls.


CONCLUSION
FNF significantly impaired the vascular supply to the FH, resulting in high incidence of small ON segments in the supero-medial quadrant of the FH. However, maintained perfusion, probably through the inferior retinacular system, coupled with urgent open anatomic reduction and stable fixation resulted in excellent clinical and radiographic outcomes despite a high rate of small ON segments noted on MRI.


LEVEL OF EVIDENCE
Level I: Prognostic Investigation.
['Lazaro|Lionel E|LE|', 'Dyke|Jonathan P|JP|', 'Thacher|Ryan R|RR|', 'Nguyen|Joseph T|JT|', 'Helfet|David L|DL|', 'Potter|Hollis G|HG|', 'Lorich|Dean G|DG|']
D015331:Cohort Studies D005265:Femoral Neck Fractures D005270:Femur Head D005593:Fracture Fixation, Internal D006801:Humans D010020:Osteonecrosis
Femoral neck fractures Dynamic contrast-enhanced MRI Femoral head osteonecrosis