LAUSR

BACKGROUND Frequent In-Out-In femoral neck screws were reported potential huge iatrogenic-injury risks , related to axial safe target area (ASTA) of femoral neck screws channel. However,orientated-quantitative ASTA based on stable coordinate system was unreported before. METHODS Three-dimensional reconstruction was performed on CT images of 139 intact normal hips, and the intersection area, defined as ASTA, was obtained by superimposing the axial CT images of each femoral neck. Taking anterior cortex of femoral neck basilar(AC-FNB) as landmark, a coordinate system was established to measure the anterior-posterior diameter (D-AP), the superior-inferior diameter (D-SI) and the oblique angle respectively. Each intersection was overlaid up to the axial CT images to determine the coronal location of the ASTA boundaries. RESULTS Each ASTA presented an inclined rounded triangle with a flat anterior base coincided with AC-FNB. There were significant gender differences in D-SI (male 33·6±2·3 mm versus female 29·4±1·9 mm) and D-AP (male 25·3±2·1 mm versus 21·9±1·9 mm), P<0·001. D-SI was found to be positively correlated with D-AP (R2=0·6).All fluoroscopic visible border isthmus completely matched the corresponding ASTA boundaries. The oblique angle was 5-53°, male 28·1±10·3°, female 27·1±8·2°, without significant difference between genders. CONCLUSION The intersection method was employed to conveniently acquire orientated-quantitative individualized ASTA.Under this coordinate system, X-ray data of screws could be convert to axial coordinates in CT ASTA ,which could help surgeons design combined screws configuration preoperatively and evaluate quantitatively their axial position intraoperatively.