Mechanical features of screw internal fixation technique for acetabular anterior column fracture:Quantitative anatomic observation

Xianquan WANG; Jinfang CAI; Xuecheng CAO

ABSTRACT

BACKGROUND:

Recently,open reduction and internal fixation has become an important therapy for pelvic and acetabular fracture. However,screw penetration sometimes occurs,which damage vessels or nerves in the pelvic cavity.

OBJECTIVE:

To measure the best entry points,direction and length of screw in acetabular anterior column fracture lag screw internal fixation technique. DESIGN,TIME AND

SETTING:

Measurement experiment was performed at the Department of Anatomy,Medical School of Shandong University from June to October 2008. MATERIALSA total of 20 semi-pelvic specimens of adult male cadavers were used to make serial cross-sections of the acetabular anterior column.

METHODS:

In single screw technique,the horizontal distance OP and vertical distance PQ from entry point O to apex of greater sciatic notch Q were measured,and screw length was measured. In double screw technique,the horizontal distance O1P1,O2P2 and vertical distance P1Q,P2Q from entry point O1 of the inner screw and entry point O2 of the outer screw,respectively to apex of greater sciatic notch Q were measured. The length of inner screw and outer screw were measured respectively. Angle ? on sagittal plane and the angle ? on coronal plane of the screw were determined. All data were put into software SPSS 10.0 for statistical analysis. MAIN OUTCOME

MEASURES:

The entry points,direction and length of screw in acetabular anterior column fracture lag screw internal fixation technique

RESULTS:

Single screw techniquethe length of OP and PQ was (23.5?2.2) mm and (16.8?1.6) mm respectively; the length of lag screw was (84.9?4.7) mm. Double screw techniquethe length of O1P1 and P1Q was (26.3?2.3) mm and (13.6?1.4) mm,respectively,and the length of medial lag screw was (69.8?4.1) mm; the length of O2P2 and P2Q was (20.7?2.1) mm and (20.1?1.8) mm,and the length of lateral lag screw was (61.2?3.7) mm. Angle ? was (123.4 ? 4.1)? and angle ? (62.2 ? 5.8)?.

CONCLUSION:

The entry point of single screw technique lies in the summit of greater sciatic notch 17 mm outward,vertical to the medial margin of the posterior column,24 mm upward,parallel to the medial margin of the posterior column; the length of the screw is 85 mm. The entry point of medial screw in double screw technique lies in 14 mm outward,vertical to the medial margin of the posterior column,and 26 mm upward,parallel to the medial margin of the posterior column; the length of the screw is 70 mm. The entry point of lateral screw in double screw technique lies in 20 mm outward,vertical to the medial margin of the posterior column,and 21 mm upward,parallel to the medial margin of the posterior column; the length of the screw is 61 mm. The angle of lag screw with respect to the parallel line of the medial margin of the posterior column is 123?,and the angle lag screw with respect to the vertical line of the medial margin of the posterior column is 62?. The position of the lag screw must be confined by intraoperative fluoroscopy in multiple projections.