[An anatomic study of lag screw placement in anterior column of acetabulum and design of targeting device].
OBJECTIVE
To provide the anatomic basis for the lag screw placement in the anterior column of the acetabulum.


METHODS
Twenty-two pelvis specimens with 44 acetabula of the native adult cadavers were studied. The anthropometric measurement was performed on 44 acetabula to determine the shape of the transverse section of the anterior column of the acetabulum, the optimal entry point for the lag screw on the outer table of the ilium, the direction of the screw, and the distance from the entry point to the obturator groove.


RESULTS
The transverse section of the anterior column of the acetabulum was almost triangle-shaped. The path for the lag screw placement was 10.5 +/- 0.8 mm in diameter. The optimal entry point on the posterolateral ilium for the screw fixation was found to exist 9.2 +/- 2.4 mm superior to the line between the anterior superior iliac spine and the greater sciatic notch and 38.5 +/- 3.8 mm superior to the greater sciatic notch. The distance from the entry point to the obturator groove was 84.1 +/- 6.2 mm. The inclination of the lag screw was 54.2 +/- 5.5 degrees at the caudal direction in the sagittal plane and 40.7 +/- 3.8 degrees in the horizontal plane. The device for the safe screw placement in the anterior column was designed.


CONCLUSIONS
The above data can facilitate an insertion of one 6.5 mm lag screw into the anterior acetabular column and minimize the risk of articular violation or cortical penetration, which has a narrow margin of safety. The safe length of the lag screw should be 70 mm. The optimal entry point on the posterolateral ilium for the screw fixation is determined to be 10 mm superior to the line between the anterior superior iliac spine and the greater sciatic notch and 40 mm superior to the greater sciatic notch. The inclination of the lag screw should be 55 degrees at the caudal direction in the sagittal plane and 40 degrees in the horizontal plane. It is safe to place the lag screw in the anterior column with the help of the targeting device.
Hong
Huaxing
H
Department of Orthopedics, Taizhou Hospital, Taizhou Zhejiang, 317000, PR China.
Pan
Zhijun
Z
Chen
Haixiao
H
D000077:Acetabulum / Q000033:anatomy & histology* / Q000601:surgery*; D000328:Adult; D001863:Bone Screws; D004867:Equipment Design; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D016268:Internal Fixators; D008297:Male