Anatomic considerations of plate-screw fixation of the anterior column of the acetabulum

Fifteen cadaveric adult bony hemipelvis specimens and 30 adult dry bone specimens were obtained to evaluate the configuration of the anterior column of the acetabulum and to develop a safe path for screw placement into it. Each cadaveric specimen was sectioned at I-cm intervals, beginning at the level of the inferior border of the acetabulum (junction between the anteroinferior edge of the acetabulum and the most anterolateral edge of the superior ramus of the pubic bone). The plane of the cross-section was perpendicular to the anterior column. The projection of the medial acetabular boundary on the anterior column was determined by analysis of each cross-section. Results showed that the average width of the anterior column at 1.0, 2.0, and 3.0 cm superior to the inferior acetabular boundary is 31.0 +/- 4.7, 34.2 +/- 5.1, and 39.4 +/- 6.2 mm, respectively. At 1.0 cm superior to the inferior margin of the acetabulum, the average medial angulation for 0.5-, 1.0-, and 1.5-cm entry points lateral to the pelvic brim were 24.9 +/- 4.4 degrees, 35.5 +/- 5.2 degrees, and 44.4 +/- 6.6 degrees, respectively. At 2.0 cm superior to the inferior acetabular margin, the corresponding average medial angulation for 0.5-, 1.0-, and 1.5-cm entry points were determined to be 29.2 +/- 5.5 degrees, 38.6 +/- 5.9 degrees, and 48.1 +/- 5.7 degrees, respectively. At 3.0 cm superior to the inferior acetabular margin, these angles were found to be 20.7 +/- 4.3 degrees, 29.4 +/- 6.0 degrees, and 39.3 +/- 5.9 degrees, respectively. All of the above mentioned angles are with respect to the perpendicular of the longitudinal axis of the anterior column without violation of the hip joint. Screws placed 1.0 cm lateral to the pelvic brim at the levels of 1.0, 2.0, 3.0, and 4.0 cm superior to the inferior acetabular margin and directed perpendicular to the anterior column penetrated the hip joint.