Clinical Anatomic Study Of Infrapectineal Plate-Screw Fixation

Objective:Screw penetration into the hip joint during operation is an unusual but potentially serious complication. The comprehensive studies on clinical anatomic study of infrapectineal plate-screw fixation have been barely reported so far. The study is designed to measure and record the the safe angles for screw placement from different entry points and the thickness of the acetabulum in the infrapectineal plate-screw fixation plane, using volume reconstruction (VR) and multiplanar reconstruction (MPR) technology.Methods:Twelve cadaveric adult antiseptic hemipelvic specimens were obtained for the purpose of the study. In preparation for this study, all soft tissue attachments were cleaned from the specimens. The CT images of the bony pelvic specimens from crista iliaca to ischial tuberosity were initially obtained for the purpose of the study. Each specimen was placed in the supine position on a radiolucent carbon fiber table. The data were postprocessed with volume reformation and multiplanar reconstruction technology. Each MPR section was perpendicular to the quadrilateral plate and the scan range was96mm. The first section went through lineae iliopectinea of pelvis. The width of pelvic reconstruction plate is10mm. The screw holes are in the form of an ellipse, of which the major axis is horizontal, and7mm long; the minor axis is vertical, and4mm long. In our study, the fifth section inferior to the pelvic brim was defined as the reference section. Four MPR sections perspecimen were selected, including the reference section, one sections superrior to it, and two sections inferior to it.In our study, the projection that acetabulum projects onto the quadrilateral was defined as the danger zone of acetabulum. The anterior and posterior boundary of the acetabulum were projected and marked on the medial line of pelvic. The distances on the medical line of plate-screw fixation plane from the anterior projection.to pubic symphysis and from posterior projection to sacroiliac joint were recorded for each section. The width of danger zone was measured. Points were then determined at intervals of every5mm posterior to anterior projection and represented proposed entry points for screw placement. The perpendicular distance (thickness) from the entry point to the inner surface of acetabular was measured and recorded for each entry point. The angle, which was formed by a line directly tangent to the subchondral plate of the acetabulum from the entry point and the line perpendicular to the medial line of pelvic, was designated0and recorded. To avoid screw penetration into the hip joint, the nearest thread should be kept more than0.5cm away from the subchondral plate.The data were analyzed using SPSS (Statistical programmed for Social Sciences, version13.0,Chicago, IL) computer software. Comparisons of the data were made by randomized block design analysis of variance. Differences were regarded as statistically significant when P values were less than0.05. In that case, Student-Newman-Keuls test and least significant difference test would be made.Result:From section4to section7,the distances on the medical line of plate-screw fixation plane from the anterior projection to pubic symphysis were (62.29±4.39) mm,(60.98±5.83) mm,(60.75±3.88) mm and (59.67±3.58) mm respectively and those from posterior projection to sacroiliac joint were (40.53±7.06) mm,(40.38±6.41) mm,(40.52±7.07) mm and (41.15±6.66) mm respectively. The differences of the distance from the anterior projection to pubic symphysis and those from posterior projection to sacroiliac joint among the specimens were statistically (P<0.05), but the differences among sections were not statistically (P>0.05). The width of danger zone were (25.83±2.19) mm,(27.81±1.97) mm,(28.46±2.12) mm and (30.45±2.61) mm respectively. The differences of the width of danger zone were statistically between specimens and sections (P<0.05)When the screws inclined forward, the safe angles for anterior projection,5,10,15,20mm and posterior projection entry points were (10.54±0.53)°,(22.01±2.94)°,(32.50±4.28)°,(41.09±5.34)°,(48.10±5.27)°and (59.00±4.22)°respectively in section4. In section5, they were (10.46±1.35)°,(22.31±2.65)°,(32.68±2.76)°,(41.23±2.27)°,(49.63±4.37)°and (63.15±3.66)°respectively. In section6, they were (10.08±1.16)°,(23.45±2.22)°,(32.47±4.13)°,(42.61±2.61)°,(51.55±4.37)°and (65.72±4.29)°respectively. In section7, they were (10.52±1.18)°,(22.23±2.30)°,(33.46±4.23)°,(42.91±4.31)°,(51.76±7.02)°and (69.41±3.27)°respectively. The differences of the safe angles were not statistically among anterior projection,5mm and10mm entry points(P>0.05). However, the differences of the safe angles were statistically among posterior projection,15mm and20mm entry points (P<0.05). When the screws inclined backward, the safe angles for anterior projection,5,10,15,20mm and posterior projection entry points were (55.01±5.31)°,(41.50±4.64)°,(33.75±4.27)°,(25.23±4.21)°,(21.26±5.16)°and (8.15±0.89)°respectively in section4. In section5, they were (58.59±5.37)°,(50.76±5.28)°,(43.43±5.60)°,(34.93±6.08)°,(25.89±5.14)°and (8.45±0.74)°respectively. In section6, they were (62.96±6.02)°,(54.66±6.97)°,(47.76±9.40)°,(38.51±6.15)°,(28.00±5.10)°and (9.03±1.10)°respectively. In section7, they were (65.27±6.26)°,(57.91±5.95)°,(51.04±4.48)°,(42.44±4.19)°,(33.47±5.56)°and (8.81±1.31)°respectively. The differences of the safe angles were statistically among anterior projection,5,10,15,20mm and posterior projection entry points (P<0.05)The thickness of acetabulum for anterior projection,5,10,15,20mm and posterior projection entry points were (27.24±1.76) mm,(21.39±1.62) mm,(19.50±2.15) mm,(19.93±2.34) mm,(22.95±2.66)mm and (36.02±2.41) mm respectively. In section5, they were (27.29±2.29)mm,(20.73±1.70) mm,(18.38±2.10)mm,(18.21±2.16)mm,(19.90±2.14)mm and(36.19±2.13) mm respectively. In section6, they were (27.46±2.57) mm,(19.86±1.40) mm,(17.56±1.73)mm,(17.36±2.51)mm,(18.82±2.43)mmand(36.41±2.89) mm respectively. In section7, they were (27.70±2.72) mm,(19.86±2.26) mm,(16.83±2.20)mm,(16.38±2.28)mm,(17.74±2.35)mmand(35.50±3.07) mm respectively. The differences of the thickness of acetabulum were not statistically among anterior projection and posterior projection entry points (P>0.05). The differences of the thickness of acetabulum were statistically among5,10,15and20mm entry points (P<0.05)Conclusion:The data derived from the study will be valuable for screw placement during infrapectineal plate-screw fixation. Screw insertion inclining forward at the points of anterior projection,5mm and10mm no less than15°,30°and45°respectively, could avoid screw penetration of the hip joint. However, when the screw inclined backward, screw insertion at the points of15mm,20mm and posterior projection no less than50°,45°and15°respectively, could avoid screw penetration of the hip joint. The method of the study is helpful to make individual perioperative planning for safer infrapectineal plate fixation.