A Digital Anatomy Study Of Modified Screw Placement Technique In Plate-screw Fixation Of Pubic Body

PurposeThis study aims to explore the screw insertion point and obtain the angles and lengths of screw inserted safely at the pubic body with the rectus abdominis origins at pubic crest undissected and inguinal canal unaffected.To provide anatomical basis and references for clinical application of this modified plate-screw technique.Methods80 cases of normal adult pelvic CT data(40 males and 40 females)were collected,with an average age of 51.65±12.46 years old(ranging from 21 to 83 years old).The Mimics 19.0 software was applied to redefine the anatomical plane of the pelvic CT data,and the each hemipelvic was reconstructed respectively.Based on the commonly used 3.5mm pelvic reconstruction plate-screw system,the plate was placed along the arcuate line from the outer edge of the pubic tubercle to determine the innermost two screw holes.Observing safe zone of the pubic body according to the fixed screw insertion point,and then measure the parameters of safe screw placement in a certain screw-placement plane.Finally,screw insertion point,length,range of screw direction and their gender differences were discussed.ResultsAccording to the axial observation of the obturator foramen tangential screw,it was found that the anterior and posterior boundary of the screw placement zone showed three patterns:blunt V-shaped,sharp V-shaped and long arc-shaped.The medial entry point was located 6.5 mm outer to the pubic tubercle and 5 mm apart from the arcuate line.The lateral entry point was located 13 mm outer to the medial entry point and 5 mm apart from the arcuate line.Males had a smaller medial inclination angle(MIA)of screw placement pane than that of females[male 21.21±4.05°<female 25.86±8.54°,P<0.05].For medial screw,the maximum anterior inclination angle(MAIA)is 12.40±9.53°.At this position,the screw length is 46.51 ±4.01mm.Gradually change the screw insertion direction from anterior to posterior,its intraosseous length becomes shorter.When screw gets to its minimum length--14mm,the screw reach to maximum posterior inclination angle(MPIA)(-11.78±10.22°).There is no significant gender difference about the above parameters.For lateral screw,the maximum MAIA was 10.35±9.460,no significant gender difference(P>0.05),while male has a larger MPIA than that of female[male-11.80±11.00°>female-6.23±7.91°,P<0.05,"-" only represents the screw direction is posterior inclined].In the MAIA position,the length of male screw(55.71 ±6.36mm)was significantly longer than that of female(48.68±8.65mm).The length of obturator tangential screw was significantly longer in males[male 53.16±8.70mm>females 45.07± 10.91,P<0.001],and there was no significant gender difference in screw MIA(31.65±9.42°)of placement plane and screw anterior/posterior inclination angle(APIA)(7.53±10.18°).(P>0.05).Female pubic tubercle-tubercle distance is longer than men's(female 61.98 ± 9.04 mm>male 58.40 ± 6.03 mm,P<0.05),while pubic symphysis longitudinal length is shorter(female 39.85 ± 3.26 mm<male 41.82 ± 4.65 mm,P<0.05).ConclusionThe modified screw placement technique of plate-screw fixation on pubic bone is achievable in the fixation of pelvic and acetabular fractures.The rectus abdominis origin at pubic crest can be retained and inguinal canal unaffected by obliquely inserting screws into pubic body from the lateral to pubic tuberosity.Medial and lateral screws and obturator foramen tangential screws have certain gender differences and individual differences.It is safe to insert screws between MAIA and MPIA,but it is necessary to pay attention to changes in screw length.