Anatomy And Clinical Significance Of The Insertion Of Psoas Minor Tendon At Pelvic Brim

Objectives: Stoppa approach could adequately expose quadrilateral surface and pelvic brim for the patients with pelvic and/or acetabular fracture.It has been widely used clinically because it is a minimally invasive incision [1].However,the screws are inserted blindly for the acetabular surface could not be exposed.Thus,the intra-articular screw placement in Stoppa approach was a common complication and may result in serious consequence [2-5].Although insertion of psoas minor tendon at pelvic brim(IPMTPB)was adjacent to hip joint cavity,there was no literature described the relationship between IPMTPB and the safe zones in Stoppa approach.The first purpose of the study was to describe the location of the IPMTPB and examine whether the IPMTPB can serve as an anatomic landmark for extra-articular screw placement in Stoppa incision.Another purpose was to find safe zones for extra-articular screw placement in Stoppa incision.Methods: 12 cadavers were dissected to get adequate exposure of IPMTPB in our study.However,there was not psoas minor for all specimens.For the specimens with IPMTPB,its posterior and anterior edges were used as the first and second pin entrances.The pelvic brim was divided into three zones(d1,d2 and d3)with the two pin entrances.The length of each zone was measured to make a better description of the location of IPMTPB and guide the screw placement for the patients without IPMTPB.Then the mean ± SD and average percentage of each zone were calculated.For the specimens without IPMTPB,the two pin entrances were determined by the calculation of measurements and the length of pelvic brim.They also divided pelvic brim into three zones(d1,d2 and d3).A reference line including the pubic symphysis and the midpoint of the connection of bilateral anterior superior iliac spine was defined.From the reference line,the first K-wire was drilled horizontally to the first pin entrance.The second K-wire was drilled perpendicularly.Fluoroscopy was conducted after the drilling to examine safety of the wires.Results: The psoas minor existed in 16 half pelvises in this study.Bilateral psoas minor was found in 6 specimens,single psoas minor was found in four specimens.There was no psoas minor in the other two specimens.The presence of the psoas minor was 66.7%.For the specimens with IPMTPB,the first wire was far away from the hip joint and absolutely did not penetrate into the articular surface in this study.For the second wire,15 half pelvises(93.75%)was absolutely safe,while a half pelvis(6.25%)was relatively safe.It was tangent to the acetabulum but did not damage the articular surface.There was no wire penetrated into the hip joint.For the specimens without IPMTPB,the first wire was far away from the hip joint and absolutely did not penetrate into the articular surface in this study.For the second wire,6 half pelvises(75%)was absolutely safe,while 2 half pelvises(25%)was tangent to the acetabulum.There was no wire penetrated into the hip joint either.Conclusion: IPMTPB could be used as an anatomic landmark for extra-articular screw placement through Stoppa incision.Screws could be inserted without penetrating into hip joint cavity in zone d1 and zone d3,which would bring great clinical difference through Stoppa incision.