[A preliminary anatomical study on design of cannulated screw channels for fixation of symphysis pubis diastasis in small samples].
OBJECTIVE
To design the channels of parallel screws and cross screws for fixation of symphysis pubis diastasis through a small sample anatomic study on pubic symphysis and its neighbor structures so as to provide anatomical basis for minimally invasive fixation of symphysis pubis diastasis.


METHODS
Eight cadaveric pelvic specimens (6 men and 2 women) were transected along L5 and the proximal 1/3 of bilateral thighs, with intact lumbar spines. The spermatic cord, womb round ligament, and corona mortis were dissected; the distance to the i psilateral pubic tubercle was measured and subsequently the distance between pubic tubercles, the height of pubic symphysis, the diameter of outer edge of pubic tubercle, the thickness of pubic symphysis and 2 cm outside the pubic symphysis (upper, central, and lower 1/3 thickness of pubic symphysis) were measured to provide anatomical basis for the design of channels of parallel screws and cross screws.


RESULTS
Parallel screw fixation: the entry point of first screw was on the outer edge of pubic tubercle, and its exit point was on the outer edge of contralateral pubic tubercle; a cannulated screw with a diameter of 4.5 mm or 6.5 mm can be suitable for this channel. The entry point of second screw was 20 mm outside the pubic symphysis and 23 mm beneath the pubic symphysis, and its exit point was symmetrical with entry point; a cannulated screw with a diameter of 4.5 mm can be appropriate for the second channel. The direction of two screws was perpendicular to the pubic symphysis. Cross screw fixation: the entry point of cross screws was on one side of the pubic tubercle, and its exit point was 20 mm outside the contralateral pubic symphysis and 23 mm beneath the contralateral pubic symphysis; two cannulated screws with a diameter of 4.5 mm can be chosen for cross screws channels. The direction of two cross screws was intersected with the horizontal line of two pubic tubercles at an angle of 25 degrees respectively; besides, two cross screws formed an anteversion angle and retroversion angle of 5-10 degrees with pubic body plane, respectively.


CONCLUSIONS
The channels of parallel screws and cross screws are feasible for fixation of symphysis pubis diastasis by analyzing the anatomical data of the pubic symphysis and its neighbor structures, but further biomechanical research is need to confirm the stability of two fixation methods.
Kunlong
K
Ma
Lei
L
Zhu
Yue
Y
Fang
D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D016268:Internal Fixators; D008297:Male; D019060:Minimally Invasive Surgical Procedures; D008953:Models, Anatomic; D010388:Pelvis / Q000033:anatomy & histology / Q000098:blood supply / Q000601:surgery; D011631:Pubic Symphysis / Q000033:anatomy & histology* / Q000098:blood supply / Q000601:surgery*; D046548:Pubic Symphysis Diastasis / Q000601:surgery*