Determinants for successful medullary fixation of the superior ramus

The purpose of this study is to determine what demographic and anatomical variables affect successful placement of a superior medullary ramus screw, and how they affect the maximal diameter of that screw.

Design: Prognostic Level IV SETTING: Level I Trauma Center Patients/Participants: Two hundred consecutive patients underwent computed tomography (CT) of the pelvis. We included those patients aged 18 and older without osseous injury or abnormalities precluding measurement.

3D reconstructions of the pelvis were created, and a virtual 3.5 mm cylindrical implant was placed from the pubic tubercle to the lateral cortex of the ilium. Success was defined as a bicortical virtual screw path from the ramus to the lateral ilium without cortical perforation. The cylinder was then expanded to model varying screw diameters. We then repeated this same process for unicortical retrograde screw insertion ending medial to the acetabular joint.

Successful screw placement and maximum screw diameter.

A 3.5 mm screw was successfully placed in 187 patients (93.5 %). One male (1/107, 0.9 %) and 12 females (12/93, 12.9 %) could not accommodate a 3.5 mm screw. All cases of perforation occurred lateral to the obturator foramen. Increasing height was associated with success, and male gender was associated with the ability to accommodate screws with a diameter 6.5 mm and larger.

Most patients can accommodate a 3.5 mm screw from the pubic tubercle to the ilium. Height and gender should be noted when planning medullary ramus fixation.