Superior Medullary Ramus Screw

Raymond D. Wright Jr
Jason L. Shewmaker

Bony Anatomy

  • The superior medullary ramus is an irregularly shaped bone that constitutes the anterior portion of the pubic region of the innominate bone.
  • The anterior surface of the superior ramus is asymmetrical and provides the origin for several hip adduction muscles that may contribute deforming forces.
  • The posterior surface is smooth but concave and forms the anterior border of the true pelvis (Fig. 13-1).
  • The superior surface has an undulating contour that begins medially with the pubic tubercle (rectus attachment) near the midline. The pectineus recess is present just lateral to the pubic tubercle and represents a narrow corridor with the femoral neurovascular bundle just above (red arrow with vessels and nerves below). As the ramus precedes cranial, lateral, and posterior, the ramus becomes wider on its superior surface. The iliopectineal eminence is present as the anterior portion of the acetabular anterior wall and lies just medial to the iliopsoas gutter. Lateral to this is another narrow corridor adjacent to the acetabular dome (red arrow) (Fig. 13-2).
  • Although 3D reconstruction CT remodeling has been advocated to determine the safe zones of the superior medullary ramus, it is important to note that the corridor is determined by the safe placement of a screw utilizing intraoperative fluoroscopy and that female gender and fracture patterns may limit acceptable screw diameter, length, and angulation.


Figure 13-1 Oblique view of a synthetic bone pelvic model demonstrating the region of the superior medullary ramus.


Figure 13-2 A linear extrapolation of the superior medullary ramus. The variance in available osseous volume for medullary screw containment is demonstrated.

Preoperative Imaging

AP View

  • Screening study—essential for all patients with pelvic fracture.
  • Should include the entire pelvis.
  • Symphysis pubis should be centered on film and be aligned with coccyx and lumbar spinous processes (Fig. 13-3).


Figure 13-3 AP pelvis radiograph.

Inlet/40- to 45-Degree Caudal View

  • Variable inlet tilt—depends on patient’s degree of lumbosacral lordosis.
  • Upper and second sacral segments should overlap.
  • Allows provider to inspect anteroposterior displacement as well as lateral displacement of osseous pelvic structures (Fig. 13-4).


Figure 13-4 Inlet pelvis view.

Outlet/15- to 40-Degree Cranial View

  • Variable outlet tilt—depends on the patient’s degree of lumbosacral lordosis
  • Ideally centers upper portion of symphysis at second sacral segment or slightly lower
  • Allows practitioner to inspect craniocaudal displacement as well as lateral displacement of osseous pelvic structures (Fig. 13-5).


Figure 13-5 Outlet pelvis view.

Judet Oblique View (Obturator Oblique)

  • Allows for preoperative planning—determining if the superior ramus will accept and contain a medullary superior ramus screw.
  • This view provides for understanding cranial or caudal displacement of the superior ramus at the pubic root.
  • Acetabular fractures (if any) can be evaluated best on this view (Fig. 13-6).


Figure 13-6 Judet oblique views of the pelvis.

Intraoperative Positioning

1. Supine Position

  • The patient is placed supine on a radiolucent table. A midline lumbosacral bump is placed to elevate the pelvis and extend the hips.
  • Both antegrade and retrograde insertion of superior ramus screws are possible in the supine position (Fig. 13-7).1


Figure 13-7 A patient is placed supine on a radiolucent table in preparation for medullary ramus screw. A lumbosacral bump is placed in the patient’s midline to elevate the pelvis from the table and extend the patient’s hips.

Two views are required to safely place medullary superior ramus screws: an inlet view and an obturator-outlet oblique view.

  • Fluoroscopic guidance for a superior screw requires accuracy and reproducibility on the part of the fluoroscope operator. The C-arm is generally set up on the unaffected side.
  • The inlet view is obtained by tilting the C-arm 15 to 25 degrees cephalad.

    • Appropriate tilt is achieved when the superior and inferior rami create a minimally visible obturator foramen.
    • The superior and inferior rami should not be superimposed (Fig. 13-8).
    • The field of view should include a hemipelvis with the affected side ASIS at approximately 1 o’clock on the left hemipelvis and the ASIS at 11 o’clock for the right hemipelvis.
    • The contralateral portion of the pubic symphysis should just be visible on screen (Fig. 13-9A and B).
    • The superior ramus centering should be equal on both views in order to prevent overpenetration.
    • In order to achieve diagnostic quality, the image intensifier should be as close to the patient as possible and accurate centering will allow for consistent collimation.

  • The second view is an obturator-outlet oblique.
  • This combined view gives an image of the superior ramus in profile.
  • The outlet tilt is achieved by angling the x-ray tube caudally 25 to 35 degrees and arcing the machine toward the affected hemipelvis approximately 25 degrees (Fig. 13-10A and B).
  • In the case of the example in Figure 13-10, the fluoroscopist is imaging the right hemipelvis.
  • Obturator-outlet oblique view of the contralateral hemipelvis can be obtained by rolling the C-arm back toward the C-arm operator (Fig. 13-11A and B).
  • The obturator-outlet oblique images should be adjusted such that the obturator canal is maximally in profile. The exact amount of outlet tilt and appropriate roll will vary from patient to patient. The superior ramus should be centered to achieve optimal imaging quality (Fig. 13-12).
  • For antegrade ramus screw insertion, the surgeon sits or stands on the ipsilateral side of the ramus being instrumented. The C-arm is brought in from the opposite side of the surgeon to allow for simultaneous image acquisition and instrumentation (Fig. 13-13). When a ramus is being instrumented in retrograde fashion, the surgeon stands contralateral to the injured ramus. The C-arm can be positioned ipsilateral or contralateral to the surgeon depending on what other injuries are present in the pelvic ring and what instrumentation is planned (Figs. 13-14 and 13-15).
  • Once the positions on the C-arm are established to obtain inlet and obturator-outlet views, the fluoroscopist can record them. This is easily done by placing strips of tape on the C-arm and on the floor to mark degrees of tilt and roll as well as the position of the C-arm in the room. When the two views can be quickly and reliably obtained, insertion of the medullary ramus screws can be most efficiently inserted.


Figure 13-8 Inlet view in the supine position. The inlet tilt should be adjusted such that the superior and inferior rami are not superimposed. This amount of inlet tilt varies based on the patient’s lumbosacral lordosis.

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Mar 25, 2020 | Posted by in ORTHOPEDIC | Comments Off on Superior Medullary Ramus Screw
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