- Discussion:
- indicated for
SI joint disruptions and for some
sacral fractures;
- Operative Technique:
- radiographs:
- surgical stratedgy:
- if
anterior pelvic injury:
- note that the biggest risk factor for postoperative SI joint displacement is failure to recognize and treat anterior pelvic injury;
- fixation failure rates are much higher when iliosacral screws are combined with anterior pelvic external fixation devices;
- in contrast, iliosacral screw fixation is useful for combined anterior/posterior injuries when percutaneous SI joint screw fixation
is augmented by rigid anterior fixation;
- if the patient is to be placed in the prone position (for SI fixation), then the anterior lesion needs to be fixed with a plate (rather than an external fixator);
- if an extenal fixator is to be used, then the patient will have to undergo posterior fixation in the supine position (if the fixator is to be applied first), otherwise
the iliosacral screws must be inserted first (prone position) and then the patient is turned for application of the fixator;
- likewise concomitant
acetabular frx should be fixed first;
- once posterior reduction is achieved, fixation of joint dislocation is done via lag screws placed across joint from ilium to sacral ala lateral
to the sacral body, avoiding nerves;
- managed in a fashion similar to that used for
sacral fracture;
- screws are directed across SI joint into the sacral ala, into the body of S1;
- often screws need to be passed across the midline inorder to achieve adequate fixation;
- when poor screw purchase is achieved, a second screw is inserted inorder to lock threads with the first screw;
- in some cases, screws are directed into the body of S2;
- patients can be placed in the supine, prone position, or lateral position;
- supine positioning allows easier closed reduction of the hemipelvis, and when SI joint dislocations
cannot be reduced closed, the supine position allows open reduction and anterior SI joint fixation;
- screws can be inserted thru percutaneous incisions thru the buttocks muscle, regardless of the condition of the local soft tissues;
- percutaneous technique is less likely to cause infection when a degloving injury is present;
- methods to decrease complications:
- surgeon's finger is passed thru the greater sciatic notch to protect anterior structures;
- Flourscopic Imaging:
- note that high quality floursoscopic equipment is required for screw placement, noting that in the series by Keating et al (JTO 1999) there
were two patients that had screws protruding through the S1 foramen that was only apparent on the postop radiographs;
- may be performed in the supine or prone position;
- typically the supine position is used if the procedure is to be performed using a percutaneous technique (and in this case it is
important that it be confirmed that a closed reduction be obtainable before the surgeon commits to this technique);
- note: adequate reduction is manditory prior to screw insertion;
- w/o reduction, left and right anterior iliac cortical densities as well as the greater sciatic notches cannot be superimposed;
- most common target on sacrum is body of first sacral segment;
- SI joint anatomy: SI joint has an L shaped configuration;
- one limb runs about 1 cm above the inferior border of the iliac wing;
- the second limb runs almost vertically for about 3 cm in length, and is positioned about 4 cm from the PIIS and about 5.5 cm from PSIS;
- references:
- The Location of the SI Joint on the Outer Table of the Posterior Ilium.
J.T. Waldrop, N.A. Ebraheim, R.A. Yeasting, and W.T. Jackson. J. Orthop Trauma Vol 7. No. 6, p 510-513.
-
outlet view is used to direct the guide pin tip cephalad to the sacral nerve foramen;
- need to identify the curvilenear iliac cortical density which parallels the anterior aspect of the SI joint;
- the safe zone lies between the alar cortex supero-anteriorly and the sacral neural foramen posteriorly;
- using inlet and outlet views, guide pins are inserted upto a point lateral to the ipsilateral S1 neural foramen;
- lateral view of sacrum helps direct the guide pin tip caudal to the ICD and then into the sacral ala;
- once the lateral view confirms that the pin is optimally placed, the pin can be driven to the midline;
- ref:
Is the lateral sacral fluoroscopic view essential for accurate percutaneous sacroiliac screw insertion? An experimental study.
-
case examples:
- Structures at Risk:
- posteriorly the cauda equina;
- anteriorly ureter & elements of
lumbosacral plexus & some branches of bifurcation of the common iliac artery;
- superiorly, the L5-S1 disk and the
L5 nerve root;
- inferiorly the
S1 nerve root
- if screw is aimed too low and crosses the S1 foramenae;
- Complications:
- S1 nerve root injury (may occur despite high quality flourscopic images);
- deep infection (more common w/ the
Morel Lavel lesion);
- acute malreduction: upto 15% of patients will have a malreduction on immediate postoperative films;
- loss of fixation: up to 25% of patients will experience loss of reduction during the first postoperative month;
- patients at risk for displacement include those with recognized anterior injuries that did not receive anterior plating or external fixation;
- pain:
- note that the majority of patients (85%) will have chronic SI joint pain, and 10% of patients may ultimately require SI joint fusion (due to pain);
- Case Example:
Early Results of Percutaneous Iliosacral Screws Placed with the Patient in the Supine Position.
M.L. Chip Routt, Jr, P.J. Kregor, P.T. Simonian, and K.A. Mayo. J. Orthop. Trauma. Vol 9. No 3. p 207-214.
Radiographic Recognition of the Sacral Alar Slope for Optimal Placement of Iliosacral Screws: A cadaveric and clinical study.
M.L. Chip Routt, Jr., Peter T. Simonian, S.G. Agnew, and F.A. Mann. J Orthop Trauma, Vol. 10. No 3. 1996. p 166.
Early fixation of the vertically unstable pelvis: the role of iliosacral screw fixation of the posterior lesion.
JF Keating et al. Journal of Orthopaedic Trauma. Vol 13. No 2. 1999 p 107.
The effect of sacral fracture malreduction on the safe placement of iliosacral screws.
Superior gluteal artery injury during iliosacral screw placement.
Biomechanical Comparison of Sacroiliac Screw Techniques for Unstable Pelvic Ring Fractures.
