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Tips for surgical repair of a sacroiliac separation

This technique for the repair of sacroiliac separations is simpler, quicker and safer than the lag screw technique.
The technique uses a Steinman pin supported by a tension band to stabilize the sacroiliac joint. One advantage is the lower risk of collateral damage from a smooth pin than from the twisting action of a drill or screw.
There are also a few other advantages with this technique mentioned later.


Positioning

  • Place the animal in ventral recumbency.  The spine, sacrum and tail should be straight and level. To get this right, the patient may need some ventral support.  Avoid, in particular, rotation of the spine and ilia.

Dissection

  • Identify the high point of each ilial spine and incise the skin just medial to the ilium at this point. If only one side is luxated, the skin incision on the normal side can be short. On the luxated side the skin incision should extend both cranial and caudal.
     
  • Dissect through the subcutaneous fat layer to expose the fascial sheath over the muscles.

  • On the normal side, make a short incision in the gluteal fascial sheath, just ventral and lateral to the highest point of the ilial spine. Dissect a small portion of the muscle off the spine.

  • For the size 1 Han-de ligature, drill a 1.5mm hole through the iliac spine.



  • Drill through the thicker bone of the ilial spine rather than through the thinner bone of the ilial wing. If the hole is too ventral, the lumbar vertebra may interfere with a straight passage for the ligature from one side to the other. A bone clamp on the ilial wing makes it easier to drill the hole.

  • On the luxated side, repeat this exposure for the drill hole.

  • Then on the medial side of the iliac spine, make a short, shallow incision through the lumbar / sacral fascia.

  • Insert  blunt pointed scissors both cranially and caudally along the line of least resistance. Incise the sheath in both directions along each path.

  • You are looking for the space between three muscle groups.  Two attach to the ilium, one group passes forwards and the other group passes backwards. They meet at an area just caudal to the highest point of the ilium [marked A]. The third group is medial to your incision and runs along the spine and tail.



Landmarks

  • Now check your landmarks. The ilial attachment to the sacrum starts just caudal to point A.


  • On the sacral side, identify the cranial sacral spine. The articular surface of the sacrum is vertically below this cranial spine.


  • The height of the cranial sacral spine varies between animals. In the cat the spinous processes are separate and sometimes the second spinous process is the more prominent. Make sure you identify the cranial spinous process.  In the dog the spines are fused to give the sacral crest

  • Gently retract the ilium laterally so you can identify the ilial articular surface and the reference point for the implant.

Surgical protocol

  • For this surgical technique, the starting point is on the ilium rather than on the sacrum. This approach has two advantages over the screw technique. First, the ilial reference point is easier to find because the bulk of the torn fibrous tissue is usually retained on the sacral side, making the view of the entry point for a drill on that side more difficult. In contrast, the medial side of the ilium is stripped relatively clear, so the reference point for the implant is more easily identified. Also with this technique the ilial wing does not have to be levered below the sacrum to find the reference point on the sacrum.

  • Having identified the two articular surfaces, move the luxated ilium back into its normal position.

  • Check for nerve entrapment

  • Then pass the loop passer through the pre-drilled holes in the ilia from the normal side to the luxated side. Draw a loop of strong suture material across between the ilial wings. Leave the loop of the suture material on the normal side.

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  • Again gently retract the luxated ilium and identify the reference point for the pin exit on the medial surface. It may help to draw a line with a scalpel blade between the two poles of the articular surface.

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  • Use a straight pair of forceps as a depth gauge to find the entry point for the pin on the lateral surface of the gluteal muscle.

  • Place the end of one arm of the forceps on the reference point for the pin exit on the medial surface. The end of the other arm gives the entry point into the gluteal muscles.



  •  Once found, keep the forceps in the original position; if the arms of the forceps move cranially or caudally then the ends are misaligned.

  • With the ilium back in its normal position and alignment, drill the pin through the ilial wing.

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  •  An assistant stabilising the ilium with a bone clamp can help with the drilling.

  •  With this technique the gluteal muscles are not dissected off the ilium.

Pin selection

  • For cats and small dogs, the pin can range from 1.5mm to 2mm diameter. For larger dogs, judge the appropriate pin size from the lateral radiographic view of the sacral body. The pin length should cross at least 60% of the sacral body.

  • The pin can be cut to the appropriate length prior to surgery, having taken the measurement from the ventro/dorsal radiograph. Otherwise cut the final pin length once the post op. radiographs have been examined.

Alignment of the articular surfaces

  • Check the exit point of the pin on the medial surface of the ilium is correct.

  • In practise, it is often difficult to decide the correct entry point for the implant into the sacral body. Much has been written about the exact entry point and angle at which a screw or pin should enter the sacral body. During surgery these exact targets are difficult to achieve because of the small target and the variations in shape, position and angles of the articular surface

  • However, align the articular facets and good results can be achieved. The lower [ventral] portion of the articular surface may be difficult to see. But align the upper [dorsal] portion and the implant should enter the sacrum correctly.

  • Before driving the implant into the sacral body, place a pointed bone forceps across both ilia close to the pin to keep the luxated ilium in position on the sacrum.

  • Check all alignments of the pelvis.

  • Then, with the pin parallel to the table and at right angles to the spine, drive the pin across the sacrum.

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  • If the pin was not premeasured, cut it short but leave enough lateral to the gluteal muscles for the chuck to get a grip.

Placement of ligature

  • Now change your surgical gloves. Open the Han-de ligature, move the toggle up the ligature. Thread the ligature into the preplaced suture loop and pull the ligature across between the ilial wings. Thread on the second toggle and tie firmly. Do not over tighten to distort the normal position of the ilium.

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Pin alignment

  • If the pin is not premeasured, make a stab incision through the skin and let the pin protrude through the skin. Suture closed all other surgical wounds and radiograph the patient.

  • If a minor deviation of the pin is a potential threat to the nerves or the blood vessels, then the pin should be partially withdrawn to reduce the risk.

  • If a major deviation is seen on the radiographs, then the pin should be withdrawn from the sacrum but remain in the ilium and then redirected back into the sacrum. This can be achieved if exact measurements are taken from the radiographs and the procedure is carried out carefully and slowly.

  • Once satisfied with the pin position cut off the excess pin and suture the final incision.

  • The pin fixation is supplemented by other stabilizing forces: the tension band; the roughness of the luxated surfaces; the surrounding muscle tone; and rapid healing. So after two or three weeks a luxation is unlikely to recur. If on follow up radiographs there is evidence of pin migration out of the sacrum, then the pin is easily removed.

For bilateral luxations, repeat the same technique on the other side.



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