The Birmingham Interlocking Pelvic (Triple) osteotomy

Surgery is performed with the patient initially in a lateral position. This allows access for the ischial osteotomy. A sling (draw sheet) is placed underneath the pelvis (A). This facilitates turning the patient into the supine position without reprepping and redraping. A posterior support is positioned over the lower thoracic spine (B). It must not be positioned more distal than this otherwise access to the iliac crest will be difficult during the second stage of the operation.

A pillow is placed between the knees. Ensue that there is enough space to apply skin prep far as the midline and above the iliac crest.

The patient is prepped and draped such that the ischial tuberosity (IT), greater trochanter (GT) are palpable. The iliac crest should also be accessible and the anterior drape should be passed along the midline towards the umbilicus.
The skin incision is approximately 6-8cm long. It is in the line of the fibres of gluteus maximus, 1/3 of the distance between the GT and IT.

The muscle fibres of gluteus maximus can be split by blunt dissection although occasional small blood vessels may be encountered and should be cauterised. The muscle is surprisingly thick. Deep Langenbeck retractors are helpful. At this stage the assistant should still be on the opposite side of the operating table.

As the muscle fibres are separated one is able to visualise fat. This is over the ischium behind the femoral head. Gentle palpation in this area will allow identification of the sciatic nerve which lies along the sub cotyloid groove. Norfolk and Norwich self retaining retractors are helpful to spread the muscle fibres and allow careful dissection around the nerve.

At this point it is advisable to flex the knee (keeping the hip extended). This position is easily maintained by resting the shin/foot against the operating surgeons (OS) abdomen. By doing this tension in the sciatic nerve is reduced.

The ischium is divided along the sub cotyloid groove from the greater sciatic notch to the obturator foramen.
The sciatic nerve enters the buttock through the greater sciatic notch beneath piriformis. It lies on top of the short external rotators. To access the ischium the short external rotators need to be split midway between the obturator foramen (OF) and sciatic notch. Retractors are placed in front of the sciatic nerve, but behind the hip joint.
Split the muscle (short external rotator and slide the retractor on top of the bone and underneath the muscle until the tip enters the greater sciatic notch proximally and a second retractor distally into the obturator foramen.

Lane’s lever retractors are ideal. The blunted/hooked end is ideal as it allows the surgeon to feel the tip ‘fall’ into the sciatic notch and obturator foramen.

It is extremely important to ensure that the proximal retractor is placed in the greater sciatic notch and not the lesser sciatic notch. It is easy to inadvertently place the retractor in the lesser notch but if this occurs the sacrospinous ligament will remain attached to the free central acetabular fragment. This will limit mobility of the free fragment and compromise correction of deformity. In addition, it is possible to ‘hook’ the sciatic nerve around the retractor if placed in the lesser sciatic notch resulting in nerve injury.

It is helpful to pre drill the ischium prior to dividing the bone with an osteotome. This reduces the chances of the osteotomy propagating in the wrong direction.
The surgeon also has the opportunity to move the hip with the drill in place. This confirms that the joint has not been entered by mistake.

A wooden handle fairly broad osteotome of limited depth is helpful. The shoulders on the osteotome allow the surgeon to have an idea how deep it has been inserted.

When dividing the ischium great care must be taken to ensure that one does not accidentally enter the hip joint. This can be avoided by ensuring that the osteotome is held vertical i.e. perpendicular to the plane of the operating table.

It is important to appreciate that the ischium is triangular in cross section at the level of the sub cotyloid groove. It may be up to 2cm thick/deep at the obturator foramen but then gently narrows as it approaches the greater sciatic notch.

It is very important to verify that the osteotomy is complete. If the osteotome is rotated through 45 degrees it should be possible to see the osteotomy displace. Sometimes a small crack is heard as any small intact area gives way when the osteotome is rotated.

The wound is closed in layers. The muscle fibres should fall into place. 2/0 vicryl to fat and subcuticular skin closure. Dressing is applied and covered with sheet of opsite/iodoban.

The patient is next turned into the supine position. This is accomplished without re prepping. The back rest is removed together with the pillow that has been placed between the patients legs.
The surgeon and first assistant each take one end of the sling (drawsheet) (A,B) that has been placed underneath the patient. Identification is aided by having the ends of the sling bundled together. The anaesthetic team turn the shoulders whilst the surgical team turn the pelvis and lower limbs.

An anterior approach is made to the hip. The incision is approximately 10cm long, parallel to and 1-2cm below the iliac crest. The central point of the incision will be below the anterior superior iliac spine (ASIS).

The lateral cutaneous nerve of the thigh should be identified approximately 2cm below the ASIS. It will be located below the deep fascia running from medial to lateral. There are invariably small blood vessels crossing the nerve.
The interval is between TFL laterally and sartorius medially. The lateral cutaneous nerve is retracted medially. Neuropraxia of the nerve is common and patients should be consented for this.

In a child and adolescent the iliac apophysis can be split with a knife. In adults the external oblique muscle has to be elevated off the iliac crest. NOTE – the abductors are left attached to the iliac crest.

Sub periosteal dissection procedes over the inner table of the ilium. In children this layer lifts very easily. A cobb elevator is ideal. Elevation of the periosteum continues over the pelvic brim.

A swab can be packed onto the space between periosteum and ilium. This helps to control bleeding from small perforating vessels. The sartorius/origin of inguinal ligament is detached and tagged with an 0 visryl stay suture. By doing this the incision along the iliac crest becomes continuous with the anterior approach between TFL and sartorius.

Periosteum will need to be elevated as far as the greater sciatic notch (A). Using a cobb elevator the periosteum is then lifted off the quadrilateral plate (B) and along the superior pubic rams (C).

A Rang retractor is specifically designed to access the inner table of the ilium. The curved blunt tip is hooked around the greater sciatic notch.

Care should be taken to ensure that the tip of the retractor slides along the surface of the ilium so that all soft tissue is retracted. Iliopsoas will be in direct contact with the back of the retractor

With the Rang retractor in place the next step is to work along the quadrilateral plate and superior pubic ramus. This is facilitated by flexing the hip and knee. This reduces the tension in psoas. It is crucial that the surgeon stays in contact with the bone since neuromuscular structures will be in close proximity.

A Lane’s lever needs to be passed over the top of the superior pubic ramus anteriorly. A curved right angle clamp (Kocher or similar) is slid along the quadrilateral plate until the tip can be passed into the obturator foramen. It is important to make the osteotomy far enough medial so that the joint is not entered. Viualisation can be enhanced by using a ‘forked’ retractor. Each limb sits astride the pubic ramus.

In this image the Lanes lever (A) lies in front of the superior pubic ramus. Right angle retractor (B) is in obturator foramen. There is a clear view of the pubic ramus (C).

A Fish Tail curved lexor type osteotome is ideal for performing the pubic osteotomy since the shape matches the contour of the bone.

The osteotomy is completed. It is advisable to use image intensification to ensure osteotomy has been performed at the optimum position.

The iliac osteotomy is performed through the same wound. Prior to performing the bone cuts it is important to insert the schanz screws. This allows optimum control of the free acetabular fragment once the osteotomy has been performed. This first screw is parallel to the quadrilateral plate (A). The correct position is as medial as possible and just above the acetabulum. The allows maximum distance between the screws.

Use of image intensifier ensures correct placement of first schanz screw (A). Note second drill hole (B)

Postitoning of second drill hole is determined by using guide block for the Orthofix external fixator. The drill hole is made but the second schanz pin not inserted until after the osteotomy has been performed.

The iliac osteotomy is constructed from 3 cuts (A,B,C). Each cut is the same length and the angle between the A-B cut should be the same as the B-C. This angle should correspond to the desired correction. Once the cuts have been performed the schanz screws are inserted and the central acetabular fragment rotated so that the acetabular A cut lines up with the iliac B cut.

The iliac cut is made from the inner table. A reciprocating saw is ideal for this purpose.

A blunt Homan retractor is slid along the outer table of the ilium from a point just above the Anterior inferior iliac spine (A). This protects the abductor muscles. The Rang retractor is essential to protect soft tissues in the sciatic notch. A Lexor osteotome can be used to complete the osteotomy at its most posterior extent.

Once it is clear that the osteotomy is complete the second schanz screw is inserted. An orthofix body or leg lengthener is then attached to the pins. The central acetabular fragment should then be free to rotate to the desired position. There may be a few soft tissue attachments tethering the central acetabular fragment. Rotation is easier if the hip if flexed to reduce tension in the hip flexors.

Version of the acetabular fragment can be adjusted by tilting the schanz screws in the transverse plane. Due to the fact that the bone cuts are interlocked only 20 degrees of versional correction is possible but this is usually sufficient. The position is then stabilised with smooth wires inserted along the iliac crest under image intensifier control.

Several options exist for definitive stabilisation. 6.5mm and 8.0mm ACE screws are ideal providing the iliac wing is of sufficient depth. The screws are cannulated and can be inserted over the guide wires used to stabilise the osteotomy.

A 3 hole DCP plate can be very useful. The distal schanz screw hole can be utilised and filled with a 6.5mm cancellous screw.

The apophysis/external oblique muscle is repaired with interrupted 1 vicryl sutures. Fat and subcuticular absorbable sutures to skin.

The aim is to achieve a lateral centre edge angle of 35 degrees. Note that the posterior acetabular wall passes through the centre of the femoral head confirming correct version. The teardrop has been elevated confirming movement of the ischial oseotomy. The teardrop should never be higher than the centre of the femoral head.