2.9.2 Image intensifier-assisted closed techniques of reduction and fixation

10.1055/b-0035-121655

2.9.2 Image intensifier-assisted closed techniques of reduction and fixation

Joshua L Gary, Peter Bates, Adam J Starr

1 Introduction

The mainstay of operative treatment for acetabular fractures remains open reduction and internal fixation. However, as techniques and instrumentation for limited open reduction have improved since their introduction two decades ago, the use of percutaneous treatment has expanded to multiple centers and for increasing indications. Advanced age [1–3], obesity [4], and early weight bearing of minimally displaced fractures [5] have been cited as indications for percutaneous or minimally invasive management. Although the exact indications for limited approaches have not been fully determined and vary by practice, direct reduction through an open approach is usually preferred when an anatomical reduction is required in a healthy patient with good bone stock. Minimally invasive acetabular surgery represents another arrow in the quiver for acetabular fracture treatment when anatomical reduction is not possible or when the risks of open surgery outweigh the potential benefits of a direct anatomical reduction.

2 Screw pathways and image intensifier visualization

The screw pathways commonly used for the percutaneous treatment of acetabular fractures are well described [6–14]. Basic knowledge of the bony corridors and the appropriate image intensification views are essential for safe and timely placement of percutaneous screws. The technique is also heavily dependent on multiple-plane image intensification and an experienced x-ray technician who can switch between the required views quickly and reproducibly. This level of expertise can take years of training, and x-ray technicians should be valued members of the pelvic trauma team. However, even with these prerequisites, passing screws percutaneously is often difficult. Bone channels may be narrow, making it critical to identify the correct entry point on two views, and the start point itself is often located on a slanting surface that tends to deflect the spinning guide wire to a different trajectory. The most common screw pathways and image intensification views required for proper placement are detailed below.

2.1 Computer-assisted navigation

Several technologies for navigating percutaneous screws are now widely commercially available, which remove the need for real-time image intensification. Computer-assisted navigation has been shown to be highly effective in terms of safety in passing percutaneous screws along many of the anatomical pathways described below [15–17].

The main benefits of navigation are the accuracy and consistency of screw placement, along with reduced radiation exposure to the operating room personnel. When performing multiple screw insertions or when training junior surgeons, image intensification screening time can be significant and this is avoided completely when using navigated systems.

One of the drawbacks with some navigation systems, which use an intraoperative 3-D x-ray scanner, is the potentially high radiation dose to the patient. Operating room personnel are encouraged to leave the operating room during scanning cycles to avoid exposure, but the total dosage to the patient has been shown to be significantly greater compared with conventional image intensification [15, 17].

However, the main limitation of navigation systems is in the context of displaced fractures, where some degree of fracture reduction is required. In this instance, the pelvis either needs to be rescanned between each reduction maneuver, which carries incremental radiation exposure, or the surgeon has to revert to image intensification. Navigation is therefore useful in the situation where pelvic anatomy is nearly normal, as with undisplaced fractures, or following an open reduction. The challenge for computer-assisted navigation systems is to be able to ‘follow’ changes in the positions of the major fracture fragments as progressive percutaneous reduction maneuvers are applied intraoperatively. This would obviate the need for multiple repeated scans, which are time consuming and require further doses of ionizing radiation to the patient.

2.2 Anterior column/superior ramus screw

The anterior column screw can be placed in an antegrade or retrograde fashion and is used for fractures involving the anterior column ( Fig 2.9.2-1 ). Antegrade screws can be placed with the patient in the supine, lateral decubitus, or prone position, although imaging is awkward with the patient in the lateral position because the entire base of the x-ray machine has to move and the C-arm swings, as the surgeon transitions between inlet and outlet views.

Antegrade insertion: On the obturator outlet view, the guide wire entry point is placed on the gluteus medius pillar, aiming down the anterior column ( Fig 2.9.2-2 ). On the iliac inlet view, the wire appears to pass directly through the femoral head and should align with the funnel of the superior ramus beyond it ( Fig 2.9.2-3 ).

Once the wire is seen to pass safely over the hip joint on the obturator outlet view, its passage within the ramus is best imaged using the straight inlet and outlet views, which show the wire exit just medial to the pubic tubercle on the inlet and two thirds the way up the pubis on the outlet view.

Retrograde insertion: This can sometimes be more challenging, particularly in obese patients because the bulk of the opposite thigh deflects the operator’s hand and prevents good entry point trajectory. Bumping up the pelvis on a radiolucent support may help with this, as it forces the contralateral hip to extend out of the way. Imaging starts with inlet and outlet views in the ramus and then moves to obturator outlet and iliac inlet views, as the wire moves past the hip joint.

**Fig 2.9.2-1** Pathway for placement of the anterior column screw. Antegrade or retrograde placement is possible. Retrograde placement is usually simpler, unless the patient is obese. In obese patients, the contralateral thigh gets in the way of the surgeon’s hand and prevents correct placement of the guide wire. During placement of the anterior column guide wire, the femoral nerve, artery, and vein are at risk. The round ligament or spermatic cord also can be damaged.

**Fig 2.9.2-2a–b** a The C-arm position for the outlet-obturator view. b This view is used to ensure that the anterior column screw guide wire does not penetrate the acetabulum or exit the anterior column superiorly. (From Starr AJ, Reinert CM, Jones AL. Percutaneous fixation of the columns of the acetabulum: a new technique. *J Orthop Trauma.* 1998,12(1): 51–58, with permission).

**Fig 2.9.2-3a–b** a The C-arm position (for the inlet-iliac view). b This view is used to ensure that the anterior column screw guide wire does not exit the superior pubic ramus either anteriorly, toward the femoral neurovascular structures, or posteriorly toward the bladder. (From Starr AJ, Reinert CM, Jones AL. Percutaneous fixation of the columns of the acetabulum: a new technique. *J Orthop Trauma.* 1998,12(1): 51–58, with permission).

2.3 Posterior column screw

This screw is used for fractures involving the posterior column, typically the posterior element of a transverse or hemitransverse fracture, and it can be placed in an antegrade or retrograde fashion. From either starting point, the screw passes posterior to the acetabulum and anterior to both sciatic notches ( Fig 2.9.2-4 ). The essential x-ray views are AP, obturator, and iliac oblique ( Fig 2.9.2-5 ). The obturator oblique view shows the wire passing down into the tuberosity and prevents any extrusion medially or laterally. The wire tends to come out laterally around the level of the lesser sciatic notch, which will be seen on this view. The iliac oblique view shows the line of the posterior column and confirms that the wire is both out of the joint yet avoiding the sciatic notches. Ideally, the screw should be inserted close to the joint without perforating it.

Antegrade insertion: This can only be done from a supine position, with the entry point starting on the iliac wing approximately 1–2 cm back from the pelvic brim. A limited lateral window is required to safely dissect down the inner table of the ilium to find the entry point, although with long rigid drill guides or tubes, the skin incision can be as little as a few centimeters in length. Given the proximity of iliopsoas and the femoral nerve, the hip should be flexed and the guide wire protected via some type of sleeve. Some surgeons routinely use plastic tubes from the percutaneous spinal kit to protect the wire, although our preference is the pig sticker device.

Retrograde insertion: This can be performed with the patient in the supine, lateral, or prone position. The entry point of the retrograde screw starts on the ischial tuberosity and with the hip flexed 90°; this can be palpated directly in most patients. Because it starts near the perineum, the extremity and buttock region must be carefully prepared to maintain sterility and when the patient is positioned supine, the pelvis has to be bolstered considerably to make the shot possible. AP, iliac, and obturator oblique view x-rays are used for safe placement, but imaging the exit point on the inner table (and therefore the length of the screw) can be difficult. A true lateral view of the pelvis may be required to estimate the exit point if it cannot be done by “feel” (resistance change) alone.

2.4 Lateral compression (LC) II screw

This screw was named after initial use in the treatment of crescent, or Young-Burgess LC type II, fractures [18]. It can also be used to stabilize acetabular fractures that have an anterior column component that extends up through the iliac wing. This screw can be placed with the patient in the supine or prone position and is inserted in the column of bone between the anterior inferior iliac spine and the posterior superior iliac spines ( Fig 2.9.2-6 ). Three radiographic views are used for safe placement: the obturator oblique or teardrop ( Fig 2.9.2-7 ), the iliac oblique ( Fig 2.9.2-8 ), and the obturator inlet or “down-the-wing” ( Fig 2.9.2-9 ) views. For an anterior-to-posterior screw, the teardrop view is first used to obtain a starting point near the anterior inferior iliac spine. Once a starting point above the acetabulum is achieved, the iliac oblique view guides placement above the sciatic notch and the obturator inlet view guides medial-to-lateral positioning within the ilium. A lateral sacral view can also be used to help estimate screw length when near the posterior iliac spines.

A variation on this screw pathway was recently described in which the screw exits in the hard bone just anterior to the greater sciatic notch [5]. This has the advantage of allowing the screw to pass closely over the top of the hip joint, which then provides maximum support to the weight-bearing dome. The screw also has strong purchase in the bone around the sciatic notch, which remains strong, even in patients with osteoporosis. The disadvantage to this pathway is the apparent danger to the contents of the sciatic notch if either the guide wire or screw is inserted too far. This small study reported no neurovascular complications, but the iliac oblique view should be scrutinized during insertion of the guide wire to prevent injury.

**Fig 2.9.2-4** Pathway for placement of the posterior column screw. The sciatic nerve and all structures that exit the greater sciatic notch are at risk. Hip flexion will relax the sciatic nerve and draw it away from the starting point at the ischial tuberosity.

**Fig 2.9.2-5a–b** Posterior column screw guide wire placement. a The iliac oblique view is used to ensure that the guide wire remains posterior to the acetabulum and does not enter the greater sciatic notch. b The AP view of the pelvis is used to ensure that the guide wire does not exit the medial or lateral cortices of the ischium. (From Starr AJ, Borer DS, Reinert CM. Technical aspects of limited open reduction and percutaneous screw fixation of fractures of the acetabulum. *Oper Techn Orthopaed.* July 2001, with permission).

**Fig 2.9.2-6** Pathway for placement of the lateral compression II screw.

**Fig 2.9.2-7a–b** a The C-arm position to initiate insertion of the lateral compression II screw. b This position is used to visualize the tube of bone in which the guide wire will be passed down. The guide wire starts at the anterior inferior iliac spine and is passed to the posteroinferior iliac spine. (From Starr AJ, Walters JC, Harris RW, et al. Percutaneous screw fixation of fractures of the iliac wing and fracture dislocations of the sacro-iliac joint [OTA types 61-B2.2 and 61-B2.3, or Young-Burgess “Lateral Compression Type II” pelvic fractures]. *J Orthop Trauma.* 2002 Feb;16(2):116–123, with permission).

**Fig 2.9.2-8a–b** a The C-arm position to obtain an iliac oblique view. b The position to watch the lateral compression II guide wire pass above the greater sciatic notch. At the bottom, the notch is visible at about the 8 o’clock position, and the acetabulum and femoral head are visible at about the 4 o’clock to 6 o’clock positions. (From Starr AJ, Walters JC, Harris RW, et al. Percutaneous screw fixation of fractures of the iliac wing and fracture dislocations of the sacroiliac joint [OTA types 61-B2.2 and 61-B2.3, or Young-Burgess “Lateral Compression Type II” pelvic fractures]. *J Orthop Trauma.* 2002 Feb;16(2):116–123, with permission).

**Fig 2.9.2-9a–b** The C-arm position to ensure that the lateral compression II screw guide wire remains centered between the inner and outer cortices of the ilium as it moves toward the posterior inferior iliac spine. As it nears to posterior portion of the ilium, the guide wire skirts the sacroiliac joint, visible at bottom. (From Starr AJ, Walters JC, Harris RW, et al. Percutaneous screw fixation of fractures of the iliac wing and fracture dislocations of the sacro-iliac joint [OTA types 61-B2.2 and 61-B2.3, or Young-Burgess “Lateral Compression Type II” pelvic fractures]. *J Orthop Trauma.* 2002 Feb;16(2):116–123, with permission).

2.5 Magic screw

The magic screw can be used to hold a quadrilateral plate fragment in a reduced position. It is effectively a variation on a posterior column screw, except it starts on the lateral face of the ilium and exits through the quadrilateral plate around the level of the ischial spine ( Fig 2.9.2-10 ). The guide wire is started on the oblique surface of the iliac wing on the gluteus medius ridge, at a point proximal and posterior to the acetabulum. The wire should exit the bone through the inner cortex of the quadrilateral plate, at, or near the ischial spine. During passage of the guide wire, the AP, inlet, and iliac oblique views are used to ensure that the guide wire does not penetrate the acetabulum or extend past the quadrilateral plate into the true pelvis.

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