Posterolateral Lumbar Spine Fusion

Patient Selection

Patient selection is a crucial factor for the success of lumbar spine fusions. Indications for posterolateral fusion of the lumbar spine include instability secondary to trauma, tumor, infection, and spondylolisthesis. Additionally, iatrogenic instability after decompression is also a common indication. More controversial is fusion for degenerative disk disease without demonstrated instability; however, in selected cases, fusion is highly effective. If preoperative instability is present, dynamic X-ray evaluation should include standing flexion–extension views, prone–supine cross-table views, and complete spine static views. These are essential for preoperative understanding of the instability and any associated deformity that needs to be considered.

Posterolateral fusion may be used as an in situ fusion, with pedicle screw fixation and in addition to interbody fusion. Choosing which techniques are best for any given patient is based upon an understanding of the biomechanics. Lumbosacral junction fusions typically use interbody grafting and pedicle screws to achieve a solid construct.

As in all surgical procedures, in addition to the surgical indication a patient’s overall medical condition should be evaluated, as well as psychosocial factors. Bleeding disorders, metabolic bone abnormalities, immunosuppression, and cancer are associated with greater risks and poorer outcomes. Obesity and diabetes are extremely prevalent. Preoperative weight loss should be encouraged, if possible. Smokers need be counseled to stop. Advanced age and general cardiovascular risk are important when deciding the appropriateness of adding pedicle screws or interbody devices to the fusion construct.

The psychosocial factors, which may prevent good outcomes, include workers compensation cases, pending litigation, psychiatric illness, and narcotic dependency or drug-seeking behaviors.

49.3 Preoperative Preparation

Routine preoperative laboratory work and diagnostic radiologic studies are obtained, supplemented by more in-depth medical evaluation as indicated by the patient’s medical condition. In cases of tumor, oncologic workup should be complete and include full metastatic workup and consultation with the patient’s oncologist to have an understanding of the patient’s life expectancy and extent of disease. If infection is suspected or known, erythrocyte sedimentation rate and C-reactive protein should be obtained, in addition to cultures of blood and urine. Blood should be available in the blood bank.

Operating rooms should be equipped with a Jackson spinal modular table or equivalent, fluoroscopy, and intraoperative neurophysiological monitoring. If desired, computerized navigation and three-dimensional fluoroscopy may also be requested. Preoperative imaging should be displayed and is easily viewable throughout the procedure.

Two large-bore peripheral IV lines and a Foley catheter should be placed. An arterial line and central line should be considered for patients with certain comorbidities and in cases where higher blood loss is expected. These cases may include multilevel fusions, osteotomies, and highly vascular tumors. Electrodes for monitoring of somatosensory evoked potentials and electromyography should also be placed at this time.

Patients are secured on the Jackson Spinal Modular Table in the prone position. Pressure points should be distributed to the upper chest, anterior superior iliac spine, and proximal thighs. Arms should be flexed to a maximum of 90° and padded, to prevent excess pressure to the brachial plexus and ulnar nerve. Knees should also be padded, and feet elevated off the table. Lack of abdominal compression avoids lower extremity venous congestion and blood loss from spinal epidural venous distention. Hips should be extended to achieve physiologic lumbar lordosis.

Mechanical deep vein thrombosis (DVT) prophylaxis should be used, either via sequential compression devices or antiembolic stockings. Warming blankets should be placed to prevent unintended hypothermia. Prophylactic antibiotics should be given before skin incision.

49.4 Operative Procedure

After positioning, we place an 18-gauge needle into the middle of a spinous process and obtain a fluoroscopic image ( ▶ Fig. 49.1). A small amount of methylene-blue is then injected, and the needle is removed ( ▶ Fig. 49.2). Care should be taken to ensure that the needle is in the tip of the process and not more anterior or interlaminar before injection. Exact localization of the injected level fluoroscopically allows for planning the location of the skin incision which is then marked.