Lumbar Artificial Disk
In situations where adequate exposure poses a problem or there has been prior abdominal surgery, an approach surgeon should be consulted. Ideally, the approach surgeon should meet with the patient separately before the procedure. Ureteral stents should be considered in patients with a history of prior pelvic and/or abdominal surgeries or history of pelvic inflammatory diseases (endometriosis).
A transverse horizontal incision can be done at L5–S1 and approached from the right side in males to permit later left-side approach to L1–L5 level(s). A left-sided approach is used for L4–L5 levels and higher.
Hybrid techniques such as an L5–S1 fusion to treat more advanced spondylosis and an L4–L5 disk replacement can be performed. Each patient and each level should be individualized for artificial disk replacement (ADR) versus other surgical procedures as clincically indicated.
Under fluoroscopic guidance, the skin is marked at the level of interest. The patient is positioned with the lumbar spine in a neutral position. The spinous process should be equidistant from both pedicles. All levels proximal to L5–S1 are approached by a left paramedian approach; a right paramedian approach should be used for access in a single level L5–S1 approach. L5–S1 multilevel cases are approached from the left side. A standard transverse incision can be used in most cases; however, a vertical incision can be used to approach the L5–S1 disk space as well (Fig. 22.1). Either a transperitoneal or retroperitoneal approach can be used. The anterior rectus fascia is identified and incised close to midline. After mobilization of the rectus muscle, the posterior rectus sheath as well as the semilunar line of Douglas is visualized. The retroperitoneal space is then developed by sweeping the peritoneum in a lateral to medial direction off the psoas. The peritoneum and ureter are then bluntly dissected off the psoas, identifying the iliac vessels. A self-retaining retractor can then be used to hold the exposure. Middle sacral vessels are divided to complete the exposure. Exposure of the L5–S1 region is fairly straightforward; this disk space can be approached between the bifurcation of the aorta and inferior vena cava into the common iliacs (Fig. 22.2). The approach to the L4–L5 disk space involves retraction of the aorta and inferior vena cava (IVC) to the right and frequently requires ligation of the iliolumbar vein at L5 and the segmental vessels. Care must be taken not to disrupt the left L5 nerve root, which is in close proximity to the ascending lumbar vein.
Fig. 22.2 Exposure of the disk space via a midline approach. Retracted aorta and superior hypogastric plexuses are shown. 1. The middle sacral artery and vein may be ligated. 2. The ascending iliolumbar vein is ligated at the L5 level. 3. The sympathetic ganglia are identified and spared. 4. The great vessels are retracted to the patient’s right side including the aorta and inferior vena cava. 5. The superior hypogastric plexus is identified and spared. 6. The incision of the anterior longitudinal ligament is as shown with a #11 or #15 blade.
An alternative to the retroperitoneal approach is the transperitoneal route. This is done by making a paramedian incision in the rectus muscle and retracting it laterally. The peritoneum is then incised and the abdominal cavity can be explored. It is important to keep the patient in the Trendelenberg position to maintain the abdominal contents out of the operative field. A lap sponge can be used to sweep away the bowel until the posterior peritoneum is encountered, then a longitudinal incision can be made through it. Care should be taken to identify the ureters.
No matter which approach the surgeon chooses, the correct level should be verified under image intensification. Pedicles should be equidistant from the spinous process on imaging; this ensures proper centering of the implant. Annular flaps are created to protect surrounding tissues. Using an endplate elevator, cartilaginous components are removed from bony endplates. Care is taken not to damage the bony endplates. Maneuvers to preserve integrity of subchondral osseous plates include not applying too much pressure when using the rasps and curettes as well as stopping when significant bleeding is encountered signifying entry into the cancellous portion of the vertebral body. Interspace distractors are inserted to mobilize the segment. Image intensification is used to ensure proper positioning of the endplate spreader. If the spreader is placed too anteriorly, damage to the endplates could occur. Decompression is then performed laterally and medially. If extruded disk fragments need to be excised, removal of the posterior longitudinal ligament is warranted.
Trial implants should be aligned to the midline (Fig. 22.3). Insertion is performed under image intensification. If the implant is loose, select the next highest size. Endplates should just lightly secure the implant. Select the smallest sized implant possible that provides a snug fit (Fig. 22.4, Fig. 22.5).
When performing multisegment surgery, each segment is addressed separately. Segments with the most severe collapse should be addressed first as this will affect sizing at adjacent levels. In multilevel cases, the most distal and most proximal levels should be addressed first and the central disks addressed last if there is any question of disk mobilization to increase ease of insertion. In cases of moderate to severe disk height collapse, the David parallel distractor (Depuy Spine, Raynham, MA) is especially useful in the remobilization of the interspace.
A retroperitoneal approach could prove very challenging in patients who are very obese or have had previous abdominal surgery with adhesions. In these instances, the procedure may not be ideal and one may not want to consider them candidates for this technique.
Due to the proximity of the sympathetic plexuses during surgical approach, male patients should be alerted to the risk of retrograde ejaculation and possible sterility. Patients should be provided the opportunity for sperm donation. When dealing with the L5–S1 region a right-sided approach should be used.
Revision surgery in cases of failed TDR that involve the posterior spinal elements should be addressed posteriorly whenever possible. In cases of failed TDR implants that necessitate anterior revision surgery, several preoperative and intraoperative evaluations and techniques should be employed. Preoperatively, plain radiographs and CT should always be obtained. The author also obtains a venogram and places a vena cava filter on the day prior to surgery. Access surgery consultation is always obtained.
In revision surgeries intraoperatively, bilateral ureteral stents placement should be considered prior to incision. The abdomen and inguinal skin down to the mid-thighs are prepped and draped. The side of approach is mandated by the level of interest. Whenever possible, an opposite-sided approach is utilized.
If an inadvertent venotomy is experienced intraoperatively, compression with sponge sticks is used immediately. The patient is placed into a reverse Trendelenberg position. If necessary a balloon-tipped catheter is placed from distal to proximal in the common femoral vein to preclude venous flow and permit repair of the venous defect. A primary or side repair is performed. If absolutely necessary, the injured vein is tied and ligated. If venous structures cannot be safely mobilized, a primary bypass may be performed to mitigate the possibility of a traumatic venous disruption. Simple epidural bleeding can usually be controlled with bipolar electrocautery.
In revision surgery, a lateral approach to the disk space should be considered if possible especially at the L4–L5 level. At the conclusion of the procedure, a retrograde uretherogram should be obtained to confirm ureteral integrity.
If a dural tear is encountered, primary repair is often difficult. If suturing is technically not possible then a dural sealant such as fibrin glue or another similar agent can be used. If the tear is rather significant a lumbar drain may also be used in conjunction.