An Introduction to Open Anterior Lumbar Interbody Fusion (ALIF); Indications, Approaches, Techniques, and Nursing Care

Spinal fusion for the management of lumbar degenerative disc disease has been available for several decades. The results of this procedure remain under constant scrutiny and progressive development. Anterior lumbar fusion was initially introduced in the early 1920s. Fibula and iliac struts, femoral rings and dowel, as well as synthetic metallic devices have been applied as fixation implements to aid in lumbar interbody fusion. Approaches to the spine have experienced similar evolutionary changes. Prior to the 1950s most anterior lumbar approaches were extensive transperitoneal exposures (i.e. through the membrane lining the walls of the abdominal and pelvic cavities). In 1957, Southwick and Robinson introduced the retroperitoneal approach (i.e., behind the peritoneum). Transperitoneal exposures (i.e., through the peritoneum) require incision of both the anterior and posterior peritoneum. In contrast, retroperitoneal exposures maintain the integrity of the peritoneum and approach the spinal column laterally behind the bowel and peritoneal contents. This has the advantage of less post–operative bowel problems. Additional changes in technique have seen the advent of minimally invasive approaches, including endoscopic and laparoscopic methods. Minimally invasive approaches are generally directed at one or two–level disease processes. Anterior lumbar interbody fusion (ALIF) may be useful in the treatment of unyielding low–back pain. The cause of this pain is often difficult to diagnose. Broad categories of pathology that may be associated with persistent low–back pain include degenerative disc disease, spondylolysis, spondylolisthesis or iatrogenic segmental instability.

[Figure 610] MRI of patient with disc and vertebral endplate changes. Perhaps a candidate for a ALIF procedure.

ALIF should only be considered following the patient's unsuccessful completion of an organized nonoperative rehabilitation program. Aids to diagnosis in the case of a patient with mechanical low–back pain expand upon a thorough history and physical examination. Radiographic studies; plain films, bone scan (SPECT), CT scan, MRI and discography, all play a role in patient evaluation. Frequently more than one of these diagnostic studies is needed for an accurate diagnosis. ALIF may be utilized as an isolated procedure or in conjunction with posterior spinal fusion. The method with which ALIF is accomplished depends largely on the surgeon's preference and experience. Minimally invasive techniques – open or laparoscopic – require greater intraoperative attention to detail and preoperative surgical planning.

Indications for ALIF Degenerative Disc Disease

The suspected lumbar level requires confirmation as a pain generator by diagnostic testing. Multilevel disease, i.e., greater than two levels of the spine, is less predictable and therefore rarely indicated for ALIF. We have found that single–level disease in a psychologically stable patient, responds well to ALIF.

Spondylolysis and Spondylolisthesis

The vast majority of patients with spondylolysis or spondylolisthesis do not require surgery. Patients with spondylolysis or spondylolisthesis (grade I) may be effectively treated with ALIF as an isolated procedure. Present data is inconclusive regarding the effectiveness of isolated ALIF in grade II spondylolisthesis. Furthermore, biomechanical data related to the degree of vertebral translation concomitant with grade III or greater spondylolisthesis implies that isolated ALIF may be associated with a high pseudoarthrosis rate (failure of fusion). Therefore, in grade III or greater spondylolisthesis, a posterior fusion in addition to ALIF is strongly recommended. ALIF as the only procedure (i.e. without a posterior operation), is not recommended in a spondylolesthesis above grade I.

Iatrogenic Segmental Instability

Hypermobility of a lumbar–motion segment requires rigid fixation to improve fusion rate. Limited sagittal translation may be addressed by isolated ALIF. As inferred above, high degrees of translation are difficult to stabilize; therefore circumferential fusion is often required.

Surgical Approaches for ALIF

Regardless of pathologic level, the anterior approaches to the lumbar spine fall into two general categories: transperitoneal or retroperitoneal. Both categories of exposure may be carried out through a vertical, horizontal, or oblique incisions. Following incision of the skin and superficial fascia the abdominal muscle wall is exposed. The muscular layer is traversed by muscle transection or muscle–splitting techniques. The most frequently used muscle–splitting technique involves the midline approach through the rectus sheath. Presumably muscle–splitting techniques result in less intrinsic muscle damage. The anterior peritoneum is isolated and incised. In approaches to the lower lumbar segments, the bladder position must be recognized and protected. Placement of a Foley catheter will decompress the bladder and improve exposure.

Transperitoneal Approach

The transperitoneal approach requires direct manipulation of the small bowel and sigmoid colon. Trendelenburg positioning is very helpful in removing the small bowel from the operative field. Lap sponges hold the bowel in position exposing the posterior peritoneum. In slender patients the content of the retroperitoneal space may be visualized through the posterior peritoneum prior to its incision. Careful palpation and visualization of the aorta and common iliac vessels improve the safety of this approach. Over zealous retraction of the venous structures should be avoided. Intraoperative bleeding and/or postoperative venous thrombosis may result. The L4–L5 level is the most problematic. The great vessels branch off at or about the L4–L5 disc space. The venous anatomy is quite varied and requires special attention when approaching this level transperitoneally. Release of the segmental veins and lumbar arteries is usually necessary. While the segmental vessels above the L4–L5 level require similar attention, mobilization of the great vessels is more effective. At the L5–S1 level, the bifurcation is not usually problematic. However, attention to the overlying anatomy at the lateral disc space must be considered, i.e., common iliac veins and ureters. Furthermore, dissection of the retroperitoneum at L5–S1 is associated with the greatest potential for retrograde ejaculation and sterility in men. The exact mechanism for the disruption of normal ejaculation is not fully understood. Theories suggest that perivascular neural tissues (sympathetic and parasympathetic) in the area are disrupted by dissection and the use of monopolar cautery. The use of blunt dissection and bipolar cautery may decrease the occurrence of this rare, but devastating complication. Upon completion of the procedure, soft tissues are closed in layers. These layers should include the posterior peritoneum.

Retroperitoneal Approach

The retroperitoneal approach to the lumbar spine can be accomplished through similar muscle–splitting techniques as discussed in the transperitoneal approach. Following penetration of the muscle layer, mobilization of the peritoneum and dissection of the retroperitoneal space are carried out. Inadvertent penetration of the peritoneum is repaired primarily with an interrupted or running suture. Dissection of the retroperitoneal space is usually performed on the left side, minimizing the need to manipulate the vena cava. Exposure of the specific vertebral levels requires mobilization of the vascular anatomy similar to the transperitoneal approach. Once again, closure of the operative incision is performed in layers.

Surgical Technique Templating

The surgical technique begins with a preoperative plan. Preoperative templating will determine the size of threaded bone dowel or the synthetic device required for interbody fusion. The intent of a surgical procedure is to apply the largest dowel or device anatomically possible. Vascular anatomy may alter this choice at the time of surgery particularly at the L4–L5 level. The normal disc spaces above and/or below the diseased level are used as a guide to anticipated distraction. The templating is performed via the axial and sagittal MRI or CT scan. Care must be taken to select the proper templating overlay which depends on image magnification. Proper implant size is suggested when two implants fit within the confines of the vertebral body on the axial projection.

Disc Space Entry

Following patient positioning on the operative table, C–arm imaging is used to demonstrate proper alignment of the disc space and intended implant introduction. It is best to confirm appropriate access to the operative level prior to draping the patient. A radiolucent table is used. The C–arm images are obtained in the AP and lateral projection. A bolster under the patient's torso with his or her arms placed to the side, may aid in obtaining an unobstructed lateral view. The spine is then exposed and the disc space addressed. A footplate guide wire is inserted at the midline of the disc space and confirmed with AP and lateral C–arm images. The footplate is rotated across the anterior annulus to ensure adequate exposure for placement of two dowels. At this point a decision can be made regarding the use of a single or double–barrel guide tube. The double–barrel tube requires greater mobility of the vascular structures and is frequently used at L5–S1. Entry points for the fusion sites are then marked on the anterior annulus.

Trephining

A trephine is inserted over the guide wire at the entry point under C–arm control. From this point forward all devices introduced into the disc space should be parallel to the vertebral endplates and watched under C–arm imaging. The preferred depth of posterior penetration is the junction of the middle and posterior thirds of the vertebral body. Trephining removes a core of annulus and disc material. This aids in the placement of disc– space dilators. Upon removal of the trephine, residual portions of the trephined core are retrieved with pituitary rongeurs.

Disc Space Dilation

Disc space dilators are inserted sequentially until soft–tissue tension is achieved within the annulus and the dilator is held secure in its position. Sizes of disc–space dilators available are determined by the preoperative templating. Each dowel size is associated with three possible dilators. Inadequate dilation will result in excessive endplate bone removal and reduced indirect foraminal decompression. Excess bone removal increases the risk of implant subsidence (settling of the implant into the vertebral body). Ideally, 3 mm of endplate are removed on either side of the disc space (16 mm dowel and 10 mm dilator, 18 mm dowel and 12 mm dilator). The guide tube with appropriate flange size, equal to the dilator size, is then introduced over the dilator. The dilator is now removed leaving a protected channel produced by the guide tube. Care must be taken when inserting the guide tube. During this phase of the procedure the vascular anatomy is at the greatest risk of injury. The lateral flange of the tube should be clearly visualized while the vein and artery are protected. The single– guide tube has designated medial and lateral borders to account for the contour of the vertebral body.

Reaming and Tapping

A vertebral reamer is manually set to appropriate length (approximately 6 mm longer than the planned dowel) and passed through the guide tube. Following each pass of the reamer a pituitary is placed to remove loose soft–tissue debris. The reaming step is then followed by tapping. A vertebral tap is manually set to appropriate length (approximately 6 mm longer than the planned dowel) and passed through the guide tube. Care is taken not to "bottom out" the tap. When the tap reaches the end of the previously reamed tunnel, its threads are destroyed by additional turning against the intact vertebra. This process is called "bottoming out." Bottoming out the tap will weaken the final fixation of the dowel or device. After tapping and prior to placement of the dowel, a final pass of the pituitary rongeur will inspect the fusion bed for residual annular or disc fragments.

Dowel Insertion

The appropriate dowel is packed with autogenous bone and applied to the dowel inserter. It is critical that proper attachment of the dowel to the inserter be achieved. Dowels are slotted posteriorly for inserter access. The fit should be flush with no toggle between the dowel and the inserter. Failure to address this point may lead to problems with insertion torque and breakage of the dowel. The dowel is then passed through the guide tube into the bone. Calibrations on the side of the inserter aid in countersinking the dowel below the anterior endplate of the vertebra. The T–handle of the dowel inserter, on final placement, is perpendicular to the midaxis of the patient. This guarantees that the central portion of autogenous bone is positioned within the cancellous vertebral body and not the empty disc space. On sagittal projection, ideal positioning for the dowel or device is within the axis of rotation of the vertebral body. Biomechanical data would suggest that this axis is at or near the junction of the middle and posterior third of the vertebral body. Patient Care Overview The field of spinal surgery has made major advances in developing new techniques to correct spinal problems and provide a solid fusion. New surgical techniques challenge physicians and nurses to become more knowledgeable and informed. Patient care is often influenced by these new techniques because the focus changes. Hospitalization time is shortened, often to 2 days or less, requiring acceleration of surgical recovery for patients. Such is the case with minimally invasive anterior techniques.

Gastrointestinal

ALIF can be performed through the peritoneum (transperitoneal) or behind the peritoneum (retroperitoneal). This is important because of the effect it will have on the gastrointestinal tract. The condition of the gastrointestinal tract becomes the immediate focus of nursing care. The goal is to have normal intestinal function return as quickly as possible. The care plan focus is directed toward the achievement of this goal. Bowel sounds should be monitored in all 4 quadrants upon arrival to the unit. Monitoring should continue every 2 hours over the next 8 hours then every 4 hours twice. When bowel sounds are active and flatus is passed, monitoring should be done every shift until discharge. The development of ilius is always a possibility. When the surgical approach is transperitoneal, that possibility may increase. The discharge goal is passing flatus. The status of bowel sounds will dictate how fast a patient will progress to a general diet. To start, ice chips and sips should be given until bowel sounds are present. Clear liquids follow until flatus is passed then a general diet can begin. This slow progression will help avoid the development of ilius. Before discharge a general diet should be tolerated. A high fiber, high protein diet should be followed. The combination of anesthesia, surgical procedure and medication all have an effect on intestinal function. One of the best ways to restore intestinal function, is to start activity as early as possible. Early mobility will help to improve GI function.

Mobility

Bedrest should be observed for the first 6 hours after returning to the unit. The head of the bed may be elevated as tolerated during this period for comfort. Out–of–bed activities are encouraged as soon as possible. Log rolling should be done every 2 hours until getting out of bed independently. Initially, nursing should assist, giving instruction in proper body mechanics while turning. As strength and condition improves the patient may move toward self turning. On the night of surgery, the patient should try to stand at the bedside at least once. Postop day 1 activity should focus on sitting, dangling, and ambulating at least 4 to 6 time during the day. Instruction in body mechanics for mobility/ambulation and daily living activities should be given. Stairs should be tried in the afternoon or evening, or at least once before discharge. Discharge goals include the use of proper body mechanics, independent ambulation, and ability to climb stairs.

Pain Management

IV fluids are given until bowel sounds are active and oral fluids are tolerated. In an effort to reduce the amount of narcotic pain medication required postop, Marcaine and Epinephrine may be given during surgery. PCA programs can give good pain relief. The goal is to make the change to oral medication as quickly as possible while providing adequate pain control. Anti–inflammatory medication (Toradol) and/or muscle relaxers (Flexaril) may be given to patients with uncontrollable pain unless they are contra–indicated. The quick action of these adjunctive medications help reduce the amount of narcotic needed. The less narcotic used, the less influence there will be on overall bowel function. However, consideration must be given to the possible adverse effects of NSAIDs on the fusion process. Pain pills, such as Percocet or Vicodin, should be started as soon as oral fluids are being tolerated. The discharge goal is for pain to be controlled by the ordered oral medication.

Neurovascular

Upon arrival to the unit, assessment of all extremities should be done. Neuro impingement of upper extremities may occur in positioning during surgery. Further assessments should be done every hour for 6 hours then every 2 hours for 18 hours. Over the next 24 hours checks should be done every shift, if stable, every 4 hours if unstable. The discharge goal is for a stable neuro condition. Numbness and/or tingling may not be resolved but should remain similar to the preop condition. Anti–embolism stockings, sequential compression devices (SCD) and foot pumps (FP) assist vascular circulation. The use of stockings and one of these devices is appropriate. They should be taken off twice a day for a half hour then replaced. SCD/FP's should be on while in bed. When a patient can arise 4 or more times SCD/FPs may be discontinued. Calf pumping needs to be done 10 times every hour while the patient is awake and should be continued at home while activity levels are decreased. The discharge goal is to have no sign or symptoms of DVT.