Anterior Lumbar Discectomy with Fusion

Anterior lumbar fusion is most often performed to treat patients with intractable back pain due to abnormalities of the lumbar discs. For the past 10 years we have performed the procedure preferentially over posterior lumbar fusions. It has produced better and more consistent relief of back pain related to disc deterioration. More recently technical advances have prompted many surgeons to follow. Presently we are performing many of these procedures laparoscopically and feel that in time, this too will become the standard of treatment.

The decision to perform Anterior Lumbar Discectomy Fusion is based on three factors: Patient symptoms, findings on physical exam, and radiographic abnormalities.

A. PATIENT SYMPTOMS

The patient's symptoms are generally categorized into three patterns of pain. Axial pain is that which occurs along the spine and the overlying musculature. Referred pain is that which occurs along the buttocks or pelvic region. Radicular pain is that which extends partially or completely along the length of the leg.

Axial pain is generally vague and is typically similar irrespective of the underlying problem. Referred pain into the pelvis or buttocks is also generally vaguely defined. These patterns which may be due to irritation of minor nerves along the surface of the^tsc or joints can be difficult to differentiate from patterns of pain due to soft tissue inflammation such as ligamentous injuries or tendonitis. Segmental instability or abnormal shifting of joints or vertebrae in the lumbar spine can also produce similar patterns of referred pain. Radicular pain typically conforms to a specific nerve root distribution or course. A radicular pattern of pain is most easily identified as specifically related to nerve root impingement and, as such is generally most accurately correlated with a specific abnormality within the spine.

B. PHYSICAL FINDINGS

Physical findings can generally be divided into three groups: Limitation of motion, the presence of tenderness, and neurological deficits. While limited range of motion in the lumbar spine is frequently present, it is a very nonspecific finding and does not reflect any particular abnormality, which would suggest an indication for performance of a anterior lumbar discectomy and fusion. Tenderness is also frequently present and may be diffusely noted along the musculature, joints, and is usually present over the sciatic notch in patients with complaints of sciatic nerve irritation. The sciatic notch is located in the lower buttock and is the point of origin of the sciatic nerve from the pelvis. Tension signs, such as the straight leg-raising maneuver, are another method of eliciting tenderness in the patient. These techniques involve stretching the affected nerve and recreating the symptomatic leg pain. In lumbar disc abnormalities, these generally include the femoral stretch test, which elicits pain along the femoral nerve, and the straight leg raise, which elicits pain along the course of the sciatic nerve.

Neurological deficits are the most specific indicator of nerve root compression. Neurological deficits include loss of a specific reflex, loss of sensation in a specific area correlating with a particular nerve, or loss of strength in a muscle or muscles conforming to a particular nerve.

Symptoms of radicular pain may be present, but generally are less severe than axial pain in patients undergoing anterior lumbar fusion. Patients typically have greater pain with activities such as sitting, bending, or lifting. Each of these activities tends to place the greatest load on the disc. In patients who demonstrate greater radicular pain than axial or referred pain, consideration should be given to performing a more minimal surgery such as decompression alone. Candidates for anterior lumbar fusion do not necessarily have positive tension signs, although frequently these maneuvers will produce severe lower back pain.

Since neural compression is not typically a feature of degenerative disc change it is uncommon for patients undergoing anterior lumbar fusion to have neurological deficits.

In contrast to more minimal procedures, anterior lumbar fusion is generally not considered until a patient has failed to respond to at least six months to one-year of non-operative treatment. Frequently, these patients have pursued more minimal surgery such as microdiscectomy and have had persistent complaints of severe back pain. Non-operative treatment preceding anterior lumbar fusion would include activity restrictions, physical therapy or chiropractic treatment, narcotic analgesics, non-steroidal anti-inflammatory medication, epidural and facet cortisone injections, and brace wear. One exception, which indicates a need for more urgent or emergent anterior lumbar fusion, would be the presence of a post-operative disc space infection unresponsive to antibiotics.

C. RADIOGRAPHIC ABNORMALITIES

Radiographic indications for anterior lumbar fusion would include advanced degenerative disc change or segmental instability. Disc deterioration is best identified on MRI. Decrease signal intensity, or blackening of the disc, is the most typical feature. Disc space narrowing, bone spur formation along the disc border, and signal intensity changes along the bone end plates consistent with loss of normal marrow and replacement are frequently seen. Ideally, patients undergoing anterior lumbar fusion should have focal abnormalities at one or two levels. Patients exhibiting abnormalities of multiple levels frequently respond poorly to surgical treatment. Presumably, this is due to failure of the fusion to address multiple pain generators or the pre-disposition of degenerative levels to become painful secondary to increased stress imposed by the fused segments.

Disc degeneration is a common finding on MRI in patients without complaints of back pain. As such, it cannot be assumed that disc degeneration is necessarily the source of a patients pain. Following the exclusion of other potential pain sources discography is recommended to ascertain whether the deteriorated disc is in fact painful. This procedure involves injections of dye into an abnormal disc and a normal disc. Injections into the normal disc should produce a normal die pattern and should not provoke any significant pain to the patient. In contrast, injections of dye into the degenerative disc should produce an abnormal pattern of dye and provoke significant pain similar to the patients symptoms. Patients demonstrating advanced degenerative change confined to one or two discs, with a positive discogram at the abnormal level, and a normal discogram at a normal control generally have a high likelihood of improvement or relief of their symptomatic back pain following anterior lumbar fusion.

II. SURGICAL TECHNIQUE

Anterior lumbar fusion has traditionally been performed through an open retroperitoneal or transabdominal approach. In the retroperitoneal approach an incision is made on the side of the abdomen and the spine is exposed in a plane posterior to the peritoneum. This results is less risk of scarring and injury to the bowel. In a transabdominal exposure the peritoneum is entered and the bowel separated to expose the lumbar spine.

More recently, we have performed the procedure in a laparoscopic fashion. This involves placing cameras within the abdomen, which is distended by air. The spine can be visualized on a television monitor and the procedure is carried out working through small portals or tubes placed through extremely small incisions.

Irrespective of the exposure, open procedures are carried out in a somewhat similar fashion. Following identification of the abnormal disc, by x-ray, the iliac artery and vein are mobilized and retracted away from the disc space to avoid injury. The ligaments over the disc are incised and the disc removed in its entirety. Cartilage along the surface of the bone end plates is removed. Decompression of the spinal canal can be performed as necessary through resection of the annulus, posterior longitudinal ligament, and removal of any disc material from the spinal canal.

Following decompression and preparation disc space fusion can be carried out in a number of manners. Typically, this involves insertion of bone graft or an implant into the disc space. There are several sources of bone graft available. Femoral rings taken from cadavers have been used extensively. This type of graft provides excellent structural stability but has been extremely slow to incorporate with development of a fusion. Tricortical iliac crest graft taken from the patient's pelvis incorporates more quickly but lacks the same strength and may be prone to collapse prior to fusion. Implants ranging in shape from cylindrical to cuboid are commonly used alternatives to bone. These implants are manufactured from titanium or more recently synthetic material such as PEEK, polyethyl ester ketone. These implants usually require the addition of bone, bone substitutes, or bone-stimulating hormones.

Laparoscopic techniques for lumbar fusion generally employ use of cages. The instrumentation utilized in preparation of the disc and insertion of the implants is amenable to the limitations imposed by laparoscopic technique. Cages are hollow threaded cylinders which are screwed into the disc space following preparation. The cage is filled with either cancellous bone or substitute. Fusion occurs to the adjacent vertebral endplate through openings along the surface of the cage.

In contrast to open procedures which allow greater visualization of the disc space, laparoscopic techniques require fluoroscopic guidance to direct and verify appropriate implant position.

The patient is positioned supine, on their back. A small incision is made in the Naval and a camera, laparoscope, is inserted. The head of the patient is lowered relative to the feet, Trendelenburg. This results in the bowel moving towards the head and out off the way. The peritoneum overlying the spine is identified and incised . The peritoneum is grasped and retracted by loops of suture. The iliac artery and vein are identified and retracted while the soft tissue over the disc is separated. Multiple small vessels are ligated. The center of the disk is marked and verified fluoroscopically .

A second incision, 1 in. in length, is made in the lower abdomen and a second portal inserted . A guide is inserted through this portal and entry holes are marked on the disk . Following enlargement of the holes with a drill , the disc space is distracted by insertion of progressively larger distraction plugs Once the disk has been distracted to an appropriate height a guide sleeve is inserted and the distractor plugs are removed. Under fluoroscopic guidance, a channel is reamed and tapped through the sleeve. Following preparation, cages are inserted into the channel bilaterally. The cage placement is verified by x-ray from both the front and side perspectives . Each cage is filled with bone. Multiple choices exist, including autograft, allograft, demineralized bone matrix, or synthetic bone substitutes. Bone may be augmented with hormones or bone marrow extracts.

This procedure may be repeated at one or more levels. The peritoneum is approximated with suture after all cages have been inserted. The muscle fascia of the two incisions is sutured after removal of the portals and instrumentation. The subcutaneous tissue and skin is closed.

On occasion, a more lengthy incision may be necessary. The most common reason for conversion to an open procedure from a laparoscopic exposure is intra-operative bleeding which either obscures visibility or that which cannot be safely managed using laparoscopic techniques. Occasionally, extensive scarring and adhesions may prevent a laparoscopic technique. Most often this problem is recognized preoperatively in patients reporting an extensive prior history of abdominal surgery.

III. POST-OPERATIVE COURSE

Patients are generally maintained at bedrest the day of surgery. They are typically advanced to ambulation on the day after surgery. Patients are usually advanced to a regular diet on a gradual basis and IV fluids are discontinued when they are able to accept liquids. It is not uncommon for patients to develop an ileus, or a decrease in bowel activity, for several days. This may delay progression of their diet. Antibiotics are given pre-operatively and for 24 hours post-operatively. If the patient is independent with ambulation, able to tolerate a regular diet, and afebrile and able to void, they are generally discharged 2-3 days following surgery. Patients undergoing laparoscopic surgery are generally discharged earlier than open procedures.

Patients are fitted with a lumbarsacral orthosis. This is a two-part hard plastic brace, which is secured by velcro straps. Patients are advised to remain in the brace except when lying flat in bed.

Patients are advised at the time of discharge to avoid activities such as bending, lifting, and vigorous twisting. They are instructed on body mechanics or techniques in sitting, standing, and transferring out of bed etc. Patients are typically prescribed pain medication to be taken by mouth as needed and occasionally anti-inflammatory medication for residual nerve root swelling and irritation.

Patients are generally advised to refrain from getting the incision wet for three days post-operatively. At that time they may shower. It is generally advisable to avoid submerging the incision in a tub or pool for at least one week.

Follow-up examinations are typically conducted at one week, one month, three months, 6 months and 1 year post-operatively.

At approximately 2-3 months post-operatively patients are referred for physical therapy and their brace discontinued. This includes a graduated course of lower extremity and lumbar flexibility, strengthening, and instructions on body mechanics and postural alignment. Patients are generally advised to increase their recreational and daily activities commensurate with their progress at physical therapy. Restrictions on bending, lifting are continued to some degree through 4-6 months post-operatively.

IV. OUTCOMES

A. Benefits

Appropriately selected patients, as previously described, can generally expect approximately an 80 likelihood of improvement, if not relief, of the majority of their back pain.

Over one hundred anterior lumbar fusions have been performed. Sixty-two have been performed as isolated anterior procedures. Of these 62 procedures, 31 were performed using allograft femoral rings, 14 using titanium Harmes cages, 13 using titanium BAK cages and 4 using autogenous iliac crest graft. Of the 31 patients using femoral rings, two were performed for pseudoarthrosis of a posterior fusion with the remainder performed for degenerative disc changes isolated to one or two levels. Of the remaining 29 primary fusions, 15 were performed for degenerative change alone with 10 of 15 successes (67%). Fourteen were performed for degenerative change following prior discectomy and yielded 13 of 14 successes (93%). The combined success rate is 79%. Of 14 patients undergoing fusion with Harmes cages, 4 were placed following corpectomy for fractures and supplemented with anterior lumbar plates. Two were performed at levels of pseudoarthrosis following prior posterior fusion. The remaining 8 primary anterior fusions yielded 6 of 8 successful outcomes (75%).

All 13 procedures performed using BAK cages have been performed as primary anterior lumbar procedures. Follow up has not exceeded one year in all patients but initial patient results indicate 11 of 13 patients have been relieved or noted significant reduction of back pain (85%).

B. COMPLICATIONS

Operative risks include infection, bleeding, neurological injury, graft failure or dislodgment, pseudoarthrosis, deep vein thrombosis, reflex sympathetic dystrophy, and retrograde ejaculation in males. Post-operative infection rates for all surgical procedures performed vary on a national basis between 1 and 2. We have experienced one infection following anterior lumbar discectomy fusion(1%),

Bleeding associated with anterior lumbar discectomy is usually minimal. Although the potential exists for enormous blood loss if one of thereat vessels anterior to the^isc space were injured, this event is fortunately rare. In our experience one vein tear occurred. This was repaired without difficulty. No transfusion was necessary.

Neurological injury is an unlikely operative complication. The exact incidence of permanent neurological injury is unknown although it is probably on the order of less than . 1 . Most frequently, post-operative neurological deficits were present pre-operatively. There have been no instances of neurological injury with anterior lumbar discectomy and fusion in our experience.

Pseudoarthrosis is the failure of the bone graft to fuse to the vertebra. This results in motion at the disc, which can produce pain. Pseudoarthrosis has been confirmed in four patients fused using femoral rings 87 (4 of 31). These results are higher than. generally reported in the literature and may include cases of fibrous union in which patients appear clinically improved as though fusion had occurred but in fact may have a failure of bone union. None of the 8 fusions with Harm cages have been noted to result in pseudoarthrosis. None of the BAK procedures has had adequate follow up to assure fusion or pseudarthrosis.

Graft failure or dislodgment is uncommon. In one patient a femoral ring was noted one month post-operatively to have fractured and partially extruded. This required revision of that level surgically. Deep vein thrombosis is the development of a blood clot in the leg, thigh or pelvis. This usually results in pain, swelling, and tenderness of the affected extremity. The greatest risk is that the clot might dislodge and travel to the lung where it might obstruct blood flow producing a potentially life threatening condition. One patient has been diagnosed post-operatively with an iliac vein thrombosis. The patient was treated uneventfully with anticoagulants.

Reflex sympathetic dystrophy is an uncommon complication secondary to anterior lumbar surgery. The Sympathetic chain of nerves lies along the anterior vertebral bodies and may be irritated or damaged in the course of disc removal or graft insertion. Stimulation of these nerves may cause dilatation of vessels in the leg resulting in increased blood flow, warmth and sometimes swelling of the leg. These findings are common after surgery and are usually limited to a slight difference in temperature between the legs. These symptoms typically resolve in a matter of days or weeks. In two patients more severe symptoms of pain and swelling persisted requiring further treatment in the form of injections of the sympathetic chain.

Retrograde ejaculation is a condition occurring among some of the men post-operatively. The condition results in semen being directed into the bladder during orgasim ratherfrom the penis. In our experience 3 men have reported the condition and in two the abnormality has resolved spontaneously with the third only a few weeks post-op at this time.