The diagnosis and treatment of symptomatic lumbar intervertebral disk degeneration remains controversial in the medical literature. Although the pathoanatomy of the diseased intervertebral disk has been understood for quite a while, changes in clinical treatment have evolved slowly, and traditional treatment options, although numerous, have failed to provide a clear-cut gold standard with reproducible outcomes. The successful treatment of diskogenic back pain requires a systematic approach to diagnosis as well as a thorough understanding of the pain generator and the physiologic effects of various treatments.
Chronic low back pain has multiple possible causes. The spine is a dynamic structure, with several potential pain generators, including the facet joints, ligaments, muscles, and intervertebral disks. Because there is no single clinical test or physical examination finding to isolate the source of pain, the definitive pain generator remains unidentified in a significant proportion of patients. Furthermore, disk abnormalities are often accompanied by other painful spinal conditions, which makes diagnosis and treatment even more challenging. For diskogenic back pain to be primarily diagnosed, all other potential pain generators must be excluded based on imaging and failure of conservative treatments such as rest, medication, epidural steroids, and/or facet injections when indicated.
The concept that pain could arise from an intervertebral disk was slow to gain acceptance. Early thought was that nerve fibers did not penetrate the outer annulus. However, as scientific methods evolved, studies began to show that nerve fibers actually did penetrate into the disk and that ingrowth was potentially substantial. These findings led to the postulate that diskogenic back pain might be a result of sensitization of these nerve fibers by nociceptive substances. Magnetic resonance imaging (MRI) has failed to definitively identify a symptomatic diseased intervertebral disk, which is evidenced by the fact that MRI shows disk abnormalities in 76% of patients without chronic low back pain. This finding supports the need for provocative testing such as diskography to differentiate a diseased symptomatic disk from a degenerated, but asymptomatic, one. No clinical test is perfect, and diskography remains regionally controversial; however, it is the only provocative test that aids the practitioner in making a definitive diagnosis of diskogenic pain. Earlier human studies had shown that after long-term (10-year) follow-up no changes were found in disks that had undergone diskography, but a more recent 10-year matched cohort study has suggested that diskography of a control disk may be related to accelerated disk degeneration. The possibility of psychological confounders in this study may detract from the magnitude of this conclusion, yet it has raised new concerns about using a normal adjacent level as a control level in diskography.
Over the past two decades many options have been developed to treat painful disk degeneration, and varying clinical results have been reported. Inconsistencies in patient selection, study design, and methods of treatment have only added more uncertainty in this evolving field. Fusion has become a mainstay in treating functionally disabling diseased intervertebral disks. Cloward first presented the technique of interbody fusion for diseased disks, in which removal of the painful disk was followed by fusion of the pain-generating segment. Interbody fusion has traditionally been done through an anterior or a posterior approach. With the anterior approach, there is greater access to the pain-generating disk and a more complete diskectomy is possible, but the potential for intraabdominal consequences such as vascular injury and sympathetic nerve injury (retrograde ejaculation in males) has deterred many surgeons and patients. The posterior approach is also not without its potential downsides—approach-related muscular damage, injury to nerve structures, and a less complete diskectomy. Studies have shown that regardless of the approach used for fusion, well-selected patients with an identifiable diagnosis have similar fusion rates and clinical outcomes. The common theme of these various fusion techniques has been to rid the spine of the pain generator, create a biomechanically rigid environment, and promote fusion across a motion segment. A significant drawback of this classic treatment is the loss of motion. The advent of total disk replacement (TDR) offered a new alternative that aims to restore and maintain motion and function of the diseased segment. With this new surgical option comes increased scrutiny, just as with all advances in surgery. When Dr. John Charnley first introduced the concept of joint replacement in 1961, fellow surgeons were skeptical of the advancement and were slow to adapt. Now, 50 years later, total hip arthroplasty is recognized as one of the most significant advancements in degenerative joint disease and is widely accepted and performed across the globe. Again, adoption of this technology was slow and not without significant criticism.
The history of disk arthroplasty began in the 1950s with insertion of metal spheres into the disk space after diskectomy by Fernström ( Figure 7-1 ). He reported his results in patients with herniated or degenerative disks treated with diskectomy and insertion of the sphere compared with 100 control patients who underwent diskectomy alone. His findings, although not statistically sound, showed that a substantially smaller number of patients reported back pain after the arthroplasty procedure than after the diskectomy alone ( Table 7-1 ). His complication rate was reported as 1.4%.
|Patients Experiencing Back Pain (%)|
|Treatment||Degenerative Disk Group||Herniated Disk Group|
|Diskectomy and arthroplasty||40||12|
The lumbar disk prosthesis continued to evolve during the 1970s as a nuclear implant, going from a metal sphere to a silicone rubber prosthesis to a polyurethane injectant. It was in 1984 that the modern lumbar disk arthroplasty implant began to be developed. Büttner-Janz and Schellnack designed a modular three-piece TDR device known as the SB Charité, and it was implanted in September 1984 at the Charité Hospital in Germany. The disk replacement underwent revision, but the third design of the Charité Artificial Disc (DePuy Spine, Raynham, Mass.) has been in worldwide use since 1987 ( Figure 7-2 ). The ProDisc-L (Synthes Spine, West Chester, Pa.) was developed in France and first implanted by Thierry Marnay in March 1990. The Charité Artificial Disc was the first TDR device implanted in the United States and was used as part of a U.S. Food and Drug Administration (FDA) Investigational Device Exemption (IDE) study protocol in March 2000 at the Texas Back Institute; the first ProDisc-L used in the United States was implanted in October 2001 at the same institute. The Charité and the ProDisc-L are currently the only two FDA-approved devices in the United States for lumbar disk arthroplasty.
This chapter presents a case example of a patient with degenerative disk disease and discusses several different surgical treatment options. Both fusion and motion-preserving devices are considered for treatment. A detailed description of the fundamental technique and tips for the preferred treatment for this patient are provided. Based on discussion of the best evidence, several surgical options are considered so that the best surgical treatment choice for this particular case can be formulated and executed.
A 38-year-old male professional athlete had a multiyear history of progressively worsening low back pain refractory to conservative treatment, including antiinflammatory medications, muscle relaxants, physical therapy, and appropriate injections. His pain scale rating was 7 out of 10 and constant. The Oswestry Disability Index score was 56%. The patient’s pain diagram portrayed 100% low back pain, without lower extremity complaints.
PSH: Partial laminectomy and diskectomy at L4-5 performed 5 years earlier with complete relief of radicular symptoms.
Exam: The patient had significant muscle spasms with lumbar tenderness and decreased range of motion (ROM) in flexion. On manual motor testing, he had full muscle strength in the lower extremities and a negative result on the straight leg raise.
Imaging: Plain radiographs ( Figure 7-3 ) showed significant disk space narrowing at the L4-5 level without instability. Sagittal and axial MRI scans ( Figures 7-4 and 7-5 ) revealed severe spondylosis and degeneration at the L4-5 level, with Modic changes within the end plates. The integrity of the left L4-5 facet joint was maintained after the initial laminectomy and diskectomy performed 5 years earlier. The diagnosis was postlaminectomy degenerative disk disease with functionally disabling mechanical low back pain, refractory to nonoperative treatment.
There are several surgical options for treating this patient. The common denominator of each option is to remove the pain generator—the diseased intervertebral disk. As for fusion options, the L4-5 disk could be addressed from an anterior approach (anterior lumbar interbody fusion), a direct lateral approach (far lateral interbody fusion), a posterolateral approach (transforaminal lumbar interbody fusion), or a posterior-only approach (posterior lumbar interbody fusion), all with the goal of achieving an interbody fusion. Pedicle screw instrumentation (or a side plate and screws in the case of the far lateral approach) with grafting material can be used in conjunction with any of these options to aid in obtaining posterolateral biologic fusion. Other nonfusion options include the use of motion-preserving devices such as a TDR or dynamic stabilization system.
Anterior Lumbar Diskectomy and Interbody Fusion
Anterior lumbar diskectomy and interbody fusion is the most attractive option for the aforementioned case. The anterior approach allows for a more complete diskectomy than a posterior approach. Complete diskectomy has been shown to lead to a better ultimate fusion rate than a more partial, “reamed channel” diskectomy. After the pain generator is addressed with a complete diskectomy, reconstruction with an anterior lumbar interbody fusion (ALIF) construct will restore disk height and indirectly distract the foramen. The anterior fusion can be used as a standalone construct in the properly selected patient or augmented with posterior instrumentation ( Figure 7-6 ). For ALIF, there are many devices available, some with FDA approval as standalone devices. Newer polyetheretherketone (PEEK) devices are available as well, some with fixation techniques and 510k approval for standalone ALIF. The addition of posterior instrumentation increases biomechanical stability and reduces motion at the operative level, but clinical necessity and effect on fusion are still open to debate. Whereas autograft was traditionally used within the cage, the advent of bone morphogenetic proteins (BMPs) has accelerated fusion time and rates in ALIF and is a preferred adjuvant for anterior fusions. Many patients who have a low body mass index and no instability and who are adherent to prescribed medical regimens may be candidates for implantation of anterior standalone fusion devices with adjuvant BMP. In most other patients typical practice is to augment the anterior construct with percutaneous pedicle screw systems and posterolateral grafting using local bone and demineralized bone matrix. An anterior approach should be considered cautiously in patients with active disk space or systemic infection, significant vascular disease, or osteoporosis. The decision to use an anterior approach in most cases is individualized and is based on the experience and comfort level of the access surgeon and spine surgeon.
Participation of an experienced access surgeon is vital to accomplishing efficient and successful anterior lumbar surgery, while minimizing potential serious vascular complications.
Absolute contraindications for an anterior approach are significantly calcified aorta or prior vascular reconstructive surgery. Relative contraindications are morbid obesity, previous intraabdominal or retroperitoneal surgery, history of severe pelvic inflammatory disease, and previous anterior spinal surgery.
Far Lateral or Trans-Psoas Approach
The far lateral or trans-psoas approach is another fusion option at the L4-5 and more cephalad levels ( Figure 7-7 ). This recently popularized approach is attractive because it allows anterior access to the disk space without the need for an anterior access surgeon. Patient positioning is vital to the success and ease of the operation, and at the L4-5 level this is especially true due to the iliac crest overlap. Preoperative planning is key in determining if the crest is too high riding in relation to the L4-5 disk space. The dissection is directly lateral, centered over the disk space. After the external and internal oblique muscle layers are pierced through, the retroperitoneal dissection is completed bluntly down to the lateral border of the psoas muscle ( Figure 7-8 ). Specialized dilators and retractors are then used to lessen the chance of neurologic injury as the approach extends through the psoas down to the disk space. After standard diskectomy and placement of the interbody lateral cage, use of a lateral plate or posterior pedicle screw construct is advisable; however, clinical and biomechanical literature evaluating these constructs is lacking. From an outcomes standpoint, the only direct lateral fusion study available is a short-term case series of patients undergoing lateral interbody fusion for degenerative scoliosis. Knight and co-workers presented perioperative data indicating that the procedure has an acceptable complication rate, comparable to that in historical controls. The incidence of major adverse events approached 9% and significant nerve irritation occurred in 3.4%. Recent cadaveric evidence has shown that use of this technique at L4-5 may result in a significant risk of iatrogenic injury to the lumbosacral plexus. This anatomic study found that the lumbosacral plexus migrates anteriorly at each successive caudal disk space from L1 to L5, with L4-5 having the least amount of “safe zone” for a posteriorly positioned dilator or retractor. Regev and associates also showed that the overlap of neural structures and retroperitoneal vascular structures increased from L1-2 to L4-5, with an 87% overlap at L4-5 ( Tips from the Masters 7-2 ). This creates a very small safe operative window (as small as 13% of the disk space) for the trans-psoas approach at the L4-5 level.
The direct lateral approach is more difficult and carries a higher risk of neurovascular complications at the L4-5 level than at more cephalad levels.
Posterior Fusion (Transforaminal or Posterior Lumbar Interbody Fusion)
Posterior fusion, either transforaminal lumbar interbody fusion (TLIF) or posterior lumbar interbody fusion (PLIF), with or without interbody fixation ( Figure 7-9 ), is also an option for the patient described in the Case Presentation. These procedures are attractive, particularly in cases in which an anterior approach is contraindicated. The downside of using a PLIF approach is the need to enter the spinal canal and retract the nerve roots and the thecal sac. The TLIF approach avoids the need for significant retraction on the thecal sac, but places the exiting nerve root in danger. Both posterior approaches obviate the need for an anterior access surgeon and also avoid the potential risks of vascular injury associated with the anterior approach. Reported rates of postoperative neuralgia after posterior interbody fusion are near 7% but are much lower in transforaminal approaches.
Total Disk Replacement
The final surgical option for the particular case described earlier is motion preservation intervention—either TDR or use of a pedicle-based dynamic stabilization device. Currently available arthroplasty implants require an anterior approach, and their use is restricted by the contraindications for anterior lumbar surgery (see earlier) as well as those specific for TDR ( Box 7-1 ).
Active systemic infection or infection localized to the site of implantation
Osteopenia or osteoporosis defined as dual energy x-ray absorptiometry (DEXA)–measured bone density T-score of less than –1.0
Bony lumbar spinal stenosis
Allergy or sensitivity to implant materials (cobalt, chromium, molybdenum, polyethylene, titanium)
Isolated radicular compression syndromes, especially due to disk herniation
Involved vertebral end plate dimensionally smaller that 34.5 mm in the medial-lateral and/or 27 mm in the anterior-posterior direction
Clinically compromised vertebral bodies at affected level due to current or past trauma
Lytic spondylolisthesis or degenerative spondylolisthesis higher than Grade 1
Regarding posterior dynamic stabilizing devices, although multiple systems are commercially available, none of them has gained FDA approval for nonfusion stabilization of a degenerative motion segment. Although multiple biomechanical studies have supported the philosophy behind dynamic stabilization, there are no clinical studies indicating that it has a favorable effect on degenerative disk disease. In fact, the only clinical study to date examining the use of these systems in degenerative disk disease showed that the dynamic stabilization devices were associated with high rates of failure and low rates of clinical success within a 2-year follow-up period.
The patient underwent TDR at the L4-5 level without complications through a mini–open retroperitoneal approach ( Figure 7-10 ). At 5 years of follow-up, the patient was free of back pain (visual analog scale [VAS] pain rating and Oswestry Disability Index score were at normal levels). He required no pain medication and was able to return to professional athletics.