Michael F. Duffy, Jack E. Zigler
The diagnosis and treatment of symptomatic lumbar intervertebral disk degenera- tion 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 out- comes. 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, liga- ments, 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.1,2 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 interver- tebral disk, which is evidenced by the fact that MRI shows disk abnormalities in 76% of patients without chronic low back pain.3 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 disk- ography remains regionally controversial; however, it is the only provocative test that aids the practitioner in making a definitive diagnosis of diskogenic pain. Earlier human studies4 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 study5 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 con- cerns 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 function- ally disabling diseased intervertebral disks. Cloward6 first presented the technique of interbody fusion for diseased disks, in which removal of the painful disk was fol- lowed 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. Studies7,8 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 draw- back of this classic treatment is the loss of motion. The advent of total disk replace- ment (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 Charnley9 first intro- duced 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 dis- ease 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 Fernström10 (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%.
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
FIGURE 7-1 Radiograph depicting a Fern- ström ball within the L5-S1 disk space.
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 Ches- ter, 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) Investi- gational 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 funda- mental 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.
CASE PRESENTATION
A 38-year-old male professional athlete had a multiyear history of progressively worsening low back pain refractory to conservative treatment, including anti- inflammatory medications, muscle relaxants, physical therapy, and appropriate injections. His pain scale rating was 7 out of 10 and constant. The Oswestry Dis- ability Index score was 56%. The patient’s pain diagram portrayed 100% low back pain, without lower extremity complaints.
• PMH: Unremarkable
• PSH: Partial laminectomy and diskectomy at L4-5 performed 5 years earlier with complete relief of radicular symptoms.
TABLE 7-1 Fernström’s Results for the Percentage of Patients
with Back Pain after Diskectomy Alone Versus Diskectomy and Placement of an Arthroplasty Device
Patients Experiencing Back Pain (%)
Treatment Degenerative Disk Group Herniated Disk Group
Diskectomy and arthroplasty 40 12
Diskectomy alone 88 60
From Fernström U: Arthroplasty with intercorporal endoprosthesis in herniated disc and in painful disc, Acta Chir Scand Suppl 357:154–159, 1966.
FIGURE 7-2 Third generation of the origi- nal SB Charité Artificial Disc, which is in use today.
• 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 narrow- ing 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 nonopera- tive treatment.
A
C
B
FIGURE 7-3 Preoperative anteroposterior (A), lateral flexion (B), and lateral extension (C) radiographs.
SURGICAL OPTIONS
There are several surgical options for treating this patient. The common denomina- tor 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
FIGURE 7-4 Preoperative MRI sagittal image showing significant Modic changes at the L4-5 end plates.
FIGURE 7-5 Preoperative MRI axial image.
Note the integrity of the left facet joint.
fusion. Other nonfusion options include the use of motion-preserving devices such as a TDR or dynamic stabilization system.