High-Grade Spondylolisthesis: Posterior Decompression and Spanning/Dowel Fibula
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CHAPTER Rick C. Sasso 66 James E. Lashley High-Grade Spondylolisthesis: Posterior Decompression and Spanning/Dowel Fibula [Au1] BACKGROUND age slip as well as degree of symptoms.20 To this day, these treat- ment pathways have remained relatively unchanged. For First described by Herbiniaux in 1782, spondylolisthesis is low-grade (Meyerding 1 and 2) slips, treatment consists of activ- defi ned as the slippage of one vertebra upon another. With ity modifi cation, bracing, physical therapy, and a return to nor- regard to the pediatric population, the L5-S1 articulation is the mal activity once symptoms subside. Surgical intervention is most common site of slippage. In children and adolescents, the reserved for those patients in whom symptoms are not relieved cause of listhesis is dysplastic changes of the posterior elements by nonoperative means. In contrast, for patients presenting of L5 and superior articular facets of S1 and/or isthmic defects with high-grade slips (Meyerding 3, 4, and 5); surgical interven- of the posterior elements of L5 (usually the pars interarticu- tion is recommended regardless of the magnitude or duration laris). The overall incidence of spondylolysis in the American of symptoms. This is true for children due to the high potential population is approximately 6%, with a male to female ratio of for these high-grade slips to progress before skeletal maturity; 2:1. It has been found that a predisposition toward spondyloly- however, treatment recommendations for adults with a high- sis is higher in the Caucasian population than in the African- grade slip are less clear. American population and may be found in up to 50% of the Several surgical options currently exist for the treatment of 5–7 Eskimo populations of North America.4,18 high-grade isthmic spondylolisthesis. The one common ele- From an etiologic standpoint, spondylolisthesis is a multifacto- ment to all surgical interventions remains arthrodesis: in situ rial disease with heredity and environmental factors being most posterolateral fusion, posterolateral fusion and decompression, important.4 Recent studies conclusively demonstrate that isthmic posterolateral instrumented fusion, and posterolateral fusion spondylolisthesis is not present at birth. Although spondylolysis is combined with interbody fusion. Traditional techniques of pos- more commonly found in males, the propensity for slip progres- terolateral fusion, with or without decompression or instru- sion appears to be higher in females. The etiology for these gen- mentation, have been utilized in the treatment of high-grade 10 der differences is unknown. Spondylolysis is more common among slips, but only with moderate success. The unfavorable biome- those engaged in activities involving hyperextension of the lower chanical environment places the posterior graft bed under ten- spine such as gymnastics, football (linemen), wrestling, etc. sion; this, in turn, leads to increased potential for nonunion, Meyerding’s defi nition of degree of slippage, Wiltse’s etiologic postoperative progression of slip angle, and translation. Hanson classifi cation, and Marchetti’s and Bartolozzi’s descriptive classifi - et al have shown that the addition of an interbody fusion utiliz- cation to defi ne surgical parameters are the most commonly ing a spanning fi bula dowel not only leads to increased fusion 5 used classifi cation schemes to categorize spondylolisthesis.9,19–22 rates but also decreases postoperative slip progression. Along with these classifi cations, various other risk factors for slip Unfortunately, the abnormal morphology of the lumbosacral progression include slip angle of greater than 55°, female gen- junction prevents the use of traditional trapezoidal anterior der, early age of diagnosis, and degree of slip at presentation and posterior interbody grafts. To overcome this abnormal (Ͼ50% slip).20 From these radiographic parameters and classifi - offset of the L5 and S1 end plates, a technique utilizing trans- cation schemes, a useful algorithm to direct nonsurgical and vertebral interbody fi bular dowel grafts has met with great 5,17 surgical management of patients with spondylolisthesis has been success. developed. The advantage of this technique is the ability to achieve a circumferential construct to maximize the fusion rate without the necessity of a complete translational reduction of L5 on S1, TREATMENT which is required for traditional block-type interbody devices. The most compelling reason not to attempt a complete transla- More than 30 years ago, Wiltse and Jackson defi ned treatment tional reduction is the extremely high incidence of L5 nerve algorithms for pediatric spondylolisthesis based upon percent- root defi cit. Cadaveric studies demonstrate a relatively low 646 LLWBK836_Ch66_p646-659.inddWBK836_Ch66_p646-659.indd 664646 55/19/11/19/11 112:07:582:07:58 PPMM Chapter 66 • High-Grade Spondylolisthesis: Posterior Decompression and Spanning/Dowel Fibula647 planning is required. This includes planning for radiographic Surgical Technique for guidance of instruments and implants, neurophysiologic moni- High-Grade Isthmic toring, determination of anterior/posterior or posterior-only Spondylolisthesis with TABLE 66.1 approach as well as levels of instrumentation, and use of bone Associated Complications, graft extenders to enhance fusion. * Fusion Rate, and Complexity Placement of instrumentation is a technically demanding skill that requires intraoperative imaging to effect perfect place- L5 Nerve Fusion Surgical ment of guidewires and screws. Image-guided navigation and Technique Injury Rate Complexity real-time fl uoroscopy are two methods used to visualize place- Partial reduction with Rare High Low ment of instrumentation. At our institution, we utilize image- fi bular strut graft and guided navigation for placement of pedicle screws, as well as posterior pedicle choosing the direction of and determining the depth for guide- screws wire placement. After the right-sided buttock is sterilely Vertebrectomy (Gaines More High Highest prepped, a reference antenna is percutaneously placed into the procedure) common right posterior–superior iliac spine and preoperative scans are Complete reduction of More High High acquired in the operating room (Fig. 66.1). This provides the translational common ability to simultaneously visualize AP, lateral, and axial views in [Au2] component real time during the procedure and visualize our instrumenta- tion in a virtual fashion on the computer screen (Fig. 66.2). * Posterior instrumented rare lower. Fusion in situ lowest. Pedicle screw length, reaming depth, and appropriate guide- wire placement are all readily determined. In contrast to real- time fl uoroscopy, the surgeon, assistant, and operative fi eld are not crowded by two separate fl uoroscopic machines; radiation strain on the L5 nerve root with the fi rst 25% translational exposure to personnel is dramatically reduced; and less time is reduction of L5; however, this nerve root stretch increases 11 spent by avoiding the numerous single fl uoroscopic images exponentially with the fi nal 50% reduction. This technique with each step of instrumentation placement. allows for the achievement of a partial reduction of the slip. Neurophysiologic monitoring is an extremely useful tool to The most important aspect of this deformity correction is the help avoid catastrophic intraoperative nerve damage by surgi- sagittal angle. The lumbosacral kyphosis reduction is easily cal instruments (i.e., drills, taps, and probes) and instrumenta- achieved with positioning on the operating table, and partial tion (e.g., pedicle screws). Continuous electromyogram (EMG) [Au3] reduction of the translational deformity also frequently occurs monitoring helps prevent nerve root damage during pedicle with this procedure. It is important, however, not to attempt a screw placement, interbody cannulation, and fi bular allograft forceful reduction of the translation to limit the chance of neu- placement. During the posterior-only approach, preparation of ral defi cit (Table 66.1). the channel for the fi bular allograft requires retraction of the S1 nerve root laterally and the dura medially to provide enough space for passage of the reamers. Continuous EMG monitoring PREOPERATIVE PLANNING is also utilized during preparation and placement of pedicle screws. In addition, each pedicle screw is independently tested In order to increase the likelihood of successful fusion as well with direct electrical stimulation via a direct monopolar nerve as prevent intraoperative nerve damage, careful preoperative stimulator to assess pedicle wall integrity. Figure 66.1. Intraoperative fl uoro- navigation scan outlining sagittal, coro- nal, and axial views of a slip. LLWBK836_Ch66_p646-659.inddWBK836_Ch66_p646-659.indd 664747 55/19/11/19/11 112:07:582:07:58 PPMM 648 Section VI • Spondylolisthesis A B Figure 66.2. Intraoperative fl uoronavigation scan with projected trajectory of transsacral transvertebral fi bular dowel graft through S1 into L5 body. (A) Intraop- erative picture with the navigation probe demonstrating the projected trajectory. (B) Coronal view of the intraop- erative image navigation with the probe across the L5-S1 disc into the L5 vertebral body. (C) Sagittal view of the intraoperative image navigation showing the probe extending from the sacrum across the high-grade spon- C dylolisthesis docking into the L5 vertebral body. Determination of the optimal surgical approach is a deci- tion. Classically, it has been taught that a high-grade spon-