Circumferential Fusion for Spondylolisthesis in the Lumbar Spine

Robert F. Heary, M.D., and Christopher M. Bono, M.D.

Disclosures

Neurosurg Focus. 2002;13(1) 

In This Article

Abstract and Introduction

There are many options for the surgical treatment of lumbar spondylolisthesis, including anterior and posterior techniques. Among the most versatile is a 360° fusion. In consideration of the added risk of morbidity of two procedures, circumferential fusion leads to the highest fusion rates. This is particularly useful for patients at high risk for pseudarthrosis, such as patients with diabetes, posttransplant recipients, and those in whom fusion procedures have failed. Likewise, a 360° fusion may also be useful in achieving fusion in biomechanically disadvantageous situations, such as at the L5-S1 level or with high-grade subluxation. The options for 360° fusion are many and are determined, among other factors, by surgical pathology and surgeon preference. Standard open techniques are still considered the gold standard, although newer less invasive methods of circumferential fusion are being used more frequently. The operating surgeon must have a thorough knowledge of all available maneuvers for critical and effective decision making.

Spondylolisthesis is a common radiographic finding in the lumbar spine. Defined as subluxation of one vertebra on the other, it occurs most frequently at the L4-5 and L5-S1 interspaces.[7,11,17,20,23] Although subluxation can result from various causes, the majority are either degenerative or isthmic types. Degenerative spondylolisthesis is thought to occur secondary to incompetence of a degenerated disc, which then places greater anteroposterior shear stresses on the eventually arthritic facet joints. With time, the complex fails, and the upper vertebra begins to migrate anteriorly onto the lower vertebra. Degenerative subluxation is most common at L4-5, although it may occur at any level. Isthmic spondylolisthesis is the product of spondylolysis. This is a presumed "stress fracture" within the pars interarticularis. Over time, the pars defect can become elongated, as it represents incompetence of the posterior elements. It is most common at the L-5 pars, allowing subluxation of the L-5 vertebra on the S-1 endplate. Again, this occurs only after the disc begins to fail under the increased shear stresses placed on it.

The majority of patients with spondylolisthesis are asymptomatic. It is often detected radiographically as an incidental finding. Unless a high-grade subluxation is recognized (Grade III or higher), asymptomatic patients are simply observed. A percentage of patients, however, develop an array of symptoms related to their subluxated vertebrae. Symptoms are usually related to axial back pain and/or the sequelae of neural compression.[17,30] Pain is thought to arise from a degenerated disc and facet joint complex. Nociceptive neural innervation of the annulus is thought to be a mechanism for pain transmission.[6] In addition, the subluxated vertebra can cause a forward shift of the weight-bearing axis. These alterations can lead to fatigue of the lumbar paraspinal muscles in an attempt to maintain sagittal balance.

Neurological symptoms are common with spondylolisthesis.[11,17,27,30] These can be related to a reduction in dimension of the overall spinal canal at the level of subluxation or compromise of the neural foramina. Thus, patients can present with exercise intolerance from neurogenic claudication and/or radicular complaints. It is not uncommon that patients present with a combination of the two, with radicular complaints worse in one leg than the other. Physical examination may demonstrate objective neurological findings, although this is not typical, because neural dysfunction is usually related to exercise.

With the exception of very high-grade subluxation, the initial treatment of spondylolisthesis is nonsurgical and includes a combination of pain medications (preferably non-narcotic) and physical therapy. Traditionally, there is an emphasis on flexion exercises and abdominal strengthening. For patients with claudication or radiculopathy, failure of these measures can be followed by selective nerve root or epidural steroid injections. These often give some symptomatic relief, although it is rarely long lasting. Surgical treatment is considered only after all nonsurgical measures have been exhausted.

Surgical treatment of spondylolisthesis typically consists of a fusion procedure with or without neural decompression.[21,23,24,30] Obviously, decompressive surgery is reserved for those with symptoms that are correlated with radiographic or advanced imaging evidence of neural impingement. Although laminectomy without fusion had been popular at one time, it is well recognized that this can lead to progressive subluxation and inferior clinical outcomes.[17,26] Fusion is performed to immobilize the subluxated segments. Arthrodesis can be accompanied by reduction of the vertebral sagittal alignment, although this might risk injury to the exiting nerve root.[32] Because of this, as well as the excellent clinical outcomes produced by in situ fusion, the benefits of reduction remain controversial. Regardless, numerous surgeons perform reduction maneuvers during fusion procedures to restore sagittal alignment.[8,23,32] These reduction maneuvers are facilitated by the use of instrumentation that most commonly includes posteriorly placed transpedicular screw constructs.

The application of posterior instrumentation for fusion of spondylolisthesis is another controversial topic. At present the gold standard for the surgical treatment of a single-level subluxation is noninstrumented posterolateral lumbar fusion.[17] Recent data, however, suggest higher fusion rates with the use of instrumentation, especially in long-term follow-up studies compared with noninstrumented procedures.[11] With fusion is the goal, in addition to clinical improvement, it would seem that the use of instrumentation would be advantageous.

Although posterior procedures are more commonly performed, fusion may be achieved by anterior techniques. Anterior lumbar interbody fusion is the most frequently performed method, with various materials, such as allograft, autograft, or biomechanical devices (such as cages) used for anterior column reconstruction.[2,20,27,28] Reports of performing ALIF alone for the treatment of lumbar spondylolisthesis are available, with some documenting good results;[20] however, it is generally recognized that the fusion rates are suboptimal, especially for more than single-level arthrodesis; and cage extrusion has been observed with stand-alone anterior constructs. These are especially common when using threaded cages, which probably do not provide sufficient torsional stability to the unstable olisthesed segment, without additional posterior stabilization.

When treating lumbar or lumbosacral spondylolisthesis, the ultimate goal is a solid osseous fusion. For the majority of cases, a posterior fusion, whether instrumented or noninstrumented, is probably adequate; however, these methods are limited by a very definite pseudarthrosis rate, which has ranged between 45 and 91%.[11,17] In patients who are at particular risk for nonunion, other methods of fusion should be contemplated. Circumferential fusion has resulted in the highest fusion rates in the lumbar spine, reaching as high as 100% in some series.[2,15,21,36,40] Patients at high risk for nonunion include smokers, diabetics, and immunocompromised individuals (those who have undergone organ transplantation).[13] It is well documented that these patients have a higher rate of nonunion than the general population; thus, it might be prudent to ensure the best possible chance for fusion from the initial procedure. Likely because of greater biomechanical tensile stresses placed across a posterior fusion mass, L5-S1 fusions are difficult to achieve by posterolateral methods alone. Although not always indicated, some patients undergoing a lumbosacral arthrodesis may be candidates for a circumferential procedure. Another high-risk situation is the failed posterior fusion. Again, these patients may be candidates for 360° fusions. Patients with high-grade subluxation should also be considered for circumferential arthrodesis. Notwithstanding the relative necessity of prophylactic fusion in these cases, posterior fusion alone would cause extremely high tensile stresses. It is also difficult to induce bridging bone in the relatively large distances between the posterior elements of the adjacent subluxated vertebrae.

Circumferential fusion can be performed in a variety of manners.[12,13,15,19,25] Traditional anterior-posterior fusion includes separate approaches for the interbody and posterior procedures. More recently, all posterior methods of 360° fusion, such as PLIF or TLIF have gained popularity.[4,16,22] Some authors consider these to be truly 270° procedures and fusion rates appear comparable with those in circumferential techniques.[36] Although extremely useful techniques, they are best performed in patients who have not undergone prior spinal procedures, because dissection through epidural scarring to gain access to the posterior disc space is risky. The anterior component of circumferential fusions can be performed via traditional open (retroperitoneal or transperitoneal), miniopen, or laparoscopic approaches. Likewise, the posterior component can be performed through standard open techniques or with newer percutaneous methods.

The appropriate use of circumferential fusion for the treatment of lumbar spondylolisthesis relies on a clear understanding of its indications, advantages and disadvantages, techniques and applications, and outcomes and complications. It is the purpose of this article to discuss these issues, with a particular focus on the latest available techniques for combined anterior-posterior fusion.

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