Preoperatively, there were 23 patients working and 10 were not working because of back pain, and 7 were retired. Postoperatively, all 23 patients who were working returned to work, 1 retired, and 8 of 10 who were not working because of back pain returned to light work postoperatively. All of the patients who were not working preoperatively remained so postoperatively.
There were no statistically significant differences in fusion rates between smokers and nonsmokers. Likewise, there were no statistically significant differences in clinical outcome between worker's compensation and non–worker's compensation patients in this series, although there were only five smokers and six worker's compensation patients in the series.
Complications other than pseudoarthrosis (4/40) included two dural tears repaired intraoperatively, one transient neurapraxia, and one late infection (>2 years) necessitating removal of pedicle instrumentation. The fusion was noted to be solid during hardware removal in that patient. There was no evidence of clinical arachnoiditis or cage-related complications in any of our patients.
Since the first reports of spinal arthrodesis 88 years ago, a variety of techniques for fusion of the lumbar spine have been developed for the management of a wide range of conditions (7,8). The rates of spinal fusion with bone graft alone have ranged from 46% to 90%(9–12,27). Because of difficulty in achieving fusion and maintaining spinal alignment and position, spinal instrumentation has become an important and popular adjunct to bone grafting in lumbar arthrodesis surgery, further increasing the fusion rates (80–90%) (13).
More recently, interbody fusion techniques have also shown high fusion rates with distinct advantages (14–17,26). Some of the advantages include immediate anterior column load sharing, a large surface area for fusion, bone graft subjected to compressive loads that is advantageous in achieving fusion, and the ability to restore normal sagittal contour while indirectly decompressing the neuroforamen (14). Interbody fusion techniques also appear to be the most effective treatment of discogenic back pain that is unresponsive to conservative care (18,19). Weatherly et al. reported on five patients during a 10-year period who had “solid” posterolateral fusions but still had positive discography under the fusion and had their back pain relieved by anterior interbody fusions (19). All five patients had positive discograms and had pain relief after anterior interbody fusion. Recently, Derby et al. noted that patients with “highly sensitive discs” as determined by pressure-controlled discography achieved significantly better long-term outcomes with combined anterior/posterior fusion than with intertransverse fusion alone (18).
Interbody fusion can be achieved through either an anterior, posterior, or combined approach. Proponents of the anterior approach cite shorter hospital stays and the prevention of “fusion disease,” which is thought to occur secondary to paraspinal muscle dissection during posterior exposure for fusion (20,21). High fusion rates and patient satisfaction have been reported with this approach (22). However, complications do occur related to improper cage placement and exposure (injury to iliac vessels, retrograde ejaculation, etc.). The efficacy of threaded cage devices as “stand alone” implants for treatment of the degenerative lumbar spine at the present time are probably not indicated for other than the “collapsed disc”(21).
Posterior interbody techniques allow the surgeon to simultaneously address all of the pathological lesions through a single approach. Shorter incisions and care in muscle stripping have resulted in less soft-tissue dissection. When combined with pedicle screw fixation, anterior and posterior column stabilization can be achieved. The addition of an interbody fusion to a posterolateral fusion provides a 360° circumferential fusion bed and may be associated with improved fusion rates, especially in patients with other medical comorbidities (i.e., diabetes, obesity, and nicotine abuse) who are at greater risk of pseudoarthrosis (13,23,24). Biomechanical studies of posterior lumbar interbody fusion without additional posterior instrumentation have suggested that significant destabilization of the fused segment may occur (23). Significant bilateral bony and ligamentous removal is often required to allow accurate placement of properly sized implants, and it is not possible to provide segmental lordosis unless posterior instrumentation is added. Perhaps the greatest concern with a standard PLIF is the amount of neural retraction needed, potentially leading to nerve root injury, dural laceration, and epidural fibrosis. Cauda equina injuries occurred in 19% of patients in one series with permanent nerve dysfunction in three patients (25). Ray noted 13 dural tears and a 10% incidence of transient foot weakness in his follow-up study of 236 patients treated with posteriorly inserted threaded cage device (16).
The transforaminal unilateral posterior lumbar interbody fusion was developed to address some of these problems. Advantages over the standard PLIF include the ability to provide bilateral anterior column support through a single posterolateral approach of the disc space. Because of the transforaminal approach, this technique preserves the anterior and most of the posterior longitudinal ligamentous complex, which provides a tension band for compression of the graft and prevents retropulsion of the graft. It avoids excessive soft tissue dissection, which may help prevent scarring and instability of adjacent segments, as well as injury to the exiting nerve root. Epidural bleeding is less of a problem than with the standard bilateral PLIF because of the unilateral transforaminal approach, and with experience, proper cage placement within the disc space is consistently achieved.
The TLIF is indicated for anterior column deficiency with chronic mechanical pain related to degenerative disc disease, recurrent disc herniation, and/or spondylolisthesis. Segmental kyphosis related to disc narrowing can be restored to a relatively normal lordotic contour, theoretically decreasing pathologic forces on adjacent motion segments, which may be a factor leading to adjacent segment degeneration or “transitional syndrome.” Grade II or III spondylolisthesis can also be reduced with this technique without the need for anterior surgery. Theoretically, there should be a higher rate of arthrodesis with the TLIF because the anterior graft is loaded in compression. Patients with multiple comorbidities potentially affecting successful arthrodesis (obesity, smoking, diabetes, previous failed fusion) are also candidates for the TLIF because it provides a circumferential fusion through a posterior-only approach. The TLIF procedure can also be used to decrease pseudoarthrosis at the lumbosacral junction in cases when long fusion to the sacrum is required such as in de novo degenerative scoliosis, where traditionally a combined anterior–posterior fusion would be required.
Our radiographic fusion rate of 90% and objective clinical excellent/good rate of 85% compare favorably with previous reports using other fusion techniques. This may be partly because of an overall favorable patient population. The majority of our patients were not heavy smokers nor were they seeking workers' compensation disability at the time of surgery. However, our results partly underscore the importance of proper patient selection when considering surgery to treat degenerative diseases of the lumbar spine.
The point system used in our questionnaire has not been entirely validated. However, using the same format in our pre- and postoperative questionnaires based on the Oswestry outcome instrument maintained consistency when comparing preoperative disability to 2-year follow-up clinical outcome. We believe that the assessment of pain and the ability to perform ADLs at latest follow-up enabled us to determine clinical success in our patient population and is consistent with the parameters used to determine clinical outcomes in previous studies.
Our study is not a comparative study. Our outcomes can be compared with similar studies in the literature for other fusion techniques, but no control group was included in our study. Our goal was merely to present our early results with this procedure and to offer it as a reasonable alternative for appropriately selected patients.
The TLIF can be easily mastered, but a learning curve exists. We have experienced no difficulties with implant failure related to the use of pedicle instrumentation as a means of distraction. The exiting nerve root must be visualized throughout the procedure. Meticulous attention to disc removal is essential. This allows the largest surface area possible for fusion and aids in proper cage placement. We have found that incomplete removal of disc material just ventral to the posterior annulus can compromise cage placement. Because a unilateral approach is used, the surgeon is relying on indirect visualization and tactile feedback when working across the disc space. Specialized instruments greatly facilitate disc removal during this portion of the case. We do not recommend this procedure for patients with severe osteopenia (bone mineral density <60% predicted). Other contraindications include bilateral epidural fibrosis pseudoarthrosis or a fusion of more than two levels.
The transforaminal posterior lumbar interbody fusion is a safe and reproducible technique to provide bilateral anterior and posterior column support through a unilateral posterior approach. The ideal patient for this procedure is one with long-standing mechanical back pain with or without a significant radicular component unresponsive to aggressive nonoperative treatment with radiographic evidence of a deficient anterior column. A sound biomechanical construct is achieved with a large surface area for achieving a successful fusion. This technique offers the additional advantage of providing for improved segmental lordosis and reduction of isthmic or degenerative spondylolisthesis. High fusion rates with good clinical outcomes can be achieved with few complications using this technique. Proper patient selection continues to be the most important factor in good clinical outcome with this procedure as well as others.
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Keywords:© 2002 Lippincott Williams & Wilkins, Inc.
Degenerative disease of the spine; Spondylolisthesis; Posterior lumbar interbody fusion; Transforaminal approach