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Pseudarthrosis
Introduction
Spinal fusions are one of the most common spine surgeries performed today. The number of spinal fusion surgeries performed has significantly increased over the past 2 decades. From 1998 to 2008, the rates of spinal fusion surgery have increased by 137%. Although there have been significant improvements in spine surgery over the years, complications still exist. One prevalent complication is pseudarthrosis, which is the failure of an attempted fusion of the spine. Pseudarthrosis can be a significant problem that may be asymptomatic or lead to pain and disability and eventually the need for revision surgery. This chapter reviews prevention, evaluation, and management of pseudarthrosis of the cervical and lumbar spine.
Risk Factors
Fusion surgery is based on bony segments of the spine growing together. The biologic and biomechanical consideration of fusion surgery must be thoroughly understood to prevent pseudarthrosis. Three fundamental requirements are needed for bony fusion: a sufficient amount of osteogenic cells, an osteoconductive matrix that can act as a scaffold for new bone to form, and osteoinductive signals that promote bone formation. Along with that, it is imperative to have adequate blood supply to the fusion bed. Proper biomechanical stability also aids in limiting micromotion and strain to allow for bony fusion.
When there is a failure of fusion, or pseudarthrosis, it is due to an inadequacy of one or more of the requirements just listed. Patient-related factors and surgical technique play an important role as well. Thus, it is imperative to optimize all of those aspects to promote successful bony fusion.
Vitamin D deficiency has been linked to longer time to fusion with higher rates of nonunion. Prevalence of vitamin D deficiency in patients undergoing spinal fusion is higher than the general population. Preoperative analysis of vitamin D levels with appropriate treatment may aid in successful fusion.
Postoperative use of nonsteroidal anti-inflammatory drugs and steroids has been linked to increased pseudarthrosis rates. Nonsteroidal antiinflammatory drugs inhibit osteogenic activity and, in turn, decrease fusion rates. Cyclooxygenase-2 inhibitors, such as celecoxib, have not caused a statistically significant increase in pseudarthrosis rates.
Smoking and use of nicotine products have been shown to significantly increase pseudarthrosis rates in both cervical and lumbar spinal fusions. Brown et al. in 1986 reported fusion rates in smokers versus nonsmokers after undergoing a two-level lumbar laminectomy and posterolateral fusion. All fusions were performed in situ without hardware or interbody devices. Nonsmokers had a pseudarthrosis rate of 8%, while smokers had a pseudarthrosis rate of 40%. Several other studies since then have validated the claim that smoking has a significant inhibitory effect on spinal fusions. A recent study by Bydon et al. analyzed the fusion rates of smokers versus nonsmokers in single-level and two-level instrumented posterolateral lumbar fusions and noted no difference in single-level fusion rates between smokers and nonsmokers. However, two-level fusions showed a significantly higher pseudarthrosis rate in smokers versus nonsmokers (29.17% vs. 10.92%, respectively). Glassman et al. analyzed patients who had undergone single-level or two-level instrumented posterolateral lumbar fusion using iliac crest autograft to analyze the fusion rates of smokers versus nonsmokers versus previous smokers who quit. The pseudarthrosis rate in smokers was almost double that of nonsmokers (26.5% vs. 14.2%, respectively). Previous smokers who quit postoperatively were noted to have a pseudarthrosis rate of 17.1%, trending toward the rate of the nonsmoking group. Hilibrand et al. evaluated smokers and nonsmokers who had undergone multilevel anterior cervical discectomy and fusion and noted solid bony fusions at all sites at a rate of 76% in nonsmokers and only 50% in smokers. Beyond smoking, any use of nicotine products has been suggested to increase pseudarthrosis rates in rabbit models.
Spinal Instrumentation and Its Effect on Fusion
Instrumentation of the spine has evolved significantly as we learn more about the biology and biomechanics of the spine. The main purpose of advances in technique and instrumentation is to improve results. Several studies have looked at the effects of spinal instrumentation on fusion rates and overall clinical outcomes. The following is a brief overview of the effect of spinal instrumentation on the fusion rates. The advances in pedicle screws, interbody devices, cervical plates, and other spinal instrumentation are substantial and warrant an in-depth discussion, which is beyond the scope of this chapter.
Lumbar Spine
Several prospective randomized control studies have analyzed the effects of pedicle screw instrumentation on fusion rates. Fischgrund et al. analyzed the fusion rates of single-level laminectomy and arthrodesis with and without pedicle screw instrumentation and noted a pseudarthrosis rate of 18% in the instrumented group compared to 55% in the uninstrumented group. However, overall clinical outcomes were similar in both groups at 2 years. Kornblum et al. analyzed those same patients from the uninstrumented group to look at clinical outcomes at 5 to 14 years. It was noted that clinical outcomes were significantly better in those patients with solid fusions compared to patients who had a pseudarthrosis (86% vs. 56%, respectively).
A prospective randomized study by Zdeblick et al. looked at the difference in fusion rates in uninstrumented, semirigid instrumented, and rigid instrumented posterolateral lumbar and lumbosacral fusions. The uninstrumented group had a fusion rate of 65% compared to 77% in the semirigid instrumentation group and 95% in the rigid instrumentation groups. Rigid instrumentation had a statistically significant improved rate of fusion. Overall, pedicle screw instrumentation has been widely used to aid in rigidity in an attempt to increase fusion rates.
In contrast, Thomsen et al. performed a similar prospective randomized study and noted no difference in fusion rates with or without the use of pedicle screws. Two other similar studies showed comparable results, with no difference in pain and functional outcomes and no difference in fusion rates. These results contradict those of Fischgrund et al. and Zdeblick et al. Christensen et al. showed improved results with uninstrumented posterolateral fusions but noted that those individuals with diagnosed preoperative degenerative instability had better results with instrumented posterolateral fusions.
Bono and Lee critically analyzed lumbar spinal fusion procedures and pseudarthrosis rates. Their review noted a statistically higher fusion rate in instrumented posterolateral lumbar fusions. However, the overall clinical outcomes were similar. The Spine Patient Outcomes Research Trial also noted significantly improved fusion rates in pedicle screw instrumented posterolateral fusions versus uninstrumented fusions (85.29% vs. 67.24, respectively).
Interbody fusion has become more common recently with the hypothesis that it aids in sagittal plane correction and provides another site for bony fusion to occur. Several randomized trials have analyzed the fusion rates and clinical outcomes of interbody fusion. Christensen et al. showed that circumferential fusion with the use of an interbody cage resulted in significantly improved lumbar lordosis at 1-year follow-up and improved fusion rates with less reoperations. Another study performed a similar randomized study with 2-year follow-up and noted that the overall clinical outcomes and fusion rates for posterolateral fusion versus interbody fusion were the same. The Spine Patient Outcomes Research Trial noted no significant difference in fusion rates between instrumented posterolateral fusion and circumferential fusions with the use of an interbody device. Several systematic reviews and meta-analysis studies suggest that circumferential fusions with interbody devices may increase fusion rates compared to posterolateral fusions alone. Jalalpour et al. compared uninstrumented posterolateral fusion with transforaminal lumbar interbody fusion (TLIF) and concluded that, at 2-year follow-up, the TLIF group had better clinical outcomes.
Controversy still remains regarding the use of pedicle screw instrumentation and interbody devices. There is data to suggest that fusion rates may be higher with the use of pedicle screws and interbody devices. However, good to excellent clinical outcomes can be achieved with or without instrumentation.
Cervical Spine
Instrumentation in the cervical spine has also been analyzed to determine whether fusion rates and clinical outcomes are affected. Anterior cervical discectomy and fusion (ACDF) is the most common cervical spine surgery performed. Several studies have looked at the fusion rates with and without the use of plate fixation for ACDF.
Wang et al. performed three studies analyzing the difference in fusion rates with and without use of plates in one-, two- and three-level ACDF. The first study on single-level ACDF showed no statistical difference in fusion rates with the use of plate supplementation. However, graft collapse was significantly less in the patients with the use of plates. The second study noted significantly higher pseudarthrosis rates in the group without plates for two-level ACDF (0% in the plate group vs. 25% in the no-plate group). The third study analyzed three-level ACDF and showed a lower pseudarthrosis rate in the group with plates (18% in the plate group vs. 37% in the no-plate group). However, this difference was not statistically significant.
A meta-analysis performed by Fraser and Hartl analyzed the fusion rates of single-, two-, and three-level cervical procedures with and without use of a plate as well as ACDF versus corpectomy and fusion. The data are summarized in Table 100.1 .
TABLE 100.1
Cumulative Fusion Rates for Each Surgical Procedure
From Fraser JF, Hartl R. Anterior approaches to fusion of the cervical spine: a metaanalysis of fusion rates. J Neurosurg Spine. 2007;6:298–303.
| OUTCOME (NO. OF PROCEDURES) | ||||
|---|---|---|---|---|
| Type of Surgery | Fusion | Pseudarthrosis | Total (No. of Procedures) | Fusion Rate (%) |
| One-Level Procedures | ||||
| ACD | 62 | 11 | 73 | 84.9 |
| ACDF | 1134 | 97 | 1231 | 92.1 |
| ACDFP | 329 | 10 | 339 | 97.1 |
| Two-Level Procedures | ||||
| ACDF | 337 | 85 | 422 | 79.9 |
| ACDFP | 174 | 10 | 184 | 94.6 |
| One-level CORP | 70 | 3 | 73 | 95.9 |
| One-level CORPP | 52 | 4 | 56 | 92.9 |
| Three-Level Procedures | ||||
| ACDF | 80 | 43 | 123 | 65.0 |
| ACDFP | 33 | 7 | 40 | 82.5 |
| Two-level CORP | 79 | 9 | 88 | 89.8 |
| Two-level CORPP | 51 | 2 | 53 | 96.2 |
| Total | 2401 | 281 | 2682 | 89.5 |
The use of plates in ACDF procedures increases the fusion rates. This is especially true in multilevel ACDF procedures. When comparing multilevel ACDF to corpectomy, the fusion rates are similar.
ACD, anterior cervical discectomy; ACDF, anterior cervical discectomy and fusion; ACDFP, anterior cervical discectomy and fusion with plate placement; CORP, corpectomy; CORPP, CORP with plate placement.
Several studies have also shown no difference in fusion rates with the use of plate supplementation for single-level ACDF. However, overall maintenance of cervical lordosis is better with the use of plates, with less graft collapse.
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