Letter to the Editor: Transsacral axial interbody fusion

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To The Editor: We read with interest the article of Hofstetter et al.3 (Hofstetter CP, Shin B, Tsiouris AJ, et al: Radiographic and clinical outcome after 1- and 2-level transsacral axial interbody fusion. Clinical article. J Neurosurg Spine 19:454–463, October 2013) that reported radiographic and clinical results in 38 patients who underwent single-level (n = 32) or 2-level (n = 6) transsacral axial interbody fusion. Through a mean follow-up of 26 months, mean back function improved by 19% and back pain decreased by 43%. Our group reported a mean 54% improvement in back function and a 63% improvement in back pain in 155 single-level presacral axial fusions and a 42% improvement in back function and a 56% improvement in back pain in a cohort of 52 two-level presacral axial fusions.6,7 Additionally, Hofstetter et al. report fusion rates of 80% for single-level and 33% for L4–S1 axial fusions in 6 patients. In contrast, we reported a 94% fusion rate for single-level presacral axial fusion in 156 patients and 93% fusion confirmed by CT in 52 two-level AxiaLIF patients.

The reason for the discrepant results between studies is unknown, but the potential influence of confounding variables cannot be denied. In the Hofstetter study, the AxiaLIF device was part of a complex fusion construct in 42% of cases. Of further note is that 45% of patients had undergone previous instrumented or noninstrumented fusions. The authors failed to perform bilateral posterior instrumentation in nearly one-third of the patients. A biomechanical study by Erkan et al. confirmed the need for bilateral segmental posterior fixation at L-4, L-5, and S-1 to provide uniform stability across each motion segment and to decrease the load transfer to the fixation points of the anterior implant.1 This might explain the prolonged operative times and as well as the inferior clinical outcomes in contrast to other reports.2,5

The lack of fusion in the 6 patients who underwent 2-level procedures might suggest less than adequate bone grafting of the interspace as well as a lack of posterior segmental fixation and posterior lateral fusion. Loss of disc height and subsidence of the AxiaLIF rod may result when excessive distraction is applied through the AxiaLIF implant.

The authors report a mean decrease of segmental lordosis of 5° and correlate this loss of lordosis with low fusion rates and poor clinical outcomes. We have found in a retrospective analysis of 52 patients who underwent L4–S1 lumbosacral fusion with AxiaLIF that there was no significant loss of global (L1–S1) or segmental (L4–S1) lordosis and that clinical outcomes and fusion rates were not compromised in the 5 patients that had a loss of lordosis of 5° or more.4

It is difficult to draw meaningful conclusions about the utility of the AxiaLIF implant given the complexity of the cases in the study of Hofstetter et al. Our multi-center study involving 52 patients demonstrates the safety and efficacy of the 2-level presacral fusion technique. This stands in sharp contrast to the current study, which is significantly limited by a small number of cases (6 two-level presacral fusions). Additional reports are needed to clarify the value of this technology.

Disclosure

Drs. Nasca, Miller, Bradley, Tobler, and Melgar report consultant relationships with Baxano. Dr. Bradley also reports stock options with Baxano.

References

  • 1

    Erkan SWu CMehbod AAHsu BPahl DWTransfeldt EE: Biomechanical evaluation of a new AxiaLIF technique for two-level lumbar fusions. Eur Spine J 18:8078142009

    • Search Google Scholar
    • Export Citation
  • 2

    Gerszten PCTobler WDRaley TJMiller LEBlock JENasca RJ: Axial presacral lumbar interbody fusion and percutaneous posterior fixation for stabilization of lumbosacral isthmic spondylolisthesis. J Spinal Disord Tech 25:E36E402012

    • Search Google Scholar
    • Export Citation
  • 3

    Hofstetter CPShin BTsiouris AJElowitz EHärtl R: Radiographic and clinical outcome after 1- and 2-level transsacral axial interbody fusion. Clinical article. J Neurosurg Spine 19:4544632013

    • Search Google Scholar
    • Export Citation
  • 4

    Melgar MATobler WDErnst RRaley TJAnand NNasca RJ: Evaluation of lumbar lordosis in patients treated with the AxiaLIF 2 level implant and posterior instrumentation. Presented at the annual meeting of the International Society for the Advancement of Spine SurgeryVancouver2013(Abstract) (http://www.isass.org/abstracts/isass13_regular_posters/isass13-408-Evaluation-of-Lumbar-Lordosis-in-Patients-Treated-with-the-AxiaLIF-2-L.html) [Accessed January 29 2014]

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  • 5

    Tobler WDFerrara LA: The presacral retroperitoneal approach for axial lumbar interbody fusion: a prospective study of clinical outcomes complication and fusion rates at a follow-up of two years in 26 patients. J Bone Joint Surg Br 7:9559602011

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    • Export Citation
  • 6

    Tobler WDGerszten PCBradley WDRaley TJNasca RJBlock JE: Minimally invasive axial presacral L5-S1 interbody fusion. Spine (Phila Pa 1976) 36:E1296E13012011

    • Search Google Scholar
    • Export Citation
  • 7

    Tobler WDMelgar MARaley TJAnand NMiller LENasca RJ: Clinical and radiographic outcomes with L4-S1 axial lumbar interbody fusion (AxiaLIF) and posterior instrumentation: a multicenter study. Med Devices (Auckl) 6:1551612013

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Keywords:

Response

We thank Dr. Tobler and colleagues for their thoughtful comments in response to our publication in the Journal of Neurosurgery: Spine.

In single-level L5–S1 AxiaLIF procedures that were not part of larger fusion constructs, our fusion rate was 87%, which is similar to the rate reported by Tobler and colleagues (94%),6 Whang et al. (85%),8 and Zeilstra et al. (88%).9 Interestingly, the patients in our L5–S1 AxiaLIF cohort who did not achieve solid arthrodesis had indeed only unilateral pedicle-rod constructs. Biomechanical studies have compared stand-alone 1- or 2-level AxiaLIF constructs with different combinations of posterior instrumentation.1,2 The authors of these 2 studies concluded that supplementary bilateral posterior instrumentation greatly increases construct stability. However, the effect of unilateral posterior instrumentation on construct stability has not been tested. Thus, we agree with Tobler and colleagues that it would be important to perform biomechanical testing on unilateral posterior instrumentation. Given our clinical results, we also agree that single-level AxiaLIF should be augmented with bilateral posterior instrumentation.

However, the failure of bilateral posterior instrumentation cannot be the explanation for the poor results in our 2-level AxiaLIF procedures, because all of these constructs were augmented with bilateral pedicle screw rod constructs. Our fusion rate in 2-level AxiaLIF cases was 33%, which is similar to the rate found by Marchi and colleagues (22%).4 These fusion rates are dismal compared to the excellent results presented by Tobler and colleagues (93%).7 As mentioned by the authors, there are a multitude of confounders that might have led to low fusion rates in our study and the study by Marchi and colleagues.4 Calcium-based bone graft substitute was used in our study and by Marchi and colleagues.4 While autologous bone remains the “gold standard” for grafting materials, calcium-based bone graft substitute has been demonstrated to support high union rates in the cervical and lumbar spine in common types of fixation.5 Another difference between studies with low fusion rates4 and those with high fusion rates7 was the use of bone morphogenetic protein (BMP). However, the use of BMP has been demonstrated to lack statistically significant impact on fusion rates in fusion constructs using axial rods in a patient cohort of 99 patients.3 The other difference was the type of transsacral rod that was used. Whereas we and Marchi et al. used a transscacral rod that was commercially available at the time of patient recruitment, Tobler and colleagues had access to the second-generation version of the axial rod, and this could have contributed to improved construct stability and higher fusion rates.

Loss of segmental lordosis at the level of the AxiaLIF procedure is the other concern we expressed. Marchi and colleagues also confirmed this finding.4 In order to analyze whether too-excessive distraction of the disc space using the axial rod may have led to loss of disc height or loss of lordosis, we re-analyzed our data: In 38 patients, the AxiaLIF device achieved on average a 1.4-mm (range −2.6 to 4.4 mm) increase of disc height measured in the center of the L5–S1 interspace on immediate postoperative radiographs. This amount of distraction did not correlate with the loss of disc height (correlation coefficient 0.29, p = 0.11) or loss of segmental lordosis (correlation coefficient 0.17, p = 0.37) at the last follow-up. Therefore, we hypothesize that there might be other potential explanations for the failure of the AxiaLIF device to provide sufficient anterior column support. In particular, we suspect that the absence of a solid weight-bearing interbody graft is responsible for the collapse of the construct.

In conclusion, we thank Tobler and colleagues for their thoughtful comments. We admit that there are multiple variables that may lead to various outcomes, particularly in retrospective clinical case series. Our patient cohort included many patients who were undergoing revision surgeries, and frequently the AxiaLIF device was part of a larger fusion construct. However, we believe that our concerns are representative for those voiced by other surgeons who may have embraced this technology too enthusiastically and may have expanded its indications too quickly. Therefore, we believe that our study is a valuable contribution to the literature. AxiaLIF can be considered with the expectation of good clinical and radiographic success for 1-level instrumentation in a well-selected patient group when correction of lordosis and foraminal decompression is not the primary goal of the procedure. In our hands and using the hardware available at the time of our study the transsacral rod did not allow us to increase or maintain segmental lumbar lordosis and disc height. Therefore, we propose that this innovative and truly minimally invasive presacral approach should be further refined and evaluated.

Disclosure

The author reports a consultant relationship with AOSpine, DePuy Synthes, BrainLAB, and Lanx and receiving study support from Baxter.

References

  • 1

    Akesen BWu CMehbod AATransfeldt EE: Biomechanical evaluation of paracoccygeal transsacral fixation. J Spinal Disord Tech 21:39442008

    • Search Google Scholar
    • Export Citation
  • 2

    Erkan SWu CMehbod AAHsu BPahl DWTransfeldt EE: Biomechanical evaluation of a new AxiaLIF technique for two-level lumbar fusion. Eur Spine J 18:8078142009

    • Search Google Scholar
    • Export Citation
  • 3

    Gerszten PCTobler WDNasca RJ: Retrospective analysis of L5-S1 axial lumbar interbody fusion (AxiaLIF): a comparison with and without the use of recombinant human bone morphogenetic protein-2. Spine J 11:102710322011

    • Search Google Scholar
    • Export Citation
  • 4

    Marchi LOliveira LCoutinho EPimenta L: Results and complications after 2-level axial lumbar interbody fusion with a minimum 2-year follow-up. Clinical article. J Neurosurg Spine 17:1871922012

    • Search Google Scholar
    • Export Citation
  • 5

    Nagineni VVJames ARAlimi MHofstetter CShin BJNjoku I Jr: Silicate-substituted calcium phosphate ceramic bone graft replacement for spinal fusion procedures. Spine (Phila Pa 1976) 37:E1264E12722012

    • Search Google Scholar
    • Export Citation
  • 6

    Tobler WDGerszten PCBradley WDRaley TJNasca RJBlock JE: Minimally invasive axial presacral L5-S1 interbody fusion: two-year clinical and radiographic outcomes. Spine (Phila Pa 1976) 36:E1296E13012011

    • Search Google Scholar
    • Export Citation
  • 7

    Tobler WDMelgar MARaley TJAnand NMiller LENasca RJ: Clinical and radiographic outcomes with L4-S1 axial lumbar interbody fusion (AxiaLIF) and posterior instrumentation: a multicenter study. Med Devices (Auckl) 6:1551612013

    • Search Google Scholar
    • Export Citation
  • 8

    Whang PGSasso RCPatel VVAli RMFischgrund JS: Comparison of axial and anterior interbody fusions of the L5-S1 segment: a retrospective cohort analysis. J Spinal Disord Tech 26:4374432013

    • Search Google Scholar
    • Export Citation
  • 9

    Zeilstra DJMiller LEBlock JE: Axial lumbar interbody fusion: a 6-year single-center experience. Clin Interv Aging 8:106310692013

    • Search Google Scholar
    • Export Citation

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Article Information

Contributor Notes

Please include this information when citing this paper: published online March 14, 2014; DOI: 10.3171/2013.11.SPINE13981.

© AANS, except where prohibited by US copyright law.

Headings
References
  • 1

    Erkan SWu CMehbod AAHsu BPahl DWTransfeldt EE: Biomechanical evaluation of a new AxiaLIF technique for two-level lumbar fusions. Eur Spine J 18:8078142009

    • Search Google Scholar
    • Export Citation
  • 2

    Gerszten PCTobler WDRaley TJMiller LEBlock JENasca RJ: Axial presacral lumbar interbody fusion and percutaneous posterior fixation for stabilization of lumbosacral isthmic spondylolisthesis. J Spinal Disord Tech 25:E36E402012

    • Search Google Scholar
    • Export Citation
  • 3

    Hofstetter CPShin BTsiouris AJElowitz EHärtl R: Radiographic and clinical outcome after 1- and 2-level transsacral axial interbody fusion. Clinical article. J Neurosurg Spine 19:4544632013

    • Search Google Scholar
    • Export Citation
  • 4

    Melgar MATobler WDErnst RRaley TJAnand NNasca RJ: Evaluation of lumbar lordosis in patients treated with the AxiaLIF 2 level implant and posterior instrumentation. Presented at the annual meeting of the International Society for the Advancement of Spine SurgeryVancouver2013(Abstract) (http://www.isass.org/abstracts/isass13_regular_posters/isass13-408-Evaluation-of-Lumbar-Lordosis-in-Patients-Treated-with-the-AxiaLIF-2-L.html) [Accessed January 29 2014]

    • Search Google Scholar
    • Export Citation
  • 5

    Tobler WDFerrara LA: The presacral retroperitoneal approach for axial lumbar interbody fusion: a prospective study of clinical outcomes complication and fusion rates at a follow-up of two years in 26 patients. J Bone Joint Surg Br 7:9559602011

    • Search Google Scholar
    • Export Citation
  • 6

    Tobler WDGerszten PCBradley WDRaley TJNasca RJBlock JE: Minimally invasive axial presacral L5-S1 interbody fusion. Spine (Phila Pa 1976) 36:E1296E13012011

    • Search Google Scholar
    • Export Citation
  • 7

    Tobler WDMelgar MARaley TJAnand NMiller LENasca RJ: Clinical and radiographic outcomes with L4-S1 axial lumbar interbody fusion (AxiaLIF) and posterior instrumentation: a multicenter study. Med Devices (Auckl) 6:1551612013

    • Search Google Scholar
    • Export Citation
  • 1

    Akesen BWu CMehbod AATransfeldt EE: Biomechanical evaluation of paracoccygeal transsacral fixation. J Spinal Disord Tech 21:39442008

    • Search Google Scholar
    • Export Citation
  • 2

    Erkan SWu CMehbod AAHsu BPahl DWTransfeldt EE: Biomechanical evaluation of a new AxiaLIF technique for two-level lumbar fusion. Eur Spine J 18:8078142009

    • Search Google Scholar
    • Export Citation
  • 3

    Gerszten PCTobler WDNasca RJ: Retrospective analysis of L5-S1 axial lumbar interbody fusion (AxiaLIF): a comparison with and without the use of recombinant human bone morphogenetic protein-2. Spine J 11:102710322011

    • Search Google Scholar
    • Export Citation
  • 4

    Marchi LOliveira LCoutinho EPimenta L: Results and complications after 2-level axial lumbar interbody fusion with a minimum 2-year follow-up. Clinical article. J Neurosurg Spine 17:1871922012

    • Search Google Scholar
    • Export Citation
  • 5

    Nagineni VVJames ARAlimi MHofstetter CShin BJNjoku I Jr: Silicate-substituted calcium phosphate ceramic bone graft replacement for spinal fusion procedures. Spine (Phila Pa 1976) 37:E1264E12722012

    • Search Google Scholar
    • Export Citation
  • 6

    Tobler WDGerszten PCBradley WDRaley TJNasca RJBlock JE: Minimally invasive axial presacral L5-S1 interbody fusion: two-year clinical and radiographic outcomes. Spine (Phila Pa 1976) 36:E1296E13012011

    • Search Google Scholar
    • Export Citation
  • 7

    Tobler WDMelgar MARaley TJAnand NMiller LENasca RJ: Clinical and radiographic outcomes with L4-S1 axial lumbar interbody fusion (AxiaLIF) and posterior instrumentation: a multicenter study. Med Devices (Auckl) 6:1551612013

    • Search Google Scholar
    • Export Citation
  • 8

    Whang PGSasso RCPatel VVAli RMFischgrund JS: Comparison of axial and anterior interbody fusions of the L5-S1 segment: a retrospective cohort analysis. J Spinal Disord Tech 26:4374432013

    • Search Google Scholar
    • Export Citation
  • 9

    Zeilstra DJMiller LEBlock JE: Axial lumbar interbody fusion: a 6-year single-center experience. Clin Interv Aging 8:106310692013

    • Search Google Scholar
    • Export Citation
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