Letter to the Editor: Transpsoas approach

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To The Editor: We read the article by Cahill and coauthors1 with interest (Cahill KS, Martinez JL, Wang MY, et al: Motor nerve injuries following the minimally invasive lateral transpsoas approach. Clinical article. J Neurosurg Spine 17:227–231, September 2012), but we have some points regarding the analysis and conclusions drawn by the article.

In particular, 2 cases of femoral nerve injury with attendant quadriceps injury were reported upon. A rate of 4.8% quadriceps palsy was noted with lateral transpsoas approaches to the L4–5 level. The authors state that the injuries occurred “during dilation of the psoas muscle for the approach to the L4–5 disc space.” However, we are not certain how this conclusion can be drawn.

First, the methods state that a posterior interbody procedure (transforaminal lumbar interbody fusion [TLIF] or posterior lumbar interbody fusion [PLIF]) would be performed in such cases, but it is not discussed in the actual case description. For both patients, what was done at L4–5, a TLIF? Was the patient examined prior to performing the other procedure(s)? Is it possible that the TLIF caused an L-4 palsy?

Generally, after new a neurological injury it is reasonable to obtain images in the patient to determine the cause. Was imaging performed? A critical analysis of the MRI sequences can show tracts through the psoas that lead to the L4–5 foramen, which could explain the palsy on the basis of technical error.

Second, was the attending surgeon performing the procedure, or was the resident/fellow operating in these cases? Third, one case was a multilevel (L2–5) procedure. It is possible that the L3–4 transpsoas surgery caused an L-3 palsy and not the attempted L4–5 approach. Was a postoperative electromyography (EMG)/nerve conduction study performed at 6–12 weeks postoperatively to characterize the neural injury?

In addition to the questions posed above, critical analysis of preoperative radiographs and MRI studies can reveal details that would have contributed to intraoperative difficulty. Transitional lumbosacral anatomy (hemisacralization of the sacrum, L-6 vertebrae, and so on) has been shown to be a risk factor for unsuccessful treatment of L4–5 performed using the transpsoas approach.4

Additionally, we disagree with the statement “In this retrospective analysis, we estimated that the overall rate of femoral nerve injury for the … L4–5 level was 4.8%....” Of the palsies, one surgery was a multilevel procedure (L2–5) with an aborted L4–5 and one was an aborted single-level L4–5. Of the successful L4–5 levels, the authors reported no femoral nerve palsies. It is very possible that the multilevel (L2–5) case with a quadriceps palsy resulted from the L3–4 surgery due to L-3 neural injury. We would urge the authors to reconsider their published rate of palsies. One could consider the rate to be 1 of 41 L4–5 single-level procedures, or 2% in your series.

Further clouding the conclusions that one can draw from the paper are omitted details such as: what neuromuscular agent was given for anesthesia? And at what time after induction was the approach to L4–5 made? If rocuronium was used, it is quite possible that residual agent could lead to fatigue and/or unreliable readings during neural injury. Houten et al.2 reported quadriceps palsy after transpsoas surgery without EMG changes. Perhaps further investigation of induction agents and neural agents after transpsoas surgery is indicated. In our center we always insist on the use of succinylcholine when performing transpsoas surgery. Additionally, what neuromonitoring system was used? Did the authors use directional nerve-seeking probes when approaching L4–5? Directional neuromonitoring has been shown to decrease the rate of complications associated with the lateral transpsoas approach.5

Finally, in the discussion portion of the paper the authors point out that “the [femoral nerve] trunk [is] found in the center of the disc space in 15% of specimens in one cadaveric study.” This datum is used to support the assertion that one can “minimize this complication [femoral nerve palsies] through judicious use of the minimally invasive lateral fusion procedure at the L4–5 level….” We found that the nerves within the psoas move with limb range of motion in a recent study.3 They are lightly tethered within the psoas and the act of dissection moves the nerves significantly. Thus, the location of the neural elements after psoas dissection is probably even more variable. It is important to note that one may retract nerves in peripheral nerve surgery and in PLIF. Is there some inherent physiological difference between the nerves inside the canal and within the psoas that does not allow retraction during transpsoas surgery? Gentle, judicious dissection within the psoas with nerve mobilization if necessary, patient selection (avoid transitional lumbar anatomy), and directional neuromonitoring can probably avoid nerve palsy when treating L4–5 via the transpsoas approach.

Disclosure

Dr. O'Brien reports direct stock ownership in Spinicity and ownership in Stryker, and he is a consultant for Globus and NuVasive. Dr. Smith reports no conflict of interest.

References

  • 1

    Cahill KSMartinez JLWang MYVanni SLevi AD: Motor nerve injuries following the minimally invasive lateral transpsoas approach. Clinical article. J Neurosurg Spine 17:2272312012

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  • 2

    Houten JKAlexandre LCNasser RAWollowick AL: Nerve injury during the transpsoas approach for lumbar fusion. Report of 2 cases. J Neurosurg Spine 15:2802842011

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  • 3

    O'Brien JHaines CDooley ZTurner ALJackson D: Femoral nerve strain at L4-5 is minimized by hip flexion and increased by table break when performing lateral interbody fusion. Spine (Phila Pa 1976) [epub ahead of print]2013

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  • 4

    Smith WDYoussef JAChristian GSerrano SHyde JA: Lumbarized sacrum as a relative contraindication for lateral transpsoas interbody fusion at L5-6. J Spinal Disord Tech 25:2852912012

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  • 5

    Uribe JSVale FLDakwar E: Electromyographic monitoring and its anatomical implications in minimally invasive spine surgery. Spine (Phila Pa 1976) 35:26 SupplS368S3742010

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Response

We thank the authors for raising several important points regarding our case series and results with the lateral interbody fusion procedure. Our group previously reviewed objective, patient-driven data, which demonstrated that the incidence of lumbosacral plexus sensory symptoms following the minimally invasive lateral approach was likely to be underreported.2 In this article we defined the incidence of postoperative abdominal flank bulge (4%), which appeared to be more common with approaches to upper lumbar vertebrae. We also report a higher incidence (4%) of femoral nerve injury with procedures that included the L4–5 level. This finding is entirely consistent with prior case reports and, more importantly, with the reported neuroanatomical location of the subcostal nerve within the abdominal muscle layers and the femoral nerve within the psoas muscle.1–5

We agree that there are numerous ways to injure a nerve during spine surgery. We considered all of the possible alternative explanations suggested by the authors for quadriceps weakness—including but not limited to TLIF-related nerve injury, foraminal nerve injury via the lateral approach, injury to the femoral nerve from the lateral approach at a level other than L4–5, and transitional lumbosacral anatomy. We would like to reinforce the important finding that intraoperative real-time EMG monitoring indicated that the femoral nerve was activated during the transpsoas approach at the L4–5 level. In our multiple-surgeon series of lateral interbody fusions we have only had femoral nerve injury when the procedure involved the L4–5 level and when associated with positive activation.

We would also like to address several of the other issues raised by the authors. At our institution the attending surgeon is present, responsible, and intimately involved for the duration of the procedure. Fluoroscopy and directional EMG probes are routinely used. We did not have postoperative MRI studies available for review, but the postoperative CT scan suggested the appropriate trajectory toward the midpoint of the disc space. We rely heavily on fluoroscopy to achieve this goal. In our institutional experience we have not seen an L-4 palsy at the level of the nerve root or dorsal root ganglion during an L3–4 or L4–5 PLIF procedure that resulted in significant quadriceps weakness. The femoral nerve is created primarily by contributions from the L-2, L-3, and L-4 roots, and it requires a more distal injury—such as the femoral nerve itself—to impact motor function to the extent seen in these cases. Regarding mobilization of the nerve, we would definitely agree that a technique that involves shallow docking of the retractor and direct visualization and manipulation of the femoral nerve can be safely performed. Although not discussed in the manuscript, a shallow docking approach has been adopted as a technique when the neuromonitoring indicates that a safe corridor through the muscle is not present due to the anterior location of the femoral nerve. We do appreciate the feedback but believe that our interpretation of the results is the simplest, most realistic, and consistent with prior literature on femoral nerve injuries.

References

  • 1

    Benglis DMVanni SLevi AD: An anatomical study of the lumbosacral plexus as related to the minimally invasive transpsoas approach to the lumbar spine. Laboratory investigation. J Neurosurg Spine 10:1391442009

    • Search Google Scholar
    • Export Citation
  • 2

    Cummock MVanni SLevi ADYu YWang MY: An analysis of postoperative thigh symptoms after minimally invasive transpsoas lumbar interbody fusion. Clinical article. J Neurosurg Spine 15:11182011

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    • Export Citation
  • 3

    Davis TTBae HWMok JMRasouli ADelamarter RB: Lumbar plexus anatomy within the psoas muscle: implications for the transpsoas lateral approach to the L4-L5 disc. J Bone Joint Surg Am 93:148214872011

    • Search Google Scholar
    • Export Citation
  • 4

    Houten JKAlexandre LCNasser RWollowick AL: Nerve injury during the transpsoas approach for lumbar fusion. Report of 2 cases. J Neurosurg Spine 15:2802842011

    • Search Google Scholar
    • Export Citation
  • 5

    Uribe JSArredondo NDakwar EVale FL: Defining the safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: an anatomical study. Laboratory investigation. J Neurosurg Spine 13:2602662010

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    • Export Citation

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Article Information

Please include this information when citing this paper: published online November 1, 2013; DOI: 10.3171/2012.11.SPINE12849.

© AANS, except where prohibited by US copyright law.

Headings

References

  • 1

    Cahill KSMartinez JLWang MYVanni SLevi AD: Motor nerve injuries following the minimally invasive lateral transpsoas approach. Clinical article. J Neurosurg Spine 17:2272312012

    • Search Google Scholar
    • Export Citation
  • 2

    Houten JKAlexandre LCNasser RAWollowick AL: Nerve injury during the transpsoas approach for lumbar fusion. Report of 2 cases. J Neurosurg Spine 15:2802842011

    • Search Google Scholar
    • Export Citation
  • 3

    O'Brien JHaines CDooley ZTurner ALJackson D: Femoral nerve strain at L4-5 is minimized by hip flexion and increased by table break when performing lateral interbody fusion. Spine (Phila Pa 1976) [epub ahead of print]2013

    • Search Google Scholar
    • Export Citation
  • 4

    Smith WDYoussef JAChristian GSerrano SHyde JA: Lumbarized sacrum as a relative contraindication for lateral transpsoas interbody fusion at L5-6. J Spinal Disord Tech 25:2852912012

    • Search Google Scholar
    • Export Citation
  • 5

    Uribe JSVale FLDakwar E: Electromyographic monitoring and its anatomical implications in minimally invasive spine surgery. Spine (Phila Pa 1976) 35:26 SupplS368S3742010

    • Search Google Scholar
    • Export Citation
  • 1

    Benglis DMVanni SLevi AD: An anatomical study of the lumbosacral plexus as related to the minimally invasive transpsoas approach to the lumbar spine. Laboratory investigation. J Neurosurg Spine 10:1391442009

    • Search Google Scholar
    • Export Citation
  • 2

    Cummock MVanni SLevi ADYu YWang MY: An analysis of postoperative thigh symptoms after minimally invasive transpsoas lumbar interbody fusion. Clinical article. J Neurosurg Spine 15:11182011

    • Search Google Scholar
    • Export Citation
  • 3

    Davis TTBae HWMok JMRasouli ADelamarter RB: Lumbar plexus anatomy within the psoas muscle: implications for the transpsoas lateral approach to the L4-L5 disc. J Bone Joint Surg Am 93:148214872011

    • Search Google Scholar
    • Export Citation
  • 4

    Houten JKAlexandre LCNasser RWollowick AL: Nerve injury during the transpsoas approach for lumbar fusion. Report of 2 cases. J Neurosurg Spine 15:2802842011

    • Search Google Scholar
    • Export Citation
  • 5

    Uribe JSArredondo NDakwar EVale FL: Defining the safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: an anatomical study. Laboratory investigation. J Neurosurg Spine 13:2602662010

    • Search Google Scholar
    • Export Citation

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