Microendoscopic decompression of conjoined lumbosacral nerve roots

Abstract

Nerve root morphological variability is often incompletely appreciated on preoperative imaging and can complicate intraoperative decision-making. This case demonstrates the utility of spinal endoscopy in the visualisation and manipulation of conjoined nerve roots and includes procedural images to promote better understanding and awareness of this anatomical anomaly. A woman in her 50s presented with 1 year of progressive left S1 radiculopathy refractory to non-operative modalities. History and examination were notable for S1 dermatomal paresthesias, positive ipsilateral straight leg raise and grade 4/5 gastrocnemius strength. MRI demonstrated an L5–S1 left paracentral disc herniation causing severe lateral recess stenosis. Endoscopic decompression revealed conjoined lumbosacral nerve roots. Laminotomies and discectomy provided circumferential decompression. The patient experienced immediate and sustained relief of her preoperative radiculopathy as manifested in patient-reported outcome measures. Evolving endoscopic spine platforms provide novel visualisation of nerve root anomalies yielding new insight on safe and effective decompressive techniques.

Background

Conjoined nerve roots in the lumbosacral spine are well characterised despite a low overall prevalence.^1–3 The presence of conjoined nerve roots in the general population is estimated to range from just over 1% to as high as 14% in cadaver studies,^{4 5} and several classification schemes exist, dating back to the early 1960s.¹ These characterisations primarily focus on how nerve roots form from the dural sac, their resultant trajectories with respect to the adjacent pedicles and foramen, and anastomoses.^5–7 Clinically, conjoined nerve roots can be radiculopathic without external compression, given their enlarged size; however, when disc herniations occur, symptoms can manifest across dermatomes and myotomes. MRI has significantly improved diagnostic capabilities, and several described signs on both axial and sagittal reconstructions have been associated with conjoined nerve roots.^{8 9}

Conjoined nerve roots necessitate additional intraoperative considerations to avoid iatrogenic injury, underscoring the importance of early recognition and management. The shared dural envelope can be difficult to retract, leading to postoperative neurapraxias and neuropathic pain.^{2 3 10} The conjoined roots may also increase the risk of inadequate decompression and persistent postoperative symptoms. Adequate exposure, sufficient mobilisation to enable disc removal and thorough decompression are of paramount importance to ensure optimal surgical outcomes.

While classically described and depicted diagrammatically, there is a relative dearth of intraoperative anatomical images available to facilitate surgeon education and to provide spine surgeons with clear mental models of conjoined nerve root anatomy. Endoscopic spine surgery has improved intraoperative visualisation and magnification of anatomical structures. While multiple endoscopic techniques exist,^{11 12} the commonality includes targeted tubular retraction and indirect visualisation to allow for smaller access channels to the spine. This reduction in collateral tissue damage has led to improved postoperative pain management and expedited recovery times¹³ while maintaining patient-reported outcome measures (PROMs) compared with traditional minimally invasive techniques.^14–17 Furthermore, endoscopy has facilitated capturing and documenting clear anatomical images and videos to augment surgeon education. We present a case report of conjoined lumbosacral nerve roots whose identification and decompression were facilitated and documented via a microendoscopic approach.

Case presentation

A healthy woman in her 50s presented with 1 year of progressive left-sided back, buttock and posterior leg pain despite activity modification, rest, medication management and physiotherapy. These symptoms had progressed to functional limitations which prompted her presentation for surgical evaluation. Exam was notable for a positive ipsilateral straight leg raise and grade 4/5 gastrocnemius strength.

Investigations

Lumbar radiographs demonstrated diffuse spondylosis with loss of disc height at the L5–S1 level and relative loss of lumbar lordosis without evidence of instability. MRI demonstrated an L5–S1 left paracentral disc herniation with severe left-sided lateral recess stenosis and S1 nerve impingement without obvious evidence of nerve root anomaly (figure 1A–C).

Figure 1.

Mid-sagittal (A), parasagittal (B) and axial (C) MRI cuts demonstrate the left paracentral L5–S1 disc herniation with moderately severe left-sided lateral recess stenosis and S1 nerve root impingement.

Treatment

The patient underwent an L5–S1 microendoscopic decompression via a paramedian approach using a 16 mm tubular retractor. Localisation was confirmed under fluoroscopy with the tubular retractor in place, with left-sided L5 and S1 laminotomies performed using a diamond tip burr. On dissection and removal of the ligamentum flavum, recess decompression and medial facetectomy, the conjoined lumbosacral nerve roots were appreciated (figure 2A–E). The nerve roots were mobilised to permit annulotomy and discectomy; use of the microendoscope permitted direct visualisation and mobilisation of both nerve roots (video 1).

Figure 2.

Intraoperative pictures demonstrating microendoscopic discectomy and conjoined L5 and S1 nerve roots. Following bony resection and removal of the ligamentum flavum, the nerve roots and thecal sac are appreciated (A). Separation and mobilisation of conjoined nerve roots are performed to permit access to and removal of the L5–S1 disc (D). Following discectomy, adequate decompression of the conjoined nerve roots is seen (E).

Video 1.

bcr-2021-248680supp001.mp4 ^{(668.9KB, mp4)}

DOI: 10.1136/bcr-2021-248680.video01

Outcome and follow-up

Immediately postoperatively, the patient’s radiculopathic symptoms resolved. Improvement was observed at 2-week follow-up as manifested in return of full gastrocnemius strength, negative nerve tension signs, and improvements in pain and physical function PROMs. Most PROM domains showed continued improvement at 4-month follow-up (table 1).

Table 1.

Preoperative versus postoperative PROMs

PROMIS components	Preoperative rating	2-week postoperative rating	4-month postoperative rating
Physical function*	43.5	46.6	61.9
Pain intensity†	67.4	30.7	57.5
Pain interference‡	66.6	41.6	41.6
Global health–physical§	39.8	57.7	67.7
Global health–mental¶	56	56	67.6

*Physical function (PROMIS Physical Function SF10A) normal >45, range 0–62.

†Pain intensity (PROMIS Pain Intensity Short Form 3A Score) normal <56, range 0–72.

‡Pain interference (Pain Interference Score–PROMIS Short Form 4A Score) normal <61, range 41–76.

§Global health–physical (PROMIS Global Health Short Form Score–Physical) normal >42, range 16–68.

¶Global Health Mental (PROMIS Global Health Short Form Score–Mental) normal >40, range 21–6.

PROM, patient-reported outcome measure.

Discussion

Conjoined nerve roots in the lumbosacral spine are a rarely encountered anatomical variant. However, their clinical significance has prompted classification schemes and characterisations generated primarily from cadaveric investigations.2 3 5 8 9 Review of the literature is notable for a lack of anatomical images depicting their appearance in situ. As a developing field, spinal endoscopy leverages indirect camera visualisation of the surgical working field in order to minimise invasiveness and tissue disruption.¹¹ While applications of this technology are evolving, its use has consistently been shown to be safe and efficacious when compared with traditional minimally invasive techniques.^18–22 In this report, we demonstrate the unique perspective of conjoined nerve roots through the use of microendoscopy with clinical images and an intraoperative video.

Microendoscopy involves the use of a single working channel through which the endoscope and multiple instruments are passed and concurrently used.²³ This technique permits smaller incisions, narrow surgical corridors and less tissue damage. In addition to the more conventional posterolateral (or interlaminar) approach wherein central and lateral recess pathologies are readily accessible, endoscopic spine surgery can also be performed through an extraforaminal (or transforaminal) approach to access far lateral disc herniations and to facilitate foraminal decompression. When using the interlaminar approach, dorsal decompression is performed until the lateral border of the traversing nerve root is visualised. This step is paramount to confirm the absence of more lateral neural structures, especially in areas of greater anatomical neural anomalies.

Conventional microdiscectomy in the presence of conjoined nerve roots has been described in a series of case reports as a safe and effective technique as long as the anatomical abnormality is adequately visualised and mobilised.^{24 25} Sharma et al describe removal of the ipsilateral facet joint to visualise the lateralmost edge of the nerve roots followed by ‘over-the-top’ decompression via contralateral facetectomies to free relatively immobile conjoined nerve roots and to permit safe retraction.²⁵ Furthermore, in cases of large herniations, the authors describe how it may be necessary to achieve partial axillary decompression between the dura and medial border of the nerve roots to allow for sufficient root relaxation and discectomy through the shoulder area.

Ultimately, the key to effective decompression of conjoined nerve roots is adequate visualisation; in this way, the utility of indirect visualisation and magnification of the surgical field is appreciated. As the endoscope and surgical instruments are passed through the same channel, an angled perspective of the working field is acquired, allowing for a unique and magnified view of the instruments and surrounding anatomy. This angled visualisation promotes adequate undercutting of the facet joint to achieve thorough decompression lateral to traversing nerve root while maximising maintenance of functional joint anatomy. In this case, the endoscope also allowed for better visualisation of the lateral conjoined nerve root, yielding a more complete appreciation of the anatomy and safe manipulation to permit discectomy. In these ways, microendoscopy provides a novel and valuable role in the recognition and treatment of this uncommon, yet important, anatomical variation.

Patient’s perspective.

Over the course of a year, I had increasing sciatica pain down my left leg, especially when sitting or lying down, though I was able to walk and stand. I was first referred to physical therapy by my primary care physician but my pain became increasingly worse. In the span of a couple months, the pain became unbearable to such an extent that I was unable to sleep unless I took 600 mg of ibuprofen when going to bed and after 4 hours, in the middle of the night, when I would wake up in pain.

After four and a half months of unsuccessful physical therapy, I returned to my primary care doctor who requested an MRI which showed a left herniated disc. I was immediately referred to a spine surgeon who clearly explained my options, including a cortisone shot, continuing physical therapy, and microendoscopic surgery. Given my level of pain and my lack of success with physical therapy, we decided to move forward with surgery.

I had microendoscopic surgery within a month of the MRI. That last month before surgery I experienced severe pain, especially at night when I was unable to sleep unless I took ibuprofen or other muscle relaxants in the days before surgery when I was unable to take ibuprofen.

The surgery itself was uneventful and straightforward. The pain relief was immediate. The only pain relief I took was 600 mg of ibuprofen and only the first two nights after surgery, as a precaution to enable me to sleep, rest, and heal. I took no other pain medication. The day after surgery I was able to slowly walk around the block. Two weeks after surgery, I started physical therapy focused on strengthening muscles. Within a month, I had worked myself up to walking at least six miles a day, have had no pain, and have taken no more ibuprofen or other pain killers. It’s been four and a half months since surgery and I feel back to normal. I believe that part of the speed of recovery can be explained by the minimal incision made during surgery, which allowed me to heal much more quickly. I just wish I had had surgery earlier!

Learning points.

• This case highlights the need for heightened suspicion of neural variability, which may not be evident on MRI, and demonstrates the unique perspective of microendoscopy in fully appreciating and manipulating conjoined nerve root anatomy.

• Conjoined nerve roots may have low diagnostic sensitivity on MRI in the setting of lateral recess or foraminal stenosis, underscoring the importance of adequate intraoperative diagnosis.

• The included intraoperative procedural images and video will provide surgeons with clear examples of this morphological anomaly and will facilitate the performance of safe and adequate neural decompression via conventional or endoscopic approaches.

Ethics statements

Patient consent for publication

Consent obtained directly from patient(s).