Relevant surgical anatomy

Cervical spondylotic myelopathy (CSM) is caused by mono- to multisegmental spinal cord compression. Relevant structures undergoing degeneration during CSM development are the disc, the endplate, the yellow ligament, and the facet joints. Osteophytes and disc bulging/herniation are the anterior components and hypertrophic yellow ligament and arthritic facet joints are the posterior components of spinal cord compression, and therefore in the focus of decompressive surgery. Spinal cord decompression in CSM is achieved either by anterior or posterior approaches. The common anterior techniques are anterior discectomy and fusion (ACDF) or anterior corpectomy and fusion (ACF). Laminoplasty (LP) and laminectomy plus fusion (LF) are viable posterior alternatives [4]. Despite yielding identical clinical results, LP is less popular in Europe and in the US because of an assumed risk of progressive kyphotic deformation of the non-lordotic cervical spine due to bilateral muscle detachment [2].

In lumbar spinal stenosis, laminotomy and bilateral decompression of dural sac and the nerve roots is an accepted concept, which has not yet been transferred to the cervical spine [5].

The concept of laminotomy and bilateral decompression of the dural sac and the nerve roots has not yet been used in CSM. However, this concept might offer advantages if compared with LP and LCF, being the avoidance of destabilizing bilateral muscle detachment and of implants. Our aim is to describe the technique of hemilaminectomy and bilateral decompression in CSM.

Description of the technique (Figs. 1 and 2, video)

Fig. 1
figure 1

Intraoperative images during trisegmental bilateral decompression via right-sided two-segmental hemilaminectomy. The hemilaminae and the thickened yellow ligaments beneath and between the hemilaminae are removed, exposing the right dorsal circumference of the dura/spinal cord. The spinous processes are preserved

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Fig. 2
figure 2

By undercutting the spinous process and thinning the contralateral inner hemilamina, exposure of the whole dorsal circumference of the dura/spinal cord is achieved

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The authors prefer performing the operation in the sitting position with the head slightly flexed. After midline skin incision (4 cm in monosegmental disease), the muscle fascia is incised on the clinically leading side or on the radiologically leading side in non-lateralized symptoms. If neither symptoms nor radiological findings guide side selection, the handiness of the neurosurgeon is decisive. The muscle is detached from the hemilamina(e). A Caspar speculum (Aesculap, Tuttlingen, Germany) is introduced and the medial border of the facet joint is identified. Depending on the number of involved segments, either a laminotomy for monosegmental CSM, monosegmental hemilaminectomy for bisegmental CSM, and so on, is performed under the microscope. Care is taken to preserve the integrity of the facet joint. The next crucial step is removal of the base of the spinous process(es) with a 5-mm spherical diamond drill, beginning at the medial edge of the hemilaminectomy and ending near the contralateral medial part of the facet joint(s), thereby thinning the inner contralateral hemilamina(e). Care is taken not to breach the outer corticalis. These maneuvers open the field for bilateral undercutting of the laminae above and below the hemilaminectomy(ies), if required. Anatomically, the yellow ligament is thinned out dorsolaterally in the vicinity of the nerve roots. With a sharp hook, the lateral ligament edge on the side of the approach is elevated. Then, the mostly hypertrophied ligament is removed with a Kerrison rongeur until the very first segment of the contralateral dorsal nerve root(s) is exposed. If needed, a foraminotomy can be added on the side of the hemilaminectomy. Occasional bleeding from the epidural veins can easily be managed by coagulation and GELFOAM. The operation wound is closed in standard fashion; a suction drain is usually not needed.

The approach in this case is from the right side. After muscle detachment from the hemilaminae, primarily a hemilaminectomy is performed. Care is taken to preserve the integrity of the facet joint. The next step is removal of the base of the spinous process(es) with the drill and Kerrison rongeur, beginning at the medial edge of the hemilaminectomy and ending near the contralateral medial part of the facet joint(s), thereby thinning the inner contralateral hemilaminae. The hypertrophied ligament is further being removed. Bleeding from the epidural veins can easily be managed by coagulation and GELFOAM (MP4 87643 kb)

Indications

In patients with mild CSM, conservative management could be discussed, as the disease is not necessarily progressive [3]. However, the majority of CSM patients require spinal cord decompression. In monosegmental CSM, ACDF is performed by many, whereas multilevel ACDF or ACF are required for anterior spinal cord decompression in bi- or trisegmental disease. However, increasing the implant length increases substantially the risk of implant failure and non-fusion. The described hemilaminectomy and bilateral decompression is best suited for these patients with CSM in more than one segment without or with unilateral radiculopathy (Fig. 1).

Limitations

As the contralateral neuroforamen cannot entirely be decompressed, patients with symptoms of myelopathy plus bilateral radiculopathy cannot be treated adequately. In patients with monosegmental disease, bilateral decompression via a unilateral laminotomy is possible. However, it is our experience that thorough visual control of the lower contralateral spinal canal via laminotomy is occasionally difficult. Thus, patients with monosegmental CSM might be not the ideal candidates. The underlying mechanism of clinical improvement in LP, LF, and probably hemilaminectomy and bilateral decompression is dorsal translation of the spinal cord after removal of space-reducing yellow ligament and dorsal bony elements [7]. It has been shown in LP and LF that clinically effective dorsal translation cannot occur in cervical kyphosis and in a spinal canal whose diameter is reduced by more than 50 % [6]. We therefore consider kyphosis and severe spinal canal stenosis as contraindications for hemilaminectomy and bilateral decompression.

How to avoid complications?

Positioning of the patients with CSM should be performed carefully irrespective of the used operative technique, as extension (for anterior approaches) or flexion (for posterior approaches) of the head might exacerbate the symptoms. Meticulous hemostasis in the area of the unilaterally detached muscle is warranted to avoid formation of an epidural hematoma. Drilling instead of bone removal with rongeurs is preferred to avoid undue compression of the spinal cord. It is crucial not to remove the yellow ligament before completion of bony decompression, as the ligament protects the spinal cord during drilling. Electrophysiological monitoring throughout the whole procedure allows avoidance of damage of the already vulnerable spinal cord.

Specific perioperative considerations

For adequate approach selection, magnetic resonance imaging and computerized tomography (CT) in bone window technique should be performed preoperatively (Fig. 3). During surgery, lateral radiography is helpful for proving sufficient decompression in cranio-caudal direction. Postoperative CT should be performed for documenting adequate dorsal decompression (Fig. 4), especially on the contralateral side (Fig. 5). We prescribe a soft collar for 6 weeks, which should be worn 24 h in the first 3 weeks, and only during the night in the next 3 weeks.

Fig. 3
figure 3

Preoperative imaging of a 56-year-old patient with bisegmental cervical spondylotic myelopathy. Upper left Sagittal T2-weighted magnetic resonance imaging (MRI) shows cervical stenosis in C5–6 and C6–7 and an intramedullary hyperintensity in C5–6. Upper right Sagittal computerized tomography (CT) demonstrates dorsal osteophytes and mild ossification of the posterior ligament in both segments leading to spinal cord compression. Lower left Axial MRI in C5–6 delineates right-sided spinal cord compression. Lower right Axial CT in C5–6 shows the mainly right-sided dorsal osteophyte; however, the central and left-sided spinal canal diameter is also reduced

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Fig. 4
figure 4

Computerized tomography (CT) of a 56-year-old patient with bisegmental cervical spondylotic myelopathy after bisegmental decompression via a right-sided hemilaminectomy C6. Upper left and middle Sagittal CT demonstrates decompression of the spinal canal from upper C5 to mid C7. Upper right Coronal CT shows sufficient decompression of the spinal canal on both sides via the unilateral approach. Lower row Axial CT C5–6 shows sufficient decompression of the spinal canal on both sides and preservation of the spinous process and contralateral hemilamina C6

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Fig. 5
figure 5

Left Drawing (axial view) of a cervical spinal canal stenosis induced by hypertrophied ligamentum flavum and calcified disc protrusion as well as osteophytes. Right The amount of bone and ligamentum flavum that is being resected is marked in red. This area demonstrates that the contralateral side can be sufficiently decompressed via a unilateral approach

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Specific information to give to the patient about surgery and potential risks

About 30 % of the patients undergoing adequate spinal cord decompression either from anterior or posterior do not improve. We expect similar percentages for unilateral hemilaminectomy and bilateral decompression and inform the patient accordingly not to raise un-fulfillable expectations. Superficial and deep wound infections are more frequent after LP and LF than anterior approaches [1]. While we have not witnessed any infectious complication so far, we nonetheless inform the patient that the infection risk might be higher than in anterior surgery. Further, the patient is informed that temporary neck pain is more frequent in dorsal approaches. Finally, while we believe that hemilaminectomy and bilateral decompression is as clinically effective as LP/LF while offering distinct advantages by less invasiveness and avoidance of implants, we inform the patient that this is a novel technique for which long-term data is lacking. A prospective study providing radiological, electrophysiological, and clinical outcome data is currently underway in the author’s institution.

Conclusions

  1. 1-

    Unilateral hemilaminectomy and bilateral decompression is a novel surgical technique for patients with CSM, and should be considered as an alternative to the common anterior and posterior approaches.

  2. 2-

    If compared to LP and LF, theoretical advantages are the reduced invasiveness due to unilateral muscle detachment and avoidance of implants.

  3. 3-

    As a novel technique, long-term follow-up data is still lacking, but it is believed that the theoretical advantages translate into similar or better results.

  4. 4-

    Adequate decompression of the complete dorsal circumference of the spinal cord is possible via unilateral hemilaminectomy.

  5. 5-

    The hypertrophied yellow ligament protects the spinal cord and should only be removed after completion of the bony decompression by drilling.

  6. 6-

    The microscope is needed after exposure of the hemilamina(e).

  7. 7-

    Unilateral hemilaminectomy and bilateral decompression is best suited in patients with bi- or trisegmental CSM.

  8. 8-

    Unilateral hemilaminectomy and bilateral decompression is not suited in the kyphotic cervical spine or decrease of the spinal canal diameter by more than 50 %.

  9. 9-

    In patients with monosegmental CSM, the exposure is reduced to a unilateral laminotomy, which occasionally makes visual control of the lower contralateral spinal cord difficult.

  10. 10-

    Intraoperative lateral radiography is useful for proving adequate craniocaudal decompression.