Sublaminar osteotomy for lumbar spinal stenosis: Surgical technique

Lumbar spinal stenosis (LSS) is the most common indication for spinal surgery in patients aged 65 and over. The ligamentum flavum contributes to the narrowing of the spinal canal. The challenge of surgical treatment for LSS is how to effectively and lastingly remove the causes of the compression whilst avoiding complications such as iatrogenic instability. We describe a technique involving lumbar recalibration followed by a sublaminar osteotomy performed through enlarged interlaminar space. This technique is simple, effective, long-lasting and reproducible.

Introduction

Lumbar spinal stenosis (LSS) is the most common indication for spinal surgery in patients aged 65 and over [1] and the impact of a narrow spinal canal is increasing due to the ageing of the population [2]. LSS is a common degenerative condition characterized by a narrowing of the space containing the neurovascular structures of the spine and can affect both the spinal canal and foramina. It causes leg pain and intermittent neurological claudication and affects patient quality of life.

Constant mechanical stress results in degeneration and hypertrophy of the ligamentum flavum [3–5] which, combined with facet joint hypertrophy, contributes to the narrowing of the spinal canal [8] and compression of the nerve roots inside. This article describes a technique for surgical lumbar recalibration incorporating sublaminar osteotomy which has several benefits as described below.
 

Diagnosis

All patients described intermittent neurological claudication and reduced walking distances combined with a greater or lesser degree of nerve root pain on both sides. Dynamic x-rays were used to identify and subsequently treat any cases of clinical instability (spondylolisthesis).

The diagnosis of LSS was then confirmed with imaging studies, either CT or MRI (Fig. 1). Dynamic myelography was useful to search for any compression not detected on the static images.

Patients eligible for this lumbar release technique therefore had symptomatic LSS without radiological instability.

Surgical technique

The patient is placed in prone  position on a Hall frame. A medial sagittal incision is made over the spinous processes at the level of the spinal stenosis. The erector spinae muscles are detached from both sides of the spinous processes and laminae, down to the facet joints laterally which are disengaged (Fig. 2).

The inferior quarter of the inferior facet joint processes subjacent to the compressed level is resected using an osteotome using  a strictly transverse osteotomy cut (Fig. 3).

The lumbar canal is recalibrated using a technique similar to the one described by Sénégas [9], with a cephalic hemilaminectomy of the inferior vertebra, and a medial facetectomy using a 4 or 5mm Kerrison rongeur. The bone cut extends directly above the pedicle to allow unroofing of the recess. Downwards and outwards, the resection must be completed to allow the hook to pass freely into the foramen without damaging the nerve root. Upwards and outwards, the cut extends directly above the inferior edge of the lamina of the superior vertebra.

Sublaminar osteotomy (Figs. 4a & 4b):

We perform the sublaminar osteotomy by passing the osteotome through the enlarged interlaminar space.

The first cut is paramedian and parallel to the target lamina.  The chisel is directed into the cancellous bone of the lamina, between its lateral and medial (intraspinal) cortex, keeping the blade edge horizontal. The lamina is thus cut into two halves through its middle (Figs. 5 & 6). 

The osteotomy is complete when the surgeon feels a lack of resistance to the hand holding the chisel and the noise suddenly becomes duller and muffled. A second cut is then made, outside the first, with the blade edge slightly inclined along the plane of the lamina, and the axis of the chisel lying outside the sagittal axis.

A third cut is sometimes needed, vertically directly above the medial edge of the inferior facet joint process of the vertebra, in order to complete the osteotomy so that a single fragment of sublaminar tissue can be extracted. The instrument should be rotated slightly on its axis to complete the laminar osteoclasia (Fig. 8).

The osteotomy fragment can then be removed using angulated forceps, extracting it slowly downwards then outwards (Fig. 9).

Examination of the single extracted fragment reveals the resected bone surface on one side, and on the other side the hypertrophied ligamentum flavum and its attachment site (Fig. 10).

At each level, the dura mater and roots are therefore decompressed whilst preserving the caudal part of the posterior arch and major part of the facet joints (Figs. 11 & 12).

Discussion

LSS is one of the most common indications for spinal surgery and its incidence is expected to rise given the ageing of the population and advances in imaging capacity [2]. Once the neurological symptoms become disabling, conservative treatment is no longer appropriate, and the patient requires surgery.

The goal and challenge are to release the neurovascular structures inside the spinal canal effectively and lastingly, without destabilising the spine. However, simply creating an interlaminar window is not enough [10]. In 1988, Sénégas insisted on the importance of completely dissecting the ligamentum flavum, including its insertion onto the caudal lamina [9]. Nevertheless, the method for performing this dissection was never sufficiently explained.

We propose an instrument-free lumbar recalibration technique, with an osteotomy through the middle of the lamina to restore a comfortable interspinal space and a smaller bone resection. By removing the bone fragment carrying the ligamentum flavum insertion, the entire sublaminar flavum can be removed in one single motion that is probably safer - being intraosseous - than ‘blindly’ introducing a Kerrison into the canal. The thickness of the remaining lamina can be used to hold the erector spinae, which could in theory both help restore their function and avoid any long-term fibrous growth directly in contact with the dura mater, which would obstruct any revision surgery. Finally, this method can also be used for the subjacent lamina when performing a posterior lumbar interbody fusion in order to prevent or delay the onset of decompensation at the subjacent level.

There are naturally numerous surgical strategies for treating LSS, from laminectomy or lamino-arthrectomy, which is reserved for elderly subjects with comorbidities, to lumbar fusion which is preferable in cases of dynamic instability. The use of instrumentation causes greater bleeding, longer hospital stays, decompensation of the adjacent segment and greater expense [11–13]. On the other hand, a laminectomy carries real complications in the more or less long term, such as adjacent stenosis, disc herniation and above all iatrogenic instability or even spondylolisthesis [11,12,14–16]. There is no real documented proof of the superiority of one surgical strategy over another in the treatment of LSS [17].

We believe our osteotomy technique has an accessible learning curve and is therefore simple, effective and reproducible for the treatment of LSS. Dr Lalouz used this technique for over 1,500 patients during his career, without any cases of iatrogenic instability.

Conclusion

Lumbar recalibration combining a cephalic laminectomy and sublaminar osteotomy appears to offer a simple, effective, long-lasting and reproducible method for treating symptomatic degenerative lumbar spinal stenosis.