Minimally invasive space shuttle laminotomy for degenerative lumbar spinal canal stenosis.

STUDY
DESIGN: Technical note.
OBJECTIVES: To show microsurgical technique, considering the meticulous anatomy of the ligamentum flavum (LF).
BACKGROUND: Different methods are available for treating lumbar spinal canal stenosis (LSCS). A minimally invasive surgery, namely, space shuttle laminotomy, has recently been proposed. Here, we describe the surgical method for this novel technique. To conduct this surgery accurately, surgeons must have perfect knowledge of anatomy, especially regarding the LF. MATERIALS AND METHODS AND
RESULTS: We use this interlaminectomy technique for all cases of LSCS. All patients with LSCS recovered from their neurological deficits in shorter hoslital stays than regular laminectomy.
CONCLUSION: Minimally invasive space shuttle laminotomy (MISSL), which involves a microsurgical technique, is a safe, complication-free procedure.

INTRODUCTION

With an aging society, the incidence of degenerative lumbar spinal canal stenosis (LSCS) has been increasing in Japan. Various operative techniques are available for treating LSCS, and minimally invasive surgery has recently been proposed including microscopic surgery and endoscopic surgery. In this report, we describe the surgical technique for minimally invasive space shuttle laminotomy (MISSL) using a microscope, for which surgeons must be very well-versed about normal anatomy, especially the anatomy of the ligamentum flavum (LF).

Background

First, we describe the normal anatomy of the LF in detail. As mentioned above, it is only possible to conduct MISSL safely and accurately if the surgeon knows the anatomy of this ligament well. The LF is thick and short and is symmetrical on both the left and right sides. On each side, the LF divides into a medial portion and lateral portion [Figure 1]. The upper attachment of the medial portion is to the lower half of the ventral surface of the lamina and the attachment of the lateral portion is to the inferior aspect of the pedicle. The medial portion passes to the back of the next lower lamina and attaches to the upper quarter or so of the dorsal surface of that lamina. The lateral portion passes in front of the zygapophysial joint formed by the two vertebrae that the ligament connects. It attaches to the anterior aspects of the inferior and superior articular processes of this joint and forms its anterior capsule.[1] The most lateral fibers extend along the root of the superior articular process as far as the next lower pedicle to which they are attached. This part of the lateral portion of the LF has continuous fibrous connections with the synovium. It lies just medial to the pars interarticularis and has a root sleeve below it. The dorsal side of the LF has continuous attachments to the ventral part of the interspinous ligaments.[1234]

Figure 1

(a) A normal level of the spine (b) Medial portion of the ligamentum flavum (LF). The part in pale yellow is the LF under the lamina (c) Combined medial and lateral portions of the LF (d) An axial section of the LF

CASE REPORT

A 65-year-old male presented with intermittent claudication and came to the hospital with the chief complaint of the sciatic pain in the right lower extremeity. Radiological findings showed the lumber spinal canal stenosis in L4/5. He underwent the surgery of L4-5 interlaminectomy, MISSL. The operation time was 1.5 h. The bleeding during the surgery was no more than 12 mL. He was discharged the day after surgery without any neurological deficit.

MATERIALS AND METHODS AND RESULTS

MISSL is performed with microscopic assistance. The current article describes basic, one-level laminotomy but if necessary, the technique can be applied to multiple levels. We believe that orthodox laminectomy would serve for treating multiple-level sclerosis just as easily as MISSL; neither has any associated problem. A recent study has proposed the midline spinous process splitting approach or unilateral approach and bilateral decompression but there is no evidence that these surgical procedures are medically advantageous.

The details of MISSL for one-level stenosis are given below. Skin incisions of 3 cm are usually adequate in the case of one-segmental stenosis. Both the rostral and caudal spinous processes of the responsible lesion are opened, and the inferior one-third of the rostral spinous process with the interspinous ligaments is resected until the base of the spinous process. Thus, the facet joint is never sacrificed and the multifidus muscles that cover the facet joint capsule can be preserved to the best possible extent. We should mention that for achieving hemostasis, we avoid using monopolar cautery and use only bipolar cautery since it is more precise. Hemostasis acts as protection for the muscle.

Next, the procedure shifts sequentially to microscopic operation. Although the shape of the facet and width of the spinal canal should be confirmed before the operation, they can be verified on the basis of the diameter of a diamond burr. In terms of the width of the laminotomy for the rostral side lamina against the responsible segment (if it is level L4-5, then the L4 side lamina is involved), about 10 mm is usually adequate. In the case of the caudal side lamina (if it is level L4-5, the L5-side lamina is involved), 16-18 mm is adequate. Maintaining the width at less than 10 mm on the rostral side can protect the facet joint and its capsule. However, this is not always the case, as L1-2 or L2-3 is physiologically narrower than L4-5 or L5-S1, and the width becomes narrower toward the rostral side. In addition to decompression of the canal, decompression of the root sleeve is necessary. Therefore, the width of the decompression must exceed the width of the lamina. This part of the operation is performed using a diamond burr of diameter 6.0 mm. Although any ragged LF or LF obstructing the operation field may be removed, it is better to preserve the LF as far into the surgery as possible. The bone of lamina is removed by the drill until the dura matter is identified at the terminal of rostral side on midline. Therefore, particular care should be taken at this point, since the dura mater emerges suddenly after the laminotomy. The silhouette of the laminotomy resembles a space shuttle [Figure 2] and hence, the designation “space shuttle laminotomy.” Meticulous decompression is performed using a diamond burr of diameter 3.0 mm. The medial side of the inferior facet is drilled off using the burr. While performing the decompression, we used KAIRison® (a pneumatic Kerrison bone punch; Aesculap AG, Tuttlingen, Baden-Württemberg, Germany) and conventional Kerrison bone punches. KAIRison can be manipulated with a single hand under the microscope. With this punch, decompression can be performed with ease for not only laminae but also floating soft structures such as ligaments and flava, as these provide strong forces assisted by the compressed air supply in standard operation rooms. During the procedure, it is essential that the operator stand on the opposite side from the side on which the surgery is conducted. While the visual axis of the microscope is inclined, it is pushed forward toward the medial side of superior facet (the so-called lateral recess). As the diamond burr gets closer to the lateral recess, the LF naturally floats. In this situation, the LF should be preserved as far as possible because it can protect the dura mater. The drilling is continued in the direction of the “rear fender of the space shuttle.” Because the most lateral fibers of the LF extend toward the pedicle, the laminotomy can be performed safely. The drilling off toward the “rear fender” should be continued until the point at which the LF gradually tapers off. At this point, the diamond burr is turned toward “the cockpit of the space shuttle” [Figure 2c] where the LF is no longer present. The bone resection area looks like a space shuttle seen from the right side, [Figure 2d] the anterior side [Figure 2e] and the oblique side [Figure 2f]. The postoperative x-ray shows the bone decompression area on X-ray can be seen as if a space shuttle is flying, shown the red in the schema [Figure 2g and h]. The operator's assistant must take care to avoid dural lacerations during drilling off at this point. The procedure is repeated on the reverse side. However, in cases in which the canal is extremely narrow, decompression should not be performed at a stretch on any one side. In such cases, alternating, step-by-step decompression on each side is safer [Figures 3–7]. Once one side is completely decompressed, it is easy to decompress the other side. For multiple-level stenosis, this MISSL procedure is performed sequentially on each segment.

Figure 2

(a) Silhouette of space shuttle laminotomy from the dorsal side (b) The dotted line shows “dome laminotomy” of the “cock pit” of the space shuttle (c) Drilling off over the lateral portion of the LF using diamond burr. The LF protects the dura mater (d) Silhouette of space shuttle laminotomy from the lateral side (e) Axial section of the silhouette of space shuttle laminotomy (f) Three-dimensional image of space shuttle laminotomy (g) The postoperative the lumbar spine x-ray of A-P. The translucent area on the lumbar spine x-ray shows the resection area of the bone to decompress during the surgery that is shown in the red part in the schema (h) The resection is shown in red on the postoperative lumbar spine x-ray

Figure 3

Despite the vertical facet joint, spinal canal decompression could be completed. Pre- (a) and postoperative computed tomography scans (b)

Figure 7

Severe osteoarthritis of the facet joint in another case. The facet joints have been preserved completely. Pre- (a) and postoperative computed tomography scans (b)

The lateral recesses were decompressed completely. Pre- (a) and postoperative computed tomography scans (b)

The width of the laminotomy for the rostral side lamina is 10 mm (arrow). Pre- (a) and postoperative computed tomography scans (b)

Severe osteoarthritis of the facet joint in one case. The facet joints have been preserved completely. Pre- (a) and postoperative computed tomography scans (b)

MISSL can be described as laminotomy against the caudal side of the lamina. However, in the strictest sense, it is “removal of the spinous process” of the base of the spinous process against the rostral side of the bone.

CONCLUSION

0MISSL, which involves a microsurgical technique, is a safe, complication-free procedure. However, it requires operators to have a good understanding of the anatomy of the LF.

Financial support and sponsorship

The authors have no personal, financial, or institutional interest in any drugs, materials, or devices used.

Conflicts of interest

There are no conflicts of interest.