The Morphometric Study of Degenerative Lateral Canal Stenosis at L4-L5 and L5-S1 Using Magnetic Resonance Imaging (MRI): Feasibility Analysis for Posterior Surgical Decompression

Abstract

This study was to evaluate the morphological features of degenerative spinal stenosis and adequacy of lateral canal stenosis decompression via unilateral and bilateral laminectomy. Measurements of facet joint angulation (FJA), mid facet point (MFP), mid facet point distance (MFPD), the narrowest point of the lateral spinal canal (NPLC) and the narrowest point of the lateral spinal canal distance (NPLCD) were performed. At L4L5 of the right and left side, the mean distance between the lateral border of the dura and MFP was 1.0 ± 0.2 cm and 1.0 ± 0.3cm respectively. The mean NPLC was seen at 0.7 ± 0.3 and 0.7 ± 0.3 cm cm from the dura. At L5S1 of the right and left side, the mean distance between the lateral border of the dura and MFP was 1.2± 0.2 and 1.3 ± 0.2 cm respectively. The mean NPLC was seen at 0.8 ± 0.4 and 0.9 ± 0.5 cm from the dura. Unilateral laminectomy may result in incomplete decompression.

Fig. 1

Measurement of the parameters involved; α, Facet Joint Angle (FJA), X, Narrowest Point of Spinal Canal (NPSC), Y, Mid Facet Point (MFP), Narrowest Point of Spinal Canal Distance (NPSCD) and Mid Facet Point Distance (MFPD).

Fig. 2

Anatomical restrictions for lateral canal decompression (a) ipsilaterally (unilateral laminectomy) and (b) contralaterally (bilateral laminectomy); the dura anteriorly, mid facet joint (MFP) laterally and mid line structures (spinous process, interspinous and supraspinous muscles) posteriorly. Working zone is an area between the lateral border of the dura and MFP. a b Feasibility Analysis for Posterior Surgical Decompression.

Fig. 3

Ipsilateral laminectomy: If the NPLC is located medially (x) to the MFP, complete decompression can be done with minimal lateral angulation. However, if the NPLC is located at or more laterally (Y), NPLC will not be addressed adequately because more than half of the facet must be removed to reach this point.

Fig. 4

Contralateral laminectomy: NPLC which are located medially, at or more laterally to MFP can be addressed adequately using this approach as more than half of the medial facet can be preserved with complete resection of NPLC. Note that, this approach provides wider working zone for safer and efficient decompression.

Fig. 5

Estimation of facet joint resection via vertically performed laminectomy. Fig. a is mathematically represented by Fig. b. Facet articular surface cutting = amount of laminectomy/ cos facet angle. Since average facet angle is 42 degrees, 1 mm laminectomy done vertically via ipsilateral laminectomy causes 1.4 mm facet joint resection.

Fig. 6

These post-operative images of patients underwent decompression for degenerative spine stenosis using unilateral laminectomy. Difficulty to decompress ipsilateral lateral canal stenosis at L4–L5 (a) and L5–S1 (b) levels caused incomplete decompression and residual symptoms.