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Koga et al. Minimal laminectomy with the interlaminar approach for PELD

endoscope insertion, and there are three different computed tomography (CT), and magnetic resonance
operative approaches: interlaminar, transforaminal, imaging (MRI) were used to identify the location and
and posterolateral. Each approach has an adequate type of LDH according to our previous report. The
[8]
pathophysiological status. [1,6,7] The interlaminar width of the interlaminar space and the LDH size
approach (ILA) is preferred for axillary-type and migrated were calculated on axial CT and MRI, respectively,
LDH. It is performed under endoscopic visualization, as described previously [the width was determined
[1]
and the visual field is similar to conventional open and/ by the widest distance between the bilateral facet
or microsurgical operative views. Therefore, the ILA is joints at the corresponding disc level, and the LDH
preferred by surgeons with experience in performing size was evaluated by the anteroposterior (AP) size
conventional procedures, rather than other PELD ratio calculated from the protruded height against
[8]
approaches. [1,8-11] the AP diameter of the spinal canal]. The extent of
migration was evaluated by using T2-weighted sagittal
Conversely, we have previously experienced and MRI according to previous reports. [13,14] High-grade
reported on relatively severe complications of the migration was defined as migration exceeding the
ILA. These complications included persistent disc-space height. Conversely, low-grade migration
[8]
numbness in the corresponding nerve area, transient was defined as a migration extent that was smaller
muscular weakness, and transient bladder and than the disc-space height [Figure 1A and B].
rectal disturbance, which may be due to excessive
compression of the nerve root and/or dural sac by the The patients were followed postoperatively for an
endoscopic sheath. As a result of these experiences, average of 6.2 months (2-11 months). Neurological
we have been more careful in performing the ILA status was evaluated preoperatively and postoperatively
and have not experienced such complications. To by using the modified Japanese Orthopaedic
avoid complications, we proposed the proper use of 2 Association (mJOA) score. [15,16] The corresponding leg
different operative routes of the ILA (via the shoulder pain was also evaluated by using the Numerical Rating
[17]
and via the axilla). Furthermore, we suggested that Scale (NRS) score. We compared data for these
the width of the interlaminar space should be at least parameters with our previous ILA data [laminectomy
20 mm for the ILA without bone removal. [8] (-) group: 41 cases]. Statistical analysis was performed
with student’s t-test. P values < 0.05 were considered
We sometimes experience cases in which the width statistically significant. The exclusion of high-grade
of the interlaminar space is < 20 mm even in LDH caudal migration is the differentiated background of the
at L5/S1. To overcome this limitation, we recently laminectomy (-) group.
[1]
started to use a high-speed drill and/or a small In addition to these previous parameters, we also
Kerrison rongeur (width 3 mm) for certain ILA cases. evaluated the shape of the upper vertebral laminae.
We have already experienced 13 such cases and Concave (-) was defined as when the caudal margin of
avoided complications. In this study, we retrospectively the upper vertebral laminae (CM-UVL) was straight and
analyzed these cases, and summarized the features of the interlaminar space appeared as a sharp triangle.
minimal laminectomy with the ILA. Concave (+) was defined as when the CM-UVL had a

concave shape and the interlaminar space appeared
METHODS to have a more rounded form [Figure 1C and D].

Thirteen consecutive patients with LDH underwent the The basic operative procedure has already been
ILA for PELD by using a 7-mm diameter spinal full- described in our previous report. In addition to the
[9]
endoscopic system (Richard Wolf GmbH, Knittlingen, basic ILA procedure, the methods for manipulation of
Germany) between March and December 2016. All a high-speed drill and/or a small Kerrison rongeur are
patients had lateral radiculopathy resistant to medical described below.
treatment, epidural steroids, and/or nerve block. To
clarify the surgical benefit of minimal laminectomy with First, the endoscope sheath is placed on the surface of
the ILA for PELD, we did not exclude patients who the yellow ligament and then tilted toward a direction by
previously underwent discectomy at the same vertebral which the area requiring bone removal is at the center
level. However, we excluded patients with spinal of the endoscopic visual field. The vertebral laminae
canal stenosis who had been operated on using the are thinned by using a high-speed drill with a diameter
percutaneous endoscopic translaminar approach. [12] of 3.5 mm (NSK-Nakanishi Japan, Tokyo, Japan).
Subsequently, the residual thin layer is removed with a
All patients underwent the ILA for PELD at only one small Kerrison rongeur. Naturally thin bone areas, such
vertebral level. Neurological examination, preoperative as the inner border of the superior articular process
Mini-invasive Surgery ¦ Volume 1 ¦ June 30, 2017 57