Hirabayashi et al. simplified the Z-plasty described by Oyama in the early 1980s with his unilateral expansive open-door laminoplasty [4
]. In this technique, a hinge is created on one side of the lamina-spinous process-ligamentum flavum complex. This allows the roof of the canal to be opened on the contralateral side leading to an expansion of the spinal canal.
Most commonly, laminoplasty is performed from C3 to C7 and all these levels need to be exposed. This starts with a midline longitudinal posterior incision from the occipital protuberance down to the T1 spinous process. With electrocautery, dissection proceeds through the midline fascia and ligamentum nuchae and the spinous processes from C2 to T1 are exposed. Levels can be identified by palpation and visualization of the prominent, bifid C2 spinous process. Preserve the supraspinous and interspinous ligaments at the proximal and distal extents of the exposure during this approach but Bovie electrocautery can be used to incise these ligaments in the midline at the planned laminoplasty and foraminotomy levels. Also preserve the muscular attachments to C2 as much as possible to minimize risk of postoperative kyphotic deformity between C2 and C3. This is facilitated by first exposing the C7 lamina, retracting the paravertebral muscles at this level, and continuing this dissection rostrally to the upper part of the C3 lamina. Complete this midline, subperiosteal dissection of the paravertebral muscles for the C3 to C7 spinous processes and retract these muscles laterally off the spinous processes, laminae, and medial aspect of the facets. Staying in the natural, avascular, subperiosteal plane prevents damage to the paraspinal muscles and minimizes blood loss. shows the exposure required to perform a laminoplasty. This dissection needs to be extended as far as the lateral masses but the facet capsules must be preserved unless fusion is being performed. Hemostasis at all times can be achieved with monopolar or bipolar electrocautery.
Figure 3 Intraoperative photo showing laminoplasty exposure. Following midline dissection along the avascular subperiosteal plane, paraspinal muscles are retracted laterally and the spinous processes, lamina, and medial aspect of the facets should be completed (more ...)
Again, the C2 extensor muscular attachments do not need to be released. If, however, a decompression is necessary at the C2 level and undercutting of the lamina with a burr is not adequate, a laminoplasty can be done at C2 as well. In this case, the C2 extensor muscles can be released or taken off with a thin osseous sleeve and subsequently sutured back down to the C2 dorsal structures. If a foraminotomy is planned at C2-C3, the extensors on the inferior half of C2 are released so the facets can be visualized adequately. At this point, once the soft tissues have been reflected off the spinous processes and laminae, retractors can be placed on the sides of the wound and, if necessary, rostrally and caudally, to facilitate visualization. The microscope may also be extremely helpful for visualization, especially during foraminotomy, decompression, and creation of the laminar osteotomies.
In the expansive open-door laminoplasty, the opening side of the lamina should be cut before the hinged side to minimize blood loss. The opening side is usually placed on the side with worse radicular symptoms or more stenosis because, on this side, it is technically easier to perform a foraminotomy to decompress the neuroforamen. If it is necessary to perform a foraminotomy on the hinged side, this should be done first to prevent detachment of the lamina and because this is technically more demanding. Using controlled, side-to-side brushing motions with a 2 or 3
mm cutting burr or high-speed microdrill, a trough is made at the junction of the lamina and lateral mass from C3 to C7 by decorticating the posterior aspect of the lamina (see ). Extra caution should be used at the superior aspect of the lamina, where there is no ligamentum flavum to protect the dural sac. The troughs, created rostral to caudal from one level above to one level below the stenotic levels, should be perpendicular to the lamina. The facets should not be violated. Following thinning of the lamina down to a thin cortical layer, use a curette to free the ligamentum flavum off the inferior aspect of the C7 lamina. Complete the laminar cuts just medial to the pedicles with a 2 or 3
mm Kerrison punch by removing the thin rim of remnant lamina and associated ligamentum flavum from caudal to rostral. Epidural venous bleeding can be controlled with thrombin gel and bipolar electrocautery.
Figure 4 Sawbones model of an open-door laminoplasty. A trough has been drilled in the lamina at the lamina-lateral mass junction with a burr until there is a thin remnant of lamina left. This cut has been completed with a Kerrison punch (a). After the complete (more ...)
Next, for the “hinged” side of the laminoplasty, another trough is made at the junction of the lamina and lateral mass with minimal disruption of the facet capsule to prevent postoperative instability. While a 2
mm cutting burr or high-speed drill can be employed for this portion of the procedure, we find that a 6
mm diamond burr is useful to cut the outer cortex in the process of creating a greenstick fracture on the hinged side as it minimizes the risk of completely breaking through the inner cortex of the lamina. This large burr tip also helps create a slightly wider trough on this hinged side so the walls of the trough do not contact each other when the door is opened which would limit the amount of decompression. Again, the lamina is thinned with a burr by removing the outer cortex and approximately one half of the cancellous bone. Do not violate the inner cortex which will act as a hinge. To prevent excessive thinning of the lamina on the hinged side and complete dissociation of the entire lamina, it is helpful to periodically assess the amount of “give” in the spinous process when it is manipulated and to use the depth of the lamina on the opened side as a reference for how deep the trough should be on the hinged side. Additionally, a curette can be placed on the open side and pulled upwards. When motion in the lamina is seen with this maneuver, the trough on the hinged side is complete. The top and bottom laminae of the open side which will be included in the laminoplasty can be separated from adjacent levels with a Kerrison Rongeur to cut the lamina and attached ligamentum flavum. This creates three free borders for the “door” which can now hinge open.
Once the laminae are thinned sufficiently, the posterior elements are more flexible and the lamina can be opened very gradually and carefully by additional thinning of the hinged bone, pulling the spinous process toward the hinged side, and lifting the lamina off the spinal cord with a curet on the opening side. Opening the laminae as a single unit preserves the intraspinous ligaments and dorsal structures that help stabilize the spine. This can be accomplished by opening the lamina at each level gradually and to the same degree as the other. In this way, the gap on the open side between the lamina and facet is increased and a greenstick fracture is established along the trough on the hinged side. If this step is performed with too much force or speed, the inner cortex on the hinged side can fracture. In this case, laminectomy with fusion or stabilization of the hinged side is required. Additionally, if control of the lamina is lost and the door inadvertently snaps closed, this can injure the spinal cord. A Penfield dissector or curette can be helpful to expand the opening and the lamina can be rotated towards the hinged side with a Kocher (see ). A Woodsen probe or elevator can be used to release any adhesions between the dura and ventral lamina on the opened side. Laminar opening is made easier with posterior elements that are more pliable, and this can be achieved with division of the supraspinous and interspinous ligaments at C2-C3 and C7-T1 and/or release of the ligamentum flavum on the opening side of the lamina. Once pulsatile flow in the dura is noted, which is usually at about 8–10
mm of opening, adequate canal expansion has been achieved. Hemostasis is achieved with gelfoam or surgicel and epidural bleeders are controlled with bipolar electrocautery. Bony bleeding is controlled with bone wax on a kittner or other local hemostatic agents.
In his initial description, Hirabayashi stabilized the laminae in an open position with sutures through the facet capsule and spinous processes on the hinged side. Titanium miniplates with or without allograft or autograft, allograft stabilized with CG clips, stainless steel wiring, facet cables with and without allograft, various suture techniques, ceramic implants, bone anchors placed through the lateral mass, and various structural wedge allografts and autografts are other modified techniques that have been described to keep the door propped in the open position [6
]. The senior authors prefer either a suture anchor or miniplate for initial stabilization.
Suture anchors are a simple way to maintain the opening of the laminae. We find them to be a safe and time-efficient method that minimizes the risk of disrupting the facet joints and nerve roots. In addition, this technique does not require grafting or fixation of the lamina to the lateral mass. The suture anchors are placed into the lateral masses on the hinged side (Figures and ). We make a hole in the base of the spinous process using a right-angle dental drill with a 2
mm burr tip. Once the laminae are hinged open, a Keith needle is used to bring the nonabsorbable suture from the suture anchor in the lateral mass through the drill hole in the spinous process (). Appropriate tension on the suture is achieved with a slip knot and then square knots are tied under tension to maintain the laminar opening ().
Figure 5 Once the door is opened, the laminae can be held in the open position with suture anchors. Suture anchors are placed into the lateral masses of the hinge as shown in (a) and (b). Next, the suture anchor is brought through a drill hole in the spinous process (more ...)
Our other preferred fixation method involves using titanium miniplates and allograft spacers to hold the laminae open, as shown in . Once the laminae are expanded, the appropriate allograft size is ascertained by inserting a trial spacer into the laminar opening (). We then choose a double pre-bent miniplate of appropriate length which can be fixed to the allograft via a center screw hole. The miniplate-allograft construct is then placed in the laminar opening such that the cut laminar edges are wedged securely in the ends of the allograft that are prenotched. The graft should fit securely in the laminar gap. We then secure the miniplate with one or two self-tapping 2.0
mm cortex screws on both the laminar and lateral mass side.
Sawbones model (a) and intraoperative photo (b) showing miniplate and allograft placed in the laminar opening. The miniplate has been fixed with 2 screws on both the laminar and lateral mass side.
For titanium miniplate fixation, once the laminae are expanded, use a trial spacer to determine the appropriate allograft size.
We have found both suture anchors and miniplate fixation to be reasonable methods of maintaining the laminar opening, as shown in .
Axial CT scans of patients following expansive open-door laminoplasty. The laminar opening has been maintained with suture anchors (a) and miniplate fixation (b).