How to Correctly Implant the Lamina Fixation Plate
The lamina fixation plate of the present invention comprises a first plate component and a second plate component that are slidably coupled to expand a gap in the lamina at the transection. An optional locking means is also provided for fixing the relative positions of the plate components like Elastic intramedullary nail in desired positions.
Insertion of the Screws
The Escalate Laminoplasty System TM (EScalate Surgical Technique) is a set of implants and instruments designed for a systematic approach to cervical laminoplasty. The system is composed of an Expandable Laminoplasty Plate, Base Laminoplasty Plate, Bone Screws for fixation, and a set of instruments to assist in implantation and removal of the device.
A 3.5-mm-diameter polyaxial screw is placed into the plate at the C1 lateral mass. The insertion is performed with fluoroscopic guidance.
We simulated bilateral screw entry points in 18 cadaveric spines using a 1-mm CT scan and 3-D reconstructions. The trajectories of each screw were compared with caliper measurements to determine the optimal diameter.
A safe zone was defined as the distance between the inferior pole of the lateral mass and the caudal edge of the mini-plate that avoided instrument-related complications3. Distancing the mini-plate from the inferior pole of the lateral mass by more than 5-6 mm at C3-C5 levels and 7-8 mm at C6-C7 levels did not ensure a safe plate placement due to the risk of screw facet violation.
Placement of the Plate
The placement of the plate is important for the stability of the replanted spinous process-lamina complex. Stability is a major factor in the fusion of the lamina-spinous process junction, thereby promoting bone healing.
Incorrect positioning of the mini-plate can cause impingement between the lateral mass and the mini-plate, which can lead to instrument-related complications. This occurs mainly when the mini-plate is located too caudally, as shown in the axial and sagittal computed tomography images (Fig. 3A and B).
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In order to avoid both screw facet joint violation and plate impingement, a safe zone should be defined. This should be a distance between the inferior pole of the lateral mass and the caudal edge of the mini-plate, corresponding to the lateral mass posterior surface length. For C3-C5, the median value is 4-to 5-mm, while for C6-C7, it should be 5-6 mm.
Adjustment of the Length of the Screws
The adjustment of the length of the screws is very important to correctly implant the lamina fixation plate. Shorter screws can prevent facet joint violation, but weak fixation strength caused by decreased screw length may cause screw pull-out.
Therefore, it is essential to adjust the screw length with an adjustable ratchet that can be turned with one hand. A fine micrometer motion can be achieved with these screw adjusters, but the accuracy of these small screws can only be guaranteed by a well-made screw with Narrow dynamic compression locking plate.
Through H&E staining on lumbar spine samples, we observed that the number of chondrocytes in the nucleus pulposus and hyaline tissue increased, while the annular fibrosus became thinner with increasing chondrocyte count. These results indicated that the chondrocytes of the intervertebral cartilage were sensitive to mechanical pressure and could change their number, arrangement, and morphology.
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Removal of the Screws
In addition to the screws that hold the plate to the bone, there are threaded pins that are anchored in the bone. These pins should penetrate the cortex on either side of the medullary space and only a few millimeters of the tip should protrude through the distal cortex and Humeral intramedullary nail.
The insertion of the screws should be performed with an adequate understanding of the spinal anatomy and a proper technique. There are several steps that should be taken in this process, including exposure, identification of entry points, pilot holes, pedicle wall checking, tapping and screw insertion.
There are different types of screws that are used in the insertion of these plates, including dynamic hip screws (DHS), parallel screws and headless screws. The DHS is used to bridge fractures of the femoral head and neck, while the parallel screws are often used for a fracture that has broken a bit more proximally in the femoral neck.
