FIELD OF THE INVENTION

The present invention relates to an improved device for use in a laminoplasty procedure, more particularly, a continually adjustable expandable laminoplasty device is disclosed in several embodiments employing a gear mechanism to adjust the distance between a superior plate and a lower or inferior plate.

BACKGROUND OF THE INVENTION

Arthritis in the cervical spine can lead to narrowing of the spinal canal at multiple levels throughout the neck. When the narrowing becomes severe, it can lead to compression of the spinal cord, referred to as “myelopathy.”

Corrective surgical procedures have one goal which is to take pressure off the spinal cord and create more space in the spinal canal. When the disease is only present at only one or two levels, a procedure commonly performed is called, “Anterior Cervical Decompression and Fusion (ACDF).” The surgeon removes the disc and bone spurs compressing the spinal cord from the front of the neck and then fuses the two levels together.

A “fusion” procedure relies on bone formation between two spinal levels until they are united. This process can take up to 6 months to be completely solid or “healed.” When a fusion fails to heal after 8-12 months, this is then considered a “non-union”. Some surgeons prefer to take pressure off the spinal cord from the back of the neck when three or more levels of compression are involved.

To take pressure off the spinal cord from the back of the neck, the surgeon must remove portions of the bones, called “laminectomy,” which creates more space for the spinal cord. Because the removal of these bones disrupts the attaching ligaments and structures in the neck, this can cause gradual neck deformity or instability. To help prevent this from occurring, laminectomy is combined with a fusion procedure using screws and rods to hold the vertebral segments together until bone grows and fuses them to one another.

Arthritis in any joint, including the spine, can cause significant pain with motion. Because spinal cord compression and myelopathy typically occur in the setting of advanced arthritis, the elimination of motion with a fusion procedure also may help decreased pain associated with arthritis in the spine. However, there are some patients who have evidence of spinal cord compression at multiple levels with myelopathy, but do not complain of any neck pain. These patients may be good candidates for cervical laminoplasty.

Cervical laminoplasty, a procedure first described in Asia, involves creating more space for the spinal cord while avoiding fusion and maintaining spinal motion. Several different types of procedures have been described, but they all involve the same basic concepts. The surgeon cuts a portion of the lamina bone all the way through allowing the spinal canal to be enlarged. The lamina forms a rigid roof over the spinal canal, a laminoplasty effectively props that roof open thus enlarging the spinal canal. This procedure is performed from the back of the neck and involves creating an “opening door hinge” with the bones to create more space for the spinal canal instead of removing portions of the bones as done with laminectomy, thus avoiding disruption of some of the supporting structures. Small plates and screws have been designed to hold open the door-hinge and maintain the increased space for the spinal canal. The spinal segments are not fused together, and post-operative motion is encouraged to avoid any residual stiffness following the procedure.

Cervical laminoplasty procedures have employed plates for maintaining the opening at a desired distance. Many patents have been granted on such devices. Most laminoplasty plates are not adjustable in length. A few are adjustable in increments.

The present invention, as described hereinafter, provides a continuously adjustable length capability giving the surgeon the ability to optimally set the device.

SUMMARY OF THE INVENTION

An expandable laminoplasty device has a superior plate, an inferior plate, threaded post having external threads, the threaded post affixed to one of the superior plate or the inferior plate, and a gear nut, the gear nut has internal threads configured to engage external threads of the threaded post. The gear nut is held in one of the superior plate or inferior plate not affixed to the threaded post and wherein the superior plate or inferior plate not affixed to the threaded post has an end with a slot or channel to receive the threaded post and a side opening to receive and hold the gear nut. Rotation of the gear nut engages the external threads of the threaded post thereby coupling the superior plate to the inferior plate to form the expandable laminoplasty device. Rotation of the gear nut causes relative movement of the superior plate and inferior plate from contracted to expanded positions wherein stopping the rotation of the gear nut fixes an amount of linear expansion between the superior and inferior plates.

The threaded post preferably has helical threads and the gear nut has complimentary helical threads. The threaded post has a pair of flats extending along the length of the threaded post. The slot or channel is an oval opening with a pair of flat sides, the flat sides prevent rotation of the threaded post while allowing linear movement of the threaded post into or out of or within the slot or channel.

In some embodiments, the threaded post has a pair of ends, a first end rigidly fixed to the superior plate or inferior plate and a second end for entering the slot or channel and threadingly engaging the gear nut. In another embodiment, the threaded post has a first end with an opening for receiving a pin, the threaded post when affixed to the superior plate having a pair of openings to hold the pin allows the superior plate to pivot about the threaded post. In all these embodiments, rotational movement of the gear nut provides a continuous adjustment of the movement between the contracted position and the expanded position.

The superior plate has a hooked end configured to engage a cut lamina of a cervical vertebra. The hooked end has an internal surface with ridges to contact and engage the lamina. The superior plate has a pair of holes to receive fasteners to attach the superior plate to the cut lamina bone.

The inferior plate has an end configured to contact the bone of a cervical vertebra. The end of the inferior plate has an inner surface for contacting the bone, the inner surface having a plurality of ridges to contact the bone. The end of the inferior plate has a pair of holes for receiving fasteners to affix the inferior plate to the cervical bone.

In other embodiments, an expandable laminoplasty device has a superior plate, an inferior plate, a racked gear post having a plurality of gear teeth, the racked gear post affixed to one of the superior plate or the inferior plate, and a pinion gear. The pinion gear has a plurality of gear teeth configured to engage the gear teeth of the racked gear post. The pinion gear is held in one of the superior plate or inferior plate not affixed to the racked gear post, wherein the superior plate or inferior plate not affixed to the racked gear post has an end with a slot or channel to receive the racked gear post and a side opening to receive and hold the pinion gear. Rotation of the pinion gear engages the gear teeth of the racked gear post thereby coupling the superior plate to the inferior plate to form the expandable laminoplasty device. Rotation of the pinion gear causes relative movement of the superior plate and inferior plate from contracted to expanded positions wherein stopping the rotation of the pinion gear fixes an amount of linear expansion between the superior and inferior plates. The racked gear post has the plurality of gear teeth complimentary to the plurality of gear teeth of the pinion gear. The racked gear post is substantially rectangular or square in cross section with one racked side and three flat sides extending along the length of the racked gear post. The slot or channel is an opening with flat sides, the flat sides prevent rotation of the racked gear post while allowing linear movement of the racked gear post into or out of or within the slot or channel. The racked gear post has a pair of ends, a first end rigidly fixed to the superior plate or inferior plate and a second end for entering the slot or channel and engaging the pinion gear. The racked gear post has a first end with an opening for receiving a pin, the racked gear post when affixed to the superior plate having a pair of openings to hold the pin allows the superior plate to pivot about the racked gear post. Rotational movement of the pinion gear provides a continuous adjustment of the movement between the contracted position and the expanded position. The superior plate has a hooked end configured to engage a cut lamina of a cervical vertebra. The hooked end has an internal surface with ridges to contact and engage the lamina. The superior plate has a pair of holes to receive fasteners to attach the superior plate to the cut lamina bone. The inferior plate has an end configured to contact the bone of a cervical vertebra, wherein the end of the inferior plate has an inner surface for contacting the bone, the inner surface having a plurality of ridges to contact the bone. The inferior plate has a pair of holes for receiving fasteners to affix the inferior plate to the cervical bone.

In other embodiments, the assembly includes a second post spaced from the racked gear post, wherein the racked gear post has the gear teeth facing inwardly and the gear is positioned in an central location on one of either the superior plate or inferior plate to expand or contract the assembly. The second post has a rectangular or square cross section. The second post has four flat sides. The combination of the second post the racked gear post fit into the slot or opening of the inferior or superior plate and prevents rotation of the two plates while allowing linear movement by the rotation of the pinion gear.

The present invention allows for the following methods to perform a laminoplasty procedure.

A method of performing a laminoplasty comprises the steps of preparing a cervical vertebra by cutting through a lamina and partially cutting through the lamina at a spaced second location; providing an expandable laminoplasty device having: a superior plate; an inferior plate; a threaded post having external threads, the threaded post affixed to one of the superior plate or the inferior plate; a gear nut, the gear nut having internal threads configured to engage external threads of the threaded post, the gear nut being held in one of the superior plate or inferior plate not affixed to the threaded post, wherein the superior plate or inferior plate not affixed to the threaded post has an end with a slot or channel to receive the threaded post and a side opening to receive and hold the gear nut; and wherein the rotation of the gear nut engages the external threads of the threaded post thereby coupling the superior plate to the inferior plate to form the expandable laminoplasty device, rotation of the gear nut causes relative movement of the superior plate and inferior plate from contracted to expanded positions wherein stopping the rotation of the gear nut fixes an amount of linear expansion between the superior and inferior plates; positioning the expandable laminoplasty device in a contracted position on the vertebra with a hooked end of the superior plated on the cut lamina and the inferior plate on the lateral mass of the vertebra; fastening ends of both superior and inferior plates to the cut lamina and the lateral mass respectively using fasteners; and rotating the gear nut to expand the expandable laminoplasty device to a location enlarging a spinal canal opening of the vertebra completing the laminoplasty.

A method of performing a laminoplasty comprises the steps of preparing a cervical vertebra by cutting through a lamina and partially cutting through the lamina at a spaced second location; providing an expandable laminoplasty device having: a superior plate; an inferior plate; a racked gear post having a plurality of gear teeth, the racked gear post affixed to one of the superior plate or the inferior plate; a pinion gear, the pinion gear having a plurality of gear teeth configured to engage the gear teeth of the racked gear post, the pinion gear being held in one of the superior plate or inferior plate not affixed to the racked gear post, wherein the superior plate or inferior plate not affixed to the racked gear post has an end with a slot or channel to receive the racked gear post and a side opening to receive and hold the pinion gear; and wherein the rotation of the pinion gear engages the gear teeth of the racked gear post thereby coupling the superior plate to the inferior plate to form the expandable laminoplasty device, rotation of the pinion gear causes relative movement of the superior plate and inferior plate from contracted to expanded positions wherein stopping the rotation of the pinion gear fixes an amount of linear expansion between the superior and inferior plates; positioning the expandable laminoplasty device in a contracted position on the vertebra with a hooked end of the superior plated on the cut lamina and the inferior plate on the lateral mass of the vertebra; fastening ends of both superior and inferior plates to the cut lamina and the lateral mass respectively using fasteners; and rotating the gear nut to expand the expandable laminoplasty device to a location enlarging a spinal canal opening of the vertebra completing the laminoplasty.

