Interspinous process spacer

The laminae are a part of the posterior arch of the vertebrae. The laminae comprise two flattened plates that extend medially from the pedicles and meet at the spinous process to form the posterior wall of the spinal foramen. A laminectomy is a procedure to remove all or part of the lamina and spinous process. This procedure is commonly performed to remove an intervertebral disc, or to decompress a nerve root. Following a decompression laminectomy, a spinal fusion is typically required to stabilize the spine, which results in some loss of mobility. There is therefore a need for a prosthetic device that can stabilize the spine following a laminectomy while maintaining some degree of flexibility.

Embodiments of an interspinous spacer that maintains spacing between a superior vertebra and inferior vertebra following a laminectomy. The interspinous spacer may include a superior arch engaging the spinous process of a superior vertebra and an inferior arch engaging the spinous process of an inferior vertebra. The superior arch and inferior arch may define a central opening in the interspinous spacer. In one exemplary embodiment, the superior arch and inferior arch may be provided with a saddle to receive the spinous processes of the adjacent superior and inferior vertebrae. Tethers may retain the spinous processes of the adjacent vertebra in the saddles.

In another exemplary embodiment, anchor plates may be disposed at the junction of the superior and inferior arches of the interspinous spacer for attaching the interspinous spacer to the pedicles of the compromised vertebra. The anchor plates may include openings for pedicle screws. The pedicle screws may pass through the openings in the anchor plates and thread into the pedicles to secure the interspinous spacer to the pedicles. Alternatively, or in addition, the interspinous spacer may include tethers that loop around the transverse processes of the compromised vertebra. A second set of tethers may pass around the spinous processes of the adjacent superior and inferior vertebrae.

FIG. 1 illustrates a vertebra as seen from above.

FIG. 2 illustrates two adjacent vertebrae as seen from one side.

FIG. 3 illustrates an exemplary interspinous spacer according to one embodiment.

FIGS. 4-8 illustrate a laminectomy procedure using the interspinous spacer shown in FIG. 3 .

FIGS. 9A-9C illustrate a tether used to secure the interspinous spacer.

FIG. 10 illustrates an alternate method of securing the interspinous spacer shown in FIG. 3 .

FIG. 11 illustrates an exemplary interspinous spacer according to one embodiment.

FIG. 12 illustrates an exemplary interspinous spacer according to one embodiment.

FIGS. 1 and 2 illustrate the structure of a vertebra indicated generally by the numeral 10 . The vertebra 10 comprises vertebral body 12 and a vertebral arch 14 . The vertebral body 12 comprises a dense ring of cortical bone 16 surrounding cancellous bone 18 . The vertebral arch comprises the pedicles 20 and laminae 22 , which together form an arch, and various spinal processes 26 - 32 that provide attachment points for ligaments and tendons. The pedicles 20 extend posteriorly from the lateral margins of the vertebral body 12 . The laminae 22 extend medially from the pedicles 20 and form the posterior wall of the spinal foramen 24 . The spinal processes include the spinous process 26 , two transverse processes 28 , and four articular processes 30 , 32 . The spinous process 26 extends posteriorly form the junction of the laminae 22 . The transverse processes 28 extend laterally from respective pedicles. The superior articular processes 30 and inferior articular processes 32 extend from the junction of the pedicles 20 and laminae 22 . The superior articular processes 30 of one vertebra 10 join with the inferior articular processes 32 of an adjacent vertebra 10 to form articulating joints called facet joints. The facet joints work in combination with the intervertebral disc 34 to allow relative movement of the vertebrae 10 .

FIG. 3 illustrates an interspinous spacer 50 to stabilize the spine following a laminectomy. In a typical laminectomy, the laminae 22 and spirious process 26 of one or more vertebrae 10 are removed creating a void between remaining superior vertebra and inferior vertebrae 10 adjacent the void. The interspinous spacer 50 shown in FIG. 3 is designed to replace one lamina 22 , however, those skilled in the art will recognize that the same design may be used to replace two or more consecutive lamina 22 . The interspinous spacer 50 may be secured by pedicles screws 56 , tethers 80 , or by a combination of pedicle screws 56 and tethers 80 .

The interspinous spacer 50 comprises a pair of anchoring plates 52 connected together by a superior arch 60 and an inferior arch 70 . The anchoring plates 52 may include an opening 54 to accommodate pedicle screws 56 , tethers 80 or other fastening devices for fastening the interspinous spacer 50 to the compromised vertebra 10 . The superior arch 60 and inferior arch 70 define a fully enclosed central opening 90 . The superior arch 60 and inferior arch 70 each include a saddle indicated respectively at 62 and 72 . The saddle 62 in the superior arch 60 receives the spinous process 26 of a superior vertebra 10 , while the saddle 72 in the inferior arch 72 receives the spinous process 26 of an inferior vertebra 10 . Small passages 64 , 74 may be formed in the superior and inferior arches 60 , 70 for tethers 80 . The engagement of the spinous processes 26 of the superior and inferior vertebra 10 maintains the desired spacing between the superior and inferior vertebrae 10 and prevents compression of the nerve root. The saddles 62 , 72 capture the spinous process 26 in a way that allows the spine to flex in the sagittal plane, but limits bending or shifting in the coronal plane. Further, the superior and inferior arches 60 , 70 may flex slightly allowing some vertical compression of the interspinous spacer 50 .

In one embodiment, the entire interspinous spacer 50 is a unitary construction made of a rigid or semi-rigid material to stabilize the spine. One suitable material is polyetheretherketone (PEEK), which is a semi-rigid material with some flexibility. In other embodiments, the saddles 62 , 72 may be constructed as separate components and fastened to the superior and inferior arches 60 , 70 . For example, the saddles 62 , 72 can be made of silicon with a polyethylene cover, and may be mounted to the interspinous spacer 50 as shown in FIG. 12 .

FIGS. 4-8 illustrate steps in a laminectomy procedure using the interspinous spacer 50 . FIG. 4 illustrates a portion of the lumbar spine. In this example, the L4 vertebra 10 requires a laminectomy. FIG. 5 illustrates the lumbar spine with the lamina 22 and spinous process 26 of the L4 vertebrae 10 removed creating a void between the L3 and L5 vertebrae 10 . With the lamina 22 removed, the spine is unstable. In FIG. 6 , the interspinous spacer 50 is positioned between the L3 and L5 vertebrae 10 to maintain decompression of the spinal canal. The saddles 62 and 72 of the superior arch and inferior arch receive, respectively, the spinous processes 26 of the L3 and L5 vertebrae 10 . In FIGS. 7 and 8 , pedicle screws 56 are inserted through screw holes in the anchor plates 52 to firmly attach the interspinous spacer 50 to the pedicles 20 of the compromised L4 vertebra 10 . To complete the procedure, tethers 80 are looped around the spinous processes 26 of the L3 and L5 vertebra 10 to retain the spinous processes 26 in their respective saddles 62 , 72 as described in U.S. Pat. No. 6,626,944, which is incorporated herein by reference.

FIGS. 9A-9C illustrates an exemplary tether 80 in more detail. The tether 80 comprises a cord made of polyethylene or other suitable material having a ring 84 at one end and a needle 82 at the opposite end as shown in FIG. 9A . The tether 80 is passed around the spinous process 26 and the needle 82 is then inserted through the ring 84 ( FIG. 9B ) to form a loop around the spinous process 26 . A metallic ferrell 86 slides over the end of the tether 80 and up against the ring 84 . The loop is tightened and the ferrell 86 is crimped. The excess cord is then cut flush with the ferrell 86 . In some embodiments of the invention, the tether 80 may pass around the superior and inferior arches 62 , 72 . In other embodiments, the superior and inferior arches 62 , 72 may include small passages 64 , 74 respectively through which the tether 80 may pass. In other embodiments, the tether 80 may comprise a simple strand or cord that can be looped around the processes and tied at the ends.

FIG. 10 illustrates an alternate method of securing the interspinous spacer 50 . As shown in FIG. 10 , the interspinous spacer 50 is held in place by two sets of tethers 80 . No pedicle screws 56 are used. A first set of tethers 80 pass around the transverse processes 28 of the compromised vertebra 10 and connect the transverse processes 28 to the anchor plates 52 . The second set of tethers 80 pass around the spinous processes 26 of the adjacent superior and inferior vertebrae 10 and connect to the superior and inferior vertebrae 10 to the superior and inferior arches 60 , 70 respectively.

FIG. 11 illustrates an alternate embodiment of the interspinous spacer 50 . This embodiment is similar to the embodiment shown in FIGS. 1-8 . Therefore, the same reference numerals are used to indicate similar components in the two embodiments. The embodiment shown in FIG. 10 comprises a superior arch 60 and an inferior arch 70 without anchoring plates 52 . The superior and inferior arches 60 , 70 join along a midline of the interspinous spacer 50 . The superior arch 60 includes a saddle to receive the spinous process 26 of a superior vertebra 10 , while the inferior arch 70 includes a saddle to receive the spinous process 26 of an inferior vertebra 10 . The interspinous spacer 50 is held in place by tethers 80 that loop around the spinous processes 26 of the adjacent of the adjacent superior and inferior vertebrae 10 as previously described.

The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.