Patent Application
20110172720
This invention relates generally to the treatment of spinal conditions, and more particularly, to the treatment of spinal stenosis using devices for implantation between adjacent spinous processes.
The clinical syndrome of neurogenic intermittent claudication due to lumbar spinal stenosis is a frequent source of pain in the lower back and extremities, leading to impaired walking, and causing other forms of disability in the elderly. Although the incidence and prevalence of symptomatic lumbar spinal stenosis have not been established, this condition is the most frequent indication of spinal surgery in patients older than 65 years of age.
Lumbar spinal stenosis is a condition of the spine characterized by a narrowing of the lumbar spinal canal. With spinal stenosis, the spinal canal narrows and pinches the spinal cord and nerves, causing pain in the back and legs. It is estimated that approximately 5 in 10,000 people develop lumbar spinal stenosis each year. For patients who seek the aid of a physician for back pain, approximately 12%-15% are diagnosed as having lumbar spinal stenosis.
Common treatments for lumbar spinal stenosis include physical therapy (including changes in posture), medication, and occasionally surgery. Changes in posture and physical therapy may be effective in flexing the spine to decompress and enlarge the space available to the spinal cord and nerves—thus relieving pressure on pinched nerves. Medications such as NSAIDS and other anti-inflammatory medications are often used to alleviate pain, although they are not typically effective at addressing spinal compression, which is the cause of the pain.
Surgical treatments are more aggressive than medication or physical therapy, and in appropriate cases surgery may be the best way to achieve lessening of the symptoms of lumbar spinal stenosis. The principal goal of surgery is to decompress the central spinal canal and the neural foramina, creating more space and eliminating pressure on the spinal nerve roots. The most common surgery for treatment of lumbar spinal stenosis is direct decompression via a laminectomy and partial facetectomy. In this procedure, the patient is given a general anesthesia as an incision is made in the patient to access the spine. The lamina of one or more vertebrae is removed to create more space for the nerves. The intervertebral disc may also be removed, and the adjacent vertebrae may be fused to strengthen the unstable segments. The success rate of decompressive laminectomy has been reported to be in excess of 65%. A significant reduction of the symptoms of lumbar spinal stenosis is also achieved in many of these cases.
Alternatively, the vertebrae can be distracted and an interspinous process device implanted between adjacent spinous processes of the vertebrae to maintain the desired separation between the vertebral segments. Such interspinous process devices typically work for their intended purposes, but some could be improved. For example, some current devices can migrate due to the constant bending and twisting of the spine. In addition, some other current devices that are less prone to migration restrict the range of motion for the patient.
Thus, a need exists for improvements in interspinous process devices.
The interspinous process device described herein includes a pair of plates, with each plate of the pair adapted to be located on opposite lateral sides of adjacent spinous processes, and a plurality of spikes located along the interior faces of at least an inferior or superior portion of each of the plates. The interspinous process device also may include a hinge along a medial portion of the plates to allow pivoting motion of the adjacent spinous process when the spine moves in flexion.
The interspinous process device of this invention is implanted such that one plate is located along one lateral side of a superior spinous process and an adjacent inferior spinous process with the other plate located along the opposite lateral side of the superior spinous process and the adjacent inferior spinous process. The spikes located along an interior surface of the plates are embedded in the spinous processes. In one embodiment, the spikes are located along both the superior and inferior interior portions of both plates. Embedding spikes in both the superior and inferior spinous processes prevents migration of the device and prevents compression of the adjacent vertebrae since the spikes and plates, which are substantially rigid, hold the adjacent spinous processes apart. In another embodiment, the spikes are located along only either the interior part of the superior portion of both plates or the interior part of the inferior portion of both plates. With this second embodiment, the adjacent spinous processes have some freedom of movement with respect to each other. A bumper may be located between the plates to limit spinal extension and prevent compression of the adjacent vertebrae and thus ensure adequate pain relief for the patient. The spikes also prevent migration of the device.
As used in this specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, the term “a member” is intended to mean a single member or a combination of members, and “a material” is intended to mean one or more materials, or a combination thereof. Furthermore, the words “proximal” and “distal” refer to directions closer to and away from, respectively, an operator (e.g., surgeon, physician, nurse, technician, etc.) who would insert the medical device into the patient, with the tip-end (i.e., distal end) of the device inserted inside a patient's body first. Thus, for example, the device end first inserted inside the patient's body would be the distal end of the device, while the device end last to enter the patient's body would be the proximal end of the device.
As used in this specification and the appended claims, the term “body” when used in connection with the location where the device is to be placed to treat lumbar spinal stenosis, or to teach or practice implantation methods for the device, means a mammalian body. For example, a body can be a patient's body, or a cadaver, or a portion of a patient's body or a portion of a cadaver.
As used in this specification and the appended claims, the term “parallel” describes a relationship, given normal manufacturing or measurement or similar tolerances, between two geometric constructions (e.g., two lines, two planes, a line and a plane, two curved surfaces, a line and a curved surface or the like) in which the two geometric constructions are substantially non-intersecting as they extend substantially to infinity. For example, as used herein, a line is said to be parallel to a curved surface when the line and the curved surface do not intersect as they extend to infinity. Similarly, when a planar surface (i.e., a two-dimensional surface) is said to be parallel to a line, every point along the line is spaced apart from the nearest portion of the surface by a substantially equal distance. Two geometric constructions are described herein as being “parallel” or “substantially parallel” to each other when they are nominally parallel to each other, such as for example, when they are parallel to each other within a tolerance. Such tolerances can include, for example, manufacturing tolerances, measurement tolerances or the like.
As used in this specification and the appended claims, the terms “normal”, perpendicular” and “orthogonal” describe a relationship between two geometric constructions (e.g., two lines, two planes, a line and a plane, two curved surfaces, a line and a curved surface or the like) in which the two geometric constructions intersect at an angle of approximately 90 degrees within at least one plane. For example, as used herein, a line is said to be normal, perpendicular or orthogonal to a curved surface when the line and the curved surface intersect at an angle of approximately 90 degrees within a plane. Two geometric constructions are described herein as being “normal”, “perpendicular”, “orthogonal” or “substantially normal”, “substantially perpendicular”, “substantially orthogonal” to each other when they are nominally 90 degrees to each other, such as for example, when they are 90 degrees to each other within a tolerance. Such tolerances can include, for example, manufacturing tolerances, measurement tolerances or the like.
Spikes 30 are designed to become embedded in the lateral surface of the spinous processes when plates 20 are squeezed laterally toward each other during implantation. Each spike 30 has a pointed or otherwise sharp tip to facilitate the engagement of each spike 30 with the bone of the spinous process into which that spike is to be embedded. With spikes 30 along the superior portion of each of plates 20 embedded in the lateral surfaces of both sides of a superior spinous process and spikes 30 along the inferior portion of each of plates 20 embedded in the lateral surfaces of both sides of an adjacent inferior spinous process, plates 20, which are substantially rigid, maintain the spacing between the adjacent vertebrae. A physician can distract the adjacent vertebrae to decompress and relieve pressure on pinched nerves and then implant device 100 to maintain the desired spacing and distraction for the patient. Thus, embedding spikes 30 in both the superior and inferior spinous processes prevents migration of device 100 and prevents compression between the adjacent vertebrae.
As shown in
First superior plate 20a is connected to first inferior plate 20b so that first inferior flange 21a and first superior flange 21b abut and overlap to form a first half lap joint 25 to allow first superior plate 20a to move with respect to first inferior plate 20b. In this orientation, post 22′ extends through first superior opening 26a. The diameter of first superior opening 26a should be slightly larger than the diameter of post 22′ to allow first superior plate 20a to pivot or otherwise move with respect to first inferior plate 20b. In addition, first superior end wall 23a, first inferior end wall 23b, the inferior end of first inferior flange 21a, and the superior end of first superior flange 21b are preferably curved to allow relative pivoting motion between first superior plate 20a and first inferior plate 20b. Second superior plate 20c is connected to second inferior plate 20d along second inferior flange 21c and second superior flange 21d, which abut and overlap to form a second half lap joint 27 to allow second superior plate 20c to move with respect to second inferior plate 20d. The diameter of second superior opening 26c should be slightly larger than the diameter of post 22′ to allow second superior plate 20c to pivot with respect to first inferior plate 20b and second inferior plate 20d. The diameter of first inferior opening 26d may be slightly smaller than the diameter of the end portion of post 22′ so that the end portion of post 22′ fits in first inferior opening 26d in an interference fit. Alternatively, second inferior plate 20d could be otherwise fixed to post 22′. This arrangement allows first inferior plate 20b and second inferior plate 20d to be substantially fixed with respect to each other yet allow first superior plate 20a to pivot with respect to first inferior plate 20b and second inferior plate 20d. Similarly, second superior plate 20c is thus allowed to pivot with respect to first inferior plate 20b and second inferior plate 20d. Preferably, a hub 31 fits over the end of post 22′ in an interference fit, or is otherwise fixed to post 22′, to hold first superior plate 20a, first inferior plate 20b, second superior plate 20c and second inferior plate 20d together so they all operate as a single unit.
As discussed in connection with the embodiment shown in
Device 100 and 100′ can be constructed with various biocompatible materials such as, for example, titanium, titanium alloy, surgical steel, biocompatible metal alloys, stainless steel, Nitinol, plastic, polyetheretherketone (PEEK), carbon fiber, ultra-high molecular weight (UHMW) polyethylene, and other biocompatible polymeric materials. The material of device 100 and 100′ can have, for example, a compressive strength similar to or higher than that of bone. Alternatively, device 100 and 100′ may have a lower elastic modulus than bone.
While various embodiments of an interspinous process device have been described above, it should be understood that they have been presented by way of example only, and not limitation. Many modifications and variations will be apparent to the practitioner skilled in the art. The foregoing description of an interspinous process device is not intended to be exhaustive or to limit the scope of the claimed invention. It is intended that the scope of the invention be defined by the following claims and their equivalents.
