Clamp for spinal cross connecting device

A clamp for attaching a cross connecting device to a spinal fixation system comprising an outer body and an inner body. The outer body defines an internally threaded bore and an outer body cavity, and the inner body defines an inner body cavity. The inner body is at least partially disposed within the outer body. A pin is provided for connecting the inner and outer bodies to each other, while allowing for a limited amount of movement therebetween. A set screw suitable for being driven into the internally threaded bore is provided for securing the inner body to the spinal fixation system.

BACKGROUND

1. Technical Field

The present application relates to connection systems for spinal fixation devices, including cross connecting devices for spinal fixation bone anchors such as bone screws and hooks.

2. Related Art

The bones and connective tissue of an adult human spinal column includes more than twenty vertebrae coupled sequentially to one another by a tri-joint complex. The complex includes an anterior disc and two posterior facet joints. The anterior discs of adjacent bones are cushioned by cartilage spacers referred to as intervertebral discs. The vertebrae are each anatomically categorized into one of four classifications: cervical, thoracic, lumbar, and sacral. The cervical portion of the spine, which comprises the top of the spine up to the base of the skull, includes the first seven vertebrae. The intermediate twelve vertebrae are thoracic vertebrae, and connect to the lower spine comprising five lumbar vertebrae. The base of the spine includes the sacral bones (including the coccyx).

The spinal column is highly complex in that it includes over twenty vertebrae coupled to one another for housing and protecting critical elements of the nervous system. These elements of the nervous system have seemingly innumerable peripheral nerves and circulatory bodies in close proximity to each other. Despite its complexity, the spine is a highly flexible structure, capable of a high degree of curvature and twisting in many different directions.

However, genetic or developmental irregularities, trauma, chronic stress, tumors and disease can result in spinal pathologies that either limit this range of motion, or threaten the critical elements of the nervous system protected by the spinal column. A variety of systems have been disclosed in the art which provide some degree of immobilization of the spine by implanting artificial assemblies in or onto the spinal column. These assemblies include anterior, posterior, and lateral assemblies. Lateral and anterior assemblies can be coupled to the anterior portion of the spine, typically between vertebral bodies. Posterior spinal fixation systems generally include a pair of rods, which can be aligned along an axis to which the bones are to be disposed, and which are then attached to the spinal column by spinal fixation bone anchors, such as pedicle hooks and/or pedicle screws. Hooks can be coupled to the lamina or attached to transverse processes, while screws can be inserted through pedicles. In order to provide enhanced torsional rigidity, these structures can include cross-connecting devices for coupling the rods together in a direction that is generally transverse with respect to the axis of the rods. These cross-connecting devices can be coupled directly to the rods themselves, or can be attached to the bone anchors.

A number of improvements to prior cross-connecting devices are desirable. For example, it is desirable to provide clamps for cross-connecting devices that are highly adjustable in several degrees of freedom.

SUMMARY

Spinal fixation devices, cross connecting devices for spinal fixation devices, and components thereof, including clamps for cross connecting devices, are described herein.

According to one aspect of the present disclosure, a clamp for attaching a cross connecting device to a spinal fixation system comprises an outer body that defines an internally threaded bore and an outer body cavity, an inner body that is at least partially disposed within the outer body cavity, the inner body defining an inner body cavity, a pin for connecting the outer and inner bodies to each other, and a set screw suitable for being driven into the internally threaded bore for securing the inner body to the spinal fixation system.

The spinal fixation system can include a rod, and the outer body can include a clearance slot for allowing the rod to extend through the outer body cavity. The inner body can include a slotted rod-receiving interface. The slotted rod-receiving interface can include a rod-receiving portion configured to snap onto the rod. The rod-receiving portion of the slotted rod-receiving interface can be configured to be tightened onto the rod as the set screw is driven into the internally threaded bore. The slotted rod-receiving interface can further include at least one expansion portion.

The outer body can include a slot that extends between the internally threaded bore and the outer body cavity. The inner body can include a lever portion that extends through the slot into the internally threaded bore.

The clamp can further comprise a stop feature for limiting pivoting movement between the outer and inner bodies about the pin. The stop feature can include a tab and a mating groove.

According to another aspect of the present disclosure, a spinal fixation system can comprise a spinal fixation device, a rod connected to the spinal fixation device, a cross-connecting device, and a clamp for connecting the cross-connecting device to the rod. The clamp can comprise an outer body that defines an internally threaded bore and an outer body cavity, an inner body that is at least partially disposed within the outer body cavity, the inner body defining an inner body cavity configured to receive at least a portion of the spinal fixation device body, a pin for connecting the outer and inner bodies to each other, and a set screw suitable for being driven into the internally threaded bore for securing the inner body to the rod.

The outer body of the clamp can include a clearance slot for allowing the rod to extend through the outer body cavity. The inner body of the clamp can include a slotted rod-receiving interface. The slotted rod-receiving interface includes a rod-receiving portion can be configured to snap onto the rod. The rod-receiving portion of the slotted rod-receiving interface can be configured to be tightened onto the rod as the set screw is driven into the internally threaded bore. The slotted rod-receiving interface can further include at least one expansion portion.

The outer body of the clamp can include a slot that extends between the internally threaded bore and the outer body cavity. The inner body of the clamp can include a lever portion that extends through the slot into the internally threaded bore.

The clamp of the spinal fixation system can further comprise a stop feature for limiting pivoting movement between the outer and inner bodies about the pin. The stop feature can include a tab and a mating groove.

The spinal fixation device can include a spinal fixation device body, and the inner body can be configured to receive at least a portion of the spinal fixation device body.

These and other features, aspects, and embodiments of the invention are described below in the section entitled “Detailed Description.”

DETAILED DESCRIPTION

FIGS. 1A and 1Bshow a spinal fixation system10that includes a plurality of spinal fixation devices12and a pair of rods14. A cross connecting device20is also provided for connecting opposing rods14and spinal fixation devices12.

The spinal fixation devices12can include pedicle screws as shown, and can include other types of bone anchors, including hooks. Each fixation device12includes a body12a, a shank12b, and a set screw12c. There are various known body styles, including the open style shown. Alternative styles include closed, reduction, and offset body styles. The shank12bcan be cannulated or non-cannulated. The shank12bcan be monoaxial or mutliaxial relative to the body12a. Each shank12bcan include a single-lead thread as shown, or can include multiple-lead threads, where there are two or more threads that wind along the shank, usually equally spaced apart from each other. Instead of a shank12b, one or more of the bodies12acan include, or be attached to, a hook that can be attached to vertebrae, for example in the cervical area where vertebrae are small.

Once the spinal fixation devices12are secured to bone, the rods14can be placed along the bodies12aand secured in place by the set screws12c. Then, once the rods14are secured to the spinal fixation devices12, the cross connecting device20can be placed over bodies12aof a pair of spinal fixation devices12as shown inFIGS. 1A and 1B.

The cross connecting device20includes a fixable pivot junction22, a first connection member24, a second connection member26, and clamps28. The cross connecting device20can be lengthwise and angularly adjusted, thereby accommodating for translational, rotational, and angular misalignments between the connected spinal fixation devices12. More specifically, the first and second connection members24and26are connected by the fixable pivot junction22such that the fixable pivot junction22allows the first and second connection members24and26to be translationally, rotationally, and angularly repositioned relative to each other. Once desired adjustments are made, the fixable pivot junction22can be locked, and the clamps28can be secured to the rods14as described in greater detail below.

FIG. 2shows an enlarged perspective view of a clamp28attached to the body12aand rod14of the spinal fixation device12.FIG. 3shows an exploded view of the clamp28, andFIG. 4shows a cross-sectional view of the clamp28. The clamp28includes an outer body30, an inner body32, a pin34, and a set screw36.

The outer body30includes an outer-body cavity38within which the inner body32resides. The outer body30also has a clearance slot40to allow the rod14to connect to the inner body32. The outer body30also has an internally-threaded bore42for receiving the correspondingly-threaded set screw36.

The outer body30and the inner body32are secured together by the pin34. The outer and inner bodies30and32include pin holes44that are aligned and receive the pin34. The pin holes44can be sized such that the pin34is press-fit into one or more of the pin holes44so that once the pin34is installed into the holes44, it cannot easily be removed from the holes44. An alternative type of connecting element can be used in place of the pin34, such as a bolt or rivet.

The clamp28preferably includes a stop feature for preventing, or at least limiting, pivoting movement between the outer and inner bodies30and32about the pin34. In the illustrated embodiment, a tab46on the underside of the outer body30engages a mating groove48of the inner body32, thereby restricting the outer and inner bodies30and32from pivoting about the pin34. Thus, the combination of the tab46and mating groove48constitute an embodiment of a stop feature. Alternatively, the tab46can be provided on the inner body30and the mating groove can be provided on the outer body32, opposite the configuration shown. Other alternative embodiments can include a pin, rivet, bolt, or other device that can be used for restricting pivoting about the pin34. Such alternatives can be used with, or in place of, the combination of the tab46and mating groove48.

The inner body32has a slotted rod receiving interface50. The interface50includes a rod-receiving portion50a, a first expansion portion50b, and a second expansion portion50c. The rod-receiving portion50ais defined by an at least somewhat circular geometry that is slightly smaller than the diameter of the rod14and is configured to snap onto the rod14. The expansion portions50band50care provided above the rod-receiving portion50a. The expansion portions50band50callow the rod-receiving portion50ato expand without permanently deforming the inner body32as the clamp28is snapped onto a rod14. The slightly undersized rod-receiving portion50aresults in a friction fit with the rod14.

The inner body32has an inner-body cavity52that is configured to fit over a body12aof a spinal fixation device12. The fit between the inner body32and the body12aof the spinal fixation device12is preferably such that a relatively small amount of clearance exists between them along the longitudinal axis of the rod14, and that more substantial clearance exists in the medial region52aand lateral region52b(shown inFIG. 5) of the inner-body cavity52. The additional clearance in the medial and lateral regions52aand52ballows for some variation in the orientation of the body12a, for example in a plane perpendicular to the longitudinal axis of the rod14.

The outer body30includes a slot54that extends between the threaded bore42and the outer-body cavity38. The slot54provides an opening for a lever portion56of the inner body32. The lever portion56is a protruding tapered geometry that extends into the threaded bore42through the slot54.

Referring now also toFIG. 5, during a surgical procedure the spinal fixation devices12and rods14are placed in a configuration such as is shown inFIGS. 1A and 1B. The cross connecting device20is then placed over two spinal fixation devices12and each clamp28is snapped onto a construct rod14. In order for this to occur, the set screw36is partially backed out of the threaded bore42to allow the inner body32to spring open to accept the rod14into the rod-receiving portion50aof the rod receiving interface50. The set screw36can then be tightened by driving the set screw36into the threaded bore42. As the set screw36is threaded into the outer body30, it eventually contacts the lever portion56of the inner body32. Once the set screw36contacts the lever portion56, the continued driving of the set screw36causes the set screw36to drive against the lever portion56and urge the lever portion56to cause the inner body32to pivot relative to the outer body30about the pin34. However, the pivoting motion is restricted due to the limiting action of the tab46of the outer body30against the mating groove48of the inner body32. Thus, continued tightening of the set screw36against the lever portion56causes the rod-receiving portion50ato tighten against the rod14, thereby clamping the clamp28onto the rod14.

The inner body32also includes a tapered surface58opposite the lever portion56. The tapered surface58includes connection-member-receiving region60. The connection-member-receiving region60is provided for attaching the clamp28to a connection member such as one of the first and second connection members24and26shown inFIGS. 1A and 1B. The mechanism used for attaching a connection member to the clamp28can vary, but examples can include press-fitting the connection member into the connection-member-receiving region60; securing the connection member into the connection-member-receiving region60using a set screw, pin, or bolt; and providing corresponding threaded surfaces on the connection member and connection-member-receiving region60so that the connection member can be threaded into the connection-member-receiving region60.