Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1999-10-20
2001-06-26
Mancene, Gene (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
Reexamination Certificate
active
06251111
ABSTRACT:
This invention relates generally to orthopaedics and spinal surgery, and more particularly to an apparatus for straightening a spinal column by reducing the extent of displacement between adjacent vertebrae.
BACKGROUND OF THE INVENTION
In many cases of deformity, such as spondylolisthesis, it is desirable to reduce the extent of displacement of a vertebra prior to fusion to an adjacent vertebra. A spondylolisthesis reduction can be a technically demanding procedure requiring great care to prevent neurological impairment and damage to surrounding soft tissue. As a result, several systems have been utilized to accomplish a necessary reduction.
An early system utilized a cable system to apply force to the displaced vertebrae. One end of an extremely long cable was anchored to a vertebra and the other end was threaded through a fixture attached to the ceiling and included a series of traction weights positioned on the cable. Such a system utilizing long cables and weights external to the operating room proved unwieldy and bulky. Moreover, the surgeon could not quickly and effectively control the force applied to the vertebra.
In addition to cable systems, systems utilizing threaded shafts to draw the vertebra upwards were also used. One such apparatus for use in straightening a spinal column by reduction is presented in U.S. Pat. No. 4,611,581. The apparatus disclosed in this patent includes a pair of rigid plates positioned along the spinal column with a double threaded screw anchored in the vertebrae requiring alignment with the vertebral column. The lower portion of the screw has a cancellous thread, which engages the bone, while the upper portion has a machine thread, which passes through a slot in the plate and is capable of receiving an internally threaded nut. Upon rotation of the internally threaded nut bearing against the plate, the misaligned vertebra is drawn toward the plate as the nut advances over the machine threads on the screw. This system requires that the machine-threaded end of the screw extend through a relatively narrow slot in the plate. Such a requirement may limit the surgeon's ability to properly place the screw or may require manipulation of the vertebrae to align the screw with the slot in the plate.
Other systems have utilized a separate threaded shaft to draw the vertebrae into alignment. In such systems, the bone screw does not include a machine-threaded portion. Instead, a separate reduction mechanism grasps the head of the screw and is braced against a rod. A threaded shaft attached to the screw head pulls the misaligned vertebra toward the rod. Here again, the devices are cumbersome and difficult to maneuver into the appropriate position so the vertebra is pulled in the desired direction. Moreover, the surgeon cannot quickly and effectively control the force applied to the vertebra because he's never completely sure how much tension is being applied to the misaligned vertebra
What is needed is reduction device that utilizes a rigid shaft to pull the vertebra with a device that indicates the amount of pulling force that the surgeon is exerting on the vertebra. The following is one solution to that need.
SUMMARY OF THE INVENTION
In one aspect, this invention is a device for pulling a vertebral anchor. The device has a cylindrical telescopic housing made of a first hollow cylinder received inside a second hollow cylinder such that the two hollow cylinders define a longitudinal passage from the proximal to the distal end of the cylindrical telescopic housing. A tension rod is slidably disposed within the longitudinal passageway and has a means mounted on or near its distal end to attach to a vertebral anchor (or bone screw). The first and second hollow cylinders are biased apart by a mechanical spring, which resides inside the second hollow cylinder. A means for moving said tension rod in a proximal direction with respect to said telescopic housing is then operatively attached to the housing, as well as, a strain gauge to directly measure the amount of tension placed on the tension rod when the device is in use.
In another aspect, the invention is an apparatus for use in reducing a displaced vertebra in the spine. The apparatus includes (1) a longitudinal member positionable along the longitudinal axis of a spine, (2) an anchor configured to be secured to a displaced vertebra; (3) an elongated member having a first portion attached to the anchor and a second portion; and (4) a clamping member positionable along said longitudinal member adjacent the displaced vertebra. The clamping member defines a channel for receiving the second portion of the elongated member. And the clamping member is operable between an open configuration permitting movement of the elongated member through the channel and a clamping configuration engaging the elongated member to prevent movement of the elongated member through the channel. Finally, the apparatus also includes (5) an improved device for pulling the longitudinal member or a jack, described in the preceding paragraph.
In still a further aspect, the present invention provides a method of controlled vertebral reduction. The method comprises applying a set tension, monitoring the tension over time until a substantial reduction is achieved, and increasing tension to a higher amount. The process of applying tension, monitoring for reduction and reapplying tension continues until there is no substantial reduction is tension or the desired distance of vertebral movement is achieved.
These and other objects of the invention will become apparent from the following description.
REFERENCES:
patent: 4399813 (1983-08-01), Barber
patent: 4611581 (1986-09-01), Steffee
patent: 5312410 (1994-05-01), Miller et al.
patent: 5395374 (1995-03-01), Miller et al.
patent: 5484437 (1996-01-01), Michelson
patent: 5632765 (1997-05-01), Holder
patent: 5782831 (1998-07-01), Sherman et al.
Barker B. Thomas
Zdeblick Thomas
Mancene Gene
Robert Eduardo C.
SDGI Holdings Inc.
Woodard Emhardt Naughton Moriarty & McNett
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