Methods and apparatus for coupling a prosthesis to a spinal segment

Abstract

A method for coupling a prosthesis to a spinal segment in a patient includes the steps of selecting first and second reference points disposed along the spinal segment and pre-operatively measuring a target distance. The target distance extends between the first and second reference points while the patient is in a preferred posture such as the standing position. A prosthesis is coupled to the spinal segment and the prosthesis is then intra-operatively adjusted in order to set the distance between the first and second reference points based on the target distance.

What is claimed is: 
     
         1 . A method for coupling a prosthesis to a spinal segment in a patient, said method comprising:
 selecting a first and a second reference point disposed along the spinal segment;   pre-operatively measuring a target distance, the target distance extending between the first and the second reference points while the patient is in a preferred posture;   coupling the prosthesis to the spinal segment; and   intra-operatively adjusting the prosthesis in order to set the distance between the first and second reference points based on the target distance.   
     
     
         2 . A method as in  claim 1 , wherein the first reference point is disposed on a first vertebra and the second reference point is disposed on a second vertebra or a sacrum. 
     
     
         3 . A method as in  claim 1 , wherein the first reference point is disposed on a superior surface of a first spinous process of a first vertebra and the second reference point is disposed on an inferior surface of a second spinous process of a second vertebra, the first vertebra disposed cranial to the second vertebra. 
     
     
         4 . A method as in  claim 1 , wherein the first reference point is disposed on an inferior surface of a first spinous process of a first vertebra and the second reference point is disposed on a superior surface of a second spinous process of a second vertebra, the first vertebra disposed cranial to the second vertebra. 
     
     
         5 . A method as in  claim 1 , wherein the preferred posture comprises the standing position. 
     
     
         6 . A method as in  claim 1 , wherein the preferred posture comprises a pain-free position. 
     
     
         7 . A method as in  claim 1 , wherein the measuring comprises observing a radiograph of the patient taken while the patient is in the preferred posture. 
     
     
         8 . A method as in  claim 7 , wherein the radiograph is taken pre-operatively. 
     
     
         9 . A method as in  claim 7 , wherein the radiograph comprises a lateral view of the spinal segment. 
     
     
         10 . A method as in  claim 1 , wherein the prosthesis comprises a tether structure and the coupling comprises engaging a first portion of the tether structure with a superior spinous process and engaging a second portion of the tether structure with an inferior spinous process or a sacrum. 
     
     
         11 . A method as in  claim 1 , wherein the adjusting comprises adjusting the prosthesis so that the prosthesis is in a neutral position when the patient is in the preferred posture and the prosthesis provides a force resistive to flexion of the spinal segment while still allowing significantly unrestricted extension of the spinal segment. 
     
     
         12 . A method as in  claim 1 , wherein the adjusting comprises adjusting the prosthesis while the patient is in a position other than the preferred posture. 
     
     
         13 . A method as in  claim 1 , wherein the adjusting comprises observing calibration markings thereon. 
     
     
         14 . A method as in  claim 1 , wherein the adjusting comprises setting the distance between the first and second reference points to the target distance. 
     
     
         15 . A method as in  claim 1 , further comprising verifying that the distance between the first and second reference points substantially matches the target distance. 
     
     
         16 . A method as in  claim 15 , wherein the verifying comprises using a gauge to determine the distance between the first and second reference points. 
     
     
         17 . A method as in  claim 15 , further comprising re-adjusting the prosthesis until the distance between the first and second reference points substantially matches the target distance. 
     
     
         18 . A method as in  claim 1 , wherein the prosthesis comprises a first compliance element and the method further comprises engaging and locking a first constraining apparatus with the first compliance element in order to limit extension or contraction thereof during adjustment of the prosthesis. 
     
     
         19 . A method as in  claim 18 , further comprising disengaging the first constraining apparatus from the first compliance element so as to allow movement thereof. 
     
     
         20 . A method as in  claim 18 , wherein the prosthesis comprises a second compliance element, the method further comprising:
 engaging a second constraining apparatus with the second compliance element in order to limit extension or contraction thereof during adjustment of the prosthesis; and   releasably locking the first and the second constraining apparatus together so as to facilitate alignment and positioning of the first and the second compliance elements on opposite sides of a midline of the spinal segment.   
     
     
         21 . A method as in  claim 20 , further comprising moving the first constraining apparatus relative to the second constraining apparatus along one degree of freedom in order to accommodate spinous processes and interspinous/superspinous ligament complex of varying thicknesses. 
     
     
         22 . A method as in  claim 20 , further comprising positioning a driver or tool in a central lumen of first or the second constraining apparatus thereby concentrically aligning the driver or the tool with a locking mechanism on the compliance element. 
     
     
         23 . A method as in  claim 20 , further comprising providing a counter torque when the first or the second compliance elements are adjusted, or when the first and the second constraining apparatus are releasably locked together. 
     
     
         24 . A method as in  claim 1 , further comprising pre-tensioning the prosthesis to a desired value. 
     
     
         25 . A method as in  claim 1 , wherein the target distance defines a major axis length, and wherein the adjusting comprises using the target distance to determine a target prosthesis circumference, and adjusting the prosthesis to the target circumference. 
     
     
         26 . A method as in  claim 25 , wherein the major axis length is correlated with the target circumference in a lookup table. 
     
     
         27 . A method as in  claim 25 , wherein the major axis length is correlated with calibration markings on the prosthesis. 
     
     
         28 . A method as in  claim 25 , further comprising verifying that the prosthesis circumference substantially matches the target circumference. 
     
     
         29 . A method as in  claim 28 , wherein verifying the prosthesis circumference comprises observing calibration markings on the prosthesis. 
     
     
         30 . A method as in  claim 28 , further comprising re-adjusting the prosthesis until the prosthesis circumference substantially matches the target circumference. 
     
     
         31 . A method as in  claim 25 , further comprising:
 selecting a third and a fourth reference point disposed along the spinal segment, the distance between the third and fourth reference points defining a minor axis having a minor axis length, the minor axis being transverse to the major axis; and   measuring the minor axis length on the pre-operative image in order to determine the target prosthesis circumference, the target circumference sufficient for the prosthesis to form a loop encircling a superior spinous process and an inferior spinous process and provide a force resistant to flexion beyond a desired posture.   
     
     
         32 . A method as in  claim 31 , wherein the third and fourth reference points are on opposite sides of a spinous process and estimate the length of the prosthesis required to accommodate spinous process width. 
     
     
         33 . A method as in  claim 31 , wherein the third and fourth reference points are disposed on a single vertebra. 
     
     
         34 . A method as in  claim 31 , wherein the minor axis length is correlated with the target circumference in a lookup table. 
     
     
         35 . A method as in  claim 31 , wherein the minor axis length is correlated with calibration markings on the prosthesis. 
     
     
         36 . A method as in  claim 1 , further comprising decompressing a portion of the spinal segment. 
     
     
         37 . A system for restricting flexion of a spinal segment in a patient, said system comprising:
 a tether structure adapted to be coupled with a superior spinous process and an inferior spinous process or sacrum;   a first compliance element coupled with the tether structure; and   a first constraining tool releasably coupled with the compliance element so as to hold the compliance element in a desired position or to limit motion of the compliance element to a predetermined range.   
     
     
         38 . A system as in  claim 37 , wherein the tether structure is substantially non-distensible. 
     
     
         39 . A system as in  claim 37 , wherein the first constraining tool comprises an elongate shaft. 
     
     
         40 . A system as in  claim 37 , wherein the first constraining tool comprises a cradle adapted to releasably hold the first compliance element. 
     
     
         41 . A system as in  claim 37 , wherein the first constraining tool comprises a plurality of elongate arms, the plurality of arms forming a constraint to elongation of the compliance element. 
     
     
         42 . A system as in  claim 37 , wherein the first tool holds the first compliance element in a desired tension. 
     
     
         43 . A system as in  claim 37 , wherein the first constraining tool applies a compressive force to the first compliance element. 
     
     
         44 . A system as in  claim 43 , wherein the compressive force is variable. 
     
     
         45 . A system as in  claim 37 , wherein the first constraining tool does not limit extension of the first compliance element until the first compliance element has extended a pre-determined distance. 
     
     
         46 . A system as in  claim 37 , wherein the first constraining tool is adjustable so as to vary the desired position, tension or the range. 
     
     
         47 . A system as in  claim 37 , further comprising:
 a second compliance element coupled with the tether structure; and   a second constraining tool releasably coupled with the second compliance element so as to hold the second compliance element in a desired position or to limit motion of the second compliance element to a predetermined range, and wherein the first and the second constraining tools are releasably and symmetrically coupled together so as to facilitate alignment and positioning of the first and the second compliance elements on opposite sides of a midline of the spinal segment.   
     
     
         48 . A system as in  claim 47 , wherein the first and the second constraining tools are movable relative to one another along one degree of freedom, thereby accommodating spinous processes of varying thicknesses. 
     
     
         49 . A system as in  claim 47 , wherein the first or the second compliance element comprises a locking mechanism, and at least one of the first or the second constraining tools comprise an elongate shaft having a lumen adapted to receive and align a driver or other tool concentrically with the locking mechanism. 
     
     
         50 . A system as in  claim 47 , wherein the first or the second compliance element releasably locks with the first or the second constraining tool. 
     
     
         51 . A system as in  claim 49 , wherein the first or the second constraining tool is adapted to provide a counter torque when the locking mechanism is actuated. 
     
     
         52 . A method for treating lower back pain in a patient, said method comprising:
 providing instructions to the patient to place the lower back into varying positions of flexion;   determining a threshold position of the lower back in which the patient does not experience lower back pain or where lower back pain is reduced;   providing a first image or a set of images of the patient's lower back while in the threshold position;   measuring features of the patient's lower back from the first image or the set of images;   coupling a constraint device to the patient's lower back;   re-measuring features of the patient's lower back with the constraint device coupled thereto;   comparing the re-measured features with the measured features; and   adjusting the constraint device so that the patient's lower back is in a position below the threshold position based on the comparison of measured and re-measured features, whereby the lower back pain or instability of the lower back is reduced or eliminated.   
     
     
         53 . The method of  claim 52 , wherein the step of determining comprises providing the patient with means for indicating when pain is experienced. 
     
     
         54 . The method of  claim 53 , wherein the means comprises an actuatable switch. 
     
     
         55 . The method of  claim 52 , wherein the first image or the set of images comprises one of an x-ray, MRI, and CT scan. 
     
     
         56 . The method of  claim 52 , wherein the providing comprises acquiring the set of images from a single continuous movement of the patient's lower back between painful and pain-free or reduced pain postures. 
     
     
         57 . The method of  claim 52 , wherein the measured features comprise one of intervertebral disc angle, interspinous process distance, and interpedicular distance. 
     
     
         58 . The method of  claim 57 , wherein the measuring comprises using calipers or an angle measuring device to quantify the features. 
     
     
         59 . The method of  claim 52 , wherein the step of coupling comprises engaging the constraint device with a superior spinous process and an inferior spinous process or a sacrum. 
     
     
         60 . The method of  claim 52 , wherein the constraint device is adapted to provide a force resistant to flexion of the lower back. 
     
     
         61 . The method of  claim 52 , wherein the step of re-measuring comprises providing a second image or a set of images of the patient's lower back with the constraint device coupled thereto. 
     
     
         62 . The method of  claim 61 , wherein the second image or the set of images comprises one of an x-ray, MRI or CT scan. 
     
     
         63 . The method of  claim 61 , wherein the step of re-measuring comprises placing one or more radiopaque markers into engagement with the patient's lower back. 
     
     
         64 . The method of  claim 63 , wherein the placing comprises coupling at least one of the radiopaque markers with a spinous process in the patient's lower back. 
     
     
         65 . The method of  claim 61 , wherein the comparing comprises visually comparing the first and the second radiographic images or sets of images. 
     
     
         66 . The method of  claim 52 , wherein the step of adjusting comprises adjusting length or tension of the constraint device. 
     
     
         67 . The method of  claim 52 , further comprising evaluating presence and shape of spinous processes of the lower back for coupling of the constraint device thereto. 
     
     
         68 . The method of  claim 52 , further comprising evaluating facet joint engagement in the lower back. 
     
     
         69 . The method of  claim 68 , wherein the evaluating comprises measuring linear overlap of articular processes. 
     
     
         70 . The method of  claim 52 , wherein the step of adjusting the constraint device comprises adjusting the constraint device so as to increase facet joint engagement in at least one facet joint in the lower back. 
     
     
         71 . The method of  claim 52 , wherein the step of adjusting the constraint device comprises adjusting the constraint device so as to prevent hyperextension or locking of at least one facet joint in the lower back. 
     
     
         72 . The method of  claim 52 , further comprising manipulating the patient's lower back intraoperatively so that the lower back is in a position at or below the threshold position based on the comparison of measured and re-measured features. 
     
     
         73 . The method of  claim 72 , wherein the manipulating comprises manipulating the patient's lower back to form or increase lordosis therein. 
     
     
         74 . A method for treating degenerative spondylolisthesis in a lower back of a patient, said method comprising:
 providing instructions to the patient to place the lower back into varying positions of flexion;   providing a plurality of images of the lower back in the varying positions;   determining a threshold position of the lower back in which a facet joint of the patient's lower back begins to sublux;   providing a first image of the patient's lower back while in the threshold position;   coupling a constraint device to the patient's lower back;   providing a second image of the patient's back intraoperatively after the constraint device has been coupled to the patient's lower back;   comparing the first and the second images; and   adjusting the constraint device so that the patient's lower back is in a position below the threshold position based on the comparison of the first and the second images, whereby the subluxation of the facet joint is reduced or eliminated.   
     
     
         75 . The method of  claim 74 , wherein the step of determining comprises providing the patient with means for indicating when pain is experienced. 
     
     
         76 . The method of  claim 75 , wherein the means comprises an actuatable switch. 
     
     
         77 . The method of  claim 74 , further comprising concurrently performing a neural decompression. 
     
     
         78 . The method of  claim 74 , wherein the determining comprises assessing engagement of a facet joint with or without concomitant decompression of the patient's lower back. 
     
     
         79 . The method of  claim 74 , wherein the first image comprises one of an x-ray, MRI, and CT scan. 
     
     
         80 . The method of  claim 74 , wherein the coupling comprises engaging the constraint device with a superior spinous process and an inferior spinous process or a sacrum. 
     
     
         81 . The method of  claim 74 , wherein the constraint device is adapted to provide a force resistant to flexion of the lower back. 
     
     
         82 . The method of  claim 74 , wherein the second image comprises an x-ray. 
     
     
         83 . The method of  claim 82 , further comprising placing one or more radiopaque markers into engagement with the patient's lower back. 
     
     
         84 . The method of  claim 83 , wherein the placing comprises coupling at least one of the radiopaque markers with a spinous process in the patient's lower back. 
     
     
         85 . The method of  claim 74 , wherein the comparing comprises comparing intervertebral disc angle, interspinous process distance, facet joint engagement, or interpedicular distance between the first and the second images or sets of images. 
     
     
         86 . The method of  claim 74 , wherein the comparing comprises using calipers or an angle measuring device to quantify lower back features in the first and the second images. 
     
     
         87 . The method of  claim 74 , wherein the comparing comprises visually comparing the first and the second images. 
     
     
         88 . The method of  claim 74 , wherein the adjusting comprises adjusting length or tension of the constraint device. 
     
     
         89 . The method of  claim 74 , further comprising evaluating presence and shape of spinous processes of the lower back for coupling of the constraint device thereto. 
     
     
         90 . A method for treating lower back pain in a patient, said method comprising:
 manipulating the patient's lower back into a position where the lower back pain is reduced or eliminated;   recording the position;   intraoperatively reproducing the position in the patient's lower back; and   coupling a constraint device to the lower back.   
     
     
         91 . The method of  claim 90 , wherein the manipulating comprises manually manipulating the patient's lower back. 
     
     
         92 . The method of  claim 90 , wherein the manipulating comprises forming or increasing lordosis in the patient's lower back. 
     
     
         93 . The method of  claim 90 , wherein the manipulating comprises placing the patient in a frame or a chair with an adjustable lumbar member. 
     
     
         94 . The method of  claim 90 , wherein the manipulating comprises flexing a hip. 
     
     
         95 . The method of  claim 94 , wherein the flexing of the hip comprises directing a force proximally through a femoral head to antevert a pelvis thereby forming or increasing lordosis in the patient's lower back. 
     
     
         96 . The method of  claim 95 , further comprising restraining a knee. 
     
     
         97 . The method of  claim 90 , wherein the recording comprises providing the patient with means for indicating when pain is experienced. 
     
     
         98 . The method of  claim 97 , wherein the means comprises an actuatable switch. 
     
     
         99 . The method of  claim 90 , wherein the reproducing comprises manually manipulating the patient's lower back into the position. 
     
     
         100 . The method of  claim 90 , wherein the reproducing comprises forming or increasing lordosis in the patient's lower back. 
     
     
         101 . The method of  claim 90 , wherein the coupling comprises engaging the constraint device with a superior spinous process and an inferior spinous process or a sacrum. 
     
     
         102 . The method of  claim 101 , wherein the constraint device is adapted to provide a force resistant to flexion of the lower back. 
     
     
         103 . The method of  claim 90 , further comprising providing an image of the patient's lower back in the position. 
     
     
         104 . The method of  claim 103 , wherein the image comprises an x-ray. 
     
     
         105 . The method of  claim 90 , further comprising providing an intraoperative image of the patient's lower back after reproducing the position. 
     
     
         106 . The method of  claim 105 , wherein the intraoperative image comprises one of an x-ray, MRI, and a CT scan. 
     
     
         107 . The method of  claim 90 , further comprising coupling a radiopaque marker with the patient's lower back. 
     
     
         108 . The method of  claim 107 , wherein the radiopaque marker is coupled with a spinous process of the patient's lower back. 
     
     
         109 . The method of  claim 90 , further comprising intraoperatively characterizing range of motion, segmental stability, linear stiffness, or bending stiffness of a segment of the patient's lower back. 
     
     
         110 . The method of  claim 109 , further comprising adjusting the constraint device based on the characterization of the patient's lower back. 
     
     
         111 . The method of  claim 110 , wherein the adjusting comprises adjusting length or tension in the constraint device. 
     
     
         112 . The method of  claim 109 , further comprising:
 comparing the characterization of the patient's lower back with a reference guide; and   adjusting the constraint device based on information provided by the reference guide.   
     
     
         113 . A method for treating spondylolisthesis in a patient, said method comprising:
 providing instructions to the patient to place the lower back into varying positions of flexion;   determining a threshold position of the lower back in which the patient does not experience translational instability or wherein translation instability is reduced;   providing a first image or a set of images of the patient's lower back while in the threshold position;   measuring features of the patient's lower back from the first image or the set of images;   coupling a constraint device to the patient's lower back;   re-measuring features of the patient's lower back with the constraint device coupled thereto;   comparing the re-measured features with the measured features; and   adjusting the constraint device so that the patient's lower back is in a position below the threshold position based on the comparison of measured and re-measured features, whereby the instability of the lower back is reduced or eliminated.