Abstract:
Spinal surgery systems are provided. In one embodiment, a system includes threaded caps and screw assemblies. Each assembly includes a cannulated and threaded screw having upper and lower ends, a polyaxial head permanently fixed to the screw upper end in a ball-and-socket engagement, and an extension portion fixed to the head wherein extension portion movement causes the head to move in concert. Each head has a receiving area for engaging a rod and a threaded area for receiving one of the caps after the rod is engaged in the receiving area. Each extension portion has: (a) two arms spaced apart such that the arms are on opposite sides of the polyaxial head receiving area; and (b) at least one point of weakness such that forcing the arms away from one another causes the extension portion to divide at the point of weakness and separate the extension portion from the head.

Description:
FIELD 
       [0001]    The present application relates to the field of implantable surgical devices and apparatus for surgically inserting such devices. In particular, the present application relates to implantable devices for stabilizing the spine, decompressing neural elements, and methods and devices for implanting such devices during spinal surgery. 
       BACKGROUND 
       [0002]    Minimally-invasive spinal procedures have increased in popularity extensively over the course of the past decade. These procedures allow patients to experience shorter hospital stays, faster post-operative recoveries, and an earlier return to work compared to open techniques. Initially these procedures were limited to simple decompressive procedures. However, over the past few years surgeons have begun to expand the applications of these systems to include spinal stabilization and spinal fusion procedures as well. 
         [0003]    With reference to  FIG. 1 , a top view of a generic vertebra  100 , the front or anterior portion of the vertebra  100  is the body  102 . The bodies  102  of adjacent vertebrae are typically separated by an intervertebral disk. Posteriorly the body  102  is joined by a left  104  and right pedicle  106  to the lamina  108 . The lamina  108  joins a posterior  114  spinous process that generally serves for muscle and ligamentous attachments. Transverse processes  110  and  112  project laterally from the junction of the pedicle and the lamina and also serve for muscle and ligamentous attachments. A supraspinous ligament attaches  114  the spinous processes of adjacent vertebrae to provide stability to the spinal column. 
         [0004]    The lamina  108  pedicles  104 ,  106 , and body  102  surround a passageway known as the vertebral foramen  116 . The vertebra also has articular processes  118  that extend above and below the vertebra to interact with adjacent vertebra (not shown in  FIG. 1 ), which are known as facet joints. adjacent vertebrae  100  are typically separated by an intervertebral disk  154 . Posteriorly, the body  102  is joined by a left pedicle  104  and right pedicle  106  to the lamina  108 . The lamina  108  joins a spinous process  114  that generally serves for muscle and ligamentous attachments. Transverse processes  110  and  112  project laterally from the junction of the respective pedicle  104 ,  106  and the lamina  108  and also serve for muscle and ligamentous attachments. A supraspinous ligament attaches the spinous processes  114  of adjacent vertebrae  100  to provide stability to the spinal column. 
         [0005]    The lamina  108 , pedicles  104 ,  106 , and body  102  surround a passageway known as the vertebral foramen  116 . The vertebra  100  also has articular processes  118  that extend above and below the vertebra  100  to interact with adjacent vertebra  100 ; these interactions are known as facet joints. 
         [0006]    While the parts of vertebrae  100  shown in  FIG. 1  and  FIG. 2  are common to most vertebrae  100  of the spinal column, details of anatomy differ with position of the vertebra  100  in the spinal column. For example, the vertebral body  102  is wider at lower levels of the spinal column, such as the lumbar region, than in vertebrae of the cervical spine; this provides greater weight-bearing capability at the lower levels. The body  102  of each vertebra is located anterior to the lamina  108  and spinous process  114 . The spinal cord—or for lumbar vertebrae  100  its caudal extension, the cauda equina—passes through the vertebral foramen  116 . Also found within the vertebral foramen  116  exiting the spinal cord are dorsal and ventral roots, arteries, veins, and a posterior longitudinal ligament  120  that attaches each vertebra  100  to its adjacent vertebrae  100 . In addition, there is an anterior longitudinal ligament  122  that attaches each vertebra  100  to its adjacent vertebrae  100 . Motor and sensory nerves exit the spinal canal together at a space between pedicles  106 ,  104  of adjacent vertebrae  100  known as intervertebral or neural foramina. 
         [0007]    As a subject ages, or suffers injury, various disease processes may narrow, or impinge on, the spinal canal defined by successive vertebral foramens  116  such that less space is available for the spinal cord, nerve roots, and other tissues. Among these disease processes may be bulging or rupture of an intervertebral disk  154  that impinges on the spinal canal, tumors, abscesses, ligamentous hypertrophy, spondylolisthesis, ossification of the posterior longitudinal ligament, bone spur formation, etc. Whenever the spinal canal, defined by successive vertebral foramina  116 , is effectively narrowed by a disease process impinging on the spinal cord, cauda equina, or nerve root, function may be impaired. This may result in symptoms of numbness, weakness, ataxia, impotence, incontinence, pain, and even paralysis. In some subjects, it is necessary to surgically decompress the neural elements to prevent further damage and provide relief of symptoms. Surgical decompression often requires a laminectomy to provide additional room for the spinal canal, which involves cutting through the lamina  108  on both sides of the spinous process  114  and subsequently removing this segment. 
         [0008]    Further, damage to (including fractures) or diseases (including arthritis) of the vertebral body  102 , the facet joints  118  between vertebrae  100 , or the intervertebral disks  154  between adjacent vertebral bodies  102  may require surgical intervention. And in some patients, vertebral bodies  102  may be anteriorly displaced in relation to each other. This may result from fractures or diseases of the facet joints  118 , or from defects in the pars interarticularis, and is known as spondylolisthesis. 
         [0009]    A known surgical stabilization technique is spinal fusion with instrumentation; this has traditionally been done using an open surgical technique where the spinal column is approached from the front through the abdomen to gain access to the vertebral body  102 , and/or from the back. In this surgery, an intervertebral disk  154  between two vertebrae  100  is often removed and replaced with an implant that is typically made of bone, metal, or another appropriate substance. This type of surgery is known as an interbody fusion. The implant provides the necessary matrix to allow bone growth and healing to fuse the adjacent vertebrae  100 . Posterolateral fusions can also be performed between the transverse processes  110  and  112  of adjacent vertebrae. Other repairs to the vertebral body  102  may also be done. 
         [0010]    After the matrix for fusion has been established (i.e. via posterolateral and/or interbody fusion), instrumentation is often utilized to stabilize the spinal column and promote fusion (arthrodesis) by preventing micromotion of the instrumented adjacent vertebra  100 . Several different forms of instrumentation have been developed in the past. However, biomechanical studies have proven that pedicle screws provide the most effective form of lumbar spinal instrumentation with the highest pull-out strength. Pedicle screws are placed from a posterior approach at the junction of the transverse process  110 ,  112  and facet  118 . These screws are then passed through the pedicle  104 ,  106  into the vertebral body  102 . The pedicle screws of adjacent vertebral bodies  102  are then attached to rods, and this construct provides stabilization to the fused segment by preventing micromotion. 
         [0011]    Conventional open surgical techniques typically utilize larger incisions, as direct visualization of the vertebral structures is required, and occasionally require both anterior and posterior approaches to the spine. Prior art minimally-invasive techniques, as noted above, typically utilize incisions that are several inches long, which results in hospitalizations and recoveries that are marginally better than comparable open surgical techniques. Micro-invasive systems and methods, such as those set forth herein, may result in shorter hospitalizations, faster post-operative recoveries, less narcotic dependence, and earlier return to work than both open and prior art minimally-invasive techniques. 
       SUMMARY 
       [0012]    Systems for use in performing spinal surgery are provided herein. In one embodiment, a system includes at least two threaded caps and at least two screw assemblies. Each assembly includes a cannulated and threaded screw having upper and lower ends, a polyaxial head permanently fixed to the screw upper end in a ball-and-socket engagement, and an extension portion fixed to the head wherein movement of the extension portion causes the head to move in concert. Each head has a receiving area for engaging a rod and a threaded area for receiving one of the caps after the rod is engaged in the receiving area such that the rod is sandwiched by the polyaxial head and the cap. Each extension portion has: (a) two arms spaced apart such that the arms are on opposite sides of the polyaxial head receiving area; and (b) at least one point of weakness such that forcing the arms away from one another causes the extension portion to divide at the point of weakness and separate the extension portion from the head. 
         [0013]    In another embodiment, a system includes for use in performing spinal surgery includes a rod, at least two threaded caps, and at least two screw assemblies. Each screw assembly includes a cannulated and threaded screw having upper and lower ends, a polyaxial head permanently fixed to the screw upper end in a ball-and-socket engagement, and an extension portion attached to the polyaxial head wherein movement of the extension portion causes the polyaxial head to move in concert. Each polyaxial head has a receiving area for engaging the rod and a threaded area for receiving one of the caps after the rod is engaged in the receiving area such that the rod is sandwiched by the polyaxial head and the cap. Each extension portion has: (a) first and second arms configured to pass the rod therebetween and guide the rod to the polyaxial head receiving area; and (b) at least one point of weakness such that forcing the arms away from one another causes the extension portion to divide at the point of weakness and separate the extension portion from the polyaxial head. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a posterior view of a pair of generic vertebrae. 
           [0015]      FIG. 2  is a top view of one of the generic vertebra from  FIG. 1 . 
           [0016]      FIG. 3  is an oblique view of the posterolateral spinal column. 
           [0017]      FIG. 4  shows a port, according to an embodiment, placed over a facet joint from  FIG. 3 . 
           [0018]      FIG. 5   a  is a perspective view of the port of  FIG. 4 . 
           [0019]      FIG. 5   b  is a side view of the port of  FIG. 5   a.    
           [0020]      FIG. 5   c  is another perspective view of the port of  FIG. 5   a.    
           [0021]      FIG. 6  is an illustration of a view through the port of  FIG. 4 , showing retraction of a descending nerve root. 
           [0022]      FIG. 7  illustrates placement of an interbody fusion device between adjacent vertebrae through the port of  FIG. 4 . 
           [0023]      FIG. 8  illustrates placement of K-wires within pedicles of adjacent vertebrae. 
           [0024]      FIG. 9  illustrates percutaneous placement of a screw assembly, according to an embodiment. 
           [0025]      FIG. 10  is a front view of the screw assembly of  FIG. 9 . 
           [0026]      FIG. 11  is a perspective view of the screw assembly of  FIG. 10 . 
           [0027]      FIG. 12  is a sectional view of a pedicle screw from the screw assembly of  FIG. 10 . 
           [0028]      FIG. 13  is a perspective view of a polyaxial head from the screw assembly of  FIG. 10 . 
           [0029]      FIG. 14  is a sectional view of the polyaxial head of  FIG. 13 . 
           [0030]      FIG. 15  is front view of the pedicle screw and the polyaxial head of  FIG. 10 . 
           [0031]      FIG. 16  is perspective view of the pedicle screw and the polyaxial head of  FIG. 15 . 
           [0032]      FIG. 17  is a perspective view of the extension portion from the screw assembly of  FIG. 10 . 
           [0033]      FIG. 18  is a partial view of the extension portion of  FIG. 17 . 
           [0034]      FIG. 19   a  is perspective view of a screwdriver, according to an embodiment, in use with the screw assembly of  FIG. 10 . 
           [0035]      FIG. 19   b  is another perspective view of the screwdriver and the screw assembly of  FIG. 19   a.    
           [0036]      FIG. 19   c  is a partial view taken from  FIG. 19   b.    
           [0037]      FIG. 20  illustrates placement of two screw assemblies of  FIG. 10  within pedicles of adjacent vertebrae. 
           [0038]      FIG. 21  illustrates a measurement device in use with the two screw assemblies of  FIG. 20 . 
           [0039]      FIG. 22  is a perspective view of a rod insertion tool, according to an embodiment. 
           [0040]      FIG. 23  is a sectional view of the rod insertion tool of  FIG. 22 . 
           [0041]      FIG. 24  is another sectional view of the rod insertion tool of  FIG. 22 . 
           [0042]      FIG. 25  is a detailed sectional view of the rod insertion tool of  FIG. 22 . 
           [0043]      FIG. 26  is a partial view of the rod insertion tool of  FIG. 22 . 
           [0044]      FIG. 27  is another detailed sectional view of the rod insertion tool of  FIG. 22 . 
           [0045]      FIG. 28  is a perspective view of a rotating end and an attachment device from the rod insertion tool of  FIG. 22 . 
           [0046]      FIG. 29  is a perspective view of a deformable crown of the attachment device of  FIG. 28 . 
           [0047]      FIG. 30  is an end view of the deformable crown of  FIG. 29 . 
           [0048]      FIG. 31  is a side view of the deformable crown of  FIG. 29 . 
           [0049]      FIG. 32  is a perspective view of an actuator of the attachment device of  FIG. 28 . 
           [0050]      FIG. 33  is a side view of the actuator of  FIG. 32 . 
           [0051]      FIG. 34  is an end view of a rod, according to an embodiment. 
           [0052]      FIG. 35  is a side view of the rod of  FIG. 34 . 
           [0053]      FIG. 36  is a perspective view of a cap, according to an embodiment. 
           [0054]      FIG. 37  is a sectional view showing the screw assembly of  FIG. 10  in use with the rod of  FIG. 35  and the cap of  FIG. 36 . 
           [0055]      FIG. 38  is a perspective view showing two screw assemblies of  FIG. 10  in use with the rod of  FIG. 35  and two caps of  FIG. 36 . 
           [0056]      FIG. 39  illustrates a compressor device, according to an embodiment, in use with the two screw assemblies of  FIG. 10 . 
           [0057]      FIG. 40  is a front view of the compressor device of  FIG. 39 . 
           [0058]      FIG. 41  is a perspective view of the compressor device of  FIG. 40 . 
           [0059]      FIG. 42  is another perspective view of the compressor device of  FIG. 40 . 
           [0060]      FIG. 43   a  is a perspective view of a salvage tool, according to an embodiment, with its extensions at an open alignment. 
           [0061]      FIG. 43   b  is a perspective view of the salvage tool of  FIG. 43   a , with its extensions at a closed alignment. 
           [0062]      FIG. 44  is a side view of the salvage tool of  FIG. 43   b.    
           [0063]      FIG. 45  is a front view of the salvage tool of  FIG. 44 . 
           [0064]      FIG. 46  is a perspective view of the extensions of the salvage tool of  FIG. 44 . 
           [0065]      FIG. 47  illustrates placement of three screw assemblies of  FIG. 10  for a two level procedure. 
           [0066]      FIG. 48  is a top view of an alignment tool, according to an embodiment. 
           [0067]      FIG. 49  is a perspective view of the alignment tool of  FIG. 48 . 
           [0068]      FIG. 50   a  is a perspective view of one receiving member of the alignment tool of  FIG. 48 . 
           [0069]      FIG. 50   b  is another perspective view of the receiving member of  FIG. 50   a.    
           [0070]      FIG. 51  is a top view of the receiving member of  FIG. 50   a.    
           [0071]      FIG. 52  is a sectional view of the receiving member of  FIG. 50   a.    
           [0072]      FIG. 53   a  is a perspective view of another receiving member of the alignment tool of  FIG. 48 . 
           [0073]      FIG. 53   b  is another perspective view of the receiving member of  FIG. 53   a.    
           [0074]      FIG. 54  is a top view of the receiving member of  FIG. 53   a.    
           [0075]      FIG. 55  is a sectional view of the receiving member of  FIG. 53   a.    
           [0076]      FIG. 56  is a perspective view of the three screw assemblies of  FIG. 47 , in use with the alignment tool of  FIG. 48 , the rod of  FIG. 35 , and caps of  FIG. 36 ; it should be appreciated that the rod would never be placed as shown until after all of the screw assemblies are received in bone, and that the caps would not be set in place until after the rod is positioned in all three screw assemblies. 
           [0077]      FIG. 57  is a flowchart summarizing various surgical procedures set forth herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0078]    The equipment and methods set forth herein may allow spine surgeons to perform posterior lumbar decompressions (e.g., laminectomies, microdiscectomies, facetectomies, and lumbar interbody fusions) in addition to posterior pedicle screw instrumentation through a small, single incision. Notably, the disclosed equipment and methods may allow spine surgeons to perform a decompressive laminectomy from a posterior approach through smaller incisions than possible with prior art systems. 
         [0079]    A minimally invasive fusion procedure (and equipment used) according to one embodiment is shown and described with reference to  FIGS. 1 through 46  of the accompanying drawings. As set forth above,  FIGS. 1 and 2  show generic vertebrae  100 .  FIG. 3  similarly shows generic vertebrae  100 . In  FIG. 4 , with the aid of fluoroscopy, a port  200  has been placed percutaneously through the patient&#39;s skin at a facet joint  118 . The incision location is shown in  FIG. 1  at line  152 . 
         [0080]    The port  200  is shown in detail in  FIGS. 5   a  through  5   c.  Unlike prior art ports, which are tubular and have upper and lower ends that are generally perpendicular to the sidewall, the port  200  has a lower end  202  that is not perpendicular to sidewall  204 . Though various angles may be appropriate, an angle between twenty and forty degrees to the horizon, and preferably an angle of approximately thirty degrees, may be most desirable. This angled configuration may allow the lower end  202  of the port  200  to be simultaneously positioned along the facet  118  and adjacent lamina  108  of the vertebrae  100 . This distinguishes the port  200  from prior art by allowing the surgeon to perform a facetectomy/microdiscectomy concomitant to performing a laminectomy through the same approach for spinal decompression. 
         [0081]    In addition, the port  200  includes a lip (sometimes referred to herein as “rim”)  208  at an upper end  206 . The rim  208  provides an advantage over the prior art in that a nerve root retractor  180  (shown in  FIG. 6  holding nerve roots  182  out of the way) and/or other equipment may be attached to the rim  208 , allowing hands-free operation of the attached equipment. And, as shown in  FIGS. 5   a  through  5   c,  an engagable portion  209  may extend upwardly from the lip  208 . Though not shown in the drawings, an arm may attach to the engagable portion  209  and secure the port  200  to the bed to stabilize the port  200 . It should be understood that other engagable configurations may additionally, or alternately, be used. 
         [0082]    While various materials and configurations would be appropriate for the port  200 , in one currently preferred embodiment, the port  200  is constructed of titanium, the sidewall  204  has a wall thickness of about one millimeter, and the rim  208  has an outer diameter that is about four millimeters greater than the inner diameter. The inner diameter of the port  200  may vary in increments (e.g., two millimeter increments, from 16 to 26 millimeters inner diameter), allowing for use in different patients with different pathology. Accordingly, multiple ports  200  may be present to allow the appropriately-sized port  200  to be selected for a given procedure. In some embodiments, the port  200  may contain a radiopaque ring at the tip for visualization by intraoperative fluoroscopy, while the port itself is radiolucent; the surgeon may thus determine exactly where the port  200  is docked in the patient by imaging this radiopaque ring. 
         [0083]    Returning now to  FIG. 4 , after the port  200  is secured in place, the facet joint  118  and lamina  108  may be resected using conventional tools and a microscope. Once the lamina  108  is removed, the contra lateral lamina may be removed as well by under-cutting the spinous process. Removal of the lamina  108  allows the spinal cord to be decompressed centrally, and removal of the facet  118  and intervertebral disc  154  allows the nerve root to be decompressed. 
         [0084]    After the necessary portions are removed, adjacent vertebrae  100  are fused together by a spinal fusion device  190  ( FIG. 7 ), which is well known in the art, and may include such devices as a bony implant, a PEEK (polyether keytone) implant, bone morphogenic protein, a titanium cage, et cetera. The fusion device  190  is attached to an insertion tool  192  placed in the port  200  and wedged into the disc space using fluoroscopy. Once the fusion device  190  is appropriately positioned, hemostasis is obtained and the port  200  is removed. 
         [0085]    As time passes, bone growth will result in spinal fusion as the spinal fusion device  190  is incorporated into the end plates of the bodies  102  of adjacent vertebrae  100 , fusing both vertebrae  100  into a single bony unit. Stabilization, which in this case involves placement of pedicle screw instrumentation, significantly improves arthrodesis rates and provides stability in patients with instability, such as may result from fractures or spondylolisthesis. 
         [0086]    Pedicle screw instrumentation begins with placement of standard Jamshidi needles (not shown) into adjacent pedicles  104  (or pedicles  106 ) with use of intraoperative fluoroscopy. This is done through the patient&#39;s skin, as the port  200  has been removed. Bone penetrating, stainless steel, “K-wires”  193  ( FIG. 8 ) are then passed through the Jamshidi needles into the pedicles  104  (or the pedicles  106 ) of each vertebra  100  and are advanced into the vertebral bodies  102  of the vertebrae  100  above and below the interbody fusion device  190 . Though the patient&#39;s skin is not shown in the accompanying drawings, it should be understood that the K-wires  193  stick out through the skin percutaneously. 
         [0087]    Next, a pedicle screw assembly  400  is inserted over each K-wire  193  and advanced into the pedicle  104  (or the pedicle  106 ) and into the vertebral body  102 .  FIG. 9  shows one screw assembly  400  in place, and the screw assembly  400  is shown in detail in  FIGS. 10 through 18 . A screwdriver  500  for use in placing the screw assembly  400  is shown in  FIGS. 19   a  through  19   c  and described below. 
         [0088]    The screw assembly  400  includes a pedicle screw  410 , a screw head  420 , and an extension portion  430 . The pedicle screw  410  ( FIG. 12 ) has an upper end  412 , a lower end  414 , and a cannulated core  416  that extends between the ends  412 ,  414  and allows the screw  410  to be inserted over (and guided by) the K-wire  193 . The upper end  412  is configured to be driven by the screwdriver  500 , and may take a variety of shapes (e.g., hexagonal cavity  413 , an octagonal cavity, etc.). 
         [0089]    The screw head  420  (which may also be referred to herein as a “polyaxial head”) is specifically shown in  FIGS. 13 and 14  and is permanently fixed to the upper end  412  of the screw  410  through a ball-and-socket joint (see  FIGS. 15 ,  16 , and  37 , though the structure that prevents the screw  410  from separating from the screw head  420  is not shown in the drawings). The ball-and-socket joint allows 360 degree rotation along the axis of the screw  410  and additionally allows the screw head  420  to pivot relative to the screw  410 . The screw head  420  defines a receiving area  421  and may include structure  424  for coupling the screw head  420  to the extension portion  430 . 
         [0090]    The extension portion  430  is attached to the screw head  420  and includes at least two arms  432  to allow percutaenous placement of the screw  410  over the K-wire  193  and to allow percutaneous manipulation of the polyaxial head  420  while inserting a rod  700  and a cap screw  900 , which are discussed below. An important development over the prior art concerns the extension portion  430  and the manner in which the extension portion  430  is coupled to the pedicle screw  410 . As detailed in  FIG. 18 , the extension portion  430  may have at least one point of weakness or “defect”  433 , allowing the extension portion  430  to be broken apart and separated from the head  420  when no longer needed. As best shown in  FIG. 37 , a catch  439  may interact with a cavity  425  in the head  420  (also shown in  FIGS. 13 and 14 ) and a passage  435  (also shown in  FIG. 17 ) in the extension portion  430  to temporarily couple the extension portion  430  to the screw head  420  (i.e., before the extension portion  430  is broken at the defect  433 ). While other means for fastening the screw head  420  to the extension portion  430  may also be used (e.g., a protrusion extending from the head  420  or the extension portion  430  interacting with a cavity in the extension portion  430  or the head  420 , etc.), the catch  439  may allow the screw head  420  to be coupled to the extension portion  430  without further weakening the defect  433 . 
         [0091]    Attention is now directed to the screwdriver  500 , shown in  FIGS. 19   a  through  19   c.  The screwdriver  500  includes a shaft  510  having an end  512  complementary to the upper end  412  of the screw  410  for driving the screw  410 , and the shaft  510  is hollow to allow the K-wire  193  to pass therethrough. In addition, a guide  520  is fixedly coupled to the shaft  510  (e.g., through welding, a set screw, or any other appropriate method/device) such that the guide  520  and shaft  510  rotate together. The guide  520  has passageways  522  configured to allow the arms  432  to pass through, temporarily securing the screwdriver  500  to the screw assembly  400 . By securing the screwdriver  500  to the screw assembly  400  (i.e., to the arms  432 ), the screwdriver/percutaneous pedicle screw complex is more rigid, which may be desirable. To increase rigidity and prevent migration of the guide  520  along the arms  432 , a set screw, complementary latching structure, and/or other fastening devices may be included to temporarily lock the guide  520  to the screw assembly  400 . Though not shown, a handle may be coupled to the shaft  510  above the guide  520 . 
         [0092]    Once the screws  410  are in place in the pedicles  104  (or the pedicles  106 ), the screwdriver  500  and the K-wires  193  may be removed ( FIG. 20 ). At this point in the procedure, the only devices extending through the patient&#39;s skin may be the extension arms  432  for each screw assembly  400 . Because of their attachment to the screw heads  420 , movement of the extension arms  432  may rotate the screw heads  420  three hundred and sixty degrees and also tilt the screw heads  420 . 
         [0093]    The desired rod  700  length is then selected. The rod length may be selected in various ways, such as by inspecting intraoperative fluoroscopic images or using a measurement device  600  ( FIG. 21 ), for example. The measurement device  600  has two arms  610  operatively coupled together (e.g., by a pivot  612 , a sliding mechanism, etc.), and a calibrated scale  614  is attached to one arm  610  such that the other arm  610  lines up with markings along the scale  614 . The arms  610  of the measurement device  600  are passed through the skin of the patient along the extension portions  430  such that each arm  610  contacts one of the heads  420  of the two screw assemblies  400 . A desired rod length is determined using the calibrated scale  614 , and the appropriate length rod  700  is selected. The rod  700  is typically curved to allow reconstruction of the normal curvature of the lumbar spine; this curvature is known as lordosis. However, in some cases, the surgeon may select a straight rod  700 . The scale  614  may add a predetermined distance (e.g., 10 mm) to the measured distance, and the ends of the arms  610  may be configured like ends of the rod  700 ; for example, each arm end may extend 5 mm (or another appropriate distance) outward from a respective screw head  420 . 
         [0094]    After the appropriate length rod  700  is selected, it is positioned using a percutaneous rod insertion tool  800  such that it is received in the receiving area  421  of the two screw heads  420 . The rod insertion tool  800  is shown in detail in  FIGS. 22 through 33 .  FIG. 22  shows the rod insertion tool  800  secured to the rod  700 . As shown, the rod insertion tool  800  includes an elongate housing  810  having upper and lower ends  812   a,    812   b.  The lower end  812   b  is shown having a smaller diameter than the upper end  812   a;  this allows the lower end  812   b  to function inside the patient&#39;s body as needed, and also allows the surgeon to easily maneuver the upper end  812   a.  The rod insertion tool  800  also includes a rotating end  820 , a control system for the rotating end  820 , an attachment device  840 , and a control system for the attachment device  840 . 
         [0095]    The rotating end  820  and the control system for the rotating end  820  are shown in  FIGS. 23 through 27 . The rotating end  820  is shown in detail in  FIG. 27  and includes an attachment side  822  which rotates from a first position facing generally the same direction as the central axis of the housing  810  ( FIG. 26 ) to a second position facing generally perpendicular to a central axis of the housing  810  ( FIG. 27 ). When the rod  700  is coupled to the attachment device  840 , the rod  700  extends generally parallel to the housing axis when the rotating end  820  is at the first position, and extends generally perpendicular to the housing axis when the rotating end  820  is at the second position ( FIGS. 22 through 24 ). The rotating end  820  is pivotably coupled to the housing  810  at pivot point  824 . 
         [0096]    The control system for the rotating end  820  includes a thumbwheel  832  ( FIGS. 22 through 25 ) and an internal plunger  834  ( FIGS. 23 through 26 ). The thumbwheel  832  and the internal plunger  834  are configured with complementary structure such that rotation of the thumbwheel  832  causes the internal plunger  834  to become higher or lower relative to the housing  810 . While various structures may be acceptably used to achieve this motion, one example is complementary threads, such that the thumbwheel  832  acts as a stationary nut and the plunger  834  acts as a linearly-moving screw. In such a configuration, only a portion of the plunger  834  needs to be threaded (i.e., the portion interacting with the thumbwheel  832  as the attachment side  822  moves between the first and second positions). To keep the plunger  834  from rotating (instead of moving linearly), the plunger  834  may interact with the housing  810  away from the threaded portion. For example, protrusions  836  ( FIG. 25 ) on the plunger  834  may interact with rails or slots (not shown) in the housing  810 . As shown in the drawings, the plunger  834  may include an internal channel  835 . 
         [0097]    To translate the linear movement of the plunger  834  into rotational movement of the rotating end  820 , a link  838  may be pivotably coupled to the plunger  834  and the rotating end  820 , as shown in  FIGS. 26 and 27 . When the plunger  834  is raised, the attachment side  822  may rotate about the pivot point  824  to the first position ( FIG. 26 ), and when the plunger  834  is lowered, the attachment side  822  may rotate about the pivot point  824  to the second position ( FIG. 27 ). 
         [0098]    Turning now to the attachment device  840  and the control system for the attachment device  840 , attention is directed specifically to  FIGS. 22 and 28  through  33 . The attachment device  840  includes a protrusion  842  ( FIG. 28 ) for aligning the rod  700 , a deformable crown  844  ( FIGS. 28 through 31 ), and an actuator  852  ( FIGS. 28 ,  32 , and  33 ). The deformable crown  844  is naturally at a cylindrical configuration, as shown in  FIGS. 28 through 31 , and includes a plurality of expansion channels  846 . While various materials and configurations may of course be acceptable, an exemplary crown  844  is constructed of a resilient material such as titanium, has an outer diameter  844   a  of approximately 0.12 inches, an inner diameter  844   b  of approximately 0.10 inches, a height  844   c  of approximately 0.216 inches, a channel depth  844   d  of approximately 0.16 inches, and a channel width  844   e  of approximately 0.02 inches. 
         [0099]    The actuator  852  ( FIGS. 28 ,  32 , and  33 ) has a first portion  854  that is generally cylindrical and a second portion  856  that is generally conical, and the actuator  852  sits inside the crown  844  ( FIG. 28 ). The actuator  852  may be configured such that the cylindrical portion  854  does not deform the crown  844 , and the conical portion  856  causes the crown  844  to expand. While various materials and configurations may of course be acceptable, an exemplary actuator  852  is constructed of the same material as the crown  844 , has an outer diameter  852   a  for the cylindrical portion  854  of approximately 0.09 inches, has a maximum diameter  852   b  for the conical portion  856  of approximately 0.11 inches, has an overall length  852   c  of approximately 0.2 inches, and has a length  852   d  for the conical portion  856  of approximately 0.12 inches. 
         [0100]    The control system for the attachment device  840  includes a screw  862  ( FIG. 22 ) and an internal cable (not shown). The internal cable extends from the screw  862  (which alternately may be a thumbwheel similar to thumbwheel  832 , or may be any other device for causing linear movement of the internal cable) to the actuator  852  (e.g., to cavity  853 ) and passes through the internal channel  835  of the plunger  834 . When the screw  862  is utilized to increase tension on the internal cable, the internal cable pulls the actuator  852  inward, causing the crown  844  to expand; when the screw  862  is utilized to reduce tension (or impart a pushing force upon) the internal cable, the internal cable pushes (or allows the actuator  852  to move) outward, allowing the crown  844  to contract ( FIG. 28 ). The internal cable may be any appropriate structure capable of providing sufficient pulling and pushing forces, as described above and understood by one of skill in the art. An exemplary internal cable is constructed of 7×49 stainless steel with an outer diameter of approximately 0.044 inches. 
         [0101]    In use, then, the rod  700  is selected, and is aligned such that the protrusion  842  mates with cavity  712  at one end  710  of the rod  700  ( FIGS. 34 and 35 ), and the crown  844  and actuator  852  are inserted in cavity  714  of the rod  700  ( FIG. 34 ) such that the crown  844  is generally cylindrical. The screw  862  is then used to increase tension on the internal cable, causing the actuator conical portion  856  to deform the crown  844 . With the crown  844  deformed, the crown  844  exerts force on the rod  700 , in effect locking the rod  700  to the attachment device  840 . 
         [0102]    Using the rod insertion tool  800 , the rod  700  is inserted through the patient&#39;s skin (i.e., inside an extension portion  430 ) such that the rod  700  is generally aligned with the center axis of the shell  820 . Once the rod  700  is inserted, the thumbwheel  832  is rotated, causing the internal plunger  834  to lower and the rotating end  820  (and the attached rod  700 ) to rotate. After the rod  700  is received in the receiving areas  421  of the two screw heads  420 , the screw  862  is used to provide a pushing force (or release tension) on the internal cable, allowing the actuator conical portion  856  to exit the crown  844  and the crown  844  to return to the cylindrical configuration. With the crown  844  at the cylindrical configuration, the attachment device  840  may be separated from the rod  700  and the rod insertion tool  800  may be removed. 
         [0103]    Turning to  FIGS. 36 through 38 , once the rod  700  is in place in the receiving areas  421  of the two screw heads  420 , a cap  900  is fixed to a threaded portion of each of the screw heads  420 . The caps  900  may be placed using the screwdriver  500  or another tool (e.g., a simple screwdriver having an appropriate driving mechanism), and the caps  900  lock the rod  700  in place by exerting force on the rod  700 . 
         [0104]    If compression is desired, one of the caps  900  is set in place and tightened, and the other cap  900  is set in place but not yet tightened. Before the second cap  900  is tightened, a compressor device  1000  is fitted onto the arms  432  of each extension portion  430  ( FIG. 39 ). Pressure is then applied from the compressor device  1000  to the arms  432  to provide compressive stress across the instrumentation construct to improve interbody fusion device surface area contact with the adjacent vertebral body endplates, thus increasing the probability of successful fusion of the vertebrae during healing and minimizing post-operative interbody graft migration. While compressive forces are applied, the second cap  900  is tightened, securing the rod  700  in a compressed position. The extension portions  430  of adjacent screw assemblies  400  may overlap slightly during compression; this is possible because the extension portions  430  of adjacent screw assemblies  400  are thin and low profile, which allows more effective compression. 
         [0105]    The compressor device  1000  is shown in detail in  FIGS. 40 through 42  and has a pivot  1002 , two arms  1004 , and a notched indicator  1006  attached to one arm  1004 . Each arm  1004  has an attachment portion  1005  ( FIGS. 41 and 42 ) configured for attachment to the extension portions  430  of the screw assemblies  400 . A tooth  1008  coupled to the second arm  1004  can be advanced along the notched indicator  1006  in the manner of a ratchet to set and maintain a desired level of compression. More particularly, the notched indicator  1006  has a toothed side that engages the tooth  1008  on the second arm  1004  to maintain a compressed state. Compression is maintained until the tooth  1008  is released from the indicator  1006  to permit removal of the compressor device  1000  from the extension portions  430  after the second cap  900  is tightened. 
         [0106]    After the rod  700  is in place and both caps  900  are tightened, the extension portions  430  may be removed from the pedicle screws  410  and the screw heads  420  by simply pulling the arms  432  away from one another, causing the extension portions  430  to fail at the defects  433 , which are best shown in  FIG. 18 . In an exemplary embodiment, approximately a 30° angle between the arms  432  is required to separate the extension portions  430  from the pedicle screws  410  and the screw heads  420 ; this of course can be altered (e.g., by altering the design of the defects  433 ), however. Once the extension portions  430  are removed, the fascia and skin may be closed, and the procedure may be concluded. 
         [0107]    In prior art percutaneous pedicle screw systems, early release of the percutaneous screw extensions is a significant problem. This typically requires complete removal of the pedicle screw, and a larger diameter pedicle screw/extension complex is then assembled and re-inserted into the pedicle over a new K-wire. This requires extensive operative time, and can be a major source of patient morbidity. Salvage tool  1500  (shown in  FIGS. 43   a  through  46 ) effectively reconstructs the extension portion  430  in the event that the extension portion  430  is released prematurely; this avoids the need for pedicle screw removal and replacement. To be clear, salvage tool  1500  is currently not intended to be used in every surgery, or even routinely, but is instead a device which may be used if necessary. 
         [0108]    The salvage tool  1500  contains two extensions  1510  that are manufactured to the same dimensions and configurations as the original extension portion  430 . Salvage tool  1500  also contains a trigger  1522  along a handle  1520 . By pulling the trigger  1522 , the two extension arms  1510  are brought from an open alignment ( FIG. 43   a ) into a closed (parallel) alignment ( FIGS. 43   b  and  45 ). This may be accomplished, for example, through linkage coupled to at least one of the extensions  1510  and operable by the trigger  1522  to rotate the extension  1510  to the closed alignment when the trigger  1522  is pressed. Various other mechanical systems may alternately be used to rotate at least one of the extensions  1510  upon pressing the trigger  1522 , as will be clear to one skilled in the art. 
         [0109]    The extension(s)  1510  may be biased to the open alignment (e.g., by one or more spring), and a lock  1530  may be employed to maintain the extension(s)  1510  at the closed alignment for a period of time. The lock  1530  shown in  FIGS. 44 and 45  is simply a catch that is rotatable about the handle  1520  to maintain the trigger  1522  at the pressed configuration until released. Again, various other mechanical devices may alternately be used to lock the extension(s)  1510  at the closed alignment, as will be clear to one skilled in the art. 
         [0110]    To use the salvage tool  1500  (e.g., in the event of premature separation of extension portions  430  from pedicle screw  410 ), the extensions  1510  are inserted adjacent the screw head  420 . The trigger  1522  is then pulled, bringing the extensions  1510  to the closed alignment along the screw head  420 , and the lock  1530  may be employed. As shown in  FIG. 46 , a ledge (or “wall”)  1511  may be located at the distal end  1510   a  of each extension  1510  to extend along the lower side of the screw head  420  when the extensions  1510  are in place. The extension portions  430  are thus reconstructed, allowing the operation to continue (e.g., the rod  700  may be positioned and/or secured) without having to convert to an open procedure or remove and replace the pedicle screw  410 . 
         [0111]    While the procedure set forth above includes only two screw assemblies  400 , multilevel procedures may also be performed using the equipment and techniques set forth above. As an example, a two level minimally invasive procedure according to one embodiment is shown and described with reference to the above description and  FIGS. 1 through 46  of the accompanying drawings, and additionally with reference to  FIGS. 47 through 56  of the accompanying drawings. 
         [0112]    For a two level procedure, the steps set forth above to fuse vertebrae  100  (i.e., the steps utilizing the port  200 ) are repeated on an additional adjacent vertebra  100  such that the additional vertebra  100  is similarly fused. This situation is shown schematically in  FIG. 47 . 
         [0113]    For a multilevel fusion, screw assemblies  400  are first fixed to the upper and lower vertebrae  100   a,    100   b  ( FIG. 47 ) in the same manner as described above (i.e., starting with placement of Jamshidi needles and ending with removal of the screwdriver  500  and the K-wires  193  after the screws  410  are in place in the pedicles  104  or  106 ). Next, an alignment tool  1600  is attached to the extension portion  430  of the fixed screw assemblies  400 . 
         [0114]    The alignment tool  1600  is shown in  FIGS. 48 through 56  and includes opposed rails  1610  (identified individually as  1610   a  and  1610   b ) and a plurality of receiving members  1620 . In some embodiments, at least one of the receiving members  1620  is permanently coupled to at least one of the rails  1610  such that it may or may not be movable along the rail  1610  but cannot be separated from the rail  1610 . In other embodiments, all of the receiving members  1620  are removably coupled to the rails  1610 . 
         [0115]    Each receiving member  1620  is configured to receive a respective extension portion  430 . In some embodiments, as shown in  FIGS. 48 through 56 , the receiving members  1620  for use at the ends  1600   a  of the alignment tool  1600  each have first and second holes  1622   a,    1622   b  configured to receive the arms  432  of respective extension portions  430  (these receiving members  1620  are identified individually as  1620   a ), while receiving members  1620  for use in a middle region  1600   b  of the alignment tool  1600  each have a single hole  1624  for receiving the arms  432  of respective extension portions  430  (these receiving members  1620  are identified individually as  1620   b ). The holes  1624  may be rectangular, as shown in  FIGS. 48 and 49 , or may be circular, as shown in  FIGS. 53   a  through  56 , or may be any other appropriate shape. A circular shape may be desirable for allowing easier rotation of the extension portion  430  inside the hole  1624 . While only one receiving member  1620   b  is shown in the drawings, it should be appreciated that additional receiving members  1620   b  may be required for procedures requiring placement of four or more pedicle screws  410 . 
         [0116]    If a receiving member  1620  is movable along the rails  1610 , a locking device is preferably included to restrict the receiving member  1620  from moving from a desired location along the rail  1610   a.  For example a set screw  1632  ( FIGS. 50   a  and  50   b ) operable by the user may extend through hole  1634  in the receiving device  1620  to interact with the rail  1610   a  passing through hole  1636  in the receiving device  1620 , effectively locking the receiving member  1620  to the rail  1610   a.  While a specific embodiment of a locking device is shown in the accompanying drawings, one skilled in the art will appreciate that other locking devices and configurations may alternately, or additionally, be used. 
         [0117]    Additionally, a locking device is preferably included to restrict the receiving member  1620  from moving from a desired location along the arms  432  of a respective extension portion  430 . For example, a set screw  1642  ( FIGS. 50   a  and  50   b ) operable by the user may extend through hole  1644  in the receiving device  1620  to interact with the rail  1610   b  passing through hole  1646  in the receiving device  1620 . Because pressure on the rail  1610   b  from set screw  1640  causes the rail  1610   b  to exert pressure on the arm  432  (which passes through hole  1622   b  for receiving members  1620   a,  and which passes through hole  1624  for receiving members  1620   b ), this effectively locks the receiving member  1620  to both the rail  1610   b  and the arm  432 . While a specific embodiment of a locking device is shown in the accompanying drawings, one skilled in the art will appreciate that other locking devices and configurations may alternately, or additionally, be used. 
         [0118]    In use, then, the extension portions  430  of the upper and lower screw assemblies  400  are coupled to respective receiving members  1620  (e.g., receiving members  1620   a ), which may require adjusting the receiving members  1620  along the rails  1610 , as set forth above. Once in place, the locking devices are used to fix the receiving members  1620  to the rails  1610  and also to fix the receiving members  1620  to the extension portions  430 . At this point, intraoperative fluoroscopy may be utilized. The unlocked receiving member  1620  (e.g., receiving member  1620   b ), and specifically the hole  1624 , is aligned with the pedicle  106  (or the pedicle  108 ) and fixed to the rails  1610 , as set forth above. 
         [0119]    Next, the remaining screw assembly  400  is fixed to the remaining vertebra  100  in the same manner as described above and used for the prior two screw assemblies  400  (i.e., starting with placement of a Jamshidi needle and ending with removal of the screwdriver  500  and the K-wire  193  after the screw  410  is in place in the pedicle  104  or  106 ), though the Jamshidi needle, the K-wire  193 , and the screw assembly  400  are all inserted through the hole  1624 . By using the alignment tool  1600  (e.g., by working through the hole  1624 ), all of the screw heads  420  will be aligned to receive the rod  700 . This is generally shown in  FIG. 56 , though it should be appreciated that the rod  700  would never be in place before all of the screw assemblies  400  are in place, and that the caps  900  would not be set in place until after the rod  700  is positioned in all three receiving areas  421 . 
         [0120]    The rod  700  is selected as set forth above. Next, using the rod insertion tool  800 , the rod  700  is positioned through the extension portion  430  of the upper screw assembly  400  or the lower screw assembly  400 , and rotated, as set forth above, such that the rod  700  is positioned in all three receiving areas  421  of the screw heads  420 . Caps  900  are then set in place as described above, and only one cap  900  (e.g., the cap  900  in the middle) is tightened. Once the caps  900  are set in place, the alignment tool  1600  may be released from the extension portions  430  and set aside. 
         [0121]    If compression is desired, the compressor device  1000  may be used generally as set forth above. The upper or lower screw assembly  400  is first compressed with the central screw assembly  400  and locked into place by tightening the appropriate cap  900 , and then the other screw assembly  400  is compressed with the central screw assembly  400  and locked into place by tightening the remaining cap  900 . To conclude the procedure, the extension portions  430  may be removed from the pedicle screws  410  and the screw heads  420  as set forth above, and the fascia and skin may be closed. 
         [0122]    A summary of the procedures described above is illustrated in the flowchart of  FIG. 57 . Procedure  2000  begins with an incision  2002  for a posterior approach to the patient&#39;s spine. The port  200  is then inserted through the skin incision until it is flush with the facet  118 . The decompression is then performed at step  2004  through the port  200 , which includes a facetectomy and microdiscectomy. If a laminectomy is needed (see step  2005 ), it is performed at step  2006  through the port  200 , and then the procedure  2000  continues to step  2008 ; if a laminectomy is not needed, the procedure  2000  continues from step  2004  to step  2008 . 
         [0123]    At step  2008 , the nerve root is gently retracted medially with a nerve root retractor  180  that may be attached to the port  200 . The discectomy is then completed at step  2010 , and the interbody fusion device  190  is inserted through the port  200  into the intervertebral space between the vertebral bodies  102  to elicit arthrodesis. The port  200  is then removed, and the procedure  2000  continues to step  2012 . 
         [0124]    At step  2012 , K-wires  193  are inserted into the pedicles  104  (or  106 ) of the vertebrae using Jamshidi needles, and cannulated pedicle screws  410  (of screw assemblies  400 ) are inserted percutaneously over the K-wires  193  into the upper and lower vertebrae  100  of the spinal segment to be stabilized. 
         [0125]    If a multilevel fusion is performed (see step  2014 ), the alignment tool  1600  is placed over the percutaneous extensions  430  of the screw assemblies  400  and then the intervening pedicle screw(s)  410  is/are inserted through the alignment tool  1600  at step  2016 . This guarantees alignment of the middle pedicle screw(s)  410  within the construct, thereby facilitating rod placement, and the procedure  2000  continues to step  2018 . If more than two vertebrae are not involved, the procedure  2000  moves from step  2012  to step  2018 . 
         [0126]    If an extension portion  430  of a screw assembly  400  is accidentally released prematurely (see step  2018 ), the salvage tool  1500  is used at step  2020  to grip the screw head  420 , allowing completion of the procedure  2000  without replacing the pedicle screw assembly  400 ; the procedure  2000  then continues to step  2022 . If the extension portion  430  is not released prematurely, the procedure  2000  moves from step  2018  to step  2022 . 
         [0127]    At step  2022 , the appropriate rod length is measured (e.g., from intraoperative fluoroscopic images or using the measurement device  600 ), and the procedure  2000  continues to step  2024 . 
         [0128]    At step  2024 , the rod  700  having the appropriate length is selected and inserted into the rod insertion tool  800 . The rod insertion tool  800  is then used to insert the rod  700  between the percutaneous screw extensions  430  of the most caudad or cephalad pedicle screw assembly  400  within the construct. Next, the rod  700  is rotated into position within the receiving areas  421  of the polyaxial heads  420 , and the caps  900  are set in place. One cap  900  is tightened, securing the rod  700  in place. 
         [0129]    The procedure  2000  then moves to step  2026 , where different paths are taken depending on whether compression is desired. If so, the procedure  2000  continues to step  2028 ; if not, the procedure  2000  continues to step  2030 . 
         [0130]    At step  2028 , the compressor device  1000  is fitted onto the extension portions  430  and adjusted to provide the amount of compression that is desired. The untightened caps  900  are tightened while compression is applied to maintain the instrumentation construct in the compressed position, and the compressor device  1000  is set aside. The procedure  2000  then moves to step  2032 . 
         [0131]    At step  2030 , the untightened caps  900  are fully tightened to finish securing the rod  700  in place, and the procedure  2000  continues to step  2032 . 
         [0132]    At step  2032 , the extension portions  430  are removed, and the incision is closed at step  2034  to end the procedure  2000 . 
         [0133]    It should be understood that the matter contained in the above description and/or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. Those skilled in the art appreciate that variations from the specified embodiments disclosed above are contemplated herein. Certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations and are contemplated within the scope of the claims. Further, various steps set forth herein may be carried out in orders that differ from those set forth herein without departing from the scope of the present methods. The description should not be restricted to the above embodiments, but should be measured by the following claims.