Spinal hook

This invention provides a spinal hook comprising a body having a rod receiving bore therethrough, a connecting portion and a shoe portion, the connecting portion extending along a plane approximately normal to the axis of the base and the shoe portion extending in a plane from the connecting portion and terminating in a tip on one end and joined to the connecting portion on the other end. Preferably, the side of the body facing the shoe portion has a convex curved outer surface to allow a closer fit to a vertebra to which the hook is attached. In preferred embodiments of the invention, the tip of the shoe is disposed closer to the body than the remainder of the shoe by either forming an acute angle between the shoe and the connecting portion or bending the tip of the shoe. The shoe may be tapered in both width and thickness and the connecting portion may be tapered in width from the body to the shoe to provide better fit between the hook and the vertebrae. The body is provided with one non-round slot or a plurality of holes on at least one side thereof to facilitate gripping and insertion of the hook. A holder adapted for use in connection with the present hook is also provided.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to spinal compression/distraction hooks of the type 
used in the Harrington.TM. system, wherein one or more rods are used to 
provide compressive or distractive force between pairs of hooks. The 
system was originally designed to be used to correct scoliotic deformities 
occurring in adolescent girls, but is now also used to correct other 
deformities and to repair or stabilize the spine following spinal 
fracture. 
2. Description of Prior Art 
The prior art includes a number of devices for use in correction of spinal 
deformities. These devices have been used primarily for the correction of 
lateral deviation of the spinal column, known as scoliosis. The spinal 
curvature which results from scoliosis is generally defined on the basis 
of specific reference points. In particular, the extreme upper and lower 
vertebrae and the most displaced vertebrae are of particular interest. The 
extreme upper and lower vertebrae are those which are the most inclined 
relative to the median longitudinal axis of the torso. The two planes 
within which the extreme upper and lower vertebrae can be found define the 
scoliotic angle. The most displaced, or apical, vertebra is defined as the 
vertebra which is the farthest from the median axis of the torso. 
It is during surgery that the correction is completed and finalized. For 
this purpose, a solid rod with anchoring hooks is typically placed in the 
concavity of the curvature and a threaded rod with hooks is placed on the 
convexity of the curvature. These rods straighten the spine and maintain 
the correction until arthrodesis is attained by means of autogenous bone 
graft. The implants used most often to correct curvature during surgery 
are known as the Harrington.TM. distraction system and the Harrington.TM. 
compression system. (Harrington is a trademark of Zimmer, Inc., Warsaw, 
Ind.). 
Another use for spinal rods is correction of kyphotic (hunchback) 
deformities produced by disease or spinal injury. In this use, either two 
compression or two distraction rods are used. Correction can be achieved 
by pushing the lamina of the apical vertebra anteriorly with the rods. 
The shape and dimensions of existing spinal hooks (FIG. 1A) were generally 
designed for use on the above-mentioned treatment of scoliosis in 
adolescent girls. In this use, the hooks and rod act together like a jack 
to direct a longitudinal (uniplanar) force to elongate the spine and 
straighten the curvature. In recent years, however, surgeons have also 
begun treating fractured spines with the same hooks and rods. The typical 
patient with a fractured thoracic or lumbar spine is an adult male with 
thicker bones than the young girls for whom most spinal hooks were 
designed. Secondly, in treating fractured or dislocated spines, two rods 
rather than one are used. Accordingly, two hooks must be placed under the 
lamina of the top and bottom vertebral segment to be fixed with the rods. 
All existing spinal hooks known to the inventor have four characteristics 
which make proper placement and implantation of the hooks unnecessarily 
difficult in many patients,(see FIG. 1A): 
The rod housing or body is square. The corners of the anterior side of the 
hook body jam into the concavely shaped lamina/spinous process junction 
95. This prevents the hook from seating fully and often makes it necessary 
for the surgeon to cut away bone to make space for the square hook body, 
using an osteotome. 
The space between the hook body and shoe 96 is not wide enough to fit 
around the lumbar spine lamina for many adult patients. 
When existing large hooks are placed on both the right and left lumbar 
lamina in the treatment of spinal injury, the existing broad and square 
hook shoes often bump into each other making proper seating of the hooks 
difficult or impossible. The hooks must then be overlapped at their shoes. 
Existing hook designs offer either a broad, blunt shoe edge 97 or a sharp 
cutting shoe edge. Neither design is optimal for placement of distraction 
hooks in the thoracic spine. In the thoracic spine hooks wedge between two 
sides of facet joints 98. The edge of the blunt hook shoes are too thick, 
making insertion difficult. The sharp hook edge can cut into the bone 
causing a small fracture which can subsequently propagate resulting in 
hook dislodgement. The sharp edged hooks can also increase the chance of 
tearing epidural veins causing bleeding when used under either thoracic or 
lumbar lamina. 
When these traction/distraction hooks are used to correct kyphotic 
deformity, the force exerted by the hook has a significant force vector in 
the posterior direction. (arrows in FIGS. 1A and 1B). Existing hooks are 
designed to exert force in the superior or inferior directions and are, 
therefore, prone to dislodgement when they are used to apply a force in 
the posterior direction. 
Although postoperative hook dislodgement occurs following treatment of all 
spinal conditions, this problem is especially frequent when hooks and rods 
are used to correct kyphotic deformity where approximately 10%-15% of the 
patients have hooks dislodge postoperatively in the first month. Most 
fractures and dislocations of the thoracic or lumbar spine result in 
kyphotic deformity. Spinal hooks and rods are used to correct this 
deformity by combining distraction with 3-point loading of the spine. In 
this usage, the rod or more ideally, a rod-sleeve pushes forward over the 
apex of the kyphotic deformity and the hooks pull backwards or 
posteriorly. Such a sleeve is described in the inventor's U.S. patent 
specification Ser. No. 159,396 (June 13, 1980), which is hereby 
incorporated by reference. All existing hook designs known to the inventor 
feature a large (greater than 5 mm) hook radius. In almost all hooks for 
use in the thoracic or lumbar spine, portion 96 of the hook between the 
body and the tip of the shoe is rounded, usually semicircular with a 
constant radius. To the contrary, the shape of the undersurface of 
thoracic lamina 99 is essentially flat or slightly concave. Hence, the 
sole point of contact between the hook and thoracic lamina is at the very 
edge of the lamina. Particularly when the hook is used to effect a 
posteriorly directed force to correct kyphotic deformity, a moment is 
produced within both the hook and the lamina. The hook is pulling the 
inferior edge of the lamina posteriorly which causes it to tilt. Likewise, 
since the lamina is making contact with the curved inner aspect of the 
hook, the hook tilts in the same direction as the lamina. The curved hook 
then acts as a skid to encourage outward migration of itself relative to 
the lamina. When the lamina and hook are tilted and the patient bends 
forward and rotates slightly the hook can dislodge from under the thoracic 
lamina. In other words, the circular shape of the inner aspect of the hook 
shoe actually encourages dislodgement from under the thoracic lamina and 
facets. 
The majority of the length of shoes on existing hooks is part of the hook's 
interior circular radius and, accordingly diverges from the hook body. As 
a result, the further the hook is advanced onto the flat underedge of the 
lamina, the further hook shoe tip 97 projects inwardly (or anteriorly) 
away from the lamina and into the spinal canal. This can be 
disadvantageous particularly for the spine-injured patient whose spinal 
cord 100 may be swollen and whose spinal canal may be already narrowed 
from fractured vertebral body fragments. Any forward tilting of the hook, 
as described previously, makes the hook shoe project yet further into the 
spinal canal. 
Generally speaking, all previous hooks of which the inventor is aware were 
designed to direct only longitudinal (compression or distraction) forces 
against the spine, as opposed to hooks designed to also transmit forces 
directed posteriorly at approximately at 90.degree. angle to the 
longitudinal axis of the spine. 
There are Harrington.TM. hooks available which have hook shoes extending 
beyond the rod-engaging body of the hook, for example Zimmer .TM. No. 
1279-01 Leatherman Hook.TM.. These hooks do not, however, exhibit a hook 
shoe which is angled inwardly with respect to the body or possess a narrow 
radius between the connecting portion and the shoe. 
There are several difficulties frequently encountered with existing hooks 
holders. These include: 
Excessive wobble between the holder and hook. 
Impingement of the holder on laminar bone. 
An uncomfortable handle. 
A handle length similar to that of the rod holder. 
Difficulty in aligning the holder. 
All existing spinal hooks attach to the hook holder by means of a single 
pair of holes 101 in the hook in FIG. 1A which articulate with a pair of 
nipples on the hook holder. Since the nipples are opposite each other, 
they have the same axis of rotation. Existing hook holders also press 
against the top of the hook body to limit rotation about the nipples. 
Particularly, when treating kyphotic deformity and spinal injury, 
corrective forces are applied to the spine manually by means of the hook 
holder attached to the spinal hook. Considerable force is often required 
for these maneuvers. As a result, the hook holder nipples wear away and 
the hook holder develops excessive "play." This results in excessive 
wobble between the hook holder and the hook. Because of the excessive 
wobble, the hook holder tilts and often bumps into the rod holder during 
the process of hook/rod engagement. Worse yet, the hook holder not 
infrequently breaks loose of the hook when corrective forces are being 
applied to the spine via the hook holder. 
Another problem with existing hook holders is that the working end of the 
instrument is essentially square. This square edge at the lower end of the 
holder often abuts the junction between the lamina and spinous process 
bone 95 making it difficult to engage the hook holder with the hook once 
the hook is implanted under the lamina. Another minor disadvantage with 
existing hook holders is that there is no way to determine correct 
placement of the holder on the hook when attempting to articulate the two 
devices. 
In the installation of a spinal hook system when repairing kyphotic 
deformities, two hook holders and one rod holder are used to grip a pair 
of distraction hooks and a rod. The unratcheted end of the rod is usually 
inserted into the inferior hook, after the ratcheted end of the rod has 
been first inserted into the superior hook. The rod is gripped near the 
inferior end, causing the rod holder to be close to the inferior hook 
holder. In inserting the rod into the inferior hook, the inferior hook is 
pulled posteriorly and a torque is applied to the hook by simultaneously 
pulling the inferior hook holder's handles superiorly. When the hook 
holder develops free play, it tends to pivot close enough to the rod 
holder to interfere with the rod holder at the handles. Since as much as 
40 kg force is being applied in this procedure, the interference can raise 
significant problems for the surgeon and his assistants. There is 
presently no hook and rod attachment system tool set which avoids the 
above problem of hook interference. 
SUMMARY OF THE INVENTION 
It is, accordingly, an object of the invention to provide a spinal hook 
which is more anatomically suited for use in supporting the adult spinal 
column. More specifically, an object of the invention is to reduce the 
amount of time and trauma necessary to install the hook onto the spine and 
to provide a hook edge which enables the hook to wedge between two sides 
of facet joints in the thoracic spine without being so sharp as to cause 
trauma to the vertebrae or adjacent tissues. It is a further object to 
provide a hook which minimizes the penetration of the hook shoe into the 
spinal canal. 
lt is a further object to provide a spinal hook which minimizes its 
tendency to become dislodged post-operatively, particularly in cases in 
which the hook applies a significant vector of force to the spine normal 
to the longitudinal axis of the rod to which a hook is attached, and 
especially when the force vector is directed posteriorly away from the 
spinal vertebrae. This is particularly important in the correction of 
kyphotic deformities involving a three-point loading of the spine. It is a 
further object to provide a hook which minimizes hook-shoe projection into 
the patient's spinal canal under either a 3-point or uniplanar loading. 
It is a further object of the invention to provide a means to more stably 
grip a spinal hook during surgery. On this point, it is an object to 
prevent excessive wobble and to provide a hook which meets with a tool in 
such a way as to avoid a tendency for the hook to tilt when being gripped 
by the tool. 
Accordingly, a hook designed to secure a compression or distraction rod is 
provided in which the radius of curvature 55 between the connecting 
portion and shoe is reduced and in which the part of the hook secured to 
the rod has a convex, curved surface 61 facing the shoe in order to 
maximize clearance for the adjacent vertebral lamina. The hook is formed 
with a shoe tip which is closer to the body of the hook than any part of 
the hook shoe so as to further retard the hook's tendency to dislodge from 
the spine and to reduce the projection of the hook shoe into the spinal 
canal. In reducing the tendency of the hook to traumatize the spinal 
tissue, especially when being inserted at the facet of a vertebra, the 
hook design offers an edge which has a semi-sharp tip which is tapered in 
both dimensions. 
In a further aspect of the invention, the hook is provided with two 
gripping dimples or holes on one or both sides of its body which mate with 
corresponding pins on a gripping tool. While the specific configuration of 
the gripping arrangement may vary, the configuration prevents the hook 
from pivoting with respect to the gripping tool. Further refinements of 
the gripping tool include a visual alignment of the hook with the tool's 
"business end" and a tapering distal end on the tool to provide increased 
clearance for the tool when the hook is being installed on the spine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is an illustration of a spine of a patient suffering from scoliosis 
schematically represented from the rear. The spinal column 1 consists of 
vertebrae 3, including the vertebrae 3' designated T1-T12 and L1-L5 (of 
which T4-T11 and L1-L3 are shown). The patient illustrated in FIG. 1 
exhibits a scoliosis involving a deviation of the vertebrae 3 to the 
right. The scoliotic curvature can be defined on the basis of the top 
vertebra T5 and the bottom vertebra T12 of the deviation, and the 
vertebrae T8 and T9 which are located at the peak of the curvature. It is 
noted that the vertebrae T5 and T12 are those which are most strongly 
inclined relative to the mediar longitudinal axis M--M of the body, while 
vertebrae T8 and T9 are those which are farthest from that axis. When the 
scoliotic curvature exceeds a given limit, it becomes necessary to 
consider surgical treatment of the scoliosis. The surgical treatment is 
known as arthrodesis and consists of fusing together the vertebrae of the 
scoliotic curvature, after correcting the scoliotic curvature to the 
maximum possible extent by straightening and opening. Such correction can 
be partially accomplished prior to the operation by continuous traction of 
the spine 1 or by corrective plaster casts. 
However, it is during surgery that the correction is completed and 
finalized. Typically, a solid rod with hooks is placed in the concavity of 
the curvature, occasionally, a threaded rod with hooks is placed on the 
convexity of the curvature. These rods straighten the spine and maintain 
the correction until arthrodesis is attained by means of autogenous bone 
graft. The implants used most often to correct curvature during surgery 
are known as the Harrington.TM. distraction system and the Harrington.TM. 
compression system, illustrated in FIG. 1. 
The distraction system of FIG. 1 includes two metallic anchoring devices 11 
and 13 of the hook type, which are attached to selected ones of the 
vertebrae T4-T12 
which comprise part of the spinal column 1. In distraction, the open ends 
of the hook are directed away from each other. A notched metal rod 17 
serves as a stay and permits the spacing between the hooks 11 and 13. Such 
rods are available, for example from Zimmer, Inc. as Distraction Rods, 
catalogue Nos. 1250-00-01 through -25. One of the ends 19 of rod 17 is 
usually notched in such a manner as to provide a ratcheted adjustment of 
the distance between the hooks 11 and 13 by means of a spreading 
instrument. Generally, the superior anchoring device 11 is intended for 
fastening toward the upper end of the spine and is hooked onto a dorsal 
vertebra T4. Usually the hook of the superior anchoring device 11 is 
directed superiorly and shaped in such a manner as to permit its insertion 
between the spinous process and a transverse process of that vertebra, 
between the superior and inferior articular facets. The hook of the 
superior anchoring device 11 penetrates into the interarticular space and 
is supported on the vertebra T4. 
Similarly, the inferior anchoring device hook 13 is intended to be fastened 
at the inferior end of the spine 1, and is often supported on a lumbar 
vertebra such as vertebra L2. It is contemplated that the hook 13 is 
directed inferiorly and supported on the lamina of the lumbar vertebra L2 
between the spinous process and the articular facet mass. 
The compression system consists of two or more metallic anchoring devices, 
hooks 21 and 23, which are attached to selected lamina or transverse 
processes of vertebrae T4-L2 which are situated on the convex side of the 
scoliotic curvature. In compression, the open ends of hooks 21 and 23 are 
directed towards each other. Threaded metal rod 25 serves as a stay or 
tension band between the hooks 21 and 23. Such rods are available from 
Zimmer, Inc., for example, as a Threaded Rod, catalogue No. 1257-00-10. 
Hooks 21 and 23 usually face each other and slide freely along threaded 
rod 25. These hooks 21, 23 are adjusted by means of hex nuts 27 so as to 
effect compression of the convexity of the scoliotic curvature. It is 
understood that more than two hooks and nuts can be used to achieve the 
desired amount of compression. 
Additional straightening of both angular and rotary components of the 
scoliosis and improved fixation of the surgically implanted device is 
accomplished by the use of sleeve members 41. Prior to securing 
compression rod 25 in hooks 21, 23, sleeves 41 are fitted over the rod and 
spaced a distance apart selected by the physician. Once the rod is secured 
in the hooks 21, 23, with appropriate tightening, the sleeves can be 
adjusted up or down so that they can rest on and provide points of 
pressure application to correct angular and rotary deformity against the 
selected vertebrae. In the case of FIG. 1, sleeves 41 rest against and 
apply pressure to the surface of the spinous process of vertebrae T8 and 
T9. 
FIGS. 2 and 3 show the use of sleeves and rods in the correction of 
kyphotic deformity. The sleeves 41, in combination with the hooks 42, 43, 
effect a side loading of the rod 44 against the vertebrae. Since this side 
loading requires a minimum of three pressure points (two hooks and one 
sleeve). the system with the sleeve 41 is said to effect a three-point 
loading, as shown by the arrows in FIG. 3. In order to more soundly secure 
rods 25 and 44 to the vertebrae under three-point loading, the hooks 42 
and 43 are contoured so as to prevent dislodgement from the vertebrae. 
FIGS. 4-6 show hook 43 which is is applied by a rod, formed so that it 
avoids dislodgement when the three-point force such as distraction rod 44, 
to the vertebrae. While the use of the hook 43 with distraction rod 44 is 
discussed, it is understood that inventive features also apply to hooks 
such as hooks 21 and 23 used with compression rods such as rod 25. The 
hook 43 comprises a body portion 45, a connecting horizontal portion 47 
and a shoe portion 49, with the connecting portion 47 connecting the shoe 
portion 49 to the body portion 45. The present hook shown in FIG. 1B can 
be distinguished from the conventional hook FIG. 1A since body portion, 
connecting portion and shoe portion form distinct angular sections rather 
than one smooth continuous curved section as in the conventional hook. As 
a result, the present hook has a generally L-shaped configuration when 
viewed from its side. For simplicity of drawing, the connecting horizontal 
portion 47 is disposed vertically in FIGS. 4-6. It will, of course, be 
understood by those skilled in the art that, when installed with the 
Harrington.TM. system, with the spine arranged vertically, the connecting 
horizontal portion 47 will, in fact, be horizontally disposed, as the 
connecting portion 47 extends in a plane anteriorly from the body portion 
45. 
The body portion 45 has a bore 51 therethrough which extends along the 
length of the body portion 45. The bore 51 is dimensioned so that the hook 
43 may be placed over a Harrington.TM. rod such as distraction rod 44. In 
the preferred embodiment, the minimum diameter D.sub.min can range between 
6.40 and 6.53 mm. Most of the bore 51 has a larger diameter D.sub.max 
which preferably ranges from 6.86-7.126 mm. A ledge 53, defined by the 
change fro D.sub.min to D.sub.max forms a ratchet-type catch as has been 
developed by Paul Harrington for distraction hooks and remains typical of 
Harrington.TM. distraction hooks. 
As mentioned before, extending from the body 45 is a connecting portion 47 
which connects to a shoe portion 49. The connecting portion 47 extends 
from the body 45 perpendicularly from the center axis of the bore 51 and 
from one end of the body 45. The connecting portion 47 joins the shoe 
portion 49 at a curve 55. 
The shoe 49 terminates at a blunt edge 57 on the opposite side of the shoe 
49 at the curve 55. This edge 57 is preferably formed by chamfering the 
shoe 49 from its exterior surface 59 at an angle c. Angle c is preferably 
about 30.degree. from the exterior surface 59, although it could range 
from 15.degree. to 60.degree.. The resulting edge is then "broken" by 
polishing to form a blunt edge 57. The blunt edge 57 is able to wedge 
between two sides of facet joints in the thoracic vertebrae without being 
likely to cut into the bone. 
It is important that the tip 58 of shoe portion 49 be disposed closer to 
the body portion 45 than the remainder of shoe portion 49. To accomplish 
this, shoe portion 49 can be angled inwardly towards the body portion 45 
at an acute angle s with respect to the axis of the bore 51 (FIG. 6). 
Angle s is within the range of about 1.degree. to 15.degree. and 
preferably 5.degree.. Alternatively, shoe portion 49 can be formed 
parallel to the body portion 45' with the end of the hook portion 49' 
being bent so that the tip 58A is situated closer to the body portion 45' 
(FIG. 6A). The distance (L.sub.58) between tip 58A and the inside surface 
of the shoe 49' generally approximately 1 mm. By placing the tip 58 or 58A 
of hook portion 49 or 49 closer to body portion 45 or 45' and using an 
"L-shaped" hook, it has been found that dislodgement of the hook after 
implantation can be prevented. 
It has been found that the surface of the vertebral facet in the thoracic 
region of the spine is either vertical or slightly inclined posteriorly as 
viewed laterally. FIG. 1B shows that in the present invention, the 
"female" surface, i.e. the interior facing surface, of the hook fits more 
properly the shape of the thoracic lamina. Shoe portion 49 engages the 
vertebra at the blunt edge 57 or along most of the length of the shoe 
portion rather than at the curve 55. This avoids the tendency for the 
curve 55 (or radius 96) to act as an inclined plane to wedge the hook out 
of engagement with the vertebra when a significant vector of force is in 
the posterior direction as shown in both FIGS. 3 and 1A. 
In order to further reduce the tendency for the curve 55 to wedge the hook 
out of engagement with the vertebra, the curve 55 is less than 1/3 the 
length of the connection portion 47 as measured from the point where 
curvate outer profile 61 of the body 45 meets the connecting portion 47 to 
the point on the exterior surface 59 of shoe portion 49 which has the 
greatest vertical distance from body portion 45. This reduces the inside 
radius of curve 55 to less than 4 mm and preferably less than 2.5 mm. 
In the testing of prototypes of this hook configuration, it has been found 
that of 25 kyphotic spine-injured patients who had the hook installed in 
the thoracic or lumbar spine, none had the hooks dislodge. This 
preliminary result contrasts with a 10% to 15% dislodgement rate for 
conventional hooks during the first month. 
When inserting a superiorly inclined hook such as hooks 11 or 42, a 
rod-like tool with a handle (not shown) is used to force the hook shoe 49 
between the facets of adjacent vertebrae. By providing a chamfer from the 
exterior surface 59 at angle c, the insertion of the hook 42, which 
usually initially occurs at about a 10.degree. angle from the eventual 
angle of placement, is facilitated. This is because the chamferred end of 
the shoe 49 at the edge 47 tends to, more-or-less, center the edge 57 
between the vertebrae. 
The connection portion 47 adjacent to the body 45 has a width which is 
substantially equal to that of the body 45. As the connection portion 
extends toward the shoe portion 49, its width decreases. This decrease in 
width continues through the shoe portion 49 until the shoe portion 49 
terminates at the blunt edge 57. This is significant because, as shown in 
FIG. 2, in cases where more than one Harrington.TM. system is used, it is 
possible that the inferior hooks 43 will be in close proximity to one 
another. In this way, the hooks are more narrow farthest away from the 
rods so that the shoe portions 49 are less likely to engage one another. 
This also simplifies positioning of the hooks 43 between the vertebrae. 
The connecting portion has a thickness dimension measured parallel to the 
bore 51. The connecting portion tapers in its thickness from adjacent to 
the body portion 45 to the curve 55. That is to say, the connecting 
portion 47 is thickest (about 30 to 40% of the length of body 45) adjacent 
to the body portion 45 and thinnest near the curve 55. This encourages the 
hook 43 to move slightly in the direction of the blunt edge 57 when the 
hook 43 is pulled posteriorly to become fully seated under the lamina 
unlike existing hook (FIG. 1A) which backs out somewhat when loaded 
posteriorly. More importantly, when the hook is loaded in distraction or 
compression alone, the taper acts as an inclined plane to move the shoe 
posteriorly against the lamina, thus reducing the hook's displacement in 
the spinal canal and against spinal cord 100. 
The body 45 of the hook 43 has a convexly curvate outer profile 61 at that 
portion of the body 45 which faces the shoe portion 49. The curvate outer 
profile 61 is generally coaxial with the bore 51 in order to provide a 
minimum of excess material at the profile 61 without compromising the 
strength of the body portion 45. The minimum of material is important 
because the curvate outer profile 61 is that part of the body portion 45 
which is most likely to engage the concave vertebral lamina-spinous 
process junction 95. The curved contour of the outer profile 61 thus 
maximizes the clearance of the hook 43 with these vertebral elements for 
any given distance of the shoe portion 49 from the rod 44. This is 
particularly important in the case of inferiorly facing distraction hooks 
attached to lumbar vertebrae since the posterior surface of the lamina of 
these vertebrae is generally concave and abuts the squared-off edges of 
existing hook bodies. The curvate outer profile 61 also facilitates use of 
the rod and hook system with the 3-point loading sleeves 41 in that the 
rod 44 can be brought closer to the vertebrae. Significantly, it is 
important that a minimum of excision be made to the vertebrae in order to 
allow insertion of the hooks. By maximizing the clearance of the hooks, 
such as hook 13, the hook shoe can be fully seated around the lamina 
without removing any bone on the posterior surface of the lamina. 
In order to further reduce the amount of cutting which may be necessary and 
in order to provide for better clearance of the installation of the hook 
43, the body portion 45 is decreased in length. Referring to FIG. 6, the 
shoe portion 49 has a length L.sub.49 which is dictated by the need to 
adequately engage a vertebra onto which the hook 43 is attached. The body 
portion 45, on the other hand, need not be as long as the shoe portion 49 
and has a length L.sub.45 which is appropriately shorter. In the preferred 
embodiment, if both L.sub.45 and L.sub.49 are measured from a back surface 
63, L.sub.45 would be at least 15 percent less than L.sub.49. In the 
preferred embodiment, L.sub.49 is approximately 15 mm and L.sub.45 is 
approximately 11.5 mm, making the body 45 at least 2 mm shorter than the 
shoe portion 49. 
Additional clearance for the lumbar vertebra is obtained by increasing the 
length of the connecting portion 47 to over 10 mm in order to increase the 
distance from the shoe 49 to the body beyond existing standard hooks. The 
increased length would not occur in hook 42 used with the thoracic 
vertebra, thereby bring the rod 44 closer to the patient's spine. 
Additional strength for the body portion 45 is facilitated by providing an 
outside profile 65 of the body portion 45 as enlarged. As shown in FIGS. 5 
and 6, the enlargement is accomplished by fabricating the outside profile 
65 with squared off edges 67. It can thus be seen that the body portion 45 
has the clearance fit advantages given by the curvate outer profile 61 
along with the maximized strength of the squared-off outside profile. The 
squared-off edges 67 also facilitate the installation of the hook 43 with 
a hook holder as will be described. 
In order to install the hooks such as hook 43, a specialized hook holder 71 
is provided, as shown in FIG. 7. The hook holder 71 has a standard 
ratcheting forceps handle 73 and a gripping end 75 contoured to fit the 
hook 43. As shown in FIGS. 7 and 8, the gripping end 75 has a pair of 
recesses 77 which match the outside profile 65 of the body portion 45 of 
the hook 43. A pair of cross-bored holes 79 are drilled across the entire 
width of body portion 45 of the hook 43, as shown in FIG. 6. These holes 
79 receive pins 81 (shown in FIGS. 7 and 8), with two pins 81 being 
located on each of a pair of scissors halves 83, 84 of the forceps 71. In 
another embodiment (not shown), two holes 79 are provided on only one side 
of the body portion 45 by drilling across one side of the body. 
Furthermore, it is not necessary that the holes 79 be drilled completely 
through the body portion 45 of the hook 43, but rather it is only 
necessary that the holes 79 be provided as dimples (not shown) on each 
side of the body portion 45. Alternatively, a non-round slot may be 
provided on at least one side of the body of the hook to facilitate 
gripping thereof. 
Each recess 77 comprises a longitudinal wall 80 and lateral wall 82 which 
intersect at 90.degree. to form a squared-off corner 87. The pins 81 are 
separated from the corner 87 by a distance L.sub.81. This distance 
L.sub.81 is equivalent to a distance L.sub.79 from the holes 79 to the 
squared-off edges 67 as shown in FIG. 6. As a result of the equivalency of 
distances L.sub.79 and L.sub.81, the corners 87 on the holder 71 meet with 
the squared-off edges 67 on the hook 43. Furthermore, the combination of 
the pins 81 and the corner 87 provides increased stability over merely 
providing multiple pins 81 or merely providing one pin on each side of the 
hook holder along with the corner 87. In other words, stability is 
achieved both by the provision of four pins 81 and by the provision of the 
corners 87 to meet with squared-off edges 67. This increased stability 
allows the hook holder 71 to be used to exert various forces on the hook 
43 to direct the hook 43 in various movements, particularly movements 
involving twisting of the hook 13 about an axis near the hook as shown in 
FIG. 9. In the preferred embodiment, the holes 79 in the hook 43 have 
center axes which are between 3.27 and 3.53 mm from the squaredoff edges 
67. They have a diameter of between 3.3 and 3.5 mm. The pins 81 have 
center axes which are between 3.582 and 3.632 mm from the corners 87 and 
have diameters which are between 3.07 and 3.17 mm wide. This arrangement 
of hook holes and hook holder pins makes it possible for the present 
hook-holder to fit prior-art hooks and for prior art hook holders to fit 
the present hooks. 
However, in order to prevent the physical dimensions of the gripping end 75 
of the hook holder 71 from engaging vertebrae and thereby impeding its 
use, the gripping end 75 is tapered and rounded. Referring to FIG. 8, the 
outer tips 91 of the gripping end 75 are rounded. Also, the external 
surface 93 of the gripping ends are rounded (not shown). This increases 
access to the areas surrounded by spinal process in a manner similar to 
that provided by the tapering ends of needle nose pliers. To further 
reduce the liklihood of the hook holder from impinging on bone, the 
distance from the pins to edge 91 is less than that from the pins to edge 
87. 
Referring to FIG. 9, the sets of hooks 42, 43 and rod 44 of FIGS. 2-3 are 
installed by first installing the hooks as described supra, and then 
inserting the distraction rod 44 into the superior hook 42. Using a rod 
holder 95, the rod 44 is forced anteriorly downward at its inferior end 
while the inferior hook 43 is pulled upward, using hook holder 71. The 
hook holder 71 is also used to rotate the inferior hook 43 by force 
exerted in the superior direction on the handle 73 (not shown in FIG. 9), 
until the rod (44) can be advanced into the bore 51 of the inferior hook 
43. The rod 44 is then ratcheted against the superior hook 42 and retained 
with a retaining ring (not shown) in the conventional manner. 
As is clear from the above description, numerous changes can be made to the 
specific embodiments shown. For example, it is possible to provide holes 
79 in pins 81 with spacing such that it is possible to engage a hook 
holder with a hook so that only a single pair of pins are engaged with the 
hook, thereby offsetting the hook holder with the hook if necessary. It is 
also possible to provide different configurations for the radiusing and 
angling of the various components of the hook. Furthermore, as described 
supra, the hook may be a compression hook such as hooks 21 and 23, rather 
than a distraction hook such as hooks 11, 13 and 43. The preferred 
dimensions of the hooks described are representative of the types of 
dimensions used in production and, as such, are not intended to be 
limitations. For this reason, the invention should be read as defined by 
the following claims.