Radiolucent head clamp

A radiolucent head clamp having a C-shaped frame with a fixed head-engaging pin on one side and a pair of head-engaging pins on the opposite side. The opposite side of the clamp has a radiolucent rotation mechanism for adjusting the angular position of the pair of head-engaging pins and a radiolucent translation mechanism for linearly moving the pair of head-engaging pins with respect to the fixed head-engaging pin.

BACKGROUND OF THE INVENTION 
This invention relates to a head clamp principally for use with 
radiological procedures and more particularly to a radiolucent head clamp 
having mechanisms for axially and rotationally adjusting the head-engaging 
pins of a head clamp, from a single side of the clamp. 
An example of a head clamp with a single side control is shown in the Day, 
et al. U.S. Pat. No. 5,269,034, assigned to the same assignee as the 
present invention, discloses a head clamp having a generally C-shaped 
frame with a head-engaging pin on one side of the frame and a pair of 
rotationally adjustable head-engaging pins on an opposing side of the 
frame. The opposing side of the frame also contains a mechanism for first, 
adjusting the rotational angular position of the pair of head-engaging 
pins, and a second, translating or linearly moving the pair of pins with 
respect to the pin. While the above head clamp works well, it is 
constructed of nonradiolucent materials. Therefore, use of the above clamp 
may introduce undesirable artifacts in radiological images taken of a 
patient with the clamp attached. 
Further, radiolucent materials are not well suited for certain components 
in the adjusting mechanisms of the above clamp design. For example, the 
head clamp disclosed in the Day, et al. '034 patent uses steel balls which 
move in and out of detents to move toothed gear rings into and out of 
engagement thereby respectively locking and unlocking the rotational 
mechanism. That construction requires very precise dimensional tolerances 
so that the motion created by the steel balls moving in and out of the 
detents consistently separates the toothed rings to disengage the teeth on 
the rings. If those components were made from a plastic-type radiolucent 
material, the clamping forces would, over time, cause the balls to deform 
and lose their circular shape. Further, the surfaces in contact with the 
balls would, over time, form tracks in the ball paths. Either or both of 
those conditions would eventually result in a loss of dimensional 
precision that over time would result in inconsistent and unsatisfactory 
clamp operation. 
An example of a known radiolucent clamp is shown in the Day, et al. U.S. 
Pat. No. 5,276,927, issued to the assignee of the present invention 
discloses a radiolucent head support with a radiolucent skull clamp 
secured to the head support. The detailed construction of the head clamp 
is shown in FIG. 5 herein. Referring to FIG. 5, the radiolucent clamp has 
a single pin mounted on an adjusting screw 2 at a first end 1 of the 
clamp. A pair of head-engaging pins are mounted on a clevis 3 which is 
rotatably mounted in an opposite end 4 the of the head clamp. The clevis 3 
is connected to one end of a shaft 5. The opposite end of the shaft 
contains threads 6 and a locking nut 7. A first toothed member 8 is 
connected to the clevis 3, and a second tooth member 9 is connected to the 
opposite end 4 of the head clamp. A compression spring 10 mounted on the 
shaft 5 between the toothed members 8,9 is used to apply a biasing force 
tending to separate the toothed members 8,9. In operation, the locking nut 
7 is rotated on the threads 6 to move the locking nut 7 away from the 
opposite end 4 of the clamp. That permits the spring 10 to move the shaft 
5 and clevis 3 to the left as illustrated in FIG. 5 thereby separating the 
toothed members 8,9 and permitting the clevis 3 to freely rotate. When the 
clevis is moved to its desired angular position, the locking nut 7 is 
rotated in the opposite direction thereby moving the shaft 5 and clevis 3 
to the right as illustrated in FIG. 5 thereby engaging the toothed members 
8,9 and locking the clevis 3 in the desired angular position. Thereafter, 
the adjusting screw 2 at the first end 1 of the clamp is rotated until the 
patient's head is secured in the clamp. 
The above construction has several disadvantages. First, after the 
patient's head is secured in the clamp, it is difficult to change the 
angular position of the clevis 3 because the clamping forces applied by 
the adjusting screw 2 override the biasing force of the spring 10 that is 
used to separate the toothed members 8,9. Therefore, to change the angular 
position of the clevis 3, the adjusting screw 2 must be turned to loosen 
the clamp sufficiently that upon loosening the locking nut 7, the toothed 
members 8,9 are able to separate. The above mode of operation is less 
desirable than a design that permits the angular adjustment of the clevis 
3 independent of the clamping screw 2. The prior art clamp of FIG. 5 
presents a further inconvenience in the bulkiness of the first end 1 of 
the clamp. Further, applying the clamping force through the single pin on 
the clamping screw 2, results in less predictable and unequal reactive 
forces by the pair of pins on the clevis 3. 
SUMMARY OF THE INVENTION 
To overcome the non-radiolucency of the head clamps referred to above, the 
present invention provides a radiolucent head clamp wherein all of the 
adjusting mechanisms are located on a common (single) side of the clamp 
and are operably connected to the pair of head-engaging pins. 
According to the principles of the present invention, the head clamp has a 
frame with opposing radiolucent first and second frame members forming a 
generally C-shaped configuration. A first, fixed, head-engaging pin which 
may be immovable, is mounted on the first frame member. A radiolucent pin 
holding member is fixed to one end of a radiolucent shaft which is 
rotatably mounted in the second frame member, and the pin holding member 
includes a pair of second and third head-engaging pins. The pin holding 
member is located on a side of the second frame member which faces 
inwardly, that is, toward the first frame member. A locking mechanism is 
mounted at the end of the second frame member and is operably connected to 
the pin holding member for releasably locking the pin holding member in 
selected angular positions. 
The locking mechanism includes a first radiolucent locking member mounted 
on an outwardly directed side of the second frame member, i.e., that is, 
opposite the inwardly directed side. The locking mechanism further 
includes a second radiolucent locking member mounted adjacent the first 
locking member and moveable with respect thereto. A fastener preferably 
threaded, and made of radiolucent material, is rotatably mounted to the 
second frame member adjacent the second locking member such that rotation 
of the threaded fastener in one direction moves or pushes the locking 
members into engagement, and rotation of the fastener in the opposite 
direction permits the locking members to separate. 
The invention includes another aspect in which the head clamp has a 
radiolucent bushing rotatably mounted within the second frame member. The 
shaft supporting the pin holding member is slidably mounted in the bushing 
to rotate with the bushing but translate relative thereto. A biasing 
spring is located between the first and second locking members to bias the 
second locking member, which is slidably mounted on the bushing, away from 
the first locking member. 
The invention has a further aspect wherein the head clamp has a radiolucent 
knob rotatably mounted to the other end of the shaft, but slidable with 
respect to the shaft, and a spring located between the knob and the shaft 
to limit forces applied to the patient's head by the second and third 
head-engaging pins. 
A head clamp of the above configuration has the advantage of being made of 
radiolucent materials to minimize artifacts or opaque shadows on 
radiological images. The radiolucent clamp design provides independent 
operation of the angular adjustment of the head-engaging pins thereby 
permitting that angular adjustment without having to loosen the clamp. The 
radiolucent clamp has the further advantages of providing all of the 
head-engaging pin position adjustments on the same, single side of the 
clamp. That design has the advantage of convenience of use, as well as 
providing a better distribution of clamping forces between the pair of 
head-engaging pins as the clamp is tightened. In addition, the clamp is 
made of radiolucent materials which has the advantage of reducing 
artifacts in images when the clamp is used in radiological applications. 
These and other objects and advantages of the present invention will become 
more readily apparent from the following detailed description and the 
drawings herein.

DETAILED DESCRIPTION 
The construction and operation of a preferred form of the surgical head 
clamp of the present invention will be described with regard to FIGS. 1 
through 4. Referring to FIG. 1, the surgical head clamp 12 includes a 
C-shaped frame 13 comprised of frame members 14 and 16 which are movable 
to "telescope" toward and away from one another. The frame members 14, 16 
of the clamp 12 are preferably made of a of a radiolucent polyethersulfone 
(PES) and carbon composite material with the carbon component being about 
30 percent of the composite by weight. Such a composite material is 
available from ICI Advanced Materials of Exton, Pa. under the commercial 
name "THERMOCOMP" JC-1006, and is also available from LNP Engineering 
Plastics of Thorndale, Pa. under the commercial name "STAT-KON" JC-1006. 
Alternatively, other radiolucent materials may be used. Frame members 14 
and 16 have parallel first arms 18 and 20, respectively, which are 
juxtaposed to each other in an innerfitting, sliding relationship with 
first arm 20 of frame member 16 cradling or surrounding the first arm 18 
of frame member 14. Extending from one end of the arm 18, frame member 14 
has an intermediate arm 22 extending diagonally away from frame member 16 
and an upper arm 24 extending angularly back toward frame member 16. 
Similarly, extending from first arm 20, frame member 16 has an 
intermediate arm 26 extending away from frame member 14 and an upper arm 
28 extending back toward frame member 14. The angled geometry of frame 
members 14 and 16 maintains frame rigidity and, at the same time, permits 
the frame members to be physically smaller than if each of the frame 
members were L-shaped. 
The first arm 20 of the frame member 16 is formed in a U-shape to receive 
the first arm 18 of the frame member 14. The first arm 20 has two sides 
30, 31 which extend past the first arm 18. A bottom plate 32 preferably 
made from the PES and composite material is mounted between the sides 30, 
31 of the first arm 20 such that there is clearance between the bottom 
plate 32 and the rack teeth 29 of the first arm 18. The bottom plate 32 is 
held in place between the sides 30, 31 of the first arm 20 by fasteners 
34, shown in phantom in FIG. 1 and perferably made of nylon. One or more 
nylon guide pins 33 having teflon tips (not shown) are threaded into the 
surface 31 so that the teflon tips are in contact with the first arm 18 to 
help guide the translation of the frame member 14 with respect to frame 
member 16. The bottom plate 32 has a cavity 35 which is sized to receive a 
retractable rack member 36 which is connected to a release pin 37. The 
retractable rack member 36 and release pin 37 are preferably made from the 
"DELRIN.RTM." acetal polymer material. The retractable rack member 36 has 
teeth 38 are sized to engage the teeth 29 on first arm 18 of frame member 
14. A metal compression spring 39 is mounted over the release pin 37 and 
extends between the releasable rack member 36 and the bottom plate 32. The 
compression spring 39 applies a force against the retractable rack 36 
which holds the teeth 38 on retractable rack 36 in engagement with teeth 
29 on the first arm 18. The engagement of teeth 38,29 prevents the frame 
members 14,16 from moving in a direction away from each other. However, 
the configuration of the teeth 38,39 permits frame members 14,16 to be 
slid toward each other to size or position the clamp 12 generally with 
respect to a patient's head 40, shown in phantom. To release the clamp, 
the release pin 37 is pulled downward as illustrated in FIG. 1, thereby 
compressing spring 39 and moving the teeth 38 of the releasable rack 36 
out of engagement with the teeth 29 of the first arm 18. With the teeth 
38,29 disengaged, the frame members 14, 16 may be separated thereby 
releasing the clamp from the patient's head 40. 
One end 41 of the clamp 12, that is, the outward extending end of the of 
frame member 14, preferably has only the minimum size necessary to receive 
and support a first head-engaging pin 42 which is generally directed 
toward the frame member 16. Therefore, the end 41 of the clamp 12 presents 
minimal potential for interference with the surgeon and the operating 
procedure. An opposite end 43 of the clamp 12, which is the outward 
extending end of frame member 16, has a radiolucent pin holding member 44. 
The pin holding member 44 includes a bracket or clevis 45, which may be 
made from the PES/carbon composite material previously identified. A pair 
of head-engaging pins, that is, a second head-engaging pin 46 and a third 
head-engaging pin 48, are mounted proximate the ends of clevis 45 and 
generally directed toward the first head-engaging pin 42. The patient's 
head 40 is secured in the clamp 12 by and between the first, second and 
third head-engaging pins 42,46,48, respectively, which are pressed into 
opposite sides of the head. The clevis 45 is pivotally mounted in clevis 
support 50 and may be made from the PES and carbon composite material. The 
clevis 45 pivots about the centerline of a pivot pin 51 in a plane 
transverse to the centerline of the pivot pin 51. The pivot pin is made 
from the radiolucent "DELRIN.RTM." acetal polymer material. A rod, or 
shaft 52, for example, made from a radiolucent "TORLON" polyamide-imide 
material has one end connected to the clevis support 50 by a radiolucent 
nylon screw 53 which extends through the clevis support 50 and is threaded 
into a threaded center hole of the shaft 52 (see FIGS. 2 and 3). 
The clamp 12 includes an angular positioning mechanism 54 for releasably 
locking the pin holding clevis 45 in selected angular (rotational) 
positions around an axis of rotation 56 which is approximately coincident 
with a centerline 58 of pin 42 and preferably passes through the 
centerline of pivot pin 51. The clamp also includes a translation or 
adjusting mechanism 60 for linearly (axially) moving the pin holding 
member longitudinally along the axis of rotation 56. 
As best shown in FIG. 2, a generally cylindrical body portion on member 62 
is formed on the outwardly extending end of the upper arm 28 at the end 43 
of the clamp 12. The body member 62 has a stepped bore 63 which has a 
first bore 64 with a layer first diameter that terminates at a shoulder or 
flange 65 within the stepped bore 63, and the stepped bore 63 has a 
centerline that is coincident with the axis of rotation 56. The stepped 
bore 63 extends past the flange 65 and has a second bore 66 concentric 
with the first bore 64. As shown in FIG. 3, the stepped bore 63 has a 
third bore 67 on the other side of the flange 65 which is concentric with 
the first and second bores 63,64 and is sized to receive a closure or cap 
68 made from the radiolucent "DELRIN.RTM." acetal polymer material. 
Referring back to FIG. 2, the angular positioning mechanism 54 comprises a 
first locking ring 70 having interlocking means preferably in the form of 
toothed ring 71 on a first end face thereof, which is engagable with a 
mating toothed ring 72 of a second locking ring 73. Applicant has found 
that when two pieces of PES and carbon material as specified herein are in 
sliding contact with each other, there is an abrading action that takes 
place between the two parts. That abrading action results in an 
undesirable dust or particles of the material collecting on other 
components of the clamp. The quantity of undesirable abraded particles can 
be reduced by manufacturing the two parts from dissimilar materials. 
Therefore, the locking ring 70 is made from the radiolucent PES and carbon 
composite material, and locking ring 73 is preferably made from the 
radiolucent "DELRIN.RTM." acetal polymer material. The first bore 64 is 
sized to receive locking rings 70,73 and maintains the locking rings 70,73 
in coaxial alignment as the locking ring 73 is moved longitudinally in the 
bore 64 with respect to the locking ring 70. The first locking ring 70 is 
immovably secured against the flange 65 such that the first end face and 
toothed ring 71 face in a direction away from the first frame member 14, 
and the toothed ring 72 of second locking member 73 faces in a direction 
toward the first frame member 14. Screws 74 made of nylon or other 
radiolucent material extend through holes in the first locking ring 70, 
through holes in the flange 65 of the cylindrical body member 62 and are 
secured in the cap 68, thereby securing the first locking ring 70 and the 
cap 68 to opposite sides of the flange 65 of the cylindrical body member 
62. A wave washer, or corrugated spring 75 is located between the locking 
rings 70,73 and surrounds toothed rings 71,72. When compressed, the spring 
75 produces a force in a direction tending to push the locking rings 70,73 
apart, thereby separating the toothed rings 71,72 from interlocking 
engagement. 
A knob or ring 76 made of the radiolucent "DELRIN.RTM." acetal polymer 
material is mounted such that an end surface 77 is in sliding contact with 
the second locking member 73. The knob 76, functioning as a manually 
operable actuator, is joined to a rotator sleeve 80 by a mechanical 
coupling, preferably, internal threads interlocking with external threads 
79 of the sleeve 80. The rotator sleeve 80 is a cylindrical bushing which 
is made from the earlier described PES and carbon composite material. The 
rotator sleeve is rotatably mounted within the body member 62 so that its 
centerline is collinear with the axis of rotation 56. An annular flange 81 
on the rotator sleeve 80 is sized to mate with and rotatably slides within 
the third bore 67, and the second bore 66 is sized to mate with and 
rotatably slide about an outer cylindrical surface of the rotator sleeve 
80. Referring to FIG. 3, the knob 76 has an annular groove 82 in one face 
which is sized to receive the side wall, or face, 83 of the body member 
62. The knob 76 has a bore 84 at an opposite end, and a cylindrical keeper 
85 which functions to limit motion of the knob 76 is press fit or 
otherwise secured within the bore 84. The keeper 85 is made from the 
radiolucent "DELRIN.RTM." acetal polymer material and has a bore 86 which 
is sized to slide snugly over a "BUNA" nitrile elastomer O-ring 87 which 
is mounted on the end of the rotator sleeve 80. 
Independent longitudinal (axial) motion of the pin holding member 44 is 
generated by a translation mechanism 60. The shaft 52 is slidably mounted 
within the rotator sleeve 80 such that the centerline of the shaft is 
collinear with the axis of rotation 56. An operating handle, or knob 88 
includes a knurled member 90 made from the radiolucent "DELRIN.RTM." 
acetal polymer material and a threaded sleeve, or threaded tube 91 made of 
"TORLON" polyamide-Imide. "TORLON" polyamide-Imide is a desirable material 
because it is commercially available in rod form, thereby reducing 
machining costs. The member 90 has a bore which is threaded onto one end 
of a external cylindrical surface 92 of the tube 91. The other end of the 
threaded external surface 92 of the threaded tube 91 is coupled with an 
internal threaded bore 93 of the rotator sleeve 80, thereby rotatably 
coupling the knob 88 to the rotator sleeve 80. The opposite end of the 
shaft 52 extends through the center of and is slidable with respect to of 
the knob 88. A stainless steel screw 89 is threaded into the opposite end 
of the shaft 52 and a stainless steel bearing washer 107 limits the linear 
motion of the shaft 52 in one direction with respect to the knob 88. 
The rotator sleeve 80 has a cross-sectional shape that includes a flat 
surface 109 that mates with the cross-sectional shape of shaft 52 that 
includes the flat surface 95. Their mating cross-sectional shapes spline, 
or key, the rotator sleeve 80 and to the shaft 52 and prevent relative 
rotation between the rotator 80 and the shaft 52 but allow them to 
translate, or slide, relative to each other. Unitary rotation of the 
rotator 80 and the shaft 52 is further provided by a nylon set screw 94 
radially threaded into the rotator 80 and slidably engaging the flat 
surface 95 on the shaft 52. The rotator sleeve 80 extends through a bore 
in the first locking ring 70 and is free to rotate with respect to the 
first locking ring 70. However, a flat surface 96 at one end of the sleeve 
80 cooperates with a flat surface 97 within an axial bore 98 of the second 
locking ring 73 so that the second locking ring 73 slides with respect to 
the rotator sleeve 80, but second locking ring 73 and the rotator sleeve 
80 rotate in unison. 
In use, the angular positioning mechanism 54 is operated to adjust the 
angular position of the clevis 45 and the head-engaging pins 46,48 about 
the axis 56 independently of the operation of the translating mechanism 60 
and independently of whether the clamp is supporting a patient's head 40. 
To change the angular position of the clevis 45, the knob 76 is rotated in 
a first, or loosening, direction, for example, a counterclockwise 
direction, relative to the rotator sleeve 80. The knob 76 backs away (to 
the right as viewed in FIG. 3), and the corrugated spring 75 exerts a 
force against the second locking ring 73, thereby moving the second 
locking ring 73 to the right away from the first locking ring 70 and away 
from the first frame member 14 until the respective toothed rings 71,72 
disengage. As the knob 76 is rotated in the first direction, the keeper 85 
slides over the O-ring 87 until the O-ring 87 contacts the bottom surface 
of the bore 86 within the keeper 85. At that point, resistance to further 
rotation of the knob in the first direction is encountered by the user, 
thereby signaling the user that the toothed rings are disengaged and to 
stop rotating the knob 76. The user may then manually rotate the clevis 45 
which causes the head 40, clevis 45, support member 50, shaft 52, rotator 
sleeve 80 and second locking ring 73 to rotate in unison. As the head 
clamp is being tightened, clamping forces parallel to the axis of rotation 
56 are applied against the clevis 45 which will tend to move the flange 81 
toward and against the flange 65. An low friction O-ring 99 made of 
"TEFLON.RTM." polytetrafluoroethylene is located between a bearing surface 
100 on a side of the flange 65 of the body member 62 and a bearing surface 
101 on a side of the flange 81 of the rotator sleeve 80. The O-ring 99 is 
used to reduce the friction between the surfaces 100, 101 when the clevis 
45 is rotated to change its angular position; and the clamping force is 
transmitted across the bearing surfaces 100,101 by the O-ring 99. The 
O-ring 99 and flange 81 are captured between the flange 65 and an end 
surface of the cap 68 which is effective to hold the rotator sleeve in its 
desired longitudinal position. 
When the desired angular position is achieved, the knob 76 is rotated in an 
opposite second, or locking, direction, for example, a clockwise 
direction, and the knob 76 moves to the left relative to the sleeve 80 as 
viewed in FIG. 4. Continued rotation of the knob 76 in the second 
direction causes the knob 76 to push the second locking ring 73 toward the 
first locking ring 70 and the first frame member 14 until the respective 
toothed rings 71, 72 contact each other and reach a fully engaged 
position. When the toothed rings 71, 72 contact each other, the user 
experiences in increased resistance to rotation which signals the user 
that the toothed rings are engaged, and the clevis 45 is locked in the 
desired position. With the second locking ring 73 locked from rotational 
motion with respect to the first locking ring 70, the rotator sleeve 80 is 
prevented from relative rotation with respect to the second locking ring 
73 by means of the flat 96 on the sleeve 80 and the mating flat 97 on the 
second locking ring 73 (FIG. 2). Further, since the shaft 52 cannot rotate 
relative to the sleeve 80, the meshed toothed rings 71,72 are effective to 
prevent the clevis 45 from rotating. 
The knob 76 threadedly mounted on the end of sleeve 80 functions as a 
manually operable actuator that is mechanically coupled to the sleeve 80. 
The mechanical coupling, for example, the interlocking threads on the knob 
76 and sleeve 80 move the knob 76 away from the first end 41 of the frame 
member 14 in response to rotation of the knob 76 in a first direction, 
thereby allowing the toothed members 71, 72 to separate. The mechanical 
coupling between the knob 76 and sleeve 80 moves the knob, or actuator, 76 
toward the first end 41 of the frame member 14 in response to rotation of 
the actuator 76 in the opposite direction, thereby moving the toothed 
rings 71, 72 into engagement. 
The translation mechanism 60 is used to change the position of the clevis 
45 and head-engaging pins 46,48 with respect to the head-engaging pin 42 
by rotating the knob 88. Rotation of the knob 88 in a first direction, for 
example, a clockwise direction, advances the shaft 52 with respect to 
sleeve 80 and causes the knob 88, shaft 52 and pin holding member 44 to 
translate along the axis of rotation toward the first head-engaging pin 
42. Therefore, the pin holding member 44 is linearly adjusted with respect 
to the first pin 42 independently of the operation and state of engagement 
of the angular position mechanism 54, that is, whether the angular locking 
mechanism 54 is in its locked or unlocked position. 
A helical compression spring 102 is located within a bore 103 of the 
threaded tube 91 and extends over and about the shaft 52. The spring 102 
is located between a shoulder of a flange 104 on the shaft 52 and a 
bearing washer 105 adjacent the knurled member 90. The flange 104 has a 
diameter such that the flange 104 contacts the side wall of the bore 103 
at the outer directed end of the threaded tube 91, thereby providing 
diametric support for the threaded tube 91 at its outer directed end. The 
spring 102 permits the surgeon to measure and control the forces applied 
by the second and third head-engaging pins 46, 48 to the patient's head 
40. After the pins contact the head, continued rotation of the knob 88 
will result in continued translation of the shaft 52 and pin holding 
member 44 which is effective to compress the spring 102. With further 
rotation of the knob 88, the spring 102 continues to compress; and the 
shaft 52 extends beyond the knob 88, i.e., to the right, as shown in FIG. 
4. Therefore, the force applied to the patient's head 40 by the 
head-engaging pins is determined by the spring constant of the spring 102. 
The shaft 52 contains a scale, or markings, 106 so that the clamping force 
may be controlled by the surgeon. Typically, each line on the scale 104 
represents about 20 pounds of force. 
The head clamp of the construction described above may be used in surgical 
applications and will result in few if any undesirable artifacts or opaque 
shadows when used in radiological applications. The disclosed invention is 
especially useful when radiological imagery is used during and to assist 
surgical procedures. The design described herein provides a radiolucent 
head clamp having an angular head positioning adjustment which can be 
operated without having to loosen the clamp, as is required by the prior 
art illustrated in FIG. 5. Further, the radiolucent head clamp of the 
present invention has one end 42 which is minimal in size, and further has 
all of the clamp adjustments conveniently located together at the other 
end 43 of the head clamp 12. This again provides a more convenient 
operation than the design of the prior art illustrated in FIG. 5. Further, 
the individual components of the head clamp of the present invention may 
be made of radiolucent materials and withstand the clamping forces and 
other forces encountered in use better than the components utilized in the 
clamp illustrated in the Day, et al. U.S. Pat. No. 5,269,034 if those 
components were made of radiolucent materials. The design provides a 
radiolucent clamp having one end 41 which is of minimal size, and wherein 
all of the clamp adjustments are conveniently located together at the 
other end 43 of the clamp 12. 
While the present invention has been set forth by a description of an 
embodiment in considerable detail, it is not intended to restrict or in 
any way limit the claims to such detail. Additional advantages and 
modifications will readily appear to those who are skilled in the art. For 
example, the generally cylindrical body member 62 may be a separate piece 
which is mechanically attached or bonded to the outward extending end of 
the frame member 16. Further, the body member 62 may be made from a 
radiolucent "DELRIN.RTM." acetal polymer material or other radiolucent 
material. In addition, different radiolucent materials may be used in 
place of those identified above. For example, the cap 68 may be made from 
the PES and carbon composite material. Further, variations may be made to 
the above described constructions. For example, the shaft 52 may be fitted 
into the rotator sleeve 80 with sufficient precision that the set screw 94 
is not required. Further, the actuator knob 76 may be coupled to the 
sleeve 80 by another mechanism such that actuation of the coupling with 
respect to the sleeve 80 is operable to move the actuator and either 
separate or engage the toothed rings 71,72. Alternatively, the cylindrical 
body member 62 and the end of the frame member 14 may be configured with a 
mating mechanical coupling, such as a dove tail configuration, and those 
members may be mechanically coupled with or without a bonding material. 
The invention in its broadest aspects is therefore not limited to the 
specific details shown and described. Accordingly, departures may be made 
from such details without departing from the spirit and scope of the 
invention.