Note: Descriptions are shown in the official language in which they were submitted.
2~ S~
PC 7583
External fixator with controllable damping
The present invention relates to the field of tra~ma-
tology and orthopedics and more particulariy has as its
ob~ect an external bone fixation device utilizing pins
inserted into the bone.
By "traumatology" is understood casualty surgery and
by "orthopedics" the correction of congenital malformations
or malformations resulting from an incorrectly positioned
bone union.
A number of devices permitting the elongation or
compressi.on of bones, whether or not a fracture or corti-
cotomy exists, have been developed over a period of many
years.
The invention relates to external fixators connected
to sets of pins inserted into the bone and permitting
longitudinal displacement of the sets of pins relative to
the bone, while retaining their angular positions.
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2~(3764
In this description reference is made to a fractured
bone, but it is obvious that the bone may also be one
intentionally cut through, for example for the purpose of
orthopedic elongation. It may also be a bone which is
not fractured or cut through, but the length of which it
is desired to vary by compression or elongation, as is
done in the case of young patients.
According to a technique which has been known for
many years the pins are connected to an external fixation
bar disposed substantially parallel to the fractured bone.
Each set of pins inserted into a bone fragment is gripped
in a support which can be oriented in relation to the
fixa'ion bar and which is fastened to a clip fixing it on
the bar. In order to achieve the desired compression or
elongation during the union of the bone i, is possible
eithel- to displace one of the clips along the bar or to
use a telescopic bar.
It is also known that in the course of the union of
a bone it is advantageous to allow 2 slight reciprocating
movement, known as biocompression, which enables the
natural forces of the muscles and of the loads supported
to act on the fracture, in order to stimulate the growth
of the bone.
In American Patent 4,502,473 for example, an
external fixator is described which has two sets of pins
inserted into the bone and fixed to fastening clips, one
of the pin fastening clips being movable along a fixation
bar disposed parallel to the bone. An elastic member is
provided in the part connecting the two clips and effects
compression of the fracture over a limited path. In
addition, this fixator can be equipped with pneumatic or
20 1 0764
3 64680-534
mechanical means enabling passive stimulation to be achieved.
French Patent 2,517,195 (=US 4,488,542) discloses a
device for the correction and reduction of bone fragments, which
comprises a rigid bar whose length is adjustable and on which are
fixed two supports for pins inserted into the bone fragments. In
a variant the longitudinal displacement is achieved through a
telescopic movement between two polygonal tubes, of which one is
fastened to a worm and the other to a nut. A sliding guide member
is interposed between these two telescopic members to prevent any
play and to allow frictionless sliding of one of the members
relative to the other.
The present invention seeks to achieve control of the
force applied on the relative displacement of the two sets of pins
inserted into the bone fragments, in the case of either
compression or elongation, in order to avoid damaging the callus
being formed when the displacement force is applied.
The invention provides an external fixator for
correcting and reducing fragments of a bone comprising in operable
communication: a bar to be disposed substantially parallel to the
bone and having a longitudinal axis therethrough; a casing
operatively connected to said bar for longitudinal movement with
respect thereto; at least a first support coupled to said casing
and a second support coupled to said bar for orienting pins to be
inserted into said bone fragments; a displacement member acting
between said bar and said second support for adjusting the
distance between said first support and said second support and
for preventing rotation between said first support and said second
support; said casing is adapted to move relative to a sliding
- 20 1 0764
4 64680-534
block fixed to said bar so as to obtain a longitudinal
reciprocating movement of said casing with respect to said bar and
so as to avoid angular displacement of said casing with respect to
said bar; a damping member acting between said bar and said casing
for damping the longitudinal displacement of said first and second
supports; an adjustable stop mounted between said bar and said
casing to limit the longitudinal movement of said first and second
supports towards one another; said second support being
displaceable longitudinally relative to said first support by
means of said displacement member; and means for adjusting the
damping action of said damping member.
The invention also provides an external fixator for
correcting and reducing fragments of a bone comprising: a bar
having a hollow interior defining a central longitudinal axis,
said bar having a first support slidably mounted thereon for
orienting bone pins to be connected to a first bone fragment; a
first tubular shaft extending along said axis rigidly mounted
within said hollow interior and extending from an end thereof; a
second shaft slidably received within said tubular shaft for
relative movement therebetween; a casing slidably mounted on said
first tubular shaft and rigidly connected to a first end of said
second shaft, said casing having a second support for orienting
bone pins to be connected to a second bone fragment; and damping
means acting between said bar and said second shaft along said
longitudinal axis to dampen relative movement between said bar and
said casing.
Through the combination of the constructional members
mentioned it is possible to obtain a fixation bar making it
CA2û1 U7~4
4a 64680-534
possible to displace a bone fragment throughout the bone univn
process without any risk of tearing the callus which is being
formed, since the surgeon can ascertain the force applied at the
time of the displacement, while in addition allowing a
biocompression movement which assists the formation of the callus
and is selected in dependence on factors personal to each patient.
In a preferred embodiment the sliding block has shapes
intended to cooperate with corresponding cutouts in a connection
member, in such a manner as to avoid any angular displacement.
This sliding block has an end having a polygonal section and
intended to slide, relative to the casing, in a needle bearing.
Provision is advantageously made for the permitted length of
longitudinal reciprocating movement to be limited in a
predetermined manner.
.~ .J
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The pin orientation supports consist of jaws
disposed one on each side of the bar and cooperating with
a curved deflection member adapted to permit the angular
pivoting of clamps gripping the bone pins. Depending on
requirements, an angle drive may be inserted between the
curved deflection member and the clamp.
In a preferred embodiment the damping member
consists of an elastic member compressed between two
bearing surfaces, for example a coil spring, and means
are provided for varying its compression. In order to
enable the surgeon to ascertain the force applied, a rod
adapted to project outside the bar is provided with
graduated markings suitable for indicating values of
forces.
rn a known manner use will be made of a tubular bar
of which one outer face carries graduations permitting
measurement of the displacement made with the aid of the
displacement member. In a preferred embodiment the bar
has a generally quadrangular shape with edges cut off at
20 in order to effect the positioning of the pin orient-
ation supports.
According to a first embodiment the displacement
member adapted to effect the displacement of one of the
supports consists of a displacement assembly disposed
outside the bar and provided with means for fastening it
to the bar and with means for the longitudinal displace-
ment of said support.
In another proposed embodiment the displacement
member adapted to effect the displacement of one of the
supports consists of a device inside a bar consisting of
telescopic tubes. This device may include a bevel gear
unit in which one of the shafts can be driven from the
outside, while the other shaft is fastened to a threaded
rod adapted to cooperate with the telescopic tube which
is to be displaced.
When the patient has to remain in bed, it is possible
to use the external fixator described by adding to it a
motor drive unit acting against the damping member and
enabling biocompression movements to be simulated.
In order to reduce to the minimum the discomfort
caused to the patient by the external fixator, it is
endeavoured to reduce as much as possible the dimensions
and weight of its components.
The accompanyinc drawings illustrate, by way of
non-limitative examples, some embodiments of the present
invention.
Figure 1 is a schematic view in perspective of a
first form of construction of an external fixator pro-
vided in addition with a device for the longitudinal
displacement, along a fixation bar, of one of the clips
fastening the pins inserted into a bone fragment.
Figure 2 is a longitudina] section of the fixation
bar and of the biocompression system which are shown in
Figure 1, taken on the lines II-II shown in Figures 4 and
5.
Figure 3 is an end view of the free end of the fix-
ation bar shown in Figure 2.
ZO~ 6~
Figure 4 is a cross-section of the connection end of
the fixation bar, taken on the line IV-IV in Figure 2.
Figure S is a cross-section of the biocompression
system, taken on the line V-V in Figure 2.
Figure 6 shows in longitudinal section a variant
form of construction of a fixation bar comprising telesc-
opic members.
Figure 7 is a cross-section on the line VII-VII of
the fixation bar shown in Figure 6.
Figure 8 is a cross-section on the line VIII-VIII of
the fixation bar shown in Figure 6.
The general view given in Figure 1 shows an external
fixation bar 1 of polygonal section, on which are placed
two clips 2 and 3 fastened indirectly to clamps 21 and 31
holding pins 25 and 35.
Each clip 2 or 3 is provided with a curved deflection
member 22, 32 cooperating with a pair of jaws 23, 33 dis-
posed one on each side of the bar 1, on which they are
fixed by a positioning device 24, 34.
The curved deflection member 22 permits the angular
pivoting of the clamp 21 in the direction of the arrow A,
on the one hand, and the continuous orientation from 0 to
360 of the set of pins 25 relative to the clamping axis
26, in the direction of the arrow B, on the other hand.
2Q~(~764
The clip 3 is in addition provided with an angle
drive means 37 enabling the clamp 31, and consequently
the pins 35, to be turned 90. An angle drive of this
kind is for example used when the pins 35 are intended to
be inserted into the epiphysis (for example the tibial or
femoral head) of a bone whose diaphysis would receive the
pins 25. In addition to the circular pivoting in the
direction of the arrow A and the angular orientation in
the direction of the arrow B, the clip 3 also permits
angular orientation in accordance with the arrow C in
relation to the axis 36 on which the pins 35 are clamped.
The arrow E represents the displacement of the clip
along the bar, effecting the elongation or compression of
the bone parallel to the bar, while the arrow F represents
the limited biocompression movement, which is adjustable
with the aid of the knurled nut 4 displaceable between
the end of the bar 1 and the biocompression system 5, as
will be seen in detail later on.
It should be noted that the biocompression system 5
is of generally cylindrical shape, thus also permitting
the angular positioning of the clip 3 in the direction of
the arrow D with the aid of an intermediate connection
member 3&, whose external shapes correspond to the inter-
nal cutouts of the jaws 33. The connection member 38 is
also provided with an external collar 39 on each side of
the clip 3, the purpose of which is to hold the connect-
ion member 38 in the clip.
The schematic view given in Figure 1 also shows a
member 6 for the displacement of the clip 2 along the bar
1, which may be provided with linear markings 11, usually
graduated in millimetres.
20~(~7~4
The displacement member 6 consists of a fastening
clip 601 composed of two parts articulated on an axis
602, and is clamped on the bar 1 by a screw 603. It also
comprises a support 604 fixed for rotation with the clip
601 and having an opening for the retention of the head
605 of a feed screw 606, along which is moved a threaded
boss 607 integral with a clamp 608 provided with two
flanges 609 intended to embrace the side portion of the
jaw 23 of the clip 2.
In the longitudinal section shown in Figure 2 the
external fixation bar 1 can be seen again under the refe-
rence 100. As already mentioned, it has a polygonal sec-
tion, which is visible in the end view shown in Figure 3,
where it will be noted that the bar 100 has parallel faces
101 and 102, each followed by faces 103 and 104 inclined
at 20 in sucn a manner as to provide optimum clamping of
the bar in internal cutouts of corresponding shapes in
the jaws of the clip. In a variant, a fixation bar of
circular cross-section can be used, on which are clamped
clips of corresponding shape.
The fixation bar 100 is tubular and has a circular
central opening 105 terminating at each end of the bar in
an internal screwthread 106 and 107 respectively.
The internal screwthread 106 receives a connection
member 110 which is of generally cylindrical shape and
has a median collar 111 serving as a stop on the one hand
for the screwthread 112 making the connection to the fix-
ation bar, or more precisely with the internal screwthread
106 of said bar, and on the other hand for the screwthread
113 intended to receive the knurled nut 4 previously
mentioned.
2()~07~i~
The connection member 110 is provided with a circular
central opening 114 ending externally in a recess 115
having at least one plane face 116 (more readily visible
in Figure 4), which is intended to prevent any rotation
of the shaft passing through the opening 114. The recess
llS forms a stop shoulder 117 for said shaft which will
be described in detail later on.
The internal screwthread 107 receives an adjusting
end piece 120 of generally cylindrical shape, which has
an external screwthread 121 matching the internal screw-
thread 107. The free end of the end piece 120 is provided
with grip means, consisting for example of a hexagon 122
integral with the end piece 120 ard following a frusto-
conical narrowed portion 123.
The adjusting end piece 120 has a circular central
opening 124, in which a rod, the purpose of which will be
mentioned later on, is slidable. The central opening 124
leads into a recess 125 forming a stop shoulder 126.
The biocompression system 5 previously mentioned in
connection with Figure 1 is shown in detail in longitud-
inal section and cross-section respectively in Figures 2
and 5.
It is composed of a casing 50 of generally cylindr-
ical shape and provided at one end with an external col-
lar 51 equipped with an internal screwthread, while the
other end is closed by a wall 52 provided with a central
passage 53 and an external recess 54. The casing 50 has
a central opening 55 leading into four inclined cutouts
56 intended to receive four shims 57 each having a
curvature corresponding to the cutouts 56 and also a
20~(~764
longitudinally inclined plane face. The cutouts 56 are
formed in such a manner that the plane faces of the shims
57 constitute the sliding faces of a needle bearing 60
provided with a cage 61 having a generally cylindrical
shape and four external plane faces 62, along which are
formed ladderlike cutouts 63 intended to receive the
needles 64 constituting the needle bearing 60 (see
Figure 5).
The shims 57 and the needle cage 60 are held in the
central opening 55 of the casing 50 by means of a washer
58 having an external screwthread intended to cooperate
with the internal screwthread formed in the collar 51.
The washer 58 is provided with cutouts 59 intended tc
receive a tightening tool of suitable shape.
Inside the needle cage 60 is disposed a sliding
block 70 constituted by a tubular shaft having in
successlon:
- an end 71 of circular section, provided with a screw-
thread 72 intended to receive a retaining nut 73;
- a median collar 74 forming a stop shoulder 75 intended
to cooperate with the stop shoulder 117 of the connect-
ing member 110, the external contour of which collar is
provided with flats 76 intended to engage against the
plane faces 116 of the connecting member 110; and
- an end 77 of quadrangular section intended to slide in
the needle cage 60.
The tubular shaft 70 has a central passage 78 of
circular section, which is intended for the passage of a
central shaft 80.
_ 2~07~4
The central shaft 80 has at one end a collar 81
intended to bear against the inside of the wall 52, and
its end 82 engages in the opening 53 in the casing 50, in
which it is fixed by means of a screw 83 engaging in a
central internally threaded opening 84 in the central
shaft 80. In order to fasten the central shaft 80 in the
casing 50 it is advantageous to dispose a washer 85 at
the bottom of the external recess 54, thus in addition
enabling the head of the screw 83 to be partly recessed.
The opposite end of the central shaft 80 to that
where the biocompression system is disposed is provided
with means for retaining the whole arrangement, consist-
ing here of a nut 86 engaged on a terminal threaded
portion 87 of the central shaft 80. The nut 86 is
dimensioned to bear against the end 71 of circular sec-
tion of the tubular shaft 70. The threaded portion 87
enables the connection to be made between the central
shaft 80 and a means 90 the damping action of which is
adjustable.
This damping means 90 consists of a rod 91 provided
at one end with a central internally threaded openina 92
intended to cooperate with the threaded portion 87 of the
central shaft. In order to make this connection the
damping means 90 is provided with tightening means con-
sisting, for example, of a hexagonal portion 93. Said
rod is also provided with a median collar 94, against
which bears the end 95 of a coil spring 96, whose other
end 97 is received in the recess 125 and bears against
the stop shoulder 126.
The means 90 ends in a rod 98 intended to slide in
the central circular opening 124 in the adjusting end
2~0~6~
piece 120. The end of the rod 98 is provided with mark-
ings 99 the purpose of which will be mentioned later on.
In the embodiment illustrated in Figure 6 the fix-
ation bar is telescopic in order to permit the displace-
ment, relative to one another, of the clips fastening the
pins. Furthermore the damping means is disposed at the
end of the casing.
In this variant the biocompressions system is found
again composed of a casing 250 which receives in four
inclined cutouts 256 shims 257 cooperating with the
needles 264 of the bearing 260 intended to facilitate the
reciprocating movement of the sliding block 270. The
needle bearing 260 is disposed between the washer 258
threaded in the external collar 251 and an intermediate
wall 253, while the damping member is located in the
extension 252 of the casing, between said intermediate
wall 253 and a plug 280 fixed in an internal screwthread
254 realized at the end of the tubular extension 252 of
the casing.
The sliding block 270 presents:
- an end 271 of circular section with an external screw-
thread 272 intended to cooperate with the end of the
inner tube 210 of the telescopic bar 200, on which it is
clamped through the hexagonal collar 273 (it is to be
noted that this connection can be realized by equivalent
means as gluing or soldering);
- an end 274 of circular section intended to slide in a
central opening of the wall 253, and having an internal
screwthread intended to receive a screw 275 bearing on a
washer 276;
14 ~a~
- an intermediate quadrangular section 277, intended to
slide in the needle bearing 260.
Along its entire length the sliding block 270 may
have a central opening 278 (Figure 8) in which a shaft
279, the use of which will be mentioned later on, is
slidable.
The plug 280 is provided with external cutouts 281
intended to receive a tightening tool for its fixation in
the internal screwthread 254 realized at the end of the
tube 253. The plug presents a central recess 282 having
circular groves 283 intended to control the position of
the damping member 290 (and consequently to measure the
force applied), as well as an screwthreaded end wall 284
intended to receive the adjusting end-piece 291 for
adjusting the force applied.
The damping means 290 is constituted by an external
screwthreaded end-piece 291, having on its external face
grip means, not represented in the drawing. The internal
face of the end-piece 291 presents an internal screwthread
intended to receive a screw 292 bearing on a washer 294.
A spring 296 is situated between the washers 276 and 294,
and its force can be adjusted by positioning the end-piece
291 in the plug 280.
In the embodiment of Figures 6 and 7, the fixation
rod 200 is constituted by an inner tube 210 and an outer
tube 220, of circular cross-section. As already mention-
ed, a graduated scale makes it possible to measure the
relative displacement of the tubes. The tubes 210 and
220 are of aluminium. As an alternative, provision may
be made for the inner tube to be formed by the superim-
position of a stainless steel tube having a thin wall and
X~7~
an outer layer of carbon fibres, in order to reduce the
weight.
To prevent any angular displacement of the tubes,
the inner tube presents a fluting 211 in which slides a
toe 221 of the outer tube. The relative movement of the
tubes is obtained by means of a threaded shaft 201, main-
tained in a central hollow 222 of the outer tube wall 223
by means of two circlips 202 disposed in circular groves
on each side of the wall 223. The already mentioned shaft
279 passes through the threaded shaft 201 and protrudes
at its free end. External]y to the bar, the shaft 201
has grip means constituted by a squared end 203 or any
other equivalent means. The threaded portion of the
shaft 201 cooperates with a internal screwthread in the
lateral wall 212.
As a variant, one can foresee not to turn the
threaded shaft 201 at the end of the fixator, but to dis-
pose a device with a bevel gear unit laterally along the
bar, this unit having a drive gear fastened to grip means
and a driven gear fastened to the threaded shaft 201.
The inner tube 210 is provided at the end receiving
the biocompression system with an external screwthread
213 intended to cooperate with the previously mentioned
knurled nut 4.
It should be noted that in order to simplify the
drawing the clips and all the parts outside the fixation
bar are not shown in Figure 2 and subsequent figures.
For the well-being of the patient the various exter-
nal components constituting the fixator according to the
16
`2~
invention have no sharp edges and for the most part are
made of light alloys in order to limit the weight of the
apparatus.
Before being used in the course of the operation,
the fixator according to the invention is assembled in
the manner illustrated in the drawing. The biocompres-
sion casing 50 is assembled by inserting the shims 57
into the corresponding inclined cutouts 56, and then
inserting the needle cage 60 surrounding the end 77 of
quadrangular section of the sliding block 70, in the
centre of which the central shaft 80 is disposed. The
collar 81 disposed at the end of said shaft is pressed
against the wall 52 by means of the screw 83 and the
washer 85, in such a manner as to secure the central
shaft 80.
This biocompression system thus formed is mounted at
the end of an external fixation bar and its movement is
facilitated by the rolling system in the needle cage 60.
In the embodiment shown in detail in ~igures 2 to S,
the retaining nut 73 is tightened on the screwthread 72
in such a manner as to fasten the biocompression system
to the external fixation bar, or more precisely to the
connection member 110. The corresponding flats 116 and
76 of the connection member 110 and of the median collar
74 prevent any rotation between the fixation bar and the
biocompression casing. The stop nut 86 is disposed on
the threaded end portion 87 of the central shaft 80, in
such a manner as to prevent the withdrawal of the bio-
compression system in the outward direction.
2~
-
The internally threaded central opening 92 at the
end of the rod 91 is screwed onto the threaded portion 87
with the aid of a tool matching the hexagonal portion 93.
The coil spring 96 is placed in position on the rod 91,
between the median collar 94 and the stop shoulder 126 on
the adjusting end piece 120.
In the course of the actual operation the surgeon
inserts sets of pins into each bone fragment, applying
known techniques. Each set of pins 25 or 35 is held in a
plane by means of the clamp 21 or 31 and is positioned
relative to the bar 1 by taking advantage of the possible
orientations in the directions of the arrows A, B, C and
D (Figure 1), which make it possible to dispose the bar
parallel to the bone which is to be compressed or elong-
ated. It is obvious that the angle drive device 37 is
dispensed with in certain cases.
The clip 2 is disposed on the bar 1 with the aid of
the positioning device 24 in such a manner as to be able
to be displaced laterally by the displacement member 6,
whose fastening clip 601 is clamped on the bar 1 with the
aid of the screw 603.
The clip 3 is fastened to the biocompression system
5 through the tightening of the jaws 33 with the aid of
the positioning device 34. It will be observed that by
constructional measures it is easily possible to modify
the relative angle between the two clips, since the clip
3 is mounted on a circular member, namely the biocom-
pression casing 50, in order to allow adjustment in the
direction of the arrow D in Figure 1.
18
20~o~
Throughout the bone union process the surgeon will
be able to adjust the elongation or compression of the
bone fragments by means of the feed screw 606 for the
lateral displacement of the clip 2 in the direction of
the arrow E.
He will also be able to adjust:
1) the biocompression stroke in the direction of the
arrow F by acting on the knurled nut 4, which in
Figure 2 is shown in an intermediate position and
which may either:
- come into contact with the corresponding face of the
casing 50, thus preventing any biocompression move-
ment, or
- come to bear against the median collar 111, thus
allowing a biocompression movement of the order of 5
~illimetres;
2) the biocompression force by acting on the end piece
120, which enables the spring 96 to be compressed to a
greater or lesser extent, the markings 99 on the rod
98 which slides in the central opening 124 in the end
piece enabling this force to be measured. For this
purpose, the markings correspond to values expressed
in kilogram force.
A displacement of the clip 2 by 1 millimetre, which
can be measured on the linear markings 11, corresponds to
a displacement by 1 millimetre of the bone when equilibr-
ium exists between the force of the spring 96 and the
resistance of the patient's limb to elongation or compres-
sion. In case of elongation, it is to be noted that the
damping means 90, through its spring 96, makes it possible
to prevent the tearing of the callus being formed (anti-
collapse) at the moment when the clip 2 is displaced. As
19
7~4
a rule a displacement of the order of 1 millimetre a day
is made, but this value may vary in dependance on the age
of the patient and other individual criteria, such as the
rate of formation of the callus.
It is obvious that the feed screw 606 may be turned
by automatic means, such as a drive motor, without
departing from the scope of the present invention.
In the case of the second embodiment illustrated in
Figures 6 to 8, its assembly is partly similar to that
previously described, except that the damping member 290
is introduced in the casing 250.
In order to fasten the biocompression system to the
external fixation bar, the casing 250 is tightened at the
end of the inner tube 21C, by means of the collar 273.
The biocompression force is adjusted by means of the
end-piece 291 and is measured on the marks 283 visible in
the recess 282 beyond the end-piece 291.
The two telescopic tubes 210 and 220 are then joined
together hy inserting the threaded shaft 201. As already
mentioned, the biocompression movements can be mechanic-
ally or electrically driven, in cases where the patient
is confined to his bed. As an example the motor drive
unit may consist of an electric motor turning an
eccentric fastened to the free end of the shaft 279,
which it drives in a reciprocating movement against the
spring 296.
The telescopic fixation bar shown in Figures 6 to 8
is placed in position in the course of the operation, as
indicated previously, and the fastening clips are clamped
2~7~4
around the biocompression casing 250, on the one hand,
and around the outer tube 220 of the telescopic tube 200,
on the other hand.
In the course of the uniting of the bone the surgeon
will be able to adjust the elongation or compression of
the bone fragments by acting on the threaded shaft 201,
ensuring the relative movement between the telescopic
tubes 210 and 220.
It should be observed that the biocompression dis-
placements are independent of the elongation or compres-
sion. As previously described, the amplitude of the
biocompression movements is adjustable with the aid of
the knurled nut 4.
As soon as a force is applied, in order to prevent
the tearing of the callus being formed, any movement of
one of the telescopic tubes relative to the other has the
effect on the bone of a displacement different from that
indicated on the graduated scale on the inner tube 210.
It is in fact first necessary to balance the compression
of the spring with the resistance reactions of the
muscles and tissues, and only then will a relative
displacement of the telescopic tubes by 1 millimetre
result in an equivalent displacement of the sets of pins
inserted into the bone.
It is obvious that the fixator according to the
invention can be used to displace a bone segment between
two parts of a long bone. In this case the fixator
comprises two fixed supports and a displaceable support
which is fastened to the bone fragment. It is further
possible tu use some of the described components in a
2010~i4
fixator maintaining the pins, without any compression or
elongation of the bone.
Without going beyond the scope of the present
invention it is of course possible to use the previously
described fixation bar with ball joint type pin supports
enabling the pins to be positioned in the desired plane
and fastened on the one hand to the fixation bar and on
the other hand to the biocompression casing.
