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FIELD OF THE INVENTION
The present invention relates to medical equipment employed in orthopedics
and traumatology for treating various congenital and acquired shortenings
and other defects or skeletal segments and, more particularly, it relates
to drives of compression-distraction apparatuses.
BACKGROUND OF THE INVENTION
There is known in the art a drive of a compression-distraction apparatus
(cf., U.S.S.R. Inventor's Certificate No. 848,011, cl. A 61 B 17/18,
published in the Bulletin of Inventions, No. 27, 1981), comprising a lead
screw, a gear mounted thereon and, series-connected with said gear via
reduction gear, a ratchet wheel, a lever with a pawl and an electromagnet
interacting with one of the lever arms. Said prior art device is further
provided with a power pack connected to an electromagnet.
The afore-described drive provides for measured and atraumatic
micromovement of bone fragments. However, said prior art drive suffers
from excessively large mass and dimensions whereby its clinical use is
rather difficult.
This disadvantage is primarily due to the low specific force per unit
weight developed by the drive.
Another prior art drive of a compression-distraction apparatus appears more
improved (cf., U.S.S.R. Inventor's Certificate No. 865,284, cl. A 61 B
17/18, published in the Bulletin of Inventions, No. 35, 1981) and
provides, analogously with the foregoing prior art drive, for atraumatic
movement of bone fragments that is close to natural physiological growth.
Said latter prior art drive of compression-distraction apparatus comprises
a lead screw mated by threading with an opening of a ratchet wheel
rotatably positioned in a housing. Interacting with teeth of the ratchet
wheel is a pawl coupled with a load-bearing element manufactured from an
alloy possessing plastic memory and having an electric heater. The ratchet
wheel of said prior art drive has internal mesh while the pawl is
positioned on the smaller arm of a lever arranged inside the wheel and
lying in the same plane therewith. The load-bearing element is fashioned
as a shackle arranged below the lever in a parallel plane therewith and
connected by its one end with the housing wall while its other end is
connected with the long arm of the lever and with a resilient member
serving to keep the load-bearing element in a bent position. The electric
heater with which the load-bearing element is provided is connected to a
power pack.
The last-described prior art unit, while exhibiting the same distraction
force as the previously described electromagnetic drive, features
considerably smaller dimensions and weight. However, attempts at expanding
the range of clinical application of said latter unit have shown that the
force it develops is insufficient for ensuring reliable operation. Thus,
an increase of the distraction force above 300-350 N leads to failures in
the drive operation caused by the fact that the load-bearing element
reaches the breaking stress. Actual loads in the course of the drive
operation may exceed considerably those cited above in view of the
functional load on an extremity reaching, as a maximum, the magnitude of
the patient's weight. Therefore, it is very important to find a solution
to the problem of ensuring an adequate distraction force.
The distraction force developed by the prior art drive may be increased by
way of increasing the cross-sectional area and dimensions of the
load-bearing element. However, an increase of thos dimensions results in
an increase of the ratchet wheel diameter, housing diameter and of the
overall weight of the drive. Second, an increase of the cross-sectional
area and dimensions of the load-bearing element involves a direct increase
in the consumption of energy required for heating the element to the
operation temperature, which affects considerably the duration of
autonomous supply of the drive.
Therefore, the prior art drive may only develop a distraction force
required for its clinical use only on condition of a considerable increase
of the drive dimensions and weight. This restricts considerably the range
of clinical application of the unit and, in a number of cases, e.g., in
apparatuses for elongation of short tubular bones (phalanges, metacarpal
bones), makes it problematic. Moreover, a rise in the energy intensity of
the drive resulting from an increase of the cross-sectional area and
dimensions of the load-bearing element reduces the autonomous supply of
the drive and further restricts the range of clinical application of the
prior art unit.
SUMMARY OF THE INVENTION
It is an object of the present invention to develop a drive of a
compression-distraction apparatus that would provide a distraction force
sufficient in all clinical cases while featuring the minimum energy
intensity, dimensions and mass.
Said and other objects of the present invention are attained owing to the
fact that in a drive of a compression-distraction apparatus, comprising a
lead screw mated with a ratchet wheel placed in a housing, and a pawl
interacting with teeth of said wheel and connected to a load-bearing
element manufactured from an alloy possessing plastic memory, said
load-bearing element having an electric heater, connected to the housing
and interacting with a resilient member, according to the present
invention, the load-bearing element has a rectiliner shape and is
essentially a tie-rod whose one end is rigidly secured to the housing
while its other end is coupled to the resilient member and the pawl.
Such an arrangement of the drive of the invention provides for the maximum
distraction force under conditions of the minimum energy intensity,
dimensions, weight and structural complexity of the drive.
It is expedient that the resilient member coupled with the load-bearing
element be likewise manufactured from a material possessing plastic memory
and featuring the temperature of inverse martensite transformation of
about 100.degree.-150.degree. C. below that of the material of the
load-bearing element.
This helps reduce the resistance to the working stroke of the mechanism.
With a view to simplifying the structure, it is expedient that the tie-rod
be fashioned as a wire.
In order to reduce the heat losses upon heating the tie-rod, it is
expedient that it should be fashioned as a thin-walled hollow tube with
the electric heater accommodated thereinside.
It is further expedient that the pawl be fashioned as a resilient clamp
whose ends are rigidly connected to the tie-rod while the middle portion
of said clamp interacts with a tooth of the ratchet wheel.
This helps simplify the structure and make it more miniature.
It is sound practice to connect one end of the tie-rod to the housing by
means of an adjusting member, this enabling one to set the best position
of the pawl connected with the other end of the tie-rod irrespective of
possible deviations from its length.
In addition, it appears beneficial in a number of cases to couple the other
end of the tie-rod to the pawl by means of a lever whose smaller arm is
connected with the tie-rod. This will help reduce the tie-rod length
required for the working stroke, as well as the consumption of energy
required for heating the tie-rod.
While so doing, it is advisable that the lever and tie-rod be positioned in
a plane normal to the plane of the ratchet wheel. This results in a
smaller transverse dimension of the housing.
In other cases, it appears more important to reduce the housing dimension
along the lead screw axis. To this end, in the housing there is provided a
channel designed to accommodate the tie-rod and positioned tangentially to
the ratchet wheel which has external mesh while the resilient member is
essentially a helical spring positioned in the same channel, with the
tie-rod being placed inside the helical spring coaxially therewith and
secured by its one end in an end wall of the channel while the helical
spring is compressed between said wall and a washer connecting the other
end of the tie-rod with the pawl.
For some applications of the drive of the invention, it is expedient that
the lead screw be provided with a longitudinal flat interacting with a
lock screw which is immovable relative to the housing. This enables one to
use the herein disclosed drive in compression-distraction apparatuses of
diverse designs, i.e., improves its universality.
BRIEF DESCRIPTION OF DRAWINGS
The present invention will be more apparent upon considering the following
detailed description of exemplary embodiments of the herein disclosed
drive of a compression-distraction apparatus, with due reference to the
accompanying drawings in which:
FIG. 1 is a diagrammatic view of the drive according to the present
invention;
FIG. 2 shows an embodiment of the load-bearing element, according to the
present invention;
FIG. 3 shows another embodiment of the load-bearing element, according to
the present invention;
FIGS. 4, 5, 6 illustrate embodiments of the pawl of the ratchet mechanism,
according to the present invention;
FIG. 7 shows diagrammatically an embodiment of the drive according to the
present invention;
FIG. 8 shows another embodiment of the drive according to the present
invention (in section), mounted in a prior art compression-distraction
apparatus for bone elongation;
FIG. 9 illustrates an application of the drive according to the present
invention in a prior art apparatus for compensating total bone defect;
FIG. 10 is a section taken along the axis of the pivoted platform mounting
the housing of the drive according to the present invention;
FIG. 11 illustrates an application of the drive according to the invention
in a prior art apparatus for bone expansion; and
FIG. 12 illustrates an application of the drive according to the present
invention in a prior art apparatus for elongation of short tubular bones
such as stumps of phalanges, metacarpal bones etc.
DESCRIPTION OF PREFERRED EMBODIMENTS OF INVENTION
Referring now to FIG. 1 of the accompanying drawings, the herein disclosed
drive of a compression-distraction apparatus comprises a housing 1 rigidly
mounted on one of the apparatus supports (not shown in the drawing) with a
ratchet wheel 2 positioned in said housing 1 with a possibility of
performing rotation. An axial opening of the ratchet wheel 2 is provided
with screw thread with which there is movably mated a lead screw 3 rigidly
attached to another support of the compression-distraction apparatus
connected with the bone fragment being moved (not shown in the drawing).
The drive is provided with a load-bearing element 4 which has a
rectilinear shape and is fashioned as a tie-rod 5 whose one end is rigidly
attached to the housing 1 while its other end is rigidly connected with a
pawl 6 resiliently biased against a toothed rim of the ratchet wheel 2 and
meshing by its end with one of ratchet wheel teeth 7. The end of the
tie-rod 5 coupled with the pawl 6 is also connected with a resilient
member 8 maintaining the tie-rod 5 in a permanently stretched out state.
The tie-rod 5 is provided with an electric heater 9 which is electrically
connected (shown at 10) with a power pack 11 which may be switched both
manually and automatically with the aid of a special control unit (not
shown in the drawing).
The load-bearing element 4 (5) is manufactured from a known alloy, say, of
nickel and titanium possessing the so-called plastic memory (or
thermomechanical recovery effect as it is also called). This effect is
characterized by the fact that an alloy capable of exhibiting it has, at a
temperature below the point of direct martensite transformation (phase
variation of the alloy structure), a modulus of elasticity which is
considerably less than that at a temperature above the point of inverse
martensite transformation. Therefore, a body manufactured from such an
alloy, subjected to cold plastic deformation and then heated to a
temperature above that specified hereinbefore tends to recover the
original (prior to deformation) shape and dimensions and, in so doing, may
develop rather considerable mechanical stresses owing to the
afore-mentioned difference between the moduli of elasticity in the cold
and hot states.
The resilient member 8 may likewise be manufactured from an alloy
possessing plastic memory, however, featuring the temperature of inverse
martensite transformation of about 100.degree.-150.degree. C. below that
of the material of the load-bearing material 4. In this case, the material
of the resilient member 8 at the operating temperature of the drive is in
the superelastic state characterized by a very flat curve. This provides
for a lower resistance to the working stroke as compared with the
embodiment in which the resilient member 8 is made of steel used for
manufacturing springs.
The tie-rod 5 may be manufactured from strip, wire, band, sheet material
and material of other shapes. In particular, one tie-rod embodiment shown
in FIG. 2 provides for the manufacture of the tie-rod 5 from a piece of
wire 12 with thickenings 13 at the ends for rigidly securing the tie-rod
in mated parts of the drive (not shown in the drawing).
The electric heater 9 is in thi case fashioned as a coil of thin wire
featuring a high ohmic resistance and insulated from the tie-rod 5 by a
thin thermostable dielectric film (not shown in the drawing). On the
outside, the electric heater 9 is covered with heat insulation made of,
say, glass fiber (not shown in the drawing).
The afore-described embodiment of the tie-rod 5 is the simplest one and
most adaptable to streamlined production methods.
Another embodiment of the tie-rod 5 shown in FIG. 3 is that in the form of
a hollow tube 14 accommodating thereinside the electric heater 9
electrically insulated from the tube surface (insulation not shown). The
ends of the hollow tube 14 may have thickenings 13 analogous with those
described above, which can be made both by expanding the tube ends and by
upsetting. This embodiment of the load-bearing element helps considerably
reduce the heat losses and, as a result, additionally increase the
autonomous supply capabilities of the herein disclosed device.
The pawl 6 interacting with the teeth 7 of the ratchet wheel 2 may also
have various embodiments. The most advantageous embodiments fo the pawl in
the herein disclosed drive are those wherein the possibility of permanent
contact of the pawl with the teeth of the ratchet wheel 2 is ensured
thanks to the intrinsic elasticity of the pawl 6. This provides for
smaller dimensions and lesser complexity of the drive as compared with
other possible embodiments of the pawl wherein it is, say, rigid and
provided with an axle and a separate resilient member for urging it
against the ratchet wheel 2 (said latter embodiments are not shown in the
drawing).
The resilient pawl 6 may be fashioned, in particular, as a plane plate 15
shown in FIG. 4 having at its end a slot 16 for engagement with the teeth
7 of the ratchet wheel 2. Provided at the othere end of the plate 15, bent
at right angles, is a slot 17 forming a seat for joining the pawl 6 with
the thickening 13 formed at the end of the tie-rod 5(4). The end of the
resilient member 8 maintaining the tie-rod 5 in a tensioned state locks
the thickening 13 at its end in the slot 17.
According to another embodiment shown in FIG. 5, the resilient pawl 6 is
fashioned as a wire clamp. Its ends have a length sufficient for ensuring
desired elasticity and are rigidly secured in a washer 19 which has a slot
17 analogous to that described above and forming a seat to accommodate the
thickening 13 at the end of the tie-rod 5. In the case illustrated in FIG.
6, when the resilient member 8 is made plane, the ends of the clamp 18 may
be attached directly to its end also having a slot 17 for securing the
thickening 13 of the tie-rod 5. In order to reduce the rigidity of the
clamp 18, it is expedient that the clamp be flattened over a portion 20
adjoining the termination point (cf., FIG. 6).
In some cases, as shown in FIG. 7, it is advisable that an end of the
tie-rod 5 be coupled with the pawl 6 by means of a lever 21 mounted in the
housing 1 on an axle 22. While so doing, the smaller arm of the lever 21
is coupled with the tie-rod 5 thereby reducing the length of the tie-rod 5
necessary to provide for the working stroke and, consequently, the
dimensions of the housing 1 and the consumption of energy required for
heating the tie-rod 5. Further, the lever 21 and tie-rod 5 may be
positioned in a plane normal to the axis of the ratchet wheel 2 to provide
for a reduction of transverse dimenion of the housing 1 of the drive. The
end of the tie-rod 5 connected with the housing 1 may be coupled therewith
by means of an adjusting member 23 fashioned as, say, a screw positioned
in the housing coaxially with the tie-rod 5 and having in its body a seat
(not shown in the drawing) for securing therein the end of the latter. The
resilient member 8 may in this case be fashioned as a tension spring 24
coupled with the lever 21 and tending to turn the latter in a direction
ensuring the tensioning of the tie-rod 5.
According to this embodiment of the drive, the pawl 6 may be fashioned as a
resilient plate 25 positioned in the plane of rotation of the lever 21 and
presenting its bigger arm. The plate 25 has at its end a bend 26 meshing
with the teeth 7 of the ratchet wheel 2. In order to preclude reverse
rotation of the ratchet wheel 2 upon idle stroke of the pawl 6, the drive
may be provided with an additional pawl 27 made as, say, a resilient wire
clamp analogous with that described above. While so doing, the pawl 27 is
immovably mounted on the housing 1. The need for such a pawl may arise
upon no-load operation of the mechanism when the friction of the pawl 25
against the back edge of the tooth 7 of the ratchet wheel 2 may exceed the
friction of the latter wheel mating with the housing 1 and lead screw 3.
For quite a few applications of the drive of the invention, for instance,
those shown in FIGS. 8, 9, 10, 11 and 12, one may find more expedient its
plane arrangement when the tie-rod 5 is positioned in the same plane with
the ratched wheel 2. Such an arrangement leads to a considerable reduction
of the axial dimension of the housing 1, i.e., its dimension along the
axis of the lead screw 3, as well as renders the housing 1 less bulky, and
permits of its use is most diverse compression-distraction apparatuses.
Consider now FIG. 8 which shows, in section, the aforementioned embodiment
of the drive mounted in a prior art compression-distraction apparatus for
bone elongation. The ratchet wheel 2 with external mesh is rotatably
mounted in a housing 1 having a connection pipe 28 forming a channel 29
designed to accommodate the tie-rod 5. The channel 29 and the tie-rod 5
coaxial therewith are arranged tangentially to the ratchet wheel 5. The
tie-rod 5 by its one end is rigidly attached to a washer 30 mounting a
resilient pawl 6 fashioned as the afore-described wire clamp 18 and
engaged with one of the teeth 7 of the ratchet wheel 2. The washer 30 is
movably mated with the channel 29. The other end of the tie-rod 5 is
rigidly secured in an adjusting member 31 fashioned as a cylindrical
stopper arranged at the channel end. Said stopper has a V-shaped flat 32
interacting with the end face of a lock screw 33 positioned in the
immediate vicinity thereof in a thickened wall of the pipe 28. Positioned
between the end face of the adjusting member 31 and the washer 30 in a
resilient member fashioned as a compression spring 34 maintaining the
tie-rod 5 in a tensioned state. The spring 34, same as the washer 30, is
movably mated with the wall of the channel 29. Interacting with the teeth
7 of the ratchet wheel 2 is the additional pawl 27 serving to preclude
reverse rotation of the ratchet wheel 2. The electric heater 9 is
fashioned as described above and is likewise electrically connected with
the power pack 11. The housing 1 of the drive is provided with screws 35
for its fastening in the compression-distraction apparatus.
In particular, the herein disclosed drive may be mounted in an apparatus
for the elongation of a bone 36. Said apparatus is conventionally shown in
FIG. 8 as portions of ring- or arc-shaped supports 37 carrying pins 38
passed through the bone 36, tensioned on said supports and attached
thereto by means of grips 39. Rigidly mounted on one of the supports 37,
say, the bottom one, are tubular pillars 40 (one of said pillars shown in
the drawing). The housing 1 of the drive is rigidly attached to the top
portion of the pillar 40 by means of the screws 35. The lead screw 3
passing through the housing 1 is in part accommodated within the tubular
pillar 40. The other end of the lead screw, positioned outside of the
pillar 40 and housing 1, is rigidly attached by nuts 41 to the top support
37 of the compression-distraction apparatus, which is analogously
connected by means of pins (not shown in the drawing) with the proximal
portion of the bone 36. Bone regenerate 42 between the proximal and distal
portions of the bone 36 binds them together.
In another apparatus (cf., FIG. 9) designed for compensating total defect
of the bone 36 by bringing down its fragment 43, provision is made of
analogous supports 37 rigidly connected by means of the pins 38 to the
distal and proximal portions of the bone 36 featuring extensive defect in
its middle portion. The supports 37 are rigidly coupled with each other by
means of threaded rods 44. Mounted on the opposite sides of the distal
support 37 with the aid of brackets 45 and platforms 47 articulated with
the latter by an axle 46 are drives whose housings 1 are rigidly attached
to said platforms 47 by the screws 35.
The lead screw 3 of each drive has a plane longitudinal flat 48 and is
passed through an opening in the platform 47 which is normal to the axle
46. The plane flat 48 interacts with the end face of a lock screw 49
thereby preventing the lead screw 3 from rotating about its axis. The
screw 49 may be positioned in the drive housing 1 as well, however, it is
most practical to position it in a part immovably mated with the housing
1, in particular, in the platform 47. The screw 49 is provided with a lock
nut 50 fixing it in position.
Passed via bone fragment 43, severed from the proximal portion of the bone
36 and bound to the latter by the subsequently formed bone regenerate 42,
are pins 51 having at their ends thickenings 52 located on the outside of
the bone fragment 43. The pins 51 are passed in the direction of the axes
of the lead screws 3 positioned on the bone side external with respect to
the thickenings 52 and are rigidly secured to the ends of said screws by
nuts 53.
According to yet another embodiment of the apparatus shown in FIG. 11 and
designed for the expansion of the bone 36, as distinct from the foregoing,
the drives are mounted with the aid of the platforms 47 on a rigid beam 54
whose ends are rigidly attached to the supports 37 with the aid of
threaded shanks 55. The lead screws are positioned transversely to the
axis of the bone 36 and are connected, by means of analogous pins 51
having thickenings 52 at their ends, with a fragment 56 longitudinally
chipped off the bone 36 and connected therewith by bone regenerate 57.
And finally described herein is the application of the drive of the
invention in a prior art apparatus for the elongation of short tubular
bones, illustrated in FIG. 12. This apparatus is used when the anatomical
position of bones such as phalanges or metacarpal bones makes difficult or
prohibits the through passage of pins as shown in the preceding drawings.
In the prior art apparatus for the elongation of short tubular bones use is
made of a drive with the lead screw 3 having the longitudinal plane flat
48. The apparatus consists essentially of nail holders 58 wherein there
are cantilever-mounted nails 59 crossing in the plane of bone fragments
(not shown in the drawing). The nail holders 58 are coupled with each
other by means of the lead screw 3 with the flat 48, which is positioned
in smooth openings formed in said nail holders and normal to the plane of
positioning of the nails 59. The nail holders 58 are further provided with
the lock screws 49 interacting by their end faces with the flat 48 for
precluding their rotation about the axis of the lead screw 3. One of the
nail holders 58 is positioned at the end of the lead screw 3 and is
rigidly secured thereon by means of the screw 49. Another nail holder 58
is positioned on the lead screw 3 for translational movement therealong,
which is attained by adjustment of the screw 49 which provides for the
minimum gap required for displacement in mating with the flat 48.
The position of the screw 49 attained as a result of adjustment is fixed by
the lock nut 50. The movable holder 58 has threaded holes 60 accommodating
the screws 35 serving to rigidly attach the housing 1 of the drive to said
holder.
The electric connection 10 and the power pack 11 are not shown in FIGS. 9,
10, 11 and 12 of the drawings.
The herein disclosed drive of a compression-distraction apparatus operates
in the following manner.
A current pulse is fed from the power pack 11 via wires 10 to the electric
heater 9, the duration of said pulse being sufficient for heating the
tie-rod 5 to a temperature at which inverse martensite transformation
occurs. The modulus of elasticity of the material of the tie-rod 5
increases considerably and the tie-rod reduces in length while overcoming
the forces of friction in the mechanism and the resistance of the
resilient member 8. In so doing, the tie-rod 5 displaces the pawl 6 which
comes by its one end against one of the teeth 7 of the ratchet wheel 2 and
performs the working stroke to turn said wheel around the axis of the lead
screw 3. The latter is incapable of rotation and starts moving along its
axis to displace the support of the compression-distraction apparatus
together with the bone fragment rigidly connected therewith (not shown in
the drawing). The working stroke of the pawl 6 continues until the
load-bearing element 4 (tie-rod 5) is reduced to the size it had prior to
the application of tensile stress from the resilient member 8. The length
of the load-bearing element 4 (tie-rod 5) is selected sufficient for
moving its end coupled with the pawl 6 through a value a defined by the
inequality t<a<2t wherein t is the pitch of the teeth 7 of the ratchet
wheel 2.
After the supply to the electric heater 9 is switched off, the load-bearing
element 4 (tie-rod 5) starts cooling down. While so doing, at a
temperature below that of direct martensite transformation, the modulus of
elasticity of its material decreases considerably. As a result, the
resilient member 8 stretches the load-bearing element 4 (tie-rod 5) to the
dimension it had before heating. In the course of elongation of the
load-bearing element 4(5), the pawl 6 performs the idle stroke to advance
by its end upon the sloping back edge of the tooth 7 and, in so doing, to
resiliently bend back. At the end of the idle stroke, the end of the pawl
6 comes to be engaged with the subsequent tooth 7. The ratchet wheel 2
stays motionless in the course of the idle stroke because the forces of
friction due to its mating with the housing 1 and screw 3 prove
incommensurably greater than the force of friction of the end of the pawl
6 against the back edge of the tooth 7.
Upon supply of subsequent pulse of current from the power pack 11 to the
electric heater 9, the afore-described process is repeated. Therefore, the
operation of the drive takes place under conditions of alternating heating
and cooling of the load-bearing element 4 (tie-rod 5). The rate of axial
displacement of the lead screw 3 depends upon the repetition rate of the
pulses of current supplying the electric heater 9, which may be preset
depending upon specific biological conditions determining whether such
rate of displacement is the optimum one. The drive may be controlled
automatically using a special control unit which does not fall within the
scope of the present patent application.
The operation of the drive embodiment illustrated in FIG. 7 is generally
analogous with that described above, however, with some distinctions. In
particular, upon alternating heating and cooling of the tie-rod 5, the
pawl 6 performs rotary reciprocation about the axle 22 of the lever 21.
The latter turns counterclockwise upon the reduction of the tie-rod 5
being heated and clockwise upon its cooling down, under the effect of the
tension spring 24 coupled with the lever 21. When the lever 21 turns
counterclockwise, the working stroke occurs as a result of which the bent
out end 26 of the pawl 6 comes against the tooth 7 of the ratchet wheel 2
to turn the latter and cause axial displacement of the lead screw 3 which
is incapable of rotation due to its rigid attachment to the support of the
compression-distraction apparatus (not shown in the drawing). In the
course of the working stroke, the additional pawl 27 enables the wheel 2
to turn, by coming upon the sloping back edge of the tooth 7 while bending
out resiliently. At the end of the working stroke, said additional pawl
gets in the subsequent gap between the teeth 7. Upon the turning of the
lever 21 in the opposite direction which starts as a result of tension of
the cooling down tie-rod 5 by the spring 24, there occurs the idle stroke
of the pawl 6 which comes upon the sloping back edge of the subsequent
tooth 7 while bending out resiliently. the pawl 27 which at this moment
engages one of the teeth 7 of the ratchet wheel 2 precludes a reverse turn
of the latter which might occur due to the force of friction of the pawl 6
against the back edge of the tooth 7. The relative position of the pawls
27 and 6 is adjusted with the aid of the adjusting member fashioned as,
say, screw 23. Axial displacement of said screw 23 causes the lever 21 to
turn and the pawl 6 to change its position relative to the pawl 27 rigidly
attached to the housing 1.
The drive embodiment shown in section in FIG. 8 generally operates
analogously with that described above. Some distinctions are due to
differences in the structural embodiment of the drive.
In particular, as distinct from rotary reciprocation of the pawl 6
according to the afore-described embodiment, in this latter embodiment the
pawl performs reciprocating motion along the axis of the channel 29. Upon
heating, the tie-rod 5 decreases in length to compress the spring 34 and
to provide for the working stroke of the pawl 6 mounted on the washer 30
movable along the axis of the channel 29. Upon cooling down, the tie-rod 5
is stretched by the spring 34 to provide for the working stroke of the
pawl 6. The additional pawl 27 operates analogously with that described in
connection with the foregoing embodiment.
The relative position of the pawls 6 and 27 is adjusted by unscrewing the
screw 33 which releases the adjusting member fashioned as stopper 31 and
by moving same along the axis of the channel 29. After that, the attained
position is secured by means of the same screw 33 resting against the
V-shaped flat 32 which ensures the reliability of fastening.
In the course of the drive operation the lead screws 3 move synchronously
along their axis to cause relative movement of the proximal and distal
supports 37 and of the like portions of the bone 36 connected therewith,
this resulting in the traction of the bone regenerate 42 joining said
portions to each other.
When compensating total bone defect, as shown in FIG. 9, axial movement of
the lead screws 3 causes the movement of the bone fragment 43 connected
therewith by means of pins 51 and gradual traction of the bone regenerate
42. As the bone fragment 43 moves, the housings 1 of the drives mounted on
the articulated platforms 47 move until the fragment being displaced comes
against the bottom portion of the bone 36. Thereupon, their joint is
knitted in a conventional manner.
In the drive embodiment illustrated in FIG. 11, the movement of the
fragment 56 longitudinally chipped off the bone 36 and connected therewith
by the bone regenerate 57 is performed analogously. The only difference is
that the bone fragment 56 is moved under the effect of the screws 3 in the
transverse direction until the cross-section of the bone 36 being expanded
becomes sufficient. After that, the movement of the fragment 56 is
discontinued and the fragment is stabilized by one of the conventional
techniques until the bone regenerate 57 is fully changed to bone tissue.
In the drive embodiment illustrated in FIG. 12, the rotation of the ratchet
wheel 2 causes translation motion of the housing 1 and of the nail holder
58 rigidly connected therewith along the axis of the lead screw 3 relative
to another nail holder 58 rigidly attached to the cone of the former nail
holder. In so doing, there occurs displacement of bone fragments (not
shown in the drawing) rigidly connected to the nail holders 58 by the
nails 59, as well as the elongation of bone at the expense of growing
regenerate joining together said bone fragments.
Surgical techniques associated with osteotomy, drawing of pins and nails
through live tissue, as well as with the assembly of
compression-distraction apparatuses, follow universally known procedures
and are not described in the instant application.
The herein disclosed structure, as distinct from prior art ones, results in
a drive capable of exhibiting sufficient force and having dimensions which
are so small as to allow of its use for the elongation of short stumps of
phalanges and metacarpal bones of the hand wherein desired relative values
of bone elongation reach 100% and more. Given such elongation values, the
efficiency of the herein disclosed drive is especially high.
The afore-mentioned possibility is primarily due to the fact that the
adequate simplicity of design permits of making the drive miniature while
high specific forces developed by the load-bearing element of the drive
provide for the margin of distraction force sufficient for reliable
operation of the drive.
Apart from the reliability in operation, the simplicity of design leads to
low manufacturing costs and, consequently, to universal utilization of the
herein disclosed drive.
It should be further noted that, along with the use of the drive of the
invention for treatment, it is expedient to use the drive in experimental
studies into biological regularities of regeneration of tissues. The small
weight and dimensions of the drive render it advantageous over prior art
inasmuch as it facilitates the use of smaller animals for experimental
purposes, which reduces the cost of studies and, at the same time,
provides a higher degree of uniformity of the starting biological material
thereby improving the reliability of obtained results.
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