CA1193506A - Apparatus for external fixation of bone fractures - Google Patents

Abstract

ABSTRACT
A non-rigid bone fracture fixator comprising first and second bone pins for connection either side of a bone fracture and primary and secondary supports clamped to the bone pins by respective fixed and guide clamps. The second support and the guide clamps are connected slidably to the primary sup-port such that the supports may execute a controlled degree of movement with respect to one another. A compression spring is arranged to bias apart the sup-ports longitudinally of a fixated limb. In use the fixator is applied to the limb with the fracture in slight compression. Exercise of the limb then pro-duces varying degrees of fracture compression stimulating bone callus formation and rapid healing. The fixator may include actuating means to provide passive fracture exercise for immobilized patients.

Description

~3S~

APPMA~U~ FOR EXTER~AL FIXATIO~ O'i' ~0~5 FRACr!'lJR~S

This invention relates to apparatus for external fixation of bone fractures during bone healing.
As is well-known in medical science, in order to obtain acceptable bone union it is necessary to preserve the appropriate bone geometry at the fracture site. For this purpose it is known to employ plaster casts for simple or comparatively minor fractures. For more complex or serious fractures, rigid or flexible clamping devices such as bone plates or external fixators have been employed. Conventional bone plates are screwed to the bone fracture parts across the fracture site.
External fixators consist of one or more supports located externally of the broken limb clamped to bone pins extending through the skin to each of the bone parts of the fracture. The bone pins connect and locate in position the broken bone portions at the fracture site, as or~ ~ample in Applicant's-~o-pe~g- ~-A~ t-i~n~

It is well-known that primary bone healing may be preceded by`
the formation of bone callus over the fracture site~ Callus forms much more rapidly than new primary bone, and affords a natural stabilising layer over the fracture under which new bone may form.
However, whereas callus formation is often experienced with fractures which are retained in plaster casts, it is found that the use of bon~ pLltes or rigid external fixators does not encourage callus formation. Accordingly, use of bone plate or rigid external fixatQr may require many months to heal a bone fracture by new primary bone formation. This is highly disadvantageous since both bone plates and fixator bone pins are surgically inserted under or through the skin of the broken limb with consequent infection risk~ Accordingly, the greater the time required for healing the greater the risk of infection due to the bone pLate or pin. However, there are many bone fracture cases in which a plaster cast is inadequate, and hitherto the `
~ 1 ~g~

the time deEiciencies of bone plates or external fixators have been tolerated.
It is also known to employ flexible external fixators to aid fracture healing. However, it has been found that prior ar-t flexible fixators may give inadequate mechanical stability to a fractured limb, with consequent risk of refracture or misalignment of a healing fracture.
It is an object of the present inven-tion to provide an improved form of external fixator adapted to encourage bone callus formation.
The present invention provides an external orthopaedic fracture fixator comprising: a primary elongate rigid support;
first clamp means connected with said primary support to secure adjustably therewith a plurality of first bone pins transfixable with a first fragment of a fractured bone; a secondary elongate rigid support; second clamp means connected wi-th said secondary support to secure adjustably -therewith a plurality of second bone pins -transEixable with a second fragment of said bone; means for interconnecting said suppor-ts to hold said fragments under com-pressive force in a predetermined mutually aligned disposition forreunion, while allowing unidirectional movement between said supports without misaligning said disposition in response to :increase oE said force; and control means cooperable wi-th said interconnected supports to limit the extent oE said movement to that wh:ich encourages ca]lous formation without inhibiting primary bone Eormation.
:[t has been Eound tha-t con-trolled rela-tive movement between the Eirst and second bone pins, which promotes callus 5~

formation, can be achieved with a fixator of the invention whilst retaining sufficient rigidity to preserve bone alignment and primary bone growth, unlike prior art flexible fixators. Moreover, the necessary relative movement may be produced merely by exercis-ing the fracture, for example by active stimulation i.e. a patient walking on a fractured leg. ~his is highly advantageous, since the time required to achieve a load-bearing healed fracture is reduced as compared to that needed for primary bone growth by prior art rigid Eixator or bone plate -techniques.
In practice, the invention may be used for example to set a fractured limb. A surgeon would insert the first and second bone pins in the first and second bone portions either side of a fracture site.

2a ~,35~

I~e would then connect the primary and secondary bone support means with the ccnnecting means and adjust them until the fracture site experiences slight compression when not under e2ercise loading.
A fracture exercise load cycle would normally involve varying degrees of fracture compression only, it being considered desirable to avoid ~racture site e~tension.
The said degree of relative movement between the bone pins may be up to 2.00mm when measured between first and second bone pins at their connections to the primary and secondary support means respectively. The movement at the fracture site may be up to 005mm between bone portionsO ~or tibial fractures1 relative bone portion movement at the ~rac-ture site may be up to 0.2mm ~ he connecting means preferably includes resilient biasing means arranged, when in use with the bone ~racture under compressive load, to bias apart the first and second bone pins longitudinally of a fixated bone, the rssilience o~ the biasing means being appropriate for execution of the said degree of relative movement during the load cycle longitudinally o~ a fi~Yated bone.
In one embodiment of the invention, the ~irst and second bone pins are rigidly securable to their respeotive primary and secondary support means by primary and secordary clamps adapted for adjustable bone pin direction; the secondary clamps are additionally mountable slidably on the primary support means, and the secondary support means are connected slidably to the primary support means, the arrangement being su¢h that the second~J support means and second2ry clamp~ are in use moveable and resiliently biased relative to the primary support means longitudinally oP a fi.xat~d limb.
Convenier,tly the primary and secondary support means are elongate members for disposition substa~tially longitudinally of a ~i~ated limb.
In a particularly preferred embodiment, the invention includes actuating means adapted to produce repetitively the said degree of relative movemerlt between the first and second bone pins thereby sim~lating bone ~racture exercise, It i9 considered that this aspec-t L93S~6 of the invention is particul~ly ~aluable, since it allows an immobile patient to have bone fracture exercise or passive 6timulation~ This produces rapid callug formation or healing in cases where patient mobility is undesirab]e or impossible, such as serious injury ca~es. Accordingly~ the use of actuating means in accordance with the invention enha~ces healing in precisely those cases for which rapid healing is ~ost desirable, but in which bone callus is unlikely to form by conventional healing te¢hnique~.
The actuating means is conveniently adapted both to act on the primary or secondary support mea~s and to produce repetitive oscillatory movement therebetwecn longitudinally of a fixated member.
~he actuating means is preferably adapted to co-operate with the re~ilient biasing means to produce oscillatory forward and return strokes. Conveniently, the actuating means may include a pneumatic or hydraulic piston-and-cylinder arra~gement adapted to introduce relative movement betveen the primary and secondary support me~ns.
Figure 1 i6 a ~chematic front elevation of R prior art ri~id external fixator, Figur0 2 is a schematic front elevation of an external fixator of the invention, Figures 3 and 4 are respectively detailed front and 6ide elevations of a fixator of the invention, Figures 5 and 6 are part-sectional views o~ fixed and guide bone pin clamps re6pectively, Figure 7 i~ a ~chematic front elevation o~ a mechanically actuated ~ixator of the invention, Figure 8 is a detailed side elevation of one end of a mechanically actuated fixator of the invention, Figure 9 is R sectional view along lines X_X o~ Figure 8, Figure 10 is an oblique elevation of the fixator of Figure 8, Fi~ure 11 is an end ~iew of the fixator oP Figureg 8 to 10, Figure 12 shows an alternative mechanically actuated ~ixator~ and Figures 13 to 15 show fixators applied to patients.
Referring to Figure 1, a prior art external fi~ator is schematically sho~ of the kind de~cribed in Applicantts-e~-~e~i~g- ~ ~ D
~ ? ~he fixator consist~ of a square-section support tube 1 arranged longitudinally and externally of a human ~hin 2~ The shin 2 has a tibia 3 with a fracture 4. ~wo upper bone piDS 5 and t~Jo lower bone pi~s 6 c~re inserted into the tibia 3 on either side o~
the ~racture 4. The pins 5 and 6 are rigidly secured to the support 1 by clamps 7 such that the alignment of the tibia 3 is rigidly preserved across the fracture 4 during healing.
Re~erring now also to Figure 27 an external fixator of the in~entio~ is sho~m, parts equivalent to those shown in ~igure 1 being like-refelenced with the pre~ix 20. Upper (or first) bone pins 25 are clamped rigidiy to a prim~ry support tube 21 by fixed clamps 27, but lower (or second) bone pi~s 26 are clamped to guide clamps 28 connec-ted rigidly to a seccndary support rod 29 and mounted slidably on the primary support tube 21 A slide clamp 30 is rigidly j connected to the primar~ support 21 and includes a collar portion 31 slidably mounted on the secondary suppor-t 29 The secondary support rod 29 carries lock-nuts 32 retaining therebetween the collar 31 and a compression spring 33 located against c~nd immediately below the oollar 31. The bone pins 25 and 26 are inserted in the tibia 23 duu~ing a surgioal operation, and the associated support equipment 25 and 33 are assembled such that the fracture 24 is under s~ight oompression.
~he apparatus of Figure 2 operates a follows. The ~ix~tor apparatus is assembled ou a human shin 22 by a surgeon for healing a tibial fracture 24. ~he assembly is such that the fraoture 24 is under slight compre~sion when unloaded. ~he fi2ator is su~fioiently rigid to allow the patient to walk without adverse e~eots on healing. However, during walking, the fraoture 24 is further oompressed when bearing a patient~s weight, and the upper ~nd lower bone pins 25,26 with their attached clamps 27 and 28 are urged together The guide clamps 28 accordingly slide upwardly on the primary suppo~t tube 21, the seoondary support bar 29 moves with the guide olamps 28 upwardly with respeot to the slide olamp 30 and oollar 31, and the spring 33 is oompressed between the oollc~r 31 and look~nuts 32. When weight is removed from the fraoture 24, the spring 33 urges tho upper and lower bone pins 25 a~ld 26 apart longitudinally of the primary s~pport 21~ ~he fixator apparatus is rigid in the plane transverse to the primc~ry support 21~ but in the longitudinal direotion a predetermined degree of s~

movement o* the bone ~racture ends towards and a~Jay from each other is obtained for a spring 33 of given force constant and a given fracture loadi~g by ths patient~s wei~htO It has been f~und that a suitable degree o* movement is up to 0.5mm approximately at the bone ~racture 24. It will be appreciated that ~ractura movement iæ dif*icult to measure reliably through intervening ~lesh and skin.
~or a tibial ~racture, up to 0~2mm movement axially o* the tibia between bone portions has been *ound suitable, ~e~erring now also to Figures 3 to 6, Figures 3 and 4 respectively show detailed ~ront and side elevations of apparatus equivalent to that illustrated schematically in ~igure 2, and Figures 5 and 6 show *ixed and guide clamps respectively.
(~B: Figure 3 corresponds to Figure 2 laterally i~vertedO) In Figures 3 to 6 parts equivalent to those shown in Figure 2 are like-referenced with the prefix 100. The primary support 121 is a square tube retaining fixed clamps 127, and the secondar~
suppo~t 129 is a solid rod rigidly retaining the guide clamps 128 which are slidable on the support 129, The compression spring 133 is provided by a pair o* belleville spring washers arranged base to base. The use of belleville washers is ad~antageous sinoe it allo~rs the force constant o~ the spring 133 to be altered by changing the number and/or relative orientation o~ the washers. ~he spring 133 is retainsd by lock-nuts 132 against the lower side o~ the collar 131 o~ the slide clamp 130, itsel~ secured to the primary suppor-t 121 by a nut 140, The ~ixed and guide bone-pin clamps 127 and 128 have similar upper pin-clamping portions 141. ~he upper portions 141 each oonsist of a hollow barrel 142 with holes 143 and 144 csntred on a diameter, and through which a sleeved pin 125 or 126 passes tra~sversely, ~he barrel 142 contains ball~bearings 145 retained by a threaded cap 1~6 and urged into clamping contact with a sleeved pinbyalockingscrew 147. ~iththecap 146s¢rew 147partially unscrewedt the pin 125 or 126 may be set in cm y desired direction (within the limits 3et by holes 143 and 144) to pin a bone, and the pin is then clamped in that direction by screwing up the cap a~d screw ~he fixed cl~p 127 rigidly retains the primary ~upport tube 121 by means o~ a clamp plate 148 and clamp ~crew 1490 The plate 148 cmd screw 149 urge the -tube 121 into clamping contact with two faces 150 and 151 of the lower body portion 152 of the fixed clc~mp 127.
The guide clamp 128 has a lower body portion 153 haYing three flat s~r~aces 154 between ~hich the primc~ry æupport tube 121 is c~
sliding fito A keep plate 155 and screw 156 retain the support 121 between the s~rfaces 154. The g~lide clamp 128 is rigidly connected to the secondary support rod 129 by means o~ a clc~mping scrcw 157 and locking bush 158. The screw 157 and bush 158 clamp the rod 129 into a recess 159 in the guide clamp lower bo~y portion 153~
~eferring now to Figure 7, there is eche~atically shown a modi~ication o~ the embodiment illustr~ted i~ Figure 2 corresponding pc~rts being like~referenced with the prefiæ 200~ The slide clamp 230 is equivalent to Elide clamp 30 of Figure 2, h~ving a central oollar portion 231 slidably mounted on the seco~ldary support rod 229 and being clamped to the primary s~lpport tube 221. The ~lide clamp 230 however possesses an additional clamping body portion 260 rigidly retaining a locatio~ bar 261. The loc~tion bar 261 is con~eoted rigidly to a pneumatic cylinder 262 ~y means of a plate 263 through which a pneumatic piston 264 protrudes. A lever 265 is mour.ted pivotally at 266 on the foot 267 ~f the locatinn bar 261.
The lever 265 eng~ages the lower end 268 of the secondary ~upport rod 229. The piston 264 engages the lever 265 at 269.
The arrangement of Fig~re 7 operates as follows. When the piston and cylinder arrangement (264 and 262) is pneumatically actuated, the piston 264 urge~ the lower 265 do~mwardly at 269 to pivot at 266. The leYer 265 accordingly urges the secondary support rod 22~ longitudinally upwards. When pneumatic pressure is reduoed, the compressioIl spring 233 actua-tes a return s~rcke of the rod 229 longitudinally downwards. This produces a compression-extension load cycle of the bone fracture 224 retained by the modified fixator. In practice~ the piston is actuated repetitively at a ~l935~6 rate appropriate to normal fracture exercise, about one cycle per second. For a tibial fracture, the piston stroke is arranged to be in the range 0~3 to 2.0mm~ moving to~ether the ~ixed and guide clamps 27 and 28 accordingl~. ~one pin ~lexure takes up some movemsnt, and movement o~ bone portions at the fracture is somewhat less.
Referring now also to Figures 8 to 11, there are sho~m detailed representations of the lower part of the fixator assembly illustrated schematically in Figure 7 having parts detailed in Figures 3, 4 and 6. Parts in Figures 8 to 11 equivalen-t to those describad earlier have similar references with the prefix 300 replacing 100 or 200 as appropriate. Figure 8 is a side elevation corresponding to Figure 4, Figure 9 is a sectional view through the ~lide clamp 330 on lines X,X in Figure 8, Figure 10 is a~ oblique side 01evation and Figure 11 an end view. Parts not equivalent to those previously described are as ~ollows. The slide cla~p 330 retains the location bar 361 in a recess 380 of its body portion 360 by means of a screw 381 and lock-ing bush 382. The lever 365 has a bifurcate end 383 retaining a lever pin 384 for engaging the lower end 368 of the secondary support rod 329. The compression spring 333 consists of a pair of belleville washers arranged base to base. The lever 365 has a stud 385 ~or engaging the piston 364~
Re~erring now also to Figure 12, there is shown an alternative ~orm oP mechanical actuation. Parts e~livalent tothose previously described have the prefi~ 400. The Figure 12 arrangement is similar to that shown in Figure 7, except that the pneumatic piston and cylinder arrangement 490 acts directly on the secondar~ support rod ~29 instead o~ via a pivoted lever. ~he pneumatic arrangement 490 also includes n internal return spring 491 to reset the piston 492 when pneumatic pres3ure is reduced. Pressurising the pneumatic arrangement 490 initiates a compression-extension cycle oP the Practure 424 as previously described.
Mechanical movement o~ a fracture employing an actuator in this ~ashion is advantageous in cases where it is unde~irable or impossible ~or the patient to exercise the ~racture. ~his is particularly important when a patient has sustained a serious injuD~J
and immobilis~tion is necessary. Mechanical actuation makes it possib1e to encourage bone callus ~ormation, and -thus rapid healing, a 3 when a co~ventional plaster cast migh~ be totally inappropriate and prior art bone plate or rigid fixator techniques would require many months to achieve he~ling, Since a~y reduction in healing time reduces the risk of infection, this is regarded as an important advantage of the inverltion.
~nereas in ~igures 7 to 12 a pneumatic piston c~nd cylinder actuator has been described, it will be apparent to skilled mechanical engineers that alternati~e drive means may be employed.
A hydr~ulic drive cylinder, a cam-operated or eleotromecharical drive may be employed for example.
The fixator of the invention has been employod in surgical operations on ten patients since ~ovember 1981, ~he majority of operations were for tibial frac-tures. However, one patient also had a fixator applied to the opposite femur, one operation was for an ununited fracture of the tibia, one replaced a splinting procedure ~rhich had given rise to soft tissue necrosis, and three were used for leg lengthening procedures, one of which involved a polio patient. This number does not allow statistical proof o~
improved bone union to be claimed, as all fractures were di~ferent in type and severity, and the subsequent operation and treatment significantly affect the healing of the fracture. However, the results at the very least demonstrate a degree of consolidation and haaling of the fracture ~ihich, by comparison with external fixation results generally, subjectively appear to give an increased respon~e in bone production and reduced osteoporosis ~rcm disuse o~ the fractured limbO The combination of a fixator o~ the invention and early patient mobilisation released hospital bed occupancy and nursing staf~ with rapid healing of the fracture. This enabled ths fixator to be removed within 3-6 months of fltting. The early results showed p~omise o~ rapld bone healing, aud thero was no obs~rved evidence of excessive fracture movement or loss of bone length, In the above tests, bone portion movement at the fracture site was measllred to be up to 0.2mm uhen load bearin~ The correspondi~g relativo movement between the fixed c~nd guide clamps 227 and 228 when passi~ely stimulated ~see Figure 7) within three weeks of the operation was between 0.2mm and 005mmO Pc~r-t of the .. .. . .. ~

~ ~3~i~6 ~o later movement was taken by bone screw flexing a~d part by strain at the fracture. Due to the co~struction of the fixator, lateral movement at the ~racture is small, the main force component being loading axially of the ~i~ated limb resulting i~ compressive strain, No distinction could be dra~m between the passive stimulation regime in which actuated cyclical loading of the ~racture cor~mences for the patient one week after the operation, and active stimulation which followed when the patient got up, and walkad with crutches a-t about two weeks post-operatively.
In one o~ the above operations involving both tibial and femoral fractures on different legs, the patient was not able to walk for about six weeks. ~owever~ the bone healing stimulus dtle to the passive or mechanically actuated regime was carried on for this period giving good radiological results. ~or part of the time the patient was also undergoing physiotherapy.
Parallel animal trials ha~e been co duc~ed~o compare a prior art rigid fixator (UX ~ ~ wiJth a ~ixator of the invention using passive stirmulation. Osteotomised sheep tibiae were c~clically loaded using the inve~tion wi-th passive or mechanical actuation. ~he results compared with similarly~
prepared sheep ~nth the prior c~rt fi~ator. The sheep at other times waIked about. ~-rc~y and post-mortem mechanical data gave a clezr indicaticn that, at the two week and f~ur week~
post~operative stages~ the fi ætor of the inven-tion produced more ~avourable results than the prior art device.
~able I gives details of four of the foregoing te~
ca~es where patients completed a fracture man~gement procedure, and the fi~tors (of the invention) on all four were removed *ollowing success~1l treatment.

3S~6 TABLE I
__ REIEV~ll DA'rES A~7D l~l~S
PATIE~T RACTU E TYPE FIY~TO~ OPERATIOE FIOFFO~ CO~E~S
_ __ ____ __ __ ~
1 Severe, open 4.11,81 30~11.81 and 15.3.82 21.4.82full fractured one week weight, ~o tibia, fibula, passi~c length loss.
bone loss. stimulation 3m. 15d. of Accident date fixation 1.11,81. a~ter operation.
__~ __--_ ____ __ ~
Severe, open 10.11081 1.12,81 and 22~3.82 21.~,.82 ~ractured one week healed tibia, fibula1 passive solidly, bone loss. stimulation 3m. 21d~ of ~raction fixation applied. Dat a~ter of accident oper~tion.
20~10~81.
~_ ___ _ __ _, .......................... __ 3 Polio. Leg 2.1108118.1.82 22.3.82 Satisfactory.
lengthening, 2m. 4d. o~
Le~t tibia. fixation after operation, __ ____ _ __ ___ ,___ 4 Leg 10.8081 16.11,818.2082 Satisfactory.
lengthening. 2m. 23d. of Right tibia. ~ixation a~ter ~ixation.
. _ ~ __ ~_ __ . __. __ ~ , ._. _ During the leg lengthening operation, ezch leg was progressively ler~thened over a period of weeks, follo~nng ~Jhich consolidation toQk plac~. To illustrate use of the fixator of t~.a invention, Figure 13 shows applied to a patient a ~ix~tor in accor~ance with Fi~ure 7.
Figures 1~ and 15 are similar ~nd show the Fi~ure 2 device ~pplied in an inverted manner.

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An external orthopaedic fracture fixator comprising:
a primary elongate rigid support;
first clamp means connected with said primary support to secure adjustably therewith a plurality of first bone pins trans-fixable with a first fragment of a fractured bone;
a secondary elongate rigid support;
second clamp means connected with said secondary support to secure adjustably therewith a plurality of second bone pins transfixable with a second fragment of said bone;
means for interconnecting said supports to hold said fragments under compressive force in a predetermined mutually aligned disposition for reunion, while allowing unidirectional move-ment between said supports without misaligning said disposition in response to increase of said force;
and control means cooperable with said interconnected supports to limit the extent of said movement to that which encourages callous formation without inhibiting primary bone for-mation.

2. An external orthopaedic fracture fixator comprising:
a primary elongate rigid support;
first clamp means connected with said primary support to secure adjustably therewith a plurality of first bone pins trans-fixable with a first fragment of a fractured bone;
a secondary elongate rigid support;
a second clamp means connected with said secondary support to secure adjustably therewith a plurality of second bone pins transfixable with a second fragment of said bone;
a linkage respectively fixable and slidably connected with said primary and secondary supports to hold said primary and secondary supports in parallel side-by-side relationship;
a seat connected with said secondary support;
compression spring means acting between said linkage and said seat to bias said primary and secondary supports into relative movement to separate said first and second clamp means; and a stop connected with one of said support and cooperable with said linkage to limit the bias action of said spring.

3. A fixator according to claim 2 wherein said seat is adjustably mounted on and separable from a free end portion of said secondary support, and said spring means is of annular form slidably engaged over said free end portion.

4. A fixator according to claim 3 wherein said stop is adjustably mounted on said secondary support.

5. A fixator according to claim 2 wherein said second clamp means embrace said primary support in sliding engagement.

6. A fixator according to claim 2 wherein said first and second clamp means each comprise at least two clamps individually slidably adjustably securable on respective ones of said primary and secondary supports, said clamps each being adapted to secure a respective individual bone pin passing therethrough in directional-ly adjustable manner.

7. A fixator according to claim 2 wherein said spring means comprises at least one pair of Belleville washers engaged on said secondary support in mutually base-to-base disposition.

8. A fixator according to claim 2 comprising an actuator operably connected between said supports repetitively to effect relative movement therebetween against the bias of said spring.

9. A fixator according to claim 8 wherein said actuator includes a fluid-powered piston-and-cylinder assembly.