Application of the Point Contact Fixator in large animals

S-B37

Application

of the Point Contact Fixator in large animals

J.A. Auerl, C. Lischerl,

B. Kaegil, U. Iselin1f2, T. Fiirstl, G. Matter1

1 Veterinary Surgery Clinic, University of Zurich, Winterthurerstr. * New address: Gemeinschaftspraxis Perl, Regi, Iselin, Maienweg

260, CH-8057 Zurich, Switzerland 10, CH-7000 Chur, Switzerland

Summary1

Introduction

Clinical tests with the prototype 4.5 mm PC-Fix system were conducted in large animals suffering long bone fractures due to trauma. Initial interfragmentary fixation of the fractures with cortex screws inserted as lag screws was followed by the application of two plates at right angles to each other. The 4.5 mm PC-Fix plates and screws were used in horses and cattle. In newborn animals, the 3.5 mm PCFix ,was used. In most cases some type of external coaptation was applied to reduce the danger of fixation breakdown during the immediate postoperative period. Of the 24 fractures treated with the PC-Fix, 18 healed which represents a success rate of 75%. Good or excellent results were achieved in cattle where 13 out of 15 (86.6%) fractures healed in a relatively short time. The fractures healed in only 5 of the 9 horses (55.5%). The percentages are similar to, if not somewhat better than those for conventional internal fixation techniques. The reasons for the failures are discussed. The results of the study revealed that the 4.5 mm prototype, and in selected cases the 3.5 mm PC-Fix systems were viable options for the treatment of long bone fractures in large animals.

After successful controlled experiments in sheep had been completed, it was decided to study the applicability of the PC-Fix in large and small animals at the Veterinary Surgery Clinic of the University of Zurich. The goal was initially to apply the PC-Fix to long bone fractures in horses and cattle and to test the implants to their limits. If they withstood the forces exerted upon them by large animals they would be strong enough to be applied in human patients. After the first successful applications in horses and cattle, more difficult fracture fixations were attempted. After the first failures occurred in fractures which would not even have been attempted with the conventional implants for large animals, such as the broad DCP (l-5), DCS / DHS (3, 6) implant systems and 4.5 and 5.5 mm cortex screws, the indications for PC-Fix application were reevaluated. From then on much stricter criteria were applied in the indications for the device and success returned. Approximately one year after the development of the 4.5 mm PC-Fix, the 3.5 mm PC-Fix was introduced into small animal surgery. These implants were only suitable in size for application in larger breeds of dogs. The experience gained with large animals led to stricter application criteria which resulted in an extremely successful series of implantations in dogs (7). More recently the 3.5 mm PC-Fix has been successfully applied in calves only a few days old. There are some obvious differences in the practice of long bone fracture treatment in animals, especially large animals, compared to humans (l-5). Animals cannot be restricted to bed rest, nor do they use crutches. Animals load their operated limb immediately after surgery. The obvious pain present may

Keywords: Large animals, internal bones, PC-Fix, titanium implants

fixation,

1 Abstracts in German, Frwwh, Italian, Spanish Japanese are printed at the end of this supplement.

long

and

S-B38 result in reduced loading of the injured limb. External coaptation is frequently applied to a limb with a fracture in the more distal region during the initial postoperative period to prevent breakdown of the fixation (3,4,8-10). In small animals, the injured limb may be fixed in a flexed position with a sling to prevent the animal from loading it (11, 12). This cannot be done in large animals because all four feet must be loaded to some extent if severe complications are to be prevented (3,5). There are differences between applications in large and small animals and between the veterinary applications of internal fixation and those in humans. These points will be discussed with reference to the use of the PC-Fix in large and small animals.

General internal

principles of open reduction and fixation (ORIF) in large animals

Some general principles of internal fixation applied in horses were mentioned in the introductory section of this paper. However, it is important to explain the guidelines used to perform successful, internal fixation in large animals briefly since these are quite different from those applied in human and small animal surgery (3-5). It is generally accepted that long bone fractures in large animals are double plated- with the plates arranged subperiosteally at right angles to each other. Additionally, the plates should be long enough to bridge the entire bone, or should be applied such that the two plates together span the entire bone. The latter would mean that the two plates were staggered. The two plates should not end at the same level on the bone, unless this occurs at one or other end of the bone. The plates should be arranged so that the corresponding screws of one plate are inserted between two screws of the other plate and perpendicular to the long axis of the bone. Additionally, one plate should cover the most distal aspect of the proximal main fragment which tends to “drive” the proximal fragment into the plate during weight-bearing and adds to the stability of the fixation (4). A 4.5 or 5.5 mm cortex screw should be implanted through every hole of each plate. Those screws crossing a fracture line should be inserted as lag screws. If a plate hole is located over a fracture line, the near cortex should be overdrilled allowing the thread hole to be prepared in the far cortex in solid bone (3). These screws are of great importance for establishing stability during immediate postoperative weight-bearing. It is clear that the physes should not be bridged by any implants, if at all possible (7, 8). However, this is difficult to achieve, especially in physeal fractures. Due to the fact that the transport fractures cannot be conducted

of foals with physeal as for humans, i.e.

without loading the injured physis, the germinal layers of the physes are continuously traumatized during transport, resulting in severe trauma to these tissues vital for continued growth (13). Therefore, the classification of Salter Harris (14) does not apply. Healing of all physeal fractures results in the majority of cases in the local interruption of growth and the subsequent development of an axial deviation. Additionally, the process of bone healing progresses slower in horses than in cattle, small animals, and humans.

Implantation

technique

of the PC-Fix

The fractures were treated using routine techniques for large animals (3-5). The periosteum, however, was retained and not stripped from the bone, as would usually be the case. The former clearly benefits the viability of the bone, but makes reduction more difficult and visual assurance of correct reduction has to be replaced by palpation. Often it is not possible to palpate the entire circumference of the bone and permanent malalignment of the fragments may result. Intraoperative radiographs or fluoroscopy may aid in the verification of correct reduction prior to plate fixation. Additionally, the periosteum which is usually tom to some degree at the fracture site, may be carefully opened to allow a clear view of the fracture line and ensure anatomical reduction. Once reduction is considered adequate, the periosteum may be sutured with a simple continuous suture line. In all but one case, the original fracture was initially fixed with one or two cortex screws inserted as lag screws after anatomical reduction of the fracture. The plates to be used were selected in accordance with the principles outlined above. Care was taken to cover the entire length of the bone with at least one plate and apply the plates perpendicular to each other (3-5). The plates were bent in the large bending press applied between the screw holes. Care was taken to prevent axial bending and to implant the screws perpendicular to the surface of the plate to achieve maximal screw head to plate hole contact. Only the 4.5 mm PC-Fix screws of 18 mm length were used. The 3.2 mm drill bit and the tap were prepared with an adjustable stop preset for a drilling and tapping depth of 20*&n to prevent inadvertent and unnecessary trauma to the medullary blood supply. The screws were firmly tightened and care was taken to insert screws in all the plate holes if at all possible. If a physis was bridged by the plate, screws were not inserted into the physis. In most cases some type of external coaptation device, consisting of a PVC-pipe splint or fiberglas cast was applied for a certain period of time postoperatively. All operations were performed by the same surgeon.

Auer: The PC-Fix in large animals Patient

selection

Between April 1992 and April 1994 a total of 8 horses and 12 cattle were treated with the prototype 4.5 mm PC-Fix at the University of Zurich (Tab. 1). Initially only animals with simple fractures of the third and fourth metacarpal/metatarsal bone, radius/ulna and tibia were selected for the implantation of the PC-Fix. After the first successful applications the selection criteria were slackened to allow the use of these promising implants in fractures with a great risk of failure. Promptly the fixation broke down, in some cases directly after the operation in the recovery room during attempts by the animal to rise or within the first week after surgery. This resulted in a return to the original strict selection criteria. Subsequently the success rate increased significantly. One horse was treated with the 3.5 mm PC-Fix with good results. Since spring 1994, the 3.5 mm PC-Fix with selftapping screws has been successfully applied to a two day old calf with a comminuted fracture of the proximal metaphysis of the third and fourth metatarsal bone, a one week old calf with a minimally comminuted diaphyseal fracture of the tibia, and to a two week old calf with an oblique humeral fracture. In the past such fractures (except humeral fractures) have been treated by external coaptation and/or transfixation casting with varied success, since ORIF was not an option due to the weak, soft bone and its poor holding capacity for the conventional screws.

Results patients

and presentation

of the selected

Of all the cases treated with the PC-Fix as summarized in Table 1, a total of 18 of 24 animals or 75% were successful. If a distinction between horses and cattle is made the success rate is as follows: horses 5 of 9 or 55.5%; cattle 13 of 15 or 86.6%. All four cases treated with the 3.5 mm PC-Fix healed well; in three of these the second generation system was applied which uses self-tapping screws. Bone healing occurred somewhat faster than with conventional techniques. Cattle have proven to be excellent candidates for the internal fixation of long bone fractures (4, 9, lo), whereas fracture healing in horses progresses more slowly (5). Of the successful equine cases one was a fourth metatarsal bone fracture, which is not a weightbearing bone and another was a mandibular fracture which is not primarily axially loaded. The three remaining successful horses all suffered a third metacarpal or metatarsal bone fracture. In two of these cases, the fracture involved the nutrient foramen. One healed with substantial callus formation after the application, of a single plate, one healed without complications and the third healed even though the fracture affected the nutrient vessels which

SB39 became infected. This was a case which would have been doomed to failure with conventional treatment associated with periosteal elevation. One of the two unsuccessful cattle cases suffered an open fracture of the third and fourth metacarpal bone associated with severe vascular damage to the distal limb. The fixation was successful in that it permitted the animal to bear weight on the treated limb, however, bone healing did not ensue and 5 months postoperatively the animal was slaughtered with an unhealed fracture. The distal limb was sent for histological investigation. In the second case, poor fixation techniques led to a revision of the fixation and the use of conventional internal fixation devices. The fracture healed subsequently without further problems. All the other fractures healed without complications. Of the cases presented in Table 1 (the cases are arranged according to the date of treatment), three have been selected for presentation in more detail.

Case 1: An 8 month

old Swiss Braunvieh

heifer

The animal was admitted with an oblique diaphyseal multifragmental fracture of the right tibia (Fig. 1). The fracture was reduced using traction on the limb and was temporarily fixed in position with two large pointed reduction forceps. The periosteum at the fracture site was tom over a length of 4 cm. Two 4.5 mm cortex screws were inserted across the main fracture plane to stabilize the fracture. Subsequently a 12 hole PC-Fix was applied to the medial and a 10 hole PC-Fix to the cranial aspect of the limb (Fig. 2). Both plates were applied supraperiosteally. The most distal plate hole was left without a screw due to the fact that it was located too close to the joint for an 18 mm screw to be implanted without penetrating it. The bone fragments located on the caudolateral aspect could not be realigned which resulted in a considerable bone defect. The periosteal tear was left open and the subcutaneous tissues and skin were closed using routine technique. Postoperatively, a pressure bandage was applied over the fracture site. The animal was bearing weight on the limb and did not develop any complications. For the first month after surgery the animal was kept in a stall. The follow-up radiographs 2X months postoperatively revealed good fracture healing with marked callus formation near the bone defect on the caudolateral aspect of the bone (Fig. 3). The owner did not request implant removal and therefore the plates were left in place. The cow is now healthy and fully productive. No further follow-up examinations were necessary.

Fig. 1: Craniocaudal (left) and lateromedial (right) radiographs of the right tibia of an 8 month old Swiss Braunvieh heifer (case 1) with a multifragmental fracture of the diaphysis.

Fig. 3: Craniocaudal (left) and lateromedial (right) radiographs of case 1 taken at the 2% month followup. Most of the fracture lines have disappeared except in the lateral cortex where some callus formation is visible. A considerable amount of longitudinal bone growth has occurred.

Case 3: An 8 month

Fig. 2: Craniocaudal (left) and lateromedial (right) radiographs of case 1 taken immediately after the operation. The fracture was repaired with two 4.5 mm cortex screws applied as lag screws and a 12 and 10 hole 4.5 mm PC-Fix applied to the medial and cranial aspects of the bone respectively. The most distal plate hole in the medial plate was left without a screw.

old Swiss Braunvieh

heifer

The animal was admitted with a severely comminuted fracture of the third and fourth metacarpal bones of the left forelimb (Fig. 4). One of the fractures penetrated the carpometacarpal joint. The skin incision was performed in the sagittal plane. This allowed fracture reduction and stabilization with a 4.5 mm cortex screw inserted as a lag screw. A 10 hole PC-Fix was then implanted dorsolaterally and an 8 hole PC-Fix dorsomedially (Fig. 5). The most distal hole in the longer plate was left without a screw because the plate bridged the physis. Nevertheless the additional plate length supplied some added support to the distal fragment. After routine closure of the tissues a splint bandage was applied to the limb for three weeks. The nine day follow-up radiographs revealed a minor widening of the sagittal fracture gap (Fig. 6). All the screws and plates appeared to be firmly in place. During the initial two months postoperatively the animal was kept in a stall. The 2?4 month follow-up radiographs revealed complete healing of the fracture (Fig. 7). At that time the implants could have been removed. However, it was decided to keep them in place because complications were not encountered and the owner elected not to spend more money on the animal.

Auer: The PC-Fix in large animals

Fig. 4: Dorsopalmar (left) and lateromedial (right) radiographs of the left metacarpal region of an 8 month old heifer (case 3) with a multifragmental fracture.

Fig. 6: Dorsopalmar (left) and lateromedial (r&ht) radiographs of case 3 nine days postoperatively. Reduction is maintained but the sagittal fracture gap can be easily recognized.

Fig. 5: Dorsopalmar (left) and lateromedial (right) radiographs of case 3 taken immediately after the operation. A 10 hole 4.5 mm PC-Fix was applied to the dosolateral and an 8 hole PC-Fix to the dorsomedial aspect of the bone after having implanted an inter-fragmentary 4.5 mm cortex screw as a lag screw across the main fragments. Good alignment was achieved with minimal displacement in the palmar cortex.

Fig. 7: Dorsopalmar (left) and lateromedial (right) radiographs of case 3 at 2?4 months. The fractures have healed completely with only minimal callus formation at the distal fracture ends in the palmar cortex. The entire bone has a more radiodense appearance.

Case 4: A 2 week old Freiberger

colt

The colt was admitted with a short oblique distal metaphyseal fracture of the right tibia (Fig. 8). The limb displayed a marked swelling. The bone was approached through a craniolateral skin incision and an interfragmentary 4.5 mm cortex screw was inserted as a lag screw following reduction of the fracture. Subsequently a 10 hole 4.5 mm PC-Fix was implanted subperiosteally laterally and an 8 hole PC-Fix to the cranial aspect of the bone. Due to the fact that the periosteum covered the bone, inadequate reduction was achieved resulting in a 4 millimetre gap on the medial aspect (Fig. 9). This gap should have been bridged by a plate. However, the gap was only noticed postoperatively; Application of one plate laterally was selected because of better soft tissue coverage compared to the medial aspect where the plate would have been immediately under the skin (15, 16). For this fracture configuration, one plate should have been applied to the medial aspect instead of laterally (5). A fiberglas cast encased the limb during the immediate postoperative period. The animal did not use the limb well and three days later the cast was removed. The following day the fixation was found to have failed (Fig. 10). The animal was then destroyed.

Fig. 8: Craniocaudal (left) and lateromedial (right) radiographs of a short oblique distal metaphyseal fracture of the right tibia in a 2 week old Freiberger colt (case 4). The radiographs were taken through a fiberglas cast applied for transport purposes.

Fig. 9: Craniocaudal (left) and lateromedial (right) postoperative radiographs of case 4. The fracture was repaired with a interfragmentary cortex screw inserted as a lag screw followed by the application of a 10 and 8 hole 4.5 mm PC-Fix to the lateral and cranial aspects of the bone respectively. Inadequate reduction of the fracture resulted in gap formation on the medial aspect.

Fig. 10: Craniocaudal (left) and lateromedial (right) radiographs of case 4 taken 4 days after the operation. The gap on the medial aspect is wider and some screws in the lateral plate are loose. The cranial plate lost contact with the bone and breakdown of the fixation occurred. The animal was subsequently killed painlessly.

B

E

8

E

E

E

E

B

1

2

3

4

5

6

7

8

1 Species

1

B

8

E

8

11

12

13

1OlE 10 E

9

I 91B

1 Case No.

2Y

7Y

10M

/1M 4M

17~ 7M

8M

12Y

3W

4W

2w

8M

3Y

8M

1 Age

F

G

F

ISS

( F

F

G

F

F

s

F

F

F

L Mnll/lV

L tibia

R Mclll

L Mclll

R tlbla

L Mclll/lV

R Mclll

L tibia

1 Bone

SBV

WB

SBV

IFrelb. Frelb.

L radius ulna

L radius ulna Lramusof marldlble

ILMtllI LMtlll

1 simm. simm 1 L. L.MCIII/N Mclll/lV

SBV

WB

Hafi.

WB

Freib.

SBV

PonV

SBV

1 Sex 1 Breed

I

MF / dbphysls long

MFllongobIiquel ~aphvsb obilque

I ~~JO/MF/ long oblique / MF / diaphVsis lzzprox. transverse / prox. mtaphysb

MF/open/ middiaphysis

MF/open/ nor&placed I middiaphysis long oblique / prox. metaphy&

nondiiaced middiiphysls

short oblique

MF I entire bone

MFlopenl transverse I middiaphysls

MF / oblique

I FractureType

3 x 5.5 n-m

none

2 x 5.5 mll

none

1 x 4.5 mm

none

4 x 5.5 mm

ho4 hole hole hole

4.5 4.5 4.5 4.5

mm mm mm mm

I

! ECAfor 1 W/ postoperative infection Breakdown of flxationdurlng rouah recovery ECA for 3 M / poor vascular supply to distal limb ECAfor3W

ECAfor 1 M

1fixation

ECA for 3 D. Breakdown of

ECAfor3W

ECA for 1 M. At 2 M breakage of 3 screws in cranial plate

Postoperative Developments bandagefor3W

6hole4.5mm

12hole4.5mm 1

ECAfor3W

12hoIe4.5mm I ECAfor3W 10 hole 4.5 mm 8hole4.5mm loosenlngofthe 4screwslnthe rostral fragment

9hole4.5mn-1 7hole4.5mm lOhole4.5mm ECAfor 1 M 8 hole 4.5 mm I

10 hole 4.5 mm 7 hole 4.5 mm osteotomy

14 hole 4.5 mm 12hole4.5mm

lOhole4.5mm

12hole4.5mm

10 8 10 8

Tr atmmt PC-FIX 12hole4.5mm 10 hole 4.5 mm 10 hole 4.5 mm 7 hole 4.5 mm

1 x 3.5 mm

none

~ 1 x4.5rrw-l

1 x4.5mn-l

none

Screws 2x5.5mm

Table 1: Overview of the large animal patients treated with the PC-Fix at the University of Zurich

none

none

repeated flushirlg of fracture site

repeated flushing of fracture site none

none

I

exchange wtih four 5.5 mm screws through plate holes none

I none

I

I

I

I

!

none

plate removal at 2 M replating after1 Wwith9 holeDCPand 5.5 mm none

Addttlonal Treatment none

nonunionat4M after surgery

none

none

SHM/healed fracture / Implant removal

skwghter2M later due to Persistent

slaughter

Immediate euttwusla

euthwwsla after2W

1iarneness

!

euttwunia after4D

excellent

after3HM

euthamla

excellent

Resuti

by telephone 1 summeronalp

/ I

excellent

healed fracture at excellent 3 M after wraerv healed fracture at gqod, slight I 3 M after surgery I devialion 1 implant removal I I healed fracture at I exceknt 3 M after surgery healed fracture at good 5 M after surgery Implant removal

I

!

PHMhealed fracfure none

2H M progressive healing 1 M after replating breakage of plate at former fracture site

Follow-up

f

B

B

B

E

B

E

B

B

B

B

15

16

17

18

19

20

21

22

23

24

2D

1W

13M

18M

4Y

3D

3W

F

F

F

F

F

F

S

F

F

2W

2Y

F

F

2M

9M

Hoist:

Fructurc Type: MF: ,multifragment; dist: distal; prox: Postopcmtiw Dcwbpmcnts: ECA: external coaptation

long

Freilx

Holstein;

Freiberger;

W: weeks;

WB: Warmblood;

HatI

Y: years

1 x 3.5 mm

none

2 x 3.5 mm

none

none

none

1 x 3.5 mm

2 x 5.5 mm

2 x 3.5 mm

3x4.5mn-l

1 x 4.5 mm

M: months;

short oblique prox. metaphysis

short oblique dii. ~taphvsis short oblique diaphVsis

MF / diaphyb

long oblique dww MF / proximal ~taphvsis involving nutrient foramen MF / dial metaph@s short @hlique transverse nonunion infected

D: days;

proximal

Bone:R: right; L: left; MC Metacarpus;MT: metatarsus

oblique

MF / diaphy& oblique

MF m

MF / diaphysis long oblique

Result:

R MtlllJlV

SBV

Followup,

R tibia

SBV

L M Ill/n/

R Mclll/lV

SBV

SBV

RhMlV

R femur

L Mt Ill

R Mclll/lV

WB

SBV

TB

SBV

R tlbla

R humerus

SBV

Hoist.

Rtibla

SBV

Legend% Species: B: bovine; E: equine Age, Postop. Dmrlopmmts, Additional Treatmnt, Sex: F: female; S: stallion; G: gelding Brccdd: SBV: Swiss Braunvieh; Simm: Siienthal;

B

14

Table 1 contd.:

Haflinger;

for 2 W

ECA for 3 W

ECA for 3 W

ECA for 3 W

ECAfor2M

drainage / bandagefor4W

bandage

postoperative infection ECA for 5W

none

ECA for 2 W

none

none

none

removd of 1 plate 12Dafter Jww

none

none

continued flushing 4 cast changes

none none

none

flxaiton breakdown during recovery breakage of 3 screw mlnorloosening of screws ECA for 2 W

TB: Thoroughbred

12hole4.5mm 9 hole 4.5 mm poor technique 12 hole 4.5 mm 6 hole 4.5 mm 10 hole 3.5 mm 8 hole 3.5 mm PC Fix II 7 hole 3.5 mm PC-Fix II

Ohole3.5mm pinless fix exi 10 hole 4.5 mm 9 hole 4.5 mm 2x3.5mm cortex screws through plate 10 hole 4.5 mm 9 hole 4.5 mm 12 hole 4.5 mm 9 hole 4.5 mm Inadequate reduction 6 hole 3.5 mm stacked pins cerclage wire 9 hole 3.5 mm

14 hole 4.5 mm 14 hole 4.5 mm

fracture 5 surgery fracture 9 surgery

healed fracture 2 M after surgery

healed fracture 2 M after surgery healed fracture 9 Waftersurgery

healed fracture 5 M after surw Implant removal hebdfracture2 M after surgery minor devtatlon

bYtelephone/ never a problem complete fracture healing5Mafter wxvimpl~ removd healed fracture 3 M after surgery

healed M after healed M after

none

excellent

excellent

excellent

good

excellent

excellent

excellent

excellent

excellent

god

euthanaslo

Auer: The K-Fix

s-B45

in large animals

Discussion It is difficdt to evalmte the results achieved with the PC-Fix statistically because during the study period several approaches were taken. For some time the attitude was to try to established the limits of the system which resulted in several failures. Then a more careful approach was assumed and good results were obtained. In some instances, the screw head jammed within the plate such that it was impossible to remove it again. As a result of this a new design of the cone shape of the screw head was developed which improved the situation dramatically. Occasionally one screw did not lock within the plate and pulled through right down to the bone surface. The new design of the screw head corrected this problem as well. Also in one or two cases the screw head broke at the head-shaft junction because the hexagonal socket was cut too deeply into the screw head. This was corrected. It was difficult to orient the insertion axis of the screw perpendicular to the plate because the early drill guides did not have a tight fit in the plate! hole. Insertion of a screw in a direction not perpendicular to the plate surface resulted in a poor screw head to plate hole contact area. In general, the PC-Fix is easy to apply and reduces operating time dramatically. Fracture reduction is, however, more difficult to achieve because anatomical reduction cannot be verified visually but only by palpation. This is especially difficult to perform on the side of the bone away from the incision because the entire circumference of the bone is rarely palpable without excessive dissection. Therefore, it is highly important to ensure correct fracture reduction and axial alignment of the bone by intraoperative radiographs or fluoroscopy. The experience gained with these cases showed that interfragmentary reduction of the bone fragments prior to application of the plate or plates is of great importance. It is also necessary to apply two plates at right angles to each other on the long bones of all but the youngest (a few days old) large animals. The screws should be tightened firmly but not jammed to facilitate their removal should the need arise. The plates should be bent between the plate holes with the bending press and axial torsion should be avoided so that the plate hole geometry is not affected. It might be possible to twist the plate with the help of a special bending press for the PC-Fix. Due to the fact that the fractured liinbs are loaded immediately after recovery from anaesthesia, it is strongly encouraged that the plates be contoured to match the bone surface as closely as possible. The 18.mm long PC-Fix screws are long enough in most cases. It might, however, be advantageous to manufacture 20 or 22 mm screws for special purposes. It is advisable to apply compression across the fracture plane. This can be achieved with the conventional articulated tension device. It is

questionable whether the self-tapping screws are suitable in large animals because of their relatively hard bone and substantial cortex thickness, especially in adult animals. The flutes for the bone debris are too small and a clean thread cannot be cut. The use of the 3.5 mm PC-Fix in newborn large animals has shown potential and provides the veterinary surgeon with a new and improved treatment possibility for these animals. Until now only conservative techniques consisting of external coaptation were used in newborn animals with long bone fractures. ln the three cases in which the PC-Fix was applied, the use of self-tapping screws proved successful.

Conclusions The PC-Fix has proven to be a successful treatment system for large animals. Fracture reduction is more challenging and implantation time could be significantly reduced relative to the application of the conventional DCP of similar dimensions. lnterfragmentary compression of the fracture planes by cortex screws functioning as lag screws is strongly recommended. For long bone fractures, two plates together spanning the entire length of the bone should be applied at right angles to each other. During the initial postoperative period external coaptation should be provided to assist in immediate weight-bearing and protect the implants. Bone healing was judged to be superior to the conventional implants. The 3.5 mm PC-Fix is a valuable implant system for newborn animals and specific non-weight bearing bones in the horse.

References 1. BramIage LR. Long bone fractures. Vet. Clin. North. Am. Pratt. Vet. 1983,285. 2. Auer JA. Internal fixation. In: Colahan P, Mayhew IG, Merritt AL, Moore JN, eds Equine Medicine and Surgery, 4th Ed. Santa Barbara: American Veterinary Publications, 1991,1235. 3. Auer JA. Principles in fracture treatment. In: Auer JA, ed. Equine Surgery, Philadelphia: WB Saunders Company, 1992,812. 4. Auer JA, Steiner A, Iselin U, L&her CJ. Internal fixation of long bone fractures in farm animals. Vet Comp Orthop Traumatol, 1993;6:36. 5. Fackelman GE, Nunamaker DM, Auer JA, eds Equine osteosynthesis; an electronic manual of the AO/ASIF technique. Bern: Huber Verlag, 1994. 6. Auer JA. Application of the dynamic condylar screw (DCS) - dynamic hip screw (DHS) implant system in the horse. Vet. Comp. Orthop. Traumatol., 1988;l:lS. 7. Salvodelli D, Montavon P.M. Clinical handling: small animals. Injury (Suppl. 2), 1995,26:49-52.

S-B46 8. Watkins JP, Auer JA. Physeal injuries. Comp. Cont. Educ. Pratt. Vet, 1984;6:226. 9. Steiner A, Iselin U, Auer JA, Lischer CJ. Physeal fractures of the metacarpus and metatarsus in cattle. Vet. Comp. Orthop. Traumatol., 1993;6:131. 10. Steiner A, Iselin U, Auer JA, Lischer CJ. Shaft fractures of the metacarpus and metatarsus in cattle. Vet. Comp. Orthop. Traumatol. 1993;6:138. 11. Brinker WO, Hohn RB, Prieur WD, eds Manual of internal fixation in small animals. Berlin: Springer Verlag, 1984. 12. DeYoung DJ, Probst CW. Methods of internal fixation: general principles. In: Slatter D, ed. Textbook of Small Animal Surgery, 2nd Ed. Philadelphia: WB Saunders Company, 1993,1611. 13. Bramlage LR. Current concepts of emergency first aid treatment and transportation of equine fracture patients. Comp. Cont. Educ. Pratt. Vet. 1983;5:564. 14. Salter RB, Harris WR. Injuries involving the epiphyseal plate. J. Bone Joint Surg. 1963;45A:587. 15. Schneider RR. Transverse and comminuted fractures of the third metacarpus/metatarsus. In: White II NA, Moore JN, eds Current Practice of Equine Surgery. Philadelphia: JB Lippincott Company, 1990,631. 16. Richardson DW. Fractures of the tibia. In: White II NA, Moore JN, eds Current Practice of Equine Surgery. Philadelphia: JB Lippincott Company, 1990,660.