0195-5616/92 $0.00 + .20
EXTERNAL SKELETAL FIXATION
TRANSARTICULAR APPLICATION OF EXTERNAL SKELETAL FIXATION James P. Toombs, DVM, MS
The resurgence of external skeletal fixation in small animal orthopedics is attributable to improvements in fixation pins and pin insertion technique3, 4, 5, 15, 22 and greater appreciation of the biomechanical characteristics of different external fixator configurations,12, 13, 20 This resurgence has prompted greater usage of external fixators for immobilization of jOints. Transarticular external skeletal fixation (TESF) has been used for primary fixation of distal fractures/' 24 to augment tenuous internal fixation of distal fractures/' 8, 20, 24 to perform joint arthrodeses,6, 7, 9, 10, 16, 17, 20, 21, 24 and to protect tendon l7, 18, 20, 24 or ligament repairs,1, 2, 7, 9, 10, 20, 22, 24 Several injury factors favor the use of TESF, including the presence of significant open wounds and involvement of two or more limbs. Compared with coaptation techniques for immobilizing the elbow, carpus, stifle, or tarsus, TESF provides superior stabilization and improved access for treatment of soft tissue injuries 24 (Fig. 1). OVERVIEW OF TRANSARTICULAA EXTERNAL SKELETAL FIXATION TECHNIQUES
Fixation pins placed through the bone proximal and distal to the joint are common elements found in nearly all TESF devices. Different methods of TESF are distinguished by the materials used to interconnect From the Department of Veterinary Clinical Sciences, Purdue University School of Veterinary Medicine, West Lafayette, Indiana
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Figure 1. Type II contoured rod Kirschner-Ehmer splint stabilizing the tarsocrural joint of a Great Dane after prosthetic repair of the medial collateral ligament complex. Note that splint allows ample access for treatment of the soft tissue shear injury.
these pins to form a fixation frame. These methods fall into three basic categories: (1) fixed configurations, (2) variable configurations, and (3) improvised fixation devices. 4 Fixed Configurations
Fixed configurations use a frame that dictates the position and number of fixation pins4 (i.e., Charnley compression clamps [Fig. 2]). Although these devices have been used successfully in arthrodesis procedures,l1 a narrow range of three-dimensional adjustability has limited their utility for TESF. Variable Configurations
Variable configurations use separate components that can be assembled into almost any spatial configuration as dictated by the nature of the orthopedic problem4 (i.e., Hoffmann and Kirschner-Ehmer fixation systems). Hoffmann fixators have been used successfully for stifle and tarsocrural arthrodeses in dogs. 21 The bulk and expense of Hoffmann
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Figure 2. Components of Charnley compression clamps: pin grippers (A); lock nuts (8) used to fix the position of pin grippers; threaded central bolt connecting rod (C); and central bolt adjustment knob (0), which turns one way to apply compression and the opposite way to apply distraction. Pin gripper design dictates placement of fixation pins perpendicular to the long axis of the connecting rod, and pin gripper number dictates use of only four pins with this device.
components, however, have limited their use in small animal patients. The Kirschner-Ehmer system provides three sizes of affordable components, the smallest of which can be used in cats and toy breed dogs. These advantages have made Kirschner-Ehmer splints the most commonly used variable configuration device for TESF in small animals. !, 7, 8, 9, 10, 14, 16, 17, 18,22, 24 Improvised Fixation Devices
Improvised fixation devices4,6, 13, 19,20 use an unsolidified substance that hardens shortly after application to interconnect the fixation pins (i.e., "pins-in-plaster technique,"4 the Murray epoxy-filled tube system,4 and acrylic bar fixators 13, 19, 20). The major advantage of improvised devices is that the angles, planes, positions, and diameters of fixation pins are not restricted by the frame. 2o Additionally, improvised devices provide the most economical method of applying TESF. The major disadvantage of these devices is limited adjustability following surgery. Rudy Boot Technique
The Rudy external fixator bootB, 17 combines elements of improvised devices and variable configurations (Fig. 3). It is most commonly used
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Figure 3. Cranial (A) and lateral (8) views of Rudy external fixator boot applied for stabilization of the tarsus. (Courtesy of Ann Johnson, DVM).
for management of injuries associated with the carpus and tarsus but has also been used as primary or supplementary fixation for distal fractures of the tibia and radius. 17 The Rudy external fixator boot involves application of a KirschnerEhmer splint to the radius or tibia and attaching it to a distally applied plaster or fiberglass cast boot. The boot covers the toes, paw, and distal 75% of the metacarpus or metatarsus. After the cast boot has been allowed to set for several minutes, a wooden block containing two fixation pins is placed on the dorsolateral or dorsomedial aspect of the boot and secured by application of additional plaster or fiberglass cast material. Once final setting of the boot has occurred, the pins exiting from the pin block are attached to the connecting rods of the KirschnerEhmer splint, the carpus or hock is placed in the desired position, and all clamps are tightened. If a single connecting rod is used, it is contoured such that the fixator will immobilize the carpus or tarsus at a normal standing angle. The Rudy boot technique is especially well suited to cats and toy breed dogs. The extremely small metacarpal and metatarsal bones in these animals are a difficult target for safe and effective passage of the %2" pins normally used with small Kirschner-Ehmer clamps.
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USE OF THE KIRSCHNER-EHMER SPLINT FOR TRANSARTICULAR EXTERNAL SKELETAL FIXATION
Basic principles for application of Kirschner-Ehmer splints are found in other articles in this issue and elsewhere. 3, 14, 23 The author's preferences for the type of fixation pins, methods of pin insertion, and aftercare of the patient and fixator are the same as those expressed by Aron elsewhere in this issue. . Kirschner-Ehmer splints have provided effective immobilization of the elbow/' 24 carpus/' 10 stifle, 4, 7, 22, 24 and tarsus l , 3, 7, 9, 14, 16, IS, 24 in carefully selected patients. Two basic types of transarticular KirschnerEhmer splints have been used: those employing straight connecting rods 7 and those in which contoured connecting rods are applied. 24 Transarticular Kirschner-Ehmer Splints with Straight Connecting Rods
In most reports of transarticular Kirschner-Ehmer splint use in small animals, straight connecting rods were used to construct the frames. I, 2, 7, 14, 16, IS, 22 This works well if the desired splint configuration is type I, but type II straight rod transarticular Kirschner-Ehmer splints can be problematic. When the elbow, stifle, or tarsocrural joints are immobilized at their normal standing angles, the number of full-pins that can be attached to a pair of straight connecting rods that span the joint is limited. To obtain greater numbers of fixation pins, multiple connecting rods bearing single clamps and pins can be interconnected using double clamps and short transverse connecting rods 7 (Fig. 4). Although such splints have been used effectively, they are bulky and susceptible to loosening at double clamp articulations. Use of stacked single clampsI4, 23 instead of double clamps to make these articulations reduces the problem of loosening. If excessive bulk of the splint is clinically significant (i.e., extremely small patients), use of a different type of transarticular external fixator is recommended. Alternative methods include contoured rod Kirschner-Ehmer splints and improvised devices such as the Rudy boot or a fixator composed of pins and acrylic bars. Transarticular Kirschner-Ehmer Splints with Contoured Connecting Rods
Application of type II transarticular Kirschner-Ehmer splints can be facilitated by the use of contoured connecting rods. Examples of contoured rod transarticular Kirschner-Ehmer splints are shown in Figures I, 5, and 6. Compared with straight rod splints, contoured rod splints provide several distinct advantages: (1) splints remain secure for longer periods of time owing to avoidance of double clamp articu-
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Figure 4. Type II transarticular K-E splint with straight connecting rods applied across the tarsus. Full pins passed through the distal tibia and proximal metatarsus are attached to connecting rod 1 laterally and connecting rod 3 medially. Laterally placed half pins in the tibia and metatarsus are attached to connecting rod 2. Double clamps and connecting rod 4 interconnect these units. (From Bjorling DE, Toombs JP: Transarticular application of the Kirschner-Ehmer splint. Vet Surg 11 :34, 1982; with permission) .
lations; (2) the number of full-pins that can be attached to a medial and lateral pair of connecting rods is maximized, producing increased splint stiffness and prolongation of secure pin-bone interfaces; and (3) splints are more compact. 24 When TESF is expected to maintain joint immobilization during a
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prolonged healing period (i.e., joint arthrodesis procedures), properly applied contoured rod splints have a definite advantage over straight rod splints. Either type of splint works well when joint immobilization for only 2 to 4 weeks is desired. Disadvantages of contoured rod splints compared with straight rod splints include: (1) More careful preoperative planning of the splint is necessary because single clamps will not slide across the contoured portion of the rod, (2) adjustability of the splint is decreased, and (3) potential for uSIng the connecting rod in subsequent patients is reduced. To apply contoured rod Kirschner-Ehmer splints, rods of appropriate length and diameter are bent to the proper angle using a table bending press, hand bending irons, or the edge of a table or counter. 24 Rods should be bent in small increments spread out over the central portion rather than applying an acute bend at a single focus. In the author's experience, breakage of contoured rods has not occurred despite application of splints to large, active canine patients (i.e., the Great Dane shown in Fig. 1). For immobilization of the elbow, stifle, or tarsus, connecting rods are usually contoured to an angle of 130 to 150 degrees. Use of goniometer to measure the normal standing angle of the joint on the contralateral uninjured limb is recommended. An angle in excess of the normal standing angle may be necessary when TESF is used to prevent tension on Achilles tendon repairs. 18 Proper contouring of the connecting rods will immobilize the joint at the desired angle and enable easy application of multiple full-pins to bones above and below the joint. Transstifle Splint
A type II contoured rod Kirschner-Ehmer splint for immobilization of the stifle joint is shown in Figure 5. Application of this splint is accomplished as follows .24 Centrally threaded pins (enhanced thread full-pin; Gauthier Medical, Inc., Rochester, MN) 1 and 2 are applied as full-pins in a mediolateral plane above and below the joint. Predrilling4 of the cortex followed by hand chuck insertion is the technique preferred by the author for placement of raised profile threaded pins. Contoured connecting rods (a short one medially and a longer one laterally) bearing single clamps are applied to pins 1 and 2. The joint is positioned at the desired angle, and single clamps A through D are tightened. Smooth pins 3 and 4 are applied as full-pins through single clamps F and H on the medial coritoured rod. Low RPM power insertion technique is used. These pins must be in the same mediolateral plane as pin 2 to ensure that they will engage single clamps E and G on the lateral contoured rod. Smooth pins 5 and 6 are applied as half-pins through laterally placed single clamps I and J. Adequate soft tissue releasing incisions around these pins are important to prevent transfixation of the quadriceps muscle group. Full-pins are avoided at these locations because they increase the likelihood of trauma to the inguinal area by the medial aspect of the splint. Single clamps K and L are stacked laterally on pins 6 and 4 to enable attachment of a straight lateral connecting rod.
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Figure 5. Type II transarticular
Kirschner·Ehmer splint with contoured connecting rods applied across the stifle joint. Identifying numbers for pins and identifying letters for clamps are explained in text. (From Toombs JP, Aron DN, Basinger RR, et al: Angled connecting bars for transarticular application of Kirschner-Ehmer external fixation splints. J Am Anim Hosp Assot 25:213, 1989; with permission).
Application of this rod is optional, but it may afford some protection of the lateral contoured rod in regard to cyclic bending loads during weight bearing. All damps are tightened fully, and protruding portions of pins and rods are trimmed off to make the splint as compact as possible and to facilitate bandaging. 24 Transe/bow Splint
Application of a contoured rod type II Kirschner-Ehmer splint across the elbow is similar to the description given for the stifle. A centrally threaded pin is inserted through the distal humerus and another through the proximal radius. Completion of the splint and restriction of medial rod length (to avoid thoracic wall trauma) are as noted for stifle. Avoidance of the radial nerve is important when selecting sites for lateral placement of half-pins in the distal humerus.
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Transtarsal Splint
A type II contoured rod Kirschner-Ehmer splint for immobilization of the tarsus is shown in Figure 6. Use of this technique is restricted to patients that have metatarsal bones large enough to accommodate safe passage of fixation pins. Application of a transtarsal contoured rod Kirschner-Ehmer splint is accomplished as follows. 24 All pins can be applied as full-pins to increase splint rigidity. Centrally threaded pins 1 and 2 are passed in a mediolateral plane through the distal tibia and proximal portions of the metatarsal bones respectively. Because metatarsal bones lie in a gentle arch that is convex along the dorsal aspect, a fixation pin can be inserted easily into only two of the four major metatarsal bones. The author prefers to place pins through the third and fourth metatarsal bones in most cases. Alternatively they can be placed through the second and fifth metatarsal bones. Pin placements should be confined to the proximal two thirds of the metatarsal bones to avoid Kirschner-Ehmer splint interference with a functional foot plant. For TESF of the tarsus, the length of the medial contoured rod is not limited by regional anatomy, contrary to TESF of the elbow or stifle. Therefore medial and lateral contoured rods of equal length are usually applied. Smooth pins 3 through 5 are inserted medially to laterally in the same plane and parallel to pins 1 and 2. Stacked single clamps are applied both medially and laterally on pins 3 and 5 if application of optional straight rods to increase fixator stiffness is desired.
Figure 6. Type II transarticular KirschnerEhmer splint with contoured connecting rods applied across the tarsus. Pin identification numbers are explained in text (From Toombs JP, Aron ON, BaSinger RR, et al : Angled connecting bars for transarticular application of Kirschner-Ehmer external fixation splints. J Am Anim Hosp Assoc 25:213, 1989; with permission) .
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USE OF ACRYLIC FRAMES FOR TRANSARTICULAR EXTERNAL SKELETAL FIXATION
Substitution of a column of acrylic to replace pin-gripping cIamI- ' and connecting rods offers several distinct advantages for application and management of TESF: (1) use of acrylic affords greater freedom in pin selection and placement,20 (2) the ability to use small-diameter pins or K-wires enables use of TESF on extremely small patients, (3) improvised acrylic fixators use less expensive materials than Kirschner-Ehmer splints, and (4) radiographic evaluation is simplified because the radiolucent frame of an acrylic fixator does not impede evaluation of underlying bone.20 In terms of mechanical performance, acrylic fixators compete favorably with Kirschner-Ehmer splints. A report by Okrasinski et aFo indicates that a type I acrylic fixator with a 2-cm frame diameter is stiffer and withstands significantly higher loads to failure than an identically designed type I Kirschner-Ehmer splint with medium-sized components. An acrylic frame can be three-dimensionally contoured to interconnect pins in many different planes; therefore multiple full-pins within a splint do not have to be placed in the same mediolateral plane as is the case for type II Kirschner-Ehmer splints. Additionally, different pin diameters can be used within the same fixator (i.e., smaller diameter pins for metatarsal bones and larger diameter pins for the distal tibia when applying a trans tarsal splint). Although aseptic technique is used throughout the initial portion of the procedure when pins are being placed, it is not necessary during the later stages when the acrylic frame is being applied. Materials for Acrylic Frame Transarticular External Skeletal Fixation. Dental acrylic (orthodontic resin; the L. B. Caulk Company, Division of Dentsply International, Inc., Milford, DE) and hoof acrylic (Technovit hoof acrylic; Jorgensen Laboratories, Loveland, CO) are methyl methacrylate products used most often to form acrylic frames. Sterilized implantation grade methyl methacrylate (bone cement) is much more expensive and offers no mechanical advantage over these other products. Materials used to apply acrylic frames are shown in Figure 7. Powder (Fig. 7A) and liquid (Fig. 7B) components of the acrylic are mixed using a disposable cup and a tongue depressor (Fig. 7C). A ratio of 3 parts powder (dental acrylic) or 2 parts powder (hoof acrylic) to 1 part liquid is recommended. Various types of plastic tubing (anesthesia circuit; King Systems Corporation, Noblesville, IN) (Fig. 7D, E) can be pressed onto the applied fixation pins and used as a mold into which liquid acrylic is injected to form a column. A cotton pledget (Fig. 7F) can be placed at the bottom of the plastic tube to prevent liquid acrylic leakage from the mold during injection. A 60-mL dose tip syringe (Fig. 7G) works well for injecting liquid acrylic. Alternatively a bar of dough stage acrylic can be pressed onto the ends of the fixation pins and then molded to the desired shape.
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Figure 7. Materials used to apply acrylic frames: acrylic powder (A) and liquid (8). disposable cup and tongue depressor for mixing (C). anesthesia delivery system (D) or plain plastic tubing (E) for a mold. cotton for a distal plug in the mold (F). and a 60·cc dose syringe (G) for injecting acrylic material into the mold to form a column.
During the setting process, acrylic goes from a viscous liquid, to a doughy semisolid, and finally to a rigid solid. Duration of the entire process is dependent on ambient temperature and usually takes from 8 to 14 minutes. During the latter stages, intense heat is liberated by this exothermic polymerization process. Moist sponges should be placed between the patient's skin and the curing acrylic column to prevent burns. Sponges are intermittently lavaged with cold tap water during the peak exothermic period.
Cutting Acrylic Frames for Removal or Adjustment
An oscillating cast saw is used for cutting acrylic frames. Cutting of the frame is indicated at the time of fixator removal or if adjustment of the fixator is necessary. Caution is recommended throughout the cutting process because of release of hot acrylic fragments, which can potentially burn the patient or surgeon. To revise an acrylic fixator"a segment of acrylic is removed at the point where realignment is desired (Le., at the. level of the major fracture line or the joint). Reduction of the limb is adjusted before
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reconnection of the column by application of a liquid or doughy acrylic patch. The acrylic column is prepared for patching by making several small channels in each cut end using an electric or pneumatic powered bur. These channels help to "key" the patch into the column for a more secure repair. Use of Bi-phase Technique for Acrylic Transarticular External Skeletal Fixation
Bi-phase technique employs temporary application of an adjustable phase 1 mechanical splint to maintain reduction until an acrylic frame (phase 2 splint) sets and becomes rigid to provide definitive fixation . Application of a transarticular acrylic fixator can be accomplished using a modification of the bi-phase technique as follows . (The nearly completed transstifie fixator shown in Figure 8 is used as an example.) Aseptic technique is used to place three full-pins in the tibia and one full-pin and two half-pins in the distal femur. The full-pins immediately above and immediately below the joint are left long,
Figure 8. Type II transarticular acrylic splint applied across the stifle using biphase technique. Single clamps and contoured rods provide a temporary phase 1 reduction device to maintain desired joint position while acrylic injected into the plastic tubes (T) sets up. Subsequent steps not shown in this drawing are as follows: After phase 2 acrylic splint becomes rigid. phase 1 reduction gear is removed. and fixation pins are trimmed short where they exit from the acrylic-filled plastic tubes.
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whereas the remaining pins are trimmed to a shorter length. Plastic tubing (T) is then pressed onto the pins bilaterally. A phase 1 reduction apparatus is formed by attachment of connecting rods (either straight or contoured rods can be used) to the full-pins that were left long. The appropriate size of Kirschner-Ehmer single clamps are used to make these attachments. The joint is temporarily held at the desired angle by the reduction device, while acrylic injected into the plastic tubing sets up to form a rigid column. Steps subsequent to those shown in Figure 8 are removal of the phase 1 reduction gear and trimming of all pins where they exit the acrylic-filled plastic tube.
SUMMARY
External skeletal fixators provide a useful alternative to external coaptation techniques for immobilization of joints in selected patients. This is especially true when the orthopedic injury involves an open wound requiring daily treatment. Devices such as the K-E splint, the Rudy external fixator boot, and acrylic frame fixators are economical and effective for transarticular fixation in small animal patients. Clinical indications for these techniques have included fixation of tibial or radial fractures with a short distal fragment; arthrodesis of the elbow, carpus, stifle, or tarsus; protection of Achilles tendon repairs; protection of collateral ligament repairs of the tarsocrural joint; and protection when multiple ligaments of the stifle joint have been reconstructed. Use of contoured rods has facilitated transarticular application of type II Kirschner-Ehmer splints. Use of acrylic frames and the Rudy boot technique have extended safe use of transarticular external fixation to extremely small patients not accommodated by the Kirschner system alone. An understanding of the advantages and disadvantages inherent in each of these techniques is critical to proper selection of the best method for a given patient. Attention to the basic principles of pin selection, pin insertion, and frame design are needed for successful execution of the chosen technique.
References 1. Aron ON: Prosthetic ligament replacement for severe tarsocrural joint instability. J Am Anim Hosp Assoc 23:41, 1987 2. Aron ON: Traumatic dislocation of the stifle joint: Treatment of 12 dogs and one cat. JAm Anim Hosp Assoc 24:333, 1988 3. Aron ON: External skeletal fixation . Vet Med Rep 1:181, 1989 4. Aron ON, Toombs ]P: Updated principles of external skeletal fixation. Comp Cont Ed Pract Vet 6:845, 1984 5. Aron ON, Toombs ]p, Hollingsworth SC: Primary treatment of severe fractures by external skeletal fixation: Threaded pins compared with smooth pins. J Am Anim Hosp Assoc 22:659, 1986
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6. Arwedsson G: Arthrodesis in traumatic plantar subluxation of the metatarsal bones of the dog. J Am Vet Med Assoc 124:21, 1954 7. Bjorling DE, Toombs JP: Transarticular application of the Kirschner-Ehmer splint. Vet Surg 11:34, 1982 8. Boone EG, Johnson AL, Hohn RB. Distal tibial fractures in dogs and cats. J Am Vet Med Assoc 188:36, 1986 9. Brinker WO, Piermattei DL, Flo GL (eds): Diagnosis and treatment of orthopedic conditions of the hindlimb. In Handbook of Small Animal Orthopedics and Fracture Treatment, ed 2. Philadelphia, WB Saunders, 1990. pp 438-464 10. Brinker WO, Piermattei DL, Flo GL (eds): Diagnosis and treatment of orthopedic conditions of the forelimb. In Handbook of Small Animal Orthopedics and Fracture Treatment, ed 2. Philadelphia, WB Saunders, 1990, pp 523-537 11. Charnley J: Positive pressure in arthrodesis of the knee joint. J Bone Joint Surg [Br) 30:478, 1948 12. Egger EL: Static strength evaluation of six external skeletal fixation configurations. Vet Surg 12:130, 1983 13. Egger EL: Management of mandibular fractures with acrylic-pin external fixation splints. In Proceedings of 15th Annual Meeting of the Veterinary Orthopedic Society, Breckenridge, CO, 1988, P 6 14. Egger EL: External fixation equipment, costs, removal time, other uses. Vet Med Rep 1:230, 1989 15. Egger EL, Histand MB, Blass CE, et al: Effect of fixation pin insertion on the bonepin interface. Vet Surg 15:246, 1986 16. Gahring DR: Use of external fixation devices in management of fractures and osteotomies. California Vet 9:19, 1980 17. Gallagher LA, Rudy RL, Smeak DD: The external fixator boot: Application principles, techniques, and indications. J Am Anim Hosp Assoc 26:403, 1990 18. Morshead D, Leeds EB: Kirschner-Ehmer apparatus immobilization following Achilles tendon repair in six dogs. Vet Surg 13:11, 1984 19. Okin R: The use of dental acrylic for external fracture repair. Canine Pract 8:35, 1981 20. Okrasinski EB, Pardo AD, Graehler RA: Acrylic external skeletal fixation: A biomechanical evaluation and a review of 11 cases. J Am Vet Med Assoc, in press, 1991 21. Olds R, Green S: Hoffmann's external fixation for arthrodesis and infected nonunions in the dog. J Am Anim Hosp Assoc 19:705, 1983 22. Palmer RH, Aron DN: Ellis pin complications in seven dogs. Vet Surg 19:440, 1990 23. Toombs JP: Principles of external skeletal fixation using the Kirschner-Ehmer splint. Semin Vet Med Surg Sm Anim 6:68, 1991 24. Toombs JP, Aron DN, Basinger RR, Ewing P: Angled connecting bars for transarticular application of Kirschner-Ehmer external fixation splints. J Am Anim Hosp Assoc 25:213, 1989
Address reprint requests to James P. Toombs, DVM, MS Department of Veterinary Clinical Sciences Purdue University School of Veterinary Medicine West Lafayette, IN 47907
EXTERNAL SKELETAL FIXATION
TRANSARTICULAR APPLICATION OF EXTERNAL SKELETAL FIXATION James P. Toombs, DVM, MS
The resurgence of external skeletal fixation in small animal orthopedics is attributable to improvements in fixation pins and pin insertion technique3, 4, 5, 15, 22 and greater appreciation of the biomechanical characteristics of different external fixator configurations,12, 13, 20 This resurgence has prompted greater usage of external fixators for immobilization of jOints. Transarticular external skeletal fixation (TESF) has been used for primary fixation of distal fractures/' 24 to augment tenuous internal fixation of distal fractures/' 8, 20, 24 to perform joint arthrodeses,6, 7, 9, 10, 16, 17, 20, 21, 24 and to protect tendon l7, 18, 20, 24 or ligament repairs,1, 2, 7, 9, 10, 20, 22, 24 Several injury factors favor the use of TESF, including the presence of significant open wounds and involvement of two or more limbs. Compared with coaptation techniques for immobilizing the elbow, carpus, stifle, or tarsus, TESF provides superior stabilization and improved access for treatment of soft tissue injuries 24 (Fig. 1). OVERVIEW OF TRANSARTICULAA EXTERNAL SKELETAL FIXATION TECHNIQUES
Fixation pins placed through the bone proximal and distal to the joint are common elements found in nearly all TESF devices. Different methods of TESF are distinguished by the materials used to interconnect From the Department of Veterinary Clinical Sciences, Purdue University School of Veterinary Medicine, West Lafayette, Indiana
VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 1 • JANUARY 1992
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Figure 1. Type II contoured rod Kirschner-Ehmer splint stabilizing the tarsocrural joint of a Great Dane after prosthetic repair of the medial collateral ligament complex. Note that splint allows ample access for treatment of the soft tissue shear injury.
these pins to form a fixation frame. These methods fall into three basic categories: (1) fixed configurations, (2) variable configurations, and (3) improvised fixation devices. 4 Fixed Configurations
Fixed configurations use a frame that dictates the position and number of fixation pins4 (i.e., Charnley compression clamps [Fig. 2]). Although these devices have been used successfully in arthrodesis procedures,l1 a narrow range of three-dimensional adjustability has limited their utility for TESF. Variable Configurations
Variable configurations use separate components that can be assembled into almost any spatial configuration as dictated by the nature of the orthopedic problem4 (i.e., Hoffmann and Kirschner-Ehmer fixation systems). Hoffmann fixators have been used successfully for stifle and tarsocrural arthrodeses in dogs. 21 The bulk and expense of Hoffmann
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Figure 2. Components of Charnley compression clamps: pin grippers (A); lock nuts (8) used to fix the position of pin grippers; threaded central bolt connecting rod (C); and central bolt adjustment knob (0), which turns one way to apply compression and the opposite way to apply distraction. Pin gripper design dictates placement of fixation pins perpendicular to the long axis of the connecting rod, and pin gripper number dictates use of only four pins with this device.
components, however, have limited their use in small animal patients. The Kirschner-Ehmer system provides three sizes of affordable components, the smallest of which can be used in cats and toy breed dogs. These advantages have made Kirschner-Ehmer splints the most commonly used variable configuration device for TESF in small animals. !, 7, 8, 9, 10, 14, 16, 17, 18,22, 24 Improvised Fixation Devices
Improvised fixation devices4,6, 13, 19,20 use an unsolidified substance that hardens shortly after application to interconnect the fixation pins (i.e., "pins-in-plaster technique,"4 the Murray epoxy-filled tube system,4 and acrylic bar fixators 13, 19, 20). The major advantage of improvised devices is that the angles, planes, positions, and diameters of fixation pins are not restricted by the frame. 2o Additionally, improvised devices provide the most economical method of applying TESF. The major disadvantage of these devices is limited adjustability following surgery. Rudy Boot Technique
The Rudy external fixator bootB, 17 combines elements of improvised devices and variable configurations (Fig. 3). It is most commonly used
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Figure 3. Cranial (A) and lateral (8) views of Rudy external fixator boot applied for stabilization of the tarsus. (Courtesy of Ann Johnson, DVM).
for management of injuries associated with the carpus and tarsus but has also been used as primary or supplementary fixation for distal fractures of the tibia and radius. 17 The Rudy external fixator boot involves application of a KirschnerEhmer splint to the radius or tibia and attaching it to a distally applied plaster or fiberglass cast boot. The boot covers the toes, paw, and distal 75% of the metacarpus or metatarsus. After the cast boot has been allowed to set for several minutes, a wooden block containing two fixation pins is placed on the dorsolateral or dorsomedial aspect of the boot and secured by application of additional plaster or fiberglass cast material. Once final setting of the boot has occurred, the pins exiting from the pin block are attached to the connecting rods of the KirschnerEhmer splint, the carpus or hock is placed in the desired position, and all clamps are tightened. If a single connecting rod is used, it is contoured such that the fixator will immobilize the carpus or tarsus at a normal standing angle. The Rudy boot technique is especially well suited to cats and toy breed dogs. The extremely small metacarpal and metatarsal bones in these animals are a difficult target for safe and effective passage of the %2" pins normally used with small Kirschner-Ehmer clamps.
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USE OF THE KIRSCHNER-EHMER SPLINT FOR TRANSARTICULAR EXTERNAL SKELETAL FIXATION
Basic principles for application of Kirschner-Ehmer splints are found in other articles in this issue and elsewhere. 3, 14, 23 The author's preferences for the type of fixation pins, methods of pin insertion, and aftercare of the patient and fixator are the same as those expressed by Aron elsewhere in this issue. . Kirschner-Ehmer splints have provided effective immobilization of the elbow/' 24 carpus/' 10 stifle, 4, 7, 22, 24 and tarsus l , 3, 7, 9, 14, 16, IS, 24 in carefully selected patients. Two basic types of transarticular KirschnerEhmer splints have been used: those employing straight connecting rods 7 and those in which contoured connecting rods are applied. 24 Transarticular Kirschner-Ehmer Splints with Straight Connecting Rods
In most reports of transarticular Kirschner-Ehmer splint use in small animals, straight connecting rods were used to construct the frames. I, 2, 7, 14, 16, IS, 22 This works well if the desired splint configuration is type I, but type II straight rod transarticular Kirschner-Ehmer splints can be problematic. When the elbow, stifle, or tarsocrural joints are immobilized at their normal standing angles, the number of full-pins that can be attached to a pair of straight connecting rods that span the joint is limited. To obtain greater numbers of fixation pins, multiple connecting rods bearing single clamps and pins can be interconnected using double clamps and short transverse connecting rods 7 (Fig. 4). Although such splints have been used effectively, they are bulky and susceptible to loosening at double clamp articulations. Use of stacked single clampsI4, 23 instead of double clamps to make these articulations reduces the problem of loosening. If excessive bulk of the splint is clinically significant (i.e., extremely small patients), use of a different type of transarticular external fixator is recommended. Alternative methods include contoured rod Kirschner-Ehmer splints and improvised devices such as the Rudy boot or a fixator composed of pins and acrylic bars. Transarticular Kirschner-Ehmer Splints with Contoured Connecting Rods
Application of type II transarticular Kirschner-Ehmer splints can be facilitated by the use of contoured connecting rods. Examples of contoured rod transarticular Kirschner-Ehmer splints are shown in Figures I, 5, and 6. Compared with straight rod splints, contoured rod splints provide several distinct advantages: (1) splints remain secure for longer periods of time owing to avoidance of double clamp articu-
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Figure 4. Type II transarticular K-E splint with straight connecting rods applied across the tarsus. Full pins passed through the distal tibia and proximal metatarsus are attached to connecting rod 1 laterally and connecting rod 3 medially. Laterally placed half pins in the tibia and metatarsus are attached to connecting rod 2. Double clamps and connecting rod 4 interconnect these units. (From Bjorling DE, Toombs JP: Transarticular application of the Kirschner-Ehmer splint. Vet Surg 11 :34, 1982; with permission) .
lations; (2) the number of full-pins that can be attached to a medial and lateral pair of connecting rods is maximized, producing increased splint stiffness and prolongation of secure pin-bone interfaces; and (3) splints are more compact. 24 When TESF is expected to maintain joint immobilization during a
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prolonged healing period (i.e., joint arthrodesis procedures), properly applied contoured rod splints have a definite advantage over straight rod splints. Either type of splint works well when joint immobilization for only 2 to 4 weeks is desired. Disadvantages of contoured rod splints compared with straight rod splints include: (1) More careful preoperative planning of the splint is necessary because single clamps will not slide across the contoured portion of the rod, (2) adjustability of the splint is decreased, and (3) potential for uSIng the connecting rod in subsequent patients is reduced. To apply contoured rod Kirschner-Ehmer splints, rods of appropriate length and diameter are bent to the proper angle using a table bending press, hand bending irons, or the edge of a table or counter. 24 Rods should be bent in small increments spread out over the central portion rather than applying an acute bend at a single focus. In the author's experience, breakage of contoured rods has not occurred despite application of splints to large, active canine patients (i.e., the Great Dane shown in Fig. 1). For immobilization of the elbow, stifle, or tarsus, connecting rods are usually contoured to an angle of 130 to 150 degrees. Use of goniometer to measure the normal standing angle of the joint on the contralateral uninjured limb is recommended. An angle in excess of the normal standing angle may be necessary when TESF is used to prevent tension on Achilles tendon repairs. 18 Proper contouring of the connecting rods will immobilize the joint at the desired angle and enable easy application of multiple full-pins to bones above and below the joint. Transstifle Splint
A type II contoured rod Kirschner-Ehmer splint for immobilization of the stifle joint is shown in Figure 5. Application of this splint is accomplished as follows .24 Centrally threaded pins (enhanced thread full-pin; Gauthier Medical, Inc., Rochester, MN) 1 and 2 are applied as full-pins in a mediolateral plane above and below the joint. Predrilling4 of the cortex followed by hand chuck insertion is the technique preferred by the author for placement of raised profile threaded pins. Contoured connecting rods (a short one medially and a longer one laterally) bearing single clamps are applied to pins 1 and 2. The joint is positioned at the desired angle, and single clamps A through D are tightened. Smooth pins 3 and 4 are applied as full-pins through single clamps F and H on the medial coritoured rod. Low RPM power insertion technique is used. These pins must be in the same mediolateral plane as pin 2 to ensure that they will engage single clamps E and G on the lateral contoured rod. Smooth pins 5 and 6 are applied as half-pins through laterally placed single clamps I and J. Adequate soft tissue releasing incisions around these pins are important to prevent transfixation of the quadriceps muscle group. Full-pins are avoided at these locations because they increase the likelihood of trauma to the inguinal area by the medial aspect of the splint. Single clamps K and L are stacked laterally on pins 6 and 4 to enable attachment of a straight lateral connecting rod.
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Figure 5. Type II transarticular
Kirschner·Ehmer splint with contoured connecting rods applied across the stifle joint. Identifying numbers for pins and identifying letters for clamps are explained in text. (From Toombs JP, Aron DN, Basinger RR, et al: Angled connecting bars for transarticular application of Kirschner-Ehmer external fixation splints. J Am Anim Hosp Assot 25:213, 1989; with permission).
Application of this rod is optional, but it may afford some protection of the lateral contoured rod in regard to cyclic bending loads during weight bearing. All damps are tightened fully, and protruding portions of pins and rods are trimmed off to make the splint as compact as possible and to facilitate bandaging. 24 Transe/bow Splint
Application of a contoured rod type II Kirschner-Ehmer splint across the elbow is similar to the description given for the stifle. A centrally threaded pin is inserted through the distal humerus and another through the proximal radius. Completion of the splint and restriction of medial rod length (to avoid thoracic wall trauma) are as noted for stifle. Avoidance of the radial nerve is important when selecting sites for lateral placement of half-pins in the distal humerus.
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Transtarsal Splint
A type II contoured rod Kirschner-Ehmer splint for immobilization of the tarsus is shown in Figure 6. Use of this technique is restricted to patients that have metatarsal bones large enough to accommodate safe passage of fixation pins. Application of a transtarsal contoured rod Kirschner-Ehmer splint is accomplished as follows. 24 All pins can be applied as full-pins to increase splint rigidity. Centrally threaded pins 1 and 2 are passed in a mediolateral plane through the distal tibia and proximal portions of the metatarsal bones respectively. Because metatarsal bones lie in a gentle arch that is convex along the dorsal aspect, a fixation pin can be inserted easily into only two of the four major metatarsal bones. The author prefers to place pins through the third and fourth metatarsal bones in most cases. Alternatively they can be placed through the second and fifth metatarsal bones. Pin placements should be confined to the proximal two thirds of the metatarsal bones to avoid Kirschner-Ehmer splint interference with a functional foot plant. For TESF of the tarsus, the length of the medial contoured rod is not limited by regional anatomy, contrary to TESF of the elbow or stifle. Therefore medial and lateral contoured rods of equal length are usually applied. Smooth pins 3 through 5 are inserted medially to laterally in the same plane and parallel to pins 1 and 2. Stacked single clamps are applied both medially and laterally on pins 3 and 5 if application of optional straight rods to increase fixator stiffness is desired.
Figure 6. Type II transarticular KirschnerEhmer splint with contoured connecting rods applied across the tarsus. Pin identification numbers are explained in text (From Toombs JP, Aron ON, BaSinger RR, et al : Angled connecting bars for transarticular application of Kirschner-Ehmer external fixation splints. J Am Anim Hosp Assoc 25:213, 1989; with permission) .
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USE OF ACRYLIC FRAMES FOR TRANSARTICULAR EXTERNAL SKELETAL FIXATION
Substitution of a column of acrylic to replace pin-gripping cIamI- ' and connecting rods offers several distinct advantages for application and management of TESF: (1) use of acrylic affords greater freedom in pin selection and placement,20 (2) the ability to use small-diameter pins or K-wires enables use of TESF on extremely small patients, (3) improvised acrylic fixators use less expensive materials than Kirschner-Ehmer splints, and (4) radiographic evaluation is simplified because the radiolucent frame of an acrylic fixator does not impede evaluation of underlying bone.20 In terms of mechanical performance, acrylic fixators compete favorably with Kirschner-Ehmer splints. A report by Okrasinski et aFo indicates that a type I acrylic fixator with a 2-cm frame diameter is stiffer and withstands significantly higher loads to failure than an identically designed type I Kirschner-Ehmer splint with medium-sized components. An acrylic frame can be three-dimensionally contoured to interconnect pins in many different planes; therefore multiple full-pins within a splint do not have to be placed in the same mediolateral plane as is the case for type II Kirschner-Ehmer splints. Additionally, different pin diameters can be used within the same fixator (i.e., smaller diameter pins for metatarsal bones and larger diameter pins for the distal tibia when applying a trans tarsal splint). Although aseptic technique is used throughout the initial portion of the procedure when pins are being placed, it is not necessary during the later stages when the acrylic frame is being applied. Materials for Acrylic Frame Transarticular External Skeletal Fixation. Dental acrylic (orthodontic resin; the L. B. Caulk Company, Division of Dentsply International, Inc., Milford, DE) and hoof acrylic (Technovit hoof acrylic; Jorgensen Laboratories, Loveland, CO) are methyl methacrylate products used most often to form acrylic frames. Sterilized implantation grade methyl methacrylate (bone cement) is much more expensive and offers no mechanical advantage over these other products. Materials used to apply acrylic frames are shown in Figure 7. Powder (Fig. 7A) and liquid (Fig. 7B) components of the acrylic are mixed using a disposable cup and a tongue depressor (Fig. 7C). A ratio of 3 parts powder (dental acrylic) or 2 parts powder (hoof acrylic) to 1 part liquid is recommended. Various types of plastic tubing (anesthesia circuit; King Systems Corporation, Noblesville, IN) (Fig. 7D, E) can be pressed onto the applied fixation pins and used as a mold into which liquid acrylic is injected to form a column. A cotton pledget (Fig. 7F) can be placed at the bottom of the plastic tube to prevent liquid acrylic leakage from the mold during injection. A 60-mL dose tip syringe (Fig. 7G) works well for injecting liquid acrylic. Alternatively a bar of dough stage acrylic can be pressed onto the ends of the fixation pins and then molded to the desired shape.
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Figure 7. Materials used to apply acrylic frames: acrylic powder (A) and liquid (8). disposable cup and tongue depressor for mixing (C). anesthesia delivery system (D) or plain plastic tubing (E) for a mold. cotton for a distal plug in the mold (F). and a 60·cc dose syringe (G) for injecting acrylic material into the mold to form a column.
During the setting process, acrylic goes from a viscous liquid, to a doughy semisolid, and finally to a rigid solid. Duration of the entire process is dependent on ambient temperature and usually takes from 8 to 14 minutes. During the latter stages, intense heat is liberated by this exothermic polymerization process. Moist sponges should be placed between the patient's skin and the curing acrylic column to prevent burns. Sponges are intermittently lavaged with cold tap water during the peak exothermic period.
Cutting Acrylic Frames for Removal or Adjustment
An oscillating cast saw is used for cutting acrylic frames. Cutting of the frame is indicated at the time of fixator removal or if adjustment of the fixator is necessary. Caution is recommended throughout the cutting process because of release of hot acrylic fragments, which can potentially burn the patient or surgeon. To revise an acrylic fixator"a segment of acrylic is removed at the point where realignment is desired (Le., at the. level of the major fracture line or the joint). Reduction of the limb is adjusted before
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reconnection of the column by application of a liquid or doughy acrylic patch. The acrylic column is prepared for patching by making several small channels in each cut end using an electric or pneumatic powered bur. These channels help to "key" the patch into the column for a more secure repair. Use of Bi-phase Technique for Acrylic Transarticular External Skeletal Fixation
Bi-phase technique employs temporary application of an adjustable phase 1 mechanical splint to maintain reduction until an acrylic frame (phase 2 splint) sets and becomes rigid to provide definitive fixation . Application of a transarticular acrylic fixator can be accomplished using a modification of the bi-phase technique as follows . (The nearly completed transstifie fixator shown in Figure 8 is used as an example.) Aseptic technique is used to place three full-pins in the tibia and one full-pin and two half-pins in the distal femur. The full-pins immediately above and immediately below the joint are left long,
Figure 8. Type II transarticular acrylic splint applied across the stifle using biphase technique. Single clamps and contoured rods provide a temporary phase 1 reduction device to maintain desired joint position while acrylic injected into the plastic tubes (T) sets up. Subsequent steps not shown in this drawing are as follows: After phase 2 acrylic splint becomes rigid. phase 1 reduction gear is removed. and fixation pins are trimmed short where they exit from the acrylic-filled plastic tubes.
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whereas the remaining pins are trimmed to a shorter length. Plastic tubing (T) is then pressed onto the pins bilaterally. A phase 1 reduction apparatus is formed by attachment of connecting rods (either straight or contoured rods can be used) to the full-pins that were left long. The appropriate size of Kirschner-Ehmer single clamps are used to make these attachments. The joint is temporarily held at the desired angle by the reduction device, while acrylic injected into the plastic tubing sets up to form a rigid column. Steps subsequent to those shown in Figure 8 are removal of the phase 1 reduction gear and trimming of all pins where they exit the acrylic-filled plastic tube.
SUMMARY
External skeletal fixators provide a useful alternative to external coaptation techniques for immobilization of joints in selected patients. This is especially true when the orthopedic injury involves an open wound requiring daily treatment. Devices such as the K-E splint, the Rudy external fixator boot, and acrylic frame fixators are economical and effective for transarticular fixation in small animal patients. Clinical indications for these techniques have included fixation of tibial or radial fractures with a short distal fragment; arthrodesis of the elbow, carpus, stifle, or tarsus; protection of Achilles tendon repairs; protection of collateral ligament repairs of the tarsocrural joint; and protection when multiple ligaments of the stifle joint have been reconstructed. Use of contoured rods has facilitated transarticular application of type II Kirschner-Ehmer splints. Use of acrylic frames and the Rudy boot technique have extended safe use of transarticular external fixation to extremely small patients not accommodated by the Kirschner system alone. An understanding of the advantages and disadvantages inherent in each of these techniques is critical to proper selection of the best method for a given patient. Attention to the basic principles of pin selection, pin insertion, and frame design are needed for successful execution of the chosen technique.
References 1. Aron ON: Prosthetic ligament replacement for severe tarsocrural joint instability. J Am Anim Hosp Assoc 23:41, 1987 2. Aron ON: Traumatic dislocation of the stifle joint: Treatment of 12 dogs and one cat. JAm Anim Hosp Assoc 24:333, 1988 3. Aron ON: External skeletal fixation . Vet Med Rep 1:181, 1989 4. Aron ON, Toombs ]P: Updated principles of external skeletal fixation. Comp Cont Ed Pract Vet 6:845, 1984 5. Aron ON, Toombs ]p, Hollingsworth SC: Primary treatment of severe fractures by external skeletal fixation: Threaded pins compared with smooth pins. J Am Anim Hosp Assoc 22:659, 1986
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6. Arwedsson G: Arthrodesis in traumatic plantar subluxation of the metatarsal bones of the dog. J Am Vet Med Assoc 124:21, 1954 7. Bjorling DE, Toombs JP: Transarticular application of the Kirschner-Ehmer splint. Vet Surg 11:34, 1982 8. Boone EG, Johnson AL, Hohn RB. Distal tibial fractures in dogs and cats. J Am Vet Med Assoc 188:36, 1986 9. Brinker WO, Piermattei DL, Flo GL (eds): Diagnosis and treatment of orthopedic conditions of the hindlimb. In Handbook of Small Animal Orthopedics and Fracture Treatment, ed 2. Philadelphia, WB Saunders, 1990. pp 438-464 10. Brinker WO, Piermattei DL, Flo GL (eds): Diagnosis and treatment of orthopedic conditions of the forelimb. In Handbook of Small Animal Orthopedics and Fracture Treatment, ed 2. Philadelphia, WB Saunders, 1990, pp 523-537 11. Charnley J: Positive pressure in arthrodesis of the knee joint. J Bone Joint Surg [Br) 30:478, 1948 12. Egger EL: Static strength evaluation of six external skeletal fixation configurations. Vet Surg 12:130, 1983 13. Egger EL: Management of mandibular fractures with acrylic-pin external fixation splints. In Proceedings of 15th Annual Meeting of the Veterinary Orthopedic Society, Breckenridge, CO, 1988, P 6 14. Egger EL: External fixation equipment, costs, removal time, other uses. Vet Med Rep 1:230, 1989 15. Egger EL, Histand MB, Blass CE, et al: Effect of fixation pin insertion on the bonepin interface. Vet Surg 15:246, 1986 16. Gahring DR: Use of external fixation devices in management of fractures and osteotomies. California Vet 9:19, 1980 17. Gallagher LA, Rudy RL, Smeak DD: The external fixator boot: Application principles, techniques, and indications. J Am Anim Hosp Assoc 26:403, 1990 18. Morshead D, Leeds EB: Kirschner-Ehmer apparatus immobilization following Achilles tendon repair in six dogs. Vet Surg 13:11, 1984 19. Okin R: The use of dental acrylic for external fracture repair. Canine Pract 8:35, 1981 20. Okrasinski EB, Pardo AD, Graehler RA: Acrylic external skeletal fixation: A biomechanical evaluation and a review of 11 cases. J Am Vet Med Assoc, in press, 1991 21. Olds R, Green S: Hoffmann's external fixation for arthrodesis and infected nonunions in the dog. J Am Anim Hosp Assoc 19:705, 1983 22. Palmer RH, Aron DN: Ellis pin complications in seven dogs. Vet Surg 19:440, 1990 23. Toombs JP: Principles of external skeletal fixation using the Kirschner-Ehmer splint. Semin Vet Med Surg Sm Anim 6:68, 1991 24. Toombs JP, Aron DN, Basinger RR, Ewing P: Angled connecting bars for transarticular application of Kirschner-Ehmer external fixation splints. J Am Anim Hosp Assoc 25:213, 1989
Address reprint requests to James P. Toombs, DVM, MS Department of Veterinary Clinical Sciences Purdue University School of Veterinary Medicine West Lafayette, IN 47907
