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EXTERNAL SKELETAL FIXATION
FRACTURES OF THE HUMERUS David T. Matthiesen, DVM
External skeletal fixation can occasionally be used as the primary method of fixation for treating humeral fractures or, alternatively, as an adjunctive device for increasing fracture stability when used with intramedullary pinning or caudomedial bone plating. A type I unilateral external fixator combined with intramedullary pinning can provide adequate rotational and axial stability for complete fracture healing. Solitary use of an external fixator is generally reserved for moderately to severely contaminated or open humeral fractures when additional surgical disruption of vascular supply or metal implantation may be contraindicated (e.g., gunshot injuries). Use of an external fixator for the treatment of open humeral fractures allows management of soft tissue infection, minimizes additional vascular damage, and provides fracture stability. FIXATOR TYPES
Because of chest wall interference by the metal connecting bar and difficulty in effectively applying additional pins in the distal humerus for use of a type III or bilateral type II external fixator, only a type I unilateral fixator can usually be used for humeral fractures. Occasionally a connecting bar can be placed from the lateral aspect of the proximal humeral pins and medially attached to the most distal humeral pin, providing additional rigidity to the device. Some interference with the chest wall may occur, however, with this type of fixation. Generally with a type I unilateral frame, fixation pins are inserted through the lateral or craniolateral aspect of the humerus passing From The Animal Medical Center, New York, New York. VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 1 • JANUARY 1992
121
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MA TIHIESEN
through both lateral and medial cortices. Fixation pins are attached to a lateral, metal connecting bar and clamps. If necessary, a second connecting bar can be added to the fixation pins, doubling the external fixator's resistance to compressive forces. 3 Alternatively methyl methacrylate can be applied to the fixation pins and used in place of the metal connecting bar and clamps. A recent report described successful use of a modified type I unilateral fixator for repair of supracondylaF fractures. The modification consisted of curved or angulated connecting bars placed laterally to medially across the supracondylar fracture for increased stability.s GENERAL PRINCIPLES
The use and application of an external fixator to the humerus is relatively simple; several principles, however, should be followed to reduce problems and complications. 1. The humeral fracture should be appropriately reduced through an open approach, while minimizing the amount of vascular and soft tissue damage. 2. Fixation pins are placed through appropriately located skin incisions along the lateral or craniolateral aspect of the humerus. 3. The most proximal pin is inserted just distal to the greater tubercle along the craniolateral aspect of the humerus. By placing the pin in this location, the acromial head of the deltoideus muscle and the insertions of infraspinatus and teres minor muscles are avoided. When applying the most proximal and distal pins, a pin angle of approximately 70 to 75 degrees perpendicular to the long axis of the humerus may offer the best compromise between bone grip and bone strength. 2, 3 4. Inside pins are similarly placed at diverging angles of 70 to 80 degrees perpendicular to the long axis of the humerus. 5. The distal fixation pin is placed into the lateral aspect of the humeral condyle. If a single pin is placed into the condyle, the pin can be inserted slightly below the lateral epicondyle and directed across the condyle into the medial epicondyle. This technique maintains some angle of divergence, thereby decreasing the possibility of pin pullout or displacement. 6. Once the distal and proximal pins are placed, a connecting bar with end clamps and the anticipated number of central clamps is placed. The connecting bar should be positioned far enough from the skin to allow for swelling and callus formation without skin contact. 3 7. If two pins are placed into the humeral condyle, the most distal pin is placed as described. The second more proximal condylar pin is placed just proximal to the lateral epicondyle and directed
FRACTURES OF THE HUMERUS
8.
9.
10.
11.
123
toward a point distal to the medial epicondyle. Care must be taken to avoid placing pins intraarticularly. The appropriate number of central fixation pins should be placed. The brachialis muscle and radial nerve should be avoided when placing each pin. Distal fixation pins may have to enter the cranial aspect of the lateral head of the triceps muscle. Methyl methacrylate bone cement cal'l alternatively be used in place of the metal connecting bar and clamps. The major advantages associated with its use include easier placement of fixation pins, more versatility in placing pins at different angles, and avoidance of soft tissue structures. The number of pins placed in each fragment affects the overall stiffness of the fixation. Although clear guidelines have not currently been established regarding the number of fixation pins optimally required for successful fracture healing, several factors should be considered. These factors include the type of fracture and inherent stability, type of primary repair, and location of the fracture. Increasing the number of fixation pins in each fragment avoids overloading the bone surrounding each pin. 3 Overloading causes microfractures around the pin, resulting in bone resorption and pin 100sening.7 This may not be a serious problem if the external fixator is used as an adjunctive device for increasing fracture stability with plating or intramedullary pinning. The fixation pins may loosen as early as 3 weeks after surgery; sufficient callus, however, is often present, eliminating the purpose of the external fixator. Conversely pin loosening occurring in animals with a humeral fracture repaired primarily with an external fixator may require a second surgery if fracture healing is not sufficient at the time of fixation failure . Threaded pins offer the greatest resistance to pullout compared with non threaded pins. The majority of pins available in veterinary orthopedics, however, have a tendency to break or bend, particularly at the junction of the threaded and nonthreaded shaft.1, 6 Because of this problem, I generally do not use threaded pins or use only one threaded pin per humeral fragment.
SPECIFIC INDICATIONS AND USE OF A HUMERAL EXTERNAL FIXATOR
Supracondylar Fractures A type I, unilateral external fixator can be used as an adjunctive means of achieving adequate stability when repairing supracondylar fractures repaired with intramedullary pinning or a caudomedially applied bone plate, An external fixator is particularly useful for treat-
124
MATTHIESEN
ment of supracondylar type I or II Salter fractures repaired with an intramedullary pin (Figs. 1 and 2), in which some degree of rotational instability remains, or with comminuted fractures, in which inadequate rotational and axial stability is present following application of an intramedullary pin (Figs. 3 and 4). Occasionally an external fixator offers additional stability to the fracture when a plate has been applied to the caudomedial aspect of the humerus (Fig. 5). Comminuted dicondylar or supracondylar fractures repaued with caudomedial bone plating and still having instability are candidates for application of this type of fixation. Because of fracture location, a minimum number of screws may be placed in the distal fragment, thereby predisposing' the fixation to failure (e.g., loss of screw holding power in the distal
Figure 1. A distal supracondylar humeral fracture repaired using a single intramedullary pin, a cross-pin, and a Type I, unilateral external fixator. The K-E device is useful in this type of fracture for achieving additional stability, particularly if the fracture is rotationally unstable after primary repair.
FRACTURES OF THE HUMERUS
125
Figure 2. A one-year-old German Shepherd presented with a comminuted supracondylar, distal humeral fracture (A). The fracture was repaired using a single intramedullary pin and cerclage wiring. A Type I, unilateral external fixator was applied for additional rotational and axial stability (8 and C).
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MATTHIESEN
Figure 3. A distal diaphyseal, supracondylar comminuted humeral fracture repaired using a single 1M pin, two full-cerclage wires, and a Type I unilateral external fixator. The device provides additional rotational and axial stability to the fracture.
FRACTURES OF THE HUMERUS
127
Figure 4. A 3-year-old Domestic Shorthair presented with a highly comminuted dicondylar humeral fracture following a fall injury (Af The fracture was repaired using a transcondylar compression screw, intramedullary pin, and several full-cerclage wires. A Type I, unilateral external fixator was applied for additional rotational and axial stability. Early fracture healing can be seen in radiographs obtained 3 weeks after surgery (8).
128
MA TIHIESEN
Figure 5. A distal diaphyseal humeral fracture repaired using caudo-medial bone plating and a Type I unilateral external fixator.
fragment) . An external fixator in these cases provides additional stability. When applying an external fixator to supracondylar fractures, sufficient space is usually available in the proximal humerus to apply a number of fixation pins successfully and easily. Some difficulty may be encountered, however, in placing one or two pins in the distal fragment. Placement of pins into the distal metaphyseal area is difficult because of fracture location, location of the intramedullary pin, and presence of the supratrochlear foramen with the possibility of intraarticular pin placement. As mentioned previously, a second unilateral device applied at 90 degrees axial rotation cranial to the first external fixator to create a biplanar configuration is difficult. Poor pin placement, possible intraarticular damage from misplaced pins, and external elbow impingement by the device during flexion prohibit effective use of this type of fixator.
FRACTURES OF THE HUMERUS
129
Transverse and Oblique Middiaphyseal Fractures
A type I, unilateral external fixator can also be used with single or multiple 1M pinning for treating diaphyseal fractures. For most middiaphyseal fracture repairs, the external fixator is used as an ancillary device for achieving additional rotational stability (Figs. 6 and 7). For more unstable fractures (e.g., comminuted fractures), the fixator provides additional resistance against compressi-ve and bending forces across the fracture (Fig. 8). Because of the relatively wide intramedullary canal in the proximal humerus, sufficient space is generally available to place the external fixator pins without impingement of the intramedullary pin. Depending on the relative size of the 1M pin, however, some difficulty can be encountered in placing pins in the diaphysis of
Figure 6. A simple transverse middiaphyseal humeral fracture repaired with a single intramedullary pin and a unilateral external fixator. The K-E device for this type of fracture is used for achieving additional rotational stability.
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MA ITHIESEN
Figure 7. A 2-year-old Siamese cat with a simple, transverse, middiaphyseal fracture (A) repaired with multiple intramedullary pins and full cerclage wires. Owing to rotational instability, an external fixator was applied (8).
FRACTURES OF THE HUMERUS
131
Figure 8. A comminuted middiaphyseal humeral fracture repaired with a single intramedullary pin. An external fixator is applied for additional rotational and axial support.
the distal humeral segment. The number of fixation pins required in each segment depends on inherent stability of the fracture and overall stability following placement of the intramedullary pins.
Open Diaphyseal Fractures Moderately to severely contaminated, open humeral fractures can be stabilized with multiple fixation pins and a unilateral metal connecting bar or methyl methacrylate (Fig. 9). If methyl methacrylate is used, fixation pins can be placed along the lateral and craniolateral surface of the humerus at various diverging angles.
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MATIHIESEN
Figure 9. A highly comminuted, humeral fracture primarily repaired using multiple fixation pins and methyl methacrylate.
COMPLICATIONS
One of the more common complications associated with external fixators is loosening of the fixation pins at the pin to bone interface. Generally some drainage is associated with pin loosening, and lucency surrounding the pin is present on radiographs. If too many pins loosen, fracture instability can occur, resulting in delayed fracture healing or nonunion. If loosening of one or two pins occurs, they should be removed. If several pins are loose and the external fixator is no longer providing stability, it should be removed. SUMMARY
A single or double bar, type I, unilateral external fixator can be used as primary or ancillary treatment for repair of many humeral
FRACTURES Of THE HUMERUS
133
fractures. Treatment of contaminated and comminuted fractures with external skeletal fixation provides rotational stability and axial align~ ment, access for wound management and bone grafting, and avoidance of vascular compromise by surgical invasion. In addition, the combi~ nation of external and internal (1M pins, cerclage wires, plates) fixation can provide greater initial fracture stability and subsequent dynamiza~ tion or loading of bone (as the fixator is removed) than either of the systems used individually.
References 1. Bennett RA, Egger EL, Histand MB, et al: Comparison of the strength and holding
2. 3. 4.
5. 6. 7.
power of 4 pin designs for use with half-pin (Type-I) external skeletal fixation. Vet Surg 16:207, 1987 Brinker WO, Flo GL: Principles and application of external skeletal fixation. Vet C1in North Am Small Anim Pract 2:197, 1975 Egger EL: External skeletal fixation. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery, ed 3. Philadelphia, Lea & Febiger, 1990, p 816 Egger EL, RunyonCL, Ribb DL: Use of Type-l double connecting bar configuration of external skeletal fixation on long bone fract\lres in dogs: A review of 10 cases. J Am Anim Hosp Assoc 22:57, 1986 K1ause SE, Schwarz PD, Egger EL, Piermattei DL: A modification of the unilateral Type 1 external skeletal fixator configuration for primary or secondary support of supracondylar humeral and femoral fractures . Vet Comp Orthop Trauma 3:130, 1990 Palmer RH, Aron DN: Ellis pin complications in seven dogs. Vet Surg 19:440, 1990 W\l H, Shyr HS, Chao FYS, Kelly PJ: Comparison of osteotomy healing under external fixation devices with different stiffness characteristics. J Bone Joint Surg [Am] 66:1258, 1984 . .
Address reprint requests to David T. Matthiesen, DVM The Animal Medical Center 510 East 62nd Street New York, NY 10021
EXTERNAL SKELETAL FIXATION
FRACTURES OF THE HUMERUS David T. Matthiesen, DVM
External skeletal fixation can occasionally be used as the primary method of fixation for treating humeral fractures or, alternatively, as an adjunctive device for increasing fracture stability when used with intramedullary pinning or caudomedial bone plating. A type I unilateral external fixator combined with intramedullary pinning can provide adequate rotational and axial stability for complete fracture healing. Solitary use of an external fixator is generally reserved for moderately to severely contaminated or open humeral fractures when additional surgical disruption of vascular supply or metal implantation may be contraindicated (e.g., gunshot injuries). Use of an external fixator for the treatment of open humeral fractures allows management of soft tissue infection, minimizes additional vascular damage, and provides fracture stability. FIXATOR TYPES
Because of chest wall interference by the metal connecting bar and difficulty in effectively applying additional pins in the distal humerus for use of a type III or bilateral type II external fixator, only a type I unilateral fixator can usually be used for humeral fractures. Occasionally a connecting bar can be placed from the lateral aspect of the proximal humeral pins and medially attached to the most distal humeral pin, providing additional rigidity to the device. Some interference with the chest wall may occur, however, with this type of fixation. Generally with a type I unilateral frame, fixation pins are inserted through the lateral or craniolateral aspect of the humerus passing From The Animal Medical Center, New York, New York. VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 1 • JANUARY 1992
121
122
MA TIHIESEN
through both lateral and medial cortices. Fixation pins are attached to a lateral, metal connecting bar and clamps. If necessary, a second connecting bar can be added to the fixation pins, doubling the external fixator's resistance to compressive forces. 3 Alternatively methyl methacrylate can be applied to the fixation pins and used in place of the metal connecting bar and clamps. A recent report described successful use of a modified type I unilateral fixator for repair of supracondylaF fractures. The modification consisted of curved or angulated connecting bars placed laterally to medially across the supracondylar fracture for increased stability.s GENERAL PRINCIPLES
The use and application of an external fixator to the humerus is relatively simple; several principles, however, should be followed to reduce problems and complications. 1. The humeral fracture should be appropriately reduced through an open approach, while minimizing the amount of vascular and soft tissue damage. 2. Fixation pins are placed through appropriately located skin incisions along the lateral or craniolateral aspect of the humerus. 3. The most proximal pin is inserted just distal to the greater tubercle along the craniolateral aspect of the humerus. By placing the pin in this location, the acromial head of the deltoideus muscle and the insertions of infraspinatus and teres minor muscles are avoided. When applying the most proximal and distal pins, a pin angle of approximately 70 to 75 degrees perpendicular to the long axis of the humerus may offer the best compromise between bone grip and bone strength. 2, 3 4. Inside pins are similarly placed at diverging angles of 70 to 80 degrees perpendicular to the long axis of the humerus. 5. The distal fixation pin is placed into the lateral aspect of the humeral condyle. If a single pin is placed into the condyle, the pin can be inserted slightly below the lateral epicondyle and directed across the condyle into the medial epicondyle. This technique maintains some angle of divergence, thereby decreasing the possibility of pin pullout or displacement. 6. Once the distal and proximal pins are placed, a connecting bar with end clamps and the anticipated number of central clamps is placed. The connecting bar should be positioned far enough from the skin to allow for swelling and callus formation without skin contact. 3 7. If two pins are placed into the humeral condyle, the most distal pin is placed as described. The second more proximal condylar pin is placed just proximal to the lateral epicondyle and directed
FRACTURES OF THE HUMERUS
8.
9.
10.
11.
123
toward a point distal to the medial epicondyle. Care must be taken to avoid placing pins intraarticularly. The appropriate number of central fixation pins should be placed. The brachialis muscle and radial nerve should be avoided when placing each pin. Distal fixation pins may have to enter the cranial aspect of the lateral head of the triceps muscle. Methyl methacrylate bone cement cal'l alternatively be used in place of the metal connecting bar and clamps. The major advantages associated with its use include easier placement of fixation pins, more versatility in placing pins at different angles, and avoidance of soft tissue structures. The number of pins placed in each fragment affects the overall stiffness of the fixation. Although clear guidelines have not currently been established regarding the number of fixation pins optimally required for successful fracture healing, several factors should be considered. These factors include the type of fracture and inherent stability, type of primary repair, and location of the fracture. Increasing the number of fixation pins in each fragment avoids overloading the bone surrounding each pin. 3 Overloading causes microfractures around the pin, resulting in bone resorption and pin 100sening.7 This may not be a serious problem if the external fixator is used as an adjunctive device for increasing fracture stability with plating or intramedullary pinning. The fixation pins may loosen as early as 3 weeks after surgery; sufficient callus, however, is often present, eliminating the purpose of the external fixator. Conversely pin loosening occurring in animals with a humeral fracture repaired primarily with an external fixator may require a second surgery if fracture healing is not sufficient at the time of fixation failure . Threaded pins offer the greatest resistance to pullout compared with non threaded pins. The majority of pins available in veterinary orthopedics, however, have a tendency to break or bend, particularly at the junction of the threaded and nonthreaded shaft.1, 6 Because of this problem, I generally do not use threaded pins or use only one threaded pin per humeral fragment.
SPECIFIC INDICATIONS AND USE OF A HUMERAL EXTERNAL FIXATOR
Supracondylar Fractures A type I, unilateral external fixator can be used as an adjunctive means of achieving adequate stability when repairing supracondylar fractures repaired with intramedullary pinning or a caudomedially applied bone plate, An external fixator is particularly useful for treat-
124
MATTHIESEN
ment of supracondylar type I or II Salter fractures repaired with an intramedullary pin (Figs. 1 and 2), in which some degree of rotational instability remains, or with comminuted fractures, in which inadequate rotational and axial stability is present following application of an intramedullary pin (Figs. 3 and 4). Occasionally an external fixator offers additional stability to the fracture when a plate has been applied to the caudomedial aspect of the humerus (Fig. 5). Comminuted dicondylar or supracondylar fractures repaued with caudomedial bone plating and still having instability are candidates for application of this type of fixation. Because of fracture location, a minimum number of screws may be placed in the distal fragment, thereby predisposing' the fixation to failure (e.g., loss of screw holding power in the distal
Figure 1. A distal supracondylar humeral fracture repaired using a single intramedullary pin, a cross-pin, and a Type I, unilateral external fixator. The K-E device is useful in this type of fracture for achieving additional stability, particularly if the fracture is rotationally unstable after primary repair.
FRACTURES OF THE HUMERUS
125
Figure 2. A one-year-old German Shepherd presented with a comminuted supracondylar, distal humeral fracture (A). The fracture was repaired using a single intramedullary pin and cerclage wiring. A Type I, unilateral external fixator was applied for additional rotational and axial stability (8 and C).
126
MATTHIESEN
Figure 3. A distal diaphyseal, supracondylar comminuted humeral fracture repaired using a single 1M pin, two full-cerclage wires, and a Type I unilateral external fixator. The device provides additional rotational and axial stability to the fracture.
FRACTURES OF THE HUMERUS
127
Figure 4. A 3-year-old Domestic Shorthair presented with a highly comminuted dicondylar humeral fracture following a fall injury (Af The fracture was repaired using a transcondylar compression screw, intramedullary pin, and several full-cerclage wires. A Type I, unilateral external fixator was applied for additional rotational and axial stability. Early fracture healing can be seen in radiographs obtained 3 weeks after surgery (8).
128
MA TIHIESEN
Figure 5. A distal diaphyseal humeral fracture repaired using caudo-medial bone plating and a Type I unilateral external fixator.
fragment) . An external fixator in these cases provides additional stability. When applying an external fixator to supracondylar fractures, sufficient space is usually available in the proximal humerus to apply a number of fixation pins successfully and easily. Some difficulty may be encountered, however, in placing one or two pins in the distal fragment. Placement of pins into the distal metaphyseal area is difficult because of fracture location, location of the intramedullary pin, and presence of the supratrochlear foramen with the possibility of intraarticular pin placement. As mentioned previously, a second unilateral device applied at 90 degrees axial rotation cranial to the first external fixator to create a biplanar configuration is difficult. Poor pin placement, possible intraarticular damage from misplaced pins, and external elbow impingement by the device during flexion prohibit effective use of this type of fixator.
FRACTURES OF THE HUMERUS
129
Transverse and Oblique Middiaphyseal Fractures
A type I, unilateral external fixator can also be used with single or multiple 1M pinning for treating diaphyseal fractures. For most middiaphyseal fracture repairs, the external fixator is used as an ancillary device for achieving additional rotational stability (Figs. 6 and 7). For more unstable fractures (e.g., comminuted fractures), the fixator provides additional resistance against compressi-ve and bending forces across the fracture (Fig. 8). Because of the relatively wide intramedullary canal in the proximal humerus, sufficient space is generally available to place the external fixator pins without impingement of the intramedullary pin. Depending on the relative size of the 1M pin, however, some difficulty can be encountered in placing pins in the diaphysis of
Figure 6. A simple transverse middiaphyseal humeral fracture repaired with a single intramedullary pin and a unilateral external fixator. The K-E device for this type of fracture is used for achieving additional rotational stability.
130
MA ITHIESEN
Figure 7. A 2-year-old Siamese cat with a simple, transverse, middiaphyseal fracture (A) repaired with multiple intramedullary pins and full cerclage wires. Owing to rotational instability, an external fixator was applied (8).
FRACTURES OF THE HUMERUS
131
Figure 8. A comminuted middiaphyseal humeral fracture repaired with a single intramedullary pin. An external fixator is applied for additional rotational and axial support.
the distal humeral segment. The number of fixation pins required in each segment depends on inherent stability of the fracture and overall stability following placement of the intramedullary pins.
Open Diaphyseal Fractures Moderately to severely contaminated, open humeral fractures can be stabilized with multiple fixation pins and a unilateral metal connecting bar or methyl methacrylate (Fig. 9). If methyl methacrylate is used, fixation pins can be placed along the lateral and craniolateral surface of the humerus at various diverging angles.
132
MATIHIESEN
Figure 9. A highly comminuted, humeral fracture primarily repaired using multiple fixation pins and methyl methacrylate.
COMPLICATIONS
One of the more common complications associated with external fixators is loosening of the fixation pins at the pin to bone interface. Generally some drainage is associated with pin loosening, and lucency surrounding the pin is present on radiographs. If too many pins loosen, fracture instability can occur, resulting in delayed fracture healing or nonunion. If loosening of one or two pins occurs, they should be removed. If several pins are loose and the external fixator is no longer providing stability, it should be removed. SUMMARY
A single or double bar, type I, unilateral external fixator can be used as primary or ancillary treatment for repair of many humeral
FRACTURES Of THE HUMERUS
133
fractures. Treatment of contaminated and comminuted fractures with external skeletal fixation provides rotational stability and axial align~ ment, access for wound management and bone grafting, and avoidance of vascular compromise by surgical invasion. In addition, the combi~ nation of external and internal (1M pins, cerclage wires, plates) fixation can provide greater initial fracture stability and subsequent dynamiza~ tion or loading of bone (as the fixator is removed) than either of the systems used individually.
References 1. Bennett RA, Egger EL, Histand MB, et al: Comparison of the strength and holding
2. 3. 4.
5. 6. 7.
power of 4 pin designs for use with half-pin (Type-I) external skeletal fixation. Vet Surg 16:207, 1987 Brinker WO, Flo GL: Principles and application of external skeletal fixation. Vet C1in North Am Small Anim Pract 2:197, 1975 Egger EL: External skeletal fixation. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery, ed 3. Philadelphia, Lea & Febiger, 1990, p 816 Egger EL, RunyonCL, Ribb DL: Use of Type-l double connecting bar configuration of external skeletal fixation on long bone fract\lres in dogs: A review of 10 cases. J Am Anim Hosp Assoc 22:57, 1986 K1ause SE, Schwarz PD, Egger EL, Piermattei DL: A modification of the unilateral Type 1 external skeletal fixator configuration for primary or secondary support of supracondylar humeral and femoral fractures . Vet Comp Orthop Trauma 3:130, 1990 Palmer RH, Aron DN: Ellis pin complications in seven dogs. Vet Surg 19:440, 1990 W\l H, Shyr HS, Chao FYS, Kelly PJ: Comparison of osteotomy healing under external fixation devices with different stiffness characteristics. J Bone Joint Surg [Am] 66:1258, 1984 . .
Address reprint requests to David T. Matthiesen, DVM The Animal Medical Center 510 East 62nd Street New York, NY 10021
