EXTERNAL SKELETAL FIXATION
0195-5616/92 $0.00
+ .20
FRACTURES OF THE FEMUR Jon G. Whitehair, DVM, and Philip B. Vasseur, DVM
Femoral fractures are the most common fracture type in the dog and cat, accounting for 20% to 26% of all fractures .6, 16 Femoral fractures are usually the result of direct trauma from a motor vehicle. Vehicular impact results in very rapid loading of bone. Because of its viscoelastic properties, bone absorbs energy in proportion to the rate of loading.1, 17 Thus very rapid loading causes high-energy absorption prior to fracture. The energy is dissipated through the surrounding soft tissues when the bone fractures and can cause significant injury to muscles and neurovascular structures. These "high-energy" fractures are typically very comminuted and highly unstable. The femur may also fracture as a result of excessive torsional and bending loads; such injuries usually cause spiral or transverse fractures, respectively. Many femoral fractures are the result of complex loading patterns, and the resulting fracture often combines some degree of comminution (e.g., butterfly fragments) with oblique and spiral fracture lines. Femoral fractures are subjected to bending (compression and tension), shear, and torsional (rotational) forces. 17 Fracture fragments tend to override and rotate because of muscular forces. Fracture healing is complicated by soft tissue injury and reduction of blood supply. Failure to neutralize the forces acting on the fracture fragments and prevent further damage to blood supply may lead to delayed union or nonunion with associated fracture disease. s, 13,23 External skeletal fixation (ESF) is generally used in conjunction with intramedullary (1M) pins when applied to the femur. When properly applied to appropriate types of femoral fractures, ESF can From the Veterinary Medical Teaching Hospital (JGW) and the Department of Surgery (PBV), University of California School of Veterinary Medicine, Davis, California
VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 1 • JANUARY 1992
149
150
WHITEHAIR & VASSEUR
effectively counteract the aforementioned destabilizing forces and provide an economical alternative to other methods of internal fixation. The purposes of this article are to present general principles regarding application of ESF to the femur and to provide specific examples of appropriate indications and methods of application. The reader is encouraged to study the introductory articles in this issue that define the basic terminology, instrumentation, and methods of application that apply to the general use of external fixation devices.
ANATOMY AND GENERAL CONSIDERATIONS
The femur is a typical long bone with a cylindrical shaft and expanded extremities. The proximal end consists of the femoral head and neck and the greater, lesser, and third trochanters. The greater trochanter is an important landmark for the insertion of ESF pins. Pins placed into and immediately distal to the greater trochanter encounter minimal soft tissues and, if angled properly, engage the heavy cortex of the proximal medial femur . Fixation pins should be directed toward the area of the lesser trochanter; pins angled proximal to the level of the lesser trochanter may penetrate the trochanteric fossa, resulting in reduced bone purchase. There is generally room for two ESF pins in the proximal femur; a third pin placed more distally will encounter muscle tissue but may be necessary in particularly unstable fractures or those with proximal cortical defects, which limit pin placement. The proximal femur tapers to the femoral isthmus located at the level of the proximal diaphysis and then flares distally toward the metaphysis. The shaft of the canine femur is slightly convex cranially, whereas in cats the shaft is almost straight with a less discernible isthmus. The isthmus is the narrowest portion of the medullary canal and is therefore the limiting factor when choosing the diameter of an 1M pin for fracture fixation. The placement of a single, large 1M pin in an attempt to "fill the medullary canal" is an ineffective method for preventing rotation in transverse fractures because of the limited 1M pin-bone contact and the smooth surface of Steinmann pins.7, 22 The most effective way to minimize rotation in transverse femoral fractures in dogs is to combine ESF with 1M fixation.22 Placement of ESF pins alongside an 1M pin requires that the diameter of the 1M pin be approximately 50% less than that of the femoral isthmus. The mid shaft of the femur is covered laterally and cranially by the bellies of the biceps femoris and quadriceps muscles, respectively. The adductor magnus attaches to the caudal aspect of the femoral diaphysis. Placement of ESF pins in the area of the femoral shaft will cause muscle irritation, pain, and limited limb use, If pins have to be used in this area to achieve adequate fracture stabilization, they should be removed as soon as possible to avoid the complications of muscle atrophy, reduced joint motion, and excessive periarticular fibrosis (quadriceps tie-down).
FRACTURES OF THE FEMUR
151
The distal aspect of the femur consists of the trochlea and condyles. The femoral condyles contain substantial bone mass and, combined with the fact that the lateral aspect of the lateral condyle has minimal soft tissue coverage, provide an excellent location for placement of transversely oriented ESF pins. The condyles are separated from each other by the intercondylar fossa, which serves as the point of origin of the cruciate ligaments. Fixation pins inserted too far distally in the femur can enter the intercondylar fossa and disrupt ligament attachment sites. In immature animals, care should be taken not to place ESF pins through or distal to the distal femoral physis. Injury to the physis or development of compression across the physis by the ESF device could delay or prevent longitudinal growth. The sciatic nerve originates from the last two lumbar and first two sacral nerves. l l It passes underneath the superficial gluteal muscle and caudal to the greater trochanter before continuing distally underneath the biceps femoris muscle. The nerve is unlikely to be injured by ESF pins; the location of the nerve is important, however, when retracting muscles and placing 1M pins. 12, 18 It is imperative that the function of the sciatic nerve be assessed before and after surgical procedures involving the femur. The major blood supply to the diaphyseal region of the femur enters the bone at the nutrient foramen located at the caudal aspect of the proximal third of the diaphysis. The adductor muscle attachment to the caudal aspect of the diaphysis is also an important source of periosteal vessels, a source that becomes especially significant in the healing of diaphyseal fractures. 14, 20 The primary blood supply for healing fractures is derived from periosteal attachments, particularly when 1M devices have damaged intramedullary vessels. A major advantage of pins and ESF devices is that minimal dissection of the fracture site is required for the placement of implants; thus vascular tissue attachments to fracture fragments are preserved and healing is enhanced.
INDICATIONS FOR EXTERNAL SKELETAL FIXATION
The aforementioned anatomic features effectively limit the number, location, depth, and angle of placement of ESF pins in the femur. As a general rule, one to three pins can be placed in the proximal and distal aspects of the femur. Placement of full-pins (through the medial skin surface) is not desirable because of the extensive soft tissues present medially and the proximity to the body walL Therefore very rigid configurations consisting of full-pins and bilateral frames are not possible. The most effective use of ESF in the femur is to augment 1M pin and wire fixation of transverse, short oblique, or mildly comminuted fractures, In highly comminuted fractures, it may not be possible to reconstruct the medial buttress, and such fixations are subjected to large
152
WHITEHAIR & VASSEUR
bending stresses. More stable techniques, e.g., plate and screw fixation, are generally indicated when medial cortical defects are present. The bending rigidity of ESF devices can be markedly improved by increasing the number of connecting bars/' 10 and that option should be considered in selected cases. SUMMARY: APPLICATION OF EXTERNAL SKELETAL FIXATION TO FEMORAL FRACTURES
1. The presence of muscle bellies around the femoral diaphysis limits the use of ESF pins to proximal and distal insertion sites. 2. Proximity to the abdominal wall prevents the use of full-pins, which penetrate the medial skin surface; therefore only uniplanar, half-pin configurations are generally used. Such configurations do not provide adequate stabilization by themselves; thus they are generally used in combination with an 1M pin, which provides axial alignment and resistance to bending. 3. External fixation devices are most effective as augmentation to 1M pin and wire fixations. Appropriate fractures include transverse, short oblique, long oblique, and mildly comminuted fractures that have been adequately reconstructed. More severely comminuted fractures in which the medial buttress cannot be reconstructed are best managed with plate and screw fixation.
PREOPERATIVE CONSIDERATIONS
Thorough preoperative planning is a prerequisite to a successful clinical outcome. A complete physical examination must be performed with special emphasis on the cardiopulmonary, neurologic, and musculoskeletal systems. Since most femoral fractures are the result of vehicular trauma, animals frequently suffer myocardial and pulmonary contusions. The minimum database, in most cases, should include radiographs of the chest and fractured limb(s), complete blood count, serum chemistries, and urinalysis. Serial physical examinations are frequently helpful to avoid overlooking problems. Clipping the hair of the affected limb is helpful to detect occult open fractures. If the fracture is open, appropriate measures such as culture and sensitivity, wound care, and systemic antibiotics should be instituted. 21 After life-threatening abnormalities have been addressed, planning of the fracture repair can begin. High-quality radiographs are mandatory for assessment of the fracture (medial-lateral and cranial-caudal views). External coaptation of femoral fractures is ineffective, and heavy bandages that do not encompass the trunk are detrimental because they become a pendulum with the proximal aspect of the bandage acting as a fulcrum, thus causing marked distraction of the fracture site. Support bandages that do encompass the trunk (Spica bandages)
FRACTURES OF THE FEMUR
153
are bulky and expensive and cause considerable pain during application. We do not routinely use external coaptation for femoral fractures unless there is marked swelling of the distal aspect of the limb. In the latter instance, a lightly padded compressive wrap that extends from the toes to the groin may be applied the day before operation to reduce swelling. The client should be informed about the costs of surgery and follow-up visits, type of fixation and possible complications, care required postoperatively, and prognosis for return to full function. With ESF in particular, the client must be advised about the appearance of the device and the need to keep sharp pins covered and should watch for excessive drainage around the pins.
METHOD OF APPLICATION
The limb is prepared for aseptic surgery and draped to permit manipulation of the limb during the procedure. A lateral approach to the femoral shaft between the biceps femoris and vastus lateralis is used. I9 The fracture fragments are identified and the fracture hematoma and proliferative tissues removed to permit visualization of the reduction and bone fissures. Care is taken during the approach and reduction process to minimize debridement of muscles from bone attachments. Most often, ESF will be combined with 1M pin fixation. To permit placement of ESF pins alongside the 1M pin, a pin is selected with a diameter that is approximately 50% of the femoral isthmus. Although insertion in a retrograde fashion is common, normograde insertion of the pin from the trochanteric fossa may be less likely to cause sciatic nerve injury, particularly in midshaft and distal fractures. IS If the pin is driven in a retrograde manner, the limb should be adducted and the coxofemoral joint slightly extended to minimize the risk of sciatic nerve injury. Distally the pin should be seated deeply within the femoral condyles. Because of the cranial convexity of the femur in many dogs, there is a tendency for the pin to penetrate the trochlea or gain insufficient purchase in the distal fragment. Overreduction of the distal fragment can help maximize purchase, particularly in distal fractures. Intramedullary fixation of transverse and short oblique fractures can be supported by hemicerclage wires before application of the external fixator. Full cerclage wires are helpful if the length of the obliquity is at least twice the diameter of the medullary canal. The ESF device generally is applied after closure of the surgical wound. Fixation pins are placed through longitudinally oriented, l-cm stab incisions in the skin. A hemostat is useful to separate and retract the soft tissues from the cortical surface. The fixation pins are driven using a power drill at low speed (150 RPM); drill sleeves are useful to protect the soft tissues. An oscillating drill bit attachment is available for the AO drill, which permits predrilling in the presence of soft tissues; we have found it to be extremely useful (oscillating drill
154
WHITEHAIR & VASSEUR
attachment; Synthes [USA], Paoli, PA). Partially threaded fixation pins provide superior pullout strength compared with smooth pins and are strongly recommended.5 The most proximal and distal pins are inserted first (Fig. lA) . The proximal pin is inserted so that it penetrates the lateral surface of the greater trochanter and exits the far cortex at or slightly distal to the lesser trochanter. The distal pin is placed perpendicular to the bone and within the femoral condyles. The pin must be placed proximal to the physis in immature dogs. In mature dogs, the pin is placed just proximal to the intercondylar fossa. One or two connecting bars with the appropriate number of "open" pin clamps are attached to the proximal and distal pins. The remaining fixation pins are driven through the open pin clamps (Fig. IB). It is helpful to angle the remaining pins to increase resistance to pullout; angling of the pins, however, may reduce the possible number of pins per fragment, and the opportunity to increase stabilization by placement of additional pins should not be lost for the sake of pin angle. With threaded pins, the angle of the pin is not as critical as the number of pins and insertion technique. If the
A
B
Figure 1. A. Schematic illustration showing initial placement of skeletal fixation pins. The proximal pin is angled slightly to engage the heavy cortex at the base of the femoral neck. The distal pin is placed transversely through the femoral condyles just proximal to the intercondylar notch. B, Open clamps placed on the connecting bar are used as guides to direct subsequent pin placement. Pins are angled slightly to reduce the possibility of pullout.
FRACTURES OF THE FEMUR
155
1M pin is encountered during the insertion process, slight redirection of the fixation pin will usually allow it to slide past the 1M pin. The trochar point of the fixation pin should completely penetrate the far cortex, thus allowing secure purchase of the threads into cortical bone. After the desired number of fixation pins have been inserted, the fixator can be adjusted and pin clamps tightened. The pin clamps should be approximately 1.5 cm away from _the skin. As soft tissues recede to their normal position, the pin clamps and connecting bar(s) can be moved closer to the bone. Frame rigidity is inversely proportional to bone-clamp distance. 2, 4 Radiographs should be taken postoperatively to evaluate the reduction and placement of fixation devices. Minor adjustments can be made to the fixation pins before final cutting and tightening of clamps. The 1M pin and ESF device can be connected using what has been termed an intramedullary pin/external skeletal fixator tie-in configuration.3 With this fixation system, the 1M pin is left protruding from the skin proximally and is connected to a type la external fixator (single connecting bar) using two double clamps and a short connecting bar (Fig. 2). Under quasistatic uniaxial compressive loading, the mean yield strength, yield energy, and ultimate strength of the tied-in configuration
Figure 2. A tie-in configuration to increase fixator rigidity. The connecting bar is attached to the intramedullary pin via a second short connecting bar.
156
WHITEHAIR & VASSEUR
were significantly larger than those not tied-in. The tied-in configuration has been used clinically with minimal complications. 3 A modification of the unilateral type I fixator has been designed for comminuted supracondylar fractures of the humerus and femur. IS The design includes a full-pin placed into the distal fracture fragment connected to the proximal lateral pin via a curved connecting bar (Fig. 3A). Stabilization of the distal fragment may be further enhanced by placement of additional half-pins medially; laterally, or both and an additional curved connecting bar over the stifle joint (Fig. 3B) . POSTOPERATIVE CARE
The animal may be discharged 24 to 48 hours after surgery when it is ambulatory with minimal assistance. An Elizabethan collar should remain in place until the sutures are removed, although some animals may require the collar until the fixator is removed. It is very important, especially in large or active dogs, that exercise be strictly controlled until the fracture has united. The pin tracts will usually drain a serosanguineous fluid for 3 to 4 days after insertion. Clients are instructed to clean the pin sites gently with a mild antiseptic solution as needed. A dry crust will eventually form around the pins, which is
Figure 3. A. A modified external fixation system useful for commi· nuted fractures of the distal femur. Note the double connecting bars placed laterally and the curved connecting bar extending to the medial aspect of the stifle joint. The external fixation device should be used in support of an 1M pin whenever possible. II/ustration continued on opposite page
FRACTURES OF THE FEMUR
157
Figure 3 (Continued). B. A more elaborate fixator design useful for larger dogs with comminuted fractures of the distal femur. Dual curved connecting bars are connected to a medial connecting bar to provide maximum stabilization.
left undisturbed. The fixator should be bandaged to protect it and the surrounding environment. One week after surgery, the wound is examined and the fixator adjusted or tightened if necessary. Rechecks are scheduled every 2 to 3 weeks thereafter depending on the anticipated rate of healing and stability of the fracture repair. In stable repairs in young animals, the fixator is often removed after 3 to 4 weeks and the intramedullary fixation left in place. Longer periods will be necessary in older animals and in those with less stable fractures. Staged disassembly of the device results in gradual transfer of stress to the bone and remaining fixation devices. It can stimulate bone union and should be considered in animals with radiographic evidence of delayed union. Careful judgment is required in these cases, since destabilization can result in collapse of the fracture. The animal should have good use of the limb, complete healing of the soft tissues, and some evidence of callus production before removal of any fixation devices. COMPLICATIONS
Most complications can be avoided by realizing the indications for and limitations of ESF. Because of the regional anatomy, ESF of femoral
158
WHITEHAIR & VASSEUR
fractures is generally limited to unilateral frame designs. Unilateral frames cannot be expected to bear the brunt of weight bearing and should assume a supportive role to intramedullary fixation devices. As an adjunct to internal fixation of the previously described fracture types, ESF works well. Use of threaded pins and placement using slowspeed power drilling increases the pullout strength and durability of the fixation pins. Complications generally occur when ESF devices are applied to very unstable fractures and are expected to provide most of the stability. Of particular concern are comminuted fractures with defects involving the medial cortex. The medial cortex is subjected to compressive loading and functions as a load-bearing buttress. Fractures in which the medial buttress cannot be reconstructed should be managed with plate fixation whenever possible. The recent development of tie-in configurations and contoured connecting bars has extended the indications of ESF in femoral fractures. Complications can be minimized by careful case selection, adherence to proper methods of surgical technique and fixator application, and conscientious aftercare and client communication. SUMMARY
The most common indications for the use of ESF in femoral fractures are closed transverse, short oblique, and minimally comminuted fractures in the central one third of the bone. External skeletal fixation is usually used in combination with 1M pins and wiring techniques. During the process of open reduction and internal fixation, the surgeon should strive for accurate anatomic alignment and stability at the fracture site. The fixator is applied after the internal fixation is in place and the surgical wound is closed. The number of fixation pins placed in each fracture fragment depends on the type of fracture and the stability gained by internal fixation. Partially threaded fixation pins are recommended. They are inserted through skin stab incisions with low-speed power equipment. Recent modifications of the Type la fixator may increase fixator rigidity. Important postoperative concerns include exercise restriction, pin tract care, and protection of the fixator from the environment. Complications associated with ESF can be minimized by realizing its indications and limitations. References 1. Arnoczky SP, Wilson JW, Schwarz PO: Fractures and fracture biology. In Slatter OH (ed): Textbook of Small Animal Surgery. Philadelphia, WB Saunders, 1985, p 1939 2. Aron ON: External skeletal fixation. Vet Med Rep 1:181, 1989
3. Aron ON, Foutz TL, Keller WG, et al: Experimental and clinical experience with an 1M pin external skeletal fixator tie-in configuration. J Comp Orthop Traumatol 4:8&94, 1991.
FRACTURES OF THE FEMUR
159
4. Aron ON, Toombs JP: Updated principles of external skeletal fixation. Comp Cont Ed Pract Vet 6:845, 1984 5. Bennett RA, Egger EL, Histand M, et al: Comparison of the strength and holding power of 4 pin designs for use with half pin (type I) external skeletal fixation. Vet Surg 16:207, 1987 6. Brinker WO, Piermattei DL, Flo GL: Fractures of the femur and patella. In Brinker WO, Piermattei DL, Flo GL (eds): Handbook of Small Animal Clinical Orthopedics and Fracture Treatment. Philadelphia, WB Saunders, 1983, p 75 7. Dallman MJ, Martin RA, Self BP, et al: Rotational strength of double-pinning techniques in repair of transverse fractures in femurs of dogs. Am J Vet Res 51:123, 1990 8. DeAngelis MP: Fractures of the femur. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery. Philadelphia, Lea & Febiger, 1975, p 453 9. Egger EL: Static strength evaluation of six external skeletal fixation configurations. Vet Surg 12:130, 1983 10. Egger EL, Runyon CL, Rigg DL: Use of the type I double connecting bar configuration of external skeletal fixation on long bone fractures in dogs: A review of 10 cases. J Am Anim Hosp Assoc 22:57,1986 11. Evans HE, Christensen GE: The spinal nerves. In Miller's Anatomy of the Dog, ed 2. Philadelphia, WB Saunders, 1979, p 972 12. Fanton JW, Blass CE, Withrow SJ: Sciatic nerve injury as a complication of intramedullary pin fixation of femoral fractures. JAm Anim Hosp Assoc 19:687, 1983 13. Hunt JM, Aitken ML, Denny HR, et al: The complications of diaphyseal fractures in dogs: A review of 100 cases. J Small Anim Pract 21:103, 1980 14. Kaderly RE, Anderson WD, Anderson BG: Extraosseous vascular supply to the mature dog's coxofemoral joint. Am J Vet Res 43:1208, 1982 15. Klause SE, Schwarz PO, Egger EL, et al: A modification of the unilateral type I external skeletal fixator configuration for primary and secondary support of supracondylar humeral and femoral fractures. Vet Comp Orthop Traumatol 3:130, 1990 16. Milton JL, Newman ME: Fractures of the femur. In Slatter DH (ed): Textbook of Small Animal Surgery. Philadelphia, WB Saunders, 1985, p 2180 17. Nordin M, Frankel VH: Biomechanics of bone. In Basic Biomechanics of the Musculoskeletal System. Philadelphia, Lea & Febiger, 1989, p 3 18. Palmer RH, Aron ON, Purington PT: Relationship of femoral intramedullary pins to the sciatic nerve and gluteal muscles after retrograde and normograde insertion. Vet Surg 17:65, 1988 19. Piermattei DL, Greeley RG: The hindlimb. In An Atlas of Surgical Approaches to the Bones of the Dog and Cat, ed 2. Philadelphia, WB Saunders, 1979, p 162 20. Rhinelander FW: Blood supply of healing long-bones. In Newton CD, Nunamaker OM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott, 1985, p 39 21. Richardson DC: Fracture first aid: The open (compound) fracture. In Slatter DH (ed): Textbook of Small Animal Surgery. Philadelphia, WB Saunders, 1985, p 1945 22. Vasseur PB, Paul HA, Crumley L: Evaluation of fixation devices for prevention of rotation in transverse fractures of the canine femoral shaft: An in vitro study. Am J Vet Res 45:1504, 1984 23. Vaughan LC: Complications associated with the internal fixation of fractures in dogs. J Small Anim Pract 16:415, 1975
Address reprint requests to Philip B. Vasseur, DVM Department of Veterinary Surgery University of California School of Veterinary Medicine Davis, CA 95616
0195-5616/92 $0.00
+ .20
FRACTURES OF THE FEMUR Jon G. Whitehair, DVM, and Philip B. Vasseur, DVM
Femoral fractures are the most common fracture type in the dog and cat, accounting for 20% to 26% of all fractures .6, 16 Femoral fractures are usually the result of direct trauma from a motor vehicle. Vehicular impact results in very rapid loading of bone. Because of its viscoelastic properties, bone absorbs energy in proportion to the rate of loading.1, 17 Thus very rapid loading causes high-energy absorption prior to fracture. The energy is dissipated through the surrounding soft tissues when the bone fractures and can cause significant injury to muscles and neurovascular structures. These "high-energy" fractures are typically very comminuted and highly unstable. The femur may also fracture as a result of excessive torsional and bending loads; such injuries usually cause spiral or transverse fractures, respectively. Many femoral fractures are the result of complex loading patterns, and the resulting fracture often combines some degree of comminution (e.g., butterfly fragments) with oblique and spiral fracture lines. Femoral fractures are subjected to bending (compression and tension), shear, and torsional (rotational) forces. 17 Fracture fragments tend to override and rotate because of muscular forces. Fracture healing is complicated by soft tissue injury and reduction of blood supply. Failure to neutralize the forces acting on the fracture fragments and prevent further damage to blood supply may lead to delayed union or nonunion with associated fracture disease. s, 13,23 External skeletal fixation (ESF) is generally used in conjunction with intramedullary (1M) pins when applied to the femur. When properly applied to appropriate types of femoral fractures, ESF can From the Veterinary Medical Teaching Hospital (JGW) and the Department of Surgery (PBV), University of California School of Veterinary Medicine, Davis, California
VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 1 • JANUARY 1992
149
150
WHITEHAIR & VASSEUR
effectively counteract the aforementioned destabilizing forces and provide an economical alternative to other methods of internal fixation. The purposes of this article are to present general principles regarding application of ESF to the femur and to provide specific examples of appropriate indications and methods of application. The reader is encouraged to study the introductory articles in this issue that define the basic terminology, instrumentation, and methods of application that apply to the general use of external fixation devices.
ANATOMY AND GENERAL CONSIDERATIONS
The femur is a typical long bone with a cylindrical shaft and expanded extremities. The proximal end consists of the femoral head and neck and the greater, lesser, and third trochanters. The greater trochanter is an important landmark for the insertion of ESF pins. Pins placed into and immediately distal to the greater trochanter encounter minimal soft tissues and, if angled properly, engage the heavy cortex of the proximal medial femur . Fixation pins should be directed toward the area of the lesser trochanter; pins angled proximal to the level of the lesser trochanter may penetrate the trochanteric fossa, resulting in reduced bone purchase. There is generally room for two ESF pins in the proximal femur; a third pin placed more distally will encounter muscle tissue but may be necessary in particularly unstable fractures or those with proximal cortical defects, which limit pin placement. The proximal femur tapers to the femoral isthmus located at the level of the proximal diaphysis and then flares distally toward the metaphysis. The shaft of the canine femur is slightly convex cranially, whereas in cats the shaft is almost straight with a less discernible isthmus. The isthmus is the narrowest portion of the medullary canal and is therefore the limiting factor when choosing the diameter of an 1M pin for fracture fixation. The placement of a single, large 1M pin in an attempt to "fill the medullary canal" is an ineffective method for preventing rotation in transverse fractures because of the limited 1M pin-bone contact and the smooth surface of Steinmann pins.7, 22 The most effective way to minimize rotation in transverse femoral fractures in dogs is to combine ESF with 1M fixation.22 Placement of ESF pins alongside an 1M pin requires that the diameter of the 1M pin be approximately 50% less than that of the femoral isthmus. The mid shaft of the femur is covered laterally and cranially by the bellies of the biceps femoris and quadriceps muscles, respectively. The adductor magnus attaches to the caudal aspect of the femoral diaphysis. Placement of ESF pins in the area of the femoral shaft will cause muscle irritation, pain, and limited limb use, If pins have to be used in this area to achieve adequate fracture stabilization, they should be removed as soon as possible to avoid the complications of muscle atrophy, reduced joint motion, and excessive periarticular fibrosis (quadriceps tie-down).
FRACTURES OF THE FEMUR
151
The distal aspect of the femur consists of the trochlea and condyles. The femoral condyles contain substantial bone mass and, combined with the fact that the lateral aspect of the lateral condyle has minimal soft tissue coverage, provide an excellent location for placement of transversely oriented ESF pins. The condyles are separated from each other by the intercondylar fossa, which serves as the point of origin of the cruciate ligaments. Fixation pins inserted too far distally in the femur can enter the intercondylar fossa and disrupt ligament attachment sites. In immature animals, care should be taken not to place ESF pins through or distal to the distal femoral physis. Injury to the physis or development of compression across the physis by the ESF device could delay or prevent longitudinal growth. The sciatic nerve originates from the last two lumbar and first two sacral nerves. l l It passes underneath the superficial gluteal muscle and caudal to the greater trochanter before continuing distally underneath the biceps femoris muscle. The nerve is unlikely to be injured by ESF pins; the location of the nerve is important, however, when retracting muscles and placing 1M pins. 12, 18 It is imperative that the function of the sciatic nerve be assessed before and after surgical procedures involving the femur. The major blood supply to the diaphyseal region of the femur enters the bone at the nutrient foramen located at the caudal aspect of the proximal third of the diaphysis. The adductor muscle attachment to the caudal aspect of the diaphysis is also an important source of periosteal vessels, a source that becomes especially significant in the healing of diaphyseal fractures. 14, 20 The primary blood supply for healing fractures is derived from periosteal attachments, particularly when 1M devices have damaged intramedullary vessels. A major advantage of pins and ESF devices is that minimal dissection of the fracture site is required for the placement of implants; thus vascular tissue attachments to fracture fragments are preserved and healing is enhanced.
INDICATIONS FOR EXTERNAL SKELETAL FIXATION
The aforementioned anatomic features effectively limit the number, location, depth, and angle of placement of ESF pins in the femur. As a general rule, one to three pins can be placed in the proximal and distal aspects of the femur. Placement of full-pins (through the medial skin surface) is not desirable because of the extensive soft tissues present medially and the proximity to the body walL Therefore very rigid configurations consisting of full-pins and bilateral frames are not possible. The most effective use of ESF in the femur is to augment 1M pin and wire fixation of transverse, short oblique, or mildly comminuted fractures, In highly comminuted fractures, it may not be possible to reconstruct the medial buttress, and such fixations are subjected to large
152
WHITEHAIR & VASSEUR
bending stresses. More stable techniques, e.g., plate and screw fixation, are generally indicated when medial cortical defects are present. The bending rigidity of ESF devices can be markedly improved by increasing the number of connecting bars/' 10 and that option should be considered in selected cases. SUMMARY: APPLICATION OF EXTERNAL SKELETAL FIXATION TO FEMORAL FRACTURES
1. The presence of muscle bellies around the femoral diaphysis limits the use of ESF pins to proximal and distal insertion sites. 2. Proximity to the abdominal wall prevents the use of full-pins, which penetrate the medial skin surface; therefore only uniplanar, half-pin configurations are generally used. Such configurations do not provide adequate stabilization by themselves; thus they are generally used in combination with an 1M pin, which provides axial alignment and resistance to bending. 3. External fixation devices are most effective as augmentation to 1M pin and wire fixations. Appropriate fractures include transverse, short oblique, long oblique, and mildly comminuted fractures that have been adequately reconstructed. More severely comminuted fractures in which the medial buttress cannot be reconstructed are best managed with plate and screw fixation.
PREOPERATIVE CONSIDERATIONS
Thorough preoperative planning is a prerequisite to a successful clinical outcome. A complete physical examination must be performed with special emphasis on the cardiopulmonary, neurologic, and musculoskeletal systems. Since most femoral fractures are the result of vehicular trauma, animals frequently suffer myocardial and pulmonary contusions. The minimum database, in most cases, should include radiographs of the chest and fractured limb(s), complete blood count, serum chemistries, and urinalysis. Serial physical examinations are frequently helpful to avoid overlooking problems. Clipping the hair of the affected limb is helpful to detect occult open fractures. If the fracture is open, appropriate measures such as culture and sensitivity, wound care, and systemic antibiotics should be instituted. 21 After life-threatening abnormalities have been addressed, planning of the fracture repair can begin. High-quality radiographs are mandatory for assessment of the fracture (medial-lateral and cranial-caudal views). External coaptation of femoral fractures is ineffective, and heavy bandages that do not encompass the trunk are detrimental because they become a pendulum with the proximal aspect of the bandage acting as a fulcrum, thus causing marked distraction of the fracture site. Support bandages that do encompass the trunk (Spica bandages)
FRACTURES OF THE FEMUR
153
are bulky and expensive and cause considerable pain during application. We do not routinely use external coaptation for femoral fractures unless there is marked swelling of the distal aspect of the limb. In the latter instance, a lightly padded compressive wrap that extends from the toes to the groin may be applied the day before operation to reduce swelling. The client should be informed about the costs of surgery and follow-up visits, type of fixation and possible complications, care required postoperatively, and prognosis for return to full function. With ESF in particular, the client must be advised about the appearance of the device and the need to keep sharp pins covered and should watch for excessive drainage around the pins.
METHOD OF APPLICATION
The limb is prepared for aseptic surgery and draped to permit manipulation of the limb during the procedure. A lateral approach to the femoral shaft between the biceps femoris and vastus lateralis is used. I9 The fracture fragments are identified and the fracture hematoma and proliferative tissues removed to permit visualization of the reduction and bone fissures. Care is taken during the approach and reduction process to minimize debridement of muscles from bone attachments. Most often, ESF will be combined with 1M pin fixation. To permit placement of ESF pins alongside the 1M pin, a pin is selected with a diameter that is approximately 50% of the femoral isthmus. Although insertion in a retrograde fashion is common, normograde insertion of the pin from the trochanteric fossa may be less likely to cause sciatic nerve injury, particularly in midshaft and distal fractures. IS If the pin is driven in a retrograde manner, the limb should be adducted and the coxofemoral joint slightly extended to minimize the risk of sciatic nerve injury. Distally the pin should be seated deeply within the femoral condyles. Because of the cranial convexity of the femur in many dogs, there is a tendency for the pin to penetrate the trochlea or gain insufficient purchase in the distal fragment. Overreduction of the distal fragment can help maximize purchase, particularly in distal fractures. Intramedullary fixation of transverse and short oblique fractures can be supported by hemicerclage wires before application of the external fixator. Full cerclage wires are helpful if the length of the obliquity is at least twice the diameter of the medullary canal. The ESF device generally is applied after closure of the surgical wound. Fixation pins are placed through longitudinally oriented, l-cm stab incisions in the skin. A hemostat is useful to separate and retract the soft tissues from the cortical surface. The fixation pins are driven using a power drill at low speed (150 RPM); drill sleeves are useful to protect the soft tissues. An oscillating drill bit attachment is available for the AO drill, which permits predrilling in the presence of soft tissues; we have found it to be extremely useful (oscillating drill
154
WHITEHAIR & VASSEUR
attachment; Synthes [USA], Paoli, PA). Partially threaded fixation pins provide superior pullout strength compared with smooth pins and are strongly recommended.5 The most proximal and distal pins are inserted first (Fig. lA) . The proximal pin is inserted so that it penetrates the lateral surface of the greater trochanter and exits the far cortex at or slightly distal to the lesser trochanter. The distal pin is placed perpendicular to the bone and within the femoral condyles. The pin must be placed proximal to the physis in immature dogs. In mature dogs, the pin is placed just proximal to the intercondylar fossa. One or two connecting bars with the appropriate number of "open" pin clamps are attached to the proximal and distal pins. The remaining fixation pins are driven through the open pin clamps (Fig. IB). It is helpful to angle the remaining pins to increase resistance to pullout; angling of the pins, however, may reduce the possible number of pins per fragment, and the opportunity to increase stabilization by placement of additional pins should not be lost for the sake of pin angle. With threaded pins, the angle of the pin is not as critical as the number of pins and insertion technique. If the
A
B
Figure 1. A. Schematic illustration showing initial placement of skeletal fixation pins. The proximal pin is angled slightly to engage the heavy cortex at the base of the femoral neck. The distal pin is placed transversely through the femoral condyles just proximal to the intercondylar notch. B, Open clamps placed on the connecting bar are used as guides to direct subsequent pin placement. Pins are angled slightly to reduce the possibility of pullout.
FRACTURES OF THE FEMUR
155
1M pin is encountered during the insertion process, slight redirection of the fixation pin will usually allow it to slide past the 1M pin. The trochar point of the fixation pin should completely penetrate the far cortex, thus allowing secure purchase of the threads into cortical bone. After the desired number of fixation pins have been inserted, the fixator can be adjusted and pin clamps tightened. The pin clamps should be approximately 1.5 cm away from _the skin. As soft tissues recede to their normal position, the pin clamps and connecting bar(s) can be moved closer to the bone. Frame rigidity is inversely proportional to bone-clamp distance. 2, 4 Radiographs should be taken postoperatively to evaluate the reduction and placement of fixation devices. Minor adjustments can be made to the fixation pins before final cutting and tightening of clamps. The 1M pin and ESF device can be connected using what has been termed an intramedullary pin/external skeletal fixator tie-in configuration.3 With this fixation system, the 1M pin is left protruding from the skin proximally and is connected to a type la external fixator (single connecting bar) using two double clamps and a short connecting bar (Fig. 2). Under quasistatic uniaxial compressive loading, the mean yield strength, yield energy, and ultimate strength of the tied-in configuration
Figure 2. A tie-in configuration to increase fixator rigidity. The connecting bar is attached to the intramedullary pin via a second short connecting bar.
156
WHITEHAIR & VASSEUR
were significantly larger than those not tied-in. The tied-in configuration has been used clinically with minimal complications. 3 A modification of the unilateral type I fixator has been designed for comminuted supracondylar fractures of the humerus and femur. IS The design includes a full-pin placed into the distal fracture fragment connected to the proximal lateral pin via a curved connecting bar (Fig. 3A). Stabilization of the distal fragment may be further enhanced by placement of additional half-pins medially; laterally, or both and an additional curved connecting bar over the stifle joint (Fig. 3B) . POSTOPERATIVE CARE
The animal may be discharged 24 to 48 hours after surgery when it is ambulatory with minimal assistance. An Elizabethan collar should remain in place until the sutures are removed, although some animals may require the collar until the fixator is removed. It is very important, especially in large or active dogs, that exercise be strictly controlled until the fracture has united. The pin tracts will usually drain a serosanguineous fluid for 3 to 4 days after insertion. Clients are instructed to clean the pin sites gently with a mild antiseptic solution as needed. A dry crust will eventually form around the pins, which is
Figure 3. A. A modified external fixation system useful for commi· nuted fractures of the distal femur. Note the double connecting bars placed laterally and the curved connecting bar extending to the medial aspect of the stifle joint. The external fixation device should be used in support of an 1M pin whenever possible. II/ustration continued on opposite page
FRACTURES OF THE FEMUR
157
Figure 3 (Continued). B. A more elaborate fixator design useful for larger dogs with comminuted fractures of the distal femur. Dual curved connecting bars are connected to a medial connecting bar to provide maximum stabilization.
left undisturbed. The fixator should be bandaged to protect it and the surrounding environment. One week after surgery, the wound is examined and the fixator adjusted or tightened if necessary. Rechecks are scheduled every 2 to 3 weeks thereafter depending on the anticipated rate of healing and stability of the fracture repair. In stable repairs in young animals, the fixator is often removed after 3 to 4 weeks and the intramedullary fixation left in place. Longer periods will be necessary in older animals and in those with less stable fractures. Staged disassembly of the device results in gradual transfer of stress to the bone and remaining fixation devices. It can stimulate bone union and should be considered in animals with radiographic evidence of delayed union. Careful judgment is required in these cases, since destabilization can result in collapse of the fracture. The animal should have good use of the limb, complete healing of the soft tissues, and some evidence of callus production before removal of any fixation devices. COMPLICATIONS
Most complications can be avoided by realizing the indications for and limitations of ESF. Because of the regional anatomy, ESF of femoral
158
WHITEHAIR & VASSEUR
fractures is generally limited to unilateral frame designs. Unilateral frames cannot be expected to bear the brunt of weight bearing and should assume a supportive role to intramedullary fixation devices. As an adjunct to internal fixation of the previously described fracture types, ESF works well. Use of threaded pins and placement using slowspeed power drilling increases the pullout strength and durability of the fixation pins. Complications generally occur when ESF devices are applied to very unstable fractures and are expected to provide most of the stability. Of particular concern are comminuted fractures with defects involving the medial cortex. The medial cortex is subjected to compressive loading and functions as a load-bearing buttress. Fractures in which the medial buttress cannot be reconstructed should be managed with plate fixation whenever possible. The recent development of tie-in configurations and contoured connecting bars has extended the indications of ESF in femoral fractures. Complications can be minimized by careful case selection, adherence to proper methods of surgical technique and fixator application, and conscientious aftercare and client communication. SUMMARY
The most common indications for the use of ESF in femoral fractures are closed transverse, short oblique, and minimally comminuted fractures in the central one third of the bone. External skeletal fixation is usually used in combination with 1M pins and wiring techniques. During the process of open reduction and internal fixation, the surgeon should strive for accurate anatomic alignment and stability at the fracture site. The fixator is applied after the internal fixation is in place and the surgical wound is closed. The number of fixation pins placed in each fracture fragment depends on the type of fracture and the stability gained by internal fixation. Partially threaded fixation pins are recommended. They are inserted through skin stab incisions with low-speed power equipment. Recent modifications of the Type la fixator may increase fixator rigidity. Important postoperative concerns include exercise restriction, pin tract care, and protection of the fixator from the environment. Complications associated with ESF can be minimized by realizing its indications and limitations. References 1. Arnoczky SP, Wilson JW, Schwarz PO: Fractures and fracture biology. In Slatter OH (ed): Textbook of Small Animal Surgery. Philadelphia, WB Saunders, 1985, p 1939 2. Aron ON: External skeletal fixation. Vet Med Rep 1:181, 1989
3. Aron ON, Foutz TL, Keller WG, et al: Experimental and clinical experience with an 1M pin external skeletal fixator tie-in configuration. J Comp Orthop Traumatol 4:8&94, 1991.
FRACTURES OF THE FEMUR
159
4. Aron ON, Toombs JP: Updated principles of external skeletal fixation. Comp Cont Ed Pract Vet 6:845, 1984 5. Bennett RA, Egger EL, Histand M, et al: Comparison of the strength and holding power of 4 pin designs for use with half pin (type I) external skeletal fixation. Vet Surg 16:207, 1987 6. Brinker WO, Piermattei DL, Flo GL: Fractures of the femur and patella. In Brinker WO, Piermattei DL, Flo GL (eds): Handbook of Small Animal Clinical Orthopedics and Fracture Treatment. Philadelphia, WB Saunders, 1983, p 75 7. Dallman MJ, Martin RA, Self BP, et al: Rotational strength of double-pinning techniques in repair of transverse fractures in femurs of dogs. Am J Vet Res 51:123, 1990 8. DeAngelis MP: Fractures of the femur. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery. Philadelphia, Lea & Febiger, 1975, p 453 9. Egger EL: Static strength evaluation of six external skeletal fixation configurations. Vet Surg 12:130, 1983 10. Egger EL, Runyon CL, Rigg DL: Use of the type I double connecting bar configuration of external skeletal fixation on long bone fractures in dogs: A review of 10 cases. J Am Anim Hosp Assoc 22:57,1986 11. Evans HE, Christensen GE: The spinal nerves. In Miller's Anatomy of the Dog, ed 2. Philadelphia, WB Saunders, 1979, p 972 12. Fanton JW, Blass CE, Withrow SJ: Sciatic nerve injury as a complication of intramedullary pin fixation of femoral fractures. JAm Anim Hosp Assoc 19:687, 1983 13. Hunt JM, Aitken ML, Denny HR, et al: The complications of diaphyseal fractures in dogs: A review of 100 cases. J Small Anim Pract 21:103, 1980 14. Kaderly RE, Anderson WD, Anderson BG: Extraosseous vascular supply to the mature dog's coxofemoral joint. Am J Vet Res 43:1208, 1982 15. Klause SE, Schwarz PO, Egger EL, et al: A modification of the unilateral type I external skeletal fixator configuration for primary and secondary support of supracondylar humeral and femoral fractures. Vet Comp Orthop Traumatol 3:130, 1990 16. Milton JL, Newman ME: Fractures of the femur. In Slatter DH (ed): Textbook of Small Animal Surgery. Philadelphia, WB Saunders, 1985, p 2180 17. Nordin M, Frankel VH: Biomechanics of bone. In Basic Biomechanics of the Musculoskeletal System. Philadelphia, Lea & Febiger, 1989, p 3 18. Palmer RH, Aron ON, Purington PT: Relationship of femoral intramedullary pins to the sciatic nerve and gluteal muscles after retrograde and normograde insertion. Vet Surg 17:65, 1988 19. Piermattei DL, Greeley RG: The hindlimb. In An Atlas of Surgical Approaches to the Bones of the Dog and Cat, ed 2. Philadelphia, WB Saunders, 1979, p 162 20. Rhinelander FW: Blood supply of healing long-bones. In Newton CD, Nunamaker OM (eds): Textbook of Small Animal Orthopaedics. Philadelphia, JB Lippincott, 1985, p 39 21. Richardson DC: Fracture first aid: The open (compound) fracture. In Slatter DH (ed): Textbook of Small Animal Surgery. Philadelphia, WB Saunders, 1985, p 1945 22. Vasseur PB, Paul HA, Crumley L: Evaluation of fixation devices for prevention of rotation in transverse fractures of the canine femoral shaft: An in vitro study. Am J Vet Res 45:1504, 1984 23. Vaughan LC: Complications associated with the internal fixation of fractures in dogs. J Small Anim Pract 16:415, 1975
Address reprint requests to Philip B. Vasseur, DVM Department of Veterinary Surgery University of California School of Veterinary Medicine Davis, CA 95616
