Description of and complications associated with reinforced, free-form external skeletal fixation for treatment of appendicular fractures in cats: 46 cases (2010–2019)

Spencer D. Yeh From the Department of Surgery, Angell Animal Medical Center, Boston, MA 02130

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Nicholas J. Trout From the Department of Surgery, Angell Animal Medical Center, Boston, MA 02130

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Deborah A. Keys Keys Veterinary Medical Statistical Consulting, Athens, GA 30606

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Abstract

OBJECTIVE

To describe a modified technique for reinforced, free-form external skeletal fixation (rFF-ESF) of appendicular fractures in cats and identify factors associated with development of complications.

ANIMALS

46 cats with fractures repaired with rFF-ESF at Angell Animal Medical Center between 2010 and 2019.

PROCEDURES

Medical records were reviewed for information on signalment, affected bone, fracture location and orientation, degree of comminution, severity (open vs closed), fixator type, number of fixation pins, use of an intramedullary pin (yes vs no), surgeon experience (staff surgeon vs surgical resident), anesthesia time, surgery time, perioperative antimicrobial administration, concurrent surgical procedures, intraoperative complications, postoperative alignment, whether fixator destabilization was performed, and time to complete fixator removal. Postoperative complications were recorded.

RESULTS

43 of the 46 (93%) cats had a successful outcome, with a median time to complete fixator removal of 8 weeks (range, 3 to 61 weeks). Twelve of the 46 (26%) cats had major (n = 3) or minor (9) complications. In univariable analyses, 4 factors were significantly associated with development of postoperative complications: body weight (OR for each 1-kg increase in weight, 1.8), tibial fracture (vs fracture of any other long bone; OR, 16), use of a type 2 fixator (vs a type 1 fixator; OR, 11), and use of destabilization (vs no destabilization; 7).

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that rFF-ESF can be successfully used to stabilize a variety of appendicular fractures in cats. Further studies are required to compare rFF-ESF with other fracture fixation methods.

Abstract

OBJECTIVE

To describe a modified technique for reinforced, free-form external skeletal fixation (rFF-ESF) of appendicular fractures in cats and identify factors associated with development of complications.

ANIMALS

46 cats with fractures repaired with rFF-ESF at Angell Animal Medical Center between 2010 and 2019.

PROCEDURES

Medical records were reviewed for information on signalment, affected bone, fracture location and orientation, degree of comminution, severity (open vs closed), fixator type, number of fixation pins, use of an intramedullary pin (yes vs no), surgeon experience (staff surgeon vs surgical resident), anesthesia time, surgery time, perioperative antimicrobial administration, concurrent surgical procedures, intraoperative complications, postoperative alignment, whether fixator destabilization was performed, and time to complete fixator removal. Postoperative complications were recorded.

RESULTS

43 of the 46 (93%) cats had a successful outcome, with a median time to complete fixator removal of 8 weeks (range, 3 to 61 weeks). Twelve of the 46 (26%) cats had major (n = 3) or minor (9) complications. In univariable analyses, 4 factors were significantly associated with development of postoperative complications: body weight (OR for each 1-kg increase in weight, 1.8), tibial fracture (vs fracture of any other long bone; OR, 16), use of a type 2 fixator (vs a type 1 fixator; OR, 11), and use of destabilization (vs no destabilization; 7).

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that rFF-ESF can be successfully used to stabilize a variety of appendicular fractures in cats. Further studies are required to compare rFF-ESF with other fracture fixation methods.

Introduction

When used for fracture repair, ESF preserves the fracture hematoma and local blood supply, meaning that it may represent a more biological approach than open reduction with internal fixation, and ESF is frequently used to stabilize fractures and luxations in dogs and cats.1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16 However, the complication rate following ESF of fractures in cats reportedly ranges from 19% to 50%, with the most common complications consisting of pin tract discharge, pin loosening or breakage, infection, and implant failure.3,4,5 Thus, use of ESF may necessitate a higher number of recheck examinations and longer duration of follow-up than does open reduction with internal fixation.3

External skeletal fixators can be constructed with clamps to connect fixation pins inserted in bone fragments to an external metal or carbon fiber frame2,17 or by anchoring fixation pins in external PMMA, epoxy, or acrylic columns in a free-form manner.1,4,8,9,10,11,16 Free-form external skeletal fixators allow more flexibility in construct formation, but some surgeons limit their use to smaller dogs and cats because of concerns that the PMMA, epoxy, or acrylic columns may be unable to resist forces associated with regular activity in larger patients.1 In appropriately sized patients, however, free-form external skeletal fixators with PMMA, epoxy, or acrylic columns have been shown to be mechanically comparable to fixators with carbon fiber, steel, or titanium connecting bars.18,19,20,21,22,23,24,25,26,27

Fixation pins traditionally extend several centimeters into PMMA columns and may be bent, filed, or knurled to increase friction at the pin-PMMA interface.19,23 Alternatively, the fixation pins can be bent and bound together with orthopedic wire to create a column that is then encased in PMMA. There are several benefits to this modified technique for fixator construction. First, the fixation pin–orthopedic wire construct provides some degree of fracture stabilization prior to application of PMMA. Second, the fixation pins span the length of the PMMA column, decreasing the chance that the pins will pull out of the PMMA. Third, incorporating the pins in the PMMA column adds strength to the column, similar to the use of reinforcing bars in concrete. Finally, alterations can be made to the fixation pin–orthopedic wire construct prior to PMMA application to improve alignment and apposition of fracture fragments. This is especially helpful in instances when fluoroscopy is not available to assess fracture alignment intraoperatively.

To the authors' knowledge, there have been no published studies regarding the use of this particular method of rFF-ESF in cats. The purpose of the study reported here, therefore, was to describe the use of rFF-ESF for treatment of appendicular fractures in cats and identify factors associated with the development of complications. We hypothesized that rFF-ESF could be successfully used to stabilize a variety of appendicular fractures in cats and would have outcome and complication rates comparable to those reported for other methods of ESF.

Materials and Methods

Cats

Medical records of the Angell Animal Medical Center were searched to identify cats in which appendicular fractures had been repaired with rFF-ESF between January 1, 2010, and December 31, 2019. Cats were eligible for inclusion if the medical record was complete, perioperative complications were recorded, and fracture healing was documented.28 Cats with incomplete follow-up information were excluded.

For each cat included in the study, information obtained from the medical record included breed, sex, spay-neuter status, and age, weight, and body condition score at the time of initial examination. Fracture information included affected bone, degree of comminution, severity (open vs closed), location, and orientation, as determined from the medical record and preoperative radiographs. Fracture location was classified as proximal (proximal metaphysis and proximal third of the diaphysis), middle (middle third of the diaphysis), or distal (distal third of the diaphysis and distal metaphysis). Data regarding specifics of fracture fixation included fixator type, total number of fixation pins, numbers of pins in the proximal and distal segments, whether an intramedullary pin was placed, whether the surgery was performed by a staff surgeon or surgical resident, duration of anesthesia, surgical time, use of perioperative antimicrobials, concurrent surgical procedures, and intraoperative complications. Data regarding postoperative alignment and fracture gap were obtained from postoperative radiographs. Postoperative alignment was scored as poor (moderate or severe varus, valgus, procurvatum, or recurvatum), good (mild varus, valgus, procurvatum, or recurvatum), or excellent (no angulation in the sagittal or frontal plane). Data regarding postoperative destabilization and time to complete fixator removal were obtained from medical records and recheck radiographs.

A successful outcome was defined as complete radiographic healing of the fracture without external fixator failure in combination with normal findings with regards to use of the limb, gait, and results of palpation. Postoperative complications were recorded and classified as major if additional surgical or medical treatment was required to resolve the complication or minor if no additional surgical or medical treatment was required to resolve the complication.28 Complications that resolved without any intervention other than construct destabilization, construct removal, or monitoring with serial radiography were classified as minor.

Surgical technique

Fractures were reduced and fixation and intramedullary pins were placed as described (Figure 1).2,17 Smooth Kirschner wires ranging from 0.045 to 0.062 inches in diameter were used as fixation pins and were inserted without predrilling. For fractures with short distal or proximal bone fragments, fixation pins were driven in the same sagittal plane but in divergent coronal planes. After fixation pins were inserted and the fracture was reduced, the fixation pins and intramedullary pin (if used) were bent with a 3-prong dental Aderer pliersa to form a continuous linear column for a type 1 (unilateral, uniplanar) or 2 continuous linear columns for a type 2 (bilateral, uniplanar) ESF construct. No other alterations (eg, filing or knurling) of the pins was performed. For transarticular constructs, the fixation pins were also bent at the level of the joint to reflect an appropriate standing angle. Orthopedic wire (22 or 24 gauge) was then tightened around the pin column to lash the separate fixation pins together, and the pins were cut to the length of the column (Figure 2). Radiographs were then obtained to assess fracture alignment, and once alignment was considered acceptable, PMMAb was molded over the pin column as a non-sterile procedure. As healing progressed, if destabilization was required, the IM pin was cut and removed (Figure 3). In addition, fixation pins could be cut on either or both sides of the bone but were not removed from the bone until the complete construct was removed.

Figure 1
Figure 1

Photographs of the right femur from a cat with a simulated mid-diaphyseal, short-oblique fracture illustrating a method for placement of an rFF-ESF construct. A—An intramedullary pin and 4 bicortical fixation pins (2 proximal and 2 distal to the fracture) have been inserted. B—A 3-prong dental Aderer pliers has been used to bend the intramedullary and fixation pins into a single column while the fracture was held in apposition with bone reduction forceps.

Citation: Journal of the American Veterinary Medical Association 259, 5; 10.2460/javma.259.5.510

Figure 2
Figure 2

Photographs illustrating additional steps in the placement of an rFF-ESF construct. A—The intramedullary and fixation pins have been bound together with 22-gauge orthopedic wire. In a clinical case, postoperative radiography would be performed at this stage to assess fracture alignment and reduction. If necessary, alignment and reduction could be improved by bending the fixation pins. B—Once alignment and reduction were considered acceptable, PMMA would be applied to the bent fixation pins in a nonsterile manner.

Citation: Journal of the American Veterinary Medical Association 259, 5; 10.2460/javma.259.5.510

Figure 3
Figure 3

Photographs illustrating methods for destabilization of an rFF-ESF construct during the fracture healing process. A—The intramedullary pin, if one has been used, can be cut and removed. B—The fixation pins can be cut on one or both sides of the bone (asterisks). Typically, the fixation pins would be left in place until the time of construct removal.

Citation: Journal of the American Veterinary Medical Association 259, 5; 10.2460/javma.259.5.510

Statistical analysis

Descriptive statistics were generated. Univariable logistic regression was used to assess whether the following factors were associated with the development of postoperative complications: breed, sex, spay-neuter status, age at the time of initial examination, weight, body condition score, fracture description, fixator type, total number of fixation pins, numbers of pins in the proximal and distal segments, whether an intramedullary pin was placed, whether the surgery was performed by a staff surgeon or surgical resident, duration of anesthesia, surgical time, use of perioperative antimicrobials, concurrent surgical procedures, intra-operative complications, postoperative alignment, postoperative destabilization, and time to complete fixator removal. P values calculated by means of log-likelihood ratio tests were reported. For the factors “fracture location,” “fracture orientation,” and “intraoperative complications,” quasi-separation was present because no postoperative complications were recorded for 1 category within each factor (ie, “proximal” for the factor “fracture location,” “spiral” for the factor “fracture orientation,” and “yes” for the factor “intraoperative complications”). As a result, these models did not converge, and Fisher exact tests were used instead. Odds ratios and 95% profile-likelihood CIs were reported for risk factors. All analyses were performed with commercially available software.c All tests were 2-sided, and values of P < 0.05 were considered significant.

Results

Medical records of 53 cats that had fractures stabilized with rFF-ESF during the study period were identified. However, 2 cats were excluded because follow-up radiographs were not available, and 5 cats were excluded because they had articular, juxta-articular, or Salter-Harris fractures. The remaining 46 cats were included in the study.

For the 46 cats included in the study, there were 32 domestic shorthairs, 4 domestic medium hairs, 3 domestic longhairs, 2 Maine Coons, 2 Ragdolls, 2 Siamese, and 1 Russian Blue. There were 27 males (17 neutered and 10 sexually intact) and 19 females (12 spayed and 7 sexually intact). Median age at the time of initial examination was 12.5 months (range, 6 to 132 months). Median weight was 4.1 kg (9.02 lb; range, 0.5 to 8.1 kg [1.1 to 17.8 lb]). Median body condition score was 5 on a scale from 1 to 9 (range, 3 to 8). Comorbidities consisted of a heart murmur (n = 5), tooth fractures (2), and pneumothorax, pulmonary contusions, digit avulsions and lacerations, heart failure, previous implant failure, incomplete acetabular fracture, hypovolemic shock, brachial plexus avulsion, and bilateral capital physeal fractures (1 each).

Affected bones consisted of the tibia (n = 25), femur (14), radius (3), and humerus (4). Fractures were located in the distal (n = 24), middle (17), and proximal (n = 5) aspects of the bone and were classified as closed (41) or open (5). Fracture orientation consisted of long oblique (n = 20), short oblique (13), transverse (7), spiral (5), and segmental (1). Fractures were further classified as simple (n = 18) or comminuted (28).

A type 1 (unilateral, uniplanar) external skeletal fixator was used in 18 cats, and a type 2 (bilateral, uniplanar) fixator was used in 28. Median total number of transfixation pins was 4 (range, 3 to 7), with a median of 2 pins (range, 1 to 4) in the proximal segment and a median of 2 pins (range, 1 to 3) in the distal segment. An intramedullary pin was placed and incorporated into the external skeletal fixator in 36 cats.

Intraoperative complications were recorded in 3 cats. In a cat with a left femoral, mid-diaphyseal fracture, the IM pin was inadvertently placed through the femoral head and neck; the pin was immediately removed. In a cat with a left proximal tibial fracture, the IM pin protruded past the proximal tibial physis, but its position was not altered. In a cat with a left tibial segmental fracture, a fixation pin in the proximal segment was in a suboptimal position and was immediately repositioned.

Mean and median surgical times were 55 and 45 minutes (range, 7 to 135 minutes), respectively; surgical times were not recorded in 9 cases. Mean and median total anesthetic times were 149 and 134.5 minutes (range, 105 to 242 minutes), respectively; anesthesia times were not recorded in 8 cases. Surgery was performed by a surgical resident in 28 cases and by a staff surgeon in 11; the surgeon was not recorded in the remaining 7 cases. Perioperative antimicrobials were administered in 34 cases and were not administered in 3; information was not available for the remaining 9 cases. Postoperative antimicrobials were administered in 20 cases and were not administered in 20 cases; information was not available for the remaining 6 cases. Postoperative alignment was determined to be excellent in 28 cases, good in 17, and poor in 1. Concurrent surgical procedures were performed in 12 cases and consisted of castration (n = 6), ovariohysterectomy (1), bone biopsy (1), bilateral femoral head and neck ostectomy (1), mass removal (1), wound exploration (1), and mandibular condylectomy (1).

Destabilization of the external fixator was performed in 13 cases. Destabilization was performed a median of 8 weeks (range, 4 to 11 weeks) after surgery in those cases in which single-stage destabilization was performed. Destabilization consisted of IM pin removal alone in 5 cases, removal of 2 fixation pins in 3 cases, concurrent IM pin removal and removal of 2 fixation pins in 2 cases, and IM pin removal followed by later removal of multiple fixation pins in 3 cases.

Forty-three of the 46 (93%) cats had complete fracture healing, with a median time from surgery to complete fixator removal of 8 weeks (range, 3 to 61 weeks; Figures 4 and 5). Overall, 12 of the 46 (26%) cats had postoperative complications. Nine of the 12 complications were minor and consisted of pin tract discharge (n = 2), premature pin loosening (2), pin breakage (1), delayed union (3), and malunion (1). The cat with a malunion initially had a distal tibial fracture and was noted to have a mild recurvatum deformity at the level of the fracture 4 weeks after fixator removal. The patient was ambulating without lameness and no further treatment was performed; therefore, this complication was classified as minor. The remaining 3 complications were classified as major. In a cat with a mid-diaphyseal, long-oblique tibial fracture, implant failure occurred as a result of fracture through a distal pin tract 7 weeks after surgery. Radiographic findings were consistent with osteomyelitis, and revision surgery was performed with placement of a bone plate and screws. Staphylococcus schleiferi was cultured from the pin site, and appropriate antimicrobial treatment was prescribed. The fracture subsequently healed without further issues. In a cat with a distal, short-oblique tibial fracture, refracture of the tibia at the original fracture site was noted 3 weeks after fixator removal 13 weeks after surgery. Revision surgery was performed with placement of a bone plate and screws. Finally, a cat with an open, distal, transverse tibial fracture developed necrosis of the distal portion of the limb 8 weeks after surgery, most likely as a result of vascular trauma, and the limb was subsequently amputated. The cat recovered without further complications.

Figure 4
Figure 4

Craniocaudal (A) and mediolateral (B) radiographic images obtained immediately after placement of an rFF-ESF construct in a cat with a mid-diaphy-seal, complete, transverse left femoral fracture. A type 1 (unilateral, uniplanar) fixator with an intramedullary pin has been placed. Radiographs were obtained prior to nonsterile application of PMMA.

Citation: Journal of the American Veterinary Medical Association 259, 5; 10.2460/javma.259.5.510

Figure 5
Figure 5

Craniocaudal (A) and mediolateral (B) radiographic images of the cat in Figure 4 obtained 6 weeks after surgery. Notice that immediately after surgery and prior to application of PMMA, 2 of the orthopedic wires were moved to prevent excessive bending of the intramedullary pin. Six weeks after surgery, there was good callus formation and bony bridging of the fracture site. The rFF-ESF construct was removed at this time without complications.

Citation: Journal of the American Veterinary Medical Association 259, 5; 10.2460/javma.259.5.510

On univariable analysis, 4 factors were significantly associated with development of postoperative complications: body weight, affected bone (tibia vs any other long bone), fixator type (type 1 vs type 2), and use of destabilization (yes vs no). For every 1-kg increase in body weight, the odds of having a complication increased by 80% (OR, 1.8; 95% CI, 1.2 to 3; P = 0.005). Complications developed in 11 of the 25 (44%) cats with tibial fractures but in only 1 of the 21 (4.8%) cats with fractures of the femur, radius, or humerus, and cats with tibial fractures were 16 times (95% CI, 3 to 304; P = 0.001) as likely to have a complication as were cats with fractures of other bones. Complications developed in 11 of the 28 (39%) cats with a type 2 fixator but in only 1 of the 18 (5.6%) cats with a type 1 fixator, and cats with a type 2 fixator were 11 times (95% CI, 2 to 212; P = 0.006) as likely to have a complication as were cats with a type 1 fixator. Finally, complications developed in 7 of the 13 (54%) cats in which destabilization was used but in only 5 of the 33 (15%) cats in which it was not used, and cats in which destabilization was performed were 7 times (95% CI, 2 to 30; P = 0.009) as likely to have a complication as were cats in which it was not performed.

Significant associations were not found between the following variables and development of postoperative complications: body condition score (P = 0.11), sex (P = 0.51), age (P = 0.07), spay-neuter status (P = 0.05), presence of comorbidities (P = 0.85), fracture location with respect to diaphysis (P = 0.39), fracture orientation (P = 0.55), fracture comminution (P = 0.23), open versus closed fracture (P = 0.09), anesthesia time (P = 0.66), surgical time (P = 0.93), surgical resident versus staff surgeon (P = 0.34), use of perioperative antimicrobials (P = 0.20), total number of fixation pins used (P = 0.404), number of pins in the proximal segment of bone (P = 0.81), number of pins in the distal segment of bone (P = 0.62), use of an intramedullary pin (P = 0.75), whether concurrent surgical procedures were performed (P > 0.99), intraoperative complications (P = 0.54), postoperative alignment (P = 0.76), use of postoperative antimicrobials (P = 0.49), and time to complete fixator removal (P = 0.19).

Discussion

In the present study, 43 of the 46 (93%) cats had a successful outcome, defined as complete radiographic healing of the fracture in combination with normal limb use and gait, with a median time to complete fixator removal of 8 weeks (range, 3 to 61 weeks). Twelve of the 46 (26%) cats had complications, which was similar to complication rates reported previously.3,4,5 We therefore accepted our hypotheses that rFF-ESF could be successfully used to stabilize a variety of appendicular fractures in cats and would have outcome and complication rates comparable to those reported for other methods of ESF.

The use of external skeletal fixators for fracture repair in cats poses unique challenges, compared with their use in dogs. In particular, cats generally appear to be less tolerant of external coaptation and external fixation devices than dogs, and anatomic characteristics unique to cats may make fixator application more difficult. In addition, the clamps and bars used with traditional external fixators can be relatively expensive, and the need for recheck examinations to ensure fixator integrity adds to the cost.

In contrast, many cats described in the present report required only a single recheck examination 6 to 8 weeks after surgery to assess function, confirm radiographic healing, and perform implant removal. In addition, the implants used (Kirschner wire, orthopedic wire, and nonsterile PMMA) were relatively inexpensive,1,21 potentially making this technique attractive for patients whose owners have financial constraints.

In our experience, application of rFF-ESF constructs can be somewhat easier than application of traditional FF-ESF constructs, in that application of FF-ESF constructs requires some method to temporarily stabilize the fracture fragments while PMMA, epoxy, or acrylic is applied to the fixation pins.1,2,11,16 Sterile application of PMMA requires an extra 12 to 15 minutes of surgical time for the curing process and precludes altering the construct if suboptimal alignment or apposition is noted on postoperative radiographs.2 With the rFF-ESF technique, bending the fixation pins and binding them together with orthopedic wire provides sufficient stabilization to allow postoperative radiographs to be obtained prior to PMMA application. Thus, if postoperative radio-graphs show suboptimal apposition or alignment of the fracture, changes can still be made to the construct prior to PMMA application.

The overall complication rate in the present study was 26% (12/46), which was comparable to rates in previous reports.3,4,5 Pin tract discharge developed in 2 of the 46 (4.3%) cats, which was similar to the findings of Beever et al,4 who reported that 9% of their study population developed this complication. Perry and Bruce3 reported a higher rate of pin tract infection (9/44 [20.4%]) but included only tibial fractures in their study population. In the present study, pin tract discharge was identified in only 1 of the 25 (4%) cats with tibial fractures, although there may have been underreporting of this complication because owners might not have reported pin tract discharge if it was minor or self-limiting. Taken together, however, findings of the present and previous studies3,4 suggest that pin tract discharge is relatively uncommon in cats undergoing ESF for treatment of appendicular fractures.

Pin loosening without associated infection was also reported in 2 of the 46 (4.3%) cats in the present study. All fixation pins used in these cats were smooth, and fixation pins were not always inserted in divergent directions. Thus, consideration should be given to using threaded pins and divergent pin placement to minimize fixation pin loosening.2,11,17 Poor bone healing (delayed union, malunion, and refracture) was reported in 5 of the 46 (10.9%) cats in the present study and represented the largest number of complications. All of these cases involved distal tibial fractures stabilized with a type 2 fixator that underwent destabilization.

There has been some controversy regarding the optimum stabilization method for tibial fractures in cats. Nolte et al29 found that type 2 fixators and tibial fractures were both risk factors for nonunion in cats. Similarly, Perry et al3 found that increasing complexity of ESF constructs in cats resulted in an increased complication rate, compared with bone plate stabilization of tibial fractures. Witte et al12 recorded 3 non-unions in 8 cats with distal tibial fractures stabilized with hybrid ESF constructs. In contrast, Beever et al4 did not report any complications associated with stabilization of tibial fractures with ESF in cats, although it was not clear whether type 1 or 2 constructs were used. Another large retrospective study26 also did not find an association between ESF and postoperative nonunion in cats with long bone fractures. Importantly, it should be noted that complications related to healing of tibial fractures in cats are not isolated to external fixation.30,31,32,33

In agreement with previous findings, our data showed that tibial fractures had a significantly higher complication rate than did fractures of the other long bones. In addition, type 2 ESF constructs had a higher complication rate than did type 1 constructs, and postoperative destabilization was identified as a risk factor for complications. However, the importance of these risk factors should be evaluated with caution owing to their large CIs. In the present study, all tibial fractures were stabilized with type 2 constructs and 12 of the 25 tibial fractures had postoperative destabilization performed. Because of the low number of complications, multivariable analyses could not be performed, and further studies on ESF construct type and postoperative destabilization protocols are needed.

In our study, we found that increasing weight was associated with an increased odds of complications. Heavier cats put more biomechanical stress on their long bones, potentially stressing fixator constructs more than lighter cats do. Similarly, Nolte et al29 found that weight was a predisposing factor for nonunion in cats, with a median weight of 4.2 kg (9.2 lb) in their control population and 5.0 kg (11.0 lb) in their case population. However, the authors were unable to assess the effects of age and weight separately and did not make specific recommendations on the basis of this finding. In contrast, Beever et al4 did not find any association between body weight and postoperative complications for fractures stabilized with external fixators in cats. The designs and objectives of these studies were different, making comparisons among them difficult. Still, results of the present study appear to support the findings of Nolte et al,29 and we recommend caution when considering whether to use rFF-ESF for fracture fixation in heavier cats.

There were several limitations to the present study. First and most importantly, the retrospective nature of the study may have introduced errors associated with selection bias, inconsistent or inaccurate record keeping, and lack of standardization related to case management. Second, the study population may not have been reflective of the feline population at large. Third, we were unable to perform multivariable analysis to determine which of the identified risk factors were most strongly associated with development of complications. Finally, there was no long-term follow-up included; therefore, there may have been unreported long-term complications.

In conclusion, we accept our hypothesis that rFFESF can be used successfully for treatment of appendicular fractures in cats. Caution should be exercised in heavier patients, which may be more prone to postoperative complications. In addition, type 2 ESF constructs may be inadequate for fixation of tibial fractures, and further studies are needed to assess the impact of postoperative destabilization.

Acknowledgments

No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.

Footnotes

a.

Miltex, Integra LifeSciences, Plainsboro, NJ.

b.

Jorgensen Laboratories Inc, Loveland, Colo.

c.

SAS, version 9.4, SAS Institute Inc, Cary, NC.

Abbreviations

ESF

External skeletal fixation

FF-ESF

Free-form external skeletal fixation

PMMA

Polymethyl methacrylate

rFF-ESF

Reinforced, free-form external skeletal fixation

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    Roch SP, Störk CK, Gemmill TJ, et al. Treatment of fractures of the tibial and/or fibular malleoli in 30 cats. Vet Rec 2009;165:165170.

  • 16.

    Aikawa T, Miyazaki Y, Saitoh Y, et al. Clinical outcomes of 119 miniature- and toy-breed dogs with 140 distal radial and ulnar fractures repaired with free-form multiplanar type II external skeletal fixation. Vet Surg 2019;48:938946.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17.

    Roe SC. External fixators, pins, nails and wires. In: Johnson AL, Houlton JE, Vannini R, eds. AO principles of fracture management in the dog and cat. Davos, Switzerland: AO Publishing, 2005;5257.

    • Search Google Scholar
    • Export Citation
  • 18.

    Tyagi SK, Aithal HP, Kinjavdekar P, et al. Comparative evaluation of in-vitro mechanical properties of different designs of epoxy-pin external skeletal fixation systems. Vet Surg 2014;43:355360.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19.

    Roe SC, Keo T. Epoxy putty for free-form external skeletal fixators. Vet Surg 1997;26:472477.

  • 20.

    Leitch BJ, Worth AJ. Mechanical testing of a steel-reinforced epoxy resin bar and clamp for external skeletal fixation of long-bone fractures in cats. N Z Vet J 2018;66:144153.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 21.

    Okrasinski EB, Pardo AD, Graehler RA. Biomechanical evaluation of acrylic external skeletal fixation in dogs and cats. J Am Vet Med Assoc 1991;199:15901593.

    • Search Google Scholar
    • Export Citation
  • 22.

    Amsellem PM, Egger EL, Wilson DL. Bending characteristics of polymethylmethacrylate columns, connecting bars of carbon fiber, titanium, and stainless steel used in external skeletal fixation and an acrylic interface. Vet Surg 2010;39:631637.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 23.

    Case JB, Egger EL. Evaluation of strength at the acrylic-pin interface for variably treated external skeletal fixator pins. Vet Surg 2011;40:211215.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 24.

    Shahar R. Relative stiffness and stress of type I and type II external fixators: acrylic versus stainless-steel connecting bars a theoretical approach. Vet Surg 2000;29:5969.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25.

    Shahar R. Evaluation of stiffness and stress of external fixators with curved acrylic connecting bars. Vet Comp Orthop Traumatol 2000;13:6572.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 26.

    Hicks DG, Pitts MJ, Bagley RS. In vitro biomechanical evaluations of screw-bar–polymethylmethacrylate and pin-polymethylmethacrylate internal fixation implants used to stabilize the vertebral motion unit of the fourth and fifth cervical vertebrae in vertebral column specimens from dogs. Am J Vet Res 2009;70:719726.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 27.

    Tyagi SK, Aithal HP, Kinjavdekar P, et al. In vitro biomechanical testing of different configurations of acrylic external skeletal fixator constructs. Vet Comp Orthop Traumatol 2015;28:227233.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 28.

    Cook JL, Evans R, Conzemius MG, et al. Proposed definitions and criteria for reporting time frame, outcome, and complications for clinical orthopedic studies in veterinary medicine. Vet Surg 2010;39:905908.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 29.

    Nolte DM, Fusco JV, Peterson ME. Incidence of and predis-posing factors for nonunion of fractures involving the appendicular skeleton in cats: 18 cases (1998–2002). J Am Vet Med Assoc 2005;226:7782.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 30.

    Rovesti GL. Delayed unions, nonunions, malunions. In: Johnson AL, Houlton JE, Vannini R, eds. AO principles of fracture management in the dog and cat. Davos, Switzerland: AO Publishing, 2005;395433.

    • Search Google Scholar
    • Export Citation
  • 31.

    McCartney WT, MacDonald BJ. Incidence of non-union in long bone fractures in 233 cats. Int J Appl Res Vet Med 2006;4:209212.

  • 32.

    Morris AP, Anderson AA, Barnes DM, et al. Plate failure by bending following tibial fracture stabilisation in 10 cats. J Small Anim Pract 2016;57:472478.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 33.

    Vallefuoco R, Le Pommellet H, Savin A, et al. Complications of appendicular fracture repair in cats and small dogs using locking compression plates. Vet Comp Orthop Traumatol 2016;29:4652.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Figure 1

    Photographs of the right femur from a cat with a simulated mid-diaphyseal, short-oblique fracture illustrating a method for placement of an rFF-ESF construct. A—An intramedullary pin and 4 bicortical fixation pins (2 proximal and 2 distal to the fracture) have been inserted. B—A 3-prong dental Aderer pliers has been used to bend the intramedullary and fixation pins into a single column while the fracture was held in apposition with bone reduction forceps.

  • Figure 2

    Photographs illustrating additional steps in the placement of an rFF-ESF construct. A—The intramedullary and fixation pins have been bound together with 22-gauge orthopedic wire. In a clinical case, postoperative radiography would be performed at this stage to assess fracture alignment and reduction. If necessary, alignment and reduction could be improved by bending the fixation pins. B—Once alignment and reduction were considered acceptable, PMMA would be applied to the bent fixation pins in a nonsterile manner.

  • Figure 3

    Photographs illustrating methods for destabilization of an rFF-ESF construct during the fracture healing process. A—The intramedullary pin, if one has been used, can be cut and removed. B—The fixation pins can be cut on one or both sides of the bone (asterisks). Typically, the fixation pins would be left in place until the time of construct removal.

  • Figure 4

    Craniocaudal (A) and mediolateral (B) radiographic images obtained immediately after placement of an rFF-ESF construct in a cat with a mid-diaphy-seal, complete, transverse left femoral fracture. A type 1 (unilateral, uniplanar) fixator with an intramedullary pin has been placed. Radiographs were obtained prior to nonsterile application of PMMA.

  • Figure 5

    Craniocaudal (A) and mediolateral (B) radiographic images of the cat in Figure 4 obtained 6 weeks after surgery. Notice that immediately after surgery and prior to application of PMMA, 2 of the orthopedic wires were moved to prevent excessive bending of the intramedullary pin. Six weeks after surgery, there was good callus formation and bony bridging of the fracture site. The rFF-ESF construct was removed at this time without complications.

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    Perry KL, Bruce M. Impact of fixation method on postoperative complication rates following surgical stabilization of diaphyseal tibial fractures in cats. Vet Comp Orthop Traumatol 2015;28:109115.

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    Gemmill TJ, Cave TA, Clements DN, et al. Treatment of canine and feline diaphyseal radial and tibial fractures with low-stiffness external skeletal fixation. J Small Anim Pract 2004;45:8591.

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    De La Puerta B, Emmerson T, Moores AP, et al. Epoxy putty external skeletal fixation for fractures of the four main meta-carpal and metatarsal bones in cats and dogs. Vet Comp Orthop Traumatol 2008;21:451456.

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    Fitzpatrick N, Riordan JO, Smith TJ, et al. Combined intramedullary and external skeletal fixation of metatarsal and metacarpal fractures in 12 dogs and 19 cats. Vet Surg 2011;40:10151022.

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    Ross JT, Matthiesen DT. The use of multiple pin and methylmethacrylate external skeletal fixation for the treatment of orthopaedic injuries in the dog and cat. Vet Comp Orthop Traumatol 1993;6:115121.

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    Worth AJ. Management of fractures of the long bones of eight cats using external skeletal fixation and a tied-in intra-medullary pin with a resin-acrylic bar. N Z Vet J 2007;55:191197.

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    Witte PG, Bush MA, Scott HW. Management of feline distal tibial fractures using a hybrid external skeletal fixator. J Small Anim Pract 2014;55:571578.

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  • 13.

    Kulendra E, Grierson J, Okushima S, et al. Evaluation of the transarticular external skeletal fixator for the treatment of tarsocrural instability in 32 cats. Vet Comp Orthop Trauma-tol 2011;24:320325.

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    Yardımcı C, Özak A, Önyay T, et al. Management of traumatic tarsal luxations with transarticular external fixation in cats. Vet Comp Orthop Traumatol 2016;29:232238.

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  • 15.

    Roch SP, Störk CK, Gemmill TJ, et al. Treatment of fractures of the tibial and/or fibular malleoli in 30 cats. Vet Rec 2009;165:165170.

  • 16.

    Aikawa T, Miyazaki Y, Saitoh Y, et al. Clinical outcomes of 119 miniature- and toy-breed dogs with 140 distal radial and ulnar fractures repaired with free-form multiplanar type II external skeletal fixation. Vet Surg 2019;48:938946.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17.

    Roe SC. External fixators, pins, nails and wires. In: Johnson AL, Houlton JE, Vannini R, eds. AO principles of fracture management in the dog and cat. Davos, Switzerland: AO Publishing, 2005;5257.

    • Search Google Scholar
    • Export Citation
  • 18.

    Tyagi SK, Aithal HP, Kinjavdekar P, et al. Comparative evaluation of in-vitro mechanical properties of different designs of epoxy-pin external skeletal fixation systems. Vet Surg 2014;43:355360.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19.

    Roe SC, Keo T. Epoxy putty for free-form external skeletal fixators. Vet Surg 1997;26:472477.

  • 20.

    Leitch BJ, Worth AJ. Mechanical testing of a steel-reinforced epoxy resin bar and clamp for external skeletal fixation of long-bone fractures in cats. N Z Vet J 2018;66:144153.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 21.

    Okrasinski EB, Pardo AD, Graehler RA. Biomechanical evaluation of acrylic external skeletal fixation in dogs and cats. J Am Vet Med Assoc 1991;199:15901593.

    • Search Google Scholar
    • Export Citation
  • 22.

    Amsellem PM, Egger EL, Wilson DL. Bending characteristics of polymethylmethacrylate columns, connecting bars of carbon fiber, titanium, and stainless steel used in external skeletal fixation and an acrylic interface. Vet Surg 2010;39:631637.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 23.

    Case JB, Egger EL. Evaluation of strength at the acrylic-pin interface for variably treated external skeletal fixator pins. Vet Surg 2011;40:211215.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 24.

    Shahar R. Relative stiffness and stress of type I and type II external fixators: acrylic versus stainless-steel connecting bars a theoretical approach. Vet Surg 2000;29:5969.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25.

    Shahar R. Evaluation of stiffness and stress of external fixators with curved acrylic connecting bars. Vet Comp Orthop Traumatol 2000;13:6572.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 26.

    Hicks DG, Pitts MJ, Bagley RS. In vitro biomechanical evaluations of screw-bar–polymethylmethacrylate and pin-polymethylmethacrylate internal fixation implants used to stabilize the vertebral motion unit of the fourth and fifth cervical vertebrae in vertebral column specimens from dogs. Am J Vet Res 2009;70:719726.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 27.

    Tyagi SK, Aithal HP, Kinjavdekar P, et al. In vitro biomechanical testing of different configurations of acrylic external skeletal fixator constructs. Vet Comp Orthop Traumatol 2015;28:227233.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 28.

    Cook JL, Evans R, Conzemius MG, et al. Proposed definitions and criteria for reporting time frame, outcome, and complications for clinical orthopedic studies in veterinary medicine. Vet Surg 2010;39:905908.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 29.

    Nolte DM, Fusco JV, Peterson ME. Incidence of and predis-posing factors for nonunion of fractures involving the appendicular skeleton in cats: 18 cases (1998–2002). J Am Vet Med Assoc 2005;226:7782.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 30.

    Rovesti GL. Delayed unions, nonunions, malunions. In: Johnson AL, Houlton JE, Vannini R, eds. AO principles of fracture management in the dog and cat. Davos, Switzerland: AO Publishing, 2005;395433.

    • Search Google Scholar
    • Export Citation
  • 31.

    McCartney WT, MacDonald BJ. Incidence of non-union in long bone fractures in 233 cats. Int J Appl Res Vet Med 2006;4:209212.

  • 32.

    Morris AP, Anderson AA, Barnes DM, et al. Plate failure by bending following tibial fracture stabilisation in 10 cats. J Small Anim Pract 2016;57:472478.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 33.

    Vallefuoco R, Le Pommellet H, Savin A, et al. Complications of appendicular fracture repair in cats and small dogs using locking compression plates. Vet Comp Orthop Traumatol 2016;29:4652.

    • Crossref
    • Search Google Scholar
    • Export Citation

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