Evaluation of transfixation casting for treatment of third metacarpal, third metatarsal, and phalangeal fractures in horses: 37 cases (1994–2004)

Timothy B. Lescun Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907-1248

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Scott R. McClure Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011-1250

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Michael P. Ward Department of Veterinary Integrated Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843-4461

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Christopher Downs Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211

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David A. Wilson Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211

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Stephen B. Adams Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907-1248

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Jan F. Hawkins Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907-1248

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Eric L. Reinertson Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011-1250

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Abstract

Objective—To evaluate clinical findings, complications, and outcome of horses and foals with third metacarpal, third metatarsal, or phalangeal fractures that were treated with transfixation casting.

Design—Retrospective case series.

Animals—29 adult horses and 8 foals with fractures of the third metacarpal or metatarsal bone or the proximal or middle phalanx.

Procedures—Medical records were reviewed, and follow-up information was obtained. Data were analyzed by use of logistic regression models for survival, fracture healing, return to intended use, pin loosening, pin hole lysis, and complications associated with pins.

Results—In 27 of 35 (77%) horses, the fracture healed and the horse survived, including 10 of 15 third metacarpal or metatarsal bone fractures, 11 of 12 proximal phalanx fractures, and 6 of 8 middle phalanx fractures. Four adult horses sustained a fracture through a pin hole. One horse sustained a pathologic unicortical fracture secondary to a pin hole infec-tion. Increasing body weight, fracture involving 2 joints, nondiaphyseal fracture location, and increasing duration until radiographic union were associated with horses not returning to their intended use. After adjusting for body weight, pin loosening was associated with di-aphyseal pin location, pin hole lysis was associated with number of days with a transfixation cast, and pin complications were associated with hand insertion of pins.

Conclusions and Clinical Relevance—Results indicated that transfixation casting can be successful in managing fractures distal to the carpus or tarsus in horses. This technique is most suitable for comminuted fractures of the proximal phalanx but can be used for third metacarpal, third metatarsal, or middle phalanx fractures, with or without internal fixation.

Abstract

Objective—To evaluate clinical findings, complications, and outcome of horses and foals with third metacarpal, third metatarsal, or phalangeal fractures that were treated with transfixation casting.

Design—Retrospective case series.

Animals—29 adult horses and 8 foals with fractures of the third metacarpal or metatarsal bone or the proximal or middle phalanx.

Procedures—Medical records were reviewed, and follow-up information was obtained. Data were analyzed by use of logistic regression models for survival, fracture healing, return to intended use, pin loosening, pin hole lysis, and complications associated with pins.

Results—In 27 of 35 (77%) horses, the fracture healed and the horse survived, including 10 of 15 third metacarpal or metatarsal bone fractures, 11 of 12 proximal phalanx fractures, and 6 of 8 middle phalanx fractures. Four adult horses sustained a fracture through a pin hole. One horse sustained a pathologic unicortical fracture secondary to a pin hole infec-tion. Increasing body weight, fracture involving 2 joints, nondiaphyseal fracture location, and increasing duration until radiographic union were associated with horses not returning to their intended use. After adjusting for body weight, pin loosening was associated with di-aphyseal pin location, pin hole lysis was associated with number of days with a transfixation cast, and pin complications were associated with hand insertion of pins.

Conclusions and Clinical Relevance—Results indicated that transfixation casting can be successful in managing fractures distal to the carpus or tarsus in horses. This technique is most suitable for comminuted fractures of the proximal phalanx but can be used for third metacarpal, third metatarsal, or middle phalanx fractures, with or without internal fixation.

Transfixation casting is a modified form of ESF that has been used to treat third metacarpal, third metatarsal, and phalangeal fractures in horses.1,2 External skeletal fixation is commonly used in humans and small animals to achieve fracture stabilization without invading the fracture site.1,3,4 This approach minimizes soft tissue and vascular disruption during fracture repair. It also decreases the potential for bacterial contamination at the fracture site and subsequent colonization of orthopedic implants. In horses, fractures are often attributable to high-energy injuries and can result in severe comminution of bone.5,6 In horses, the bones distal to the carpus or tarsus have little soft tissue coverage, compared with bones proximal to the carpus or tarsus. As a result, open fractures of the third metacarpal or metatarsal bones are common,6 and open fractures of the proximal phalanx may also occur.5,7 External skeletal fixation is indicated in horses for treatment of fractures distal to the carpus or tarsus that are not amenable to internal fixation, particularly comminuted or open fractures and fractures associated with considerable soft tissue trauma.1,2

Transfixation casting involves the insertion of transcortical pins proximal to the fracture site and their incorporation into a cast that encases the foot.1,2 The original use of transfixation casting was associated with multiple complications, and their use was not recommended in horses.8 However, results of another study9 indicated favorable outcomes with transfixation techniques. The walking cast, constructed by use of plaster of Paris, Steinmann pins, and a metal walking frame, had an overall success rate of 57% when used for treatment of fractures in horses and ponies.9

Two factors determine the stability of a transfixation cast, the strength of the construct and stability at the BPI. Compared with plaster of Paris, fiberglass casting material is stronger (approx 3-fold), has a faster curing rate, and has decreased weight.10–12 Despite these advantages, the strength of fiberglass casting tape and its attachment to the transcortical pin remain the weakest components of a transfixation cast construct when tested in axial loading.13 Incorporating pins into the cast as the casting material is applied to the limb is presently recommended as the most convenient method of cast-to-pin attachment without sacrificing construct strength.13 The optimum combination of pin size, pin location, and number of pins in the construction of a transfixation cast in horses is presently not known. However, some information is available from studies14–16 with cadavers. Recommendations on hole diameter, and therefore pin size, are that it should not be > 20% of the dorsopalmar bone diameter.15,17,18 The use of as many as three 6.35-mm transfixation pins in the radius of an adult horse has been recommended.15 Placement of pins divergent from the frontal plane reduces bone strength less than does parallel pin placement.16 The use of fiberglass casting material without a metal walking frame enables a divergent pin configuration to be used clinically. Most authors recommend that transfixation pins be placed as far distal in the cast as possible to reduce the likelihood of catastrophic fracture through the pin hole.2,9

The use of fiberglass casting material, appropriately designed centrally threaded positive-profile pins, and better knowledge of pin placement and cast-to-pin attachment methods has improved the acceptance of transfixation casting in horses.1,2,13,16,19,20 We believe reevaluation of this technique is warranted because application of the growing body of knowledge on transfixation casting should result in an improved success rate when managing fractures below the carpus or tarsus in horses. Presently, there are no comprehensive reports on the use of transfixation casting with modern materials and techniques for the treatment of fractures of the third metacarpal or metatarsal bone, proximal phalanx, or middle phalanx in horses. The purpose of the study reported here was to evaluate clinical findings, complications, and outcome of horses and foals with fractures of the distal aspects of limbs that were treated with transfixation casting. We hypothesized that the use of transfixation casting can be successful in managing fractures below the carpus or tarsus and that the outcome for these fractures would be better than previously reported for transfixation techniques in horses.

Criteria for Selection of Cases

The study included medical records and radiographs of horses evaluated at the Veterinary Teaching Hospitals at the School of Veterinary Medicine, Purdue University; the College of Veterinary Medicine, Iowa State University; and the Large Animal Hospital at the College of Veterinary Medicine, University of Missouri, with fractures of the third metacarpal or metatarsal bone, proximal phalanx, or middle phalanx that were treated with transfixation casting from December 1994 to December 2004.

Procedures

Information collected from the medical records including signalment, body weight, bone fractured, limb affected, emergency care given prior to referral, cause of the fracture, time from injury to hospital admission, initial status of the fracture (open or closed), status of the fracture at hospital admission (open or closed), fracture details (configuration and articular or nonarticular), results of bacterial culture and antimicrobial susceptibility testing, details of transfixation casting (number, size, type, and location of pins; methods of pin placement; and number and duration of transfixation casts), additional treatment details (additional orthopedic fixation used for treatment, number and duration of casts, and antimicrobial and anti-inflammatory treatments administered), details of pin loosening (pin location and time from insertion), radiographic findings (pin hole lysis, radiographic union, osteopenia), pin-associated complications, additional case complications, duration of hospitalization, and final outcome were recorded in a spreadsheeta for further analysis. Methods of pin placement included drilling, tapping, insertion, and insertion direction categories. Drilling was recorded as either 1 hole drilled or multiple holes drilled (sequentially increasing the size of drill bits) prior to each pin placement. Tapping pin holes for threaded pins was recorded as either hand tapped, power tapped, or not tapped. Pin insertion method was recorded as hand insertion or power insertion. Insertion direction was recorded as either lateral to medial or medial to lateral. Additional orthopedic fixation was recorded as none, lag screw fixation, dynamic compression plating, or additional transcortical pins placed distal to the fracture site.

Horses < 6 months old at the time of hospital admission were considered as foals. Final outcomes were obtained from the medical records and follow-up telephone conversations with owners, trainers, and referring veterinarians. Outcomes were categorized as survived and performed intended activities, survived and did not perform intended activities, died, or euthanatized. Horses and foals that died or were euthanatized for reasons not associated with a fracture were excluded from statistical analysis.

Statistical analysis—Logistic regressionb was used to assess associations between recorded clinical variables and case outcomes (survival, fracture healing, and horses returning to their intended use). Logistic regression was also used to assess variables associated with pin loosening, radiographic pin hole lysis, and complications associated with the use of transfixation casts. χ2 Analysis or a Fisher exact test (for frequency counts < 5 in any cell) was used to compare survival between specific categoric variables. A value of P < 0.05 was considered significant.

Results

Thirty-eight fractures in 29 horses and 8 foals were treated with transfixation casting. One horse treated for a comminuted fracture of a proximal phalanx developed a complete transverse fracture through the proximal pin hole in the third metacarpal bone, which was subsequently treated by use of full-limb transfixation casting. This fracture was included as a separate transfixation cast in the series reported here, except for analysis of survival. Location and type of fractures treated were summarized (Table 1). Fourteen fractures were nonarticular, 10 involved a single joint, and 14 involved 2 joints. Six transverse fractures were treated; including 5 fractures of third metacarpal or metatarsal bones (3 open) and 1 closed fracture of the proximal phalanx in a foal. There were 2 oblique fractures of the third metatarsal bone, 1 of which was open on hospital admission. One closed spiral fracture of a proximal phalanx was treated. Sixteen fractures were treated at the Veterinary Teaching Hospital, School of Veterinary Medicine, Purdue University; 13 fractures were treated at the Veterinary Teaching Hospital, College of Veterinary Medicine, Iowa State University; and 9 fractures were treated at the Large Animal Hospital, College of Veterinary Medicine, University of Missouri.

Table 1—

Distribution of fracture locations and types among 35 horses (27 adults and 8 foals) with fractures distal to the carpus or tarsus treated with transfixation casting. Horses that died or were euthanatized for reasons unrelated to their fracture or its treatment (n = 2) were excluded.

Fracture location and typeNo. of foalsNo. foals healedNo. of adultsNo. adults healedTotal horsesTotal healed
Third metacarpal bone4363106
  Open214263
  Comminuted226385
  Articular113041
Third metatarsal bone223254
  Open220022
  Comminuted113243
  Articular110011
Overall (MC3 and MT3)65951510
Proximal phalanx (forelimb)226587
  Open000000
  Comminuted225476
  Articular006565
Proximal phalanx (hind limb)004444
  Open001111
  Comminuted004444
  Articular004444
  Overall (proximal phalanx)221091211
  Middle phalanx (forelimb)006565
  Open000000
  Comminuted006565
  Articular006565
  Middle phalanx (hind limb)002121
  Open000000
  Comminuted002121
  Articular002121
Overall (middle phalanx)008686
All fractures
  Open435396
  Comminuted5526193124
  Articular2221152317
  Overall8727203527

MC3 = Third metacarpal bone. MT3 = Third metatarsal bone.

Median age and weight of horses and foals treated was 4 years (range, 1 day to 11 years) and 409 kg (900 lb; range, 45 to 660 kg [99 to 1,452 lb]), respectively. Twenty females, 13 sexually intact males, and 4 castrated males were treated. Breeds included Quarter Horses (n = 16), Standardbreds (5), Arabians (3), Hackney ponies (3), a mule, and a Thoroughbred. A specific breed was not identified in the medical record for 8 horses. In 7 horses, no emergency treatment was given prior to hospital admission; in 6 horses, a bandage was placed on the affected limb; and in 23 horses, the limb was immobilized in a heavy bandage capable of immobilization, a splinted bandage, or a cast for transportation. One third metacarpal bone fracture, in which a bandage and splint were placed for transportation, was closed at the time of initial emergency care but open at the time of hospital admission. The distal portion of the limb subsequently developed ischemic necrosis during treatment. None of the other 28 closed fractures became open during transport. Twentysix forelimbs and 11 hind limbs were treated. Ten fractures occurred while horses were on pasture, 6 were the result of a handling or training event, 3 occurred during athletic activity, 2 were the result of a kick by another horse, and 1 foal was stepped on by another horse. The cause of the remainder of the fractures was not known. The median time from injury to hospital admission was 12 hours (range, 0 to 336 hours).

Samples for bacterial culture and antimicrobial susceptibility testing were obtained from 5 of 10 open fractures, yielding bacterial growth in 2 fractures. Antimicrobial impregnated polymethylmethacrylate beads were placed adjacent to the fracture (3 fractures) or intravenous regional limb perfusion (2 fractures) was used at the time of initial transfixation casting in 5 open fractures. Systemic antimicrobial treatment was initiated at the time of transfixation casting in 35 horses. The combination of a β-lactam antimicrobial and an aminoglycoside was used initially in 30 of those horses, a β-lactam antimicrobial was used alone in 3 horses, a fluoroquinolone was used alone in 2 horses, and an aminoglycoside was used alone in 1 horse. Fourteen horses were treated with trimethoprim-sulfamethoxazole (30 mg/kg [13.6 mg/lb], PO, q 12 h) following discontinuation of parenteral antimicrobial treatment.

Treatment with antimicrobials was continued for a median of 13 days (range, 3 to 98 days) for closed fractures and 34 days (range, 6 to 86 days) for open fractures.

Eighteen fractures (in 17 horses) were treated with transfixation casting alone (Tables 2 and 3). In 20 horses, additional orthopedic fixation was used for treatment of the fracture. Two horses that died because of reasons unrelated to fracture treatment were excluded from the tables because of the inability to legitimately assess fracture healing in these horses. One third metatarsal bone fracture was initially repaired by use of dynamic compression plating. A transfixation cast was applied following failure of the initial repair and removal of implants. Two proximal phalanx fractures were initially repaired with lag screw fixation; however, both limbs were subsequently placed in a transfixation cast after complications associated with the initial repair developed. In 1 horse, osteomyelitis and failure of the repair developed after surgery, and in the second horse, a comminuted fracture of the bone occurred during anesthetic recovery. In 24 horses, ranging in weight from 136 kg to 660 kg (299 to 1,452 lb), pins of 6.3-mm (1/4-inch) shank diameter were used in the transfixation cast, and in 17 of those horses, centrally threaded positive-profile pinsc were used. In 9 horses, ranging in weight from 45 to 159 kg (99 to 350 lb), positive-profile pinsd of 4.8-mm (3/16-inch) shank diameter were used in the transfixation cast.

Table 2—

Distribution of treatment variables among the same horses as in Table 1.

TreatmentNo. of foalsNo. foals healedNo. of adultsNo. adults healedTotal horsesTotal healed
Fixation method
  TC alone4313101713
  TC + lag screws3396129
  TC + DCP002222
  TC + distal pins113243
Pin location
  MC3 or MT3 only4419162320
  Radius only325385
  Tibia only110011
  Combination003131
Pin type*
  Threaded8716122419
  Smooth008686
  Combination002222
Pin size (mm)
  4.8 only771087
  6.3 only1022182318
  8.7 or 9.5 only002222
  Combination002020
Number of pins
  28715132320
  3009595
  4002121
  5001111

In 1 horse, the pin type was not recorded.

TC = Transfixation casting. DCP = Dynamic compression plate.

See Table 1 for remainder of key.

Table 3—

Distribution of treatment variables among fracture locations in the same horses as in Table 1.

TreatmentMC3/MT3No. fractures healedP1No. fractures healedP2No. fractures healed
Fixation method
  TC alone536664
  TC + lag screws536511
  TC + DCP110011
  TC + distal pins430000
Pin location
  MC3/MT3 only33121186
  Radius only850000
  Tibia only110000
  Combination310000
Pin type*
  Threaded107111032
  Smooth211154
  Combination220000
Pin size (mm)
  4.8 only662200
  6.3 only7410964
  8.7 or 9.5 only000022
  Combination200000
Number of pins
  21196665
  3304421
  4002100
  5110000

P1 = Proximal phalanx. P2 = Middle phalanx.

See Tables 1 and 2 for remainder of key.

Transfixation casts were maintained for a median of 45 days (range, 4 to 150 days) in adult horses and 30 days (range, 14 to 76 days) in foals. The median number of transfixation casts used per horse was 2 (range, 1 to 7). In 29 horses, fractured limbs were placed in a standard cast for a median of 28 days (range, 6 to 90 days) following transfixation pin removal. Four horses did not have a standard cast placed following transfixation pin removal, and the limb was bandaged. Twelve transfixation casts did not have loose pins at the time of cast removal; the mean time of removal was 30.5 days. In 13 horses, 1 or more pins loosened prior to discontinuing transfixation casting and required removal or replacement. In 12 horses, loose pins were recorded at the time of discontinuing transfixation casting. Pin loosening occurred at the proximal pin only in 5 horses, at the distal pin only in 8 horses, at the second most proximal pin only in 2 horses, and in more than 1 pin in 10 horses. In all 10 horses in which multiple pins loosened, loosening included the proximal pin and the second most proximal pin. In adults in which threaded pins were used, the median time for the first pin to loosen was 40.5 days (range, 17 to 84 days). In adults in which smooth pins were used, loosening occurred in multiple pins in all cases in a median time of 30 days (range, 24 to 62 days). In foals, only threaded pins were used, and the median time for the first pin to loosen was 27.5 days (range, 14 to 44 days).

A discernible zone of bone lysis surrounding a transfixation pin was evident on radiographs a median of 30 days (range, 17 to 84 days) following pin placement. In 17 horses in which bone lysis was detected radiographically and medical records indicated pin loosening, bone lysis preceded pin loosening by a median of 9 days (range, 2 to 22 days) in adult horses (n = 15) and by 2 days in foals (2). For horses in which radiographs were available for review, there were no cases in which pin loosening occurred prior to radiographic evidence of bone lysis surrounding the pin.

Complications directly attributable to transfixation pins included fracture through a pin hole in 5 adult horses. Four of these were complete diaphyseal fractures at the most proximal pin hole. One fracture was a nondisplaced dorsal cortical fracture of the distal portion of the third metacarpal bone. This occurred secondary to severe bone lysis associated with osteomyelitis of the pin hole from which Escherichia coli was detected via bacterial culture. This horse had a new transfixation cast placed with transfixation pins in the radius; the initial and pathologic fractures healed, and the horse survived. Another horse sustained a complete third metacarpal bone diaphyseal fracture at the most proximal pin hole immediately after rearing up in the stall. In this horse, a new cast was placed with transfixation pins in the radius but the horse was euthanatized 77 days after the pin hole fracture occurred because of chronic severe laminitis in the contralateral limb. At the time of euthanasia, the initial proximal phalanx fracture had healed, and the pin hole fracture in the third metacarpal bone was stable and healing. The other 3 horses with pin hole fractures, 1 involving the radius (Figure 1), 1 involving the tibia, and 1 involving the third metatarsal bone, were euthanatized without further treatment. All of the pin hole fractures occurred in female horses. In 3 horses, smooth pins were used; in 1 horse, a positive-profile pin was used; and in 1 horse, the pin type was not recorded. All pins were 6.3 mm or larger and were located at the mid-diaphysis in the 4 horses in which a complete fracture occurred. In 2 horses, 2 pins were used; in 2 horses, 3 pins were used; and in 1 horse, 4 pins were used for transfixation casting. Complete pin hole fractures occurred on days 4, 13, 31, and 45 following pin placement, and horses weighed from 409 to 636 kg (900 to 1,400 lb) at admission. Three complete pin hole fractures (1 in a third metacarpal bone, 1 in a third metatarsal bone, and 1 in a radius) occurred prior to pin removal, and 1 complete pin hole fracture of the tibia occurred 3 days following pin removal while the horse was wearing a fulllimb cast. In 2 cases of complete pin hole fracture, pins were placed in a parallel orientation in the frontal plane, and in 2 cases, pins were placed divergent from the frontal plane. Four fractures had parallel pin orientation, and 30 fractures had a divergent pin orientation. In 2 horses, the pin hole was observed to be directly adjacent to the dorsal cortex on postoperative radiographs.

Figure 1—
Figure 1—

Craniocaudal (A) and lateromedial (B) radiographic views of the left radius in a horse after fracture through the proximal pin hole 13 days after transfixation casting for treatment of a third metacarpal bone fracture. Notice the mid-diaphyseal location of the proximal transfixation pin and the close proximity of the pin hole to the dorsal cortex of the radius.

Citation: Journal of the American Veterinary Medical Association 230, 9; 10.2460/javma.230.9.1340

Other pin-associated complications included 4 pin hole sequestra, 3 broken pins, and 2 bent pins. Hand insertion of pins was used in 2 fractures in which bone sequestration occurred; the method of pin insertion was not recorded for the other 2 fractures. Sequestra were removed and the pin hole was debrided at the time of pin removal in all cases. A single broken pin (6.3 mm threaded; proximal pin in a third metacarpal bone) was detected during removal 38 days following placement in 1 horse, and 2 broken pins (6.3 mm threaded; 2 most proximal pins in a third metacarpal bone) were detected during removal 60 days following placement in another horse. Both bent pins (9.5 mm smooth and 6.3 mm threaded; both proximal pin locations) were identified on postoperative radiographs and remained in place until transfixation casting was discontinued. Both bent pins were removed without complications.

Other complications were encountered in 14 horses or foals during fracture treatment and included 8 cases of laminitis, 3 cases of colitis, 2 cases of osteomyelitis, 2 cases of delayed fracture union, 2 cases of excessive tendon and ligament laxity following cast removal, and 1 case each of cecal impaction, ischemia of the distal portion of a limb, and biaxial proximal sesamoid fracture of a previously casted limb. Two horses were euthanatized because of severe laminitis in the contralateral limb. Both cases of osteomyelitis and both cases of delayed union were associated with open fractures. In 5 horses, more than 1 complication occurred during fracture treatment. Overall, 9 horses were euthanatized, 3 because of fracture through a pin hole, 2 because of laminitis, 2 because of severe colitis, 1 because of biaxial proximal sesamoid bone fracture, and 1 because of ischemic necrosis of the distal aspect of the limb.

Twenty-five horses had radiographic evidence of osteopenia distal to the transfixation pins. The earliest radiographic indication of osteopenia was a punctate or granular appearance of the proximal sesamoid bones, compared with initial radiographs. This was evident in adult horses a median of 46 days (range, 30 to 103 days) and foals a median of 40 days (range, 24 to 60 days) following initial transfixation casting. In 1 horse in which a transfixation cast was maintained for 150 days, severe osteopenia contributed to biaxial proximal sesamoid bone fractures, which resulted in euthanasia of the horse.

Overall, 28 (76%) horses survived and were discharged from the hospital. However, 1 pony was discharged subsequent to amputation of the distal aspect of a limb following unsuccessful management of osteomyelitis associated with an open fracture. Two horses died of colitis and were excluded from evaluation of successful fracture healing. Therefore, in 27 of 35 (77%) horses, the fracture healed and the horse survived. In adult horses and foals, the median time from injury until evidence of radiographic union was 72 days (range, 42 to 153 days) and 45 days (range, 24 to 68 days), respectively. Followup information for > 6 months was available for 24 of the surviving horses. Twelve horses (7 adults and 5 foals) survived and performed intended activities. Of these, 3 adults with articular fractures returned to intended breeding activities, and a foal with an articular fracture involving the tarsometatarsal joint was not lame and was in show training at 2 years of age. The other horses that performed their intended activities had nonarticular fractures. This included 1 Standardbred and 1 Thoroughbred foal, both with third metatarsal bone fractures that were not lame at the time they were sold as yearlings. Twelve horses survived and did not perform their intended activities. Nine of those horses had lameness associated with an articular fracture (7 horses with fractures involving 2 joints and 2 horses with fractures involving 1 joint). Two of those horses had lameness associated with laminitis, and 1 pony was not used as intended although no signs of discomfort were detected while in a prosthesis following amputation. Long-term follow-up was not available for 4 horses.

Overall, 21 (75%) adult horses and 7 (88%) foals survived after treatment. There were no differences in survival between forelimb or hind limb fractures, open or closed fractures, and articular or nonarticular fractures. Ten horses with third metacarpal or metatarsal bone fractures, 11 horses with proximal phalanx fractures, and 6 horses with middle phalanx fractures survived with the fracture healed. Twenty-two (92%) horses in which only 2 transfixation pins were placed above the fracture site and 7 horses in which more than 2 transfixation pins were placed above the fracture site survived; this difference was significant (P = 0.03). There were no differences in survival between horses with pins placed in only 1 bone or pins placed in more than 1 bone, horses with positive-profile or smooth pins, and horses in which transfixation casting alone or additional fixation methods were used. Four horses with open fractures had lag-screw fixation used in addition to transfixation casting, and local antimicrobial treatments were initiated at the time of surgery (regional limb perfusion [n = 2] and antimicrobial impregnated polymethylmethacrylate beads [2]), and 3 survived. Both horses in which bone plating was used in addition to transfixation casting had closed fractures, and both survived.

No significant associations were detected between the clinical variables evaluated and survival or fracture healing. Increasing body weight (OR, 0.997; 95% CI, 0.995 to 0.999; P = 0.009), fracture involving 2 joints (OR, 0.034; 95% CI, 0.003 to 0.391; P = 0.007), nondiaphyseal fracture location (OR, 0.167; 95% CI, 0.031 to 0.882; P = 0.035), and increasing duration until radiographic bone union (OR, 0.125; 95% CI, 0.019 to 0.805; P = 0.029) were associated with horses not performing their intended use. Estimation of weight- and age-adjusted risks could not be calculated because of sparse data for this outcome. Weight was found to be a more important confounder than age when evaluating pin loosening, pin hole lysis, and pin complications. After adjusting for weight and age, pin loosening was significantly increased with diaphyseal pin location (OR, 2.4; 95% CI, 1.135 to 5.102; P = 0.022), pin hole lysis significantly increased with increasing number of transfixation cast days (OR, 1.05; 95% CI, 1.007 to 1.090; P = 0.005), and pin complications were significantly decreased with power insertion of pins (OR, 0.06; 95% CI, 0.005 to 0.720; P = 0.026).

Discussion

Results of the study reported here indicated that transfixation casting can be a successful method of treating fractures of the third metacarpal or metatarsal bone, proximal phalanx, and middle phalanx in horses, with an overall success rate of 77%. Transfixation casting is indicated for treatment of comminuted fractures that cannot be reconstructed with internal fixation, open fractures, and fractures with extensive soft tissue injury. Our findings compared favorably with results of a report by Nemeth and Back9 in which a walking cast was used successfully in 69% of third metacarpal or metatarsal bone and proximal phalanx fractures. In that study, only 15 of the 56 horses treated were > 18 months old, and heavy horses placed considerable stress on the walking cast. Fiberglass casting material and centrally threaded positive-profile pins have eliminated the need for a walking bar and in the study reported here permitted successful treatment of horses weighing up to 660 kg.

Despite the good overall success rate in our study, secondary pin hole fractures are an important complication of transfixation casting. Kraus et al5 reported that 38% of horses with comminuted proximal phalanx fractures treated with an ESF device or transfixation casting developed third metacarpal or metatarsal bone fractures through a pin hole. In the study reported here, 4 horses (14%) had complete fracture through a pin hole, and 1 horse had a nondisplaced pathologic fracture secondary to a pin hole infection. Weight was found to be a confounding factor when pin complications were evaluated and may be a factor in the occurrence of pin hole fractures.1 All pin hole fractures occurred in adult female horses, 2 of 4 complete pin hole fractures were associated with smooth pins (in 8 fractures in which smooth pins were used), 2 of 4 fractures were associated with parallel pin placement (in 4 fractures in which pins were placed parallel), and all pin hole fractures occurred with pins that were ≥ 6.3 mm. We believe the most revealing observations from the 4 horses with complete pin hole fractures were that pin location was mid-diaphyseal, that the most proximal pin site in the cast was involved, and that in 2 horses the pin location was in close proximity to the dorsal cortex of the bone. Although power insertion of pins was found to be protective for pin complications, there were too few pin hole fractures to evaluate these risk factors using logistic regression. Nemeth and Back9 recommended that pins be placed as distal as possible and that casts be placed as proximal as possible on the limb to reduce the risk of pin hole fractures. Our findings support this recommendation. We also found that a diaphyseal pin location was associated with faster pin loosening, although the importance of this in relation to pin hole fractures is not clear. The axial and bending forces of the limb are transferred to the proximal pin in a transfixation cast to a greater extent than pins lower in the cast,21,22 and bone resorption around a proximal or a diaphyseal pin may be more rapid, resulting in a larger hole and weaker bone at this location. A combination of factors likely contributes to pin hole fractures, and despite a lower frequency reported in this study, compared with results of previous reports,5,9 further research efforts are warranted to define the associated risk factors and explore effective methods of prevention.

We presently recommend the use of 2 transcortical pins placed in the distal aspect of the metaphysis or distal aspect of the diaphysis of the supporting long bone for transfixation casting in horses. Horses in which 2 pins were used were significantly more likely to survive than horses in which more than 2 pins were used. Pin number was not associated with pin complications; however, placement of more than 2 pins results in the need for a more proximal, often mid-diaphyseal pin location. We suspect that diaphyseal pin location within the bone may be a more important factor than pin number itself when trying to minimize pin complications associated with transfixation casting. This was supported by the findings that complete pin hole fractures occurred at a mid-diaphyseal location and that a diaphyseal pin location was associated with an increased rate of pin loosening. Other authors have commented on their experience of observing complications associated with a diaphyseal pin location.1 However, evaluation of a larger number of horses is necessary to substantiate these observations.

Third metacarpal or metatarsal bone fractures account for approximately a third of all long bone fractures in horses.6 McClure et al6 reported an overall success rate of 67% when using primarily internal fixation techniques for the treatment of complete third metacarpal or metatarsal bone fractures. In the study reported here, 16 third metacarpal or metatarsal bone fractures were treated by use of transfixation casting. Of these, 12 were comminuted and 9 were open fractures. One pony underwent amputation following unsuccessful management of osteomyelitis in an open fracture of the third metacarpal bone. The fracture was initially managed with plate fixation. Three horses with open fractures of the third metacarpal bone were euthanatized because of severe colitis (n = 1), pin hole fracture (1), and laminitis (1). Osteomyelitis was not detected at the time these horses were euthanatized. The addition of a transcortical pin distal to the fracture site in 5 third metacarpal or metatarsal bones was used to overcome the inevitable palmar or plantar displacement of the distal fragments that occurs during application of a transfixation cast when the third metacarpal or metatarsal bone is unstable. A pin placed distally would be expected to change the biomechanics of load transfer through the transfixation cast. Although a 67% success rate in treating third metacarpal or metatarsal bone fractures is similar to that reported by McClure et al,6 the type of fractures treated by use of transfixation casting were those in which internal fixation was considered inappropriate because of severe comminution, contamination of open fractures, or severe soft tissue damage from the fracture. We recommend transfixation casting for this type of fracture. However, further studies and clinical experience are needed to more fully define when transfixation casting should be used for third metacarpal or metatarsal bone fractures.

Transfixation casting should be used when treating fractures of the proximal phalanx that are comminuted and not amenable to internal fixation. In our study, 10 proximal phalanx fractures in adult horses treated with transfixation casting were comminuted fractures of this type.5 In a study7 of 30 comminuted fractures of the proximal phalanx, 23% of horses without an intact strut of bone spanning from the proximal to the distal articular surfaces survived. In that study, an unacceptably high infection rate was associated with invasive surgical techniques, and all horses with open fractures that were treated were eventually euthanatized. In another study5 from the same hospital, 20 proximal phalanx fractures with severe comminution (ie, no intact strut) were treated. An ESF device was successfully used in 62% of horses, and transfixation casting was successfully used in 67% of horses. In the study reported here, a 92% successful outcome rate for proximal phalanx fractures compared favorably with results of those reports. A complete pin hole fracture of the third metacarpal bone and severe laminitis in the contralateral limb occurred in the 1 horse that was euthanatized in our study. The original proximal phalanx fracture had healed both radiographically and clinically at the time of euthanasia.

Transfixation casting does not appear to be more effective for treating comminuted middle phalanx fractures than double plate fixation.23 In the study reported here, all of the fractures treated with transfixation casting were comminuted. In a study24 of 47 horses with fractures of the middle phalanx, 38 had comminuted fractures, of which 55% survived. In a study23 in which 10 horses had comminuted fractures of the middle phalanx that were treated by use of double plate fixation, all horses survived. In our study, 9 horses with comminuted fractures of the middle phalanx were treated by use of transfixation casting. Three of those horses were euthanatized, 2 because of complications associated with treatment and 1 because of severe colitis. Three of the surviving horses eventually had ankylosis of the proximal interphalangeal joint, and 1 of those horses had ankylosis of the distal interphalangeal joint. The double-plating repair technique, reported in 1995,23 would have been considered by the surgeons choosing to use transfixation casting in the study reported here. Previously, horses with middle phalangeal fractures treated with transfixation casting may have been euthanatized without attempts at treatment if double plate fixation was considered unsuitable. Transfixation casting can play a role in supporting other repair or arthrodesis methods used in the treatment of highly comminuted middle phalanx fractures. Arthrodesis of the proximal interphalangeal joint at the time of repair of middle phalanx fractures is recommended because this joint will eventually ankylose or require arthrodesis in 50% of horses that are treated.

Combining internal fixation with transfixation casting does not appear to result in a detrimental effect. This approach was used in 14 horses in the case series reported here. Lag-screw fixation was used in 4 horses with open fractures, of which 3 survived. The ability of lag screws to improve bone alignment and joint surface congruity should be considered when using transfixation casting. In the 2 horses in which bone plating was combined with transfixation casting, the latter was used to decrease the load on a fracture that was not able to be optimally repaired. These fractures were closed and comminuted and healed successfully by use of this approach.

In our study, pin loosening occurred prior to discontinuation of transfixation casting in 68% of horses. Bone resorption at the BPI results from thermal and microstructural bone damage during pin placement and cyclic loading and infection over time.17 Bone resorption leads to pin instability and, eventually, pain.2,17 Consequently, lameness is a common clinical sign of pin loosening during transfixation casting and a major cause of patient morbidity.2 Our results suggest that bone lysis surrounding the pins seen on radiographs occurs prior to pin loosening. This finding is in agreement with results of an experimental study25 in dogs in which radiographic lucency was evident prior to gross pin loosening. Assessment of pin loosening during transfixation casting is difficult, and lameness is often the first clinical sign observed. Occasionally, loose pins will shift in relation to the surface of the cast or cause a crack in polymethylmethacrylate overlying the pin. In our study, the recorded time of pin loosening may have been an overestimate of the actual time of pin loosening. In addition, radiographs were not available for review at consistent time points after surgery. However, we recommend radiographic evaluation of pins in any horse that becomes lame during transfixation casting. Loose pins should be removed and replaced with a larger pin in the same hole or replaced by another pin in an additional hole, or the remaining pins should be left in place for continued transfixation casting. In our study, threaded pins remained stable 33% longer than smooth pins in adult horses. Threaded pins afford greater pull-out strength, allow less medial-to-lateral migration, and decrease pin loosening, compared with smooth pins.17,26

A diaphyseal pin location was found to be significantly associated with pin loosening when adjusted for the weight of the horses. Surgeons should attempt to minimize excessive heat generation and pin hole damage during placement of transcortical pins in dense equine bone because this can contribute to early pin loosening.19,27 Predrilling and tapping of pin holes, the use of power equipment at low speeds (< 300 rpm) during drilling and pin insertion, and thinner cortical bone all reduce heat generation during pin placement.17,27,28 It has been suggested that drilling sequentially larger holes when placing pins in adult horses will reduce heat transfer to the BPI.1 In our study, development of bone sequestration at the pin hole in 4 horses most likely resulted from excessive heat production and thermal bone damage during drilling, tapping, or pin insertion.1,2,19,27 Bone sequestration could result in a significantly larger pin hole and a weakened bone susceptible to fracture.1 In our study, the use of power insertion of pins was found to be protective against pin complications. When a pin is being placed in dense equine bone, the amount of torque required to insert a transcortical pin may be large. The ability of the surgeon to maintain pin alignment and fine control of the direction of the pin may be enhanced when power equipment is used. The use of pretapped holes, methods to minimize thermal and structural bone damage, and power equipment for placing positive-profile threaded transfixation pins is recommended to minimize pin loosening during transfixation casting in horses.

As important as pin placement and casting methods are for constructing an effective transfixation cast, postoperative management is equally important for a successful outcome. A significant reduction of bone strain occurs distal to transfixation pins, resulting in protection of fractures lacking axial stability from collapse in horses that are often fully weight-bearing during fracture healing.20–22 The primary disadvantages of this effective weight transfer are stress concentration at the BPI and a reduction of mechanical stimulus on bones distal to the pins. In our study, osteopenia and pin loosening both developed approximately 6 weeks after transfixation casting in 68% of horses, and the median time to radiographic union was approximately 10 weeks. Transfixation casting can prevent axial collapse and allow initial stabilization of highly comminuted fractures during fibrocallus formation. Increasing stress on a fractured bone is important for mineralization of the fibrocallus. Balancing the introduction of greater mechanical load on the healing bone, the level of patient comfort, the degree of osteopenia, the progression of pin loosening, and the risk of pin hole fracture or other related complications is essential when managing patients with transfixation casting. We recommend removing transfixation pins 6 to 8 weeks following injury if there is stability at the fracture site when manipulated, despite the likely absence of radiographic union, and placement of the limb in an appropriate cast for a further 3 to 4 weeks.

Transfixation casting offers several advantages, compared with internal fixation. Minimizing orthopedic implants and the amount of soft tissue disruption necessary for their application has the advantage of reducing the risk of infection at the fracture site.29,30 In our study, 2 horses with open fractures developed osteomyelitis, and the infection was not treated successfully in only 1 of those 2 horses. Another advantage of transfixation casting supported by results of our study was the consistent results achieved in a wide range of clinical situations. Although transfixation casting is a straightforward method of fracture management, use of transfixation casting was successful in managing a wide variety of fracture types and locations. None of the clinical variables evaluated significantly affected survival of horses treated or successful fracture healing. The primary determinant of success when using transfixation casting may be the avoidance of severe complications, such as pin hole fracture, rather than osteomyelitis or implant failure.29,31

Transfixation casting can be used successfully for managing fractures below the carpus or tarsus in horses, and the outcome for these fractures is better than previously reported using transfixation techniques.5,9 We recommend using 2 centrally threaded positiveprofile transcortical pins distally in the supporting long bone above the fracture site. Fiberglass casting material should be used to complete the transfixation cast. We routinely use polymethylmethacrylate to cover pin ends following cast application. Supplementing transfixation casting with internal fixation methods can be used to improve anatomic alignment of the fractured bone and joint congruity in cases of articular fracture. When development of arthritis appears inevitable, methods of arthrodesis should be used during fracture treatment to minimize the period of lameness after fracture. Radiographic healing may not be complete during transfixation casting, and removal of pins should be performed when fibrocallus has stabilized the fracture, usually 6 to 8 weeks following injury. Further studies should investigate risk factors associated with and methods of preventing pin hole fracture and pin loosening in horses because they contribute considerably to the mortality rate and morbidity, respectively, in horses treated with transfixation casting.

ABBREVIATIONS

ESF

External skeletal fixation

BPI

Bone-pin interface

OR

Odds ratio

CI

Confidence interval

a.

Microsoft Excel, version 10.0.6501, Microsoft Corp, Redmond, Wash.

b.

SPSS, version 11.5, SPSS Inc, Chicago, Ill.

c.

Centerface LA transfixation pin, part No. 21140, Imex Veterinary Inc, Longview, Tex.

d.

Centerface LA transfixation pin, part No. 2131LA, Imex Veterinary Inc, Longview, Tex.

References

  • 1

    Auer JA. Principles of fracture treatment. In:Auer JA, Stick JA, ed.Equine surgery. 3rd ed.St Louis: Saunders Elsevier, 2006;10001029.

    • Search Google Scholar
    • Export Citation
  • 2

    McClure SR, Honnas CM, Watkins JP. Managing equine fractures with external skeletal fixation. Compend Contin Educ Pract Vet 1995;17:10541062.

    • Search Google Scholar
    • Export Citation
  • 3

    Taljanovic MS, Jones MD, Ruth JT, et al. Fracture fixation. Radiographics 2003;23:15691590.

  • 4

    Lewis DD, Cross AR, Carmichael S, et al. Recent advances in external skeletal fixation. J Small Anim Pract 2001;42:103112.

  • 5

    Kraus BM, Richardson DW, Nunamaker DM, et al. Management of comminuted fractures of the proximal phalanx in horses: 64 cases (1983–2001). J Am Vet Med Assoc 2004;224:254263.

    • Search Google Scholar
    • Export Citation
  • 6

    McClure SR, Watkins JP, Glickman NW, et al. Complete fractures of the third metacarpal or metatarsal bone in horses: 25 cases (1980–1996). J Am Vet Med Assoc 1998;213:847850.

    • Search Google Scholar
    • Export Citation
  • 7

    Markel MD, Richardson DW, Nunamaker DM. Comminuted 1st phalanx fractures in 30 horses—surgical vs nonsurgical treatments. Vet Surg 1985;14:135140.

    • Search Google Scholar
    • Export Citation
  • 8

    Fackelman GE. Specific complications of fracture treatment. In:Auer JA, ed.Equine surgery. Philadelphia: WB Saunders Co, 1992;834844.

    • Search Google Scholar
    • Export Citation
  • 9

    Nemeth F, Back W. The use of the walking cast to repair fractures in horses and ponies. Equine Vet J 1991;23:3236.

  • 10

    Fessler JF, Turner AS. Methods of external coaptation. Vet Clin North Am Large Anim Pract 1983;5:311331.

  • 11

    Wilson DG & Vanderby R Jr. An evaluation of six synthetic casting materials: strength of cylinders in bending. Vet Surg 1995;24:5559.

  • 12

    Arighi M. Drains, dressings and external coaptation devices. In:Auer JA, ed.Equine surgery. Philadelphia: WB Saunders Co, 1992;159176.

    • Search Google Scholar
    • Export Citation
  • 13

    McClure SR, Watkins JP, Hogan HA. In vitro evaluation of four methods of attaching transfixation pins into a fiberglass cast for use in horses. Am J Vet Res 1996;57:10981101.

    • Search Google Scholar
    • Export Citation
  • 14

    Seltzer KL, Stover SM, Taylor KT, et al. The effect of hole diameter on the torsional mechanical properties of the equine third metacarpal bone. Vet Surg 1996;25:371375.

    • Search Google Scholar
    • Export Citation
  • 15

    Hopper SA, Schneider RK, Ratzlaff MH, et al. Effect of pin hole size and number on in vitro bone strength in the equine radius loaded in torsion. Am J Vet Res 1998;59:201204.

    • Search Google Scholar
    • Export Citation
  • 16

    McClure SR, Watkins JP, Ashman RB. In vitro comparison of the effect of parallel and divergent transfixation pins on breaking strength of equine third metacarpal bones. Am J Vet Res 1994;55:13271330.

    • Search Google Scholar
    • Export Citation
  • 17

    Clary EM, Roe SC. Enhancing external skeletal fixation pin performance—consideration of the pin-bone interface. Vet Comp Orthop Traumatol 1995;8:613.

    • Search Google Scholar
    • Export Citation
  • 18

    Nunamaker DM. On bone and fracture treatment in the horse, in Proceedings. 48th Annu Conv Am Assoc Equine Pract 2002;90101.

  • 19

    McClure SR, Hillberry BM, Fisher KE. In vitro comparison of metaphyseal and diaphyseal placement of centrally threaded, positive-profile transfixation pins in the equine third metacarpal bone. Am J Vet Res 2000;61:13041308.

    • Search Google Scholar
    • Export Citation
  • 20

    McClure SR, Watkins JP, Bronson DG, et al. In vitro comparison of the standard short limb cast and three configurations of short limb transfixation casts in equine forelimbs. Am J Vet Res 1994;55:13311334.

    • Search Google Scholar
    • Export Citation
  • 21

    Hopper SA, Schneider RK, Johnson CH, et al. In vitro comparison of transfixation and standard full-limb casts for prevention of displacement of a mid-diaphyseal third metacarpal osteotomy site in horses. Am J Vet Res 2000;61:16331635.

    • Search Google Scholar
    • Export Citation
  • 22

    Schneider RK, Ratzlaff MC, White KK, et al. Effect of three types of half-limb casts on in vitro bone strain recorded from the third metacarpal bone and proximal phalanx in equine cadaver limbs. Am J Vet Res 1998;59:11881193.

    • Search Google Scholar
    • Export Citation
  • 23

    Crabill MR, Watkins JP, Schneider RK, et al. Double-plate fixation of comminuted fractures of the second phalanx in horses: 10 cases (1985–1993). J Am Vet Med Assoc 1995;207:14581461.

    • Search Google Scholar
    • Export Citation
  • 24

    Colahan PT, Wheat JD, Meagher DM. Treatment of middle phalangeal fractures in the horse. J Am Vet Med Assoc 1981;178:11821185.

  • 25

    Pettine KA, Edmund YSC, Kelly PJ. Analysis of the external fixator pin-bone interface. Clin Orthop Relat Res 1993;293:1827.

  • 26

    Anderson MA, Mann FA, Wagner-Mann C, et al. A comparison of nonthreaded, enhanced threaded, and Ellis fixation pins used in type I external skeletal fixators in dogs. Vet Surg 1993;22:482489.

    • Search Google Scholar
    • Export Citation
  • 27

    Morisset S, McClure SR, Hillberry BM, et al. In vitro comparison of the use of two large-animal, centrally threaded, positive-profile transfixation pin designs in the equine third metacarpal bone. Am J Vet Res 2000;61:12981303.

    • Search Google Scholar
    • Export Citation
  • 28

    Toews AR, Bailey JV, Townsend HG, et al. Effect of feed rate and drill speed on temperatures in equine cortical bone. Am J Vet Res 1999;60:942944.

    • Search Google Scholar
    • Export Citation
  • 29

    Trotter G. Osteomyelitis. In:Nixon AJ, ed.Equine fracture repair. Philadelphia: WB Saunders Co, 1996;359366.

  • 30

    Schneider RK. Synovial and osseous infections. In:Auer JA, Stick JA, ed.Equine surgery. 3rd ed.St Louis: Saunders Elsevier, 2006;11211130.

    • Search Google Scholar
    • Export Citation
  • 31

    Nunamaker DM. Orthopedic implant failure. In:Nixon AJ, ed.Equine fracture repair. Philadelphia: WB Saunders Co, 1994;350353.

  • Figure 1—

    Craniocaudal (A) and lateromedial (B) radiographic views of the left radius in a horse after fracture through the proximal pin hole 13 days after transfixation casting for treatment of a third metacarpal bone fracture. Notice the mid-diaphyseal location of the proximal transfixation pin and the close proximity of the pin hole to the dorsal cortex of the radius.

  • 1

    Auer JA. Principles of fracture treatment. In:Auer JA, Stick JA, ed.Equine surgery. 3rd ed.St Louis: Saunders Elsevier, 2006;10001029.

    • Search Google Scholar
    • Export Citation
  • 2

    McClure SR, Honnas CM, Watkins JP. Managing equine fractures with external skeletal fixation. Compend Contin Educ Pract Vet 1995;17:10541062.

    • Search Google Scholar
    • Export Citation
  • 3

    Taljanovic MS, Jones MD, Ruth JT, et al. Fracture fixation. Radiographics 2003;23:15691590.

  • 4

    Lewis DD, Cross AR, Carmichael S, et al. Recent advances in external skeletal fixation. J Small Anim Pract 2001;42:103112.

  • 5

    Kraus BM, Richardson DW, Nunamaker DM, et al. Management of comminuted fractures of the proximal phalanx in horses: 64 cases (1983–2001). J Am Vet Med Assoc 2004;224:254263.

    • Search Google Scholar
    • Export Citation
  • 6

    McClure SR, Watkins JP, Glickman NW, et al. Complete fractures of the third metacarpal or metatarsal bone in horses: 25 cases (1980–1996). J Am Vet Med Assoc 1998;213:847850.

    • Search Google Scholar
    • Export Citation
  • 7

    Markel MD, Richardson DW, Nunamaker DM. Comminuted 1st phalanx fractures in 30 horses—surgical vs nonsurgical treatments. Vet Surg 1985;14:135140.

    • Search Google Scholar
    • Export Citation
  • 8

    Fackelman GE. Specific complications of fracture treatment. In:Auer JA, ed.Equine surgery. Philadelphia: WB Saunders Co, 1992;834844.

    • Search Google Scholar
    • Export Citation
  • 9

    Nemeth F, Back W. The use of the walking cast to repair fractures in horses and ponies. Equine Vet J 1991;23:3236.

  • 10

    Fessler JF, Turner AS. Methods of external coaptation. Vet Clin North Am Large Anim Pract 1983;5:311331.

  • 11

    Wilson DG & Vanderby R Jr. An evaluation of six synthetic casting materials: strength of cylinders in bending. Vet Surg 1995;24:5559.

  • 12

    Arighi M. Drains, dressings and external coaptation devices. In:Auer JA, ed.Equine surgery. Philadelphia: WB Saunders Co, 1992;159176.

    • Search Google Scholar
    • Export Citation
  • 13

    McClure SR, Watkins JP, Hogan HA. In vitro evaluation of four methods of attaching transfixation pins into a fiberglass cast for use in horses. Am J Vet Res 1996;57:10981101.

    • Search Google Scholar
    • Export Citation
  • 14

    Seltzer KL, Stover SM, Taylor KT, et al. The effect of hole diameter on the torsional mechanical properties of the equine third metacarpal bone. Vet Surg 1996;25:371375.

    • Search Google Scholar
    • Export Citation
  • 15

    Hopper SA, Schneider RK, Ratzlaff MH, et al. Effect of pin hole size and number on in vitro bone strength in the equine radius loaded in torsion. Am J Vet Res 1998;59:201204.

    • Search Google Scholar
    • Export Citation
  • 16

    McClure SR, Watkins JP, Ashman RB. In vitro comparison of the effect of parallel and divergent transfixation pins on breaking strength of equine third metacarpal bones. Am J Vet Res 1994;55:13271330.

    • Search Google Scholar
    • Export Citation
  • 17

    Clary EM, Roe SC. Enhancing external skeletal fixation pin performance—consideration of the pin-bone interface. Vet Comp Orthop Traumatol 1995;8:613.

    • Search Google Scholar
    • Export Citation
  • 18

    Nunamaker DM. On bone and fracture treatment in the horse, in Proceedings. 48th Annu Conv Am Assoc Equine Pract 2002;90101.

  • 19

    McClure SR, Hillberry BM, Fisher KE. In vitro comparison of metaphyseal and diaphyseal placement of centrally threaded, positive-profile transfixation pins in the equine third metacarpal bone. Am J Vet Res 2000;61:13041308.

    • Search Google Scholar
    • Export Citation
  • 20

    McClure SR, Watkins JP, Bronson DG, et al. In vitro comparison of the standard short limb cast and three configurations of short limb transfixation casts in equine forelimbs. Am J Vet Res 1994;55:13311334.

    • Search Google Scholar
    • Export Citation
  • 21

    Hopper SA, Schneider RK, Johnson CH, et al. In vitro comparison of transfixation and standard full-limb casts for prevention of displacement of a mid-diaphyseal third metacarpal osteotomy site in horses. Am J Vet Res 2000;61:16331635.

    • Search Google Scholar
    • Export Citation
  • 22

    Schneider RK, Ratzlaff MC, White KK, et al. Effect of three types of half-limb casts on in vitro bone strain recorded from the third metacarpal bone and proximal phalanx in equine cadaver limbs. Am J Vet Res 1998;59:11881193.

    • Search Google Scholar
    • Export Citation
  • 23

    Crabill MR, Watkins JP, Schneider RK, et al. Double-plate fixation of comminuted fractures of the second phalanx in horses: 10 cases (1985–1993). J Am Vet Med Assoc 1995;207:14581461.

    • Search Google Scholar
    • Export Citation
  • 24

    Colahan PT, Wheat JD, Meagher DM. Treatment of middle phalangeal fractures in the horse. J Am Vet Med Assoc 1981;178:11821185.

  • 25

    Pettine KA, Edmund YSC, Kelly PJ. Analysis of the external fixator pin-bone interface. Clin Orthop Relat Res 1993;293:1827.

  • 26

    Anderson MA, Mann FA, Wagner-Mann C, et al. A comparison of nonthreaded, enhanced threaded, and Ellis fixation pins used in type I external skeletal fixators in dogs. Vet Surg 1993;22:482489.

    • Search Google Scholar
    • Export Citation
  • 27

    Morisset S, McClure SR, Hillberry BM, et al. In vitro comparison of the use of two large-animal, centrally threaded, positive-profile transfixation pin designs in the equine third metacarpal bone. Am J Vet Res 2000;61:12981303.

    • Search Google Scholar
    • Export Citation
  • 28

    Toews AR, Bailey JV, Townsend HG, et al. Effect of feed rate and drill speed on temperatures in equine cortical bone. Am J Vet Res 1999;60:942944.

    • Search Google Scholar
    • Export Citation
  • 29

    Trotter G. Osteomyelitis. In:Nixon AJ, ed.Equine fracture repair. Philadelphia: WB Saunders Co, 1996;359366.

  • 30

    Schneider RK. Synovial and osseous infections. In:Auer JA, Stick JA, ed.Equine surgery. 3rd ed.St Louis: Saunders Elsevier, 2006;11211130.

    • Search Google Scholar
    • Export Citation
  • 31

    Nunamaker DM. Orthopedic implant failure. In:Nixon AJ, ed.Equine fracture repair. Philadelphia: WB Saunders Co, 1994;350353.

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