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Use of a Locking Compression Plate as an External Fixator for Repair of aTarsometatarsal Fracture in a Bald Eagle (Haliaeetus leucocephalus)Author(s): Ronald D. Montgomery, DVM, MS, Dipl ACVS, Elizabeth Crandall, BS, and Jamie R. Bellah,DVM, Dipl ACVSSource: Journal of Avian Medicine and Surgery, 25(2):119-125. 2011.Published By: Association of Avian VeterinariansDOI: http://dx.doi.org/10.1647/2009-016.1URL: http://www.bioone.org/doi/full/10.1647/2009-016.1

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Clinical Reports

Use of a Locking Compression Plate as an External Fixatorfor Repair of a Tarsometatarsal Fracture in a Bald Eagle

(Haliaeetus leucocephalus)

Ronald D. Montgomery, DVM, MS, Dipl ACVS, Elizabeth Crandall, BS, andJamie R. Bellah, DVM, Dipl ACVS

Abstract: We describe the successful treatment of a tarsometatarsal fracture in a mature bald

eagle (Haliaeetus leucocephalus) using a locking compression plate as an external fixator. The

anatomy of the area (inelastic dermis and minimal subcutaneous space) and the high forces

placed on a fracture at that site necessitated a unique approach to fixation. The unconventional

use of a locking compression plate as an external fixator was minimally invasive, well tolerated

by the eagle, and provided adequate stability in opposing fracture forces. This technique may

serve as a method of fixation for tarsometatarsal fractures in other large avian species.

Key words: fracture, external fixator, locking compression plate, avian, bald eagle, Haliaeetus

leucocephalus

Clinical Report

A mature, female bald eagle (Haliaeetus

leucocephalus) weighing 4.6 kg was presented to

the Auburn University Southeastern Raptor

Center (Auburn, AL, USA) for not flying, the

presence of blood on the head, and lice infesta-

tion. Abnormalities on physical examination were

a moderately thin body condition (body condition

score, 2 of 5), lice, blood in the oral cavity, a small

nondisplaced crack in the upper beak, and

swelling with deformity of the right tarsometa-

tarsal area. A small wound present at the

midlateral aspect of the right tarsometatarsal area

allowed partial visualization of a type II open

fracture. Instability was limited because of

swelling and the tight, inelastic nature of the

scaled dermis in that region. When at rest, the

bird was able to bear only minimal weight on the

affected limb, but it could place moderate weight

on the leg and grip with considerable force when

interacting with caregivers.

A blood sample was submitted for a complete

blood cell count and serum biochemical analysis,

and a fecal sample was submitted for flotation

(abnormalities were mild anemia and increased

aspartate aminotransferase and creatine kinase).

Initial therapy administered consisted of 0.9%

sodium chloride (16 mL/kg SC; Normosol-R,

Hospira Inc, Lake Forest, IL, USA), enrofloxacin(15 mg/kg IM; Baytril, Bayer HealthCare, Shaw-

nee Mission, KS, USA), and fipronil (topical

application; Frontline Spray, Merial Ltd, Duluth,

GA, USA).

Radiographic imaging revealed a comminuted

fracture of the right tarsometatarsal bone (Fig 1).

One fracture line was transverse middiaphyseal,

and a second fracture, medial to the first, wasoriented sagittally from the transverse fracture to

the proximal metaphysis. Displacement and

malalignment of both fractures were minimal.

The fracture was initially treated by splinting.

On physical examination, 1 month later, instabil-

ity was readily palpable at the transverse fracture

site, although the eagle was still able to grip with

considerable force. Radiographs were repeated(Fig 2), and findings included significant widen-

ing of the gap at the transverse fracture site,

consistent with delayed union and progression to

nonunion, as well as osseous proliferation and

indistinct fracture margins at the sagittal fracture

site, suggestive of progression toward bone union.

From the Department of Clinical Sciences, Veterinary

Teaching Hospital, College of Veterinary Medicine, Auburn

University, 519 Hoerlein Hall, Auburn, AL 36849, USA.

Journal of Avian Medicine and Surgery 25(2):119–125, 2011

’ 2011 by the Association of Avian Veterinarians

119

Failure of external coaptation to stimulate

healing of the transverse fracture dictated treat-

ment with surgical stabilization. Specific anatom-

ic and physiologic aspects taken into account

during the planning of the surgical protocol

included the high impact forces to which the

fracture site would be subjected, even when the

eagle was confined (eg, striking action), and the

inelastic, scaled dermis overlying the minimal

subcutaneous space for placement of the implant.

The rigidity of a plate or interlocking nail was

indicated to counter the significant impact forces;

however, the relatively small medullary canal of

the tarsometatarsal bone, accessible only through

a joint surface, eliminated the possibility of using

an interlocking nail. Conventional, internal place-

ment of a plate was not possible because of the

relative lack of subcutaneous space.

A 3.5-mm locking compression plate (LCP;

Synthes Inc, West Chester, PA, USA) was chosen

as the stabilization device. However, because of

the site’s lack of adequate soft tissue coverage, the

LCP was placed externally on the lateral aspect of

the tarsometatarsus as an external fixator with

only the screws penetrating the dermis. After

manual alignment and compression were

achieved, 3 screws each were placed proximal

and distal to the transverse fracture (Fig 3).

Recovery from anesthesia was uneventful.

Fracture healing progressed normally based on

serial radiographic evaluations (Fig 4). Radiolu-

cency was appreciated around the central 2 screws

by 9 weeks after surgery but did not develop at

any time around the other screws. Screw tightness

was assessed at least weekly, and loosening of a

single screw occurred only once 2 weeks after

plate application. At 12 weeks after surgery,

controlled destabilization of the LCP-bone con-

struct was begun by removing the 2 central

screws. The most distal and proximal screws were

removed 15 weeks after surgery, and the remain-

ing 2 screws and the plate were removed 18 weeks

after surgery. The small wounds resulting from

the screws penetrating the soft tissue healed

without complication.

As the bone union progressed, so did the eagle’s

use of the leg and foot, until it was considered

sound (Fig 5). After the soft tissue wounds healed,

the eagle was placed in a large (92 m long 3 28 m

wide 3 28 m high) flight mew for 3 months for

self-rehabilitation of flight muscles. The eagle’s

condition was observed daily and formally eval-

Figure 1. Initial radiographic imaging ([a] dorsoplantar and [b] lateromedial) of a mature, female bald eagle

presenting with swelling over the right tarsometatarsal area. Evident are both a nondisplaced transverse

middiaphyseal fracture and a medial sagittal fracture extending from the transverse fracture proximally to the

proximal metaphysis of the tarsometatarsal bone. Note the lack of subcutaneous space between the dermis and

the bone.

120 JOURNAL OF AVIAN MEDICINE AND SURGERY

uated approximately once monthly for landing

ability, feather condition, maneuverability, endur-

ance, vertical lift, and symmetry. Each trait was

given a score of 0–4, and a total score of 22 was

required for the bird to be considered releasable.

The combined scored was 24 on the last evalua-tion. The eagle was captured in the mew for

physical examination 30 weeks after surgery and

was subsequently released to the wild.

Discussion

In this case, excessive motion at the fracture

site, resulting from the inability of the external

coaptation to maintain fragment stability, result-

ed in delayed union. The avian tarsometatarsal

bone is tightly covered by soft tissue and skin,

resulting in insufficient space for application of a

subcutaneous plate. Additionally, this bone has a

small medullary cavity accessible only through

articular surfaces, eliminating interlocking nail

and intramedullary pin stabilization options.

External fixation is the primary method for

treatment of tarsometatarsal fractures.1 Previous

investigations have shown that threaded pins are

more resistant to axial pull-out than smooth pins

are in birds and other species,2–5 and recently,

threaded pins with relatively less pitch (4 threads/

Figure 2. Radiographic imaging ([a] dorsoplantar and [b] lateromedial) of the bald eagle described in Figure 1

taken after 1 month of external coaptation reveals delayed union and a widening gap at the transverse

tarsometatarsal fracture site.

MONTGOMERY ET AL—REPAIR OF TARSOMETATARSAL FRACTURE IN AN EAGLE 121

mm versus 3 threads/mm) were shown to have

greater holding strength than do smooth pins orpins with greater pitch.6 The more threads there

are per millimeter, the more metal-to-bone

interface exists, increasing the friction and de-

creasing the risk of the metal pulling out of the

bone. However, in bones with relatively thicker

cortices, thread pitch comparisons have not made

a significant difference.4,7,8 The thick cortex of the

bald eagle’s tarsometatarsal bone implies thatthread pitch may not play as significant a role in

resisting axial pull-out as it may in bones with

thinner cortices (eg, pneumatic bones). The screws

used in this construct were designed to maximize

the screw holding power in the cortical bone.

The LCP, applied as an external fixator, was

also chosen in this case because it supports the

concept of minimally invasive percutaneous

osteosynthesis. The goals of fracture treatment

are perfect anatomic alignment, rigid fixation of

that alignment, and induction of minimal surgical

trauma to maximize biological wound healing.

Using contemporary implants and techniques, the

first 2 goals are mutually exclusive of the third.

Achievement of optimal alignment necessitates

touching bone fragments, and the most rigid

fixation involves direct application of plates and

interlocking nails to the bone; however, minimi-

zation of soft tissue trauma precludes incising the

skin (ie, external coaptation). External skeletal

fixation is a minimally invasive percutaneous

osteosynthesis technique that satisfies some of

these requirements. Minimally invasive percuta-

neous osteosynthesis prioritizes the biology of

fracture healing via stab incisions through which

metal is connected to bone.4,6 Fracture stability

Figure 3. Radiographic imaging ([a] dorsoplantar and [b] lateromedial) performed after surgical placement of a

locking compression plate on the external (lateral) aspect of the fractured right tarsometatarsal bone in the bald eagle

described in Figure 1.

122 JOURNAL OF AVIAN MEDICINE AND SURGERY

Figure 4. Serial radiographic imaging of the bald eagle described in Figure 1, taken 6–18 weeks after surgery,

showing progressive bone healing and controlled destabilization of the external fixator. Postsurgery times: (a)

6 weeks, (b) 9 weeks, (c) 12 weeks, (d) 15 weeks, and (e and f) 18 weeks.

MONTGOMERY ET AL—REPAIR OF TARSOMETATARSAL FRACTURE IN AN EAGLE 123

depends primarily on construct stability, and

limited additional stability is provided from

compression of the bone cortices at the fracture

site. The rigidity of minimally invasive percuta-

neous osteosynthesis is considerably superior to

that of external coaptation, approaching the

rigidity of plates with some constructs.8,9 This

type of fixation has limited elasticity, which

results in secondary healing with callus formation.

Type II external skeletal fixation has been

effectively used to treat fractures of the type

described in this report. In the bird described

here, the LCP system functioned mechanically as

an external fixator, with the plate serving as the

connecting bar. As such, guidelines for applica-

tion of the LCP generally followed those for the

use of external fixators. For example, similar to a

conventional external fixator, the LCP does not

need to be precisely contoured to the bone. There

are, however, some noteworthy differences be-

tween the mechanics of the LCP and conventional

external fixators. Locking compression plates use

screws with threads cut into the underside of each

screw head that engage threads in the plate holes

to create a rigid mechanical ‘‘lock’’ between the

screw and plate (Fig 6). This mechanism is likely

more secure than the clamps used with conven-

tional external fixators. The necessary, minimal

2 points of fixation are the trans and cis cortices

with conventional plates and screws and external

fixator pins, whereas the 2 fixation points

required for the LCP are the cis cortex and the

screw head to plate threads.9

This report describes a practical use for the

LCP as an external fixation treatment for repair

of a tarsometatarsal fracture in a mature bald

eagle. The plate was well tolerated and provided

good stability, allowing the bird full use of the

extremity without destabilization of the construct

and promoting ongoing physical therapy after

surgery. The potential use of this technique in

Figure 6. The locking compression plate system,

similar to the one used in this case, consists of (a) a

screw containing threads on the underside of head, and

(b) a plate containing threaded screw holes.

Figure 5. (a) The bald eagle, described in Figure 1, shown 12 weeks after placement of a locking compression plate

(LCP) as an external fixation device for a comminuted tarsometatarsal fracture. (b) A close-up view of the LCP

demonstrates that the surrounding skin appears healthy.

124 JOURNAL OF AVIAN MEDICINE AND SURGERY

other anatomic locations and avian species should

be considered, keeping in mind that, because of

available screw sizes versus bone size and cortex

thickness, use of an external LCP technique may

need to be reserved for larger birds.

References

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Medicine. 2nd ed. London, UK: Mosby Elsevier;

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MONTGOMERY ET AL—REPAIR OF TARSOMETATARSAL FRACTURE IN AN EAGLE 125