Montgomery 2011 Use of a Locking Compression Plate as an External Fixator for Repair of a Ta
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Transcript of Montgomery 2011 Use of a Locking Compression Plate as an External Fixator for Repair of a Ta
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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
1. Redig P, Cruz L. Fractures. In: Samour J, ed. Avian
Medicine. 2nd ed. London, UK: Mosby Elsevier;
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2. Degernes LA, Roe SC, Abrams CF. Holding power
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3. Anderson MA, Mann FA, Wagner-Mann C, et al.
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MONTGOMERY ET AL—REPAIR OF TARSOMETATARSAL FRACTURE IN AN EAGLE 125