Keywords
canine radius - fracture repair - craniolateral approach - craniomedial approach
Introduction
Fractures of the radius and ulna bones account for 17% of all dog fractures, making
them the third most common site of fracture.[1] Fractures in the distal third of the radius are common in small breed dogs.[2] Radial and ulnar fractures in large breed dogs compared with small breed dogs frequently
are in the mid-shaft, are commonly comminuted, and require additional proximal surgical
exposure for plate fixation.[3] Open reduction and internal fixation is a frequently used surgical procedure for
treating fractures of the radius.
The reported surgical approaches to the radius include lateral, craniolateral (CLA),
craniocaudal, medial, craniomedial (CMA), and caudomedial approaches.[4] Many veterinary surgeons use a craniomedial surgical approach with cranial plating,
due to the tension side of the radius being cranial.[4]
[5] Furthermore, cranial plating has been advocated with minimally invasive plate osteosynthesis.[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13] When applying a bone plate to the cranial surface of the radius, surgeons must navigate
around the cephalic vein and the extensor carpi radialis tendon. Retracting the extensor
carpi radialis laterally to expose the radius can cause underreduction of the fracture,
leading to valgus and external rotational malalignment of the limb.[14] Placement of the plate cranially, below the extensor carpi radialis tendon, can
lead to tendon irritation.[14] However, with meticulous technique, those very rare concerns can be avoided, as
has been shown in many publications.[9]
[10]
[14]
[15]
Medial plating of the radius via a medial surgical approach was successful in 22 small
and large breed dogs and cats and reported to be a less difficult approach than the
traditional CMA and repair.[14] One challenge of the medial plating is the in-plane contouring of the standard nonlocking
or locking bone plates, to accommodate the natural procurvatum of the radius . Plates
spanning only half of the radius will require minimal in-plane contouring. Another
challenge of medial plating of the radius is that the most proximal aspect of the
radius is more difficult to expose, and neurovascular structures will be encountered
and need to be preserved.
Tension side plating of the radius, as indicated from Wallace's biomechanical study,
is not necessary and validates consideration of other surgical approaches to the radius.[16]
The purpose of this study is to compare the bone exposure of the traditional surgical
CMA with the CLA. We hypothesized that the CLA provides greater exposure to the radius
than the CMA for plating.
Materials and Methods
Study Design
Animals
Six mixed-breed and skeletally mature canine cadavers consisted of three males, one
neutered male, and two female dogs with unknown reproductive status. The mean weight
of the canine cadavers was 23.8 kg (range: 18.5–38). The cadavers were obtained from
a local animal control center, and we obtained full permission from them to use them
for our research study.
Exclusion Criteria
Lateral and craniocaudal orthogonal radiographs of the left and right forelimbs were
made to rule out fractures, aggressive bone lesions, and asymmetry of the radii.
Preparation
The frozen cadavers were thawed for a minimum of 48 hours at room temperature before
collecting any data. Hair was removed from both forelimbs using clippers. Randomizing
forelimbs for CMA or CLA involved a coin flip.
Approaches to the Radius
Craniolateral Approach
A craniolateral antebrachial skin incision was made with a scalpel from the proximal
end of radius to the carpus along the muscular furrow between the extensor carpi radialis
and common digital extensor, lateral to the cephalic vein. The deep antebrachial fascia
was incised between muscle bellies and tendons of the extensor carpi radialis and
common digital flexor. The abductor pollicis longus was transected on the lateral
aspect of the radius ([Fig. 1]). The attachment of the supinator muscle was sharply incised along its lateral and
distal borders and elevated to expose the proximal radius. Gelpi retractors (not shown
in [Fig. 2]) were placed between the extensor carpi radialis and common digital extensor to
maintain exposure of the radius ([Fig. 2]).
Fig. 1 Cranial view of the left forelimb. The dotted lines depict the separation of the
extensor carpi radialis and the common digital extensor and transection of the abductor
pollicis longus in the craniolateral approach.
Fig. 2 Cranial view of the left forelimb. The craniolateral aspect of the radius was exposed
following the separation of the extensor carpi radialis and common digital extensor,
transection of the abductor pollicis longus, and elevation of the supinator muscle
in the craniolateral approach.
Craniomedial Approach
A skin incision was made with a scalpel on the craniomedial aspect of the antebrachium
from the level of the proximal end of radius to carpus, medial to the extensor carpi
radialis muscle and tendon. The cephalic vein was preserved as it traversed the distomedial
surface of radius. The deep fascia between the extensor carpi radialis and the pronator
teres was incised. The tendon sheath was incised along the medial and lateral borders
of the extensor carpi radialis tendon. The medial and distal aspects of the supinator
muscle attachment to the radius was elevated to expose the proximal end of radius.
Gelpi retractors (not shown in [Fig. 3]) were placed to retract the extensor carpi radialis muscle and tendon laterally
to expose the radius ([Fig. 3]).
Fig. 3 Cranial view of the left forelimb. The cranial aspect of the radius is exposed with
the craniomedial approach with lateral retraction of the extensor carpi radialis.
Data Collection
A latex sheet cut from a surgical glove (ENCORE, Ansell) was placed on the exposed
radius, and a black marking pen was used to trace around the borders of the exposed
radius for both CMA and CLA. The template was cut from the rubber sheet. To ensure
accuracy of size and shape, the rubber template was placed back onto the exposed radius
([Fig. 4]). The templates from left and right limbs and a measuring caliper (Aratana Therapeutics,
Kansas) were placed on a flat surface and photographed ([Fig. 5]). The images were analysed with ImageJ 1.53. The set scale function was used to
calibrate pixels into centimeters using the 1-cm length on the caliper in the image.
The surface areas of the templates were obtained by measuring around the edge of the
piece with the freehand selection function. Three surface area measurements were taken
for each template.
Fig. 4 Cranial view of left antebrachium (paw is to right). The latex template was laid
over the exposed bone after completion of the craniolateral approach to ensure the
accuracy of exposed bone measurement.
Fig. 5 Exposed radius craniolateral approach (top) and craniomedial approach (bottom) templates
depicting a significantly larger area of exposed bone for the craniolateral approach.
Length of Canine Radius
The radiographs were standardized using a 10-cm calibration bar (BioMedtrix, St. Augustine,
United States). The anatomic axis was drawn on the radius on the craniocaudal view,
and the bone length was measured from the proximal to distal articular surfaces using
image viewing software (Horos, Osirix) measuring tool. The Horos software has a built-in
calibration for radiographic measurements.
Length of Exposed Canine Radius
A line was drawn from the lateral to the medial edge as proximally as possible on
the template, the same is repeated distally. A line was drawn from the midpoint of
the most proximal end to the midpoint of the most distal end of the template using
ImageJ (National Institutes of Health, Bethesda, Maryland, United States).
Width of Exposed Canine Radius
A line drawn at 50% of length and width was measured (M). The width was measured at
6.25% intervals of the total length of template from the most proximal end to M, the
same was repeated from the most distal end to M. The measurements from the most proximal
and distal end to M was at 6.25% (P1, D1), 12.5% (P2, D2), 18.75% (P3, D3), 25% (P4,
D4), 31.25% (P5, D5), 37.25% (P6, D6), and 43.75% (P7, D7) of total template length.
Statistical Analysis
Three surface area measurements obtained from each piece were averaged. The CLA and
CMA surface area, length on orthogonal view of radiographs, length and width of exposed
radii of all six dogs were calculated as a mean. All the statistical analysis was
performed with t-test with paired two samples for means, defining p < 0.05 as statistically significant.
Results
Radiographs
Both lateral and craniocaudal views of left and right forelimbs of cadavers were symmetrical.
No fractures, deformity, or short radius syndrome were seen.
Length of Radius on Craniocaudal View of Forelimb Radiographs
Amongst cadavers, the average difference between left and right forelimb radial length
was 0.1 cm (range: 0–0.4). The length of radius was 16.5 ± 3.5 and 16.6 ± 3.3 cm of
the left and right forelimbs, respectively, and no significant statistical difference
between limbs was found (p = 0.38).
Surface Areas of Canine Radius
The average surface area of the exposed radius with the CMA (13.8 ± 3.2 cm2) was less than with the CLA (19.4 ± 4.7 cm2; p = 0.01).
Length of Exposed Canine Radius
The length of the exposed radius for the CMA (11.4 ± 2.8 cm) and the CLA (12.9 ± 1.4 cm)
were not significantly different (p = 0.08).
Width of Exposed Canine Radius
The width of exposed canine radius with the CMA at P2 (1.2 ± 0.2 cm) was significantly
less than the CLA (1.4 ± 0.3 cm; p = 0.01). The remaining width measurements were not statistically significant between
CMA and CLA ([Table 1], [Fig. 6])
Table 1
Proximal width measurements for exposed radius
|
CMA
|
CLA
|
|
|
Location of measurement
|
Exposed width of radius (cm)
|
± Standard deviation (cm)
|
Exposed width of radius (cm)
|
± Standard deviation (cm)
|
p-Value
|
|
P1
|
0.89
|
0.22
|
1.15
|
0.25
|
0.077
|
|
P2
|
1.16
|
0.21
|
1.39
|
0.31
|
0.016
|
|
P3
|
1.35
|
0.25
|
1.53
|
0.35
|
0.222
|
|
P4
|
1.5
|
0.28
|
1.59
|
0.38
|
0.527
|
|
P5
|
1.55
|
0.31
|
1.67
|
0.39
|
0.476
|
|
P6
|
1.55
|
0.35
|
1.77
|
0.39
|
0.29
|
|
P7
|
1.52
|
0.3
|
1.8
|
0.38
|
0.116
|
Abbreviations: CLA, craniolateral approach; CMA, craniomedial approach.
Fig. 6 Width measurements of exposed radius for craniomedial approach and craniolateral
approach.
General Observations Noted in All Dogs
Proximally, the extensor carpi radialis muscle belly was much more easily retracted
medially rather than laterally; thus, perpendicular access to the radius was achieved
in the CLA. Branches of the radial nerve that innervate the antebrachial extensors
were not encountered proximally between the extensor carpi radialis and common digital
extensor bellies in the CLA. With elevation of the lateral aspect of the supinator
during the CLA, neurovascular bundles were not encountered at the proximal radius
within 1 cm of the articular surface. In contrast, a neurovascular bundle (median
nerve/artery/vein) was always encountered with proximal exposure of the radius during
the CMA. The CMA mandated liberation of the extensor carpi radialis tendon from its
sulcus with lateral retraction. The proximal surface of the radius on all dogs was
tilted laterally. The distal portion of the radius had a flat cranial face and a flat
craniolateral face.
Discussion
The radius had more exposed surface area of CLA compared with the CMA. One of the
CLA proximal measurements had larger exposure, which can be explained by a lack of
neurovascular bundles present in the area. The CLA had wider exposure proximally than
the CMA. The width of bone exposure in both the CLA and CMA was adequate for the placement
of a bone plate of appropriate size.
Based on the overall larger exposed surface area with the CLA compared with the CMA,
the former might provide better visualization of the bone fragments during surgery
and therefore allow more precise reconstruction of the bone. However, as this was
a cadaveric study, and the effect of soft tissue retraction as well as surgeon experience
could not be included, a clinical study comparing those approaches in bones with similar
fracture patterns is needed to examine, if our findings have any clinical importance.
A potential number of benefits of the CLA exist. The craniolateral aspect of the radius
has a corridor that is relatively free of tendons aside from the abductor pollicis
longus, which obliquely crosses the radius. This muscle must be transected distally
to allow for plate placement; however, the proximal aspect of the muscle and its tendon
may be preserved by placing the plate beneath it. There is little evidence to suggest
that a transected abductor pollicis longus in dogs would have any clinical impact.
One case report reported the development of carpal osteoarthritis following transection
of the abductor pollicis longus in a dog. However, it is uncertain if this association
is true for all dogs.[17] Extensor carpi radialis is an important extensor tendon of the carpus, irritation
must be avoided during bone plating. Abductor pollicis longus is a minor tendon to
the first digit of manus and therefore is unimportant to the overall function of canine
manus.
The distal radius has two faces: the cranial face and the craniolateral face. The
extensor carpi radialis runs along the cranial face of the radius, where cranial plating
may be necessary. Distally placed plates on the cranial surface encroach on the extensor
carpi radialis tendon sheath and the sulcus where the extensor carpi radialis lies.
The placement of a plate on the craniolateral aspect of the radius avoids tendon interference
and may have other advantages. Screws inserted obliquely across the bone increase
screw purchase and the strength of the bone–plate construct.[16] Placing a plate on the craniolateral surface of the bone can reduce the risk of
a surgically induced valgus deformity, because the flat surface of the plate is juxtaposed
to the bone. In addition, retracting the extensor carpi radialis medially may help
to collapse the medial fracture gap, minimizing valgus deformity.[14]
Minimally invasive plate osteosynthesis is beneficial for radial fractures in large
breed dogs, as these fractures tend to be comminuted and require a long plate spanning
the length of the radius. The CLA principles may also be applied to minimally invasive
plate osteosynthesis by making small proximal and distal incisions along the same
tissue planes. A challenge with locking plates used in minimally invasive plate osteosynthesis
is the perpendicular placement of the locking drill guide to the plate in a limited
and deep surgical approach. The CLA provides good vertical access to the proximal
radius, whereas the CMA does not.
A reported benefit of medial plating is the avoidance of placing screws through both
the radius and ulna bones, a potential complication of cranial plating.[14]
[15] Similarly, with CLA, screws directed in a craniolateral to caudomedial direction
may also avoid engaging the ulna bone, except in the most proximal region of the antebrachium.
However, with appropriate planning and intraoperative measurement, this complication
is often a technical error and cannot be related to the approach. The proximal cranial
surface of the radius is tilted laterally; thus, with cranial plate application, the
proximal aspect of the plate should be twisted laterally, in addition to a cranial
contour over the mid radius to accommodate for the natural procurvatum of the radius.[18] With craniolateral plating, minimal twisting of the proximal plate may be needed.
Cranial bowing of the plate will likely still be needed and should be based on a preoperative
lateral oblique radiograph of the contralateral limb positioned to highlight the craniolateral
surface.
With the CLA, internal fixation of the ulna can be achieved without requiring a separate
incision on the skin. A deep fascial incision and retraction of the flexor carpi ulnaris
and ulnaris lateralis provides good exposure to the ulna bone. The CMA would require
a separate skin incision to repair a concurrent ulnar fracture.
Limitations of this study primarily include small numbers of samples and use of cadavers.
Cadaveric tissue is more pliable than living tissue that has been previously injured
days prior to surgery. This may have increased the exposure to the bone artificially
in our study. We only used large breed dogs, assuming similar muscle anatomy in small
breeds for CLA utilization.
In summary, the CLA has many advantages over the CMA for the repair of antebrachial
fractures in dogs.
