Keywords
olecranon fracture - sheep - String of Pearls - fracture - tension band wire
Introduction
Correction of proximal ulna and olecranon fractures is extensively described in veterinary
literature.[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9] Their prevalence is, however, somewhat uncommon when compared with other antebrachial
fractures. Such fractures may be non-articular or articular in nature, with the latter
most common, and have been reported in dogs,[1]
[2]
[3] cats,[1] horses[4]
[5]
[6]
[7]
[8] and a bull.[9] To counteract the tensile force of the triceps brachii muscle group on the olecranon,
various repair techniques, including tension band wiring (TBW) and plate osteosynthesis
(PO), have been described to convert tensile forces to compressive forces while achieving
interfragmentary compression and anatomical reduction.[1]
[3]
[4] Open reduction and internal fixation with application of a TBW have been proposed
as the treatment of choice for proximal ulna fractures in dogs, but is associated
with a higher complication rate than PO.[3]
Type of repair and implant selection is not only based on fracture configuration but
is also defined by specific species characteristics, including anatomical differences
and the physiological requirement for pronation and supination. The ulna bone characteristically
tapers along its diaphyseal length distally, forming the metaphysis and articulation
with the carpus.[10] In domestic animals, the width of the ulna provides sufficient bone stock and medullary
cavity for plating laterally, medially and caudally, or for application of a TBW or
intramedullary pin. Small ruminants dissimilarly do not require the ability for pronation
and supination, which consequently results in the development of a narrower ulna with
reduced medullary canal diameter distally[10] ([Fig. 1]). Distinct to the horse, the proximal ulna diaphysis is well developed but is fused
to the radius, with the distal ulna absent and no carpal articulation.[10] The anatomical variations between domestic animals and that of the equine and ovine
antebrachium are important for surgical planning and appropriate implant selection.
Fig. 1 Medial and lateral views of the anatomy of the antebrachium in the sheep.
Antebrachial fractures in small ruminants are infrequently reported despite being
well-documented in cattle.[9]
[11] The decision to treat a fracture in small ruminants is often made by considering
economic or genetic value of the animal, cost of treatment, morbidity and mortality
rates and fracture location and configuration.[11] Literature describes the use of casting or splinting,[11] internal plate fixation,[11] semicircular external fixation[12] and combined positive profile transfixation pins with casting[13] for the treatment of mid-body radius–ulnar fractures in sheep. To the authors' knowledge,
olecranon fractures and their subsequent repair have not been described in the sheep.
This report describes the use of the String of Pearls locking plate system, intramedullary
pin and lag screws for the treatment of an intra-articular olecranon fracture in a
lamb.
Case Description
Clinical History and Examination
A 6-month-old, 20 kg, purebred male Merino lamb was referred to a referral veterinary
hospital for the evaluation of a non-weight bearing lameness of the left thoracic
limb of unknown duration. Ten days prior, the lamb was found recumbent on the side
of the road and unable to stand, and subsequently able to stand with a left thoracic
limb non-weight bearing lameness.
Findings on physical examination included a temperature of 39.4°C, tachycardia (100
bpm) and tachypnoea (60 bpm). The lamb was non-weight bearing on the left thoracic
limb, with swelling and crepitus noted on palpation of the left elbow, as well as
displaying a “dropped elbow” stance with carpal flexion. Range of motion of the affected
elbow was reduced in both flexion and extension, with pain appreciated on full extension
and full flexion. Further orthopaedic and neurological examination was unremarkable.
Diagnostic Imaging and Surgical Planning
Orthogonal radiographic (craniocaudal and mediolateral projections) assessment of
the left elbow revealed a complete, closed, long sagittal oblique, minimally displaced
fracture of the olecranon involving the ulnar shaft at the level of the radial physis,
extending proximally through the distal semilunar notch to the mid-body of the olecranon
([Fig. 2A], [2B]). Additionally, a small lateral humeral epicondylar avulsion fracture was also apparent
([Fig. 2B]). Secondary proliferative callus formation was apparent over the caudoproximal aspect
of the olecranon ([Fig. 2A]), suggestive of fracture chronicity. The proximal ulna epiphyseal plate remains
open.
Fig. 2 Preoperative and immediate postoperative radiography (mediolateral projection, A and C; craniocaudal projection, B and D) of the left elbow. Red arrow: fracture of the olecranon involving the ulnar shaft
at the level of the radial physis, extending proximally through the distal semilunar
notch to the mid-body of the olecranon. Yellow arrow: small lateral humeral epicondylar
avulsion fracture. Green arrow: secondary proliferative callus formation.
The medullary canal of the ulna is incomplete and remained radiographically open for
8.8 cm from the most proximal aspect of the olecranon to the proximal ulna diaphysis,
which is the most distal aspect of the medullary canal, before fusing with the caudal
aspect of the proximal radius. The greatest width of the medullary canal of the ulna
was 3.8 mm.
Surgical Technique
The lamb was pre-medicated with methadone (0.2 mg/kg intramuscularly; Methadone, Ilium,
Troy Laboratories Australia Pty Ltd, Australia). Anaesthesia was induced with propofol
(4 mg/kg intravenously [IV]; Lipuro 1%, Braun Australia Pty Ltd, Bella Vista NSW,
Australia) and maintained with isoflurane (Isoflo, Zoetis Australia Pty Ltd, Rhodes
NSW, Australia) in oxygen. The left thoracic limb was clipped and prepared with chlorhexidine
and an alcohol solution, and the patient positioned in dorsal recumbency.
A lateral approach to the left elbow was performed. The large amount of proliferative
callus was debrided, allowing exposure of the fracture site. A 3/32 inch (2.4 mm)
intramedullary pin was placed normograde from the most proximal aspect of the olecranon
across the fracture and into the distal ulna. The pin was observed to exit the cortex
distally at the most distal aspect of the medullary canal. The fracture was reduced
and maintained in reduction using pointed reduction forceps. Two 2.0 mm lag screws
were placed in a lateral–medial direction across the fracture site. An additional
1.5 mm lag screw was also placed in the same direction. Due to the lack of bone stock
available in the distal ulna, a 2.7 mm String of Pearls plate (Orthomed Australasia
Pty Ltd, Mandurah, WA, Australia) was contoured over the lateral aspect of the proximal
radius and lateral aspect of the olecranon and attached to the proximal radius and
olecranon using 2.7 mm cortical screws. Two screw holes were left empty over the fracture
site. The elbow was stable on palpation and when manipulated through range of motion.
Based on this stability combined with the chronicity of the injury and amount of firm
callus identified laterally, we elected not to explore the avulsion fracture from
the lateral humeral epicondyle. A routine multilayer closure of the incision was performed.
Postoperative radiographs revealed appropriate implant positioning and anatomic fracture
reduction ([Fig. 2C, 2D]).
Perioperative and Postoperative Management
Perioperative antibiotic therapy consisted of cefazolin (22 mg/kg IV; Cefazolin-AFT,
AFT Pharmaceuticals, North Ryde, NSW, Australia) at least 30 minutes prior to the
first incision, and every 90 minutes during surgery thereafter. Perioperative analgesia
included methadone (0.1mg/mg IV) administered once intraoperatively. Postoperative
analgesia consisted of methadone (0.2 mg/kg IV q6h), meloxicam (0.1 mg/kg subcutaneously;
Meloxicam, Ilium, Troy Laboratories Australia Pty Ltd, Australia) and a transdermal
fentanyl patch (50 mcq/h; Durogesic 50, Janssen-Cilag Pty Ltd, Macquarie Park NSW,
Australia). Pain scores were performed every 4 hours with appropriate administration
of methadone as required until activation of the transdermal fentanyl patch 12 hours
following application.
The patient was discharged from hospital the following day, with meloxicam (0.1 mg/kg,
1.5 mg/mL; Meloxicam, Ilium, Troy Laboratories Australia Pty Ltd, Australia) dispensed
for oral administration during the postoperative period. The patient was to be restricted
to a small pen for 8 weeks.
Clinical Outcome
The patient presented 8 weeks postoperatively for the re-evaluation by their primary
care veterinarian. Physical examination revealed a grade 1/5 left thoracic limb lameness.
Range of motion of the elbow was now considered within normal limits. Digital pressure
application over the lateral humeral epicondyle, site of previous avulsion fracture,
elicited a mild pain response. Orthogonal radiographic assessment of the left elbow
revealed implant quiescence with radiographic union of the fracture site ([Fig. 3]). Indirect bone healing is evident at the site of previous lateral humeral epicondylar
avulsion fracture. Ongoing thoracic limb lameness is hypothesized to be a result of
periarticular inflammation associated with secondary bone healing. The patient was
no longer receiving non-steroidal anti-inflammatory medication at the time of recheck.
Fig. 3 Radiographs of the left elbow obtained 8 weeks postoperatively.
Telephone updates were provided at both 3 and 6 months postoperatively by the client.
According to the client, the patient was no longer restricted in activity, with free
access to the field, and was not displaying an overt lameness. Follow-up of the patient
was lost thereafter.
Discussion
Despite their uncommon prevalence, olecranon fractures are generally associated with
satisfactory outcomes despite relatively high complications rates of up to 52% in
dogs.[3] Plate osteosynthesis is associated with a more biomechanically robust construct,
fewer complications and improved outcomes when compared with TBW[3]
[4]
[7]
[8]
[14]
[15] however, the use of TBW remains advocated in some cases of non-displaced, non-articular
olecranon fractures.[11] Fournet and colleagues[3] hypothesized that anatomical differences of the proximal ulna between the dog and
cat, as well as patient weight, are a major factor associated with selection of repair
technique, emphasizing the importance of appropriate implant selection and placement.
Several classification systems for olecranon fractures have been described in humans.[16]
[17]
[18] Currently, factors such as fracture type, location and its open verses closed status
are the main characteristics that guide management of such cases in dogs.[3] A universally accepted classification system has been adopted for equine ulnar fractures,[19] classifying fractures as Type 1 through to Type 5 dependent on their configuration,
although variations of these fracture configurations have been reported. Given the
anatomical similarities between the antebrachium of the horse and sheep and the high-energy
traumatic nature of ulna fractures in both species, the authors postulate that the
aforementioned classification system for ulnar fractures may also be ascribed to that
of small ruminants. This case report describes a fracture most closely mirroring a
Type 5 olecranon fracture in a horse, as the fracture configuration includes the involvement
of the ulnar shaft at the level of the radial physis that extends proximally into
the semilunar notch. The results of plate fixation of Type 5 olecranon fractures in
horses have most recently been described by Swor and colleagues,[15] with long-term follow-up (16–146 months following surgery) revealing 85% of horses
were sound and used for their intended athletic purpose. The same study[15] suggested that tension band plating provides several advantages over conservative
management and other internal fixation methods, including increased inherent repair
stability, an anticipated decrease in degenerative changes of the joint and faster
healing times. Type 5 fractures managed with TBW in five horses reported sound outcomes
in three cases and one case with a fair long-term outcome.[20] It is now widely recognized that TBW is associated more readily with complications
than with plate fixation, particularly in adult horses due to increased risk of cyclical
implant fatigue and failure of the biomechanically inferior TBW.[3]
[4]
[7]
[8]
[14]
[15]
While conservative therapy may be an option in patients with olecranon fractures,
∼90% and the vast majority of olecranon fractures in dogs[3] and horses,[19] respectively, have intra-articular involvement, and are therefore not amenable to
the application of a cast or external fixation and require interfragmentary compression
techniques. In a field setting, non-surgical management of ulna fractures may include
the application of a Thomas splint-cast; however, disadvantages include possible significant
injury to the contralateral limb due to increased weight bearing, bandage-associated
sores and malunion.[11] Difficulties in patient activity restriction and bandage monitoring may increase
the risk of splint or cast failure. An early return to weight bearing is also more
commonly observed in patients with internal plate fixation than those managed conservatively.[15]
The authors believe that the slender nature of the ulna in the sheep prohibited the
ability to apply plate fixation caudally or laterally from the olecranon to the proximal-mid
diaphysis. Implant selection that is strong enough to withstand ongoing cyclic fatigue
would require greater bone stock distally. Further, orthopaedic wire anchored distally
through a transversely drilled hole in the proximal diaphysis with a reduced medullary
canal diameter would likely create a stress riser effect and predispose to fracturing
through this anchor site. These factors contributed to the selection of a biomechanically
robust implant, the String of Pearls locking plate system, with the capability to
contour the implant to the sites of greatest bone stock while bridging the fracture
gap. In this instance, these sites were the proximal radius and proximal olecranon.
The implant was reinforced with cortical screws applied in lag fashion across the
fracture line and an intramedullary pin to assist with resist bending forces. These
adjuvant implants will likely reduce the cyclic load applied to the plate. Olecranon
fracture repair by plate fixation in horses involves the application of a locking
compression or dynamic compression plate caudally from the most proximal aspect of
the olecranon distally to beyond the transition from ulna to radius, with caudally
inserted screws ideal for rigid fixation in adult horses.[21] Inadvertent penetration of the lateral cortex of the radius with locking head screws
is a possible complication following caudal plate application[21] and may result in devastating radial fracture and subject these patients to euthanasia.
In the authors' opinion, the lateral application of the plate improves accuracy of
central screw insertion through increased bone stock, thereby reducing the likelihood
of implant-associated complications.
In this report, a screw was inadvertently inserted through the proximal ulna epiphyseal
plate; however, this is not believed to be of clinical significance given the reduced
remaining longitudinal growth expected from this growth plate. A limb length discrepancy
was not apparent on follow-up examination. Plate application to the caudal aspect
of the olecranon often avoids soft tissue disruption over the proximal olecranon[22] but is associated with no biomechanical superiority when compared with lateral plating.
The authors elected a lateral approach, sacrificing some soft tissue to improve access
to the points of greatest bone stock and apply a more inherently stable implant. The
patient demonstrated a satisfactory clinical outcome with no overt pain or lameness
apparent at 6 months postoperatively.
Conclusion
This report illustrates a successful functional outcome of an intra-articular olecranon
fracture in a lamb repaired using a String of Pearls locking plate system, intramedullary
pin and lag screws. To the authors' knowledge, this is the first report to describe
an olecranon fracture and its subsequent repair in the sheep utilizing a novel fixation
method. This report further documents the importance of proper case selection and
appropriate surgical planning when treating olecranon fractures.
