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RUNNING HEAD: Traumatic Myositis Ossificans in a Dog
Surgical Treatment of Traumatic Myositis Ossificans of the Extensor Carpi Radialis
Muscle in a Dog
Bridget A Morton1 DVM, MS, Bianca F Hettlich1 Dr. med vet, Diplomate ACVS, and
Roy R Pool2 DVM, PhD
1
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio
State University, Columbus, OH; 2Department of Veterinary Pathobiology, College of
Veterinary Medicine and Biomedical Sciences, Texas A & M University, College
Station, TX
Corresponding author: Bianca Hettlich, Dr. med vet, Diplomate ACVS, The Ohio State
University, Veterinary Medical Center, 601 Vernon L Tharp St, Columbus, OH 43210.
E-mail: [email protected]
Submitted: December 2013
Accepted: September 2104
ABSTRACT
Objective: To report clinical signs, diagnostic imaging findings, and outcome in a dog
with traumatic myositis ossificans of the origin of the extensor carpi radialis muscle.
Study design: Clinical report
Animal: An 8-month-old intact female Irish Setter Dog
Methods: After radiographic and computed tomographic evaluation of an osseous
proliferation arising from the cranial cortex of the right distal humeral diaphysis, the
protruding bone was surgically removed and evaluated by histopathology.
Results: Traumatic myositis ossificans was successfully treated with surgical removal of
the osseous proliferation resulting in improved postoperative range of motion of the right
elbow joint. There was no evidence of lameness or abnormal bone regrowth associated
with the surgical site radiographically at follow up.
Conclusion: Surgical removal of a traumatic myositis ossificans lesion resulted in full
return to function in a young, competitive show dog.
CLINICAL REPORT
History
An 8 month-old Irish Setter intact female dog was referred for an intermittent
right thoracic limb gait change. Three months previously, the dog reportedly slipped
while playing, resulting in acute onset right thoracic limb lameness. On examination by
the referring veterinarian the dog had pain on manipulation of the elbow and shoulder
joint; however, range of motion was considered normal in extension and flexion of both
joints. Radiographs were not taken. The dog was treated with anti-inflammatory
medication and exercise restriction for 1 week and lameness resolved completely within 2
weeks. Two months later the dog began displaying a subtle right thoracic limb gait
change. With heavy activities there was occasional circumduction of the right thoracic
limb but no other signs of lameness or pain. On radiographs, a triangular and irregularly
shaped bone proliferation was identified associated with the cranial aspect of the right
distal aspect of the humerus (Fig. 1A) There was bulging of the soft tissues along the
cranial aspect of the elbow. Mild periarticular new bone formation was found associated
with the right elbow joint.
Clinical Findings
On orthopedic evaluation after admission, a subtle intermittent, fully weight
bearing right thoracic limb lameness was observed. There was mild atrophy of the right
supraspinatus and infraspinatus muscles and mild periarticular thickening of the right
elbow with no obvious effusion. A firm, non-painful, non-moveable mass was palpated
on the cranial aspect of the right distal humerus. Elbow range of motion was normal in
extension at ~165º, but came to an abrupt stop in flexion at ~100°. Direct palpation of the
protuberance, and passive range of motion of the elbow joint did not elicit pain. Other
elements of the physical and orthopedic examinations were unremarkable.
Diagnostic Imaging Findings and Interpretation
Computed tomographic (CT) examination (GE lightspeed 3.X, GE Medical
Systems, Waukesha, WI) of the right elbow confirmed a large protrusion of well-defined
bone arising craniodistally from the lateral epicondylar crest and extending, in close
contact to but not connected, to the level of the humeral condyle where it became
truncated and irregularly margined. (Figs. 2, 3) The associated soft tissues were thickened
and bulging cranially. There was mild bony proliferation along the medial and lateral
humeral epicondyles. The cranial aspect of the radial head was mildly irregular. The left
elbow was unremarkable. Based on the dog’s apparently normal elbow range of motion
before the traumatic event and subsequent development of this bone protrusion, ossifying
myopathy of the extensor carpi radialis origin was suspected. Because of the very mild
clinical signs, the owner elected to pursue conservative management for several months.
The dog was rechecked 4 months later and the same orthopedic abnormalities
were found (namely markedly reduced flexion of the right elbow). Repeat radiographs
showed that the bone proliferation had increased homogenous opacity and was now
smoothly marginated when compared with the previous radiographs (Fig. 1B) There was
also an increase in periosteal new bone formation along the cranial aspect of the radial
head. To prevent further damage because of repetitive impact of the bone protrusion with
the cranial aspect of the radial head as well as improve range of motion in flexion,
surgical intervention was recommended.
Surgical Procedure
On a craniolateral approach to the distal aspect of the humerus, the origin of the
extensor carpi radialis muscle was not clearly identifiable among a dense layer of fibrous
tissue that arose along the lateral epicondylar crest. After identification of the radial
nerve, fibrous tissues were reflected from the bony protrusion using elevators. Careful
sharp dissection was used to free the distal margin of the protrusion from adherent soft
tissues, and a sagittal saw was used to remove the protrusion. Fibrous tissue and possible
extensor carpi radialis muscle remnant were sutured to lateral periarticular tissue and
anconeal fascia.
Histopathologic Findings
The specimen was cancellous bone covered by mature fibrous tissue that arose from and
was continuous with the lateral epicondyle of the humerus (Fig. 4). The protuberance did
not contain a cartilage cap and its distal extremity contained haphazard and disorganized
cancellous bone with entrapped nests of hyaline cartilage. The surface of the distal border
was covered by maturing fibrous tissue containing foci of chondroid metaplasia
commonly found in stressed tendons and ligaments. Collagen fibers present in the border
were continuous with, and originating in, cartilage cores of the cancellous bone. It is
likely that this primarily bony mass originally consisted primarily of fibrous tissue and
fibrocartilage that later underwent endochondral ossification. Cancellous bone replaced
much of the originally traumatized fibrotic sheet of damaged fascia of the extensor carpi
radialis (based on the anatomic location of the protuberance). Additional biopsy
fragments included mineralized and ossified collagenous remnants of the epimysium and
perimysium that entrapped clusters of muscle fibers from the origin of the extensor carpi
radialis muscle. Based upon these findings a histopathologic diagnosis of ossifying
myopathy was made.
Outcome
Postoperative radiographs revealed successful removal of most of the bony
protuberance (Fig. 1C) Postoperative range of motion in flexion improved from 100° to
~50°. Within 24 hours of surgery, the dog began weight bearing on the right thoracic
limb and had no evidence of radial nerve iatrogenic deficiency. Postoperative care
included administration of carprofen (2 mg/kg orally twice daily), tramadol
hydrochloride (4 mg/kg orally every 6-8 hours), and cephalexin (30 mg/kg orally twice
daily), as well as strict activity restriction to low-impact exercise for 4 weeks.
On recheck examination at 8 weeks, the dog was fully weight bearing with no
obvious lameness noted at the walk or trot. Scapular muscle atrophy had subjectively
improved. There was very mild soft tissue swelling of the cranial aspect of the right
elbow with no obvious effusion or pain on palpation. Elbow range of motion was normal
in extension but continued to be decreased in flexion at ~50°. Orthogonal radiographic
projections of the distal right humerus showed that the osteotomy site was smoothly
margined with no evidence of new bone production (Fig. 1D). The changes associated
with the cranial aspect of the radial head and soft tissue thickening cranial to the elbow
joint were unchanged. At 10 months, the owner reported normal function during all
activities at home with no evidence of lameness or pain. Recheck examination confirmed
no gait abnormalities and no noticeable muscle atrophy of the right thoracic limb. Soft
tissues around the right distal aspect of the humerus were pliable and non-painful and
seemed symmetrical to the left. Elbow range of motion was pain-free and remained
unchanged with normal extension and flexion to 50°. No evidence of bone regrowth was
noted on radiographs (Fig. 1E).
DISCUSSION
New bone formation after trauma can occur because of several pathologies such
as exuberant periosteal reaction secondary to injury, ossifying myositis, and
osteochondroma.1-3 Histopathology of the excised lesion supported a diagnosis of
ossifying myositis in this dog.
Myositis ossificans is a heterotopic formation of bone within soft tissues,
particularly involving the connective tissue support of skeletal muscles. This is also
termed fibrodysplasia ossificans and is an infrequent condition of the dog, cat, horse, and
human.1,4-9 In people, 3 types have been described using the general term of localized
traumatic myositis ossificans: myositis ossificans circumscripta, localized traumatic
myositis ossificans, and myositis ossificans progressiva.1 This should be distinguished
from ectopic calcification, which involves a calcium deposit rather than new bone
formation. Fibrodysplasia ossificans progressiva has been reported in the cat and dog. It
is a rare and inherited disorder that occurs at multiple sites and is typically fatal.10,11 The
localized (circumscript) form is typically non-neoplastic, but rather metaplastic formation
of bone after fibrotic contracture or myopathy.
Florid reactive periostitis ossificans is a dissecting periostitis that in animals is
associated with dissection of an inflammatory cell exudate that spreads between the
cortical surface of a bone and beneath the elevated periosteum. This is typically seen in
juvenile species in which the periosteum has not strongly attached to the bone surface.
In myositis ossificans, the abnormal bone formation takes place within the
connective tissues of skeletal muscle and occurs either as a generalized or localized form.
The localized form of myositis ossificans in the dog has been described in the caudal
thigh muscles, triceps, zygomatic arch, and caudal cervical region.3,7,8,12 We are unaware
of other reports of myositis ossificans involving the origin of the extensor carpi radialis
on the lateral epicondylar crest in a dog.
In dogs, the lesion is typically secondary to trauma and the affected muscle
initially becomes firm and swollen.13 It is unlikely that the lesion in this dog was initially
caused by a traumatic avulsion of the origin of the extensor carpi radialis muscle from the
humeral crest since clinical signs resolved after treatment with anti-inflammatory
medication and were followed by a 2.5 month interval without apparent clinical signs
before onset of limb restriction.
Previous reports of surgical removal or reduction have been successful
therapeutically in dogs and a cat, with no recurrence of the lesions or lameness.3,7,12 In
this dog, surgical intervention was recommended because of the persistent gait change at
high activity levels as well as progressive changes involving the cranial aspect of the
distal humerus. The bone changes associated with the head of the radius were likely
because of repeated trauma secondary to the interaction of the bony proliferation and
radial head during locomotion. Surgical reduction resulted in a substantial improvement
in maximum flexion from 100º to 50º long term. We suspect that the mild residual loss of
normal flexion angle of the elbow in this dog was because of fibrosis of the joint capsule
secondary to chronic repetitive trauma. Partial synovectomy and release of adhesions
around the affected joint capsule, as well as physical rehabilitation therapy, may further
improve flexion range of motion in this dog.
DISCLOSURE
The authors report no financial or other conflicts related to this report.
REFERENCES
1. Vanden Bossche L, Vanderstraeten G: Heterotopic ossification: A review. J Rehab
Med 2005;37:129-136.
2. Koehler JW, Johnson CM, Beard DM, et al: Pathology in Practice. J Am Vet Med
Assoc 2010, 237:45-47.
3. Guilliard MJ: Fibrodysplasia ossificans in a German shepherd dog. J Small Anim
Pract 2001;42:550-553.
4. Lipscomb AB, Thomas ED, Johnston RK: Treatment of myositis ossificans traumatica
in athletes. Am J Sports Med 1976; 4:111-120.
5. Waldridge BM, Beard D, Livesey LC: What is your diagnosis? Myositis ossificans. J
Am Vet Med Assoc 2004;225:1533-1534.
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two dogs. J Small Anim Pract 1976;17:371-377.
7. Tambella AM, Palumbo Piccionello A, Dini F, et al: Myositis ossificans circumscripta
of the triceps muscle in a Rottweiler dog. Vet Comp Orthop Traumatol
2013;26:154-159.
8. Vilar JM, Ramirez G, Spinella G, et al: Kinematic characteristics of myositis
ossificans of the semimembranosus muscle in a dog. Can Vet J 2010;51:289-292.
9. Warren HB, Carpenter JL: Fibrodysplasia Ossificans in 3 Cats. Vet Pathol
1984;21:495-499.
10. Aron DN, Rowland GN, Barber DL: Report of an Unusual Case of Ectopic
Ossification and Review of the Literature. J Am Anim Hosp Assoc 1985;21:819829.
11. Yabuzoe A, Yokoi S, Sekiguchi M, et al: Fibrodysplasia Ossificans Progressiva in a
Maine Coon Cat with Prominent Ossification in Dorsal Muscle. J Vet Med Sci
2009;71:1649-1652.
12. Dillon EA: Traumatic Myositis-Ossificans in a Dog. NZ Vet J 1988; 36:152-153.
13. Van Vleet JF, Valentine BA: Muscle and Tendon. in Maxie JM (ed): Jubb, Kennedy
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FIGURE LEGENDS
Figure 1 Lateral radiographic projections of the right humerus and elbow of a young Irish
Setter dog with ossifying myositis of the extensor carpi radialis origin. A) 2 months after
traumatic event to right thoracic limb: note the irregularly shaped bony proliferation
associated with the cranial aspect of the distal humerus; B) 6 months after traumatic
event: the bony proliferation appears larger along distal edge, smoothly marginated and
more homogenous; C) immediately postoperatively: most of the bony proliferation has
been successfully removed; D) 2 months: the osteotomy surface remains smooth with
increased bone density along the cut surface. No evidence of new bone formation; E) 10
months: no bone regrowth with smooth cortical bone surface.
Figure 2 Sequential transverse CT images from proximal to distal through the right distal
humerus. There is a large new bone formation associated with the craniolateral aspect of
the right distal humerus (A) involving the lateral epicondylar crest (B). The bony
proliferation separates from the distal humerus (C) as it continues craniodistally but
returns to close proximity to the lateral aspect of the humeral condyle (D).
Figure 3 Sequential sagittal CT images from lateral to medial through the right humeral
condyle. The bony proliferation arises from the distal humerus and lateral epicondylar
crest (A, B) but is not attached to the medial side of the distal humerus or the humeral
condyle (C). Note the increased soft tissue density in the cranial aspect of the elbow joint
surrounding the bony proliferation.
Figure 4 Photomicrograph illustrates a sagittal section of the bony protrusion removed
from the crest of the lateral epicondyle of the humerus. There is evidence of the orderly
cancellous origin of this proliferation in which hematopoietic bone marrow elements are
present. The cancellous bone in the more narrow outer end of the protrusion is haphazard
in appearance and contains some islands of hyaline cartilage. This hyaline cartilage is
believed to be associated with the chondroid metaplasia related to the tendon insertion
lines of the attachment of the extensor carpi radialis muscle before it was dissected from
the surface of this bony protrusion. 10x Hematoxylin and eosin stain.