Small Animal Orthopedic Radiology Lecture 3 – Acquired Bone Diseases Fracture Healing and...

Small Animal Orthopedic Radiology

Lecture 3 –

Acquired Bone Diseases

Fracture Healing and Evaluation VCA 341 Fall 2011

Andrea Matthews, DVM, Dip ACVR Assistant Professor of Radiology

Hypertrophic Osteopathy (HO)

Occurrence Middle aged to older dogs Usually due to concurrent thoracic or abdominal

disease• Often pulmonary neoplasia; also reported with

pulmonary abscesses, bronchopneumonia, bacterial endocarditis, heartworm disease, esophageal pathology, as well as hepatic and bladder neoplasia

Gradual or occasional acute onset in lameness Animal reluctant to move Symmetric, non-edematous, firm swelling of the

distal limbs

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Roentgen signs Solid, irregular periosteal reaction

• Palisading or columnar new bone formation

Never confined to a single location - Usually bilaterally symmetrical and generalized

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Roentgen signs Begins on the abaxial surface of the 2nd and

5th metacarpal/metatarsal bones and progresses proximally

Spares the small bones of the carpus and tarsus• But is seen on the accessory carpal bone and

calcaneus

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Location of periosteal reaction is diaphysis of tubular bones

Radiographs of the thorax and abdomen should be obtained to investigate for underlying disease

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Fungal Osteomyelitis

Occurrence Typically seen in young to middle-aged dogs May be seen in any breed; however, more

common large breeds such as working or sporting breeds

Usually hematogenous in origin

Often systemically ill Fever Lethargy Anorexia Lymphadenopathy, etc…

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Roentgen signs Variable radiographic appearance

• Both lytic and productive changes• Periosteal reaction usually semi-aggressive• Osteolysis may extend through the cortex

Usually in the metaphyseal region of long bones• May be joint involvement with extensive bone destruction

Often polyostotic but can be monostotic

Differential Diagnoses Primary bone tumors Metastatic bone tumors

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Fungal Osteomyelitis and arthritis

Bacterial Osteomyelitis

Occurrence Usually secondary to…

• Direct inoculation (bite wound, open fracture, or surgery)

• Extension from soft tissue injury May be hematogenous in young or

immunocompromised animals• Hematogenous route is much less common in small

animals

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Roentgen signs Earliest stage

• No bony abnormalities, just soft tissue swelling

May take 7-14 days before periosteal reaction visible

Periosteal reaction typically solid and extends along shaft of diaphysis; however, can be lamellar to palisading/columnar

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Nonhematogenous origin Lesion location depends on affected area May affect multiple bones in the same limb Lucencies around surgical implants May see draining tract from surgical implant or foreign

body

Hematogenous origin Metaphyseal due to extensive capillary network Often multiple limbs affected (polyostotic)

Differential Diagnoses Healing fracture Primary or metastatic bone tumor Fungal osteomyelitis

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Primary Bone Tumors

Occurrence Mostly large and giant breed dogs; no breed

predilection Mean age = 7 years

• Bimodal distribution seen in animals as young as 6 months

Slightly more common in male dogs May be associated with a previous fracture or

metallic implant

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Primary Bone Tumors

Roentgen signs Radiographic appearance is variable

• Primarily osteoblastic• Primarily osteolytic• Combination of both

Lytic and/or productive changes are aggressive in nature

Typically monostotic Located often in metaphyseal region of a

long bone Does not typically cross the joint

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Primary Bone Tumors

Osteosarcoma Most common primary bone tumor (>85%) “Away from the elbow, toward the knee”

Chondrosarcoma

Fibrosarcoma

Hemangiosarcoma

Differential diagnoses Osteomyelitis Metastatic neoplasia

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Primary Bone Tumors

Fracture Evaluation and

Bone Healing

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Fracture Evaluation

Initial radiographs Two orthogonal views (90o to one another) Include the joint proximal and distal to the fracture

• Determine joint involvement Special radiographic views may be necessary to

determine the extent of the fracture• Oblique, etc

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Fracture Recognition

Most are visible as abnormal radiolucent lines Some may not be as obvious Ex. Compression, non-displaced or

pathologic fracture Occassionally, compression

fractures may result in alteration in size or opacity, creating a summation opacity (more opaque than normal)

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Fracture Recognition

Non-displaced fractures May not be seen initially Seen days later when resorption of

bone at fracture margins has occurred

Some are recognized by presence of bony callus

If clinical suspicion of fracture is high but equivocal Nuclear medicine

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Fracture Description

Fracture types Open vs closed Incomplete vs complete Simple vs complex/comminuted Transverse, oblique or spiral Extra-articular, articular,

compression, avulsion Displaced vs. non-displaced

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Bone Healing

Primary bone healing Occurs with rigid internal fixation Results in bony union through direct

growth of haversian system across the fracture

Minimal to no bony callus Cannot occur across a fracture gap Usually occurs with compression

plate reduction

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Primary Bone Healing

Radiographic signs of primary bone union Lack of callus Gradual loss in opacity of fracture

ends Progressive disappearance of

fracture line

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Bone Healing

Secondary bone healing Lack of rigid internal fixation

and excellent anatomic reduction

Bone heals through initial deposition of fibrous tissue • Callus formed by series of

maturations

• Granulation tissue cartilage mineralized cartilage replaced by bone

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Most common type of fracture healing in small animals

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Secondary Bone Healing

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Secondary Bone Healing

Bone Healing

Factors that affect bone healing Fracture location Vascular integrity Degree of immobilization Fracture type Degree of anatomic reduction Degree of soft tissue trauma Degree of bone loss Type of bone involved Presence of infection Local malignancy Metabolic factors

Age, breed, species Presence of systemic disease Steroid administration

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And on and on and on…

Initial Postoperative Evaluation

Evaluate; Fracture alignment Degree of fracture reduction

• Needs to be at least 50% reduction of fracture margins

Presence of joint incongruities• Step deformities

• If fracture is articular Rotation of fracture fragments

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Initial Postoperative Evaluation

Evaluate; Placement of fixation devices

• With bone plate, ideally want 6 corticies engaged with cortical screws above and below the fracture site

• Pins of external fixator should be angled 65-70o to bone Not possible with all types of external fixators

• Cerclage wires should be of adequate size, be perpendicular to the long axis of the bone, be a minimum of 1 cm apart, be adequate in number and fit snugly against the cortex

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Growth Plate Injuries

Good prognosis

Poorer prognosis

Guarded prognosis


Occurrence Etiologies

• Trauma• Severe hypertrophic osteodystrophy (HOD)• Retained cartilaginous core

Skeletally immature animals <1 year Prognosis

• Salter Harris Type I and II have better prognosis• Type III and IV have poorer prognosis due to

disturbance of resting cell layer• Type V have guarded prognosis due to damage of

proliferative zone

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Roentgen signs Unilateral or bilateral

• Radiographs both limbs for comparison Affected physis may initially appear normal or may

be closed Skeletal deformities Distal ulnar physis is commonly affected due to

shape• Often type V

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Premature Distal Ulnar Physis Closure

Roentgen signs Affected ulna is measurably

shorter than contralateral side (unless bilateral)

Styloid process of ulna may be separated from carpus

May have cranial and/or medial bowing of radius• Cortical thickening of the concave

side of the radius (due to stress remodeling)

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Roentgen signs Distal radius is subluxated

craniomedially from the radiocarpal bone

Manus deviates laterally• Carpal valgus

Humero-ulnar joint space may be widened (subluxation)

+/- osteoarthrosis

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Note widening of the humero-ulnar joint (black arrows)

Note the UAP that can occur secondarily (green arrow)

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Premature Distal Radial Physis Closure

Roentgen signs Shortened length of the radius compared to

contralateral side (unless bilateral) Increased radiocarpal joint space Increased humero-radial joint space (subluxation)

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The elbow is key to determine origin of slowed growth

Normal Radial physeal closure

Ulnar physeal closure

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Premature Distal Radial Physis Closure

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End

Small Animal Orthopedic Radiology Lecture 3 – Acquired Bone Diseases Fracture Healing and...

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