DI musculoskeletal imaging

Plan for radiographing a dog with localised lameness

Radiograph the joint or long bone that the lameness is localised to

• Joint - include 1/3 of the bone above and below

• Long bone - include the joint above and below

Plan for radiographing a dog with unlocalised lameness

Screening radiographs

Radiograph all of the limbs - 2 views + other leg

Centring for screening radiographs

Not important even in large breed dogs as limbs are thin - there is very little distortion of a joint when not centred on the joint

How many screening radiographs are needed

Radiograph each joint (most lameness originates from joint) and increase the collimation to include the long bones

• So, 6 radiographs for each limb - 3 lateral and 3 CC

Thoracic vs pelvic limb screening radiographs

Thoracic - the elbow and carpus cannot be straight at the same time so separate radiographs are needed for lateral and CC

Pelvic - the whole limb is straight at the same time

Thoracic vs pelvic limb screening radiograph positioning

Superman for thoracic limb lateral views and extend the neck dorsally

Peeing position for pelvic limb lateral views and foam under the rump

• ONLY one limb per image (apart from hip extended VD)

Periosteal new bone

New bone on the outside of the bone → made by the periosteum which is the fibrous lining on the outside of bones

Benign causes of periosteal new bone

Trauma, panosteitis, inflammation in the soft tissues beside the bone

Aggressive causes of periosteal new bone

Bone neoplasia (primary, metastatic, polyostotic), osteomyelitis (bacterial, fungal)

Sclerosis

New bone on the inside of the bone

Causes of sclerosis

Stress remodelling eg third carpal bone in racing horses (Wolff’s Law), sequestrum – dead bone, panosteitis, bone infarction, fracture healing

Osteophyte

New bone on the edge of a joint (periarticular) is an osteophyte. It indicates osteoarthritis (OA) of that joint

Enthesophyte

New bone at the attachment of a ligament tendon or joint capsule. It indicates degenerative pathology in that ligament, tendon or joint capsule

Continuous periosteal new bone

Can draw a continuous line along it - benign

Continuous periosteal new bone Ddx

Trauma, panosteitis, adjacent soft tissue inflammation, low grade osteomyelitis, hypertrophic osteopathy

Interrupted periosteal new bone

Cannot draw a continuous line around it - aggressive

Interrupted periosteal new bone Ddx

Neoplasia, osteomyelitis

Geographic bone lysis

Single, well-defined

Usually benign

Rare → almost never seen in cats & dogs

Geographic bone lysis Ddx

Bone cyst, pressure atrophy, benign dental tumour, bone abscess, arteriovenous malformation

Moth eaten bone lysis

Multiple smaller areas of lysis that are less well defined

Aggressive

Moth eaten bone lysis Ddx

Neoplasia, osteomyelitis

Permeative bone lysis

Multiple pin-point areas of lysis

Poorly defined and hard to see

Highly aggressive and uncommon

Permeative bone lysis Ddx

Neoplasia, osteomyelitis

How can you tell if a bone lesion is aggressive

The assessment comes from the most aggressive periosteal new bone or bone lysis

So if there is both aggressive and nonaggressive new bone or bone lysis, ignore the less aggressive

Codman’s triangle

Continuous periosteal new bone on the edge of an aggressive lesion

Periosteum is lifted

Signs of an aggressive bone lesion

• Periosteal new bone – interrupted

• Bone lysis – moth eaten, permeative

• Cortex lysis - present

• Change over time – progression in 3 weeks

• Clinical information – signalment, recent orthopaedic surgery/dog attack

Neoplasia bone lesion Ddx

Primary – osteosarcoma (most aggressive bone lesions), others are uncommon

Secondary - metastasis eg carcinoma, haemangiosarcoma

Multicentric - eg lymphoma, multiple myeloma, histiocytic sarcoma, myeloproliferative (eg leukaemia)

Osteomyelitis bone lesion Ddx

Fungal - uncommon in Australia

Bacterial - only seen with open fracture and orthopaedic surgery (haematogenous infection is very rare in cats & dogs)

Metastatic neoplasia

Monostotic or polyostotic aggressive lesion

Diaphysis (often)

Older animals

Primary neoplasia: carcinoma, melanoma, haemangiosarcoma

Fungal osteomyelitis

Monostotic or polyostotic aggressive lesion

Lysis or new bone or both

Any age; often young

Located anywhere

Bacterial osteomyelitis

From the outside (open fracture or orthopaedic surgery)

Haematogenous → never see in adult cats & dogs; rare in puppies and kittens

Common in foals and calves

Often polyostotic

Location of osteoscarcoma in the forelimb

Metaphysis

“Away from the elbow”: distal radius and proximal humerus most common. Extremely rare to be close to the elbow

Location of osteosarcoma in the hindlimb

“Close to the stifle”: distal femur, proximal tibia, but distal tibia is of equal prevalence; Proximal femur slightly less common

So ‘away from the stifle’ is not so uncommon

Osteosarcoma signalment

Older, large breed dogs

• Biphasic – small peak at 2y & large peak at 8y

Small breed dogs - less often affected, older, similar prognosis

Appearance of osteosarcoma

Aggressive new bone & aggressive lysis

• Ranges from mostly lysis to mostly new bone

Metaphysis

Does not cross the joint

• Aggressive lesions that may be on both sides of the joint are soft tissue neoplasia (synovial cell sarcoma) or septic arthritis

Diagnosis of osteosarcoma

Thorax radiographs for pulmonary metastasis

FNA the bone with ultrasound guidance (diagnostic sample 90% of the time)

Bone biopsy centre of the lesion (not ideal)

Radiographic signs of panosteitis

Sclerosis - new bone on the inside → compare to the other limb!!

• Main and usually the only sign

+/- Periosteal new bone – continuous

Signalment of panosteitis

Relatively common in large breed dogs, most commonly the GSD

6 – 18 months old → but reported 2mths to 7 years

Clinical signs of panosteitis

Acute onset intermittent lameness in one or more limbs (no trauma)

• Each episode ~ 2 weeks and can go on for 2 - 9 months.

• Commonly a shifting lameness (ie. owner says last week they were painful on left limb, now right)

Pain on palpation on the long bones. It is often mistaken for joint pain as the long bones have to be held to flex and extend the joint

Describe the appearance of a fracture on radiographs

Complete/ incomplete

Open/ closed

Where - diaphysis, metaphysis, epiphysis

Type - transverse, oblique, spiral

Simple or comminuted

Displacement

Salter-Harris fractures

Fractures of the open physis

Only young dogs/ cats can get Salter-Harris fractures as the physis has to be open

Salter-Harris Type I

Straight across → traverses the growth plate only (physeal separation)

Salter-Harris Type II

Above → traverses the growth plate and exits through the metaphysis

Salter-Harris Type III

Lower → traverses the growth plate and exits through the epiphysis

Salter-Harris Type IV

Two or through → passes through the metaphysis, growth plate and epiphysis

Salter-Harris Type V

Rammed → crushing of the growth plate

Pathologic fractures

Occur due to underlying pathology in the bone

Suspect from the history – no history of trauma (toy breed dogs sometimes have no history of trauma but have fractures that are not pathologic)

Pathologic fractures Ddx

• Aggressive bone lesion – neoplasia, osteomyelitis

• Incomplete ossification of the humeral condyle

• Secondary nutritional hyperparathyroidism

• Orthopaedics – empty screw hole, weak bone at end of plate

Secondary hyperparathyroidism

Metabolic bone disease → affects all bones

It is caused by high parathyroid hormone which causes loss of calcium from the bones

• This only affects the bones in young patients, as the bones are growing and more susceptible to abnormal calcium metabolism

Pathophysiology of renal secondary hyperparathyroidism

Only clinically affects the head

1. Kidney failure in puppies due to renal dysplasia

2. Reduced phosphorus excretion and reduced production of vitamin D

3. Parathyroid glands release parathyroid hormone

4. Loss of calcium from the bones

Pathophysiology of secondary nutritional hyperparathyroidism

1. All meat diet in puppies and kittens

2. Meat contains a large amount of phosphorus → poor calcium: phosphorous ratio in the diet

3. High phosphorus causes reduced production of vitamin D in the kidneys

4. Parathyroid glands release parathyroid hormone

5. Loss of calcium from the bones

Subluxation

The shorter bone pulls away from the elbow joint

Carpal valgus

The longer bone has to bow sideways to fit in

This causes the carpus to rotate outwards/ laterally

Causes of angular limb deformity

Normal for the breed

Due to trauma when growing

Breed related angular limb deformity

Chondrodystrophic breeds

Legs bow out and carpus rotates outwards (carpal valgus)

Can still cause lameness

Trauma related angular limb deformity

Most of the length of the radius and ulna come from growth at the distal physis

Trauma and early closure of one of these physes causes angular limb deformity

Causes bowing of the longer bone and carpal valgus

Who and where does angular limb deformity due to trauma effect

Happens most often in the distal ulna physis as it is cup shaped and therefore more affected by trauma

The distal ulna physis in cats is not cup shaped so it is not affected as often

Hypertrophic osteodystrophy

Uncommon, usually self-limiting

Suspect systemic infection

Distal radius, ulna and tibia

Hypertrophic osteodystophy signalment

Young (2-7 mo), large breed dogs

Hypertrophic osteodystrophy clinical signs

Painful swelling over metaphysis

Fever, lethargy, diarrhoea, anorexia

Hypertrophic osteopathy

Continuous or interrupted periosteal new bone on all limbs secondary to pathology elsewhere

Usually lung neoplasia so radiograph the thorax

Not always neoplastic - resolves when the primary cause is removed

Hypertrophic osteopathy signalment

Older dog, all 4 limbs affected (painful and swollen)

Hypertrophic osteopathy clinical signs

Present with clinical signs of lameness before clinical signs of the primary cause

Systematic approach to joints

SABCD

1. Soft tissues (may indicate where the problem is)

2. Alignment - angular limb deformity, fracture, congenital

3. Bone - cortex (outside) and medulla (inside)

4. Cartilage - joints + physes

5. Device - orthopaedic implants

Intracapsular soft tissue swelling

Inside the joint capsule (joint effusion)

Eg joint effusion, proliferation of the synovial lining

Extracapsular soft tissue swelling

Outside the joint capsule ie of skin, subcutaneous tissue, muscle

Eg cellulitis, oedema in the skin overlying the joint

Which joints can you tell if it is intracapsular or extracapsular soft tissue swelling

Confidently - stifle, tarsus as there is fat in the joint

Quite confidently - carpus, manus/pes (no muscles → mostly just skin)

Cannot tell - the rest (too much muscle around the joint)

Joint effusion Ddx

• Osteoarthritis (OA)

• Cruciate ligament disease

• Osteochondrosis

• Immune mediated (polyarthropathy)

• Septic arthritis

• Trauma to intra-articular structures

• Rarely, patella luxation

Neoplasia of the joint on radiographs

E.g. synovial sarcoma

The soft tissue opacity is actually tissue not effusion, but fluid and tissue are the same opacity so they cannot be differentiated on radiographs

Signs of osteoarthritis on radiographs

• Joint effusion

• Periarticular osteophytes – new bone at the edge of the articular cartilage (ie ‘periarticular’)

• Enthesophytes - new bone at the attachment site of the joint capsule, ligaments or tendons

The key to recognising aggressive joint disease:

Bone lysis on both sides of the joint

However, lysis may start on just one side, or when it is early, there may only be the soft tissue swelling (joint effusion or neoplasia)

Joint neoplasia

Soft tissue sarcomas → synovial cell sarcoma, histiocytic sarcoma, haemangiosarcoma

Lysis on both sides of the joint

Little or no periosteal new bone as the bone lysis is from the neoplasia outside so the periosteum gets destroyed on the way into the bone

Signalment of joint neoplasia

Older dogs, medium to large breed

Location of joint neoplasia

Stifle and elbow

Septic arthritis

Often haematogenous but usually direct inoculation

Radiographic signs of septic arthritis

Joint effusion ± bone lysis that may be on one side or both sides of the joint

No periosteal new bone as the infection is inside the joint where there is no periosteum

Signalment septic arthritis

Common in foals and calves with bone lysis

Rare in puppies (only inoculation), almost never in adult dogs

Location of septic arthritis

Haematogenous >1 joint

Direct inoculation 1 joint

Osteochondrosis

Focal, abnormal joint cartilage in young, large breed dogs

It has to also affect the underlying subchondral bone to be seen on radiographs as cartilage is not seen on radiographs

Locations of osteochondrosis

Head of the humerus

Medial aspect of the humeral condyle

Medial or lateral femoral condyle

Medial ridge of the talus

Joint mice

Little pieces of bone in the joint

Joint mice Ddx

• Osteochondrosis fragment

• Fracture fragment - trauma eg chip fracture

• Avulsion of ligament or tendon eg cruciate

• Osteophyte - broken off & in the joint (uncommon)

• Synovial osteochondroma – dystrophic mineralisation in the joint capsule (not uncommon)

• Mineralised meniscus - common in cats

Why are both shoulder and elbow radiographs often made

The shoulder cannot be assessed for pain without also loading the elbow joint → so it can be very difficult to determine if the pain is shoulder or elbow pain

Ddx of elbow and shoulder lameness in a young dog

• Elbow dysplasia - young large breed

• Osteoarthritis

• Panosteitis – young large breed

• Incomplete ossification of the Humeral Condyle (IOHC) – Springer spaniel > Cocker spaniel > French Bulldog

• Fractures - Salter Harris & articular fractures

• Incongruency – angular limb deformity (breed related or premature closure of the radial or ulna distal physis)

• Shoulder OC – shoulder and elbow pain are difficult to differentiate – young large breed

Shoulder osteoarthritis radiographic signs

Osteophyte on the caudal aspect of the humerus

Elbow dysplasia signalment

Young, large breed dogs

In young large breed dogs with elbow pain, it is due to elbow dysplasia until proven otherwise

Elbow dysplasia

Ununited anconeal process

Osteochondrosis

Suspected fragmented cornoid process

Ununited anconeal process

Anconeal process usually closes between 20-22 weeks - if it is still seen after this time it is ‘ununited’

Suspected fragmented coronoid process

Can only see properly on CT due to superimposition

If not available rule out UAP, elbow OC and shoulder OC

Incomplete ossification of the humeral condyle

The growth centre in the humeral condyle fails to close/ ossify

Closure normally starts at 2 weeks, and is complete by 8-12 weeks

IOHC signalment

French bulldog, Spaniel & spaniel cross breed dogs most common (but any breed)

Age – can present at any age. 55% present <1yo.

Male > Females (3:1)

Clinical signs of IOHC

Lameness can be caused by the IOHC itself (no fracture)

Pathological fracture with minimal trauma (eg jumping)

Radiography for IOHC

Make sure the centre of the olecranon is over the mid condyle

Shoulder radiography views

2 standard views - lateral and craniocaudal

Just lateral is acceptable if OC is most likely

Elbow radiography views

2 standard views - lateral (flexed) and craniocaudal

Flexed view is better for seeing osteophytes

How to assess for hip subluxation

Subluxation and osteoarthritis can be seen on extended pelvis VD radiographs

How to identify hip dysplasia/ subluxation on radiographs

Extended VD view

1. Find the edge of the acetabulum

2. Find the centre of the femoral head

3. The centre of the femoral head should be inside the acetabulum

Signs of hip OA

• Osteophytes along the femoral neck (Morgans line)

• Osteophytes around the femoral head

• Remodelling of the femoral head and neck

• Osteophytes on the acetabulum

• Flattening & widening of the acetabulum

Morgans line

Enthesophyte along the attachment of the joint capsule on the neck of the femur

It can be a normal finding

Earliest sign of OA

Ring of osteophytes hip OA

Ring of osteophytes around the femoral head (remember osteophytes are periarticular - around the articular part of the joint)