Diagnostic Imaging Test 1

Standard views of distal phalanx (P3)

Lateral, 45 DP (optionally, obliques and horizontals).

Lateral / lateromedial P3 view

Marker on dorsal hoof wall, horse standing on a block with the centre on the coronary band.

60 DP P3 view

Foot placed on block with a tunnel, with the centre on the coronary band, and the cassette in the tunnel.

Lateral, medial oblique views

45 DP shots of the lateral, medial sides of the foot.

Horizontal DP P3 view

Vertical cassette, with flat horizontal beam (can assess weight bearing).

Laminitis

Separation of P3 from the hoof wall due to loss of laminae in the hoof capsule, often bisymmetrical in the front. Observed radiographically by the displacement of P3 within the hoof capsule.

Evaluation of laminitis

Lateral, DP views bilaterally or on all four feet which are repeated to follow progression.

Acute / progressive laminitis

May show no radiographic changes, but may have P3 rotation, sinking, or increased lucency. Measured through the dorsoproximal and dorsodistal hoof thickness, parallellism, and shifting.

Chronic laminitis

May show remodeling of dorsodistal P3 (ski-tip appearance), pedal osteitis.

Assessing P3 fractures

Seen as linear, radiolucent defects in P3 which may be visible for years (heal by fibrosis). May require multiple projections.

Types of P3 fractures

I: abaxial, non-articular.

II: abaxial, articular DIJ.

III: midline sagittal, articular.

IV: extensor process, articular.

V: comminuted, articular or non-articular.

VI: solar margin.

Pedal osteitis

Idiopathic roughening of P3 solar border, resulting in P3 inflammation. May be accompanied by enlarged vascular channels, solar margin thinning, and a positive hoof tester response.

Infectious / septic osteitis

Lucent defect due to bony lysis, without a periosteal reaction. Due to a solar abscess or penetrating wound.

Mineralisation of the collateral cartilages

Usually incidental, may have a separate ossification centre (thus, appearing like a fracture). Draught horses predisposed.

Keratoma

Growth of keratin tissue between P3 and the hoof wall, visible as a smooth, focal radiolucent area without surrounding sclerosis.

Navicular syndrome

Forelimb lameness associated with the navicular bone and bursa, DDF tendon, and impar ligaments. Quarterhorses predisposed.

Standard projections for navicular bone

Lateromedial, 60 DP cone-down, skyline (PPPO).

60 DP cone-down view of navicular bone

Visualises distal navicular border (bone is superimposed on P2). Should be centered on coronary band, can be done upright pedal (vertical cassette) or high coronary (horse stands on cassette tunnel, easier but more distortion).

Skyline view of navicular bone

Angle x-ray beam along back of distal pastern to analyse the flexor surface, corticomedullary distinction, and vascular channels.

Radiographic findings of navicular syndrome

Increased number, size of synovial channels (radiolucent), irregularly shaped distal border, radiolucent areas in spongiosa, loss of corticomedullary distinction, enthesiopathy, distal border fragments, or a bipartate navicular bone.

Osteomyelitis of navicular bone

Usually due to penetrating wound to navicular bursa, resulting in lysis or flexor surface erosion.

Osteoarthritis

Common in the forelimbs of older horses at the distal and proximal interphalangeal joints (low, high ringbone). Displays as joint space narrowing, osteophyte formation, subchondral sclerosis and joint effusion.

Normal structure of P1

Radiolucent centre (no trabeculae, fatty marrow cavity). Note nutrient foramina, ligamentous attachments.

Differentiation of sesamoid bones

Lateral sesamoid bones are more apically pointed (“L-shaped”).

DLPMO / DMPLO

DLPMO: highlights dorsomedial, lateropalmar leg (beam enters dorsolateral, exits mediopalmar).

DMPLO: highlights dodrsolateral, mediopalmar leg (beam enters dorsomedial, exits lateropalmar).

Fetlock oblique view

Visualises sesamoids without superimposition, can be done DLPMO or DMPLO.

Flexed lateral view

Non-weight bearing, allows viewing of sagittal ridge of metacarpal III and the articular surfaces of the sesamoid bones.

Signs of degenerative joint disease

Osteophytes, entheseophytes, subchondral sclerosis, joint space narrowing, and soft tissue swelling.

Fetlock osteochondrosis / OCD

May see flattening and fragments of dorsoproximal sagittal ridge, best seen on flexed lateral view. May see flattening, sclerosis and fragments of the palmar or plantar aspect of P1 condyle, usually induced by trauma. Mild lameness is good with surgical remooval.

Distal metacarpal III condylar fracture

Usually lateral to sagittal ridge, may require multiple obliques.

Sesamoiditis

Non-infectious inflammation, resulting in strain on suspensory branches and distal sesamoidean ligaments, as well as bony proliferation on the non-articular surface of the proximal sesamoid, and enlarged vascular channels. May result in pathologic fractures or cyst formation but primarily affects the soft tissue.

Bucked shins / dorsal metacarpal periostitis

Painful, acute periostitis on the dorsal surface of P3, appearing as thickening of the dorsomedial cortex with periosteal reaction. Common in young racehorses due to cyclic loading, progressive microfractures and eventually stress fractures.

Metacarpal / metatarsal III fractures

Stress fractures generally occur in the mid dorsal cortex and form a lucent “saucer shaped” line.

Osteomyelitis

MC/MT III especially prone in the dorsal cortex if traumatised, due to low soft tissue and blood supply.

Splint bone fractures

Most common is simple fracture in distal third, if proximal may be more complicated and be comminuted or involve osteomyelitis. Should assess the surface, sesamoid bones, and suspensory ligament.

Splints / exostosis of MC/MT III

Associated with young racehorses, swelling of interosseus suspensory muscle between MC II & III, affecting mainly the medioproximal aspect.

Standard views of stifle

Lateral, caudolateral craniomedial oblique (CLCMO), or caudocranial joint views.

Lateral view of stifle

Larger, more cranial medial trochlear ridge, with visualisation of the femoropatellar joint, medial and lateral femorotibial joints.

Caudocranial view of stifle

Fibula is lateral, may have separate ossification centres that do not fuse (vestigal, do not mistake for fracture).

Flexed lateral view of stifle

Non weight-bearing view, patella is dorsal (so can evaluate proximal trochlear ridges). Check for cranial cruciate avulsion fragments.

Skyline view of patella

Cranioproximal-craniodistal, observing for fracture or fragmentation (usually medial), common in chase or event horses.

Caudolateral craniomedial oblique (CLCMO)

Highlights most common young horse abnormalities: lateral trochlear ridge of femur and medial femoral condyle.

Stifle OCD

Usually found on lateral trochlear ridge of the femur, observed in lateral and oblique views.

Osseus cyst-like lesion of stifle

Found on medial femoral condyle, appearing as a round radiolucent subchondral defect with a sclerotic rim.

Stifle DJD

Sequelae to stifle injury, common in medial femorotibial joint accompanied with large osteophytes, enthesiophytes, effusion and sclerosis. Note that joint space narrowing does not mean DJD, moreso meniscal damage.

Tibial fractures

Common in tibial tuberosity of adult horses (doesn’t fuse until age 3 so consider for younger horses). Incomplete fractures common in proximal 1/3, beginning laterally.