Equine Lameness and Diagnostic Imaging

Basic sequence of orthopaedic lameness examination

1. Physical examination (before trotting)

   • Heat

   • Swelling

   • Palpable pain

   • Wounds

2. Testing pain (manipulative tests)

   • Care needed → may exacerbate lameness

   • Not very area specific

   • Flexion tests

     • Thoroughbreds → flex carpus to test fractures or synovitis

   • Wedge/plank test

     • Hyperextend joint with wedge/plank

     • Often used for DIP → puts pressure on navicular apparatus

   • Varus/valgus stress test

3. Lameness identification

   • Which limb(s) - trotting/walking for lameness recognition patterns

   • Origin of discomfort - diagnostic imaging

   • Cause of pain - nerve blocks

Equine forelimb lameness pattern

Head nod

• Sound limb weight bearing → head drops down

• Lame limb weight bearing → head raises up

  • reduces load placed on painful limb

Equine hindlimb lamness pattern

Pelvic hike

• Sound limb weight bearing → tuber coxae (ilium) drops down

• Lame limb weight bearing → ilium hikes up

  • Shifting CoM towards sound limb

Additional features for lameness recognition

• Not necessarily associated with gait symmetry

• Asymmetry of <20-25% difficult to detect

• Foot placement → heel → toe strides

• Limb flight → affected by joint flexion

• Joint angles

• Stride length

• Stance duration

Objective lameness exam- location of inertial motion sensors [5]

1. Poll

2. Withers

3. Tuber coxae

4. Sacrum

5. Back

Mixed results from objective scanning

Example:

• Sacrum sensor

  • Right hindlimb pushoff indicates lameness

  • Measurements show slight asymmetry to the right

• Poll and wither sensors indicate contradicting results → mildly right and left forelimb lame

  • Indicates right forelimb lameness is referred due to right hindlimb lameness

  • contradiction means not primary lameness

• Takeaway → can refer lameness from 1 leg to another

• Multi limb lameness → always examine the most lame leg first

• Laminitis can impact all 4 legs

Multilimb lameness

• Lameness referred: fore → hind:

  • CONTRALATERAL side

• Lameness referred: hind → fore:

  • IPSILATERAL side

• Example presentation:

  • Asymmetrical hip hike

  • Extreme head nod

    • More likely that forelimb is primary

Peripheral nerve blocks (distal → proximal)

• Roughly localise source of lameness

• Abnormality found with imaging after localisation with block

1. Palmar digital nerve block (PIP) → removes sensation beyond fetlock

2. Abaxial sesamoid nerve block (MCP)

3. Palmar metacarpal/tarsal nerve block → removes sensation beyond metacarpal/tarsal

4. Palmar nerve block (between suspensory ligaments + ddft)

3 + 4} 4 point blocks - medial and lateral side

1. Low palmar/plantar digital block → navicular bursa and distal phalanx

2. Midpastern palmar/plantar digital block → DIP joint + all deep structures EXCEPT lamellar corium

3. Abaxial sesamoid block → PIP joint, distal sesamoidean ligaments, lamellar corium

4. Low palmar/plantar block → MCP/MTP joints and proximal sesamoids

   • 4a → distal ends of both splint bones

   • 4b → distal to communicating branch

DP → DIP → PIP → MCP/MTP

Examination - inside the foot

• 80% of lameness originates from foot

  • 60-70% of these are foot abscesses

• Inaccessible to palpation → requires hoof capsule imaging

• ACCESSIBLE structures palpated:

  • Dorsal coffin joint capsule

  • Proximal coffin joint collateral ligaments

  • Collateral cartilages

  • Tendons (+ sheaths) in heel bulbs

Positive response to palmar digital nerve block

Contenders:

• Soft tissue

• Intra-articular synovial problem

  • PIP

  • DIP (dorsal/palmar synovial recesses)

  • Navicular bursa

  • All 3 separated by T ligament

• DDFT

Additional nerve blocks

• Dorsal DIP (coffin) block

• Navicular bursa block (palmar/plantar)

  • Otherwise known as the Hickmans block

  • Navicular apparatus block between heel bulbs

Imaging

1. Radiographs

2. CT → dome

3. Standing CT

4. Ultrasonography

5. MRI

6. Nuclear scintigraphy

• Radiographs can be sufficient for diagnosis → don’t trot horse

  • fractures → surgery

  • Acute laminitis → black air in hoof

  • Severe navicular bone disease

    • Extensive bone formation

    • Lytic areas

• CT distal limb up to fetlock

• Standing CT

  • Distal limb

  • also can be used for head and cranial neck

• Ultrasonography → flexor tendons

  • Palmar aspect → look for central area of hypotenicity

    • Central area core lesion → haemorrhage and granulation tissue

    • Histology → irregular collagen and haematoma

  • Breakage or rupture of tendon

  • Fluid accumulation and irregular contours for bones (e.g. ilium wing stress fracture)

• MRI

  • Do around distal limb

  • Stimulates tissue with radio frequency

  • Measures signal + convert to computerised image

  • Often used for inside hoof

• Nuclear scintigraphy

  • Inject horse with radioactive substance binding to skeleton hydroxyapatite

  • 2-3 hr later → measure radiation and convert to 2D image

  • Compare L/R for abnormalities