P3 & distal sesamoid fractures

Question 1

Causes of navicular and P3 fractures

Answer 1

• acute onset trauma
• developmental / osteochondral fragments
• repetitive wear and tear / chronic disease

Question 2

Types of fracture

Answer 2

• small fragments
• large complete fractures
• stable or unstable
• articular and non-articular

Question 3

Causes of non-articular fragments from the sole surface of the pedal bone

Answer 3

• usually caused by repetitive wear and tear
  – usually horses with poor foot conformation and repeated concussive forces
  – will heal with rest and re-shoeing
• They can also occur due to acute onset trauma with a penetrating injury and infection
  – in which case the fragment will need removing
• But both of these options have good outcomes - it’s a small area of bone, it doesn’t involve substantial part of the bone and it doesn’t involve an articular surface.

Question 4

Clinical signs of navicular and P3 fractures

Answer 4

▪Clinical signs depend on fracture site and severity

▪Small extra articular fragments – low grade lameness with minimal
localising signs

▪Significant / complete fractures – acute onset, severe lameness with localising signs (bounding digital pulses, heat in hoof, positive response to hoof testers)

▪Articular fragments – Distal interphalangeal joint effusion (pedal bone and navicular bone)

▪Tendon involvement – digital flexor tendon sheath effusion (navicular bone)

Question 5

Diagnosis of navicular and P3 fractures

Answer 5

• Both bones are enclosed within the hoof capsule, therefore there’s often minimal displacement of the fractures and identification on PE is difficult
• Careful palpation of the hoof and pastern region for heat, pain and swelling (including synovial effusions)
• Use of hoof testers to identify site of pain

▪Radiography
▪ MRI
▪CT
▪Gamma scintigraphy
▪Nerve and joint blocks – only for mild / chronic cases – avoid in severe / significant fractures

Question 6

Challenges of radiography

Answer 6

▪The hoof structure holds the bones together so fractures may not be
visible initially, until some bone resorption has occurred (7-10 days)
– consider repeat radiographs around 10-14 days
▪Some fractures only heal with a fibrous union (fracture line remains on radiographs [black line], but are stable) – chronic fractures may need additional tests to confirm if clinically significant
– MRI, CT or bone scans can be useful for both these scenarios - both to tell you whether there’s other tissues involved and if it is still active, if budgets allow.

Question 7

Causes of a fragment at the site of the extensor process

Answer 7

▪ Recent fracture
▪ Previous fracture, now healed and stabilised
▪ Separate centre of ossification
▪ Dystrophic mineralisation in the extensor tendon

Question 8

Radiographic technique - 5 views for a standard foot radiographic series

Answer 8

1. Lateromedial
2. Dorsopalmar
3. Dorsoproximal Palmarodistal 60o oblique centered on pedal bone (upright pedal)
4. Dorsoproximal Palmarodistal 60o oblique centered on navicular bone (upright navicular)
5. Palmaroproximal Palmarodistal 45o oblique (flexor navicular)

▪Of both feet
▪Plus additional oblique views of the pedal bone

Question 9

Latero-medial

Answer 9

▪ Feet on blocks – Even when X-ray machine on floor the light beam diaphragm cannot open to floor- so need to raise the horse. They are more comfy with both feet on blocks at the same time.
▪ Use heel bulbs to help you – line something straight along them (as long as they are symmetrical). Then align side of X-ray machine to that- this helps prevent rotation of image by aligning the primary beam perpendicular to the sagittal plane of P3.
▪ Dorsal wall marker/Frog marker if clinical signs require measurements
▪ Check horizontal beam (use spirit level or X-ray machine may have ball baring at side)
▪ Set exposures (exposure book/chart)
▪ Check focal film distance
▪ Centre 1cm below coronary band half way between dorsal and palmar
▪ Collimate- tight as possible

Question 10

Dorsopalmar/plantar (DPa)

Answer 10

▪ Foot on block
▪ Make sure limb is straight – or may cause image to look like horse has foot imbalance when it doesn’t
▪ Check horizontal beam
▪ Centre on the middle of the coronary band

Question 11

Upright Pedal/D60Pr-PaDi oblique

Answer 11

▪ Upright - leg positioned against block, beam horizontal. Better image, but need/expose extra person (wear gloves)
▪ Tunnel – foot positioned on top of block, x-ray machine angled down 60o, needs less people, but get some image distortion
▪ Both: Center on coronary band and open out to include all of pedal bone
▪ Pack foot with play doh to avoid air artefact
– air within the frog sulci underneath the foot creates black lines and shadows that can look like fractures

Question 12

Upright Navicular/D60Pr-PaDi oblique

Answer 12

▪ Same approach as for pedal bone views
▪ If upright in block, tip foot over slightly so dorsal hoof wall about 85 degrees from horizontal
▪ Tunnel as for P3 view
▪ Centre 1-2 cm above the coronary band
▪ Collimate right down to reduce scatter
▪ Pack the foot with play doh
– air within the frog sulci underneath the foot creates black lines and shadows that can look like fractures.

Question 13

Flexor Navicular / Pa45Pr-PaDi oblique

Answer 13

▪ Foot on tunnel
▪ Foot caudal on block
▪ Access: Toe in/ block out
▪ Not always at 45°
▪ steepest angle possible
without hitting back of fetlock
▪ Centre between heel bulbs
▪ Collimate, and check your film focal distance
▪ For safety, try and sort film focal distance, angle and collimation away from horse beforehand