Radiography of the equine fetlock

A case study explaining the indications, preparations and techniques required to carry out a radiograph of the Fetlock joints in equine practice. For veterinary use.

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Radiography of the equine fetlock

Equine Radiography – the Metacarpo- and Metatarsophalangeal Joints (Fetlocks): ‘Standard Views’

Indications

  • Investigation of lameness localized to the region of the fetlock joint (as determined by perineural/intra-articular anaesthesia).
  • Pre-purchase examinations.
  • Investigation of traumatic/penetrating wounds to the fetlock region.
  • Assessment of angular limb deformities.
  • Monitoring progression of disease.

Preparation

  • Ensure the hair coat is clean to minimize the likelihood of artefacts appearing on the radiograph.
  • Particularly nervous horses may need to be sedated, although radiography of this region is usually well-tolerated by most horses.
  • The horse should be standing as square as possible, evenly weight-bearing on all four limbs, with the cannon bone of the limb to be radiographed as vertical as possible in both planes.
  • Remember that use of markers is very important – LEFT and RIGHT but also FORE LIMB and HIND LIMB (easily added on modern digital systems). By convention the L/R markers are placed either laterally on a DP view, or dorsally on lateral and oblique views.

Views

  • Four or five ‘standard’ views:
    • lateromedial
    • dorsopalmar
    • dorsolateral-palmaromedial oblique
    • dorsomedial-palmarolateral oblique
    • (flexed lateromedial)
  • Various other ‘specialist’ views for identifying specific lesions or when the ‘standard’ views have found no pathology.
  • Note that the techniques are the same for the hind limb as for the fore limb but for the sake of brevity only the fore limb terminology is given below.

Technique

  • Lateromedial view (LM):

 

  • the x-ray beam should be horizontal, and perpendicular to the dorsopalmar axis of the leg at the level of the fetlock joint.
  • centre on the joint space.
  • beware animals standing with the limb slightly turned out (or in) – a true lateral view is necessary to fully evaluate the sagittal ridge of the cannon bone.
  • Dorsopalmar view (DP):

 

  • center on the joint space.
  • a horizontal x-ray beam will lead to superimposition of the proximal sesamoid bones on the joint space, but…
  • a dorsoproximal-palmarodistal angulation of 10-15o will prevent this from happening.
  • Dorsolateral-palmaromedial oblique (DLPMO):
    • highlights the dorsomedial and palmarolateral (abaxial) aspects of the joint, as well as the sesamoid bones.
    • the x-ray beam should be horizontal, and at a 45o angle to the dorsopalmar axis of the leg, aiming from a dorsolateral position towards a palmaromedial position.
    • center on the joint space.
  • Dorsomedial-palmarolateral oblique (DMPLO):

    • as for the DLPMO but from a dorsomedial position aiming towards a palmarolateral position.
  • Flexed lateral:
    • highlights the articular surfaces of the proximal sesamoid bones.
    • raise the foot either by placing on a wooden block or by holding the toe with a gloved hand (to a height of 20-30cm).
    • center on the centre of the condyles of MC III.
    • remember to aim to get a true lateral view as with the standard LM view.
    • this view may require a lower mAs setting.

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