Ultrasonographic Evaluation of the Distal Extremity

Despite the increasing use of magnetic resonance imaging
(MRI), ultrasound remains a valuable tool to diagnose
injuries that cause distal extremity lameness in
the horse. The key to a successful examination is a strong
knowledge of anatomy in combination with proper ultrasonographic
technique and the patience and dedication
to learn these skills. Similar to all imaging
modalities, it is equally important to recognize and consider
the limitations of ultrasound in this region so that
findings can be interpreted appropriately. Ultrasound
can be used to diagnose injuries to the deep digital flexor
tendon (DDFT), straight distal sesamoidean ligament
and branches of the superficial digital flexor tendon using
standard pastern ultrasonographic technique. The
addition of newer techniques to image the DDFT at
the level of P2, the navicular bursa and the collateral sesamoidean
ligament can enhance the diagnostic utility of
ultrasound in horses with distal extremity lameness. Although
visibility is limited, ultrasound can be used to diagnose
collateral ligament injuries of the coffin joint in
many affected horses. Transcuneal imaging may be useful
in some horses to detect abnormalities of the distal
sesamoidean impar ligament and navicular bone, but
evaluation of the DDFT is limited. Ultrasound should
be considered in all horses with distal extremity lameness,
regardless of the ability to perform advanced
imaging procedures. Information gained is often complementary
to other imaging modalities and may provide
the basis for recheck examination purposes.