Sonographic anatomy of the palmarodistal aspect of the equine digit

Although ultrasonography is widely used in equine orthopedics, its use in the distal portion of the digit is still limited. The purpose of this descriptive study was to document the normal ultrasonographic appearance of the palmarodistal aspect of the digital area imaged between the bulbs of the heels. Ultrasonographic images were obtained with a 7.5 MHz microconvex transducer in 10 fresh equine cadaver forelimbs and five sound horses. Sagittal, parasagittal, and transverse images were obtained from the proximal aspect of the middle phalanx to the distal sesamoid bone. Anatomic sections were obtained from five cadaver specimens to correlate the sonographic appearance with the anatomic findings. The remaining cadaver limbs were dissected to confirm normalcy. Ultrasonographic examinations were possible on all digits but distal images were more difficult to obtain in digits with long heels. Bony structures (palmar surface of the middle phalanx and proximal border of the distal sesamoid bone) and soft tissue structures (deep digital flexor tendon, digital tendon sheath, proximal palmar recess of the distal interphalangeal joint, proximal recess of the podotrochlear bursa, collateral sesamoidean ligaments) identified on the anatomic slices were seen on the matched sonographic images. Ultrasonography provides good anatomic details of the palmarodistal aspect of the digit. The images of this study will serve as a reference for clinical studies on ultrasonography of the palmarodistal aspect of the digit.