IN-DEPTH: HIND LEG FROM THE PELVIS DOWN
ated with the stifle. To be complete, the stifle should be scanned in both standing and flexed positions. Flexed imaging of the stifle allows imaging of the fem- oral condyles and associated cartilage, the cranial meniscal attachments to the tibia, and the cranial cruciate attachments. Radiographically, it is impor- tant to take high-quality radiographs. The author’s practice performs 6 standard views of the stifle: lat- eral, caudo-cranial, caudolateral-craniomedial oblique, caudomedial-craniolateral oblique, flexed lateral, and skyline of the patella.
11. Combined Imaging of the Tarsus
The tarsal region is also a complex region for sonog- raphy and includes the bone surfaces, all associated ligaments and tendons (calcanean, plantar, collat- eral, and dorsal), trochlear cartilage surfaces, and joint capsule/synovial membrane. The flexed hock allows the deep collateral ligaments and gastrocne- mius tendon (relaxed when fully weight bearing), to be viewed in tension, and exposes the caudal cartilage surfaces of the talus. Most practitioners are familiar with evaluation of radiographs of the tarsus. Again, it is important to take good-quality radiographs, with exposures that allow evaluation of distal tarsal bone densities. In addition to the standard 4 views, the author’s practice frequently adds a flexed lateral and a skyline of the calcaneus.
12. Combined Imaging of the Metatarsus
Structures of the metatarsal region are a common source of lameness and should be evaluated care- fully. Evaluate the entire metatarsal region when this is the localized region. Sonographically, sur- vey the plantar metatarsal soft tissues from the proximal metatarsus through the ankle and proxi- mal pastern. Carefully evaluate the superficial digital flexor tendon (SDFT), DDFT, accessory liga- ment to the DDFT, suspensory ligament, plantar annular ligament, plantar (intersesamoidean) liga- ment and its metatarsal attachment, digital tendon sheath, mannica flexorum, the bony entheses of these structures, and the axial surfaces of MTII and MTIV. Again, good-quality radiographs of the metatarsal region are essential. In addition to the four standard views (lateral, DP, DPLMO, and DPMLO), the author will also take a 15° plantarol- ateral to dorsomedial oblique view to better eluci- date the proximal suspensory enthesis. The proximal hind suspensory is one of the more difficult and controversial structures to evaluate. That is why it is important to use every ultrasound tool available when there are concerns about this struc- ture. Always compare it to the opposite limb, always scan in both weighted and unweighted posi- tions, always perform ACUST imaging in standing and flexed positions, and always evaluate associated bone surfaces carefully. Flexed imaging allows the tendons to deform side by side and serve as a stand- off to elucidate all borders of the structure. ACUST imaging allows visualization of the ultrastructure of
336 2019 Vol. 65 AAEP PROCEEDINGS
the ligament (revealing the proper percentage of ligament to fat and muscle). Enlargement of the lig- ament compresses these fat/muscle bundles. En- largement also fills the normal anterior space between the suspensory and MTIII and changes the contour of the plantar border. Cross-sectional and longitudinal views need to be compared to elucidate fiber density and fiber pattern. The axial aspects of the metatarsal bones can be fully elucidated for the proverbial “blind” splint, utilizing ultrasound and its ability to elucidate bone surface detail. The distal metatarsal region will be covered in the next section.
13. Combined Imaging of the Digital Tendon Sheath/ Metatarsophalangeal Joint Complex
This is another very complex region and a very common source of lameness. Clinical signs can overlap between the joint and tendon sheath, so both are imaged simultaneously. Radiographs of the re- gion should include lateral, DPLMO, DP, DPMLO, flexed lateral, and flexed DP views. Sonography is a very good tool for evaluating articular cartilage, subchondral bone, and joint margins. This should be done in both standing and flexed positions to expose more articular surface. Continuing with ul- trasound of the metatarsophalangeal joint compo- nents are the superficial and deep components of the medial and lateral collateral ligaments and collateral sesamoidean ligaments. The suspensory branches, oblique, straight, and cruciate sesam- oidean ligaments, plantar (intersesamoidean) liga- ment and the associated sesamoid entheses, are also part of the complete metatarsophalangeal joint ul- trasound survey. The digital tendon sheath com- plex includes the superficial and DDFTs, digital tendon sheath, mannica flexorum, plantar annular ligament, and plantar (intersesamoidean) ligament. ACUST imaging in this area defines the fibrocarti- lage layers of the superficial digital flexor tendon, the plantar annular ligament, plantar (intersesam- oidean) ligament, and the mannica flexorum. It also defines the chronicity of lesions within these structures, highlighting scar tissue. Dynamic flex- ing imaging elucidates the tissue relationships be- tween these structures. For example, many horses with chronic digital tendon conditions will have thickening and adhesions involving the plantar fi- brocartilage layer of the SDFT, the plantar annular ligament, and the plantar metatarsal fascia. Slight plantaromedial and plantarolateral orientation of the probe in a transverse and ACUST orientation allow “symmetrical” imaging to define the mannica flexorum attachments on the anterior fibrocartilage layer of the SDFT, the plantar annular ligament attachments on the sesamoid bones, and the borders of the SDFT. A technique is being developed in the author’s practice of transectional imaging of the DDFT from the distal metatarsus through the pas- tern in a dynamically flexing distal limb to attempt elucidation of longitudinal splits, a condition typi-
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