IN-DEPTH: ULTRASONOGRAPHY IN LAMENESS DIAGNOSIS Palmar annular ligament (PAL) injuries are rela-


tively rare in racing Thoroughbreds. There are generally two specific presentations. One is the acute onset overstrain type injury, with an obvious ultrasonographic region of decreased echogenicity corresponding with a sudden onset region of heat swelling and pain. Alternatively, PAL syndrome is where a combination of digital flexor tendon sheath pathology results in a generalized PAL desmopathy, resulting in thickening of the PAL.


Curb


In the past, particularly in the author’s Australian practice setting, all curbs were diagnosed predom- inately on clinical findings of plantar hock swell- ing and assumed to be overstrain injuries of the long plantar ligament. They were treated with anti-inflammatories and turned out for approxi- mately 12 weeks. More recently, over the last 15 years, ultrasound has been of great benefit to in- vestigate curb swellings. It allows the injury causing the swelling to be identified as an over- strain of one of the following structures: plantar ligament, SDFT, or DDFT. Those with an obvi- ous disruption of fibers and a core lesion of any of these structures will typically be managed with anti-inflammatories and 12 weeks of rest unless the injury is severe, in which case a follow-up ultrasound is advised. Not all curb swellings have obvious damage to the above structures, but some are instead caused by a peritendinous and periligamentous soft tissue swelling and or hema- toma in the region of the plantar hock.17 In ad- dition, many of these cases have an obvious thickening of the plantar tarsal fascia on ultra- sound examination, along with the subcutaneous tissues. These cases can be managed with a shorter duration of rest, with only 6 weeks out of training. However, they should be carefully mon- itored in the first 1–2 weeks for a recognized but uncommon complication of bacterial infection.17


3. Additional Regions Commonly Investigated with Ultrasound


Carpal Sheath


Swollen carpal sheaths are primarily investigated radiographically; however, ultrasound provides an important adjunct when radiographs fail to identify the more common causes of carpal sheath effusion, which include fractured accessory carpal bone, radial osteochondroma, or caudal radial physeal spikes. Careful evaluation of the accessory liga- ment of the SDFT, radial head of the DDFT, and the intrathecal parts of SDFT and DDFT tendons and musculocutaneous junctions is often rewarding, identifying primary pathology of these structures.18 It is a difficult region to scan given that the typically used tendon probe (7–10MHz linear) fails to image the whole sheath in cross section and needs to be used in a systematic technique. The region is often


4 2018  Vol. 64  AAEP PROCEEDINGS


best scanned with a combination of linear and a large convex probe if available and both weightbear- ing and non-weightbearing. Many cases ultimately require MRI or diagnostic tenoscopy to confirm and potentially treat pathology identified on radiographs and ultrasound. Ultrasound can be a useful diagnostic in a variety


of other less-commonly affected synovial structures, including calcaneal bursa, biceps bursa, extensor tendon sheaths, and tarsal sheaths.


Joint Injuries


Ultrasound is occasionally used to better define soft tissue injuries within a variety of joints, the most common being the fetlock or stifle joints. In the fetlock, it allows assessment of dorsal synovial pad pathology, particularly as a preoperative assess- ment of a chronic thickened joint and planned re- moval of thickened and torn dorsal synovial pads. Dorsal lateral or medial capsular tears are also not uncommon and can be imaged with ultrasound. Lameness localized to the stifle joint where there is no obvious radiographic pathology is an indication for a thorough ultrasound examination prior to or in combination with a diagnostic arthroscopy. This may change with an increase in availability of MRI or computed tomography suitable to the stifle imaging.


Muscle Injuries


The most common muscle injuries in the author’s practice setting involve the hamstring muscles in the hind limbs and brachiocephalicus or biceps muscles in the forelimbs. Ultrasound is com- monly used particularly in the hamstrings to de- fine the degree of pathology. Regions of altered echogenicity and muscle structure represent in- flammation, fibrosis, and tears in the muscle tissue. Ultrasound findings can help determine acute tears with obvious loss of structure and limited fibrosis compared with the more chronic fibrotic changes. Although relatively rare, some horses are identified with a generalized chronic fibrosis of the hamstrings associated with a change in action or poor perfor- mance. These cases typically are not obviously lame, are generally 3-year-olds or older, and a ham- string provocation stretch will often elicit a lame- ness response.


Pelvic Injuries


With pelvic injuries, ultrasound has been well de- scribed as a useful adjunct to other diagnostics, includ- ing rectal exam, radiographs, and scintigraphy.19 For stress fractures of the iliac wing or displaced fractures of the ilium, ultrasound is used to map the contour of the iliac wing and shaft to identify dis- ruptions to the normal bony surface of the pelvis. Ultrasound investigation of the coxofemoral joint can be useful but does not replace quality radio- graphs of the coxofemoral joint.


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