There are a variety of causes of hoof pain; conditions related to the hoof wall and keratinized structures, the coffin bone, and the podotrochlear (navicular) region all can be responsible. So before performing any tests, Turner recommended the veterinarian conduct a thorough examination of the entire foot to determine if the horse has any predisposing factors. This includes evaluating the external hoof, hoof balance, and conformation, checking for deep pain in the frog, and then using imaging modalities to assess what could be behind clinical findings.
“MRI is now the gold standard to identify factors that create lameness, and often the MRI reveals more than one area of pathology (disease or damage),” he said, which emphasizes the importance of starting with a thorough clinical exam of the entire foot and then using imaging to determine the significance of each lesion found.
Turner said one of the most common foot manipulations veterinarians perform is the hoof tester exam, followed by standard distal limb flexion tests to note any lameness (or exacerbation thereof, both considered a positive result). Turner also described using various wedge tests, which are designed to extend the hoof and related structures to reveal possible pathology. In all cases veterinarians place a block under a specific area of the foot, the horse’s opposite limb is held up for 60 seconds, and then the horse is trotted off.
Turner described the diagnostic significance of each of these tests:
- A hoof tester exam is nonspecific for deep pain but can help the veterinarian locate abscesses, bruises, or fractures. For example, pain over the frog represents deep pain within the foot, sometimes revealing navicular disease; however, study results indicate that hoof testers have only a 50% predictive value for this condition. This is in part due to anatomical limitations in where the practitioners can squeeze the pinchers.
- Distal limb flexion exacerbates 90% of foot lameness, yet it has low specificity in identifying exactly where pain is coming from. However, a positive flexion strongly suggests joint issues. Veterinarians should follow a strong positive with abaxial wedge testing.
- Abaxial wedge testing stretches the opposite side of the foot from where the wedge is placed. Ninety percent of collateral ligament injuries are positive on a lateral wedge test.
- Toe wedge testing stretches the back of the lower leg and increases compression between the deep digital flexor tendon (DDFT) and the navicular bone. If positive, it suggests deep flexor tendon pain and the need to pursue imaging of the DDFT with ultrasound or MRI.
- Frog wedge testing (also called palmar wedge testing) has an 85% predictive value for navicular pain because it compresses the frog and digital cushion and puts pressure on the navicular bursa.
“By methodically performing these manipulative tests, a source of lameness is more readily pinpointed, appropriate imaging can be performed, and then specific treatment can be targeted to that area,” Turner said.