Negative palmar angle syndrome in racing horses

Early recognition and correcton can prevent this potentially career-ending pathology
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Dec 01, 2010

A client calls to say his performance horse is slightly off. You arrive at the barn and begin your examination by pulling out your hoof testers, expecting to find an abscess or perhaps a close nail. The hoof testers indicate pain over the heels and navicular area. You mentally go down the differential list: bruising, corns, sheared heels, thrush, foreign body, navicular lesions, bursitis, tendonitis, desmitis, synovitis, arthritis, fracture, etc.

But one thing missing from that list, a common cause of lameness that's often overlooked, is negative palmar angle syndrome (NPAS). NPAS refers to the condition of progressive heel collapse and its consequences on gait and performance. Treatment and outcome are facilitated by grading the severity according to physical and radiographic features. While Grades I (mild) and II (moderate) can be corrected with trimming and routine shoeing, Grades III (severe) and IV (complicated by flexor contracture) require more intensive mechanical intervention and patience.

Physical characteristics

The typical foot with NPAS is often labeled as a long toe, low heel foot or the specific heel abnormality as an under-run or under-slung heel. While these terms ably describe some of the common external abnormalities of the hoof capsule, they do little to describe what's going on inside. The damage to the tissues within the collapsing or collapsed heel area, including the various coria (e.g., wall, sole, bar, frog), and the bony, synovial and connective tissue structures is, as the saying goes, out of sight, out of mind.

In addition to the classic long toe, low heel appearance of the hoof, signs of NPAS include landing toe first, painful or awkward breakover medially or laterally when asked to turn, anxiety when shoeing, resistance during training, inability to take canter leads and lameness that ranges from mild to severe depending on the type and severity of the associated pathology.


Photo 1: A horse with collapsed heels often has 50 percent to 60 percent of the solar surface area in front of the frog.
Unfortunately, it usually takes persistent lameness for us to realize that something is profoundly wrong with these feet. And even then, we search for specific abnormalities to which we can pin a medical label, such as navicular bursitis or deep flexor tendonitis. We continue to miss the point that these medical conditions often are an end result of structural failure of the hoof capsule and, thus, damage to its contents. In my opinion, recognizing this problem early and working to correct it can prevent many of these potentially career-ending pathologies.

Identifying this problem is easy. Horses with weak or collapsed heels often have an elongated foot instead of a nicely rounded one. A well-trimmed healthy hoof has strong heels that are set back to the widest part of the frog. And when looking at the solar surface of the hoof, two-thirds of the surface area is behind the apex of the frog. In contrast, a horse with collapsed heels often has 50 percent to 60 percent of the solar surface area in front of the frog (Photo 1).