Head-bobbing lame: Differential diagnosis

The day after Harvey's "brush with death" (actually a moderate head gash), I got a call from Riley's barn manager. "Hi, Stacey, Riley is pretty lame. Are you planning to go out to the barn tonight?" My plans to check on Harvey went out the window. "Yes, I'll be there by 5:30." Riley is not Harvey. Harv has had two abscesses since the age of 10, and he is stoic about pain. Riley has now had two abscesses this summer alone, and he doesn't have the same pain threshold -- maybe even a little theatrical?

I hope it's an abscess or stone bruise, but you never know. There are four types of injuries that commonly cause head-bobbing sudden lameness, and they have similiar symptoms...

1. Laminitis. Okay, this is not the high order probability for Riley. Books have been written about it so I'll give it cursory treatment only. Laminitis symptoms include sudden onset lameness, strong digital pulse, heat in hooves, and reluctance to bear weight on the front feet. Laminitis typically occurs in the front feet. Rocking from one foot to another is common, as is a rocked back stance.
   
2. Abscess. Here's the likely cause of Riley's problem. Symptoms are acute onset lameness in any hoof, strong digital pulse, heat in the hoof (often), tenderness in a localized area (sometimes), or evidence of puncture wound or mushy area in the sole or coronary band (sometimes).
   
3. Stone bruise. Again, a rapid onset lameness in one foot and strong digital pulse are typical symptoms. Examination may reveal spots (areas of blood) in the sole. Stone bruises are more "subtle" than abscesses; there may or may not be heat present, and the lameness might not be as dramatic as an abscess.
   
4. Coffin bone fracture. Traumatic injury can cause a crack or fracture of the coffin bone. Sit up and pay attention to this one! The scary thing is, the symptoms are very similar to an abscess: strong digital pulse, heat, sudden lameness. It is less common than an abscess but the symptoms are similar, if not the same. I read an article by a vet that felt that pain/heat is toward the back of the hoof is an indication for coffin bone fracture (of course sometimes abscesses occur in the back of the hoof too). Coffin bone fractures near the joint interface are very severe and typically worse on soft ground, since this applies more pressure to the sole of the foot. Fractures of the wing tend to show up more when the horse is turning. The frightening thing about coffin bone fractures is that if they are not treated immediately, the prognosis is more guarded. Th pictured radiograph shows the internal structures of the hoof: A) coffin bone, B) navicular bone, C) third phalanx (P3), and second phalanx (P2)
   

So when I went to see Riley, his symptoms were:

• He's headbobbing lame on the right front.
  
• Strong digital pulse on RF only
  
• He's more acutely lame on a hard surface than a soft surface, and reluctant to walk down an incline.
  
• I could find no heat in hoof wall.

The first time he abscessed(left hind hoof), I happened to read an article that said coffin bone fractures are often misdiagnosed as an abscess. Primarily because of that article, I called the vet and shelled out $250 in x-rays to find out if he had a fracture in his hoof. The outcome? I'm now in possession of some radiographs of the abscess. There was some eye-rolling at the barn and a few people actually chided me for wasting money. Riley is a little bit better today (day 3), but Bob saw him for the first time and thought he looked pretty bad. He thought it was terrible that I made him trot even a few steps. We both took turns making him stand in Epsom salts. I'll probably have a vet out Monday. Regardless of what people may think -- people who have no reason to care one way or another--in the end he's my responsibility. The picture to the left is an older one but it captures Riley's present demeanor. This hoof pain is for the birds!