Vet Tip of the Day: The Hock
Key Words: Equine tarsus, horse hock anatomy, bone spavine, degenerative joint disease
Today we will look at the hock, which is the hind limb joint that sits above the cannon/splint bones. It corresponds anatomically to your heel. There are 4 joints in the hock (identify them on the radiograph). From top to bottom they are the tibotarsal joint, the proximal and distal intertarsal joints, and the tarsometatarsal joints.
The two distal intertarsal and tarsometatarsal joints are low motion joints that are very common sites for arthritic changes (degenerative joint disease or bone spavin) in all athletic horses. This is a very common, and very treatable condition. Most horses with bone spavin continue in full work with maintenance veterinary care in the form of intra-articular injections with corticosteroids and hyaluronic acid in conjunction with a regimen of oral or injectable chondoprotectant agents such as Adequan, Legend, or oral chondroitin sulfate/glucosamine products.
The hock is a complex joint and is the site for many different problems that can cause lameness. We will spend a few days looking at it in more depth, but since today is a
Veterinary Tale day, this is the end of this Vet Tip - here's the story - hope you enjoy it.
Chapter 2 Good News Bad News
Thursday was a good news/bad news day. In the truck, my cell phone in its normal position, wedged between my head and left shoulder, in what I consider my personal “hands free” mode, I’m speeding of course, steering with my left hand while rubbing my dog Sticky behind her ears with my right hand. Sticky is in her favorite spot, curled up beside me with her shoulder pushing into my right hip and her head in my lap. This pretty much describes how I spend the majority of my life – motoring from one appointment to the next, multi-tasking on the phone, and rubbing my dog’s ears because I don’t have time to meditate. One of my two veterinary hopeful college student assistants completes our travelling circus, doing her best to keep me on track as I zoom around trying to protect the well-being of the equine population of northern Washoe County. On this particular day I was on the phone with a third year medicine resident from UC Davis who was telling me that Brandy was on her way home, fully recovered after her experience dancing with a T-post. Good news.
Sticky has been my constant companion for the past 8 years – she is much cuter than me, with better manners and a distinctly more endearing personality. She’d been in the truck when I treated Brandy, but she knew better than to get into the middle of that mess, and slept through the drama on the front seat. My clients, without exception, adore Sticky, and there is an ongoing debate among them whether or not she is part coyote. The physical resemblance is remarkable, but her disposition is so quiet, consistent and loving that it is hard to imagine she is related to those conniving rascals that lure puppies out into the desert and rip them to shreds. I tell everyone Sticky is a PCD, or Prostitute Companion Dog, descended from the gentle dogs that were friends to the girls in Julia Bouillet’s Bordello in Virginia City at the turn of the century. Some folks find this confusing, but it works for me.
I met sticky 8 years ago while responding to a call from a new client. Tanya Buckman was a cowgirl with a lame foal. Tanya was about 40 years old, 5’7”, with hair so blond, teeth so white, breasts so perky and jeans so tight if I wasn’t in Nevada I wouldn’t have believed it possible. When I first moved west these women were a real challenge to me, and I still look at them with some puzzlement and more than a little envy. They all are so beautiful, and so NICE, and SO TOUGH, they belong in movies. Every one of them wears their womanhood like a ship’s flag: the big belt buckles, the white cowgirl hats, the long stride and the high heeled Ropers. How they get their Levi’s to bunch up just so over the tops of their boots is beyond me. I’m a Yankee, I grew up in New England, I wear a string of pearls every day and my idea of risque is leaving the top button on my polo shirt open.
I’m going to digress for a minute here, but just to give you an example of what these gals are like, here’s what happened when I volunteered to draw blood for pseudorabies testing from a 4-H project pig belonging to one of my cowgirl client’s daughters. When I arrived the pig was loose in a large pen and since my generosity stopped short of chasing it around like a lunatic I asked the daughter to catch Charlotte for me. I watched her futile attempts to contain the pig until my head was about to explode then announced my impending departure if the pig wasn’t under control within 5 minutes. The daughter pulled out her cell phone and made a quick call.
The next thing I know, a bright red 1 ton Dodge diesel pickup comes screaming down the driveway from the house to the barn where we waited with the pig. The truck stops in a cloud of dust, the driver’s door flies open and Raquel Welsh in skin tight Levi’s gets out, struts over the to the pig enclosure, climbs the fence, grabs the pig by a back leg so fast I never saw her move, and hollers over her shoulder at me, “Hurry up and bleed this damn thing, I’ve got to get my nails done at three o’clock.” That was my client, the cowgirl mom, and I guarantee you that when she sashayed away from that pig pen she smelled just as fresh as a daisy.
Tanya Buckman was one of these Nevadan women, and like so many of them she was a savvy hand with horses. She had a buckskin quarter horse mare which had foaled 2 weeks previously. Everything was fine, until yesterday when the filly’s leg became swollen and it began to have trouble walking. Tanya easily cornered the wary 100 pound youngster and held her while I began my examination, questioning her as I did.
“ Has the mare ever foaled before, Tanya?” I asked as I took the foal’s temperature.
“No, this is her first, and she was real nervous about letting it suckle for the first couple of days,” she replied. “Does she have a fever?”
“Her temp’s 102.5, which is a little higher than I’d like to see. Maybe she didn’t get enough colostrum when she was born.”
Colostrum is the special milk that mares only produce for a few days after the birth of a foal. Horses are born with what is called a “naïve” immune system. They have no antibodies to protect them against infection, and must drink enough antibody rich colostrums within the first 24 hours of life or they are at high risk of developing serious infections. One of the most common ways for such infection to manifest is as a septic joint, which causes severe lameness and can be life threatening if the infection invades the bone or spreads to other organ systems.
After palpating the fluid in the foal’s fetlock joint and asking a few more questions, I was certain that the most likely cause of the lameness and fever was a bacterial infection in the joint that needed immediate attention. Tanya was clear that she wanted the foal treated there on the farm, so we began preparations to flush the joint. Needles are inserted in 2 locations, one to allow delivery of sterile fluid that lavages the joint space, the second to provide an exit route for the infected joint fluid and bacteria. This procedure is ideally performed under sterile, or aseptic, conditions. This presents a challenge in a field setting. The trick is not to make matters worse by introducing more bacteria into the joint than already are present.
The best environment Tanya could offer was a 3 sided shed with manure rich shavings covering a dirt floor. On our side was the fact that there was very little wind. In general I love the climate in northern Nevada – we enjoy over 300 sunny days a year and while winter is winter, the sun and 5,000 foot elevation usually melt snow within a few days to weeks. The climate is very dry, so the summer heat, typically 85 to the rare 100+ degree days, is very tolerable. Our one weather detractor is the wind. We have it frequently, and when it blows it is not unusual to experience gusts in excess of 45 mph. But this was a clear, quiet days, so it was unlikely we’d have chunks of windswept manure and sand landing on our sterile field.
We laid down some fresh shavings and put a clean sheet on the ground. Fern held the foal in a classic “foal grip” with one hand grapsing the base of the tail, her other arm looped under the foals neck, holding the head snuck against her chest. I sedated the foal using 50 milligrams of intravenous xylazine. Within three minutes she was a wet noodle, and we laid her down on the sheet, Tanya sitting at her head and my assistant Fern holding the affected leg in elevation. After wrapping the hoof in clean gauze and performing a sterile prep of the leg from well above the joint to hoof, I donned sterile gloves and quickly inserted the needles into the joint on either side. We were half-way through the flush procedure using a 1 litre bag of lactated ringers solution when a coyote stuck it’s head around the corner of the shed and stared at us.
“Chloe, you git!” snarled Tanya.
“My God, Tanya, is that a coyote?” I asked, trying not to lose my concentration.
“Heck no, that’s Chloe, she came from the pound in San Diego. My husband says he’s gonna divorce me if I don’t get rid of her, we’ve got so many dogs. You want her? “
“No thanks. Hey, let’s pay attention here, this foal is going to wake up soon.”
The foal responded well to a series of three joint flushes and systemic antibiotics. Her x-rays showed no evidence of invasion of the infection into the bone, and a sample of joint fluid obtained after the third lavage procedure indicated that the infection was resolving. What didn’t resolve was Chloe’s fascination with veterinary medicine, and on our last visit to see the foal the little coyote dog hopped into my truck and made it very clear that she belonged there for better or worse. I changed her name to Sticky after a few weeks because she stuck to me like a little flea, and over the years she became as much a part of my practice as my stethoscope.
Eight years later, as I’m speeding along, speaking with the UC Davis resident about Brandy and rubbing Sticky’s ears, my fingers discover a lump under Sticky’s jaw. When we arrive at our next call I take a closer look at my little dog with the piercing topaz eyes. Not only can I palpate an enlarged lymph node at the base of her neck, when I examine her oral cavity I discover a dense mass of tissue covering the floor of her mouth between her lower canines.
“Oh shit, Fern, look at this - I think Sticky has cancer,” I say quietly.
Bad news.
Diseases are like brush fires. Some smolder for awhile and are easily extinguished, others flare up and have devastating effects. Choosing vaccinations for your horse has a lot to do with the nature of each disease we are attempting to prevent. Toward this goal, here are the answers to yesterday's questions. 
