This is going to be a long one. As you’ve probably noticed already, I get chatty when I write, and if you thought last month’s posts were long, you’re in for a treat, because it’s not one joint I have to describe here, but 5. So get a cup of tea, get comfi, and read on 🙂
First we’re going to talk about the bones. I’m not going to go into too much details, but I’m going to bring the information that I think are quite cool/interesting to know for anyone around horses 🙂 Then we’ll see the joints!
The radius-ulna combo: for those of you who aren’t aware, there’s 2 bones in your forearm. The ulna is the one that has the point of the elbow, aka the olecranon, and the radius is the other one. But for horses, it’s a different story, because those bones fuse together at a very young age, so the radius and ulna become one unit, the radius being the main bone out of the 2. But the ulna still has its olecranon, so horses have an elbow point too, just in front of where we do the girth 🙂
The carpus: if you’ve read my blog article on fun facts in your horse’s body, you will already know that the carpus is commonly called the knee, but that it’s actually the equivalent of the wrist. This area is fascinating as it’s not one bone, but 7 tiny square bones! They are organised on 2 lines of 3 bones each, the last remaining bone being at the back of the carpus.
The canon bone: you might be in a bit of a surprise again as there’s actually 3 canon bones on the horse’s legs 🙂 The main one is called metacarpus III, and is the one the horse stands on. The other 2 are on each side of III, and are called metacarpus II and IV. The numbers refer to when horses had several fingers, and so several canon bones! Nowadays, II and IV are rudimentary, but still quite cool to remember that our horses evolved too, just like us 🙂
Phalange: onto the finger of the horse! There’s 3 phalange on the horse, just like on us, and P1 and P2 are similar in shape, they are rectangular bones, fairly small. It’s P3 that’s the od one, shaped like a weird cornetto cone (in my mind that’s how I see it anyway :)). The first 2 phalange are visible, they are what we call the pastern! But the bottom of P2 is hidden is the hoof, and P3 is fully inside the hoof.
The sesamoid bones: Their’s 2 sesamoid bones, and they are located behind the fetlock. Well, I say behind, but they’re actually part of the fetlock joint, and they are super important in choc absorption mechanism, but that’s for next week 😉
The small sesamoid bone: The last bone of the foreleg, the small sesamoid bone, also known as… (I feel like I need a dramatic music for this) THE NAVICULAR! Very sadly famous because of the navicular syndrome, this bone is located in the hoof, behind P3! It’s a very tiny bone, but can cause all sorts of problems. More on that another time 😉
Now that’s we’ve seen all the bones of the foreleg, let’s talk about how they maintain each other. Just as little reminder, the joints and ligaments are what holds bones together passively, meaning that no energy is needed. Ligaments are very dense connective tissue that are actually considered by a lot as being part of the fascia system, the system that connects all body parts, facilitate the energy transmission during movement, and helps the body cope with daily strain. And yes, I’m happy to have been able to mention fascia here. Because if you don’t know already, it’s my favorite subject ever and would happily continue talking about fascia right now. For ever ^^
Humero-radio-ulnar joint: between the humerus and the radius/ulna. What’s interesting here, is that there’s a lot of synovial bags around the joint, to protect the bones from touching each other. It’s a joint that works a bit like the suspension of a car and give us that lovely impression of rebound during movement.
Carpus joint: that’s where it’s really busy, although saying this, I think the joints of the bottom of the legs are pretty busy joints anyway from this point. We have here:
- ligaments to join each bones of the first line together
- ligaments to join each bones of the second line together
- ligaments to join the bones of the second line with the metacarpus bones
- ligaments to link the 7th bone with both lines AND the radius AND the metacarpus
- and finally, a badass ligament at the back.
That final ligament is really important as it will continue into the suspensory ligament, as well as in a carpal flange that will help maintain the flexor tendons against the back of the canon bone! Very often there’s restriction of movement in this ligament after a tendon injury. Almost inevitable to separate the 2.
The fetlock: There’s a lot going on here too, as we have ligaments to maintain the canon bone and P1 together, plus ligaments to maintain both of the sesamoid bones together as well as with the canon bone and P1. It’s a busy place 🙂 What I always find interesting about this joint, is that it give you a really good idea of how well the energy is transmitted from the hoof to the top of the leg, as well as how the shock absorption is. Sometimes the shoulder might seem stiff or limited in motion, when actually it’s the fetlock that’s the one to blame! Really fascinating 😀
The proximal interphalangeal joint: What I find particularly cool about this joint is that, even though it’s a lot more simple than the previous 2, it has a specificity: it has 3 palmar ligaments that cover the back of the joint to help maintain the angle without having to spend energy. It makes sense right? The pastern of the horse isn’t vertical but at an angle, think about the energy that would be spent trying to maintain that angle at all times if the palmar ligaments weren’t there! Well done evolution, well done.
The distal interphalangeal joint: Once again, a busy joint. And of course, it’s hidden deep a hoof so that if anything goes wrong, it’s super hard to fix. Alala. Anyway, this is the place where we find ligaments to join P2 and P3, as well as P3 and the navicular!
That’s it for today, I hope I haven’t lost too many of you and well done if you made it here 😉As always, don’t hesitate to leave a comment below and ask any question, next week we’ll talk about the muscles and the movements of the foreleg, and I’m thinking about changing things up for week 3 and 4 and pick a pathology to cover each week, any thoughts on that?