VNatomy - Equine stay apparatus
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- Опубликовано: 5 сен 2024
- In this video, I will explain the major components of the equine stay apparatus.
VNatomy is perfect for students studying veterinary anatomy, veterinary nursing or animal science.
English subtitles available
Sources:
Phillips, C. (2015) 'The horse' in Aspinall and Cappello (eds) Introduction to Veterinary Anatomy and Physiology Textbook 3rd edn. Elsevier. pp. 191-210
Additional diagrams:
www.atlantaequi...
en.wikivet.net...
The focus of today’s lesson is the equine stay apparatus. This is a collective term referring to specially adapted muscles, tendons and ligaments, which reduce muscle fatigue and exertion whilst standing. This is best known as the reason why horses can rest whilst standing, but it also reduces muscular effort whilst the horse is moving during exercise.
The main adaptation is that muscles have increased the fibrous collagen content of many muscles, which work in conjunction with tendons and ligaments especially within the distal limb. This can be further divided into the suspensory apparatus and the check apparatus, which are present in all four distal limbs. We will look at the distal limb first.
The suspensory apparatus primarily consists of the interosseous muscle, which has been completely replaced with fibrous material to form the suspensory ligament. This runs along the palmar or plantar surface of metacarpal or metatarsal three, then bifucates proximal to the fetlock joint. It then runs distally on the dorsal surface of the proximal phalanx to join the common digital extensor tendon. Along with associasiated distal sesamoidean ligaments in this area, the suspensory apparatus supports the fetlock and the pastern joint.
Now let’s look at the rest of the forelimb to view the check apparatus.
The superficial and deep digital flexor tendons run down the caudal and palmar aspect of the forelimb. There are slips of ligamentous connection from these tendons to the bony column of the leg, which will prevent extension and passive collapse of the joints the tendons pass over.
The superficial digital flexor tendon has a check ligament joining it as it passes over the radius. The deep digital flexor tendon has a check ligament joining it at the level of the metacarpals.
The extensor carpi radialis is located on the cranial aspect of the forelimb and will stabilise the carpus, in conjunction with the digital flexors.
More proximally on the limb, the serratus ventralis and biceps brachii muscles have increased fibrous components to support the limb in this area.
Let’s now move on to look at the stay apparatus and adaptations in the hind limbs.
The hindlimbs also support a large proportion of the horse’s weight, so in addition to the suspensory apparatus and a check ligament on the deep digital flexor tendon, there are other adaptations; the patellar locking mechanism and the reciprocal mechanism. Although strictly speaking, the patellar locking mechanism is not a part of the stay apparatus, as there is no increase in fibrous contents of muscle, it is a very important way for the horse to conserve energy and will be included here.
The patellar locking mechanism allows the horse to immobilise the stifle joint. When this is engaged, the horse can rest the weight from the caudal part of its body on the immobilised limb. The locking is achieved due to several adaptations around the stifle joint; the trochlear groove of the femur and the patella. During normal locomotion, the patella moves in the trochlear groove.
There are three patellar ligaments in the horse and a medial patellar cartilage. The medial patellar ligament attaches to this cartilage. To lock the stifle, the joint is extended past a certain point and then twists medially to hook the patellar cartilage over the trochlea tubercle and the medial and middle patellar ligaments are stabilised over the medial ridge. This locks the patella in place and therefore prevents flexion of the stifle joint without any muscular effort. To release the stifle and allow movement once more, the horse shifts its weight to the other leg then contracts the quadriceps muscle to move the patella proximally, allowing it to then move laterally and then proximally to move it back in to the trochlear groove.
The reciprocal mechanism is the final major component of the stay apparatus in the hindlimb.
The reciprocal mechanism ensures that when the stifle is in extension, the hock is also in extension. This is due to muscle attachments meaning that when the femur moves caudally, the distal limb moves caudally and vice versa - this is what is mean by reciprocal movement.
The reciprocal mechanism is composed of the peroneus tertius cranially and caudally, the superficial digital flexor tendon and gastrocnemius. This adaptation also ensures that when the patella is locked, the hock is also immobilised. Both of these functions can occur without additional muscular effort or fatigue.
To re-cap, the stay apparatus refers to adaptations within the equine musculoskeletal system that help reduce muscle fatigue. The suspensory and check apparatuses are found in both forelimbs and hindlimbs. The hindlimb has additional adaptations: the stifle locking mechanism and the reciprocal apparatus.
You should now have a better understanding of the structures involved in the equine stay apparatus and associated specialisations in both the forelimb and hindlimb.
Appreciate your effort to simplify such a valuable information.
This has helped me no end for my exam this upcoming Monday. I was really struggling to visualise and condense it all but you've done it so well and in such an interactive way. Thank you!
I am glad it helped and I hope you were successful with your exam!
@@VNatomy Yes. Passed all exams first time with a first (70%+) and I'm studying veterinary medicine. Thank you for the help!
@@EquestrianMadness25 That's great news! Best of luck with your continued studies!
The best and short video to explain stay app. Thanks🎉
Videos like this make me wish I went to school for equine science
Wow. It’s so complicated well designed and thought out. It blows my mind anyone could look at all this and call it “adaptations.”
There is so much evidence for design it’s overwhelming
So helpful! Love the diagrams
Thank you very much for the visuals and explanation :)
Great Video!
Great video!! thanks for sharing.
Thank you, i have been told that the hind limb check ligament (subtarsal check ligament) is considered by most to be vestigial, sometimes absent in horses and sometimes absent in mules. If it plays a role in the stay apparatus that would indicate to me that it is not vestigial and actually plays an important role.?? I love to learn, please may you help clarify?
I love it! Thanks for sharing.
Excellent thanks
thank you so much for this video was so helpful
You're very welcome!
Great explanation! Thank you.
Does the stay apperatus engage when the horse relaxes, or does the horse have to physically engage it? And can/do horses rest their front limbs as well?
Hello Jackie, most of these adaptations are passive so they do not require conscious effort from the horse, except for the patella locking mechanism (which requires effort to unlock). The first part of the video outlines some of the adaptations in the front limbs (suspensory and check apparatus) but in addition many of the muscles e.g. serratus ventralis have increased fibrous content that can provide passive support
Im a little confused about the representation of the serratus ventralis thoracis muscle as I thought the muscle ran in a downward direction from what was drawn. From ribs 1-8/9 to the underside of the scapula.
Hello - thanks for this observation. I drew it insertion to origin rather than origin to insertion as you have described.
damn thats actually so interesting. i dont do any animal science but thought a system like this would be useful for humans just because I do rock climbing and often need to rest on the wall. turns out horses have beat us to this one
So what is wrong/hurt if horse's appratus is failing?
Very helpful
thanks a million!!!
Thank you
Thank you so much
Thanks
Great😊
Does the elbow also have a locking mechanism? and thank you!
Hello Judit - the biceps brachii muscle has more fibrous tissue in it to help stabilise the shoulder and the elbow joints along with the triceps. There isn't a specialised system in the front leg as there is with the patellar locking system in the hindlimb.
your video was good but too fast !
Thank you for the feedback. Have you tried slowing down the playback speed in the settings?