Muscle of the Month: Serratus Ventralis
This month I am writing about the Serratus Ventralis, a large muscle in the shoulder which has an important role in stability and movement. Have a read to learn more about this muscle.
The Serratus Ventralis is a muscle in the forelimb, which covers a large area over the shoulder blade, coming up into the neck, and down into the ribs. The muscle is flat and wide and the name 'Serratus' comes from the latin word for saw 'Serrare'. As you can see from the image the muscle has a zig zag like edge, as a saw would. It lies underneath the shoulder blade which is where it gets the second part of its name 'Ventralis' - ventral meaning beneath.
The muscle is made up of thin flat strips with the fibres running at various angles to form a a fan like structure, fanning out from the top of the shoulder blade. It is split into two portions, the cervical portion and the thoracic portion, relating to its position in alignment with the spine.
The muscle's origin, where it begins, is a structure called the Facies Serrata, which is the top section of the scapula or shoulder blade. The two portions then come down to different insertions or end points. The cervical portion inserts onto the cervical vertebrae in the neck, more specifically C2-C7. The thoracic portion fans out in the opposite direction and inserts onto the ribs 1-7. This shows you how large this muscle spans and indicates how important its role is.
What does it do?
Due to the size and span of the serratus ventralis, the muscle has several functions. The basic function states it supports the trunk, raises the neck and has a role in inspiration, but in reality it does much more than this. It makes a link between the shoulder, neck and ribs, so is key in supporting the trunk and stabilising the body but it is also at work during movement.
During movement, the forelimbs take a lot of weight and they have a role in braking. Research has shown that the serratus ventralis helps to achieve this - dogs moving faster on a decline had increased muscular activity in the serratus ventralis (Carrier et al., 2006). The muscle is an anti-gravity muscle in the shoulder, it keeps the body upright especially at times when there is increased weight and force on the forelimbs. In a standing position, the serratus ventralis takes the weight of the body and holds the body up, and when the dog jumps down, the muscle can absorb some of the shock and force.
As well as this, when the serratus ventralis contracts, it pulls the shoulder blade forward and downward, so the shoulder can move in relation to the forelimb. If there were concerns that the muscle was injured, we may see a decrease in range of motion at the shoulder. Finally, as the muscle has an attachment on the ribs it has a small role in inspiration.
Can the Serratus Ventralis become injured?
Yes it can, although this muscle isn't commonly reported as injured. Research has found the muscle has been strained in sled dogs that compete in endurance races and the factors they suggested were involved included; fatigue, overexertion, and intensified muscle contraction (Frye et al., 2018).
In simple terms this means that the muscle is more prone to injury if it is tired or overworked. This can happen if your dog is travelling at fast speeds on a decline, having to do increased amounts of downhill braking, as this puts excess force on the forelimbs. Depending on how and where you exercise your dog, they may be experiencing these types of forces, so it is worth considering their muscular health to prevent an injury occurring. Injuries to the muscle can also be linked to road traffic accidents, if the initial impact is at the shoulder.
If the serratus ventralis was injured you may notice your dog limping, they may be reluctant to come down the stairs or jump down. The movement at the shoulder may look stiff and awkward, and the area could be swollen or hot to touch with a pain reaction shown by your dog.
As I previously mentioned, injury of this muscle has been reported in sled dogs, and the same research investigated the effect of physiotherapy in treating the strain. In this case, a husky that went lame during a race was diagnosed with a strain of the serratus ventralis muscle. The dog underwent a rehabilitation programme which included range of motion exercises, weight shifting and slow lead walking. Overtime this progressed on to more difficult exercises like pole work and hill walking, and a year later the same dog was back competing and placing.
As well as treating muscular strains, physiotherapy can also help prevent them. Physiotherapists can identify if the muscle is weak in anyway and help to correct this with manual therapy and remedial exercises. The stronger and healthier the muscle is the less likely it is to become injured. Correctly warming up and cooling down the muscle will also reduce injury risk, and this can be a simple addition into your dog's routine, whether they compete in sport or not.
For more information please get in touch. I strive to educate owners so they can keep their dogs as happy and healthy as possible whether they be your average pet dog, or competing to a high standard, I can help! See you again next month - Nancy
Carrier, D., Deban, S., and Fischbein, T. (2006) 'Locomotor function of the pectoral girdle 'muscular sling' in trotting dogs'. Journal of Experimental Biology, 209, 2224-2237.
Frye, C., Hansen, C., Gendron, K. and von Pfeil, D. (2018) 'Successful medical management and rehabilitation of exercise-induced dorsal scapular luxation in an ultramarathon endurance sled dog with magnetic resonance imagining diagnosis of grade ii serratus ventralis strain'. The Canadian Veterinary Journal, 59, 1329-1332.