Muscle of the Month: Trapezius
November has been a busy month so I'm squeezing in my Muscle of the Month just in time - the Trapezius - a large muscle that crosses the shoulder blade. Read on to find out more.
The Trapezius is located in the forelimb, in the proximal part, closest to the spine and neck. The muscle is broad and thin, and in the shape of a triangle which lies over the shoulder blade. It is a superficial structure, meaning it is close to the surface of the skin so can be felt easily.
The trapezius is split into two sections, the cervical part, which starts in the cervical portion of the spine, and the thoracic part which starts in the thoracic part of the spine. The origin of the muscle, where it begins, is the middle of the neck at the third cervical vertebrae, it then attaches all along the spine up to the ninth thoracic vertebrae.
From the origin, the muscle comes downwards to form a triangular shape. Both parts of the muscle insert (end) on the same structure, the scapular spine. However, the cervical portion of the muscle attaches onto the upper 2/3 of the spine, whereas the thoracic portion is only attached to the upper 1/3 of the spine.
What does it do?
The key function of the trapezius is in movement of the shoulder, when the muscle contracts it elevates the shoulder, raising the scapula upwards, which is essential for locomotion and also jumping. In the normal cycle of limb movement, the shoulder is lifted before the limb is extended forward and replaced on the ground.
The cervical part of the muscle also helps to move the shoulder up and forwards, referred to as cranio-dorsal movement, in protraction of the limb (forward movement). The thoracic part in contrast helps to move the shoulder up and backwards, known as caudo-dorsal movement, in retraction of the limb (backward movement). This shows how important the role of the trapezius is in overall movement of the forelimb.
As well as producing movement, both parts of the trapezius help to stabilise movement so that the limb is not excessively moved forward or backward. Excessive protraction or retraction can cause injury to the soft tissues and joint, so this role of the muscle is helpful in preventing injury.
Can the Trapezius become injured?
This muscle is not often reported as a common injury problem in dogs, however due to its role in movement the muscle can be strained. Muscle strains are more likely to occur when the muscle tone is high, meaning the muscle is tight and less flexible. Increased tension in a muscle could be caused by overuse or a repetitive movement, for example playing fetch.
Muscles also become more prone to strains if they have not been properly warmed up before activity, or cooled down effectively. If the muscle is fatigued injury risk is increased, so over working/exercising your dog may cause issues. Finally, a muscle can be strained if a sudden forceful contraction occurs e.g. a jump, or sudden turn.
If the trapezius was strained you may notice your dog limping, they may find it hard to use the stairs, they might have difficulty jumping. The area may be hot to touch, swollen, or painful, and their stride on their forelimb may be shortened with stiffness present.
Muscles strains can be effectively managed with rest, icing of the area to bring down heat and swelling, and anti-inflammatory medication. A physiotherapist would be able to advise on an appropriate and gradual return to exercise to help with healing and prevent reinjury.
A physiotherapist is also able to identify whether your dog's trapezius muscle is tight, or under developed, and can then help you to address these issues. Massage, range of motion exercises, and stretching can all be used to keep the muscle supple and flexible, with the hope of preventing strains from occurring.
Exercises can be recommended to help strengthen the trapezius muscle, and a physio can advise on correct warm ups and cool downs for your dog before they are active. This is especially important for sporting dogs because if they go from inactivity, to completing an agility course, or racing round a track, the sudden forceful contractions of cold muscles can cause strains.
For more information please get in touch, come back next month to learn about another muscle.