From the hindquarters, I will move on to describing common muscle linings and their possible meaning in the necks. A new post will be published every two days. Today, I’d like to start with the Rhomboid muscle. The Rhomboid is a deep muscle is located in the top line of the horse’s neck. The cervical portion of the muscle originates from the funicular cord of the Nuchal Ligament and the thoracic portion attaches at the spinous processes of T2-T7. However, there is no differentiation between the cervical and thoracic portions of the muscle dorsal to the spine of scapula.
The muscle inserts at medial aspect of the cartilage of scapula, dorsal to the Serratus Ventralis – of which muscle fibers intertwine.
The Rhomboid functions to lift the scapula and drawing it forward. Furthermore, it assists in raising and telescoping the neck when the limb is fixed.
As such, the Rhomboid has an important effect on shaping the base of the neck. Since, the base of the neck drives the whole neck arch – and subsequently the so-called freedom of the shoulders – it is important to understand these basic mechanics. The Rhomboid works in an antagonist relationship with muscles arising from the chest such as the cybernetic Longus Colli and Scalenus. These muscles are especially important for horses lacking attachment of the Nuchal Ligament Lamella at C6-C7 since when they contract and shorten (concentric contraction), they support the vertebrae from below and raise the base of the neck. In response, the Rhomboid – and Trapezius for that matter – can lengthen and aid in the telescoping ability of the neck. On the opposite, if the Rhomboid would contract and shorten (concentric contraction), if would drive the base of the neck downwards and deepening it’s U-shaped declivity. This results in poor head/heck carriage and the horse would be unable to free it’s shoulders. In some horses, the Rhomboid appears to be hypertrophied – not to be confused with a crested neck. This usually has two main causes: 1) Hind end lameness. The Rhomboid often hypertrophies when there are problems in the hind end as the head acts as a counter lever in movement. In my practise, palpating the rhomboid has proven to be a reliable indicator – NOT DIAGNOSIS – of hind end issues. Furthermore, I also use it to measure progress: if i start to rehabilitate a horse with a heavy hypertrophied rhomboid I know i am on the right track when the rhomboid starts to normalize. When it doesn’t normalize, I know I still have to look deeper or change my approach. I would advise you to always palpate both sides when the horse is standing square with the neck straight to give you an indication of (a)symmetry in development as well. 2) Poor training practises. The Rhomboid gets heavily compromised when the horse is asked in a hyper flexed position as well as when the horse is ‘against the hand’. When a rider holds tension in the reins, the base of the neck will be driven downward and the horse cannot move in correct and efficient self-carriage.
Hypertrophied Rhomboid muscles
As such, USE your horse’s muscle linings to judge your management and training. The horse’s body doesn’t lie. The rhomboid should not be visible from the outside. If it is, start to look for the problem and let the horse guide you. The horse is always right. Today, we have so much more knowledge available that we don’t need to subdue the horse to any simplistic training practises anymore. We can do better. We can evolve!