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One of the most thought-provoking conversations for me during the dissection centered around the brachial plexus and the role a healthy thoracic sling plays in protecting the structures that pass through this region.

It’s important to remember that the anatomy we memorize from textbooks is not what we see in dysfunctional horses.

In a balanced horse, the thoracic sling supports the ribcage and allows the base of the neck to remain lifted, with C7 and T1 positioned forward of the scapula, as they’re often depicted in anatomical models. But when the sling collapses, the entire structure shifts. The cervical spine is pulled down and back, the base of the neck drops, and in some horses C7 can end up sitting between the scapula rather than in front of it.

This creates a structural bottleneck or pile-up.

Everything that needs space suddenly has less of it.

The initial hypothesis we explored was whether the brachial plexus itself was being compressed by scapular restriction. Seeing it in situ challenged that idea. The plexus is well protected by surrounding tissue, and the concavity of the scapula suggested it may not be as vulnerable to direct compression at that level as many of us had assumed.

However, that conclusion depends on everything being where it should be.

In dissection, there is no nervous system driving muscle contraction, and no chronic tension distorting alignment. The body is neutral in a way a live, dysfunctional body often isn’t.

But the conversation didn’t stop there.

As we followed the nerves proximally, another potential site of compromise became more compelling, and it was before the brachial plexus ever fully forms. When the lower neck is pulled down and the horse carries a chronically high-headed posture, the scalenes are placed under constant strain. The nerves that will eventually form the brachial plexus pass directly between these muscles.

That space matters.

If the scalenes are braced and overworked, it’s easy to see how those nerve pathways could become irritated or compressed long before they reach the shoulder. Additionally, when the lower cervical spine loses integrity, compression may also occur at the level of the cervical nerve roots as they exit the foramina, particularly between C5 and T2.

However, the impact of a dysfunctional thoracic sling isn’t isolated to the neck.

As posture deteriorates, whether from injury, weakness, or long-term compensatory patterns, the thoracic spine becomes less mobile, and the ribs lose their subtle swing. The sternum drops, the chest narrows, and scapular motion becomes restricted causing weight to shift forward, and the forelimbs begin to absorb concussion they were never designed to manage alone.

To stabilize this imbalance, the triceps and pectorals tighten, stride length shortens, shock absorption decreases, and the elbow becomes a stress point.

In this dissection, that reality showed up clearly: mild synovitis paired with significant cartilage loss and moderate bony change in the elbow joint.

All of these pieces are connected.

Whether nerve compression occurs directly at the brachial plexus, earlier at the scalenus gate, at the cervical nerve roots, or through a global collapse that simply leaves no room for tissues to function freely, the takeaway for me was the same:

When the thoracic sling and lower cervical spine lose integrity, nothing downstream is unaffected.

What I appreciated most about this experience was that it didn’t exist to confirm what we already believe. It asked us to question it.

Dissection is a way to check our work and challenge assumptions. It gives us the opportunity to refine how we interpret what we feel under our hands and see in movement. And while not every question gets a definitive answer, the process itself sharpens our understanding.

It reminded me that responsible horsemanship isn’t about defending a single explanation. It’s about staying curious, staying honest, and staying willing to revise our understanding in service of the horse.

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A big thank you to Celeste and Trinity Equine Services for modeling what thoughtful, horse-centered dialogue can look like. Watching two people with immense knowledge and differing hypotheses engage in respectful debate, grounded in curiosity, and a shared commitment to the welfare of the horse, was so refreshing. This kind of discourse moves our industry forward, not by proving who is right, but by staying devoted to the truth and to the horses who depend on us to keep asking better questions.