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Osteopathic approach to the equine thorax

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There are many reasons why a horse may have restrictions in his thorax. As osteopaths, we know that immobility in one area can certainly influence other regions of the body.

There are many reasons why a horse may have restrictions within his thorax. Not the least of these is that the saddle may be resting on his withers. As osteopaths, we know that immobility in one area can certainly influence other regions of the body. Working on the viscera in the thorax is difficult, however, because of the anatomical restrictions. I will first explore the different anatomical features of the thorax and its closely-related structures, then speak about indications for osteopathic treatment.

Basic anatomy of a horse’s thorax

The thorax contains two lungs, separated into left and right lobes by the mediastinum. Many species have two or three lobes on each side, but horses have very small cranial lobes (a little larger on the right than the left), and one accessory lobe that is more connected to the right than the left. The heart sits cranio-ventrally and slightly to the left. It is encased in a firm double parietal pericardial layer and parietal pleural layer called the pericardial sac, which prevents the heart from getting too enlarged. Following are the borders of the thorax:

  • Dorsal: The ventral portion of the vertebrae and hypaxial muscles of the spine
  • Ventral: Sternum, costo-sternal junctions and lower ribs
  • Caudal: Diaphragm (excluding opening for aorta, vena cava and esophagus)
  • Lateral: Rib, parietal pleura and intercostal muscles
  • Cranial: Suspensory ligament of the thoracic dome and all soft tissue connections between the first ribs, pleura, first thoracic vertebrae and surrounding structures.

The heart contains a vast neural network, and secretes neuropeptides and hormones, including oxytocin. It has many more afferent than efferent fibers running to it, and appears to have some function in short and long term memory. Studies in human medicine have shown that the nervous system around the heart can independently influence the brain, and vice versa.

Osteopathic approach to the equine thorax

The parietal pleura is tightly attached to the underside of the ribs and intercostal muscles. Anatomy photos courtesy of Paige Poss in conjunction and cooperation with Anatomy of the Equine.

For the above two pictures:  A view from above plus a close-up the organs in the chest, and how they sit. Note how the diaphragm and liver are as far cranial as the seventh thoracic rib ventrally.

With the right lung removed, you can visualize the azygous vein, cranial and caudal vena cava and its branches. You can also see how the phrenic nerve travels with the mediastinal and pericardial tissues to the diaphragm. The esophagus and aorta lie further to the left and dorsal to the vena cava.

This picture shows the second rib still in place. You can imagine the cervicothoracic and medial thoracic ganglions sitting in between the first and second ribs just below the spine. The cervicothoracic ganglion (or stellate ganglion) is important for regulating blood flow to the pituitary gland and base of the brain. Large lymph nodes and vessels, the brachiocephalic trunk of the aorta, venous trunk, cardiac plexus, brachial plexus, vagus nerve, phrenic nerve and esophagus are all squeezed together in this area and surrounded by fascia that connects the parietal pleura to the scalenus muscle in the neck.

The lungs and heart have autonomic, motor and sensory innervations from the region of T 1-5, the cervical ganglions, cardiac plexus, pulmonary plexus and vagus nerve. The intercostal regions and esophagus are innervated segmentally through the thorax. Lymph vessels drain the pelvic limbs and abdomen by draining into the cisterna chyli and then travelling on the left side of the body, opposite the azygous vein, to empty into the left subclavian venous trunk and travel in to the vascular system. The right side only drains the lymph of the thorax, head and neck on the right. Restrictions affecting the left shoulder may have a greater influence on drainage of lymph from the hind limbs.

The forearm covers the thorax. It also is innervated from similar segments of the spine.  The scapula and humerus cover the region of the first four or five ribs and protect the heart. The innervation and blood vessels to the forearm (brachial plexus) leave from the region of the sixth cervical to the second thoracic vertebrae. Problems in one area will affect the other.

Each nerve going to the axilla (cranial pectoral, suprascapular, subscapular, thoracodorsal, axillary, musculocutaneous, median, radial and ulnar) and exiting the vertebrae from C6 to T2 has its own group of functions. Because they are so closely connected through the fascia in the brachial plexus, and also from restrictions in movement in the pleural dome,  immobility in one may affect another. Generally, the branches from C6 and C7 go the pectoral muscles, scapula and latissiumus dorsi (area of saddle/girth sensitivity behind the withers). C7 and C8 innervate the forearm and flexors of the forearm. C8 to T1 innervate the radial nerve, which stimulate the extensors of the limb. T1 and 2 is the ulnar nerve, which includes digital flexors of the limb. Many of these nerves move through the area on the forearm with the muscle bellies of these flexors. Opening the space between these muscles using fascial release can improve mobility of the fetlock, carpus, scapula and thoracic vertebrae in the withers, and the temporal mandibular joint.

Superficial innervation also interconnects, including an area over the scapula that is innervated from the third and fourth thoracic spinal segments, which may indicate a possible visceral thoracic disorder.

Lymphatic flow moves to the medial side of the forearm and continues into the axilla and then the thoracic duct, so it may also be influenced by restrictions in the thorax.

The next area that connects with the thorax is the neck, and then the TMJ. From the pectoral region and forelimbs, we see an influence on the subclavius muscle. From the sternum, we see influence on the sternohyoideus, sternothyroideus, sternocephalicus and brachiocephalicus muscles. This will influence mobility in the hyoid, larynx, mandible and temporal bone, as well as the occiput and many others. Sympathetic cervical ganglions will influence blood flow to the head, as well as the function of the many glands in the head, the baroreceptors for the heart and more. Movement restriction in the TMJ may influence the cranial nerves exiting through the jugular foramen (CNN 9, 10, 11) and those leaving through the petrous temporal bone, such as CNN 7 (facial), that innervates the digastricus muscle and also the muscles of facial expression.

Osteopathic diagnosis and treatment

First check for structural immobility in the thoracic vertebrae, ribs, sternum and shoulder girdle. Also check more distally for restrictions in rotational movement in the forelimbs.  Palpate for mobility and motility in the lungs (pleural restrictions). I asked her how to do this. If you find disorders in this region, you may want to treat the thoracic visceral and thorax.

Many times, you might find liver or stomach immobility from the restrictions in the thorax, as well as a loss of mobility in the esophagus. Pain or immobility (sometimes even lameness) associated with most caudal cervical vertebrae could be a sign of thoracic visceral involvement. Horner’s syndrome or any other autonomic nervous system signs that could be related to dysfunction of the stellate ganglion could be related.

Conditions and situations treated by releasing restrictions in the thorax include:

  1. Horner’s syndrome
  2. Loss of mobility
  3. History of respiratory disease – all such horses could benefit from an examination of the pleura for mobility and motility
  4. Girthiness and resistance to saddling
  5. Resistance to going forward or downhill
  6. Lameness or imbalance in the front limbs.

Methods of treatment

Osteopathic treatment can involve direct or indirect techniques. Often, a combined approach is more effective. Myofascial release is helpful as both a diagnostic aid and therapy adjunct.

The photos below show two examples of myofascial releases for the thorax and shoulder girdle:

I usually follow up any myofascial releases by the structural release of any further immobilities. Adding flexion of the neck and rotation of the sternum to vertebral manipulations can make them much more effective. I believe this is because these manipulations have an indirect impact on the intrathoracic fascia and mediastinum.

In young horses, treatment of the thorax with an eye to its visceral components can be very effective because it can stimulate thymus development. At any age, improving lymphatic flow and function of the organs of the thorax can help mobility and immunity. Movement of the forelimbs, neck and jaw can be improved, and manipulations of the jaw and poll can be more easily perfomed, thereby yielding longer-lasting results when combined with attention to the thorax and thoracic viscera.

References

Visceral Manipulation, Jean-Pierre Barral and Pierre Mercier.  Eastland Press 2005.

Rooney’s Guide to the Dissection of the Horse, 7th edition, Orsini and Sack.  Veterinary Textbooks, 2003.

Atlas of Equine Anatomy, 3rd Edition, Pasquini.  Sudz Publishing, 1991.

Clinical Anatomy of the Horse, Hilary Clayton, Peter Flood and Diana Rosenstein.  Elsevier Limited, 2005.

Brain Stars: Glia illuminating craniosacral therapy, Tad Wanveer.  Upledger Productions, 2015.

Anatomy of the Horse 6th ed, Klaus-Dieter Budras, W.O. Sach and Sabine Rock. Schlutershe Verlagsgesellschaft, 2011.

Champeroux P, Fesler P, et al. “High Frequency Autonomic Modulation:  a new model for analysis of autonomic cardiac control”, Br J of Pharmacology, 2018 May 3.

Wetzler G,  Roland M, et al.  “Craniosacral Therapy and Visceral Manipulation: a New Treatment Intervention for Concussion Recovery”, Med Acupuncture. 2017 Aug1: 239-248.

Castro-Sanchez AM, Mataran-Penarrocha GA, Sanchez-Labraca N, et al. “A randomized controlled trial investigating the effects of CranioSacral therapy on pain and heart rate variability in fibromyalgia patents”. Clin Rehabili. 2011;25 (1) 25-35.

Roger VL. “The heart-brain connection from evidence to action” Eur Heart Journal, 2017 Nov 14;38 (43) 3229-3231.

Skalec A, Egerbacher M. “The deep fascia and retinacula of the equine forelimb-structure and innervation”.  Journal of Anatomy, 2017 Sep;231 (3) 405-416.

Dr. Ann-Marie Hancock graduated from Colorado State University with a BS in Equine Science, an MS in Anatomy and Neurobiology, and a DVM in 2003. She worked at a general equine practice in North Carolina for ten years. She completed the IVAS Acupuncture course in 2007, the Equine Osteopathy Course at the Vluggen Institute in Texas, and became certified as an Equine Osteopath. Dr. Hancock owned Rectortown Equine Clinic in 2013, then relocated to Marshall, Virginia to open True North Equine Veterinary Services, an expanding hub for practitioners supporting equines in any life stage or discipline.