Musculus trapezius pars thoracica
The thoracic trapezius is a broad, triangular superficial muscle over the wither region. It originates from the supraspinous ligament over T3-T10 and inserts on the spine of the scapula. Its actions are to elevate the scapula and draw it caudally during retraction. It is innervated by the accessory nerve (cranial nerve XI) and ventral branches of cervical nerves. It is visible over the withers and contributes to scapular mobility.
Origin: Supraspinous ligament over T3-T10
Insertion: Spine of the scapula
Action: Elevates the scapula; draws it caudally during retraction
Innervation: Accessory nerve (CN XI) and ventral branches of cervical nerves
Isolated injury is uncommon. Relevant in evaluations of wither and scapular function and after trauma or poor saddle fit.
## Overview Saddle-induced atrophy is muscle wasting directly under the saddle from chronic pressure. It appears as hollows on either side of the withers. The saddle may slip or bridge, and the horse
## Overview Fistulous withers is infection and inflammation of the supraspinous bursa located between the nuchal ligament and the dorsal spinous processes of the withers. It produces painful swelling
Persistent wither pain or reduced scapular mobility after saddle trauma should be evaluated. Correct saddle fit is important.
## Overview Saddle-induced atrophy is muscle wasting directly under the saddle from chronic pressure. It appears as hollows on either side of the withers. The saddle may slip or bridge, and the horse is sensitive when the withers are groomed. Removing the pressure and rebuilding muscle with correct work reverses much of the atrophy. ## Causes Chronic focal pressure from a poorly fitted saddle. ## Diagnosis Visual hollows and saddle-fit evaluation. ## Treatment Correct saddle fit and progressive conditioning to rebuild the wasted muscle. ## Recovery and Prognosis Good with time and correct work. ## Prevention Regular saddle fitting. Signs include: hollows on either side of the withers; visible muscle wasting in the saddle region; saddle slipping or bridging; sensitivity when grooming
## Overview Fistulous withers is infection and inflammation of the supraspinous bursa located between the nuchal ligament and the dorsal spinous processes of the withers. It produces painful swelling and draining tracts. Historically associated with Brucella, it can also result from other bacteria or trauma. ## Causes Bacterial infection (including Brucella abortus in some regions), trauma from ill-fitting tack, or penetrating wounds. ## Diagnosis Clinical appearance of withers swelling and draining tracts, culture of discharge, and imaging to assess bursal involvement. ## Treatment Surgical debridement of infected tissue, prolonged antibiotics based on culture, and local wound care. Recurrence is common. Recovery is often prolonged. ## Recovery and Prognosis Guarded. Many cases require multiple surgeries. Chronic fibrosis can remain. ## Prevention Proper saddle fit, hygiene, and separation from cattle in Brucella-endemic areas. Signs include: swelling, heat, and pain over the withers; draining tracts with purulent discharge; extreme sensitivity; girthiness; fever in systemic cases
Isolated injury is uncommon. Relevant in evaluations of wither and scapular function and after trauma or poor saddle fit.
Persistent wither pain or reduced scapular mobility after saddle trauma should be evaluated. Correct saddle fit is important.
See the Thoracic Trapezius on our interactive 3D horse model. Open 3D Model