Musculus extensor digitorum communis
The common digital extensor (forelimb) originates from the lateral epicondyle of the humerus and the lateral radius. Its long tendon runs down the dorsal aspect of the cannon bone, crosses the fetlock, and inserts on the extensor process of the coffin bone (P3). It extends all the joints of the digit and also contributes to carpal extension. In the hind limb the analogous muscle is the long digital extensor. The tendon is subcutaneous and easily palpated. It is essential for the swing phase of the stride. Innervation is via the deep branch of the radial nerve (C7–T1). Extensor tendon lacerations or ruptures (sometimes associated with flexural deformities or trauma) cause the horse to knuckle forward at the fetlock.
Origin: Lateral epicondyle of the humerus and lateral radius
Insertion: Extensor process of the distal phalanx (coffin bone, P3)
Action: Extends all joints of the digit; extends the carpus
Innervation: Deep branch of the radial nerve (C7-T1)
Lacerations of the common digital extensor tendon are relatively common because of its exposed position. Primary tendonitis is less frequent than in the flexor tendons. Avulsion of the extensor process of P3 can occur. Radial-nerve damage affects its function along with other extensors.
## Overview Tenosynovitis of the extensor tendon sheath where it crosses the dorsal carpus produces visible soft swelling on the front of the knee. Lameness is often mild or absent. It may be primary
## Overview Wounds on the front (dorsal) aspect of the cannon bone can lacerate the extensor tendons. Damage to the common digital extensor or lateral digital extensor compromises the horse’s ability
A horse that knuckles forward at the fetlock or cannot advance the limb properly after a wound on the front of the cannon or pastern needs immediate veterinary care: the extensor tendon may be cut. Protect the front of the lower limb with boots when working in conditions where overreaching or interference is likely.
## Overview Tenosynovitis of the extensor tendon sheath where it crosses the dorsal carpus produces visible soft swelling on the front of the knee. Lameness is often mild or absent. It may be primary or secondary to carpal joint issues. ## Causes Strain, trauma, or extension of carpal inflammation. ## Diagnosis Palpation, ultrasound, and lameness evaluation with diagnostic analgesia if needed. ## Treatment Rest, anti-inflammatories, and bandaging. Intrabursal medication for persistent cases. Address concurrent carpal disease. ## Recovery and Prognosis Good. Swelling may remain as a cosmetic change. ## Prevention Avoidance of repetitive trauma to the dorsal carpus. Signs include: soft fluctuant swelling on the dorsal carpus; mild or absent lameness; cosmetic concern
## Overview Wounds on the front (dorsal) aspect of the cannon bone can lacerate the extensor tendons. Damage to the common digital extensor or lateral digital extensor compromises the horse’s ability to advance the limb, resulting in knuckling or toe dragging. Complete severance produces more severe dysfunction. ## Causes Trauma from kicks, wire, or other penetrating injuries. ## Diagnosis Visual inspection of the wound plus assessment of limb function (knuckling, inability to extend the digit). Ultrasound evaluates tendon integrity. ## Treatment Wound care, antibiotics, and, when tendons are lacerated, surgical repair or prolonged external support (splinting or casting) to allow healing. Rehabilitation is lengthy. ## Recovery and Prognosis Fair if tendons are partially damaged and supported. Complete severance carries a more guarded outlook for full function. ## Prevention Safe fencing and turnout management. Signs include: wound on the front of the cannon; knuckling; inability to advance the toe; toe dragging if the extensor tendon is severed
Lacerations of the common digital extensor tendon are relatively common because of its exposed position. Primary tendonitis is less frequent than in the flexor tendons. Avulsion of the extensor process of P3 can occur. Radial-nerve damage affects its function along with other extensors.
A horse that knuckles forward at the fetlock or cannot advance the limb properly after a wound on the front of the cannon or pastern needs immediate veterinary care: the extensor tendon may be cut. Protect the front of the lower limb with boots when working in conditions where overreaching or interference is likely.
See the Common Digital Extensor on our interactive 3D horse model. Open 3D Model