Superficial Flexor....green Deep Digital Flexor & Check Ligament.....yellow Suspensory....blue The image on the left is the leg as it would appear during weight bearing, the right is unloaded so that the check ligament between the DDF and suspensory is visible.

Tendons are made of carefully arranged protein fibers. Bundled together into tough connective tissue strands, they connect muscle to bone. When the muscle contracts, it pulls on the tendon, which pulls on the bone, creating movement. Tendons can vary from very short 1/2 inch structures to very long 2 foot structures. The superficial and deep digital flexor tendons are long large tendons that start as muscle in the upper leg, change over to tendon just above the level of the knee or hock and then run down the back of the knee or hock, the cannon, and foot. As the superficial enters the pastern it bifurcates then surrounds the deep digital finally ending on the back of the pastern. This area of the SDF tendon surrounding the DDF tendon is called the manica flexoria. The DDF tendon continues distally across the pastern, under and in contact with the navicular bone, and finally inserts on the bottom of the coffin bone.

Along with the suspensory ligaments, the flexors are responsible for holding up the horses fetlocks up while standing. During movement the flexors contract contributing greatly to the forward motion of the horse. As the foot leaves the ground bending (flexing) the fetlock and the coffin joint back during the forward (anterior) phase of the gait. Certainly one of the hardest working structures in the body and so it is not surprising that it is one of the most common areas injured.

Tendons usually slide within the connective tissue matrix of the body. However, at places of high motion and friction, the tendon may travel within a synovial sheath. The primary flexor sheath starts just proximal to the fetlock and travels distally all the way into the hoof. This sheath secretes and sequesters a lubricating fluid called synovial fluid, similar to that found in joints. It is important to understand this relationship and to know where these sheaths are as you can better understand the swelling you might see, what type disease process is going on, the best treatment plan, and the possible complications. It is possible to have the sheath alone inflamed: synovitis or both the tendon and sheath inflatable: tenosynovitis.