Tendons and Tendon Transfers

TENDON ANATOMY

1. Epitenon: The outer covering of a tendon within its sheath. Most important structure in the tendon repair process.

2. Endotenon: A loose acellular tissue carrying blood vessels that surrounds small bundles of collagen fibers throughout the tendon

3. Paratenon: The loose elastic areolar tissue surrounding the entire tendon, which allows the tendon to slide. It supplies the blood supply to the tendon and should be reapproximated after tendon surgery. Supplies the majority of a tendon’s blood supply.

4. Mesotenon: A delicate connective tissue sheath attaching a tendon to its fibrous sheath. A part of the paratenon that attaches the paratenon to the epitenon, which can stretch several centimeters, and allows a blood supply to be transferred from the paratenon to the tendon. The point at which it attaches to the epitenon is called the hilus.

5. Peritenon: All the connective tissues associated with a tendon (epitenon, endotenon, paratenon, mesotenon)

6. Fascicles: A group of collagen fibers bundled together and surrounded by an endotenon

7. Collagen fibers: Formed from a polymer of tropocollagen, which is the basic molecular unit of a tendon. Healthy tendon is mostly composed of type I collagen fibers.

Collagen

The main collagens found in connective tissue are Types I, II, and III. These collagens form fibers that give tensile strength to tissues.

Type I	Most abundant, found in skin, ligaments, tendon, fibrocartilage, bone
Type II	Found in articular cartilage (Hyaline cartilage)
Type III	Skin, vessels, lymphatics, granulation tissue, tendinosis

Tendonitis vs. Tendinosis

Tendonitis	Tendinosis
Inflammation	Degenerative
Caused by acute overloading	Caused by chronic over use
Tendon appears white, glistening, and firm	Tendon appear gray, dull-appearance, soft (lipid or mucoid degeneration)
Composed of type I (normal) collagen fibers	Composed of type III (abnormal) collagen fibers
Treatment takes days to weeks	Treatment takes months
	Disrupted collagen fibers, increased cellularity, neovascularization (angiofibroblastic hyperplasia)
	Increased bulk, decreased strength
Treatment: Anti-inflammatory modalities, RICE, NSAIDs	Treatment: break the cycle of injury, reduce ground substance, pathological vascularization, and subsequent tendon thickening. Optimize collagen production and maturation so the tendon regains strength.
	Rest, braces, inserts, stretching, ice, eccentric strengthening, massage

TENDON REPAIR

Anchoring Tendon to Bone

Trephine Plug

A round cortical plug is removed with a trephine, the tendon is inserted, and the plug is replaced.

Three-Hole Suture

The tendon is anchored to a piece of suture, the tendon is then inserted in a hole in the bone, and the two suture ends exit the bone through two additional holes and are tied.

Buttress and Button Anchor

The tendon is anchored to a piece of suture, the tendon is then inserted in a hole in the bone, and the suture ends continue through the bone and exit the skin on the other side of the foot and is fixated with a button.