There are 3 phases to Healing
- inflammatory phase
- repairing phase
- remodeling phase
Red blood cells and white blood cells, enter the site of injury. In the first twenty-four hours, the job of these white blood cells is to ‘clean up’ any dead materials.
Special substances or factors are released which
- increase permeability of the blood vessels (this allows these blood cells to get out of the blood vessels and into the ‘building site’ of the scar area)
- initiate new blood vessel growth
- stimulate an increase in the numbers of the cells (tenocytes) that make new tendon
- recruit more inflammatory cells
Tenocytes gradually migrate to the wound, and type-III collagen production begins.
This provides a mesh of fibres upon which scar formation takes place
After a few days, the proliferative phase begins.
Production of type-III collagen peaks during this stage and lasts for a few weeks.
Glycosaminoglycans are large carbohydrate molecules that can bind to protein molecules to build connective tissue which in this case is tendon fibres.
Glycosaminoglycan concentrations remain high during this stage due to the increase in production of new tendon tissue at this stage.
After approximately six weeks, the remodeling phase commences, with decreased production of cells and connective tissue from the proliferative stage.
The remodeling phase can be divided into a consolidation stage and a maturation stage.
The consolidation stage begins at about six weeks and continues for up to ten weeks.
In this period, the repair tissue changes from cellular to fibrous – it changes from a ‘soup of cells’ into a collection of fibres which are arranged to form the tendon repair.
Tenocytes and collagen fibers become aligned in the direction of stress (see pictures below). A higher proportion of type-I collagen is produced during this stage.
Type-I collagen is the main constituent of tendons, as opposed to type-III which is more the connective tissue found in blood vessels and skin.
After ten weeks, the maturation stage occurs, with gradual change of the fibrous tissue to scar-like tendon tissue over the course of one year. During the later remodelling phase cross-linking between the collagen fibres increases which results in repaired tissue with the highest stiffness and strength.
Relevance of Tendon Healing
The maturation stage of the ‘remodelling phase’ at 10 weeks post-injury is the key time for recovering from a ruptured tendon.
It is at this stage that the fibres of the scar align.
Look at this Photomicrograph of an anterior cruciate ligament tear at eight weeks after rupture.
You are looking ‘down a microscope’ at the cells in the repairing ligament.
You can see that the cells, with their dark centre (nucleus), are not particularly organised and lack a visible orientation.
Compare that with this photomicrograph of cells from the same structure at 16 weeks after rupture.
In this picture you can see that the cells have become arranged in lines.
The fibres have become much less ‘higgildy-piggildy’ in their alignment.
Applying a suitable degree of stress on the repairing tendon improves this alignment even further and promotes cross linking between fibres.
It is this early moving and then gradually stressing the healing tendon that has resulted in the dramatically reduced recovery times from a ruptured tendon. This applies to the surgically treated patients as well.
The secret of effective rehab is to apply the appropriate amount of stress – enough to encourage this alignment of the cells and fibres of the tendon. Applying too much stress at the wrong time results in re-rupture of the healing tendon.
Wearing specialised braces allows for the early application of these stresses which produce the excellent results now being achieved in tendon repair.