REHABILITATION

Fibroplasts and endothelial cells

PROLIFERATION migrate into

damaged tissue from adjacent areas

proliferate and increase activity

COLLAGEN LAID DOWN

Myofibroplasts

angiogenesis (for- mation of new local circulation

initiate

early wound contraction

Figure 3: The major components of the proliferative events KEY POINT

The result of various therapies on these combined effects requires further investigation, but immobilisation effec- tively inhibits this process while early movement will encourage quality scar material production. Immobilisation has significant effects on collagen structure and behav- ioural characteristics, and the effects of early immobilisa- tion may still be influential at this stage and in relation to long term outcomes (27,28).

the mobility and extensibility of the scar tissue.

The angiogenenic response that occurs alongside the fibroblastic activity is receiving a deal of attention at the present time (29-32). Angiogenesis (the formation of new local blood vessels in the injured area) is essential in that the production of collagen by the fibroblasts is inhibited in low oxygen environments. The angiogen- esis results in increased local flow and thus an increased availabil- ity of oxygen, enabling the fibroblasts to generate their product. A wide range of mediators have been shown to exert an influence on these events, and interestingly a range of stimulants (including ultrasound, electrical stimulation and exercise) have been shown to stimulate this normal reaction (33-36).

Myofibroblasts are derived from fibroblasts activated by a variety of chemical mediators, and are responsible for wound contraction and the early strength of the repair. They draw the edges of the wound together, particularly in skin lesions, thus reducing the size of the final scar (7,16,37,38).

Scar/granulation tissue matures with lymphatic development (in much the same way as capillary development), nerve fibre ingrowth and mast cell invasion. Collagen fibres are oriented in response to local stress thus providing tensile strength in the required direc- tions (see Figure 4). As the granulation tissue matures, there is a process of devascularisation with obliteration of the lumen of the

www.sportex.net Fig.4

Reabsorbtion of type III collagen

REMODELLING

Orientation of collagen fibres

Replacement with more type I collagen

Figure 4: The major components of the remodelling events vessels.

Remodelling phase The remodelling phase is an essential component of tissue repair and is often overlooked in terms of its importance. It is neither swift nor highly reactive, but does result in an organised and func- tional scar which is capable of behaving in a similar way to the par- ent tissue (that which it is repairing). The remodelling phase has a more extensive overlap with the proliferative phase than has been previously thought, and it is now considered to start in the first week following injury – the scar is remodelled as it is constructed rather than after the event (21).

The remodelling phase primarily involves the newly deposited col- lagen and its associated extracellular matrix. The initial deposition of collagen produces relatively weak fibrils with random orientation. With maturity, the collagen becomes more obviously oriented in line with local stresses (39,40). A proportion of the original fine (Type III) collagen is reabsorbed (due to the action of collagenas- es) and is replaced with Type I collagen with more cross links and greater tensile strength (23,26). Collagen synthesis and lysis both occur at a greater rate in a normal wound compared with non- wounded tissue as old fibrous tissue is removed and new scar tis- sue is laid down. The maturing scar is therefore a dynamic system rather than a static one. There are several influential factors during this long phase, including physical stress (6,27,33,41). Final remodelling may continue for months, and possibly over a year beyond the obvious healing of the damage. See Hardy (16) for a comprehensive consideration of collagen behaviour in remodelling and Culav (39) for an excellent review of collagen and its roles. Frank et al (42) have provided a very useful paper with regards the optimisation of soft tissue repair.

Cytokines, growth factors and future potential The volume of literature published over recent years that concern the influence of a significant range of cytokines and growth factors on various aspects of the repair process is considerable. It is well beyond the scope of this paper to even begin to touch on this work, but it is expected that this field will continue to expand in the com- ing years, and the relationship between therapies, including exer- cise, manual therapy and electrotherapy and various cytokines is likely to be become more important and better understood. The possibility remains that future treatments (eg. various electrother- apies, manual therapy and exercise) will be overtly employed in order to influence these mediators and hence influence the repair process.

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