Muscle injuries account for around 30% of all injuries in the English Premier League. A muscle strain typically keeps a player out of action for 3 to 4 weeks and clubs employ full time medical staff in order to reduce this down time. Conventionally, this treatment comprises physiotherapy which uses prescribed procedures such as ice, electrotherapy, massage, mobilisation, manipulation and exercise to optimise the healing process.
Some sports medicine doctors are very interested in the use of new technologies, which promise to enhance injury healing and reduce a player’s injury time. Growth Factor therapy is a new treatment which is being applied in the treatment of sporting injuries.
Using technology that was developed for the treatment of cancer, Growth Factor therapy involves the use of proteins that occur naturally in our body, called Growth Factors. Growth Factors are chemical messenger cells and there are lots of different biological functions that they can induce by binding to receptors on cell surfaces. In cancer patients, Growth Factors called ‘Cytokines’ can help the immune system recognize and destroy the cancerous cells.
Growth Factors occur naturally as part of the body’s immune system, but can also be produced in the laboratory these are known as recombinant Growth Factors.
There are many different types of Growth Factors, some of which have an effect on muscle tissue healing. To understand how, it helps to know a little about muscle injury and repair.
Muscle Injury and Repair
A muscle strain is damage caused by over-stretching of muscle tissue. In football, this is thought to occur most frequently when movements such as sprinting, stretching for the ball or kicking the ball are carried out in an uncoordinated manner. The muscle tissue becomes overloaded and reaches a breaking point where a tear or partial tear occurs. The player will experience pain that will persist if they attempt to stretch or contract the muscle.
Depending on their severity, muscle strains are categorised into grades 1, 2 or 3:
Grade 1 Strain
There is damage to individual muscle fibres (less than 5% of fibres). This is a mild strain that requires 2 to 3 weeks rest.
Grade 2 Strain
There is more extensive damage, with more muscle fibres involved, but the muscle is not completely ruptured. The rest period required is usually between 3 and 6 weeks.
Grade 3 Strain
This is a complete rupture of a muscle. In a sports person this will usually require surgery to repair the muscle. The rehabilitation time is around 3 months.
The healing process of a muscle strain begins with an inflammatory response that can last for three to five days. The muscle cells that are damaged during the muscle tear release chemicals called Growth Factors and Cytokines which mediate the healing response. These chemicals attract cells that remove dead muscle fibres and start the repair process.
The repair process consists of three stages:
- Regeneration of Muscle FibresNew muscle fibres grow from special cells within the muscle called satellite cells.
- Formation of Scar TissueThere is bleeding in the gap between the torn muscle ends and from this blood a matrix, or scaffold, is formed to anchor the two ends together. This matrix eventually forms a scar within the muscle that makes the muscle more resistant to further stretch damage.
- Maturation of the Scar TissueThe collagen fibres which make up the scar tissue become aligned along lines of external stress and are able to withstand more force.
Growth Factor Research
Growth Factors and Cytokines are very important during all three phases of muscle healing. Researchers have suggested that the therapeutic use of Growth Factors and Cytokines has a positive effect on the healing process.
Researchers reported that they had identified three Growth Factors – basic fibroblast growth factor (bFGF), nerve growth factor (NGF) and insulin-like growth factor-1 (IGF1) – which they claimed lead to an increase in the cells responsible for muscle regeneration and improved healing, although there are many more Growth factors and Cytokines.
Further research has revealed that the therapeutic use of Growth Factors and Cytokines in soft tissue injury reduces inflammation, minimises scar tissue formation and promotes the restoration of normal soft tissue.
The conclusion was that getting Growth Factors and Cytokines to the site of soft tissue damage would have a positive effect on healing.
Direct injection of synthetic Growth Factors and Cytokines can be useful but, because the life cycle of these substances is short, repeated injections may be required. This is uncomfortable and increases the risk of infection. Because of this drawback, new techniques have been sought to deliver these substances to the injury site.
Gene therapy is a method whereby the genetic material of Growth Factors and Cytokines are removed from the injured tissue, the genes are manipulated outside the body, packaged into a vector and re-injected into the target cells. This allows the continued production of these Growth Factors and Cytokines at the injury site.
The major concern about using the still developing gene therapy in sports injuries is safety. Whilst the risks of gene therapy may be acceptable for severe disorders such as cancer or cystic fibrosis, the risk of side effects may be unacceptably high in the treatment of sports induced soft tissue injury. The integration of vectors into the host may cause the gene to mutate. Abnormal regulation of cell growth, toxicity from chronic over production of the Growth Factor and Cytokines, and the threat of tumour formation are all theoretically possible, although no cases have as yet been reported. However, these side effects may not occur until years later.
Due to these potential risks, other techniques are being used to try and deliver increased Growth Factors and Cytokines to the injury site. One technique, evolved from Oral and Maxillofacial surgery, involves the laboratory production of ‘Platelet Rich Plasma'(PRP) which is blood with a high concentration of Platelets (irregular shaped cells in the blood that form blood clots). Platelets are the source of one Growth Factor that is part of the healing process Platelet Derived Growth Factor (PDGF).
Platelet Rich Plasma is derived by taking a sample of the patient’s blood and subjecting it to a centrifugal force by spinning it very fast in a device called a centrifuge. The machine spins the blood at about 6000rpm, before being slowed to 2500rpm. This separates the constituent parts of the blood allowing the PRP to be ‘harvested’.
Blood counts have shown that this method of preparation increases the number of platelets by 300% to 700%, leading to a 7 to 30 fold increase in Platelet Derived Growth Factor. This harvested Platelet Rich Plasma is then re-injected into the injury site in an attempt to optimise tissue healing.