This is a much debated subject. A study in the American Journal of Sports Medicine in July 2009 shows that there are anthropometric differences between the knees of subjects with a non contact ACL injury and those without an ACL injury, suggesting that ACL volume may play a direct role in non contact ACL injury.

The study showed that the volume of the ACL on the uninjured side as measured on MRI was significantly smaller in subjects who tore their ACLs than in subjects who had no injury.

With up to 70% of ACL injuries non-contact in nature this new information is enlightening. Previous studies have shown that women have smaller ACL volume than men when subjects of the same height are compared. This study shows that the ACL volume in subjects who injure their ACLs is less than in non-injured subjects. It provides the strongest evidence to date of a link between ACL size and injury risk because it directly compares injured subjects to matched controls.

It may be possible to pre-screen individuals and direct them in neuro-muscular training where proprioception would be improved. Such programmes have already been shown to decrease injury rates in the ACL. There is a gradual movement away from concentrating on pure strength and stretching to prevent injury and a greater understanding of the importance of proprioceptive training.

It may also be possible to use growth factors in relatively small ACLs to increase volume and prevent injuries. This area needs more research and it is unlikely that growth factors will be used on a widespread basis in the next 5 years to promote growth of the ACL. However there is no doubt that growth factors is where the next big break through in ACL injury will be. They will be used in normal ligaments to make them stronger, partially torn ligaments to make them heal and reconstructed grafts to integrate faster.

Breandán Long