The prevention, diagnosis, and management (including rehabilitation) of injuries related to participation in physical activity are key components of the scope of clinical practice of the sport and exercise medicine physician. These components of the scope of clinical practice are not only confined to dealing with injuries in elite athletes, but are as important for 1) the recreational athlete of any age or gender who participates in school, college, or club sports, or 2) patients who are given an exercise prescription as part of a lifestyle intervention program for the primary and secondary prevention of chronic disease.
It is well established that the majority of injuries related to participation in physical activity occur in the "soft tissues." The term "soft-tissue injuries" is not well defined, but usually refers to injuries to muscle, tendon, and ligamentous tissue. However, "soft tissue" injuries also can include injuries to vascular tissue, nervous tissue, and other tissues. For the purposes of this commentary, I will use the loose definition of "soft-tissue injuries" to refer mainly to muscle, tendon, and ligamentous injuries.
As clinicians, we spend considerable time with our patients to prevent these soft-tissue injuries, diagnose them correctly, and then prescribe the correct treatment and rehabilitation before making the correct decision in allowing an individual to return to full activity. In recent years, there has been growing interest in these injuries, and this has resulted in a rapid growth in our knowledge regarding all aspects of soft-tissue injury prevention, diagnosis, and management.
Sports Injuries as Connective Tissue Injuries
One of the most notable recent advances in my understanding of soft-tissue injuries in sport has been the fact that soft-tissue injuries (and indeed other injuries, such as bony and cartilaginous injuries) are, in fact, injuries of connective tissue. Tendons, ligaments, and bone are connective tissue structures, whereas muscle consists of contractile tissue that is linked to an intricate connective tissue network. Therefore, the vast majority of sports injuries are, in fact, connective tissue injuries. This realization has led to a rapid growth in interest, and therefore research activity, relating connective tissue biology to 1) adaptation to mechanical loading (training), 2) sports injury risk, 3) healing response of injuries, and 4) interventions that are used in the treatment of sports injuries.
Interindividual Differences in Connective Tissue Structure and Function
It is obvious that not all connective tissue is the same, and more importantly, the same connective tissue structure (e.g., tendons) is not the same between different individuals and within an individual. There are many factors that would account for these interindividual differences in connective tissue structure and function. Broadly speaking, these factors will include environmental factors (e.g., exposure to mechanical loads during training, nutritional factors, exposure to drugs) and genetic factors (genetic variation in genes encoding for a specific collagen type or other protein). Therefore, in any individual who participates in physical activity, the ability of any connective tissue structure, such as an Achilles tendon, to accommodate the mechanical load on the tissue will be dependent on genetic factors and environmental factors (gene-environment interaction). Until fairly recently, the majority of research activity has been focused mainly on understanding the environmental factors and nongenetic intrinsic risk factors. A group of researchers in our unit has identified only recently the concept that there may be intrinsic genetic factors.
Genetics and Intrinsic Risk Factors for Injury of Connective Tissue
As a result of this research, clinicians have been made aware only recently that genetic factors that may influence the risk of developing a sports injury. There is now a growing body of evidence that genetic factors may be important intrinsic risk factors for injuries. More specifically, there is evidence that there are genetic risk factors for Achilles tendinopathy, Achilles tendon ruptures, anterior cruciate ligament injuries, and stress fractures. It is becoming increasingly important for the clinician to consider these factors when evaluating potential risk for injury, in the same manner as other intrinsic risk factors for sports injuries are identified (e.g., previous injury, age, sex, body mass index, quinolone antibiotic use). The logical extension of this argument is that, in the future, the assessment of genetic risk will become an additional tool for the clinician to determine risk of injury. The implication of this requires careful consideration (including ethical considerations) before the use of this tool can progress from its current pilot testing phase to wider implementation.
Genetics and Injury Management: A Future Perspective
Following on from the concepts that 1) there are inter-individual differences in connective tissue structure and function, and 2) that genetic risk factors for connective tissue injury are being identified, it is clear that there also is likely to be an interindividual difference in the tissue response to injury (healing response) and the fact that the responses to therapeutic interventions for connective injuries also will vary.
There is a rapidly growing body of research that is focused on understanding the healing response of injured tissue and possible "manipulation" of this healing response to improve scar tissue formation and optimize the healing of tissue. Of particular recent interest has been the study of the possible use of medications (e.g., anabolic steroids), physical modalities (therapeutic ultrasound), and more recently growth factors and antifibrotic agents in facilitating healing. However, what has not been fully appreciated is the probable interindividual response to these interventions and the possible role that genetic factors may play in these responses. The clinician would be advised to consider very carefully these differences in individual responses to therapeutic modalities for connective tissue injury management. This, of course, means that there is a significant opportunity for clinician-researchers to further the understanding of these responses by forming research collaborations with colleagues working in the field of genetics and molecular biology. This is certainly an area where I will focus my clinical and research attention over the next few years so that I can take better care of the athletes under my care.