Physiology plus activity can equal injury

Experts say some people more prone to joint damage

While sports, exercise and physical activity are essential to good health, there’s a potential downside as well: getting hurt. Each year, millions of Americans visit their doctors with musculoskeletal complaints and impairments, often involving sports- or activity-related joint injuries.

Knee problems are most frequent (an average of 2.5 million visits to emergency rooms annually). It’s been estimated that one in 3,500 Americans will suffer damage to their anterior cruciate (ACL) ligament — one of four major ligaments in the knee — each year. That’s roughly 95,000 significant knee injuries annually from just one type of damage, one that frequently requires surgical reconstruction. Shoulder injuries are the second-most common complaint.

We asked Dr. Christopher J. Wahl, an associate professor and chief of sports medicine in the UC San Diego Health System’s Department of Orthopedic Surgery, to diagnose the current situation.

Q: Are there inherent factors that predispose some people’s joints, specifically the knee and shoulder, to become unstable or more susceptible to injuries?

A: There are myriad factors, some of which we understand well and others we don’t, that may predispose an individual to injury. The shoulder is perhaps the best example. It is the least inherently stable joint in the body — a trade-off of incredible mobility at the expense of stability. There is enormous variation from individual to individual in the degree of elasticity of the connective tissues that make up our joints. It is a genetically inherited trait. We sort of “inherit” or adopt our interests or activities as well — the manner in which we’ve been given the encouragement or opportunity to participate in certain activities that involve movements known to put the shoulder at high risk for dislocation, such as surfing or kayaking.

So you can imagine that a person who genetically has very elastic connective tissues and who has taken an interest in activities that can predispose one to shoulder dislocation is at a much higher risk than a person without this elasticity or who doesn’t participate in “at risk” activities.

Q: Why is the incidence of female athletes suffering from ACL injuries rising? Is it a result of more women in sports or something particular to their physiology?

A: The increased incidence of ACL injury among females is probably a combination of several factors. The number of women competing has grown exponentially with the emphasis of organized competition at every level from junior club sports to professional athletics.

Second is what I like to call the “Just Do It” effect: The intensity of practice and play today is far increased over what it was 20 years ago. Even among recreational athletes, there is a huge emphasis on speed and power (high-energy injuries), endurance (overuse/fatigue injuries) and precision (more practice increases the chance of injury).

Finally, there is sound scientific evidence that there are modifiable and innate, sex-specific factors that predispose to ACL injuries. Differences between males and females in the way they tend to jump, change direction and land can be addressed. Anatomic differences play a huge role. I recently published a study looking at differences in knee joint shape between males and females and the association with cruciate injury. The findings indicated that people who suffered ACL injuries had relatively smaller, highly curved joint surfaces on the outer aspect of the knee. Interestingly, the majority of females studied shared this anatomic trait while only a minority of males did. However, males with the shorter, more curved joint surfaces were the ones who suffered ACL tears.


