In part 1 of this series (click her for part 1), we discuss the prevalence of FAI in hockey players and why it may be a cause for concern. In part 2, we are going to present some information on the different factors contributing to FAI and how some of these factors put hockey players at risk for the condition.
Factor #1 – “at-risk” hip positions
Stull et al (2011) suggest that two “at-risk” hip positions have been identified that increase the risk of FAI. The suggested positions are a combination of abduction and external rotation of the hip and a combination of flexion and internal rotation, suggesting that FAI could occur from the repetitive microtrauma from contact between the femur and the acetabular rim. In the same paper, they looked at sprint starts in Peewee ice hockey players to identify these “at-risk” positions in the sprint start. They identified that with every stride during the sprint start, the Peewee hockey player was found to be in both “at-risk” positions at some point throughout the stride cycle. Throughout the push phase, the skater is in extension and abduction while during the swing/recovery phase and at ice contact, they are in flexion and abduction.
Factor #2 – Mechanical Stress
As mentioned in part 1, Kuhn et al (2016) found that hockey players with closed growth plates had greater alpha angles than those with open plates, suggesting that playing high level hockey in childhood could be a predisposing factor for FAI. They also suggest that it may be the repetitive axial loading on the hips during skating may play a role, which has been measured between 1.5-2.5 times body weight (Sim and Chao, 1978). Tibor and Leunig (2012) also bring up the previous thought of cam deformities being calcification from subclinical slipped capital femoral epiphysis, or SCFE. SCFEs are a pediatric condition where the head of the femur may actually slide up on the femoral neck. However, they quickly note that the bony physeal scar from a SCFE is substantially different than the cam deformity, suggesting that they are unrelated.
Factor #3 – Genetics
Some studies have suggested that FAI may also have a genetic component (here), suggesting that if your parents had FAI, you are at in increased risk of having FAI as well. This has been theorized in a very vague sense, and there is research showing that if your parents or siblings have FAI, there is a good chance you will too. However, there is no actually genetics research to back this up because I don’t believe there is an actual gene sequence for FAI, like there would be for conditions like muscular dystrophy or Parkinson’s. We know that the expression of human traits depends not only on genes but also on environmental factors. Typically, if mom or dad was a high-level athlete, their kids will grow up in a athletic household, creating a favorable environment for the expression of athletic genes in the kids. We already know that kids who play elite level sports put more mechanical stress on the femoral head and predisposing them to increased alpha angles. Although it seems that FAI does not occur from the expression of certain genes, genetic anatomical differences are likely to play a large role in the development of the condition. Let’s take for example a youth hockey player with retroverted acetabulum or a player with deeper acetabulum. These are genetic traits that are passed down from generations of ancestors. Because of these variations, there is going to be a limitation into flexion and internal rotation as the neck of the femur will bump the acetabular rim much sooner than someone with anteverted acetabulum. Combine these genetic anatomical variances with the demands of skating, in particular the flexion and internal rotation required in the recovery phase of the stride as discussed with factor #1, and we have a perfect storm for the development of FAI.
Those are 3 of likely many factors contributing to FAI. There is a good chance that not one factor alone would explain the large epidemic of FAI in hockey players. There is also the fact that we now have better technology and diagnostics which make diagnosing and studying FAI much easier, leading to more diagnoses and more knowledge of this bony morphology.