Where Are We Now?
Femoroacetabular impingement (FAI) consists of abnormal bony morphology of the femoral head/neck junction (cam morphology) and/or acetabulum (pincer morphology), which can lead to articular cartilage and labral injury as well as clinical symptoms from altered mechanical loading of the hip joint in some patients. Although some have considered FAI (and the cam morphology, more specifically) to be modern phenomena , there is evidence that this is not the case . Regardless, there seems to be some evidence that environmental factors matter, since participation in high-intensity and high-impact sports during skeletal maturation appears to be associated with the development of FAI .
Multiple studies have shown radiographic findings consistent with FAI in high-level adolescent and young adult male athletes [3, 8-10]. Another study of 63 women collegiate athletes (soccer, track/field, volleyball) showed 48% of hips had radiographic findings for cam morphology . Based on data from these and other similar studies, researchers generally believe that elite athletes in high-intensity/impact sports have increased risk for FAI because of factors associated with their training and with sports that alter physeal growth during skeletal development . To further evaluate the development of FAI during skeletal maturation, one research team prospectively followed a cohort of elite pre-professional adolescent male soccer players from the Netherlands over 5 years and found that cam morphology in plain radiographs developed in 73% of players by skeletal maturity at age 18 [1, 11].
The current study by Hanke et al.  sheds additional light on this process. They shared findings from a prospective, longitudinal MRI analysis about the development of cam morphologies in adolescent ice hockey players. Performing baseline, 1.5-year, and 3-year follow-up MRIs on players beginning at age 12 to 13 years, the authors found that 12 of 23 (52%) players developed a cam morphology within 3 years. They also found a correlation between physeal extension of the proximal femoral physis and higher alpha angle, indicating an underlying growth disturbance may be associated with cam development. The authors conclude that cam morphology develops during the early phase of the final growth spurt of the proximal femur between ages 13 to 16 years. This is important because understanding that cam morphology develops from a growth plate disturbance during a specific period of skeletal development will help to direct future research focused on prevention of this phenomenon. Surgeons caring for young athletes might also consider thorough counseling of this pathology for their patients as well as close clinical examination to survey for signs and symptoms consistent with cam development.
Where Do We Need To Go?
Based on these novel findings, researchers should develop studies that can pinpoint the exact causes of growth disturbances to the proximal femoral physis with an ultimate goal of establishing preventative measures. One initial area of focus should assess whether there is a specific activity such as running, jumping, or cutting that increases the likelihood that cam morphology will develop. There are several questions to consider: Are there particular motions or movements inherent to ice hockey, soccer, basketball, and American football that cause athletes to form cam morphologies? Is it simply the act of overloading the hip through intense running/sprinting or rather a cutting/pivoting motion with repetitive flexion and internal rotation of the hip that leads to the physeal disturbance?
Another possibility is that the activity level and duration of training during skeletal maturation may be a greater risk factor for cam development than the types of activities themselves. Should there be a critical limit to hours of training per day or number of days per week in adolescent athletes? This threshold would be akin to a pitch count limit in skeletally immature pitchers in order to protect the long-term health of their arms. Lastly, can FAI development be one of the oft-discussed perils of single-sport specialization? Topical research has shown many deleterious effects of early single-sport specialization for youth such as increased risk for overuse injuries. It would therefore be valuable to assess whether cam development is more common in single-sport athletes compared to multisport athletes.
The good news is that the above-mentioned potential culprits leading to the development of the cam morphology all are modifiable. If we can identify the exact stressors and modify those activities in high-risk groups, then we may see a decrease in the incidence of FAI.
How Do We Get There?
Reducing the frequency of FAI is within our grasp. One reason for my optimism is that we don’t need to develop new technology to answer the main questions I listed earlier. With clinical and translational research tools such as advanced imaging techniques already at our disposal and the knowledge we now possess about the most at-risk populations and the most vulnerable time periods, studies can be started immediately to identify the causes of cam development.
The first step should be to enroll high-level adolescent athletes—both boys and girls—at ages 11 to 13 years (before the final growth spurt phase) from sports such as basketball, soccer, and football into prospective cohorts. Matching the cohorts can help to control for certain variables, such as age, gender, BMI, sport, and competition level. Longitudinal evaluation of the duration of training as well as types of exercises/activities performed will build a database on individual activity level and the types of exercises/activities being performed. Additional interval biomechanical analyses may be helpful in understanding hip and lower extremity kinematics during growth. Lastly, routine MRI evaluation at regular timepoints, such as that performed by Hanke et al. , will be crucial for future studies to evaluate early changes in bony morphology as well as physeal disturbances.
One translational tool that may provide a breakthrough for this analysis is the use of quantitative MRI (qMRI) sequences such as T1rho or T2 mapping to assess changes in cartilage composition at the molecular level [2, 4]. By adding qMRI sequences to surveillance MRI during skeletal growth, we may be able to detect and localize early changes to the proximal femoral physis that would later develop into cam morphologies. Thus, with the ability to target high-risk cohorts and the availability of modern imaging techniques, I expect that our insights on the development of the cam morphology will grow exponentially in the next decade.
Although arthroscopic surgery for FAI can provide significant clinical improvement, not every patient with symptomatic FAI can be successfully treated, and irreversible degenerative changes may occur at an early age, sometimes even before patients exhibit symptoms. Therefore, decreasing the incidence of FAI in high-risk groups as well as the general population should be a focal point for future research.
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