The cumulative incidence and incidence rates for the development of new PFP in this population were 14.9% and 1.57 per 1000 athlete exposures, respectively. All new cases of PFP developed in middle school–aged female athletes. In similar populations, that also included high school–aged female athletes’ incidence risk; the rates were lower in this group, at 9.66 per 100 athletes and 1.09 per 1000 athlete exposures, respectively.17
These data suggest that PFP develops most frequently in early adolescence.
Patellofemoral pain is one of the most common disorders among young adolescent athletes.8,16,41,42
Patellofemoral pain often limits participation in sport activities and may lead to cessation of participation.8,41,43
Restricting participation in physical activities can result in a reduction in the physical and psychosocial health benefits that are gained from physical activity.44,45
We hypothesized that young adolescent female athletes who developed PFP would have higher BMIs compared with those who did not. Our results showed no difference in BMI or BMI z-scores or relative body fat percentage between athletes who developed PFP and those who did not develop PFP. Thus, the association previously found (ie, that athletes with increased BMI sustained a higher proportion of knee injuries than normal-weight counterparts) was not observed in the present study, which focused on PFP in a younger population than similar studies.30
Body mass index does appear to be a predictor of injury in adults and older adolescents.30
Previous research has been conflicting regarding the association between BMI and PFP. Some studies have found a correlation between higher BMI and clinically significant PFP, but others have not. Two studies reported a correlation between those with a lower BMI score and knee pain.9,11,22,26,29–31,46
Theories supporting a correlation between an increase in BMI and PFP include BMI and its relation to decreased joint space in the knee, and BMI and its relation to an increased q-angle in the lower extremity.23,47
Leppälä et al13
showed that BMI had no relation to decreased bone mineral density.
The risk of developing long-term degenerative changes, such as osteoarthritis (of which PFP may be a precursor) is strongly associated with BMI.48
In addition, higher BMI is associated with common orthopedic conditions in adults.49
Older adolescents also demonstrated a relationship between higher BMI and history of lower leg pain among cross-country runners.50
The present results, which indicated no difference in either relative body composition between those with and without incident PFP lead us to suspect an alternative underlying factor in the etiology of PFP in this age group, most notably lack of neuromuscular control. Lopes et al51
found an inverse relationship between motor coordination and BMI; subjects with higher BMIs had lower levels of motor coordination across ages 6 to 14 years. The obese children (BMI ≥ 30 kg/m2
) showed markedly worse motor control levels than those with a normal-range BMI score.51
Motor coordination deficits do not appear to be transient and may even deteriorate further relative to age in overweight and obese children.52
In 2010, Myer et al17
found that athletes who developed PFP demonstrated increased knee abduction moment at initial contact when landing compared with uninjured controls.17
They hypothesized that dynamic knee abduction loading during a landing task contributed to the onset of PFP during the basketball season.17
Females with increased knee abduction moment and load during dynamic tasks also showed increased incidence of knee injury, such as PFP.53
This impaired neuromuscular control may be the modulator to the pathomechanics of PFP in this population, as opposed to the anthropometric measures that we assessed.
Based on our findings and previous research showing no association between PFP incidence and BMI,54
young adolescents with higher BMI should not be prohibited or restricted from participating in athletic activities due to the risk of developing PFP. Rather, young females should be encouraged to regularly participate in sports, because it can enhance their health and well-being.55,56
Participation in organized sports should evolve out of regular participation in a well-rounded preparatory conditioning program designed to reduce the neuromuscular deficits that increase the risk of PFP.57–59
There are potential limitations to the current study. The first is that the screening examinations were performed by different physicians each year. However, we standardized both the questionnaires and physician training for identification of PFP to limit potential for inter-rater diagnosis differences. Second, this study was limited to basketball players; therefore, inferences to athletes in other sports should be limited. This analysis does not differentiate between athletes who had unilateral or bilateral PFP. The final limitation concerns information about the PFP condition itself, including treatment that was undertaken, severity, and outcome measures, with all positive cases of PFP being treated equally. Not all diagnoses included under PFP, as shown in , may be individually influenced by body composition measures. The authors acknowledge that PFP often occurs on a continuum and treatment is related to severity. Some athletes may not complain of PFP unless specifically asked, whereas others will openly acknowledge that it is disabling. Although more research is needed to determine both who should be treated and what interventions should be employed, the reported incidence should focus greater attention to screening and study of the natural history of this condition in youth.