The incidence and potential pathomechanics of patellofemoral pain in female athletes
Introduction
Retropatellar and peripatellar pain, clinically referred to as patellofemoral pain (PFP), is a common pain disorder experienced by young adult and adolescent athletes who participate in jumping cutting and pivoting sports (Heintjes et al., 2005, Louden et al., 2004, Natri et al., 1998, Witvrouw et al., 2000, Kannus et al., 1987). Up to 40% of clinical visits for knee problems are attributed to PFP (Natri et al., 1998, Kannus et al., 1987) and adolescent females and young adult women are affected more often (2 to 10 times) with PFP than their male counterparts (Robinson and Nee, 2007, Fulkerson, 2002, Fulkerson and Arendt, 2000). Fairbanks and colleagues reported PFP symptoms can affect up to 30% of young students (13–19 years) and the symptoms may cause 74% to limit their sport activities or lead to sports cessation (Blond and Hansen, 1998, Fairbank et al., 1984). Symptoms of PFP that restrict young athletes from participating in recreational activities may also limit them from the health benefits of regular physical activity (CDC, 2006, Heintjes et al., 2005, Crossley et al., 2005, Christou, 2004). In addition, current evidence contradicts the assumption that PFP runs a benign and self-limiting course; on the contrary, PFP is a likely contributor to long term patellofemoral osteoarthritis (Utting et al., 2005).
Prior biomechanical investigations have reported altered neuromuscular recruitment strategies in patients with active symptomatic PFP (Bolgla et al., 2008, Willson et al., 2008, Robinson and Nee, 2007, Macintyre et al., 2006). Differences in whole body power and static alignments found in patients with symptomatic PFP may also be risk factors that contribute to the genesis of PFP. Witvrouw et al. (2000) conducted one of the early investigations that aimed to prospectively determine the intrinsic risk factors for the development of PFP. Prior to the start of physical education training they evaluated male and female students enrolled in a physical education class for anthropometric variables, motor performance, general joint laxity, lower leg alignment characteristics, muscle length and strength, static and dynamic patellofemoral characteristics, and psychological parameters. Over a two year period, they found that shortened quadriceps muscles, an altered vastus medialis obliquus muscle reflex response time, decreased explosive strength and jumping power, and a hypermobile patella were significantly related to the incidence of PFP. A recent study by Stefanyshyn et al. (2006) prospectively followed long distance runners to determine predictive factors that lead to PFP. Their results indicated an increased knee frontal plane impulse moment was evident during single support stance phase of running in subjects who developed PFP. Similarly, Rauh et al. (2007) reported that high school cross-country runners with abnormal frontal plane static alignments (Q-angle measures of 20 or more degrees) were more likely to miss practice or competition from an injury to their knee. While increased frontal plane alignments and loads are associated with patellofemoral pain and knee injury incidence in endurance athletes, this association has not been reported in random, intermittent, dynamic sport (Bloomfield et al., 2007) athletes (Cahue et al., 2004, Huberti and Hayes, 1984).
Altered or decreased neuromuscular control during the execution of sports movements, which result in excessive resultant out of plane (especially frontal plane) knee joint motion and load, appear to increase risk of acute knee injury in female athletes and may contribute to the development of PFP (Hewett et al., 2005). Army recruits who landed from a jump with a combination of reduced knee flexion, increased out of plane hip rotation and frontal plane foot laxity were at increased risk for the development of PFP (Boling et al., 2009). Previous authors have suggested that abnormal frontal plane kinematics and moments that are associated with acute injury may also be related to PFP development in young athletes, but this relationship has not been prospectively examined in random, intermittent, dynamic sport populations who develop PFP injury (Powers, 2003, Hewett et al., 2005). At small knee flexion angles (19–22°) commonly reported in female athletes when initiating a landing, abnormal frontal plane patellofemoral joint kinematics are evident in PFP patients (Ford et al., in press, Macintyre et al., 2006). Specifically, at 19° of knee flexion, patients with symptomatic PFP pain presented with a laterally aligned patella, which is also associated with increased knee abduction (MacIntyre et al., 2006). Cumulatively, the current evidence indicate that increased frontal plane knee alignments and loads, especially at small knee flexion angles similar to those found at initial contact of a jump landing, should be evaluated to determine their contribution to PFP onset.
The absence of consensus regarding factors that increase the risk of PFP in random, intermittent, dynamic sport athletes limit the potential to optimize prevention and treatment of this disorder in these populations. The objectives of this study were 1) to determine the prevalence and incidence of patellofemoral pain (PFP) in young female athletes, and 2) to prospectively determine the relationships between measures of frontal plane knee loading during landing and development of patellofemoral pain. We hypothesized that increased dynamic knee abduction measured during preseason biomechanical testing of landing mechanics would be increased in those who developed PFP relative to teammates who did not develop PFP.
Section snippets
Subjects
Female basketball players were recruited from a county public school district with five middle schools and three high schools. From the six high school and fifteen middle school basketball teams identified from these schools, 174 middle school and 66 high school basketball players (mean age 13.4 years, height 160.6 cm, body mass 54.5 kg and percent of adult stature 91.1%) agreed to participate in this study. Group specific (PFP and CTRL) demographic and anthropometric data are presented in Table 1.
Results
Table 1 presents the aggregate demographic and static anthropometrics that showed no inherent confounding between-group effects for these measures (P > 0.05). Vertical jump height performance measured during the DVJ, a measure of whole body power, was also not different between the PFP (30.1 ± 4.8 cm) and CTRL (31.8 ± 4.2 cm; P > 0.05) study groups.
The point prevalence of unilateral PFP at the beginning of the season was 16.3 per 100 athletes. Prospective tracking of exposures in the middle and high
Discussion
Patellofemoral pain (PFP) is one of the most common disorders of the lower extremity, with its greatest incidence in young, physically active female athletes (Heintjes et al., 2005, Louden et al., 2004, Natri et al., 1998, Witvrouw et al., 2000, Kannus et al., 1987). PFP limits participation in recreational and sports activities and, more importantly, may be a precursor to long term patellofemoral osteoarthritis (Natri et al., 1998, Utting et al., 2005, Witvrouw et al., 2000). The point
Conclusion
Nearly a quarter of the athletes were affected with PFP in the current sample at any cross section of the competitive season. These data provide an indication of the relevance of identification and amelioration of potential predisposing risk factors to prevent this syndrome that affects a large percentage of young female athletes. The relationship of increased knee abduction moment to PFP indicates that further examination of these potential biomechanical and neuromuscular correlates to
Acknowledgements
The authors would like to acknowledge funding support from National Institutes of Health Grant R01-AR049735, R01-AR055563 and R01-AR056259. We would also like to thank Randy Poe, Ed Massey and Mike Blevins and the Boone County public school board and the entire Boone County school district for their participation in this study.
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