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1.  Is Body Composition Associated With An Increased Risk of Developing Anterior Knee Pain in Adolescent Female Athletes? 
To determine the relationship between relative body composition and body mass to height, anterior knee pain, or patellofemoral pain (PFP) in adolescent female athletes.
Patellofemoral pain is common in female athletes and has an undefined etiology. The purpose of this study was to examine whether there was an association among higher body mass index (BMI), BMI z-scores, and relative body fat percentage in the development of PFP in an adolescent female athlete population. We hypothesized that female athletes who developed PFP over the course of a competitive basketball season had higher relative body mass or body fat percentage compared with those who did not develop PFP.
Fifteen middle school basketball teams that consisted of 248 basketball players (mean age, 12.76 ± 1.13 years; height, 158.43 ± 7.78 cm; body mass, 52.35 ± 12.31 kg; BMI, 20.73 ± 3.88 kg/m2) agreed to participate in this study over the course of 2 basketball seasons, resulting in 262 athlete-seasons. Testing included the completion of the Anterior Knee Pain Scale (AKPS), International Knee Documentation Committee (IKDC) form, standardized history, physician-administered physical examination, maturational estimates, and anthropometrics.
Of the 262 athlete-seasons monitored, 39 athletes developed PFP over the course of the study. The incidence rate of new PFP was 1.57 per 1000 athlete-exposures. The cumulative incidence of PFP was 14.9%. There was no difference in BMI between those who developed PFP (mean body mass, 20.2 kg/m2; 95% CI, 18.9–21.4) and those who did not develop PFP (mean body mass, 20.8 kg/m2; 95% CI, 20.3–21.3; P > 0.05). Body mass index z-scores were not different between those who developed PFP (mean, 0.3; 95% CI, 0.7–0.6) and those who did not develop PFP (mean, 0.4; 95% CI, 0.3–0.6; P > 0.05). A similar trend was noted in relative body fat percentage, with mean scores of similar ranges in those who developed PFP (mean body fat percentage, 22.2%; 95% CI, 19.4–24.9) to the referent group who did not (mean body fat percentage, 22.9%; 95% CI, 21.8–24.1; P > 0.05).
Our results do not indicate a relationship between relative body composition or relative body mass to height to the propensity to develop PFP in middle school–aged female basketball players. Although previous data indicate a relationship between higher relative body mass and overall knee injury, these data did not support this association with PFP specifically. These data suggest the underlying etiology of PFP may be neuromuscular in nature. Further research is needed to understand the predictors, etiology, and ultimate prevention of this condition.
PMCID: PMC3398745  PMID: 22508247
patellofemoral pain; anterior knee pain; biomechanics; body mass index; BMI z-score; anthropometrics; body fat; patellofemoral pain
2.  Gender differences in the incidence and prevalence of patellofemoral pain syndrome 
The purpose of this investigation was to determine the association between gender and the prevalence and incidence of patellofemoral pain syndrome (PFPS). One thousand five hundred and twenty-five participants from the United States Naval Academy (USNA) were followed for up to 2.5 years for the development of PFPS. Physicians and certified athletic trainers documented the cases of PFPS. PFPS was defined as retropatellar pain during at least two of the following activities: ascending/descending stairs, hopping/jogging, prolonged sitting, kneeling, and squatting, negative findings on examination of knee ligament, menisci, bursa, and synovial plica, and pain on palpation of either the patellar facets or femoral condyles. Poisson and logistic regressions were performed to determine the association between gender and the incidence and prevalence of PFPS, respectively. The incidence rate for PFPS was 22/1000 person-years. Females were 2.23 times (95% CI: 1.19, 4.20) more likely to develop PFPS compared with males. While not statistically significant, the prevalence of PFPS at study enrollment tended to be higher in females (15%) than in males (12%) (P50.09). Females at the USNA are significantly more likely to develop PFPS than males. Additionally, at the time of admission to the academy, the prevalence of PFPS was not significantly different between genders.
PMCID: PMC2895959  PMID: 19765240
epidemiology; chronic knee injury; anterior knee pain; injury rate; males; females
3.  Quadriceps Activation Following Knee Injuries: A Systematic Review 
Journal of Athletic Training  2010;45(1):87-97.
Arthrogenic muscle inhibition is an important underlying factor in persistent quadriceps muscle weakness after knee injury or surgery.
To determine the magnitude and prevalence of volitional quadriceps activation deficits after knee injury.
Data Sources:
Web of Science database.
Study Selection:
Eligible studies involved human participants and measured quadriceps activation using either twitch interpolation or burst superimposition on patients with knee injuries or surgeries such as anterior cruciate ligament deficiency (ACLd), anterior cruciate ligament reconstruction (ACLr), and anterior knee pain (AKP).
Data Extraction:
Means, measures of variability, and prevalence of quadriceps activation (QA) failure (<95%) were recorded for experiments involving ACLd (10), ACLr (5), and AKP (3).
Data Synthesis:
A total of 21 data sets from 18 studies were initially identified. Data from 3 studies (1 paper reporting data for both ACLd and ACLr, 1 on AKP, and the postarthroscopy paper) were excluded from the primary analyses because only graphical data were reported. Of the remaining 17 data sets (from 15 studies), weighted mean QA in 352 ACLd patients was 87.3% on the involved side, 89.1% on the uninvolved side, and 91% in control participants. The QA failure prevalence ranged from 0% to 100%. Weighted mean QA in 99 total ACLr patients was 89.2% on the involved side, 84% on the uninvolved side, and 98.5% for the control group, with prevalence ranging from 0% to 71%. Thirty-eight patients with AKP averaged 78.6% on the involved side and 77.7% on the contralateral side. Bilateral QA failure was commonly reported in patients.
Quadriceps activation failure is common in patients with ACLd, ACLr, and AKP and is often observed bilaterally.
PMCID: PMC2808760  PMID: 20064053
arthrogenic muscle inhibition; voluntary activation; twitch interpolation; superimposed burst; central activation ratio
4.  Expected Prevalence From the Differential Diagnosis of Anterior Knee Pain in Adolescent Female Athletes During Preparticipation Screening 
Journal of Athletic Training  2012;47(5):519-524.
Anterior knee pain is a common disorder in female athletes with an undefined cause. The relative prevalence of specific patellofemoral disorders associated with anterior knee pain in adolescent females remains undetermined.
To determine the prevalence of specific patellofemoral disorders obtained using the differential diagnosis of anterior knee pain in adolescent female athletes during preparticipation screening.
Descriptive epidemiology study.
Preparticipation screening evaluations at a county public school district in Kentucky.
Patients or Other Participants
A total of 419 unique middle and high school–aged female athletes.
Main Outcome Measure(s)
Participants were evaluated by physicians for anterior knee pain over 3 consecutive basketball seasons. Given the longitudinal nature of this study, some participants were tested longitudinally over multiple years.
Over the course of 3 basketball seasons, 688 patient evaluations were performed. Of these, 183 (26.6%) were positive for anterior knee pain. A statistically significant difference was noted in the prevalence of anterior knee pain by school level, with 34.4% (n = 67) in high school–aged athletes versus 23.5% (n = 116) in middle school–aged athletes (P < .05). In the 1376 knees evaluated, patellofemoral dysfunction was the most common diagnosis, with an overall prevalence of 7.3% (n = 100). The only diagnosis shown to be statistically different between age levels was Sinding-Larsen-Johansson disease or patellar tendinopathy, with 38 cases (9.7%) in high school–aged and 31 (3.1%) in middle school–aged athletes (P < .05).
Anterior knee pain was present in 26.6% of the adolescent female athletes screened over 3 years. Symptoms of anterior knee pain likely persist after middle school–aged onset and reach peak prevalence during the high school years.
PMCID: PMC3465032  PMID: 23068589
patellofemoral disorders; biomechanics; plica; Osgood-Schlatter disease; patellar tendinopathy
5.  The relative timing of VMO and VL in the aetiology of anterior knee pain: a systematic review and meta-analysis 
Anterior knee pain (AKP) is a common musculoskeletal complaint. It has been suggested that one factor that may contribute to the presence of AKP is a delay in the recruitment of the vastus medialis oblique muscle (VMO) relative to the vastus lateralis muscle (VL). There is however little consensus within the literature regarding the existence or nature of any such delay in the recruitment of the VMO within the AKP population. The purpose of this systematic review and meta-analysis was to examine the relative timing of onset of the VMO and VL in those with AKP in comparison to the asymptomatic population.
The bibliographic databases AMED, British Nursing Index, CINAHL, EMBASE, Ovid Medline, PEDro, Pubmed and the Cochrane Library were searched for studies comparing the timing of EMG onset of the VMO and VL in those with AKP versus the asymptomatic population. Studies fulfilling the inclusion criteria were independently assessed. Heterogeneity across the studies was measured. A meta-analysis of results was completed for those studies where adequate data was supplied. Where comparable methodologies had been used, results were pooled and analysed.
Fourteen studies met the inclusion criteria; one prospective and thirteen observational case control. Eleven compared VMO and VL EMG onset times during voluntary active tasks while four investigated reflex response times. All used convenience sampling and did not state blinding of the assessor. Study methodologies/testing and assessment procedures varied and there was considerable heterogeneity within individual samples. Whilst a trend was identified towards a delay in onset of VMO relative to the VL in the AKP population during both voluntary active tasks and reflex activity, a substantial degree of heterogeneity across the pooled studies was identified (I2 = 69.9–93.4%, p < 0.01).
Findings are subject to substantial and unexplained heterogeneity. A trend was demonstrated towards a delayed onset of VMO relative to VL in those with AKP in comparison to those without. However not all AKP patients demonstrate a VMO-VL dysfunction, and this is compounded by normal physiological variability in the healthy population. The clinical and therapeutic significance is therefore difficult to assess.
PMCID: PMC2386790  PMID: 18452611
Historically, patellofemoral pain syndrome (PFPS) has been viewed exclusively as a knee problem. Recent findings have suggested an association between hip muscle weakness and PFPS. Altered neuromuscular activity about the hip also may contribute to PFPS; however, more limited data exist regarding this aspect. Most prior investigations also have not concurrently examined hip and knee strength and neuromuscular activity in this patient population. Additional knowledge regarding the interaction between hip and knee muscle function may enhance the current understanding of PFPS. The purpose of this study was to compare hip and knee strength and electromyographic (EMG) activity in subjects with and without PFPS.
Eighteen females with PFPS and 18 matched controls participated in this study. First, surface EMG electrodes were donned on the gluteus medius, vastus medialis, and vastus lateralis. Strength measures then were taken for the hip abductors, hip external rotators, and knee extensors. Subjects completed a standardized stair-stepping task to quantify muscle activation amplitudes during the loading response, single leg stance, and preswing intervals of stair descent as well as to determine muscle onset timing differences between the gluteus medius and vastii muscles and between the vastus medialis and vastus lateralis at the beginning of stair descent.
Females with PFPS demonstrated less strength of the hip muscles. They also generated greater EMG activity of the gluteus medius and vastus medialis during the loading response and single leg stance intervals of stair descent. No differences existed with respect to onset activation of the vastus medialis and vastus lateralis. All subjects had a similar delay in gluteus medius onset activation relative to the vastii muscles.
Rehabilitation should focus on quadriceps and hip strengthening. Although clinicians have incorporated gluteus medius exercise in rehabilitation programs, additional attention to the external rotators may be useful.
Level of Evidence: 4
PMCID: PMC3230156  PMID: 22163090
gluteus medius; knee; patella; surface electromyography
7.  Patellar Osteoid Osteoma as a Cause of Anterior Knee Pain in Adolescents: A Case Report and Literature Review 
Case Reports in Medicine  2013;2013:746472.
Anterior Knee Pain (AKP) is an important cause of complaint in adolescents which can suggest many possible diseases. Scientific literature concerning this complex symptom is wide and diversified. We report a rare case of patellar osteoid osteoma which affected a thirteen-year-old female who had suffered from anterior left knee pain for almost six months. The diagnosis was suspected from an accurate anamnesis, a careful clinical examination, and confirmed by imaging. Several minimally invasive techniques can be employed to treat osteoid osteoma. However, we consider CT-guided percutaneous drilling the safest and most effective procedure in case of patellar location. Despite its rarity, patellar osteoid osteoma ranges in the differential diagnosis for all patients suffering from AKP.
PMCID: PMC3608179  PMID: 23554815
To quantify the role patellofemoral and tibiofemoral kinematics may play in development of anterior knee pain (AKP) in individuals with cerebral palsy (CP).
Clinical Research Center
Twenty knees from individuals diagnosed with CP and 40 control knees were evaluated. Controls were matched for sex and age based on the group average. Matching by height and weight was a secondary priority. Subjects in the control cohort were asymptomatic with no history of lower leg abnormality, surgery, or major injury. Only individuals who were physically capable of sustaining slow cyclic knee flexion-extension for 2.5 minutes and had no contraindications to MR imaging were enrolled. Both groups were samples of convenience.
Not applicable.
Main Outcome Measure
The 3D patellofemoral and tibiofemoral joint kinematics, acquired during active leg extension, under volitional control.
Participants with CP and AKP (n=8) demonstrated significantly greater patellofemoral extension, valgus rotation, superior, and posterior displacement relative to controls and to the subgroup of participants with CP and no AKP (n=12). Patellofemoral extension discriminated AKP in individuals with CP with 100% accuracy.
In quantifying the 3D in vivo knee joint kinematics during a volitional extension task, kinematic markers that discriminate AKP in individuals with CP were identified. This provides an ability to predict which individuals with CP are most likely to advance into AKP and could enable aggressive conservative treatment, aimed at reducing patella alta and excessive PF extension to be prescribed prior to considering surgical options. The current findings will likely lead to improved clinical diagnostics and interventions for individuals with CP, with the ultimate goal of helping maintain, if not improve functional mobility throughout the lifespan.
PMCID: PMC3568741  PMID: 22465585
MRI; patellofemoral; tibiofemoral; dynamics
9.  Adolescent patellofemoral pain: implicating the medial patellofemoral ligament as the main pain generator 
The purpose of this study is to define the clinical presentation of adolescent patellofemoral pain.
A review was completed of all patients with patellofemoral pain at a children’s hospital sports clinic over a 3-year period.
One hundred and one patients (91 female) with 136 symptomatic knees were identified. Mean age was 14.4 years. Knee pain was localized to the anteromedial or anterior region of the knee in 96% of patients and was typically produced with running (94%), jumping (92%) and stair use (69%). On physical examination there was usually a non antalgic gait (99%), no patellofemoral crepitation (98%), normal lower extremity angular (84%) and rotational alignment (94%), with no foot malalignment (>97%). The medial patellofemoral ligament (MPFL) was the most palpably tender area of the knee in 98% of patients. During “lateral apprehension” testing, 89% had pain at the MPFL, but not true apprehension. A “J-sign” was present at terminal knee extension in 65%. Mean Q-angle was 18.7°. Means of all radiographic measures were within normal ranges.
The prototypical patient had anterior/anteromedial knee pain of insidious onset during running and jumping. The most consistent physical findings were focal tenderness at the MPFL, positive terminal J-sign, and an elevated Q-angle. Most patients required only nonsurgical treatments, but 18% underwent surgical interventions for persistent pain.
PMCID: PMC2656832  PMID: 19308554
Patellofemoral pain; Anterior knee pain; Nonoperative treatment; Lateral retinacular release
Introduction and Background:
The subject of this case study, a 16‐year‐old female triathlete, presented to physiotherapy reporting a 6 month history of anterior knee pain, with symptoms unchanged upon resuming a graduated triathlon training program, despite 3 months rest from all training.
Case Description:
The case describes the differential diagnosis and management of patellofemoral pain syndrome (PFPS), iliotibial band syndrome (ITBS), and discoid lateral meniscus (DLM) in an adolescent female triathlete. Clinical reasoning and rehabilitation strategies are presented with respect to literature base. Final outcome was full resolution of symptoms and return to full athletic function, however, symptoms were relatively persistent and atypical.
This case report discusses the differential diagnosis and management of persistent and atypical anterior knee pain in a sixteen‐year‐old female triathlete. In such cases, the diagnostic process is often iterative, where intervention serves both therapeutic and diagnostic purposes.
Recent changes in the understanding of the pathophysiology of ITBS and links between the anterior and lateral knee compartments through highly innervated knee synovial tissue assist the therapist's understanding of how these conditions may occur concomitantly, with resulting atypical symptoms. The potential influences of likely changes in the subject's peripheral and central nervous system on symptom perception is also discussed.
Level of Evidence:
Level 5; Single case report.
PMCID: PMC3867078  PMID: 24377071
Adolescent; anterior knee pain; discoid lateral meniscus; iliotibial band syndrome; patellofemoral pain syndrome
11.  Pain and Hip Lateral Rotator Muscle Strength Contribute to Functional Status in Females with Patellofemoral Pain 
Background and Purpose
Patellofemoral pain (PFP) is a common musculoskeletal pain condition, especially in females. Decreased hip muscle strength has been implicated as a contributing factor, yet the relationships between pain, hip muscle strength, and function are not known. The purpose of this study was to test the hypothesis that pain and hip muscle strength explain unique portions of variance in the functional status of females with PFP.
An observational, cohort study.
Twenty-one females with PFP (age: 26±7 yrs; height: 163±4 cm, and body mass: 62±10 kg,). Subjects had a minimum pain duration of two months (mean pain duration: 4.9±3.6 years).
Main Measures
Pain during a unilateral squat measured with a visual analog scale (VAS); isometric muscle force of gluteus medius, gluteus maximus, and hip lateral rotators; Kujala score (self-report measure of function).
Statistical Analysis
Hierarchical multiple regression analysis was performed with Kujala score as the dependent variable. Pain and hip lateral rotator muscle strength were independent variables, entered in that order. Other strength measures were not correlated with the Kujala score, and as such, were not used in the analysis.
Pain explained 22% of the variance in the Kujala score (p=.03). Hip lateral rotator strength explained an additional 14% of the variance, after accounting for pain level (p=.06).
Pain and hip lateral rotator strength contributed to the functional status of females with PFP. Improving pain and hip lateral rotator muscle strength may improve function in females with this common pain condition.
PMCID: PMC3226064  PMID: 19790109
Visual Analog Scale; Kujala Score; Hand-held Dynamometry; Knee Pain
12.  The Incidence and Potential Pathomechanics of Patellofemoral Pain in Female Athletes 
The aims of this study were to determine the prevalence and incidence of patellofemoral pain (PFP) in young female athletes and prospectively evaluate measures of frontal plane knee loading during landing to determine their relationship to development of PFP. We hypothesized that increased dynamic knee abduction measured during preseason biomechanical testing would be increased in those who developed PFP relative to teammates who did not develop PFP.
Middle and high school female athletes (n=240) were evaluated by a physician for PFP and for landing biomechanics prior to their basketball season. The athletes were monitored for athletic exposures and PFP injury during their competitive seasons.
At the beginning of the season, the point prevalence of PFP was 16.3 per 100 athletes. The cumulative incidence risk and rate for the development of new unilateral PFP was 9.66 per 100 athletes and 1.09 per 1000 athletic exposures, respectively. All new PFP developed in middle school athletes who demonstrated mean International Knee Documentation Committee score of 85.6 ± 7.7 at diagnosis. The new PFP group demonstrated increased knee abduction moments at initial contact (95% CI: 0.32 to 4.62 Nm) on the most-symptomatic limb and maximum (95% CI: 1.3 to 10.1 Nm; p=0.02) on the least-symptomatic (or no symptoms) limb relative to the matched control limbs. Knee abduction moments remained increased in the new PFP group when normalized to body mass (p<0.05).
The increased knee abduction landing mechanics in the new PFP group indicate that frontal plane loads contribute to increased incidence of PFP.
PMCID: PMC2900391  PMID: 20466469
Patellofemoral Pain Syndrome; Anterior Knee Pain; Biomechanics; Neuromuscular Control; Knee Valgus
13.  Do Females with Patellofemoral Pain have Abnormal Hip and Knee Kinematics during Gait? 
Physiotherapy theory and practice  2010;26(3):150-159.
To test the hypothesis that females with patellofemoral pain (PFP) have increased hip adduction, hip medial rotation, and knee valgus (medial collapse) during the stance phase of gait.
Twenty subjects with PFP and 20 pain-free subjects participated. Subjects underwent 3-dimensional motion analysis during free speed and fast speed walking. Hip frontal and transverse plane angles and knee frontal plane angles were calculated at 2 time points (peak knee extensor moment (PkMOM), and maximum knee extension/hyperextension angle (MxExt)) and averaged over 3 trials. Within each walking task, Student’s t-tests compared group differences in all variables. A post-hoc analysis was performed comparing a subgroup of 4 PFP subjects (those whose pain level was above 30/100) to pain-free subjects.
Initially, there were no group differences during free speed walking. During fast speed walking, subjects with PFP had less hip adduction at PkMOM and greater hip adduction at MxExt. The subgroup of PFP subjects had greater hip adduction at PkMOM and greater knee valgus at MxExt during free speed walking and greater hip adduction and knee valgus at MxExt during fast speed walking.
During low-level tasks, frontal plane components of medial collapse were present at the hip and knee in a subgroup of PFP subjects with higher pain levels. Symptom behavior may be important in identifying individuals with medial collapse movement impairments.
PMCID: PMC3226335  PMID: 20331371
biomechanics; medial collapse; 3-d motion analysis; lower extremity overuse injuries
Anterior knee pain is a clinical syndrome characterized by pain experienced perceived over the anterior aspect of the knee that can be aggravated by functional activities such as stair climbing and squatting. Two taping techniques commonly used for anterior knee pain in the clinic include the McConnell Taping Technique (MT) and the Kinesio Taping® Method (KT®).
The purpose of this study was to compare the effectiveness of KT® and the MT versus no tape in subjects with anterior knee pain during a squat lift and stair climbing.
Pretest‐ posttest design.
A total of 20 subjects (15 female, 5 male) with unilateral anterior knee pain were recruited. The mean age of the subjects was 24 (+/–3) years, with a mean weight of 160 (+/–28) pounds.
Each participant was tested during two functional activities; a squat lift with a weighted box (10% of his/her body weight, plus the weight [8.5 pounds] of the box) and stair climbing under three conditions: 1) no tape, 2) MT and 3) KT®. Pain levels were assessed (verbally) using the 0‐10 Numeric Pain Intensity Scale.
The median (interquartile range [IQR]) pain during squat lift was 2 (2.75) for no tape, 1 (1) for KT®, and 0.5 (2) for McConnell, with no significant differences between the groups. During the stair activity the median (IQR) pain was 1.5 (2.75) for no tape, 1 (1.75) for KT®, and 1 (1.75) for MT with a significant difference (p=0.024) between the groups. Further analysis determined that the only a significant difference was (p=0.034) between the no tape and the KT® conditions.
The results of this study found that both the KT® and the MT may be effective in reducing pain during stair climbing activities.
Level of Evidence:
Level 2, Prospective Cohort study
PMCID: PMC3625789  PMID: 23593548
Anterior Knee Pain; Kinesio Taping® Method; McConnell Taping Technique
15.  Relationships between the Foot Posture Index and foot kinematics during gait in individuals with and without patellofemoral pain syndrome 
Foot posture assessment is commonly undertaken in clinical practice for the evaluation of individuals with patellofemoral pain syndrome (PFPS), particularly when considering prescription of foot orthoses. However, the validity of static assessment to provide insight into dynamic function in individuals with PFPS is unclear. This study was designed to evaluate the extent to which a static foot posture measurement tool (the Foot Posture Index - FPI) can provide insight into kinematic variables associated with foot pronation during level walking in individuals with PFPS and asymptomatic controls.
Twenty-six individuals (5 males, 21 females) with PFPS aged 25.1 ± 4.6 years and 20 control participants (4 males, 16 females) aged 23.4 ± 2.3 years were recruited into the study. Each participant underwent clinical evaluation of the FPI and kinematic analysis of the rearfoot and forefoot during walking using a three-dimensional motion analysis system. The association of the FPI score with rearfoot eversion, forefoot dorsiflexion, and forefoot abduction kinematic variables (magnitude, timing of peak and range of motion) were evaluated using partial correlation coefficient statistics with gait velocity entered as a covariate.
A more pronated foot type as measured by the FPI was associated with greater peak forefoot abduction (r = 0.502, p = 0.013) and earlier peak rearfoot eversion relative to the laboratory (r = -0.440, p = 0.031) in the PFPS group, and greater rearfoot eversion range of motion relative to the laboratory (r = 0.614, p = 0.009) in the control group.
In both individuals with and without PFPS, there was fair to moderate association between the FPI and some parameters of dynamic foot function. Inconsistent findings between the PFPS and control groups indicate that pathology may play a role in the relationship between static foot posture and dynamic function. The fair association between pronated foot posture as indicated by the FPI and earlier peak rearfoot eversion relative to the laboratory observed exclusively in those with PFPS is consistent with the biomechanical model of PFPS development. However, prospective studies are required to determine whether this relationship is causal.
PMCID: PMC3064639  PMID: 21401957
16.  Are mechanics different between male and female runners with patellofemoral pain? 
Patellofemoral pain (PFP) has often been attributed to abnormal hip and knee mechanics in females. To date, there have been few investigations of the hip and knee mechanics of males with PFP. The purpose of this study was to compare the lower extremity mechanics and alignment of male runners with PFP with healthy male runners and female runners with PFP. We hypothesized that males with PFP would move with greater varus knee mechanics compared with male controls and compared with females with PFP. Further, it was hypothesized that males with PFP would demonstrate greater varus alignment.
A gait and single leg squat analysis was conducted on each group (18 runners per group). Measurement of each runner’s tibial mechanical axis was also recorded. Motion data were processed using Visual 3D (CMotion, Bethesda, Md., USA). Analyses of Variance were used to analyze the data.
Males with PFP ran and squatted in greater peak knee adduction and demonstrated greater peak knee external adduction moment compared with healthy male controls. In addition, males with PFP ran and squatted with less peak hip adduction and greater peak knee adduction compared with females with PFP. The static measure of mechanical axis of the tibial was not different between groups. However, a post-hoc analysis revealed that males with PFP ran with greater peak tibial segmental adduction.
Males with PFP demonstrated different mechanics during running and during a single leg squat compared with females with PFP and with healthy males. Based upon the results of this study, therapies for PFP may need to be sex-specific.
PMCID: PMC3475738  PMID: 22843103
Patellofemoral Pain; Running; Biomechanics; Sex Differences
17.  Anterior knee pain in younger adults as a precursor to subsequent patellofemoral osteoarthritis: a systematic review 
Patellofemoral osteoarthritis (PFOA) is a common form of knee OA in middle and older age, but its relation to PF disorders and symptoms earlier in life is unclear. Our aim was to conduct a systematic review to investigate the strength of evidence for an association between anterior knee pain (AKP) in younger adults and subsequent PFOA.
The search strategy included electronic databases (Pubmed, EMBASE, AMED, CINAHL, Cochrane, PEDro, SportDiscus: inception to December 2009), reference lists of potentially eligible studies and selected reviews. Full text articles in any language, - identified via English titles and abstracts, were included if they were retrospective or prospective in design and contained quantitative data regarding structural changes indicative of PFOA, incident to original idiopathic AKP. Eligibility criteria were applied to titles, abstracts and full-texts by two independent reviewers. Data extraction included study location, design, date, sampling procedure, sample characteristics, AKP/PFOA definitions, follow-up duration and rate, and main findings. Foreign language articles were translated into English prior to examination.
Seven articles satisfied eligibility (5 English, 2 German). Only one case-control study directly investigated a link between PFOA and prior AKP, providing level 3b evidence in favour of an association (OR 4.4; 95%CI 1.8, 10.6). Rough estimates of the annual risk of PFOA from the remaining six small, uncontrolled, observational studies (mean follow-up range: 5.7 to 23 years) ranged from 0% to 3.4%. This was not the primary aim of these studies, and limitations in design and methodology mean this data should be interpreted with caution.
There is a paucity of high-quality evidence reporting a link between AKP and PFOA. Further, well-designed cohort studies may be able to fill this evidence gap.
PMCID: PMC2944218  PMID: 20828401
18.  Patellar Taping, Patellofemoral Pain Syndrome, Lower Extremity Kinematics, and Dynamic Postural Control 
Journal of Athletic Training  2008;43(1):21-28.
Context: Patellar taping has been a part of intervention for treatment of patellofemoral pain syndrome (PFPS). However, research on the efficacy of patellar taping on lower extremity kinematics and dynamic postural control is limited.
Objective: To evaluate the effects of patellar taping on sagittal-plane hip and knee kinematics, reach distance, and perceived pain level during the Star Excursion Balance Test (SEBT) in individuals with and without PFPS.
Design: Repeated-measures design with 2 within-subjects factors and 1 between-subjects factor.
Setting: The University of Toledo Athletic Training Research Laboratory.
Patients or Other Participants: Twenty participants with PFPS and 20 healthy participants between the ages of 18 and 29 years.
Intervention(s): The participants performed 3 reaches of the SEBT in the anterior direction under tape and no-tape conditions on both legs.
Main Outcome Measure(s): The participants' hip and knee sagittal-plane kinematics were measured using the electromagnetic tracking system. Reach distance was recorded by hand and was normalized by dividing the distance by the participants' leg length (%MAXD). After each taping condition on each leg, the participants rated the perceived pain level using the 10-cm visual analog scale.
Results: The participants with PFPS had a reduction in pain level with patellar tape application compared with the no-tape condition (P = .005). Additionally, participants with PFPS demonstrated increased %MAXD under the tape condition compared with the no-tape condition, whereas the healthy participants demonstrated decreased %MAXD with tape versus no tape (P = .028). No statistically significant differences were noted in hip flexion and knee flexion angles.
Conclusions: Although patellar taping seemed to reduce pain and improve SEBT performance of participants with PFPS, the exact mechanisms of these phenomena cannot be explained in this study. Further research is warranted to investigate the effect of patellar taping on neuromuscular control during dynamic postural control.
PMCID: PMC2231393  PMID: 18335009
anterior knee pain; McConnell taping
19.  Different effects of femoral and tibial rotation on the different measurements of patella tilting: An axial computed tomography study 
The various measurements of patellar tilting failed to isolate patellar tilting from the confounding effect of its neighboring bone rotation (femoral and tibial rotation) in people sustaining patellofemoral pain (PFPS). Abnormal motions of the tibia and the femur are believed to have an effect on patellofemoral mechanics and therefore PFPS. The current work is to explore the various effects of neighboring bone rotation on the various measurements of patellar tilting, through an axial computed tomography study, to help selecting a better parameter for patella tilting and implement a rationale for the necessary intervention at controlling the limb alignment in the therapeutic regime of PFPS.
Forty seven patients (90 knees), comprising of 34 females and 11 males, participated in this study. Forty five knees, from randomly selected sides of bilaterally painful knees and the painful knees of unilaterally painful knees, were enrolled into the study. From the axial CT images in the subject knees in extension with quadriceps relaxed, the measurements of femoral rotation, tibial rotation, femoral rotation relative to tibia, and 3 parameters for patella tilting were obtained and analyzed to explore the relationship between the different measurements of patella tilt angle and the measurements of its neighboring bone rotation (femoral, tibial rotation, and femoral rotation relative to tibia).
The effect of femoral, tibial rotation, and femoral rotation relative to tibia on patella tilting varied with the difference in the way of measuring the patella tilt angle. Patella tilt angle of Grelsamer increased with increase in femoral rotation, and tibial rotation. Patella tilt angle of Sasaki was stationary with change in femoral rotation, tibial rotation, or femoral rotation relative to tibia. While, modified patella tilt angle of Fulkerson decreased with increase in femoral rotation, tibial rotation, or femoral rotation relative to tibia.
The current study has demonstrated various effects of regional bony alignment on the different measurements of the patellar tilt. And the influence of bony malalignment on the patellar tilt might draw a clinical implication that patellar malalignment can not be treated, separately, independent of the related limb alignment. This clinical implication has to be verified by further works, with a comprehensive evaluation of the various treatments of patellar malalignment.
PMCID: PMC2267450  PMID: 18269751
Decreased strength of the hip musculature and altered mechanics of the lower extremity have been identified in individuals with patellofemoral pain (PFP). The aim of this study was to determine if a relationship exists between hip muscle strength and transverse and frontal plane motion at the hip and knee, and ipsilateral trunk flexion during a jump‐landing task in individuals with PFP.
Fifteen individuals (10 females, 5 males) with PFP participated in this investigation. A three‐dimensional motion analysis system was utilized to assess trunk, hip, and knee kinematics during a jump‐landing task. An isokinetic dynamometer was utilized to assess concentric and eccentric strength of the hip musculature. Simple correlation analyses were performed to determine the relationships between hip muscle strength and peak frontal and transverse plane hip and knee kinematics and ipsilateral trunk flexion.
Decreased eccentric strength of the hip external rotators and abductors was significantly correlated to increased frontal plane motion at the hip and trunk, respectively (P<0.05).
Based on these findings, eccentric strengthening exercises for the hip musculature may be an important component for clinicians to include when rehabilitating individuals with PFP who display increased frontal plane motion at the hip and trunk.
Level of Evidence:
PMCID: PMC3811740  PMID: 24175145
anterior knee pain; biomechanics; hip musculature; jump
21.  Early intervention for adolescents with Patellofemoral Pain Syndrome - a pragmatic cluster randomised controlled trial 
Self-reported knee pain is highly prevalent among adolescents. As much as 50% of the non-specific knee pain may be attributed to Patellofemoral Pain Syndrome (PFPS). In the short term, exercise therapy appears to have a better effect than patient education consisting of written information and general advice on exercise or compared with placebo treatment. But the long-term effect of exercise therapy compared with patient education is conflicting. The purpose of this study is to examine the short- and long-term effectiveness of patient education compared with patient education and multimodal physiotherapy applied at a very early stage of the condition among adolescents.
This study is a single blind pragmatic cluster randomised controlled trial. Four upper secondary schools have been invited to participate in the study (approximately 2500 students, aged 15-19 years). Students are asked to answer an online questionnaire regarding musculoskeletal pain. The students who report knee pain are contacted by telephone and offered a clinical examination by a rheumatologist. Subjects who fit the inclusion criteria and are diagnosed with PFPS are invited to participate in the study. A minimum of 102 students with PFPS are then cluster-randomised into two intervention groups based on which school they attend. Both intervention groups receive written information and education. In addition to patient education, one group receives multimodal physiotherapy consisting primarily of neuromuscular training of the muscles around the foot, knee and hip and home exercises.
The students with PFPS fill out self-reported questionnaires at baseline, 3, 6, 12 and 24 months after inclusion in the study. The primary outcome measure is perception of recovery measured on a 7-point Likert scale ranging from "completely recovered" to "worse than ever" at 12 months.
This study is designed to investigate the effectiveness of patient education compared with patient education combined with multimodal physiotherapy. If patient education and multimodal physiotherapy applied at an early stage of Patellofemoral Pain Syndrome proves effective, it may serve as a basis for optimising the clinical pathway for those suffering from the condition, where specific emphasis can be placed on early diagnosis and early treatment.
Trial Registration reference: NCT01438762
PMCID: PMC3328242  PMID: 22280484
Patellofemoral Pain Syndrome; Anterior Knee Pain; Physiotherapy; Adolescents
22.  Intrarater Reliability of Functional Performance Tests for Subjects With Patellofemoral Pain Syndrome 
Journal of Athletic Training  2002;37(3):256-261.
Objective: Patellofemoral pain syndrome (PFPS) is a common clinical entity seen by the sports medicine specialist. The ultimate goal of rehabilitation is to return the patient to the highest functional level in the most efficient manner. Therefore, it is necessary to assess the progress of patients with PFPS using reliable functional performance tests. Our purpose was to evaluate the intrarater reliability of 5 functional performance tests in patients with PFPS.
Design and Setting: We used a test-retest reliability design in a clinic setting.
Subjects: Two groups of subjects were studied: those with PFPS (n = 29) and those with no known knee condition (n = 11). The PFPS group included 19 women and 10 men with a mean age of 27.6 ± 5.3 years, height of 169.80 ± 10.5 cm, and weight of 69.59 ± 15.8 kg. The normal group included 7 women and 4 men with a mean age of 30.3 ± 5.2 years, height of 169.55 ± 9.9 cm, and weight 69.42 ± 14.6 kg.
Measurements: The reliability of 5 functional performance tests (anteromedial lunge, step-down, single-leg press, bilateral squat, balance and reach) was assessed in 15 subjects with PFPS. Secondly, the relationship of the 5 functional tests to pain was assessed in 29 PFPS subjects using Pearson product moment correlations. The limb symmetry index (LSI) was calculated in the 29 PFPS subjects and compared with the group of 11 normal subjects.
Results: The 5 functional tests proved to have fair to high intrarater reliability. Intrarater reliability coefficients (ICC 3,1) ranged from .79 to .94. For the PFPS subjects, a statistical difference existed between limbs for the anteromedial lunge, step-down, single-leg press, and balance and reach. All functional tests correlated significantly with pain except for the bilateral squat; values ranged from .39 to .73. The average LSI for the PFPS group was 85%, while the average LSI for the normal subjects was 97%.
Conclusions: The 5 functional tests proved to have good intrarater reliability and were related to changes in pain. Future research is needed to examine interrater reliability, validity, and sensitivity of these clinical tests.
PMCID: PMC164353  PMID: 12937582
step-down; squat; limb symmetry; knee
23.  Eccentric Hip Muscle Function in Females With and Without Patellofemoral Pain Syndrome 
Journal of Athletic Training  2009;44(5):490-496.
Patellofemoral pain syndrome (PFPS) is a common knee condition in athletes. Recently, researchers have indicated that factors proximal to the knee, including hip muscle weakness and motor control impairment, contribute to the development of PFPS. However, no investigators have evaluated eccentric hip muscle function in people with PFPS.
To compare the eccentric hip muscle function between females with PFPS and a female control group.
Cross-sectional study.
Musculoskeletal laboratory.
Patients or Other Participants:
Two groups of females were studied: a group with PFPS (n  =  10) and a group with no history of lower extremity injury or surgery (n  =  10).
Eccentric torque of the hip musculature was evaluated on an isokinetic dynamometer.
Main Outcome Measure(s):
Eccentric hip abduction, adduction, and external and internal rotation peak torque were measured and expressed as a percentage of body mass (Nm/kg × 100). We also evaluated eccentric hip adduction to abduction and internal to external rotation torque ratios. The peak torque value of 5 maximal eccentric contractions was used for calculation. Two-tailed, independent-samples t tests were used to compare torque results between groups.
Participants with PFPS exhibited much lower eccentric hip abduction (t18  =  −2.917, P  =  .008) and adduction (t18  =  −2.764, P  =  .009) peak torque values than did their healthy counterparts. No differences in eccentric hip external (t18  =  0.45, P  =  .96) or internal (t18  =  −0.742, P  =  .47) rotation peak torque values were detected between the groups. The eccentric hip adduction to abduction torque ratio was much higher in the PFPS group than in the control group (t18  =  2.113, P  =  .04), but we found no difference in the eccentric hip internal to external rotation torque ratios between the 2 groups (t18  =  −0.932, P  =  .36).
Participants with PFPS demonstrated lower eccentric hip abduction and adduction peak torque and higher eccentric adduction to abduction torque ratios when compared with control participants. Thus, clinicians should consider eccentric hip abduction strengthening exercises when developing rehabilitation programs for females with PFPS.
PMCID: PMC2742458  PMID: 19771287
hip abduction; hip external rotation; torque
24.  Hip and Knee Strength Is Not Affected in 12-16 Year Old Adolescents with Patellofemoral Pain - A Cross-Sectional Population-Based Study 
PLoS ONE  2013;8(11):e79153.
One of the rationales behind using strength training in the treatment of adolescents with Patellofemoral Pain (PFP) is that reduced strength of the lower extremity is a risk factor for PFP and a common deficit. This rationale is based on research conducted on adolescents >15 years of age but has never been investigated among young adolescents with PFP.
To compare isometric muscle strength of the lower extremity among adolescents with PFP compared to age- and gender-matched pain-free adolescents.
In 2011 a population-based cohort (APA2011-cohort) consisting of 768 adolescents aged 12–15 years from 8 local schools was formed. In September 2012, all adolescents who reported knee pain in September 2011 were offered a clinical examination if they still had knee pain. From these, 20 adolescents (16 females) were diagnosed with PFP. Pain-free adolescents from the APA2011-cohort (n = 20) were recruited on random basis as age- and gender-matched pairs. Primary outcome was isometric knee extension strength normalized to body weight (%BW) and blinded towards subject information. Secondary outcomes included knee flexion, hip abduction/adduction and hip internal/external rotation strength. Demographic data included Knee Injury and Osteoarthritis Outcome Score (KOOS) and symptom duration.
Adolescents with PFP reported long symptom duration and significantly worse KOOS scores compared to pain-free adolescents. There were no significant differences in isometric knee extension strength (Δ0.3% BW, p = 0.97), isometric knee flexion strength (Δ0.4% BW, p = 0.84) or different measures of hip strength (Δ0.4 to 1.1% BW, p>0.35).
Young symptomatic adolescents with PFP between 12 and 16 years of age did not have decreased isometric muscle strength of the knee and hip. These results question the rationale of targeting strength deficits in the treatment of adolescents with PFP. However, strength training may still be an effective treatment for those individuals with PFP suffering from strength deficits.
PMCID: PMC3827322  PMID: 24236101
25.  Patellofemoral pain syndrome (PFPS): a systematic review of anatomy and potential risk factors 
Patellofemoral Pain Syndrome (PFPS), a common cause of anterior knee pain, is successfully treated in over 2/3 of patients through rehabilitation protocols designed to reduce pain and return function to the individual. Applying preventive medicine strategies, the majority of cases of PFPS may be avoided if a pre-diagnosis can be made by clinician or certified athletic trainer testing the current researched potential risk factors during a Preparticipation Screening Evaluation (PPSE). We provide a detailed and comprehensive review of the soft tissue, arterial system, and innervation to the patellofemoral joint in order to supply the clinician with the knowledge required to assess the anatomy and make recommendations to patients identified as potentially at risk. The purpose of this article is to review knee anatomy and the literature regarding potential risk factors associated with patellofemoral pain syndrome and prehabilitation strategies. A comprehensive review of knee anatomy will present the relationships of arterial collateralization, innervations, and soft tissue alignment to the possible multifactoral mechanism involved in PFPS, while attempting to advocate future use of different treatments aimed at non-soft tissue causes of PFPS.
A systematic database search of English language PubMed, SportDiscus, Ovid MEDLINE, Web of Science, LexisNexis, and EBM reviews, plus hand searching the reference lists of these retrieved articles was performed to determine possible risk factors for patellofemoral pain syndrome.
Positive potential risk factors identified included: weakness in functional testing; gastrocnemius, hamstring, quadriceps or iliotibial band tightness; generalized ligamentous laxity; deficient hamstring or quadriceps strength; hip musculature weakness; an excessive quadriceps (Q) angle; patellar compression or tilting; and an abnormal VMO/VL reflex timing. An evidence-based medicine model was utilized to report evaluation criteria to determine the at-risk individuals, then a defined prehabilitation program was proposed that begins with a dynamic warm-up followed by stretches, power and multi-joint exercises, and culminates with isolation exercises. The prehabilitation program is performed at lower intensity level ranges and can be conducted 3 days per week in conjunction with general strength training. Based on an objective one repetition maximum (1RM) test which determines the amount an individual can lift in good form through a full range of motion, prehabilitation exercises are performed at 50–60% intensity.
To reduce the likelihood of developing PFPS, any individual, especially those with positive potential risk factors, can perform the proposed prehabilitation program.
PMCID: PMC2443365  PMID: 18582383

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