***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Objectives Describe proportions of individuals with patellofemoral pain ( PFP ) with an unfavourable recovery over 12 months ; identify clinical predictors of poor recovery at 3 and 12 months ; and determine baseline values of predictors that identify those with poor 12-month prognosis . Methods An observational analysis utilised data from 310 individuals with PFP enrolled in two r and omised clinical trials . Thirteen baseline variables ( participant , PFP , study characteristics ) were investigated for their prognostic ability . Pain , function and global recovery were measured at 3 and 12 months . Multivariate backward stepwise regression analyses ( treatment-adjusted , p<0.10 ) were performed for each follow-up measure . Receiver operator characteristic curves identified cut-points associated with unfavourable recovery at 12 months . Results 55 % and 40 % of participants had an unfavourable recovery at 3 and 12 months , respectively . Longer baseline pain duration was significantly associated with poor 3-month and 12-month recovery on measures of pain severity ( β 11.36 to 24.94 ) , Anterior Knee Pain ( AKP ) Scale ( −4.44 to −11.33 ) and global recovery ( OR : 2.32 to 6.11 ) . Greater baseline pain severity and lower AKP Scale score were significantly associated with poor recovery on multiple measures ( p<0.05 ) . Baseline duration > 2 months and AKP Scale score < 70/100 were associated with unfavourable 12-month recovery . Conclusions A substantial number of individuals with PFP have an unfavourable recovery over 12 months , irrespective of intervention . Knee pain duration > 2 months is the most consistent prognostic indicator , followed by AKP Scale score < 70 . Sports medicine practitioners should utilise interventions with known efficacy in reducing PFP , and promote early intervention to maximise prognosis . Trial registration Australian study : Australian Clinical Trials Registry ( ACTRN012605000463673 ) , Clinical Trials.gov ( NCT00118521 ) ; Dutch study : International St and ard R and omised Controlled Trial Number Register ( IS RCT N83938749 Background : Patellofemoral pain ( PFP ) is a common condition and often presents without evidence of arthritis on radiographs . Magnetic resonance imaging ( MRI ) has shown good correlation between T1ρ and T2 relaxation times and changes in the cartilage matrix , but as of yet , there are limited data in the literature utilizing these modalities to evaluate the patellofemoral joint . Hypothesis : Patients with PFP and patellar tilt will show longer T1ρ relaxation times in the lateral facets of their patella but no difference in T2 values . Study Design : Cross-sectional study ; Level of evidence , 3 . Methods : A total of 20 patients aged 18 to 45 years with anterior knee pain , patellar tilt , and no evidence of osteoarthritis were identified and consented to undergo MRI including axial T1ρ and T2 relaxation time mapping sequences . Knee cartilage was segmented on spoiled gradient recalled acquisition in steady state ( SPGR ) images using a spline-based algorithm . These results were then compared with those of 10 age-matched controls . Results : The mean T1ρ values of the lateral facets were significantly elevated in patients with PFP compared with controls ( 46.33 ± 4.92 ms vs 42.32 ± 3.67 ms , respectively ; P = .031 ) , while no significant difference was observed in the medial facets ( 42.20 ± 5.55 ms vs 41.42 ± 4.09 ms , respectively ; P = .69 ) . Significantly higher mean T1ρ values were noted in the lateral facets of the patients with PFP ( 46.33 ms ) compared with the medial facets ( 42.20 ms ) ( P = .0001 ) , while no significant differences in T1ρ values were observed between the medial and lateral facets of the controls ( P = .502 ) . No significant differences were noted in T2 relaxation times . A high correlation was noted between the mean T1ρ values of the whole patella of patients with PFP and the degree of patellar tilt ( r = 0.72 ) . Conclusion : There were significantly higher T1ρ values in the lateral facets of patients with PFP and patellar tilt that were not seen in control patients . These higher values approach the numbers seen in patients with early osteoarthritis BACKGROUND An increased pronated foot posture is believed to contribute to patellofemoral pain syndrome ( PFPS ) , but the relationship between these phenomena is still controversial . The objectives of this study were to investigate the prevalence of PFPS in high school students and to compare passive internal and external hip rotation , passive dorsiflexion , and navicular drop and drift between healthy high school students and students with PFPS . METHODS All 16- to 18-year-old students in a Danish high school were invited to join this single-blind case-control study ( N = 299 ) . All of the students received a question naire regarding knee pain . The main outcome measurements were prevalence of PFPS , navicular drop and drift , passive ankle dorsiflexion , passive hip rotation in the prone position , and activity level . The case group consisted of all students with PFPS . From the same population , a r and omly chosen control group was formed . RESULTS The prevalence of knee pain was 25 % . Of the 24 students with knee pain , 13 were diagnosed as having PFPS . This corresponds to a PFPS prevalence of 6 % . Mean navicular drop and drift were higher in the PFPS group versus the control group ( navicular drop : 4.2 mm [ 95 % confidence interval ( CI ) , 3.2 - 5.3 mm ] versus 2.9 mm [ 95 % CI , 2.5 - 3.3 mm ] ; and navicular drift : 2.6 mm [ 95 % CI , 1.6 - 3.7 mm ] versus 1.4 mm [ 95 % CI , 0.9 - 2.0 mm ] ) . Higher passive ankle dorsiflexion was also identified in the PFPS group ( 22.2 ° [ 95 % CI , 18 ° -26 ° ] versus 17.7 ° [ 95 % CI , 15 ° -20 ° ] ) . CONCLUSIONS This study demonstrated greater navicular drop , navicular drift , and dorsiflexion in high school students with PFPS compared with healthy students and highlights that foot posture is important to consider as a factor where patients with PFPS diverge from healthy individuals Data regarding validity of clinical and radiographic findings in diagnosing patellofemoral pain syndrome are inconclusive . We prospect ively assessed how sensitive and specific key patellofemoral physical examination tests are , and evaluated the prevalence of physical examination and radiographic findings . Sixty-one infantry soldiers with patellofemoral pain syndrome and 25 control subjects were evaluated . The sensitivity of the patellar tilt , active instability , patella alta , and apprehension tests was low ( less than 50 % ) ; specificity ranged between 72 % and 100 % . Although the prevalence of positive patellar tilt and active instability tests was significantly greater in subjects with patellofemoral pain syndrome , there were no significant differences between the groups in the results of the other two tests . Soldiers with patellofemoral pain syndrome presented with increased quadriceps angle , lateral and medial retinacular tenderness , patellofemoral crepitation , squinting patella , and reduced mobility of the patella . There were no differences between the groups in the prevalence of lower limb and foot posture alignment and knee effusion .  Plain radiography showed increased patellar subluxation in soldiers with patellofemoral pain syndrome . Other radiographic measures ( sulcus angle , Laurin angle , Merchant angle , and Insall-Salvati index ) were similar in both groups . We provide evidence regarding the validity of clinical and radiographic features commonly used for diagnosing patellofemoral pain syndrome . Physical examinations were more useful than plain radiography . Level of Evidence : Diagnostic study , Level I. See the Guidelines for Authors for a complete description of levels of evidence Abstract Ten consecutive patients ( 12 knees ) , all women , with anterior knee pain syndrome participated in the study . The patellofemoral joints were examined with the knee in 0 ° , 10 ° , 20 ° , and 30 ° of flexion . At each knee position , kinematic and dynamic , an axial magnetic resonance ( MR ) image was used to focus on the sagittal plane , followed by an axial image focused through the middle of the patella . Ten healthy volunteers ( 20 knees ) with no history of previous or current knee problems or anterior knee pain also underwent  MRI scanning following the same procedure . Three angles were measured : patellar tilt angle ( PTA ) , sulcus angle ( SA ) , and congruence angle ( CA ) . For statistical analyses , we used the Mann-Whitney U-test . Compared with the control knees , five patterns of malalignment were identified . The most frequently observed was tilt and lateralisation , with elevated CA and decreased PTA . In extension , the average CA for this group was 22 ° and PTA –4.8 ° vs –8.1 ° and 14.3 ° for control knees respectively . Contraction of the muscles caused tilt of the patella in symptomatic knees . This decrease of the PTA was statistically significant in extension ( P < 0.05 ) and in 10 ° of flexion ( P < 0.05 ) . Contraction of the thigh muscle increased CA in 30 ° of flexion . This lateral pull was statistically significant ( P < 0.05 ) . There were no statistically significant differences of SA between the groups , regardless of muscle contraction or flexion angle . At 30 ° of flexion , muscle contraction increased CA and decreased PTA . In our opinion , imaging in the first 30 ° of flexion with thigh muscle contraction is necessary for a correct diagnosis Background : Quadriceps atrophy and in particular atrophy of the vastus medialis obliquus ( VMO ) muscle have been frequently related with patellofemoral pain syndrome ( PFPS ) , despite very little objective evidence . Hypothesis : Patients with PFPS exhibit atrophy of the VMO in comparison with healthy controls . Study Design : Case-control study ; Level of evidence , 3 . Methods : Forty-six patients with PFPS and 30 healthy control persons with similar age , gender , body mass index , and activity index distributions underwent magnetic resonance imaging ( MRI ) of the quadriceps .  The muscle size was determined by calculating the cross-sectional area of the total quadriceps and its components . Results : The cross-sectional area ( CSA ) of the VMO was significantly smaller in the PFPS group than in the control group ( 16.67 ± 4.97 cm2 vs 18.36 ± 5.25 cm2 ) ( P = .040 ) . A tendency was noted for a smaller total quadriceps CSA for the PFPS patients at midthigh level ( 66.99 ± 15.06 cm2 vs 70.83 ± 15.30 cm2 ) ( P = .074 ) . Conclusion : This is the first study to examine VMO size in PFPS patients by MRI . Patients with patellofemoral problems exhibited atrophy of the VMO . Although it is not clear whether this atrophy is a result or a cause of PFPS , the results of this study do show that atrophy of the VMO is a contributing factor in PFPS . Longitudinal , prospect i ve studies are needed to establish the cause-effect relation of VMO atrophy and PFPS OBJECTIVE : To evaluate the patellar height of volunteers with and without patellofemoral pain syndrome ( PPS ) during maximal voluntary isometric contraction ( MVIC ) in open kinetic chain ( OKC ) and closed kinetic chain ( CKC ) exercises . METHODS : Twenty healthy women , and nineteen women with patellofemoral pain syndrome were evaluated and subjected to nuclear magnetic resonance imaging during rest and MVIC in OKC and CKC at 15 ° , 30 ° , and 45 ° knee flexion .  The patellar height was assessed by the K-Pacs program , using the Insall-Salvati index . For each exercise and knee position , patellar height was measured three times and the procedure was repeated after seven days . RESULTS : These data did not confirm our hypothesis that OKC exercises promote increased patellar height . CONCLUSION : Patellar height is not associated with PPS and suggests that CKC exercises lead an increased patellar height during knee position at 15º and 45º flexion for the PPS group . Level of Evidence II , Comparative Prospect i ve The purpose of this study was to correlate the trochlear shape and patellar tilt angle and lateral patellar displacement at rest and maximal voluntary isometric contraction ( MVIC ) exercises during open ( OKC ) and closed kinetic chain ( CKC ) in subjects with and without anterior knee pain . Subjects were all women , 20 who were clinical ly healthy and 19 diagnosed with anterior knee pain . All subjects were evaluated and subjected to magnetic resonance exams during OKC and CKC exercise with the knee placed at 15 , 30 , and 45 degrees of flexion . The parameters evaluated were sulcus angle , patellar tilt angle and patellar displacement using bisect offset . Pearson 's r coefficient was used , with p < .05 . Our results revealed in knee pain group during CKC and OKC at 15 degrees that the increase in the sulcus angle is associated with a tilt increase and 
    Output:
    
Limited evidence was found to support the association of other imaging features with PFP .
Certain PFJ imaging features were associated with PFP .