***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 
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    ***EXAMPLES*** 
    Input: 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 Background The goals of this study were to ( 1 ) define the epidemiology of acute patellar dislocation , ( 2 ) determine the risk of subsequent patellar instability  episodes ( subluxation and /or redislocation ) during the study period , and ( 3 ) identify risk factors for subsequent instability episodes . Study Design Prospect i ve cohort study . Methods The authors prospect ively followed 189 patients for a period of 2 to 5 years . Historical data , injury mechanisms , and physical and radiographic measurements were recorded to identify potential risk factors for poor outcomes . Results Risk was highest among females 10 to 17 years old . Patients presenting with a prior history of instability were more likely to be female ( P < .05 ) and were older than first-time dislocation patients ( P < .05 ) . Fewer first-time dislocators ( 17 % ) had episodes of instability during follow-up than patients with a previous history of instability ( 49 % ) ( P < .01 ) . After adjusting for demographics , patients with a prior history had 7 times higher odds of subsequent instability episodes during follow-up than first time dislocators ( adjusted odds ratio = 6.6 , P < .001 ) . Conclusions Patellar dislocators who present with a history of patellofemoral instability are more likely to be female , are older , and have greater risk of subsequent patellar instability episodes than first-time patellar dislocators . Risk of recurrent patellar instability episodes in either knee is much higher in this group than in first-time dislocators Different surgical techniques have been described to correct trochlear dysplasia , without clear descriptions of the various types of trochlear dysplasia . In describing trochlear dysplasia , there exist no clear criteria to distinguish between decreased trochlear depth ( heightened trochlea floor ) and flattened lateral and /or medial condylar height . The current study aims to build a data base of axial MRI measurements of normal and abnormal trochlear shape to create a foundation for the selection of the necessary surgical correction to more normal trochlear anatomy . We prospect ively examined 152 subjects : 30 patients with patellar instability due to trochlea dysplasia and 122 subjects without any symptoms or objective findings related to the patellofemoral joint .  MRI was performed in both groups . The height of the medial and lateral condyle , and the center of the trochlea was measured on axial MR images . The height of these different locations was compared to the total width of the femoral condyle and expressed in percentages . The statistical analysis was conducted with the Student ’s t test at SPSS software . For intraobserver reliability 20 r and omly taken MRI were evaluated twice . The intraobserver reliability was determined by calculating the kappa values investigated parameter . In normal subjects , the height of the lateral condyle was 81 % of the width of the femoral condyle ( 100 units),the trochlear central height was 73 % , the medial condylar height was 76 % . In patients with patellar instability , the lateral condylar height was 82 % and showed no significant difference compared to the normal group ( P = 0.082 ) . The trochlear central ( 77 % ) and medial condylar height ( 79 % ) were significantly different ( P < 0.001 ) compared to the normal subjects . The location of pathology in patients with patellar instability was decreased lateral condylar height in five cases ( 16.6 % ) and decreased central /medial height in 25 cases ( 83.4 % ) . A height of the lateral condyle < 77 % was documented to be pathologic . There was also a significant difference ( P < 0.001 ) between males and females comparing the different heights of the trochlea to the total width of the femoral condyle . The result ant percentages of all three height measurements , the lateral , central , and medial heights , were greater in males than in females . The intraobserver reliability was perfect for all investigated parameters . In conclusion , ( 1 ) the presented measurement scheme on axial MRI is a reliable method to calculate the height of the trochlea in different locations , ( 2 ) a more objective assessment of the trochlear pathology is possible , ( 3 ) in five of six cases the pathology is located in the center and /or medial trochlea , and ( 4 ) in our series of patellofemoral instability patients , most would benefit from a deepening trochleaplasty as the surgical procedure of choice to correct dysplasia Objective Recent advances in surgical intervention for patellar instability have led to a need for long-term radiological monitoring . The aim of this study is to determine whether or not magnetic resonance imaging ( MRI ) or ultrasound ( US ) can replace computed tomography ( CT ) as the st and ard of care for the evaluation of the femoral sulcus . Material s and methods This was a prospect i ve study comparing the reliability of CT , magnetic resonance ( MR ) , and US for measuring the femoral sulcus in patients with patellar instability . Twenty-four patients were recruited to undergo a CT , MR , and US examination of each knee . Two observers independently measured femoral sulcus angles from subchondral bone and hyaline cartilage on two occasions . Intraclass correlations and generalizability coefficients were calculated to measure the reliability of each of the techniques . Thereafter , two observers measured the femoral sulcus angle from ultrasound images recorded by two independent operators to estimate interobserver and interoperator reliability . Results Forty-seven knees were examined with CT and US and 44 with MRI .  The sulcus angle was consistently smaller when measured from subchondral bone compared to cartilage ( 5–7 ° ) . Interobserver reliability for CT , MR , and US measurements from subchondral bone were 0.87 , 0.80 , and 0.82 and from cartilage 0.80 , 0.81 , and 0.50 . Generalizability coefficients of measurements from subchondral bone for CT , MR , and US were 0.87 , 0.76 , and 0.81 and for cartilage 0.76 , 0.73 , and 0.05 . Most of the variability in the US occurred at image acquisition rather than measurement . Conclusion In patients with patellar instability , CT and MR are reliable techniques for measuring the femoral sulcus angle but US , particularly of the articular cartilage , is not . MR is therefore the most suitable tool for longitudinal studies of the femoral sulcus We prospect ively studied the characteristics and early recovery of an unselected population of patients who had acute first-time lateral patellar dislocation . The recovery program used st and ardized rehabilitation , emphasizing range of motion , muscle strength , and return of function . Patients returned to stressful activities including sports as tolerated when they regained full passive range of motion , had no effusion , and when quadriceps muscle strength was at least 80 % compared with the noninjured limb . Seventy-four patients met the enrollment criteria ; 37 men and 37 women . The average age was 19.9 years , and preinjury sports participation was similar to that of ligament-injury patients . Four percent of patients ( N 3 ) had a history of birth complications , 3 % ( N 2 ) had a history of lower extremity problems as an infant or child , and 9 % ( N 7 ) had a family history of patellar dislocation . Radiographs revealed a 50 % incidence ( N 37 ) of patella alta ; all patients demonstrated lateral patellar overhang . Patients regained range of motion ( mean , 0 ° to 132 ° ) by 6 weeks . Sports participation remained significantly reduced throughout the first 6 months after injury , with the greatest limitations in kneeling and squatting . At 6 months , 58 % of patients ( N 43 ) noted limitation in strenuous activities . The patients who had acute primary patellar dislocation were young and active . Most injuries occurred during sports , and few patients had abnormal physical features , contradicting any stereotype of an overweight , sedentary , adolescent girl whose patella dislocates with little or no trauma Minor degrees of malalignment of the patella and anatomical abnormalities including a flattened sulcus angle and an increased ratio between patellar tendon length and patellar length ( PT : P ) have been suggested as predisposing factors in the causation of chondromalacia patellae , as well as patellar instability . In order to confirm or refute this hypothesis a prospect i ve study has been performed comparing the congruence and sulcus angles and the PT : P ratio  in a group of 35 patients with chondromalacia confirmed by arthroscopy and a group of 33 patients with instability , with those of a group of 50 knees in normal volunteers . While there was a statistically significant correlation between an increased sulcus and congruence angle and a high-riding patella in patients with instability , no correlation could be identified in patients with idiopathic chondromalacia This is a prospect i ve study of 431 patients ( 862 knees ) with patellofemoral pain , patellar dislocation , or other abnormalities of the knee joint . There were 217 asymptomatic knees with no contralateral problems for comparison . All patients had a history and physical and radiographic examination of both knees . The radiographs included st and ard anteroposterior views , axial views at 30 ° of knee flexion , and st and ing lateral views at 0 ° and 30 ° of flexion . The presence of patellar tilt or subluxation was noted on the axial view . The lateral view of the patella , with precise overlap of the posterior femoral condyles , allowed determination of relationships between the patella 's medial edge , median ridge , and lateral edge to assess patellar tilt . Sixty-two percent of patients with patellar dislocations demonstrated subluxation on the axial view , while 98 % demonstrated an abnormal lateral view . Eighteen percent of the control knees revealed evidence of subluxation on the axial view while 35 % demonstrated subluxation on the extended lateral view . The axial view demonstrated 62 % sensitivity for dislocation , while the lateral view taken in full extension demonstrated 98 % sensitivity . The specificity for previous dislocation was 82 % for the axial view and 93 % for the lateral flexed view . Given the high sensitivity of the lateral view for detecting prior patellar dislocation , a normal result on this view can virtually eliminate the question of previous dislocation . Also , with the high specificity of the axial view and lateral view with knee flexion , the two views combined can confirm a clinical impression of patellofemoral malalignment The present study compares the repeatability of patellofemoral malalignment ( PFM ) indices obtained by 20 degree flexion axial radiography ( AR ) and computerized tomography ( CT ) with 0 degree and 20 degree flexion of the knees in children and adolescents . Thirty-one patients with a mean age of 14.2 years ( range 8 to 19.2 years ) suffering from PFM were examined using these two radiographic techniques . The  lateral patellofemoral angle ( LPA ) , the lateral patellar tilt ( LPT ) , and the lateral patellar displacement ( LPD )  were measured by by two different investigators on different occasions , and the agreement of these indices between CT and AR was evaluated according to Bl and and Altman 's statistical method . LPT and LPD obtained by AR were more reliable and repeatable than those obtained by CT . The quadriceps muscle contraction exacerbates PFM indices significantly with the knees in full extension ( P = 0.0001 ) .  LPT and LPD  measured at 20 degrees AR show reliably the two pathological components ( the patellar tilt and the lateral patellar displacement ) of PFM which are necessary for diagnosis and treatment planning . CT with quadriceps contractions is better in qualitative screening of more subtle cases of PFM 
    Output:
    
The findings indicated that there was acceptable inter-observer and intra-observer reliability and validity for different methods of assessing patellar height and the sulcus angle with X-ray , MRI and CT methods , and the tibial tubercle-trochlear groove ( TT-TG ) assessed using CT .
There was poor reliability or validity for the assessment of severity of trochlear dysplasia and the sulcus angle using US .
Conclusion There is insufficient evidence to determine the reliability , validity , sensitivity or specificity of tests such as the congruence angle , lateral patellar displacement , lateral patellar tilt , trochlear depth , boss height , the crossing sign or Wiberg patellar classification .