***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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    Input: Objective To prospect ively evaluate prognostic factors for new onset or progression of degenerative change on follow-up MRI one year after knee trauma and the association with clinical outcome . Methods Within a prospect i ve observational cohort study in general practice , we studied a subgroup of 117 patients with acute knee trauma ( mean age 41 years , 43 % women ) .  Degenerative change was scored on MRI at baseline and after one year follow-up . Multivariate logistic regression analysis was performed to evaluate prognostic factors for new onset or progressive degenerative change on follow-up MRI . Association between new or progressive degeneration and clinical outcome after one year was assessed . Results On follow-up MRI 15 % of patients with pre-existing knee osteoarthritis showed progression and 26 % of patients demonstrated new degenerative change . The only statistically significant prognostic variable in the multivariate analysis was bone marrow oedema on initial MRI ( OR 5.29 ( 95 % CI 1.64–17.1 ) , p = 0.005 ) . A significant association between new or progressive degenerative change and clinical outcome was found ( p = 0.003 ) . Conclusion Bone marrow oedema on MRI for acute knee injury is strongly predictive of new onset or progression of degenerative change of the femorotibial joint on follow-up MRI one year after trauma , which is reflected in clinical outcome A system has been constructed to evaluate the design , implementation , and analysis of  r and omized control trials ( RCT ) . The degree of quadruple blinding ( the r and omization process , the physicians and patients as to therapy , and the physicians as to ongoing results ) is considered to be the most important aspect of any trial . The analytic techniques are scored with the same emphasis as is placed on the control of bias in the planning and implementation of the studies . Description of the patient and treatment material s and the measurement of various controls of quality have less weight . An index of quality of a RCT is proposed with its pros and cons . If published papers were to approximate these principles , there would be a marked improvement in the quality of r and omized control trials . Finally , a reasonable st and ard design and conduct of trials will facilitate the interpretation of those with conflicting results and help in making valid combinations of undersized trials The aim of this study is to evaluate the relation between bone bruise and (peri-)articular derangement and to assess the impact of bone bruise on presentation and short term course of knee complaints . We recorded MR abnormalities in 664 consecutive patients with sub-acute knee complaints . Patients were divided in four groups : patients with and without intra-articular knee pathology , subdivided in patients with and without bone bruise . We assessed function and symptoms at the time of MR and 6 months thereafter . Bone bruises were diagnosed in 124 of 664 patients ( 18.7 % ) . Patients with bone bruise had significantly more complete ACL , lateral meniscal , MCL and LCL tears . Both with and without intra-articular pathology patients with bone bruise had a significantly poorer function at the time of MR ( Noyes score of , respectively , 313.21 versus 344.81 and 306.98 versus 341.19 ) . Patients with bone bruise and intra-articular pathology showed significantly more decrease in activity ( decrease of Tegner score from 6.28 to 2.12 versus 5.70–2.55 ) . At 6 months there were no significant differences in clinical parameters between the four groups . We concluded that bone bruise in combination with MCL tear is an important cause of initial clinical impairment in patients with sub-acute knee complaints . Clinical improvement within 6 months is more pronounced than in patients without bone bruise Context Bone marrow edema on magnetic resonance imaging ( MRI )  correlates with pain in patients with knee osteoarthritis , but its association with progression of joint changes is unknown . Contribution Among 223 patients with knee osteoarthritis , bone marrow edema on MRI  was associated with radiographic progression in the same compartment over the following 15 to 30 months after adjustment for age , sex , body mass index , and limb malalignment ( another predictor of progression ) . Caution s While this study shows that bone marrow edema is associated with the progression of knee osteoarthritis , we do not know whether it is causal or an epiphenomenon . These findings do not define a role for MRI in the routine evaluation of knee osteoarthritis . The Editors Osteoarthritis , the most common form of arthritis , is the leading cause of mobility-related disability in elderly persons ( 1 ) . With the aging of the population , the prevalence of osteoarthritis is increasing . Loss of hyaline articular cartilage is a central pathologic event in osteoarthritis , but the pathogenesis of cartilage loss is poorly understood . Specifically , there is a paucity of information about what factors identify joints at high risk for progression . Identification of such factors might permit better underst and ing of the disease process . While cartilage loss is a major pathologic feature of osteoarthritis , abnormal bone has been documented as another important element . Bone scan studies of persons with osteoarthritis have reported late-phase uptake of tracer in subchondral bone , signifying accelerated bone turnover . This increase in tracer has been associated with joint pain ( 2 ) and with a markedly increased risk for radiographic progression in osteoarthritis of the knee ( 3 ) and h and ( 4 ) . The study in knees , however , was limited by the use of out date d radiographic techniques ( 5 ) . Increased uptake on bone scan has a parallel finding on magnetic resonance imaging ( MRI ) :  bone marrow edema ( 6 , 7 ) . Bone marrow edema is indicated by focally increased signal in the marrow on fat-suppressed T2-weighted images . McAlindon and colleagues ( 7 ) found that of 12 knees with bone scan lesions , 11 had bone marrow edema lesions in the same location . The question of whether bone marrow edema lesions on MRI affect structural change in the osteoarthritic joint has not been longitudinally evaluated . We previously reported that among persons with radiographic knee osteoarthritis , those with bone marrow edema lesions more often had knee pain than those without ( 8) . In patients without osteoarthritis , these edema lesions have been associated with bone trauma ( 9 , 10 ) . Like lesions on bone scans , limb malalignment has also been reported as a potent risk factor for structural progression of osteoarthritis . In a recent longitudinal study ( 11 ) , patients with varus alignment were at high risk for subsequent medial progression of knee osteoarthritis , while limbs with valgus alignment were at commensurately high risk for lateral progression . The accepted mechanism for the effect of malalignment is that increased stress on one side of the joint leads to cartilage loss . We performed a natural history study of knee osteoarthritis using MRIs and knee radiography . One goal of our study was to examine the effect of bone marrow edema lesions on structural deterioration of the joint , as indicated by joint space loss on radiographs . Previous work ( 12 ) documented the correlation between joint space width and articular cartilage thickness , and other studies ( 11 , 13 ) have used joint space loss as a proxy for cartilage loss . Our ob jectives were to investigate the relation of bone marrow edema lesions to joint space loss in patients with osteoarthritis , to evaluate whether these lesions were associated with malalignment , and to determine whether some of the relation of marrow lesions to progression could be explained by their association with malalignment . In addition , if bone marrow edema lesions were associated with malalignment , we postulated that they had a local effect and that the contralateral side of the joint was protected . Methods Patients were recruited to participate in a natural history study of symptomatic knee osteoarthritis . All patients in the current study are a subset of patients whose recruitment has been described in detail elsewhere ( 8) . Briefly , patients were recruited from two prospect i ve studies , one in men and one in women , of quality of life among veterans ; from clinics at Boston Medical Center in Boston , Massachusetts ; and from advertisements in local newspapers . Potential participants were asked two questions : Do you have pain , aching , or stiffness in one or both knees on most days ? and Has a doctor ever told you that you have knee arthritis ? For patients who answered yes to both questions , we conducted a follow-up interview in which we asked about other types of arthritis that could cause knee symptoms . If no other forms of arthritis were identified , then the individual was eligible for recruitment . A series of knee radiographs were obtained for each patient to determine whether radiographic osteoarthritis was present . If patients had a definite osteophyte on any view in the symptomatic knee , they were eligible for the study . Because they had frequent knee symptoms and radiographic osteoarthritis , all patients met American College of Rheumatology criteria for symptomatic knee osteoarthritis ( 14 ) . For the natural history study , we enrolled patients who were interested in participating and who could walk with or without a cane . Of 351 patients from the cross-sectional study ( 8) , 324 met these criteria . Of these , 193 men and 19 women received care from the Veterans Administration Health Care System and were recruited from the outpatient clinics there . Eight men and 104 women were recruited from the community . The study included a baseline examination and follow-up examinations at 15 and 30 months . At baseline , patients who did not have contraindications to MRIs  had MRI of the more symptomatic knee . At all examinations , patients had knee radiography and answered question naires about the severity of knee symptoms , including the Western Ontario McMaster Osteoarthritis ( WOMAC ) question naire . Patients were also weighed , with shoes off , on a balance-beam scale , and height was assessed . At the first follow-up visit , long-limb films were obtained with a 14 51 cassette , using methods described elsewhere ( 15 ) . Our study focuses on baseline MRI findings as predictors of change in radiographs over follow-up . The institutional review boards of Boston University Medical Center and the Veterans Administration Boston Health Care System approved the baseline and follow-up examinations . Assessment s Magnetic Resonance Imaging All studies were performed with a Signa 1.5 T MRI system ( General Electric Corp. , Milwaukee , Wisconsin ) using a phased-array knee coil . A positioning device was used to ensure uniformity among patients . Coronal , sagittal , and axial images were obtained . Coronal spin-echo fat-saturated proton density and T2-weighted fat-saturated images ( repetition time , 2200 milliseconds ; echo time , 20/80 milliseconds ) with a slice thickness of 3 mm , a 1-mm interslice gap , one excitation , a field of view of 11 to 12 cm , and a matrix of 256 128 pixels were obtained . To evaluate bone marrow lesions , we used the coronal T2-weighted fat-saturated images . As previously reported ( 8) , each femur and tibia were divided into medial , central , and lateral quadrants , result ing in six potential sites of lesions for each knee . We defined lesions as areas of increased signal adjacent to the subcortical bone ; a single radiologist , blinded to patient characteristics and radiographs , grade d lesions from 0 to 3 on the basis of their size . Because previous work ( 8) demonstrated that lesions of grade 2 or greater were more strongly associated with the presence of knee pain ( grade 1 lesions were common in those with and without knee pain ) , we focused on lesions that were grade 2 or larger . Such lesions encompassed at least one quarter of the width of the compartment on two or more slices ( Figure 1 ) . For intraobserver agreement for reading of these lesions , the value was 0.66 ( P < 0.001 ) . We defined a lesion as occurring in either the medial or lateral compartment if it was present in the femur or tibia of that compartment . Figure 1 . Bone marrow edema lesion ( B ) on magnetic resonance imaging . Radiography Patients underwent weight-bearing posteroanterior radiography using the protocol of Buckl and -Wright ( 16 ) . Using fluoroscopic positioning , we aligned the beam relative to knee center , and the knee was flexed so that the anterior and posterior lips of the medial tibial plateau were superimposed . Feet were rotated until the tibial spines were centered in the notch , and outlines of foot rotation were then made on foot maps so that the foot rotation would be the same for subsequent films . Fluoroscopic positioning has been shown to more accurately assess joint space compared with nonfluoroscopic acquisition and to improve reproducibility of joint space assessment . Other films obtained at baseline included weight-bearing skyline ( 17 ) and weight-bearing semi-flexed lateral films ; the latter were obtained according to the Framingham Study protocol . For evaluation of progression , we focused on the width of the joint space in medial and lateral compartments , since that has been found to correlate with cartilage thickness ( 12 ) . Films were read by using the Osteoarthritis Research Society International Atlas ( 18 ) , in which each medial and lateral tibiofemoral joint space is grade d from 0 ( normal ) to 3 ( bone on bone ) . We defined progression of joint space narrowing in a knee compartment as progression by at least one grade . A reader unfamiliar with the MRI findings read all films . All films were read unblinded to sequence ; however 
    Output:
    
There was strong evidence for relationships of mechanical knee alignment and meniscal pathology with BMLs in osteoarthritis population s. There was a paucity of evidence for a relationship between physical activity and BMLs .
CONCLUSION Despite the heterogeneity of included studies , these data suggest that mechanical knee alignment and meniscal pathology are risk factors for BMLs in knee osteoarthritis .
It suggests that BMLs in individuals with osteoarthritis are more susceptible to mechanical knee alignment .