***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: Background and Purpose Although various hop tests have been proposed as performance-based outcome measures following anterior cruciate ligament ( ACL ) reconstruction , limited reports of their measurement properties exist . The purpose of this study was to investigate the reliability and longitudinal validity of data obtained from hop tests during rehabilitation after ACL reconstruction . Subjects Forty-two patients , 15 to 45 years of age , who had undergone ACL reconstruction participated in the study . Methods and Measures The study design was prospect i ve and observational with repeated measures . The subjects performed a series of 4 hop tests on 3 separate occasions within the 16th week following surgery and on a fourth occasion 6 weeks later . The tests were a  single hop for distance  , a 6-m timed hop , a triple hop for distance  , and  crossover hops for distance .  Performance on the ACL-reconstructed limb was expressed as a percentage of the performance on the nonoperative limb , termed the “ limb symmetry index . ” Subjects also completed the Lower Extremity Functional Scale and a global rating of change question naire . Results Intraclass correlation coefficients for limb symmetry index values ranged from .82 to .93 . St and ard errors of measurement were 3.04 % to 5.59 % . Minimal detectable changes , at the 90 % confidence level , were 7.05 % to 12.96 % . Changes in hop test scores on the operative limb were statistically greater than changes on the nonoperative limb . Pearson correlations ( r ) between change in hop performances and self-reported measures ranged from .26 to .58 . Discussion and Conclusion The results show that the described series of hop tests provide a reliable and valid performance-based outcome measure for patients undergoing rehabilitation following ACL reconstruction . These findings support the use and facilitate the interpretation of hop tests for research and clinical practice A more sports-specific and detailed strength assessment has been advocated for patients after anterior cruciate ligament ( ACL ) injury and reconstruction . The purpose of this study was to develop a test battery of lower extremity strength tests with high ability to discriminate between leg power development on the injured and uninjured sides in patients after ACL injury and in patients who have undergone ACL reconstruction . Twenty-three patients were tested 6 months after ACL injury and 44 patients were tested 6 months after ACL reconstruction . Twenty-four of the 44 patients were operated on using a hamstrings graft and 20 patients were operated on using a patellar tendon graft . All the patients performed a test battery of three strength tests for each leg in a r and omised order . The three strength tests were chosen to reflect quadriceps and hamstring muscular power in a knee-extension and a knee-flexion test ( open kinetic chain ) and lower-extremity muscular power in a leg-press test ( closed kinetic chain ) . There was a higher sensitivity for the test battery to discriminate abnormal leg power compared with any of the three strength tests individually . Nine out of ten patients after ACL reconstruction and six out of ten of the patients after ACL injury exhibited abnormal leg power symmetry using the test battery . Thus , this test battery had high ability in terms of discriminating between the leg power performance on the injured and uninjured side , both in patients with an ACL injury and in patients who have undergone ACL reconstruction . It is concluded that a test battery consisting of a  knee-extension , knee-flexion  and  leg-press muscle power test had high ability to determine deficits in leg power 6 months after ACL injury and reconstruction . Only a minority of the patients had restored leg muscle power . The clinical relevance is that the test battery may contribute to the decision-making process when deciding whether and when patients can safely return to strenuous physical activities after an ACL injury or reconstruction Background : R and omized controlled trials after anterior cruciate ligament reconstructions with long-term follow-up including assessment of health-related quality of life are rare . Purpose : To compare clinical outcome and health-related quality of life 8 years after  anterior cruciate ligament reconstruction  using 2 types of graft . Study Design : R and omized controlled trial ; Level of evidence , 1 . Methods : Long-term follow-up of 164 patients with anterior cruciate ligament injury r and omized to arthroscopic reconstruction with a quadrupled semitendinosus graft or a bone – patellar tendon – bone graft was undertaken . After a mean 8 years , 153 patients were available for follow-up , including instrumented laxity , 1-legged hop test , a knee-walking test , and assessment with International Knee Documentation Committee , Lysholm , Tegner , and patellofemoral pain score . Health-related quality of life was assessed with Knee Osteoarthritis Outcome Score and Short Form–36 . Results : Patients in both graft groups retained the same stability , knee function , and health-related quality of life . The patellofemoral pain score was similar for both groups ; the bone – patellar tendon – bone group had more donor site morbidity from kneeling and knee walking . In the bone – patellar tendon – bone group , 19 patients had no kneeling problems , 23 slight problems , 31 moderate problems , and 5 unable to kneel . Corresponding figures for the semitendinosus group were 25 , 32 , 16 , and 2 ( P < .001 ) . Patients with early reconstructions ( < 5 months ) had a lower risk for meniscal injuries ( 37 % ) than did later reconstructed ( 62 % , P = .008 ) . Health-related quality of life regarding physical functioning in Short Form–36 was better for the early-reconstructed patients than for the later reconstructed ( 92 vs 85 ; P = .014 ) . Patients without medial meniscal surgery had higher Knee Osteoarthritis Outcome Scores for all subscales than did patients with medial meniscal surgery , with most significant difference for sport and recreation ( 63 vs 75 , P = .008 ) . Conclusion : In the long term , the semitendinosus graft provided similar stability , knee function , and health-related quality of life but with less kneeling morbidity than did the bone – patellar tendon – bone graft The purpose of this study was to evaluate prospect ively the results of  anterior cruciate ligament ( ACL ) reconstruction with doubled hamstring tendon graft in a selected group of 18 rugby players . The graft was fixed with a transcondylar screw ( Transfix ) on the femur , and with an absorbable interference screw and a metallic staple on the tibia . All the patients followed the same rehabilitation program . Return to sports activities was allowed after 6 months . Follow-up was 2 years in all cases . The athletic level of the patients was rated according to the Tegner scoring system . Clinical results were evaluated using the International Knee Documentation Committee ( IKDC ) scoring system . Furthermore , an instrumented evaluation of the anterior laxity with a KT–1000 arthrometer , and an isokinetic evaluation were performed 6 and 24 months after surgery . The Tegner mean score at follow-up ( 8.2 ) was similar to that prior to injury ( 8.3 ) . IKDC overall results were normal in ten cases ( 55.6 % ) , nearly normal in six cases ( 33.3 % ) , and abnormal in two cases ( 11.1 % ) . Side-to-side difference of anterior laxity measured with KT–1000 at 6 and 24 months did not show an impairment of knee stability with time . Isokinetic evaluation showed a significant improvement on peak torque both in extension and flexion on comparison between 6- and 24-month measurements . The results reported in this study showed that the use of doubled hamstring tendon graft for ACL reconstruction in athletes that were at risk for high-energy traumas to the knees , such as rugby players , gave normal or nearly normal results in about 90 % of the cases . Recovery of muscle strength was almost complete 2 years after surgery , and there was no impairment of knee stability with time PURPOSE The aim of this study was to determine the rates of contralateral anterior cruciate ligament ( ACL ) rupture and of ACL graft rupture after  ACL reconstruction  using either patellar tendon or hamstring tendon autograft , and to identify any patient characteristics that may increase this risk . TYPE OF STUDY Case series . METHODS Over a 2-year period , 760 endoscopic ACL reconstructions were performed in 743 patients .  Bone-patellar tendon-bone autograft was used in 316 patients and 4-str and hamstring tendon in 427 patients . Those patients with a previous contralateral ACL rupture or those who underwent a simultaneous bilateral ACL reconstruction were excluded , leaving 675 knees ( 675 patients ) for review . Persons not involved in the index operation or the care of the patient conducted follow-up assessment by telephone interview conducted 5 years after surgery . Patients were question ed about the incidence of ACL graft rupture , contralateral ACL rupture , symptoms of instability or significant injury , family history of ACL injury , and activity level according to the International Knee Documentation Committee scale . From our prospect i ve data base we obtained further information on graft source , meniscal or articular surface injury , and gender . Binary logistic regression was used to measure the relative association between the measured variables and the risk of graft rupture and contralateral ACL rupture . RESULTS Five years after primary ACL reconstruction , 612 of the 675 patients ( 90.7 % ) were assessed . ACL graft rupture occurred in 39 patients ( 6 % ) and contralateral ACL rupture occurred in 35 patients ( 6 % ) . Three patients suffered both a graft rupture and a contralateral ACL injury . The odds of ACL graft rupture were increased 3-fold by a contact mechanism of initial injury . Return to level 1 or 2 sports increased the risk of contralateral ACL injury by a factor of 10 . The risk of sustaining an ACL graft rupture was greatest in the first 12 months after reconstruction . No other studied variable increased the risk of repeat ACL injury . CONCLUSIONS After reconstruction , repeat ACL injury occurred in 12 % of patients over 5 years . Twelve months after reconstruction , the ACL graft is at no greater risk than the contralateral ACL , suggesting that adequate graft and muscular function for most activities is achieved by this time . Risk factors for repeat ACL injury identified included a return to competitive side-stepping , pivoting , or jumping sports , and the contact mechanism of the index injury . Female patients were at no greater risk of repeat ACL injury than male patients and graft choice did not affect the rate of repeat ACL injury . LEVEL OF EVIDENCE Level IV , case series In a two-centre study , 164 patients with unilateral instability of the anterior cruciate ligament were prospect ively r and omised to arthroscopic reconstruction with either a patellar tendon graft using interference screw fixation or a quadruple semitendinosus graft using an endobutton fixation technique . The same postoperative rehabilitation protocol was used for all patients and follow-up at a median of 31 months ( 24 to 59 ) was carried out by independent observers . Four patients ( 2 % ) were lost to follow-up . No significant differences were found between the groups regarding the Stryker laxity test , one-leg hop test , Tegner activity level , Lysholm score , patellofemoral pain score , International Knee Documentation Committee ( IKDC ) score or visual analogue scale , reflecting patient satisfaction and knee function . Slightly decreased extension , compared with the non-operated side , was found in the patellar tendon group ( p < 0.05 ) . Patients with associated meniscal injuries had lower IKDC , visual analogue ( p < 0.01 ) and Lysholm scores ( p < 0.05 ) than those without such injuries . Patients in whom reconstruction had been carried out less than five months after the injury had better final IKDC scores than the more chronic cases ( p < 0.05 ) . We conclude that patellar tendon and quadruple semitendinous tendon grafts have similar outcomes in the medium term . Associated meniscal pathology significantly affects the final outcome and early reconstruction seems to be beneficial STUDY DESIGN Nonexperimental method ological study . OBJECTIVES To determine the interrater and intrarater reliability and validity of using observational risk-screening guidelines to evaluate dynamic knee valgus . BACKGROUND A deficiency in the neuromuscular control of the hip has been identified as a key risk factor for noncontact anterior cruciate ligament ( ACL ) injury in postpubescent females . This deficiency can manifest itself as a valgus knee alignment during tasks involving hip and knee flexion . There are currently no scientifically tested methods to screen for dynamic knee valgus in the clinic or on the field . METHODS Three physiotherapists used  observational risk-screening guidelines  to rate 40 adolescent female soccer players according to their risk of ACL injury . The rating was based on the amount of dynamic knee valgus observed on a drop-jump l and ing . Ratings were evaluated for intrarater and interrater agreement using kappa coefficients . Sensitivity and specificity of ratings were evaluated by comparing observational ratings , with measurements obtained using 3-dimensional ( 3-D ) motion analysis . RESULTS Kappa coefficients for intrarater and interrater agreement ranged from 0.75 to 0.85 , indicating that ratings were reasonably consistent over time and between physiotherapists . Sensitivity values were inadequate , ranging from 67 % to 87 % . This indicated that raters failed to detect up to a third of " truly high-risk " individuals . Specificity values ranged from 60 % to 72 % , which was considered adequate for the purpose s of the screening . CONCLUSION Observ 
    Output:
    
Conclusions Measurement of functional performance more than 2 years after ACL reconstruction consists of concentric or isometric strength , the single-leg hop for distance or a combination .
The Limb Symmetry Index is used as the main outcome parameter to compare the involved leg with the uninvolved .