***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: Background The effectiveness of anterior cruciate ligament reconstruction for restoring normal knee kinematics is largely unknown , particularly during sports movements generating large , rapidly applied forces . Hypothesis Under dynamic in vivo loading , significant differences in 3-dimensional kinematics exist between anterior cruciate ligament-reconstructed knees and the contralateral , uninjured knees . Study Design Prospect i ve , in vivo laboratory study . Methods Kinematics of anterior cruciate ligament-reconstructed and contralateral ( uninjured ) knees were evaluated for 6 subjects during downhill running 4 to 12 months after anterior cruciate ligament reconstruction , using a 250 frame/s stereoradiographic system .  Anatomical reference axes were determined from computed tomography scans .  Kinematic differences between the uninjured and reconstructed limbs were evaluated with a repeated- measures analysis of variance . Results Anterior tibial translation was similar for the reconstructed and uninjured limbs . However , reconstructed knees were more externally rotated on average by 3.8 ± 2.3 ° across all subjects and time points ( P = .0011 ) . Reconstructed knees were also more adducted , by an average of 2.8 ± 1.6 ° ( P = .0091 ) . Although differences were small , they were consistent in all subjects . Conclusions Anterior cruciate ligament reconstruction failed to restore normal rotational knee kinematics during dynamic loading . Clinical Relevance Although further study is required , these abnormal motions may contribute to long-term joint degeneration associated with anterior cruciate ligament injury/reconstruction Background : Limited knee flexion and increased muscle co-contraction during jump l and ing are believed to diminish outcomes after anterior cruciate ligament ( ACL ) reconstruction . The efficacy of jump training to improve patients ’ mechanical and neuromuscular deficits is understudied . Hypothesis : Jump training will improve functional , mechanical , and neuromuscular outcomes and higher repetition training augmented by body weight support will result in better retention of gains . Study Design : R and omized controlled trial ; Level of evidence , 1 . Methods : Thirty athletes ( 18 months after surgery ) were screened , and 19 with mechanical deficits and limited clinical outcomes were enrolled in the trial . Testing included the International Knee Documentation Committee ( IKDC ) question naire , leg l and ing mechanics via motion analysis , knee joint effusion using a stroke test , and a surface electromyography – generated co-contraction index during a single-legged l and ing . Participants were r and omly assigned to 1 of 2 groups : jump training with normal body weight ( JTBW ) and high-repetition jump training with body weight support ( JTBWS ) . Knee effusion grading throughout training was used to assess joint tolerance . Changes in outcomes over time were analyzed with mixed-effects modeling . Immediate outcomes were compared with retention testing at 8 weeks after training by use of 2-way analyses of variance with effects of time and group . Results : Significant effects of time were found during the training phase for all outcome measures , but no effects of group or sex were found . IKDC score ( pooled ; mean ± SD ) increased from 76 ± 12 to 87 ± 8 ( P < .001 ) . Knee flexion during single-legged l and ing increased from 57 ° ± 11 ° to 73 ° ± 9 ° ( P < .001 ) . Average co-contraction index decreased from 37 ± 15 to 19 ± 6 ( P < .001 ) . All measures were retained over the retention period in both groups . The relative risk of knee effusion of the JTBW group versus the JTBWS group was 4.2 ( 95 % CI , 2.25 - 7.71 ; P < .001 ) . Conclusion : Jump training mitigated some risk factors for second injury and osteoarthritis in patients after ACL reconstruction . Training made lasting improvements in physical function measures as well as mechanical and neuromuscular coordination deficits . Higher repetitions used with body weight support did not improve retention but substantially reduced risk for effusion . Clinical Relevance : Jump training is an efficacious intervention for athletes with poor outcomes after ACL reconstruction , and training with body weight support lessens the risk for excessive joint stress during practice . Registration : NCT02148172 ( Clinical Trials.gov identifier Background Knee reinjury after ACL reconstruction is common and increases the risk of osteoarthritis . There is sparse evidence to guide return to sport ( RTS ) decisions in this population . Objectives To assess the relationship between knee reinjury after ACL reconstruction and ( 1 ) return to level I sports , ( 2 ) timing of RTS and ( 3 ) knee function prior to return . Methods 106 patients who participated in pivoting sports participated in this prospect i ve 2-year cohort study . Sports participation and knee reinjury were recorded monthly . Knee function was assessed with the Knee Outcome Survey — Activities of Daily Living Scale , global rating scale of function , and quadriceps strength and hop test symmetry . Pass RTS criteria were defined as scores > 90 on all tests , failure as failing any . Results Patients who returned to level I sports had a 4.32 ( p=0.048 ) times higher reinjury rate than those who did not . The reinjury rate was significantly reduced by 51 % for each month RTS was delayed until 9 months after surgery , after which no further risk reduction was observed . 38.2 % of those who failed RTS criteria suffered reinjuries versus 5.6 % of those who passed ( HR 0.16 , p=0.075 ) . More symmetrical quadriceps strength prior to return significantly reduced the knee reinjury rate . Conclusions Returning to level I sports after ACL reconstruction leads to a more than 4-fold increase in reinjury rates over 2 years . RTS 9 months or later after surgery and more symmetrical quadriceps strength prior to return substantially reduce the reinjury rate Background : It has been hypothesized that quadriceps muscle weakness is directly associated with the onset and progression of posttraumatic osteoarthritis after  anterior cruciate ligament ( ACL ) injury and reconstruction ( ACLR ) .  This relationship , however , has not been studied with a prospect i ve approach that includes the use of tibiofemoral joint space width difference ( JSW-D ) measurements to characterize the onset of posttraumatic osteoarthritis before the clinical manifestation of the disease . Purpose : To assess the relationship between thigh muscle strength and JSW-D at presurgery baseline and at 1- and 4-year follow-up after ACLR compared with healthy , noninjured participants of similar sex , age , body mass index , and activity level . Study Design : Cohort study ; Level of evidence , 3 . Methods : A total of 39 unilateral ACL-injured patients and 32 healthy controls were followed prospect ively . During each follow-up , JSW , isokinetic knee strength , single-legged hop , and clinical - and patient-oriented outcomes were assessed . At final follow-up , ACL-injured participants who had JSW-D values ( considered as the injured minus normal knee ) that were less than the 95 % confidence interval of controls were considered to be in the ACLR-narrow group , while those with JSW-D values that fell within the confidence intervals were in the ACLR-normal group . Relationships were evaluated between ACLR groups and controls via multilevel regression , as well as Kruskal-Wallis tests for between-group comparisons at 4-year follow-up . Results : At 4-year follow-up , 30 participants ( 79 % ) were in the ACLR-normal group and 8 ( 21 % ) were in the ACLR-narrow group . At baseline , the extension , flexion , and extension/flexion ratio strength values for both ACLR groups were significantly lower than those of controls ( P ≤ .05 ) , while the ACLR-narrow group had significantly lower extension strength at 60 and 180 deg/s ( P = .04 and .03 , respectively ) , as well as extension/flexion ratio at 60 deg/s ( P = .04 ) in comparison with the ACL-normal group . At 4-year follow-up , 60 deg/s extension strength deficits persisted in the ACLR-narrow group compared with controls and ACLR-normal participants ( P = .01 and .04 , respectively ) . Flexion strength at 180 and 300 deg/s was also significantly lower in the ACLR-narrow group compared with ACLR-normal ( P = .02 and .04 , respectively ) , as was single-legged hop distance ( P = .04 ) . Conclusion : Strength deficits present within months after ACL injury and persist through 4 years after ACLR in participants with significantly narrowed JSW-D , compared with ACLR participants with normal JSW-D and controls . This study revealed a significant relationship between quadriceps strength loss that occurred soon after injury and JSW narrowing Purpose Unrealistic patient expectations have been shown to negatively influence patient-reported outcomes in orthopaedic surgery . Knowledge about patient expectations is important to associate preoperative expectations with the reasonable outcome of a specific procedure . The purpose of this study was to prospect ively analyse and to compare patient expectations of  primary and revision anterior cruciate ligament reconstruction ( ACLR )  and to assess the factors associated with patient expectations . Methods Preoperative expectations of 181 consecutive patients undergoing ACLR  were assessed prospect ively using a 5-item question naire . Primary ACLR ( P-ACLR ) was performed in 133 patients ( 73 % ) , whereas 48 patients ( 27 % ) underwent revision ACLR ( R-ACLR ) .  The question naire assessed the expectation of the overall condition of the knee joint , return to sports , instability , pain , and risk of osteoarthritis . Results All patients expected a normal ( 38 % ) or nearly normal ( 62 % ) condition of the knee joint . Return to sports at the same level was expected by 91 % . With regard to instability ( pain ) , no instability ( pain ) independent of the activity level was expected by 77 % ( 58 % ) . No or only a slightly increased risk of the development of osteoarthritis was expected by 98 % . The R-ACLR group showed a significantly lower expectation of the overall condition ( p = 0.001 ) , return to sports ( p < 0.001 ) , and pain ( p = 0.002 ) . No statistically significant difference was found between female and male patients ( n.s . ) . In the P-ACLR group , patients with a history of previous knee surgery showed inferior expectations of return to sports ( p = 0.015 ) and risk of osteoarthritis ( p = 0.011 ) . Age , number of previous knee surgeries , and pre-injury sports level significantly influenced patient expectations . Conclusions Overall , patient expectations of ACL reconstruction are high . Patients undergoing revision ACL reconstruction have lower but still dem and ing expectations . Younger patients , patients without a history of knee surgery , and highly active patients have higher expectations . Explicit patient information about realistic goals of ACL reconstruction seems to be necessary in order to prevent postoperative dissatisfaction despite a successful operation in the surgeons ’ point of view . Level of evidence Prospect i ve case series , Level IV Abstract Purpose To compare the ability of three different anterior cruciate ligament ( ACL ) reconstruction techniques  to normalize rotational knee stability 1 year after ACL reconstruction . Two of these techniques are so-called anatomic techniques . Methods Three different ACL reconstruction techniques were tested for their ability to normalize rotational knee stability in a prospect i ve r and omized study . Forty-seven ACL-deficient ( ACLD ) patients were r and omized to transtibial single-bundle ( SB ) , anatomic SB , and double-bundle ACL reconstruction . Three-dimensional motion analysis was performed preoperatively and at 1-year follow-up to evaluate tibial rotation and rotational stiffness . Motion data were captured using an eight-camera motion analysis system . Tibial rotation was determined during walking , running , and a pivoting task . Other outcome parameters were KT-1000 knee laxity measurements and the subjective outcome scores KOOS and IKDC . Results Three-dimensional motion analysis demonstrated that the tibial internal rotation and the rotational stiffness did not differ between the ACL reconstruction techniques during walking , running , and pivoting at 1-year follow-up . Objective knee stability and subjective outcome scores did not differ between the reconstruction groups . Conclusion No significant difference in rotational stability walking , running , and pivoting was seen between anatomic and nonanatomic ACL reconstruction techniques at 1-year follow-up . Level of evidence Therapeutic study , Level OBJECTIVES To examine the effects of 2 gait retraining protocol s on the gait patterns of patients with bone-patellar tendon-bone anterior cruciate ligament ( ACL ) reconstruction . DESIGN R and omized control , repeated- measures design . SETTING Private orthopedic center and research facility . PARTICIPANTS Sixteen patients with bone-patellar tendon-bone ACL reconstruction , r and omly subdivided into 2 groups ( group 1 , n=8 ; group 2 , n=8 ) , and a healthy control group of 8 subjects . INTERVENTION The 16 subjects with ACL reconstruction were r and omly assigned to 2 different gait retraining protocol s over a 6-week training interval : ( 1 ) . a protocol using a predicted stride frequency calculated from the resonant frequency of a force-driven harmonic oscillator ( FDHO ) model or ( 2 ) . a protocol using the preferred stride frequency ( PSF ) . MAIN OUTCOME MEASURES Gait analyses examining the lower-extremity kinematic , kinetic , and energetic gait patterns of each group . RESULTS Gait retraining with the FDHO model showed improvements in lower-extremity positions , hip and knee extensor angular impulse , and work parameters . Gait re 
    Output:
    
Inconsistent results were found for both peak vertical ground reaction force and impact forces after ACL-R. Patellofemoral and tibiofemoral joint contact forces differed from both contralateral or control limbs up until at least 2.5 years after ACL-R and moderate evidence indicated no difference for muscle activations during moderate speed running .
Quadriceps and hamstring strength asymmetries , and knee function , but not surgical techniques , were likely to be associated with both knee kinematics and kinetics during running after ACL-R. Conclusion After ACL-R , knee flexion motion and internal knee extension moment are the most affected variables and are consistently smaller in the injured limb during running when pooling evidence .
Clinicians should be aware that these deficits do not appear to resolve with time and , thus , specific clinical interventions may be needed to reduce long-term disability .