***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 Objectives Femoral nerve block ( FNB ) , a commonly used postoperative pain treatment after total knee arthroplasty ( TKA ) , reduces quadriceps muscle strength essential for mobilization . In contrast , adductor canal block ( ACB ) is predominately a sensory nerve block . We hypothesized that ACB preserves quadriceps muscle strength as compared with FNB ( primary end point ) in patients after TKA . Secondary end points were effects on morphine consumption , pain , adductor muscle strength , morphine-related complications , and mobilization ability . Methods We performed a double-blind , r and omized , controlled study of patients scheduled for TKA with spinal anesthesia . The patients were r and omized to receive either a continuous ACB or an FNB via a catheter ( 30-mL 0.5 % ropivacaine given initially , followed by a continuous infusion of 0.2 % ropivacaine , 8 mL/h for 24 hours ) . Muscle strength was assessed with a h and held dynamometer , and we used the percentile change from baseline for comparisons . The trial was registered at clinical trials.gov ( Identifier : NCT01470391 ) . Results We enrolled 54 patients , of which 48 were analyzed .  Quadriceps strength as a percentage of baseline was significantly higher in the ACB group compared with the FNB group : ( median [ range ] ) 52 % [ 31–71 ] versus 18 % [ 4–48 ] , ( 95 % confidence interval , 8–41 ; P = 0.004 ) . There was no difference between the groups regarding morphine consumption ( P = 0.94 ) , pain at rest ( P = 0.21 ) , pain during flexion of the knee ( P = 0.16 ) , or adductor muscle strength ( P = 0.39 ) ; neither was there a difference in morphine-related adverse effects or mobilization ability ( P > 0.05 ) . Conclusions Adductor canal block preserved quadriceps muscle strength better than FNB , without a significant difference in postoperative pain Purpose Providing effective analgesia for total knee arthroplasty ( TKA ) patients remains challenging . Femoral nerve block ( FNB ) offers targeted pain control ; however , its effect on motor function , related fall risk and impact on rehabilitation has been the source of controversy . Adductor canal block ( ACB ) potentially spares motor fibres of the femoral nerve , but the comparative effect of the two approaches has not yet been well defined due to considerable variability in pain perception . Our study compares both single-shot FNB and ACB , side to side , in the same patients undergoing bilateral TKA . Methods Sixty patients scheduled for bilateral TKA were r and omised to receive ultrasound-guided FNB on one leg and ACB on the other , in addition to combined spinal epidural anaesthesia . The primary outcome was comparative postoperative pain in either extremity at six to eight , 24 and 48 hours postoperatively . Secondary comparative outcomes included motor strength ( manually and via dynamometer ) , physical therapy milestones and patient satisfaction . Results While pain levels were lowest at six to eight hours postoperatively and increased thereafter ( P < 0.001 ) , no significant differences were seen between extremities at any time point with regard to pain in the quantitative comparison using visual analogue scale ( VAS ) scores ( P = 0.4154 ) , motor strength ( P = 0.7548 ) , physical therapy milestones or patient satisfaction . However , in the qualitative comparison , a significant proportion of patients reported the leg receiving ACB to be more painful than that receiving FNB at 24 h [ 50.9 % ( n = 30 ) vs 25.42 % ( n = 15 ) , P = 0.0168 ) ] . Conclusions Although we could not confirm a benefit in motor function between ACB and FNB , given the equivalent analgesic potency combined with its potentially lower overall impact if neuropraxia should occur , ACB may represent an attractive alternative to FNB Background There are several methods for postoperative analgesia for knee surgery . The commonly utilized method is multimodal analgesia based on continuous femoral nerve block . The aim of this study was to investigate the application of continuous adductor canal block for analgesia after total knee replacement and compare this method with continuous femoral nerve block . Methods Sixty patients scheduled for total knee replacement from June 2013 to March 2014 were r and omly divided into a femoral group and an adductor group . Catheters were placed under the guidance of nerve stimulation in the femoral group and under the guidance of ultrasound in the adductor group . Operations were performed under combined spinal and epidural anesthesia . After the operations , 0.2 % ropivacaine was given at a speed of 5 ml/h through catheters in all patients . Visual analogue scale ( VAS ) pain scores at rest and while moving were noted at 4 , 24 , and 48 hours after the operation , and quadriceps strength was also assessed at these time‐points . Secondary parameters such as doses of complementary analgesics and side effects were also recorded . Results There were no significant differences between the groups in VAS pain scores at rest or while moving , at 4 , 24 , or 48 hours after the operation ( P > 0.05 ) . At these time‐points , mean quadriceps strengths in the adductor group were 3.0 ( 2.75‐3.0 ) , 3.0 ( 3.0‐4.0 ) , and 4.0 ( 3.0‐4.0 ) , respectively , all of which were significantly stronger than the corresponding means in the femoral group , which were 2.0 ( 2.0‐3.0 ) , 2.0 ( 2.0‐3.0 ) , and 3.0 ( 2.0‐4.0 ) , respectively ( P < 0.05 ) . There were no significant differences between the groups in doses of complementary analgesics or side effects ( P > 0.05 ) . X‐ray images of some patients showed that local anesthetic administered into the adductor canal could diffuse upward and reach the femoral triangle . Conclusions Continuous adductor canal block with 0.2 % ropivacaine could be used effectively for analgesia after total knee replacement . Compared with continuous femoral nerve block , this analgesic method has similar analgesic effects and is associated with less weakness of quadriceps muscle Background : This prospect i ve double-blinded , r and omized controlled trial compared adductor canal block ( ACB ) with femoral nerve block ( FNB ) in patients undergoing total knee arthroplasty . The authors hypothesized that ACB , compared with FNB , would exhibit less quadriceps weakness and demonstrate noninferior pain score and opioid consumption at 6 to 8 h postanesthesia . Methods : Patients received an ACB or FNB as a component of a multimodal analgesic . Quadriceps strength , pain score , and opioid consumption were assessed on both legs preoperatively and at 6 to 8 , 24 , and 48 h postanesthesia administration . In a joint hypothesis test , noninferiority was first evaluated on the primary outcomes of strength , pain score , and opioid consumption at 6 to 8 h ; superiority on each outcome at 6 to 8 h was then assessed only if noninferiority was established . Results : Forty-six patients received ACB ; 47 patients received FNB .  At 6 to 8 h postanesthesia , ACB patients had significantly higher median dynamometer readings versus FNB patients ( median [ interquartile range ] , 6.1 kgf [ 3.5 , 10.9 ] ( ACB ) vs. 0 kgf [ 0.0 , 3.9 ] ( FNB ) ; P < 0.0001 ) , but was not inferior to FNB with regard to Numeric Rating Scale pain scores ( 1.0 [ 0.0 , 3.5 ] ACB vs. 0.0 [ 0.0 , 1.0 ] FNB ; P = 0.019 ) , or to opioid consumption ( 32.2 [ 22.4 , 47.5 ] ACB vs. 26.6 [ 19.6 , 49.0 ] ; P = 0.0115 ) . At 24 and 48 h postanesthesia , there was no significant statistical difference in dynamometer results , pain scores , or opioid use between the two groups . Conclusion : At 6 to 8 h postanesthesia , the ACB , compared with the FNB , exhibited early relative sparing of quadriceps strength and was not inferior in both providing analgesia or opioid intake Total knee replacement ( TKR ) produces severe postoperative pain . Peripheral nerve blocks can be used as analgesic adjuncts for TKR , but the efficacy of femoral nerve blocks alone is controversial . The sciatic nerve innervates posterior regions of the knee ; thus , performance of both sciatic and femoral nerve blocks may be necessary to improve analgesia after TKR . We performed this study to determine whether peripheral nerve blocks improve analgesia after TKR . In a r and omized , double-blind fashion , 36 patients undergoing TKR received either femoral , sciatic-femoral , or sham nerve blocks after a st and ardized spinal anesthetic . Further postoperative analgesia was provided by patient-controlled IV morphine and ketorolac .  Pain at rest and with physical therapy , morphine use , nausea , pruritus , sedation , and patient satisfaction were assessed . Patients receiving peripheral nerve  blocks reported better analgesia at rest for at least 8 h after transfer to the hospital ward ( P < 0.05 ) . Morphine use was decreased by approximately 50 % in the peripheral nerve block groups until the second postoperative day ( P < 0.02 ) . Side effect profiles and patient satisfaction were similar between groups . We conclude that femoral nerve blocks improve analgesia and decrease morphine use after TKR . The addition of a sciatic nerve block to the femoral nerve block did not further improve analgesic efficacy . Implication s : Performance of femoral nerve blocks improves analgesia and decreases the need for morphine after total knee replacement surgery . The addition of a sciatic nerve block to the femoral nerve block does not provide additional benefits . ( Anesth Analg 1998;87:93 - 7 Background and Objectives Adductor canal block ( ACB ) has been suggested as an analgesic alternative to femoral nerve block ( FNB ) for procedures on the knee , but its effect on quadriceps motor function is unclear . We performed a r and omized , blinded study to compare quadriceps strength following adductor canal versus FNB in volunteers . Our hypothesis was that quadriceps strength would be preserved following ACB , but not FNB . Secondary outcomes included relative preservation of hip adduction and degree of balance impairment . Methods The ACB was performed in one leg and the  FNB  in the contralateral leg in 16 volunteers using a r and omized block sequence . For all blocks , 15 mL of 3 % chloroprocaine was injected under ultrasonographic guidance . Maximal voluntary isometric contraction of knee extension and hip adduction was measured at baseline and at 30 and 60 minutes after block . After 60-minute assessment s were complete , the second block was placed . A test of balance ( Berg Balance Scale ) was performed 30 minutes after the first block only . Results Quadriceps strength and balance scores were similar to baseline following ACB . Following FNB , there was a significant reduction in quadriceps strength ( 95.1 % ± 17.1 % vs 11.1 % ± 14.0 % ; P < 0.0001 ) and balance scores ( 56 ± 0 vs 37 ± 17.2 ; P = 0.02 ) compared with baseline . There was no difference in hip adductor strength ( 97.0 % ± 10.8 % vs 91.8 % ± 9.6 % ; P = 0.17 ) . Conclusions Compared with FNB , ACB results in significant quadriceps motor sparing and significantly preserved balance Background : Whether decreasing the local anesthetic concentration during a continuous femoral nerve block results in less quadriceps weakness remains unknown . Methods : Preoperatively , bilateral femoral perineural catheters  were inserted in subjects undergoing bilateral knee arthroplasty ( n = 36 ) at a single clinical center . Postoperatively , right-sided catheters were r and omly assigned to receive perineural ropivacaine of either 0.1 % ( basal 12 ml/h ; bolus 4 ml ) or 0.4 % ( basal 3 ml/h ; bolus 1 ml ) , with the left catheter receiving the alternative concentration/rate in an observer- and subject-masked fashion . The primary endpoint was the maximum voluntary isometric contraction of the quadriceps femoris muscles the morning of postoperative day 2 . Equivalence of treatments would be concluded if the 95 % CI for the difference fell within the interval −20%–20 % . Secondary endpoints included active knee extension , passive knee flexion , tolerance to cutaneous electrical current applied over the distal quadriceps tendon , dynamic pain scores , opioid requirements , and ropivacaine consumption . Results : Quadriceps maximum voluntary isometric contraction for limbs receiving 0.1 % ropivacaine was a mean ( SD ) of 13 ( 8) N · m , versus 12 ( 8) N · m for limbs receiving 0.4 % [ intrasubject difference of 3 ( 40 ) percentage points ; 95 % CI −10–17 ; P = 0.63 ] . Because the 95 % CI fell within prespecified tolerances , we conclude that the effect of the two concentrations were equivalent . Similarly , there were no statistically significant differences in secondary endpoints . 
    Output:
    
Conclusions The present study suggests that TKA patients who receive ACB can achieve similar or even better recovery of quadriceps strength and mobilization ability than those treated with FNB .
Taken as a whole , ACB may be a better analgesia strategy after TKA at present