Single-injection or continuous femoral nerve block for total knee arthroplasty?
BACKGROUND
The ideal local anesthetic regime for femoral nerve block that balances analgesia with mobility after total knee arthroplasty (TKA) remains undefined.


OBJECTIVE
We compared two volumes and concentrations of a fixed dose of ropivacaine for continuous femoral nerve block after TKA to a single injection femoral nerve block with ropivacaine to determine (1) time to discharge readiness; (2) early pain scores and analgesic consumption; and (3) functional outcomes, including range of motion and WOMAC scores at the time of recovery.


METHODS
Ninety-nine patients were allocated to one of three continuous femoral nerve block groups for this randomized, placebo-controlled, double-blind trial: a high concentration group (ropivacaine 0.2% infusion), a low concentration group (ropivacaine 0.1% infusion), or a placebo infusion group (saline 0.9% infusion). Infusions were discontinued on postoperative Day (POD) 2. The primary outcome was time to discharge readiness. Secondary outcomes included opioid consumption, pain, and functional outcomes. Ninety-three patients completed the study protocol; the study was halted early because of unanticipated changes to pain protocols at the host institution, by which time only 61% of the required number of patients had been enrolled.


RESULTS
With the numbers available, the mean time to discharge readiness was not different between groups (high concentration group, 62 hours [95% confidence interval [CI], 51-72 hours]; low concentration group, 73 hours [95% CI, 63-83 hours]; placebo infusion group 65 hours [95% CI, 56-75 hours]; p = 0.27). Patients in the low concentration group consumed significantly less morphine during the period of infusion (POD 1, high concentration group, 56 mg [95% CI, 42-70 mg]; low concentration group, 35 mg [95% CI, 27-43 mg]; placebo infusion group, 48 mg [95% CI, 38-59 mg], p = 0.02; POD 2, high concentration group, 50 mg [95% CI, 41-60 mg]; low concentration group, 33 mg [95% CI, 24-42 mg]; placebo infusion group, 39 mg [95% CI, 30-48 mg], p = 0.04); however, there were no important differences in pain scores or opioid-related side effects with the numbers available. Likewise, there were no important differences in functional outcomes between groups.


CONCLUSIONS
Based on this study, which was terminated prematurely before the desired sample size could be achieved, we were unable to demonstrate that varying the concentration and volume of a fixed-dose ropivacaine infusion for continuous femoral nerve block influences time to discharge readiness when compared with a conventional single-injection femoral nerve block after TKA. A low concentration of ropivacaine infusion can reduce postoperative opioid consumption but without any important differences in pain scores, side effects, or functional outcomes. These pilot data may be used to inform the statistical power of future randomized trials.


METHODS
Level II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
Department of Anesthesia, Toronto Western Hospital, 399 Bathurst Street, Toronto, Ontario, M5T 2S8, Canada.
Eric
E
Albrecht
Dorothea
D
Morfey
Vincent
V
Chan
Rajiv
R
Gandhi
Arkadiy
A
Koshkin
Ki Jinn
KJ
Chin
Sylvie
S
Robinson
Philippe
P
Frascarolo
Richard
R
Brull
D000368:Aged; D000577:Amides / Q000008:administration & dosage*; D000701:Analgesics, Opioid / Q000627:therapeutic use; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000009:adverse effects; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D001696:Biomechanical Phenomena; D004311:Double-Blind Method; D057239:Early Termination of Clinical Trials; D005260:Female; D005267:Femoral Nerve; D006801:Humans; D007263:Infusions, Parenteral; D007267:Injections; D007719:Knee Joint / Q000294:innervation / Q000503:physiopathology / Q000601:surgery*; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000009:adverse effects / Q000379:methods*; D009864:Ontario; D010147:Pain Measurement; D010149:Postoperative Pain / Q000175:diagnosis / Q000209:etiology / Q000517:prevention & control*; D010351:Patient Discharge; D011446:Prospective Studies; D016059:Range of Motion, Articular; D020127:Recovery of Function; D000077212:Ropivacaine; D018401:Sample Size; D013997:Time Factors; D016896:Treatment Outcome
D000577:Amides; D000701:Analgesics, Opioid; D000779:Anesthetics, Local; D000077212:Ropivacaine