Continuous femoral nerve block (CFNB) is effective for pain management after total knee arthroplasty (TKA), but leads to quadriceps femoralis muscle weakness, which causes postoperative ambulation disability and falls.1 However, no study has compared quadriceps strength during CFNB using different levobupivacaine concentrations. We tested the hypothesis that different concentrations of levobupivacaine (0.5 mg ml−1 as the low concentration vs. 1.0 mg ml−1 as the high concentration) administered at the same rate (4 ml h−1) cause similar muscle weakness when used for CFNB following TKA.
This study (JPRN-UMIN000006893) was performed after approval from the Institutional Review Board of Osaka University Medical Hospital, Japan (Chairperson Prof. K. Asano, Committee No. 11246) and with written informed consent. Patients aged more than 20 years, who were scheduled to undergo primary TKA from January to August 2012, were randomised to continuous 0.5 mg ml−1 (low concentration: 0.05% wt/vol) or 1.0 mg ml−1 (high concentration: 0.10% wt/vol) levobupivacaine infusion for CFNB with a portable infusion pump (Coopdech Baloonjector 300; Daiken Medical, Osaka, Japan). The patients, research evaluators and study coordinator were blinded to the contents of the infusion pump.
All patients received a selective tibial nerve block with 15 ml of levobupivacaine 2.5 mg ml−1 under ultrasound guidance (M-Turbo; SonoSite Inc., Seattle, Washington, USA) using a CFNB catheter (Contiplex D; B. Braun, Melsungen, Germany). The catheter was inserted using an in-plane approach into the lateral segment of the groove formed by the iliopsoas muscle.2 After general anaesthesia was induced, a leg tourniquet was inflated to 300 mmHg for up to 120 min. At the end of surgery, the randomised levobupivacaine infusion, at 4 ml h−1, was commenced through the CFNB catheter and continued to 60 h postoperatively when the CFNB catheter was removed.
Muscle strength was evaluated using an isometric force electromechanical dynamometer (μ-TAS F1; Anima, Tokyo, Japan), which measures the force produced during maximum voluntary isometric contraction (MVIC).1,3 These MVIC measurements were performed on the day before surgery (baseline) and at 24, 48 and 72 h postoperatively. All measurements were expressed as a percentage of the baseline.1,3 The visual analogue pain scores (VAPS, 0 to 100 mm) for pain at rest, rehabilitation and the evaluation of straight leg raise (SLR) were also recorded. The numbers of days required to achieve 120° knee flexion and early discharge criteria (including a VAPS <30 mm at rest, 70 m of ambulation with a walker and 90° knee flexion)4 were recorded.
The primary endpoint was the difference in quadriceps MVIC 24 h after surgery, expressed as a percentage [MVIC% = (postoperative MVIC/preoperative MVIC) × 100]. We applied the two one-sided test procedure with the 90% confidence interval (CI) to evaluate equivalence. We considered a less than 15% difference in MVIC% clinically irrelevant.1 Data are presented as mean (SD) or median (range) or count (%). Unpaired Student's t-test, Mann–Whitney U test and Fisher exact test were used as appropriate. A P value less than 0.05 (two-sided) was considered significant.
Seventeen patients were enrolled in each group. Quadriceps MVIC% declined to 29.5% (9.0) and 30.6% (13.4) in the low and high concentration groups, respectively, at 24 h after surgery. As the 90% CI of the difference at –5.5 to – 7.8 (P = 0.99; Table 1) was within the equivalence range of ± 15%, we concluded equivalence for the effect of the levobupivacaine concentrations on quadriceps MVIC%. Similarly, it was also equivalent at 48 h. However, MVIC% at 72 h was not equivalent. Other endpoints including VAPS were not significantly different (Table 1).
This double-blind trial has provided evidence that low and high concentrations of levobupivacaine induce equivalent quadriceps weakness at up to 48 h postoperatively. These results suggest the difficulties in managing quadriceps strength are not influenced by simply adjusting levobupivacaine concentrations. CFNB is a good alternative for pain management after TKA, but it may be unsuitable for fast-track rehabilitation. Options available are to use CFNB with intermittent bolus techniques5 and knee-stabilising supports until complete motor function is regained, periarticular injection or adductor canal block with a robust multimodal analgesia protocol.6,7
Our trial had some limitations. The preoperative administration of 37.5 mg of levobupivacaine at 2.5 mg ml−1 into CFNB could contribute to quadriceps weakness at 24 h postoperatively, as only half of the individuals could perform SLR. It is also difficult to control for any effect of the surgery itself on motor function with this design.
In conclusion, we found equivalent quadriceps weakness from CFNB with 0.5 and 1.0 mg ml−1 levobupivacaine with CFNB following TKA.
Acknowledgements relating to this article
Assistance with the study: the manuscript has been carefully reviewed by Enago, Crimson Interactive Pvt. Ltd.
Dr Takayuki Yoshida (Department of Anaesthesiology, Niigata University Hospital, Niigata, Japan) and Dr Kayo Takimoto (Department of Anaesthesiology, Ikeda City Hospital, Ikeda, Japan) provided advice to the authors.
Financial support and sponsorship: the research was funded by Maruishi Pharmaceutical Ltd., Osaka, Japan, who had no input or influence into any aspect of the study design or manuscript preparation.
Conflicts of interest: none.
1. Ilfeld BM, Moeller LK, Mariano ER, et al. Continuous peripheral nerve blocks: is local anaesthetic dose the only factor, or do concentration and volume influence infusion effects as well? Anesthesiology
2. Fanara B, Christophe JL, Boillot A, et al. Ultrasound guidance of needle tip position for femoral nerve blockade: an observational study. Eur J Anaesthesiol
3. Roy MA, Doherty TJ. Reliability of hand-held dynamometry in assessment of knee extensor strength after hip fracture. Am J Phys Med Rehabil
4. Sakai N, Inoue T, Kunugiza Y, et al. Continuous femoral versus epidural block for attainment of 120° knee flexion after total knee arthroplasty: a randomized controlled trial. J Arthroplasty
5. Soltész S, Biedler A, Saxler G, et al. Intermittent sciatic block combined with continuous femoral block for patients undergoing knee arthroplasty: a retrospective analysis of 208 patients. Eur J Anaesthesiol
6. Carli F, Clemente A, Asenjo JF, et al. Analgesia and functional outcome after total knee arthroplasty: periarticular infiltration vs continuous femoral nerve block. Br J Anaesth
7. Jaeger P, Zaric D, Fomsgaard JS, et al. Adductor canal block versus femoral nerve block for analgesia after total knee arthroplasty: a randomized, double-blind study. Reg Anesth Pain Med