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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptNIH Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Anesth Analg. Author manuscript; available in PMC Feb 3, 2012.
Published in final edited form as:
PMCID: PMC3271722
NIHMSID: NIHMS352611

The Association Between Lower Extremity Continuous Peripheral Nerve Blocks and Patient Falls After Knee and Hip Arthroplasty

Abstract

Background

Continuous peripheral nerve blocks (CPNB) may induce muscle weakness, and multiple recently published series emphasize patient falls after post-arthroplasty CPNB. However, none have included an adequate control group, and therefore the relationship between CPNB and falls remains speculative.

Methods

We pooled data from 3 previously published randomized, triple-masked, placebo-controlled studies of CPNB involving the femoral nerve after knee and hip arthroplasty.

Results

No patients receiving perineural saline (n=86) fell (0%, 95%CI = 0–5%), but there were 7 falls in 6 patients receiving perineural ropivacaine (n=85; 7%, 95%CI = 3–15%; Fisher’s exact test p=0.013).

Conclusions

Our analysis suggests there is a causal relationship between CPNB and the risk of falling after knee and hip arthroplasty.

Introduction

More than one-million knee and hip arthroplasties are performed every year in the United States alone, and that number is expected to grow to 4-million annually within the next 20 years.1 Continuous peripheral nerve blocks (CPNB) are often used to provide postoperative analgesia for these often painful procedures. Although inhibition of pain fibers is the primary goal of CPNB, currently available local anesthetics approved for clinical use often decrease other afferent (e.g., nonpain-related sensory and proprioception) and efferent (e.g., motor) nerve fibers as well,2 resulting in undesirable side effects such as muscular weakness that is particularly undesirable in CPNB that affect the femoral nerve and quadriceps femoris function required for ambulation.3 Also, in contrast to the numerous articles in anesthesiology-centered journals emphasizing the multiple benefits of CPNB, publications of patient series emphasizing falls associated with CPNB have recently appeared within the surgical literature.4;5 For example, Feibel et al. report a 0.7% fall rate in a series of 1190 post-knee arthroplasty patients with a femoral CPNB.5 Unfortunately, none of these series included an adequate control group to determine whether the CPNB added to the risk of patient falls. Therefore, it remains unknown whether the falls, common in elderly surgical patients after joint arthroplasty without regional analgesia,6 would have occurred regardless of the perineural local anesthetic infusion.7 In the current report we pool data from 3 previously published randomized, triple-masked, placebo-controlled studies of CPNB involving the femoral nerve to determine if there is a causal relationship between lower extremity CPNB and postoperative falls after knee and hip arthroplasty.

Methods

Data available from previously published multicenter, randomized, triple-masked, placebo-controlled reports involving CPNB affecting the femoral nerve after knee and hip arthroplasty were pooled.810 No IRB oversight was required since the Common Rule exempts research “involving the collection or study of existing data… if these sources are publicly available or if the information is recorded by the investigator in a manner that subjects cannot be identified, directly or through identifiers linked to the subjects.”11,12 The primary outcome of the analysis was prospectively specified as the number of patient falls in each treatment group: either perineural ropivacaine 0.2% or perineural normal saline. Secondary outcomes included the association of other patient variables with the risk of falls. We first analyzed descriptive summaries of fall status for age, gender, weight, height, body mass index, surgical time, hospitalization duration, quadriceps weakness leading to local anesthetic basal infusion decrease, and ambulatory distance for each of the 3 days after surgery in the subgroup of patients that received ropivacaine. The primary end point, the comparison of proportion of falls across treatment groups, was analyzed with Fisher’s exact test applied to the pooled sample. We also checked for balance across treatment arms with respect to relevant covariates with, two-sample t-tests and Fisher's exact tests within each study and in the pooled sample. We applied the same tests to check for balance between those who fell and those who did not fall in order to identify any covariates that might also explain differential fall rates. We applied Pearson’s chi-squared test to examine differences in the fall rate across the 3 studies, and generated one sample 95% confidence intervals for the fall rate by inverting the score test and clipping the interval to 0–1.13 All analyses were performed using R version 2.11 (2010).

Results

Of the 3 multicenter studies included in the analysis, 2 involved femoral and one posterior lumbar plexus (blockade of the lateral femoral cutaneous and obturator nerves in addition to the femoral nerve) CPNB. No patients of the control groups (pooled n=86) fell (0%, 95% confidence interval = 0–5%) while receiving perineural normal saline, but there were 7 falls in 6 patients receiving perineural ropivacaine (pooled n=85; 7%, 95% confidence interval = 3–15%); p=0.013 (Tables 1 and and2).2). In addition, among patients who received ropivacaine, the fall rate was not different across the 3 studies to a statistically significant degree (Pearson’s Chi-squared = 1.47, df=2, p=0.48). Of the secondary outcomes (Table 3), it is noteworthy that of patients who experienced a fall (n=6), the time to discharge was less (mean [SD] = 3.0 [0.0] days) than in patients who did not experience a fall (n=165; 3.4 [1.0] days; p<0.001).

Table 1
Details on the individual patient falls
Table 2
Key covariates by treatment assignment (pooled data)
Table 3
Key covariates by outcome (No Fall vs. Fall, pooled data)

Discussion

While all 3 previously published multicenter, randomized, triple-masked, placebo-controlled investigations reported patient falls during ropivacaine perineural infusion and none during saline perineural saline infusion, these between-treatment differences did not reach the level of statistical significance and no conclusions were offered regarding the association of CPNB and the risk of falling.810 However, when pooled for the current analysis, the 7 falls in 6 patients receiving ropivacaine versus no patients receiving saline (p=0.013) does suggest that there is a causal relationship between CPNB affecting quadriceps strength and the risk of falling after knee and hip arthroplasty (none wore a knee immobilizer). While the major limitation of this analysis is selection bias, until additional data are available practitioners may want to consider steps that may minimize the risk of falls. Such steps include, but are not limited to, minimizing the dose/mass of local anesthetic;14 providing limited-volume patient-controlled bolus doses which allow for a decreased basal dose without compromising analgesia in some cases,15;16 although not all;17 using a knee immobilizer and walker/crutches during ambulation;18 and educating physical therapists, nurses, and surgeons of possible CPNB-induced muscle weakness and necessary fall precautions. In addition, since the risk of falling was associated with earlier discharge (P<0.001) and 4 of the 7 falls occurred after discharge (after previous successful in-hospital ambulation), practitioners may wish to include the risk of falling as part of patient informed consent before ambulatory CPNB after knee and hip arthroplasty.

Acknowledgments

Financial Support: Funding for this project provided by National Institutes of Health grant GM077026 (P.I.: Dr. Ilfeld) from the National Institute of General Medical Sciences (Bethesda, Maryland, USA); National Institutes of Health grant RR000827 from the National Center for Research Resources (Bethesda, Maryland, USA); and the University of California San Diego Department of Anesthesiology, San Diego, California.

Footnotes

Conflict of Interest: Dr. Ilfeld received funding for the 3 previously published studies included in this analysis from Arrow International (Reading, Pennsylvania, USA), B. Braun Medical (Bethlehem, Pennsylvania, USA), and Stryker Instruments (Kalamazoo, Michigan, USA). These companies had absolutely no input into any aspect of the present study conceptualization, design, and implementation; data collection, analysis and interpretation; or manuscript preparation of the previously published investigations or the current study.

R Software Environment for Statistical Computing, R Foundation for Statistical Computing, Vienna, Austria. Available at: http://www.r-project.org. Accessed May 17, 2010.

References

1. Kurtz S, Ong K, Lau E, Mowat F, Halpern M. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg.Am. 2007;89:780–785. [PubMed]
2. Ilfeld BM, Yaksh TL. The end of postoperative pain--a fast-approaching possibility? And if so will we be ready? Reg Anesth Pain Med. 2009;34:85–87. [PubMed]
3. Borgeat A, Kalberer F, Jacob H, Ruetsch YA, Gerber C. Patient-controlled interscalene analgesia with ropivacaine 0.2% versus bupivacaine 0.15% after major open shoulder surgery: The effects on hand motor function. Anesth.Analg. 2001;92:218–223. [PubMed]
4. Kandasami M, Kinninmonth AW, Sarungi M, Baines J, Scott NB. Femoral nerve block for total knee replacement - a word of caution. Knee. 2009;16:98–100. [PubMed]
5. Feibel RJ, Dervin GF, Kim PR, Beaule PE. Major complications associated with femoral nerve catheters for knee arthroplasty: a word of caution. J Arthroplasty. 2009;24:132–137. [PubMed]
6. Stevens JE, Mizner RL, Snyder-Mackler L. Quadriceps strength and volitional activation before and after total knee arthroplasty for osteoarthritis. J Orthop.Res. 2003;21:775–779. [PubMed]
7. Ackerman DB, Trousdale RT, Bieber P, Henely J, Pagnano MW, Berry DJ. Postoperative patient falls on an orthopedic inpatient unit. J Arthroplasty. 2010;25:10–14. [PubMed]
8. Ilfeld BM, Le LT, Meyer RS, Mariano ER, Vandenborne K, Duncan PW, Sessler DI, Enneking FK, Shuster JJ, Theriaque DW, Berry LF, Spadoni EH, Gearen PF. Ambulatory continuous femoral nerve blocks decrease time to discharge readiness after tricompartment total knee arthroplasty: a randomized, triple-masked, placebo-controlled study. Anesthesiology. 2008;108:703–713. [PMC free article] [PubMed]
9. Ilfeld BM, Ball ST, Gearen PF, Le LT, Mariano ER, Vandenborne K, Duncan PW, Sessler DI, Enneking FK, Shuster JJ, Theriaque DW, Meyer RS. Ambulatory continuous posterior lumbar plexus nerve blocks after hip arthroplasty: a dual-center, randomized, triple-masked, placebo-controlled trial. Anesthesiology. 2008;109:491–501. [PMC free article] [PubMed]
10. Ilfeld BM, Loland VJ, Donovan JF, Le LT, Mariano ER. A multicenter, randomized, triple-masked, placebo-controlled trial of the effect of ambulatory continuous femoral nerve blocks on discharge-readiness following total knee arthroplasty in patients on general orthopaedic wards. Reg Anesth Pain Med. 2010;35(2):A2. [PMC free article] [PubMed]
11. The Common Rule, Title 45 (Public Welfare), Code of Federal Regulations, Part 46 (Protection of Human Subjects) U.S. Department of Health and Human Services, National Institutes of Health, and Office for Human Research Protections. 2001:1–18.
12. Ilfeld BM. Informed consent for medical research: an ethical imperative. Reg Anesth Pain Med. 2006;31:353–357. [PubMed]
13. Newcombe RG. Two-sided confidence intervals for the single proportion: comparison of seven methods. Stat Med. 1998;17:857–872. [PubMed]
14. Ilfeld BM, Moeller LK, Mariano ER, Loland VJ, Stevens-Lapsley JE, Fleisher AS, Girard PJ, Donohue MC, Ferguson EJ, Ball ST. Continuous Peripheral Nerve Blocks: Is Local Anesthetic Dose the Only Factor, or Do Concentration and Volume Influence Infusion Effects as Well? Anesthesiology. 2010;112:347–354. [PubMed]
15. Capdevila X, Dadure C, Bringuier S, Bernard N, Biboulet P, Gaertner E, Macaire P. Effect of patient-controlled perineural analgesia on rehabilitation and pain after ambulatory orthopedic surgery: A multicenter randomized trial. Anesthesiology. 2006;105:566–573. [PubMed]
16. Ilfeld BM, Morey TE, Enneking FK. Infraclavicular perineural local anesthetic infusion: a comparison of three dosing regimens for postoperative analgesia. Anesthesiology. 2004;100:395–402. [PubMed]
17. Ilfeld BM, Morey TE, Wright TW, Chidgey LK, Enneking FK. Interscalene perineural ropivacaine infusion: a comparison of two dosing regimens for postoperative analgesia. Reg Anesth Pain Med. 2004;29:9–16. [PubMed]
18. Muraskin SI, Conrad B, Zheng N, Morey TE, Enneking FK. Falls associated with lower-extremity-nerve blocks: a pilot investigation of mechanisms. Reg Anesth Pain Med. 2007;32:67–72. [PubMed]