Impact of peripheral nerve block with low dose local anesthetics on analgesia and functional outcomes following total knee arthroplasty: a retrospective study

Abstract

Objective: While the safety and efficacy of peripheral nerve blocks for postoperative pain management has been established in several well controlled prospective trials, the local anesthetic (LA) concentration and volume used in these studies was associated with a significant increase muscle weakness due to motor nerve block. The purpose of the present retrospective study of patients undergoing total knee arthroplasty was to assess the relative analgesic efficacy and functional outcomes of the low concentration, low volume of LA used in peripheral nerve blocks for postoperative pain management.

Methods: Twenty-four months of deidentified patient data were extracted from an electronic medical record system. All patients received opioids with or without continuous femoral and sciatic nerve block infusions for postoperative analgesia. Pain (resting and with activity), cumulative opioid and LA use were primary endpoints, participation in physical therapy (PT), muscle strength deficits and length of hospital stay (LOS) were secondary endpoints.

Results: Postoperative pain and opioid use were significantly lower in patients with peripheral nerve blocks (n = 1,329) than those with opioids alone (n = 439). There was no detectable decrease in strength associated with nerve blocks, while a significantly greater proportion of patients with nerve blocks were able to participate in PT on postoperative day 1 (96.4% vs 57.1%). These differences were not due to the impact of the surgeon per se, but whether or not the surgeon used nerve blocks for pain management. There was a small but statistically significant decrease in the average LOS in patients with blocks.

Conclusion: This analysis supports the use of low concentration, low volume of LA based peripheral nerve blocks for postoperative pain management.

Keywords: Acute Pain; Analgesic; Knee Pain; Narcotics; Regional Pain.

Figure 1

Flow of screening process used inclusion of patient data extracted from the electronic medical record system in the retrospective analysis.

Figure 2

Pain, opioid use and PT participation in TKA patients with and without peripheral nerve blocks. Patient report of pain intensity on the visual analog scale (VAS) was used to assess average pain at rest (A), in patient with and without peripheral nerve blocks in the post-anesthesia care unit (PACU), and on post-operative day (POD), 1, 2 and 3. Data were analyzed with a mixed design two-way ANOVA which revealed patients with nerve blocks were associated with significantly less pain (A) and less opioid use (B) (p<0.01). Percentage of patients participating in PT on POD 1 was compared between those with blocks and those without using Chi-square test (C). The analysis indicated that significantly more patients with blocks were able to participate in PT on POD1 (C) (p<0.01). ** is p < 0.01

Figure 3

Average resting pain (A) and opioid use (B) on POD1 in TKA patients analyzed as a function of the surgeon who performed the procedure. Surgeon 1,2, 3 and 4 used nerve blocks for their TKA patients, while surgeon 6,7 and 8 did not. Surgeon 5 had roughly equal numbers of patients who received nerve blocks vs. no blocks. The number of patients for each surgeon is indicated above the bars. + indicates patients with peripheral nerve blocks, − indicates patients with no nerve blocks; ** is p < 0.01

Figure 4

Pain (A), opioid use (B) and PT participation (C) on POD1 for patients from surgeon #5 in Figure 3 analyzed as a function of whether or not the received peripheral nerve blocks. The number of patients in each group is indicated in parentheses above the columns. ** is p < 0.01