Is changing the postoperative pain management in total knee arthroplasty from femoral nerve block to local infiltration analgesia successful? Retrospective trial with the first and last 100 patients
Authors: Najfeld Michael , Hube Robert , Kujat Ann-Kathrin , Mayr Hermann Otto , Thiele Kathi 
Published: October 2020

Abstract
Purpose
In recent years, there has been an increasing interest in local infiltration analgesia (LIA) as a technique to control postoperative pain. We compared this technique to the gold standard the 3 in 1 femoral nerve block (FNB) in postoperative pain management after total knee arthroplasty (TKA) in a large patient population. This trial analyzes in the early postoperative phase the pain, range of motion, and consumption of pain medications after TKA.

Methods
We conducted a retrospective trial that included all patients who were undergoing primary TKA by one single surgeon in a high-volume arthroplasty center in 2015. Patients who have secondary osteoarthritis due to rheumatoid arthritis or previous knee arthrotomy, as well as revision cases, were excluded. The included patients were divided into 2 groups according to the applied pain management (group 1 FNB, group 2 LIA). Concerning the LIA group, a modified form of composition compared to the first describer without the use of adrenaline was carried out. Post-operative additional pain medications were given on a fixed scheme to the patient. The primary outcome was pain at rest over 7 days after surgery labeled by the numeric pain rating scale (NRS). The secondary outcome measures were the total amount of opioid consumption over the hospital stay and the additional need for non-opioid medication. The conversion of the opiate medications on the morphine preparation was carried out according to the conversion data from the literature. For functional recovery, we compared the range of motion in both groups, which was recorded from the second postoperative day by the attending physiotherapist.

Results
In total, 202 patients were assessed for eligibility and included in this clinical trial. Hundred patients were allocated to the continuous FNB group (group 1) and 102 patients to the LIA group (group 2). No statistical difference was found between the two groups regarding demographic data. Primary outcome measurements: The LIA group had a significantly lower NRS score than the continuous FNB group for the measurement in the morning on days 1, 2, and 3 after surgery (day 1, 1.5; day 2, 1.6; day 3, 1.3; p < 0.05). Secondary outcome measurements: The total volume of morphine consumption for the first six postoperative days was significantly lower in the LIA group than the FNB group (FNB 159.8 vs. LIA 96.07). There is also a significant difference between the total morphine consumption of both groups in the direct postoperative course with respect to time and group (two way ANOVA, p < 0.05) On the day of the operation and on the first postoperative day, the intake of additional non-opioids in the LIA group was also significantly reduced compared to the FNB group. No significant difference was observed on the second to sixth postoperative day concerning an additional consumption of non-opioid medications. In terms of range of motion, the LIA group showed a higher active range of motion at the operated extremity than the FNB group during the hospital stay.

Conclusion
The local intraarticular infiltration therapy (LIA) is a sufficient alternative to regional anesthesia avoiding the known risks of regional procedures. The results of this study reflect the efficiency of this pain management with a lower consumption of analgesics, identical to reduced postoperative pain ratings and an improved ROM in the first postoperative days.

Level of evidence
Retrospective trial