Abstract
Objective
Postoperative pain is severe after total knee arthroplasty (TKA). Therefore, femoral nerve block (FNB) is commonly used as an adjuvant to spinal anesthesia for TKA. Some anesthesia providers perform this preoperatively, while others perform it postoperatively. To our knowledge, no study has compared the relative benefits of the timing of performing the procedure. In this study, we investigated whether preoperative FNB would provide better analgesic effects than postoperative FNB in patients undergoing unilateral TKA.
Methods
In this double-blind, randomized, controlled trial, we divided 82 patients (ASA physical status I–III) undergoing unilateral TKA into four groups: (1) a pre-treatment group, in which FNB was performed with 0.4 mL/kg 0.375% bupivacaine plus 1:200,000 epinephrine after spinal anesthesia but before the operation; (2) a post-treatment group, in which FNB was performed with the same drugs at similar dosages immediately after the operation; (3) a pre-control group, in which FNB was performed with normal saline in the same volume as the tested drugs before the operation; and (4) a post-control group, in which FNB was performed with normal saline in the same volume as the tested drug after the operation. At 2, 4, 6, 24, 48 and 72 postoperative hours, we recorded cumulative morphine consumption, visual analog pain scales (VAS), the time of first request for morphine and its side effects. We also measured knee maximum flexion range of motion once a day for 3 days. Our primary aim was to obtain cumulative morphine consumption in 24 hours.
Results
Within the postoperative 24 hours, we found significant differences in cumulative morphine consumption between patients who received true FNB and those who did not (at 24 hours, treatment groups = 45.6 ± 31.7 and 33.5 ± 20.6 mg vs. controls = 70.8 ± 31.2 and 78.8 ± 37.7 mg, p < 0.001). We also found significant differences in VAS (at 24 hours, p < 0.001) and time to first request of morphine (p = 0.005) between the treatment group and the sham group. However, there were no significant differences in these values between the pre-surgical treatment group and the post-surgical treatment group. Beyond 24 hours, there were no significant differences in morphine consumption or maximum flexion range on day 2 and day 3 among the four groups.
Conclusion
Patients who received FNB used for total knee arthroplasty consumed significantly less postoperative morphine and had significant relief of post-TKA pain on postoperative day 1 than those who did not have FNB. However, at follow-up we found no significant differences in these values between those receiving FNB before surgery and those receiving it after surgery.
Keywords
arthroplasty, replacement, knee; femoral nerve; nerve block; pain, postoperative;
1. Introduction
Most patients who undergo total knee arthroplasty (TKA) will experience severe postoperative pain. Inadequate analgesia may impede early physical therapy and affect joint range of motion.1 Treatment regimens for managing post-TKR pain include oral analgesics, parenteral analgesics, intrathecal morphine, epidural analgesia and peripheral nerve blocks.2, 3, 4 Peripheral nerve blocks provide optimal analgesia with fewer side effects than intrathecal or epidural analgesia.3, 4
Femoral nerve block (FNB) is most commonly used in patients undergoing TKA. A single-injection FNB is reported to provide effective analgesia, facilitate physical therapy, and reduce length of stay in hospital.1 With regard to administration, one study found little difference between a single-injection FNB and continuous FNB in length of stay in hospital and functional recovery in TKA patients.5 Another study seeking ways to improve the effect of FNB by additionally blocking the sciatic nerve, found no synergic action.6 Therefore, a single-injection FNB is usually combined with intravenous patient-controlled analgesia (IVPCA), to effectively treat TKA pain.
Preemptive analgesia, which refers to the blockade of afferent nerve fibers before a painful stimulus, has been reported to result in more effective pain relief than the same pain drug is given after the stimulus.7 However, clinical studies are far from being unanimous in support of the relevance.7, 8 In addition, to our knowledge, no study has yet investigated the preemptive effect of nerve block alone in patients undergoing TKA. Therefore, we ventured to investigate whether preoperative FNB would have a better effect than postoperative FNB in patients receiving TKA. To do this, we performed a randomized, double-blind study in which patients scheduled for unilateral, primary TKA were randomly assigned to one of four groups: two treatment groups with one receiving bupivacaine FNB before surgery and one receiving the same bupivacaine FNB after surgery, and two control groups with one receiving normal saline (identical in volume as the tested drugs) before and one after surgery. Our primary goal was to ascertain the accumulated self-administered morphine consumption at 24 hours. Secondary intents were to know the visual analog scale (VAS) scores (at rest and on movement), the times to first request of morphine, morphine-related side effects at the same time point and maximal range of knee flexion on postoperative days 1, 2 and 3.
2. Materials and methods
In this randomized, double-blinded, placebo-controlled trial, we recruited patients scheduled for unilateral, primary TKA. We excluded patients aged <40 and >80 years old, of ASA (American Society of Anesthesiologists) physical status >3, with known hypersensitivities to any of the test substances used in this study, a history of substance abuse, contraindications to spinal anesthesia, having femoral neuropathy or a poor ability to communicate. Premedication was omitted. All patients received spinal anesthesia with 0.5% hyperbaric bupivacaine 10∼13 mg at the L2-5 interspace. Intraoperative sedation with incremental midazolam of 0.5 mg was left to the discretion of the anesthesiologist in charge. Informed written consent was obtained from each participant.
Patients were randomly assigned to four groups using computer-generated random numbers enclosed in envelopes. The patients, the pain management team, and the chart analysts were not informed of the patients' group assignment. Patients were told that, FNB if performed would result in motor blockade and decreased sensation of the anterior aspect of the thigh for 1 day. Patients were also taught how to use the patient controlled analgesic (PCA) apparatus postoperatively. Pre-treatment patients received FNB with 0.4 mL/kg 0.375% bupivacaine and 1:200,000 epinephrine after spinal anesthesia but before the surgical procedure was performed. Post-treatment patients received identical drugs for the FNB immediately after completion of surgery. Pre-controls received a volume of normal saline equal to that of FNB before surgery and post-control group patients received the saline as in the pre-control group after surgery. Under ultrasound guidance, a 22-gauge insulated Stimuplex A needle (B. Braun, Melsungen, Germany) connected to Stimuplex HNS 11 nerve stimulator (B. Braun) was laterally inserted to the pulsatile femoral artery at the level of the inguinal crease. After eliciting a quadricep contraction at 0.2 to 0.5 mA, the drug solution was injected. Success of the block could not be evaluated in the operating room because patients were under spinal anesthesia.
All patients in the four groups received the femoral nerve block (true or sham) after spinal anesthesia. In so doing, the patient's comfort would be increased in exchange for an increased risk of nerve injury, because after spinal anesthesia, patients do not feel pain upon nerve damage. Therefore, we combined ultrasound imaging and nerve stimulators to avoid nerve injury9 and added epinephrine to the local anesthetic to increase the duration and intensity of the block.10
A PCA pump was started to convey morphine hydrochloride when the patient arrived in the post anesthesia care unit (PACU), the delivery of which was programmed with a bolus dose of 1 mg, a lockout interval of 5 minutes, and a 4-hour maximum dose of 30 mg. A nurse anesthetist followed up the patients at 2 hours, 4 hours, 6 hours, 24 hours, 48 hours and 72 hours postoperatively and recorded the data. Bolus dosage could be adjusted by increasing or decreasing 0.4 mg every 1 to 2 hours, if postoperative pain control was unsatisfactory. Postoperative nausea and vomiting (PONV) was treated with prochlorperazine 5 mg. Pain was rated using the 0–10 Numeric Pain Intensity Scale (0 = no pain, 10 = worst pain). Our hospital routinely starts postoperative physiotherapy after 1 postoperative day. Flexion range of motion was recorded at each physiotherapy session. Our primary outcome variable was cumulative morphine dosage. Secondary outcome variables were time to first request of morphine, VAS score (during rest and physiotherapy), morphine-related side effects at various post-operative time points and maximal flexion range of motion on days 1, 2, and 3. The protocol for this study was approved by our hospital's Institutional Review Board.
All values were presented as mean ± standard deviation. Patient characteristics were analyzed using χ2 tests (or Fisher's exact test) and one-way ANOVA with post-hoc comparisons. In a preliminary trial, morphine consumption between 6 and 24 postoperative hours within each subject group was normally distributed with a standard deviation (SD) of 5.1. If the true difference in mean scores of the treatment and control groups was one SD, we needed to study 17 experimental subjects and 17 control subjects to be able to reject the null hypothesis. The mean number of subjects in the treatment groups and control groups were enough to give us a probability (power) of 0.8. The Type I error probability associated with this test of null hypothesis was 0.05. All statistical analyses were performed using SPSS version 12.0 (SPSS Inc., Chicago, IL, USA).
3. Results
Eighty-eight patients were recruited, of whom 6 were excluded from the study due to severe allergy to morphine, communication difficulties, multiple operations and loss of follow-up, leaving 82 participants to complete the study. The four groups were similar in age, height, weight, ASA status and history of medical diseases (Table 1). The average operation time was 2.51 hours. No patient was found to have nerve injury 3 days after surgery.
We wanted to know if there was a difference in morphine consumption between the pre- and post-treatment groups (Table 2). We found no significant difference between the two groups on postoperative day 1, although the patients in these two treatment groups consumed significantly less morphine than patients in untreated groups (accumulative morphine consumption being 18.24 ± 12.68 mg and 13.3 ± 8.24 mg vs. 28.32 ± 12.48 mg and 31.25 ± 15.08 mg, respectively, at 24 hours; p < 0.001). Patients in the post-treatment group consumed less morphine than those in the pre-treatment group within the first 6 postoperative hours, although by 6 hours, the differences were not significant statistically (accumulative morphine consumption in mg at 6 hours, being 8.9 ± 10.0 in the pretreatment group vs. 4.08 ± 3.76 in the post-treatment group; p = 0.28). By postoperative days 2 and day 3, there was no significant difference in daily morphine consumption among any of the four groups.
On post-operative day 1, the treatment groups had significantly lower pain scores at rest and during physical therapy than the control groups at 24 hours (VAS-R, treatment groups = 1.9 ± 1.2 and 1.6 ± 1.3 vs. controls = 3.9 ± 1.2 and 3.8 ± 1.3, p = < 0.001; VAS-M, treatment groups = 3.8 ± 1.8 and 3.7 ± 1.2 vs. controls = 5.3 ± 1.2 and 4.7 ± 1.5, p = 0.002). Later, the patients in the two treatment groups reported significantly less pain at rest than did the control groups on post-operative day 2 (VAS-R, treatment groups = 1.7 ± 1.0 and 1.6 ± 1.1 vs. controls = 2.8 ± 1.3 and 3.3 ± 1.3, p = 0.001) and day 3 (VAS-R 1.4 ± 0.9 and 1.4 ± 1.6 vs. 1.9 ± 1.0 and 2.5 ± 1.2, respectively, p = 0.02), although during physical therapy on post-operative days 1 and 2, there were no significant differences in reporting pain among the four groups (Table 3).
Patients in the two treatment groups had a significantly longer time to first request for morphine than the controls (247.0 ± 380.0 and 258.1 ± 56.3 minutes vs. 60.9 ± 13.6 and 65.3 ± 14.2 minutes, respectively; p = 0.05) (Table 3), although there was no significant difference between the pre- and post-treatment groups. There was no statistical group difference in maximal range of knee motion values on days 1, 2 or 3 among any of the four groups (Table 3). The controls had significantly more morphine-related dizziness and vomiting than the treatment groups, although the treatment groups complained about tension on the back of the knee more frequently than the controls (Table 4).
4. Discussion
This study found no significant difference in the effect of pre- and post-operative treatment with FNB in our patients receiving TKA. Compared with untreated groups, those in the treatment group receiving FNB had significant reductions in post-operative pain, morphine dosage, and morphine-related side effects on post-operative day 1 (Table 2, Table 3, Table 4), during which those receiving FNB used 50% less morphine than those who did not receive FNB. However, we found no significant difference in morphine usage between pre- and post-operative treatment groups on that day. In addition, we did not find a significant difference in the range of motion in any of the four groups on post-operative days 1, 2, and 3.
There are a number of treatments for postoperative pain. The doctrinaire sense appears to shift towards multimodal techniques principally with regional anesthesia.11, 12, 13 These approaches have been found to have preemptive effects.11 We did not find regional anesthesia alone to have a preemptive effect in our studied subjects. On the contrary, the treatment group receiving postoperative FNB in our study tended to require less morphine than those treated with FNB preoperatively in the early postoperative period, although the difference was not significant. This difference might have been due to the analgesic effect of FNB, which wore off about 6 or 7 hours after surgery in the preoperative treatment group, whereas it wore off after 9 to 10 hours in the postoperative group.
It has been reported that most of the analgesic benefit of peripheral blockade seems to occur during the early post-operative period after TKA, with very little effect extending beyond 48 hours.14, 15 Good postoperative pain control has been reported to accelerate rehabilitation.16 However, we did not find a significant difference in this measure among the four groups, even though the treatment groups reported had less postoperative pain than the controls. The reason for this is unclear, but it may be related to goal-setting. If the patients were given goals emphasizing the range of motion by the nurses, they might have worked toward that goal despite the pain they were experiencing during physical therapy.
We found a significant difference between the patients in the treatment groups and controls with regard to the time to first request for morphine (treatment group = about postoperative 4 hours vs. controls = 1 hour; p = 0.005). This difference might be the result of the durability of the single-injection FNB and spinal anesthesia. One previous study reported a single-injection FNB with 0.25% bupivacaine to be an effective method for post-TKA analgesia, particularly at the first 10 hours after spinal anesthesia,17 with which our findings completely accorded, as no morphine was requested until about 7 hours after spinal anesthesia in our patients. Therefore, FNB greatly reduced pain in the early postoperative period, regardless of whether it was administered before or after surgery.
As expected, patients who did not receive FNB had more morphine-related side effects (dizziness, vomiting) in postoperative day 1. Interestingly, however, patients who received FNB treatment complained of tension in the back of the knee that had been subjected to surgery more than those who did not have surgery in that way. The difference might be related to the fact that FNB just blocked the anterior aspect of the knee, making the pain over the back of the knee, where the sciatic nerve is obviously located. This might be resolved by adding a sciatic nerve block to the FNB.18
Neuropathy of FNB is rare (0.34:100), and 99% of neuropathy is transient.19, 20, 21 In our study, no patient had neuropathy within the first three postoperative days. FNB is carried out with the risk of falls within the first 2 post-operative days due to persistent quadricep weakness.22 In our hospital, patients after TKA are allowed to walk after removal of the drain, which is performed after the second postoperative day. None of the patients in our study sustained a fall.
Our study has some limitations. FNBs were entrusted to two different anesthesiologists and the TKAs were performed by four different surgeons. Therefore, our findings might be confounded somewhat by personal skillfulness. Furthermore, although we could blind patients to know to which group they belonged, we could not blind them whether they belonged to the pre- or post-treatment group.
5. Conclusion
Although this study found that FNB could improve post-TKA pain, we found no significant benefit between performing FNB block preoperatively and performing it postoperatively. Therefore, preoperative and postoperative treatment using femoral nerve block combined with IVPCA can be used equally well to treat post-TKA pain. We did not, however, find that they shortened the time needed for rehabilitation therapy in our study.
Financial support
VGHKS98-065, VGHKS97-084 from Kaohsiung Veterans General Hospital.