Femoral nerve block complications for total knee... : Clinical Orthopedics and Related Research® (2023)


Multimodal and preemptive analgesia protocols for TKA have been effective in reducing the need for narcotics in the immediate postoperative period. These pain control protocols are associated with decreased side effects of intravenous narcotics such as nausea, vomiting, hypotension, respiratory depression, and constipation.3, 4, 8, 17, 18], which can delay rehabilitation [10, 16] Optimal postoperative analgesia can lead to early mobilization, ambulation, and return to a normalized gait pattern. Prevention of arthrofibrosis is achieved with early maximization of range of motion [5, 13, 22].

Single-dose femoral nerve block is reportedly effective in reducing pain and accelerating rehabilitation after TKA [19, 21] The risk of peripheral neuropathy after femoral nerve block has been estimated to be approximately three in 10,000.2] However, there is limited information on complications associated with femoral nerve blocks and TKA [7, 19, 21] Singelyn et al. compared femoral nerve block, epidural anesthesia, and patient-controlled anesthesia [19] There was a significant decrease in urinary retention in patients treated with a femoral nerve block. Toftdahl et al. compared peri- and intra-articular analgesia with femoral nerve block [21] There was no difference in terms of nausea, vomiting and dizziness.

Therefore, we hypothesized that patients with a femoral nerve block for postoperative analgesia after TKA would have a shorter hospital stay, a reduced number of postoperative complications and accelerated rehabilitation, leading to earlier maximization of range of motion, decreased arthrofibrosis and earlier mobilization than patients not receiving a femoral nerve block.

Patients and methods

From our database, we retrospectively identified and reviewed the medical records of all 970 patients with primary, bilateral, and revision TKA performed between January 1, 2005 and December 31, 2007. Seven hundred and fifty-seven TKA in 729 (75%) patients were treated with a preoperative femoral nerve block. Patients were divided into two groups: those who received a femoral nerve block (FNB, n = 729) and those who did not (non-FNB, n = 241). The selection of patients for BNF was at the discretion of the anesthesiologist. Data on all patients undergoing total joint arthroplasty are collected prospectively as part of our shared institutional record database. Patients' hospital records, morbidity and mortality minutes, and the registry were reviewed to identify patients in whom an operative or perioperative complication secondary to BNF occurred. The preoperative characteristics of both groups were similar (Table 1), including the mean body mass index (32.1 kg/m²)2in the FNB group and 32.5 kg/m2in the non-FNB group). The minimum follow-up was 12 months (mean 24 months; range 12 to 36 months). No patients were lost to follow-up. Institutional Review Board approval was obtained prior to conducting this study.

Patients diagnosed with pneumonia had a documented postoperative diagnosis of pneumonia recorded in their postoperative codes, resulting in a prolonged infectious hospital stay beyond the usual 4-5 day hospital stay. Neuralgia or neuritis was diagnosed based on electromyography/nerve conduction test studies that documented abnormality with motor or sensory changes in the femoral nerve more than 3 months after BNF and TKA. In addition, clinical presentation, physical examination and patient history confirmed symptoms of femoral neuropathy/neuritis in the affected extremities. Symptoms such as extreme weakness of the quadriceps (giving way in the affected extremity) and severe burning, irritation or neurological discomfort in the anterior thigh prompted additional neurological examinations including electromyography/nerve conduction testing.

The anesthetist performed BNF after obtaining informed consent. Patients were monitored with electrocardiogram, pulse oximetry and automatic blood pressure cuff. Oxygen was provided by nasal cannula or face mask. Patients were anesthetized with 1 to 2 mg midazolam ± 50 μg fentanyl. The groin and knee on the operative side were exposed and the groin was prepped with chlorhexidine or Betadine (Purdue Pharma, Stamford, CT). A 2-inch, 21-gauge Stimuplex needle (B. Braun Medical Inc, Bethlehem, PA) with a Stimuplex nerve stimulator is used to locate the femoral nerve. The Stimuplex needle was attached to the nerve stimulator and washed with a local anesthetic solution. Using sterile technique, the femoral artery was palpated and the Stimuplex needle was inserted laterally to pulsate the femoral artery. The assistant repeatedly attempted to aspirate the local anesthetic syringe to identify inadvertent placement of the intravascular needle.

The nerve stimulator was set at 1 to 1.5 mA and the needle advanced until contractions in the thigh muscles were observed. The needle was directed deeply and then laterally until contractions in the quadriceps femoris were observed, usually accompanied by upward movement of the patella. In obese patients, it was sometimes necessary to palpate the thigh to assess muscle contraction. The nerve stimulator current was reduced while the contraction was observed in an attempt to maintain a contraction equal to or less than 0.5 mA; the needle position has been adjusted to achieve this.

Thirty to 40 ml of 0.5% ropivicaine or 0.5% bupivicaine (Naropin; AstraZeneca, Wilmington, DE) plus 1:200,000 to 1:400,000 epinephrine were injected in 5 ml aliquots after observation of pulse and heart rate of the patient. altered mental status, tinnitus, or perioral numbness or tingling. FNB usually takes at least 30 minutes to kick in and can last up to 24 hours. Decreasing the onset time can be achieved by adding 2 to 4 mg of midazolam to the local anesthetic solution.

All TKAs were performed using a midline skin incision with medial parapatellar arthrotomy. All patients followed a clinical course of admission that included early mobilization, continuous passive movement, and weight bearing as tolerated with a walker or crutches.

After discharge, we followed the patients for 2 weeks, 6 weeks, 12 weeks and 1 year postoperatively. Patients undergoing bilateral TKA were specifically studied to identify any increased risk of complications.

Using Fisher's exact test, we compared the overall total number of complications between the two study cohorts, as well as individual complications (Table 2). Major complications were listed individually and minor complications were listed as “other complications”. We used the SPSS Version 11.5 statistical system (SPSS, Chicago, IL) for all analyses.


The length of stay was similar between the two groups, but the BNF group had a shorter length of stay (p = 0.058). The number of patients who required hospitalization in a rehabilitation center after acute hospital discharge was similar (p = 0.741). We observed similar percentages of complications in both groups: 56 among the 729 patients (8.2%) who received BNF and 22 (9.1%) among the 241 patients who did not receive blockade (Table 2). A higher percentage (p = 0.036) of non-BNF patients had arthrofibrosis than those with BNF (four out of 241 versus two out of 729, respectively). Patients who required manipulation under anesthesia underwent the procedure on average 52 days postoperatively (range, 28 to 84 days). All patients with arthrofibrosis underwent manipulation under anesthesia. Six patients developed postoperative pneumonia, but more (p = 0.036) in the non-BNF group, four out of 241 versus two out of 729.

Thirteen patients documented postoperative falls on the medical/surgical floor with similar percentages (p = 0.204 in both groups; 12 of the 13 patients had a femoral nerve block preoperatively) (Table 2). All falls occurred within 48 hours after surgery. All three patients subsequently operated on for injuries suffered falls, but there was no difference in the percentage of patients reoperated between those with and without blockade (0% and 0.4%, respectively). One patient suffered rupture of the extensor mechanism along the medial arthrotomy (patient 1, Table 3). He was taken to the OR 1 week after the index procedure for review of the arthrotomy closure. There were no additional complications with this patient. Another patient suffered a medial collateral ligament (MCL) tear and rotated off a rotating platform polyethylene liner (Patient 2, Table 3). The patient was taken back to the operating room for MCL repair and conversion of a rotating platform TKA to a fixed tibial component. The third patient (patient 3, Table 3) suffered patellar dislocation and MCL rupture. This patient was brought back to the operating room for primary MCL repair. Seven falls occurred before the end of the first postoperative day. Eight patients documented quadriceps weakness before the fall, while another four patients fell on the first postoperative day before being formally assessed by the physiotherapy team. Four patients documented confusion at the time of the fall.

Six patients had neuropathy/neuritis, but there was no difference in percentages between groups. The patient who did not undergo BNF underwent bilateral TKA under epidural anesthesia. The neuropathy resolved in four of the five patients who received BNF without further intervention. One patient who received BNF had residual sensory symptoms in the femoral nerve distribution 1 year after TKA.


Femoral nerve blocks have been used in TKA to minimize postoperative discomfort and promote faster rehabilitation. The effectiveness of FNB as part of a multimodal analgesic protocol has been well documented [1, 6, 11, 14, 20, 22] Single-injection FNB is reportedly as effective for pain control as continuous-infusion 3-in-1 FNB [8, 12] Despite the literature confirming the effectiveness of BNF and the increased clinical use of BNF in TKA, there are few published data discussing complications associated with BNF. Therefore, we evaluated the safety (as reflected by complications) of using a BNF in an unselected group of patients undergoing TKA. In addition, we examined length of stay, overall and specific rate of complications, rate of falls and reoperations, and rate of neuralgia/neuritis in patients undergoing TKA with or without BNF.

There are several limitations to this study. First, it was not a prospective randomized study of patients undergoing TKA receiving BNF, and the cohorts were constructed retrospectively. However, data were prospectively collected from patients undergoing BNF for postoperative analgesia after TKA. Patients undergoing TKA who refused BNF or anesthesiologists who would not perform BNF on some patients formed the control group. Second, there was no standardization of the surgical and anesthetic technique. Third, it is possible that complications occurring after the patient's hospital discharge were not captured in the review of TKA patients' medical records, in the records of morbidity and mortality conferences, and in the total joint arthroplasty database records. Fourth, we did not define the complications to be investigated prospectively; therefore, there may be an underestimation of the incidence in both groups. Finally, surgeons were not involved in the selection of patients who received BNF for postoperative analgesia after TKA.

Wang et al. [22] reported that patients with BNF had a shorter hospital stay than those who did not receive BNF. These results were confirmed by Munin et al. [15] It was not possible to confirm a significant reduction in the length of hospital stay for patients who received BNF before TKA. The mean length of hospital stay for patients who received BNF was reduced by 0.35 days.

Wang et al. also suggested that patients with BNF would benefit from early ambulation, thereby reducing the risk of postoperative deep vein thrombosis [22] We found no difference in deep vein thrombosis or pulmonary embolism between patients who received BNF and those who did not.

The overall rate of femoral neuropathy/neuritis in this cohort was 0.59%. Five patients (0.66%) who received BNF had neuropathy/neuritis. In all but one of the patients who received BNF, neurological deficits resolved within 1 year after TKA. It is unclear whether ultrasound guidance for BNF or continuous infusion catheters would alter the incidence of femoral neuritis/neuropathy after BNF. More studies are needed to determine whether the technique associated with single-injection BNF is associated with the occurrence of femoral neuritis/neuropathy. The reported incidence of femoral nerve palsy has been reported to be as low as three in 10,309 [2] However, in contrast to our series, where none of the nerve injuries resulted in femoral paralysis, more than half of the patients with nerve injuries in the series by Auroy et al. had residual symptoms 6 months after the injury [2].

The incidence of arthrofibrosis requiring manipulation under anesthesia in patients receiving BNF was half that of patients not receiving BNF (Table 2). Although the incidence was low in each group, 1.7% versus 0.3%, respectively, this finding suggests that the reduction in pain and acceleration of range of motion experienced by patients with BNF in the immediate postoperative period may be associated to a lower incidence of arthrofibrosis.

We observed a non-significant trend towards a higher percentage of postoperative falls among patients who received BNF. Furthermore, although patients who had femoral nerve blocks and falls tended to have more reoperations after the fall than patients who had falls without femoral nerve blocks, this trend was not statistically significant (Table 2). However, the numbers are small, so there could be a Type II error.

Quadriceps weakness appears to be a contributing factor to falls because 67% of patients had weakness documented by the physiotherapist and four of the remaining patients fell before being examined by the physiotherapist on the first postoperative day. YaDeau et al. reported that 29% of patients who received FNB had buckling due to decreased quadriceps strength, whereas only 3% of patients who did not receive FNB had buckling [23] In this study, patients who had quadriceps weakness delayed ambulation training exercises. All patients had adequate quadriceps strength on the second postoperative day. Quadriceps weakness may also be explained by the finding that a substantial proportion of patients undergoing TKA report quadriceps weakness even after sham injections of FNB [9] The fall data in this series suggest the need for more fall protection measures for patients undergoing TKA treated with and without BNF. Patients in this series were not treated with knee immobilizers. To allow for early ambulation and full weight bearing after TKA and to prevent falls associated with BNF, we added the use of knee immobilizers to our TKA clinical course during the first 48 hours postoperatively until quadriceps function returned.

As the use of BNF in TKA becomes more common, the problems identified in this study should be confirmed in a prospective, randomized, multicenter study. FNB before TKA is not a harmless procedure. Femoral neuropathy, neuritis and postoperative falls, which can lead to injuries that require reoperation, are complications of BNF after TKA that deserve further investigation. We recommend that postoperative FNB protocols be modified to account for reduced quadriceps function in postoperative patients undergoing TKA in the immediate postoperative period to prevent falls. We continue to use BNFs for postoperative TKA analgesia as a result of high patient satisfaction with the pain relief provided compared to traditional analgesics alone. But now we use knee immobilizers in the first 48 hours after TKA to compensate quadriceps weakness caused by BNF and prevent falls.


We thank John Garfi for his assistance in preparing this article and John Tilzey, MD, and Michael Thompson, MD, for their contributions to this work.


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