With current trends toward anterior cruciate ligament reconstruction (ACLR) procedures in ambulatory settings, pain management is becoming exceedingly important. Femoral nerve blocks (FNB) have been utilized with the aim to improve pain management and to allow early rehabilitation; thereby improving patient satisfaction and outcome measures.
Furthermore, early discharge can reduce costs.
In this chapter, we summarize the modalities of pain control, discuss the evidence for and against the use of FNB in ACLR, and explore novel strategies.
Methods of Pain Control
Traditionally, ACLR can be performed under general anesthesia or regional anesthesia, including spinal or epidural anesthesia.
Local injections at incision or portal site or intra-articular opioids are often supplemented with systemic medications. Common medications include paracetamol, nonsteroidal anti-inflammatory drugs (NSAIDs), and opioids in the form of oral, intramuscular/intravenous injection, or patient-controlled analgesia.
Surgeons should be aware of potential chondrotoxic effects of local anesthetic (LA) agents when given as intra-articular injection. Following initial reports of chondrolysis after the use of intra-articular LA pain pumps; Piper et al. advised caution in intra-articular LA injections after reviewing current literature on LA associated chondrotoxicity in human and animal studies.
Methodology for Femoral Nerve Block
In the orthopedic and anesthetic literature, many “recipes” for FNB have been described. Traditional method is based on the description by Labat; using the inguinal ligament and a vertical line just lateral to the femoral artery as landmarks.
In our center, we utilize a combined approach under ultrasound guidance and nerve-stimulation (
).
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1.
Timing of the block:
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a.
Most FNB are performed before the general anaesthesia/spinal anaesthesia to aid monitoring and communication with the patient. Two of the three cases of neural injuries occurred in FNB performed in anaesthetized patients in an early series.
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a.
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2.
Continuous with catheter versus single injection:
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a.
Continuous technique can prolong the analgesic effect of the FNB. However, most studies report mechanical failure and malfunction or failure to insert catheter in around 5-12% of patients.
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b.
Different regimes with basal infusion or on-demand boluses have been described. Svediene et al. studied the use of 0.1% bupivacaine and found that on demand boluses with basal infusion was more efficient than on demand boluses alone.
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a.
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3.
Choice of medication/concentration/volume
There is again, significant variability in the LA agent used, the concentration and volume instilled. Most commonly the long acting agents such as bupivacaine and ropivacaine are used. Levobupivacaine replaces bupivacaine to minimize the cardiotoxicity.
Wulf studied a standardized volume of 30mL of either normal saline (NS), ropivacaine (0.2%, 0.75%), and bupivacaine (0.25%).
ALL regimes were efficacious in reducing pain scores compared to NS. There was no evidence of central nervous system toxicity detected in all four groups. They were unable to identify an ideal concentration of medication without motor block; even with reduced concentration of the LA.
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4.
Nerve stimulator/ultrasound-guided/combined approach
Orebaugh reviewed the practice at the University of Pittsburgh from 2006-2011. During the time period there was a shift toward ultrasound-guided regional anesthesia (UGRA) with peripheral nerve stimulator compared with landmark approach (LM-PNS). The study revealed reduction in LA Systemic toxicity in UGRA for upper limb blocks. The other benefits for UGRA include faster block onset, reduced block failure and fewer episodes of vascular puncture.
However, it is difficult to perform study with large enough patient numbers to detect differences in rare complications such as nerve injury.
Ultrasound and peripheral nerve stimulation-guided femoral nerve block injection over the left femoral nerve region showing the transducer position and needle insertion.
Ultrasound image showing the needle path (needle) to block the femoral nerve (FN). Blue dot marks the lateral side and femoral artery (FA) can be seen.
Risks of Femoral Nerve Blocks: Are They Rare But Real?
Regional anaethesia has been performed increasingly since the 1980s. Large scale studies were performed to assess the safety and efficacy.
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1.
Nerve injury/infection
Amongst 10,309 femoral nerve blocks studied by Auroy et al in a survey of major complications in regional anaesthesia, there were three cases of peripheral neuropathy (2.9 per 10,000).
Capdevila et al reported in three cases of nerve lesions and one case of abscess following 683 continuous femoral nerve blocks.
The nerve lesions were completely resolved between 36 hours-10 weeks postoperatively.
The patient with abscess recovered with targeted antibiotic treatment.
There was also frequent colonization of catheters of uncertain clinical significance.
Edkin concluded that “FNB is a highly effective form of analgesia with excellent patient satisfaction” in an early retrospective series of 161 outpatient ACLR procedure. However, more recent studies do not share the same enthusiasm.
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2.
Weakness and Falls
Kandasami advised caution during early mobilization of patients with FNB. He reported a 2% (5 out of 250 patients) risk of serious postoperative falls requiring re-operation after total knee replacement (TKR).
At 6 months following ACLR, quadriceps and hamstring deficits were found in adolescent patients given FNB compared with controls.
FNB group was also less likely to meet clearance to return to sports criteria.
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3.
Bleeding/Intravascular injection
Weigel reported a 5.7% intravascular puncture rate amongst 628 femoral nerve blocks.
However, one patient had permanent nerve injury related to a retroperitoneal haematoma requiring surgical intervention. Subsequent electrophysiological studies confirmed complete denervation of quadriceps.
Benefits of FNB in ACLR, are They Clinically Relevant?
Mall and Wright concluded that current literature does not show significant benefit of FNB, in a systematic review of all Level I and II studies comparing FNB with traditional multimodal analgesia in ACLR.
Thirteen studies reached the inclusion criteria, while only five studies showed a significant improvement in pain relieve compared to control.
However, the benefit is of a small magnitude. Visual analogue scale (VAS) score was 1-2cm better on a 10cm scale; or 19-23 points better on a 100-point scale.
Therefore this raise questions about the clinical significance. The authors also highlighted the “small
but potentially catastrophic
risks” of FNB.
The Cochrane collaboration also produced a review of peripheral nerve blocks for postoperative pain after major knee surgery.
The author’s conclusion is in favor of the use of peripheral nerve block following major surgery with the following limitation: “However, the benefits may be limited to those undergoing total knee arthroplasty.” They also recommend multicenter trials to improve the power of the studies, with sham/placebo block to improve future research design.
In the 2012 American Academy of Orthopaedic Surgeons Exhibits selection, lower extremity peripheral nerve blocks were summarized for all orthopedic procedures.
In relation to ACLR, peripheral nerve block use will likely increase due to the trend away from intra-articular injections related to potential chondrotoxicity.
However, the efficacy of FNB remains controversial. The benefits of reduced pain, reduced opioid side effects, improved mobilization and discharge as well as cost savings are not always reproducible.
More recent studies have questioned the efficacy of FNB. Fristensen reported in
Knee Surgery, Sports Traumatology, Arthroscopy
2014 a randomized controlled trial showing no difference when FNB is compared with local infiltration analgesia.
Similarly, Astur et al also reported a double-blinded RCT on ACRL under spinal Anaesthesia, with concomitant FNB vs controls. After the initial pain relief within 6 hours postoperative, there appears to be a trend towards higher pain score once the FNB wears off from Day 3-7 postoperatively compared with control groups.
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