Ultrasound-Guided Peripheral Nerve Stimulation for Knee Pain: A Mini-Review of the Neuroanatomy and the Evidence from Clinical Studies

Objectives Peri- and postoperative pain frequently develops after joint replacement for severe knee osteoarthritis. A continuous nerve block is commonly used for pain relief, but the risks of infection and catheter dislodgement should be considered. The present mini-review aimed to brief the innervation and neural sonoanatomy of the knee joint and summarize the newest evidence of peripheral nerve stimulation (PNS) use in the management of knee pain. Methods We used a systematic approach to search for relevant articles. We used the combination of “peripheral nerve stimulation” and “knee pain” as the key words for the literature search using the electronic database without language or article type restriction. The search period was from the earliest record to August 2019. Results The present review identified six studies, four of which were related to PNS for management of postoperative knee pain and two of which probed neuropathic pain. Most of the studies were either case series or case reports. Based on our search result, PNS is likely to be a feasible and safe treatment for knee pain, but its effectiveness remains uncertain. Conclusions The present review reveals that PNS is feasible for the management of knee pain, especially in the postoperative period. The procedure is safe under ultrasound guidance used for proper placement of the electrodes near the target nerves. In the future, more prospective randomized controlled trials are needed to validate the effectiveness of PNS in acute and chronic knee pain.

Utilization of a Continuous Pericapsular Nerve Group (PENG) Block with an Opioid-Sparing Repair of a Femoral Neck Fracture in a Pediatric Patient

In the pediatric population, femoral neck fractures are usually associated with high-impact trauma and often present with pain in the groin area. Regional anesthesia can offer adjunctive therapy for acute pain management. Various techniques have been employed to circumvent pain related to hip fractures and resultant hip surgery. Neuraxial, lumbar plexus, caudal, epidural, fascia iliaca, and femoral continuous nerve block techniques are advantageous in mitigating hip pain. However, these approaches require patient repositioning during placement and carry the potential for motor blockade with resultant weakness. A newly described method, the Pericapsular Nerve Group (PENG) block, allows for analgesia of the anterior hip capsule via the obturator, accessory obturator, and femoral nerves while sparing motor blockade. PENG blockade has demonstrated efficacy in both adult and pediatric patients. Herein, we describe the perioperative course of a 9-year-old girl with a transcervical femoral neck fracture who underwent an opioid-sparing open repair with the utilization of a continuous PENG block. PENG blockade via a continuous nerve block resulted in optimal analgesia and markedly reduced perioperative opioid consumption with preserved motor function. Our experience facilitated early discharge and rehabilitation mobility while reducing potential rebound hyperalgesia and enabling parental/patient satisfaction.

Hip Fracture

This chapter discusses hip fracture, which is a significant public health problem associated with substantial morbidity and mortality. Pain with hip fracture is often severe but despite this is frequently undertreated in the elderly population. Untreated pain not only is inhumane but also is a significant risk factor for delirium in this population that is already at increased risk due to age-related cognitive decline. Hip fracture patients benefit from early intervention with regional analgesic techniques such as femoral or fascia iliaca block, as well as a scheduled regimen of nonopioid analgesics such as acetaminophen and nonsteroidal anti-inflammatory medications. While opioids are known to contribute to risk for delirium, pain itself is a much stronger risk factor, and when nonopioid options are exhausted, opioids should be carefully considered. Continuous nerve block techniques provide opportunities for extended pain relief, which is associated with improved recovery profile, greater satisfaction, and a decreased risk for complications.

Using Pulsed Radiofrequency Ablation to Treat Pain Associated with a Tumor Involving the Brachial Plexus

Pain associated with cancer is often difficult to treat, even more so when tumors involve peripheral nerves. Therapy is complex and often requires a multimodal approach that can include medications, radiation, and interventional techniques. These components are utilized with variable success, but are also limited by known complications or adverse effects. We present the case of a 53-year-old woman with a metastatic axillary tumor that involved her brachial plexus. Attempts to control her pain with medication were unsuccessful despite escalation and use of adjunct agents. She was not deemed to be a surgical candidate due to the size and location of the tumor. Radiation was discussed but, obviously, would not work immediately. Our team decided to employ a brachial plexus catheter for continuous nerve block, which provided almost complete relief of pain. Since her pain was deemed to be of peripheral etiology, pulsed radiofrequency ablation of her brachial plexus was used for more long-term pain relief. The patient responded very well with minimal pain issues and no apparent complications. On follow-up, the patient had good relief for almost 2 months. Pulsed radiofrequency is a poorly understood technology that has increasing evidence for certain pain conditions; however, for cancer and peripheral nerves the evidence is slim to none. Our case presents a successful use for pain management of a brachial plexopathy due to a tumor. We propose that pulsed radiofrequency may present a non-neurodestructive pain management technique for tumors involving peripheral nerves, though more data is definitely needed. Key words: Pulsed radiofrequency, brachial plexopathy, brachial plexus, tumor, cancer, pain

The perception threshold counterpart to dynamic and static mechanical allodynia assessed using von Frey filaments in peripheral neuropathic pain patients

Background and aimPain due to a usually non-painful mechanical stimulus, mechanical allodynia, is an oppressive symptom in subgroups of patients with neuropathic pain. Dynamic mechanical allodynia (DMA) is evoked by a normally innocuous light moving mechanical stimulus on the skin and static mechanical allodynia (SMA) by a sustained, normally innocuous pressure against the skin. DMA is claimed to be mediated by myelinated fibres and SMA by C-fibres. Also A-delta fibres have been implicated in the static subtype. A low intensity vertically applied stimulus of 1 second (s) is expected to activate predominantly rapidly adapting A-beta mechanoreceptors thus recruiting the same peripheral substrate as a horizontally moving brush on top of the skin. In patients with SMA we assumed an activation of Cbut also A-delta fibres from a static 10 s von Frey filament stimulus. The aim was to investigate if DMA and SMA could be assessed at perception threshold level using short or longer lasting usually non-painful von Frey filament prodding of the neuropathic skin.Patients and methodsEighteen patients with painful unilateral partial peripheral traumatic nerve injury suffering from SMA (n= 9) and/or DMA (n= 18) in a limb were studied. A compression/ischemia-induced (differential) nerve block in conjunction with repeated quantitative sensory testing of A-delta and C-fibre function using cold and warm stimuli was used to assess which nerve fibre population that contributes to pain at perception threshold level using 1 s (vF1) and 10 s (vF10) von Frey filament stimulation of the skin.ResultsThe main outcome was the finding that elevation of vF1 and vF10 occurred simultaneously and significantly prior to an increase in the perception level to cold or warmth during the continuous nerve block. Single patients demonstrated a slight decrease in cold perception levels at the time of elevation of vF1 or vF10 and a possible contribution to mechanical allodynia from A-delta-fibres can therefore not completely be ruled out although the recorded alterations were minor. None of the patients reported an elevation of the perception level to warmth at the time of elevation of vF1 or vF10 excluding contribution from C-fibres. Further, only patients with clinically established SMA (n= 9) reported continuous pain to a sustained 10 s von Frey filament stimulation (vF10). Patients with only DMA (n= 9) reported pain merely for the initial 1–3 s of the total stimulus duration of 10 s and for a few seconds after the filament was lifted from the skin.ConclusionsThese findings support the role of A-beta fibres as peripheral mediators of both vF1 and vF10 although different receptor organs may be involved, i.e., rapidly (RA) and slowly (SA-I) adapting mechanoreceptors.ImplicationsTechniques to quantify the different allodynias at perception threshold level deserve further attention as possible adjuncts to suprathreshold stimuli in intervention studies aimed at modifying these stimulus-evoked phenomena.