• PENG block
• quadriceps weakness
• regional anesthesia
• hip surgery

Dear Editor,

We read with interest the report by Giron-Arango and colleagues on the novel pericapsular nerve group (PENG) block and its use for postoperative analgesia in five patients with hip fractures.1 Regional anesthesia practitioners have long awaited a primarily sensory block for patients with hip fracture. To that end, we have fully embraced the PENG block at our institution and have successfully performed a number of these blocks for preoperative analgesia for hip fracture as originally described. In these patients, we noted significant postoperative pain control from the PENG block and as a result, we have also performed PENG blocks for other hip surgeries such as hip arthroplasty and hip resurfacing procedures. Similarly, for these patients, we have noted significant improvement in postoperative analgesia and patient satisfaction. Our surgical colleagues have also been impressed with the reduction in postoperative opioid consumption as well as the improved analgesia and are now requesting the PENG block as part of their patients’ perioperative anesthetic management.

Since the first published description of the PENG block, we have performed over 100 blocks for hip fracture and various other hip surgeries. Similar toGiron-Arango and colleagues, we perform the blocks using 20 mL of either 0.25% or 0.5% bupivacaine with 1:400 000 epinephrine, but use 50 mcg/mL of preservative-free dexamethasone in an effort to extend the duration of the nerve block. We also have performed the block postoperatively in some patients in an effort to extend further their duration of postoperative analgesia. While the vast majority of these blocks have been highly effective, we have noted two cases of inadvertent motor block in the form of quadriceps weakness. Patient consent was obtained to report the findings of these two cases.

The first case was a 68-year-old woman who presented for elective left total hip arthroplasty. Her medical history was significant for bilateral hip osteoarthritis for which she occasionally took one tablet of tramacet daily, as well as obesity with a body mass index (BMI) of 37.2 kg/m². She also had untreated mild to moderate obstructive sleep apnea, and probable obstructive lung disease with short prednisone courses 3 and 5 months prior to surgery. She underwent an uneventful spinal anesthetic and surgery. A postoperative PENG block was performed with 20 mL 0.5% bupivacaine with 50 mcg/mL of preservative-free dexamethasone and 1:400 000 epinephrine using the technique described by Giron-Arango et al .1 The block was technically challenging and resulted in a needle insertion point slightly more cephalad and much of the injectate was delivered more superficially than the approach described by Giron-Arango et al .1 This was largely because manual displacement of her pannus was required in order to gain access to her inguinal region and needle visualization was difficult. Three hours later, the patient was noted to have decreased sensation to the left lower extremity throughout the distal medial and anterior thigh and knee as well as in a saphenous nerve distribution below the knee. She also displayed significant quadriceps weakness with the inability to perform a straight leg raise. She was still able to flex her hip. She retained full motor function of her foot and ankle, suggesting no sciatic nerve involvement. This weakness was not attributed to surgical causes and was determined to be a result of the PENG block inadvertently causing a femoral nerve or fascia iliaca block. On postoperative day 1, approximately 24 hours after the block, quadriceps motor function returned and the patient was able to fully weight bear and perform a straight leg raise. However, persistent decreased sensation to ice throughout the distal medial and anterior thigh and knee was noted along with decreased sensation in a saphenous nerve distribution in the lower leg. On postoperative day 2, motor function remained normal and sensory function returned to baseline. With respect to analgesia, the patient had indicated that her pain was well managed for the duration of the block. However, the patient used 95 mg of oral morphine equivalents in the first 24 hours postoperatively, which would suggest much of her pain control was achieved via a combination of oral and intravenous analgesics and not due to the nerve block. Of the total opioid intake, 30 mg of morphine equivalents was in the form of scheduled long-acting hydromorphone, and the rest was through a combination of intravenous hydromorphone, intravenous morphine, and oral oxycodone. Her pain scores were 7/10 with movement and 5/10 at rest immediately postoperatively, and ranged from 2/10 to 8/10 in the first 24 hours following surgery.

The second case was a 51-year-old woman who had an elective right total hip arthroplasty. Her medical history was significant for congenital hip dysplasia resulting in bilateral hip osteoarthritis. She had a normal BMI of 24.1 kg/m². A preoperative PENG block was performed with 0.25% bupivacaine 20 mL with 1:400 000 epinephrine and 50 mcg/mL preservative-free dexamethasone using the technique described by Giron-Arango et al .1 Sonographic visualization of the relevant anatomy was noted to be easy, with good needle visualization and local anesthetic spread during the block itself. However, the final needle tip location and site of injection was noted to be more medial than the classic description of the PENG block, with the needle tip located on the medial side of the psoas tendon. The local anesthetic spread was noted to be similar to that in the original description of the block. She underwent an uneventful spinal anesthetic and surgery for total hip arthroplasty. On postoperative day 1, the patient was found to have a sensory deficit in a distribution on the operative limb over the distal half of the anterior, lateral, and medial thigh and knee as well as in a saphenous nerve distribution below the knee. With respect to motor power, her quadriceps function was significantly impaired and she was unable to do a straight leg raise. Her hip flexion strength was 3/5 with a flexed knee. The patient had full motor function of her foot and ankle suggesting no sciatic nerve involvement. Again, this weakness could not be attributed to surgical causes and thought to be as a result of the PENG block inadvertently causing a femoral nerve or fascia iliaca block. On postoperative day 2, motor function had completely returned to normal and she was able to perform a straight leg raise without difficulty. The patient had recovered sensation throughout the thigh, knee and lower leg. With respect to analgesia, the patient reported 5/10 pain at rest and with movement preoperatively. Following surgery, her pain scores were 2/10 at rest and with movement. Over the first 24 hours, her pain scores were 0/10. Her total opioid consumption was 25 mg of oral morphine equivalents in the first 24 hours following surgery, all in the form of oral hydromorphone on an as needed basis.

On review of our two cases of inadvertent quadriceps weakness, we hypothesize that superficial local anesthetic injection, needle-positioning medial to the psoas tendon and possibly performing the block postoperatively, after surgical tissue disruption, may have been contributing factors. The PENG block is often a deeper block which requires the use of a low-frequency curvilinear probe, which can make visualization of the needle during the PENG block difficult. Hydrolocation by injecting small volumes (1–2 mL) of local anesthetic or other fluid, such as normal saline, can aid in identifying the needle tip location during this block.2 The fascia iliaca and femoral nerve are located superficial to the structures of interest in the PENG block, as shown in figure 1A,B.3 Thus, superficial injection of local anesthetic while performing the PENG block may result in an inadvertent fascia iliaca block or femoral nerve block, which could explain the presence of quadriceps weakness postoperatively in our first case.3

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Figure 1

(A) An ultrasound image using a low-frequency curvilinear probe of the pericapsular nerve group (PENG) block as originally described by Giron-Arango et al .1 (B) An ultrasound image using a high-frequency linear probe of the PENG block with depth optimized to visualize the structures of interest for the PENG block. (C) An ultrasound image using high-frequency linear probe of the region caudad to the PENG block at the inguinal crease where a femoral nerve block would ideally be performed. AIIS, anterior inferior iliac spine; FA, femoral artery; FI, fascia iliaca; FN, femoral nerve; IPE, iliopubic eminence; PT, psoas tendon.

Additionally, we speculate that medial needle placement during the PENG block may lead to inadvertent femoral nerve or fascia iliaca block. In our limited experience with the PENG block thus far, it is sometimes difficult to visualize the needle clearly while maintaining the optimal ultrasound image, likely due to the narrow ultrasound window of the block combined with the steeper angle of insertion. As a result, we have noticed that the needle trajectory sometimes deviates towards the medial side of the psoas tendon in order to maintain needle visualization in the optimal ultrasound window. When local anesthetic is injected, the spread is similar, with much of the local anesthetic ending up spreading in a plane beneath the psoas tendon and above the plane between the iliopubic eminence and anterior inferior iliac spine. It is plausible given the location of the femoral nerve relative to the psoas tendon, that some of the local anesthetic may spread superficially and result in an inadvertent femoral nerve or fascia iliaca block. Additionally, it should be highlighted that with this more medial approach there could be a higher risk of theoretical nerve injury to the femoral nerve, as can be seen in figure 1B.

Finally, performing the block postoperatively may result in inadvertent femoral nerve blockade due to the normal tissue planes being disrupted from surgery and allow further spread of local anesthetic to the femoral nerve. With our limited experience, it is unclear the relative risk of inadvertent femoral nerve or fascia iliaca block with preoperative versus postoperative PENG blocks, as the vast majority of the blocks we have performed have been placed preoperatively as described by Giron-Arango et al 1 versus postoperatively. More experience and perhaps a dedicated study may be needed to elicit the optimal time to perform the PENG block to maximize analgesic benefit while minimizing risk of inadvertent quadriceps weakness and other possible adverse effects.

Despite these two cases, we are ecstatic with the PENG block and have embraced it in our clinical practice for multiple hip surgery patient populations. We are keen to hear from Giron-Arango and colleagues regarding any further experience that they have with hip surgery patients and any adverse effects after the block, particularly inadvertent quadriceps weakness. Additional clinical and anatomical studies may also be needed to fully understand and refine this block, which may result in a safer and more effective block. In the meantime, we have elected to use normal saline or D5W for hydrolocation during our PENG blocks until the needle is in the optimal position. We have also placed greater emphasis on visualization of the needle and ascertaining proper needle location lateral to the psoas tendon just superficial to the plane between the iliopubic eminence and anterior inferior iliac spine, as originally described, prior to injecting local anesthetic, in an effort to avoid a femoral nerve or fascia iliaca block. We have affectionately termed this anatomical area the ‘deep outside pocket’. We are optimistic that we can continue to provide excellent postoperative analgesia with the PENG block and thank Giron-Arango and colleagues for their hard work in developing this novel regional anesthesia technique.