Pericapsular Nerve Group Block and Iliopsoas Plane Block: A Scoping Review of Quadriceps Weakness after Two Proclaimed Motor-Sparing Hip Blocks

Abstract

Iliopsoas plane (IP) is a fascial plane deep to the iliopsoas complex that can serve as a potential space for the injection of local anesthetics to selectively block the articular branches of femoral nerve and accessory obturator nerve to the anterior hip capsule. Two highly similar ultrasound-guided interfascial plane blocks that target the IP, pericapsular nerve group (PENG) block and iliopsoas plane block (IPB), were both designed to achieve motor-sparing sensory block to the anterior hip capsule. However, the most recent evidence shows that PENG block can cause 25% or more of quadriceps weakness, while IPB remains the hip block that can preserve quadriceps strength. In this scoping review of quadriceps weakness after PENG block and IPB, we first performed a focused review on the complicated anatomy surrounding the anterior hip capsule. Then, we systematically searched for all currently available cadaveric and clinical studies utilizing PENG block and IPB, with a focus on quadriceps weakness and its potential mechanism from the perspectives of fascial plane spread along and outside of the IP. We conclude that quadriceps weakness after PENG block, which places its needle tip directly deep to iliopsoas tendon (IT), may be the result of iliopectineal bursal injection. The incidental bursal injection, which can be observed on ultrasound as a medial fascial plane spread, can cause bursal rupture/puncture and an anteromedial extra-IP spread to involve the femoral nerve proper within fascia iliaca compartment (FIC). In comparison, IPB places its needle tip lateral to IT and injects just one-fourth of the volume of PENG block. The current evidence, albeit still limited, supports IPB as the true motor-sparing hip block. To avoid quadriceps weakness after PENG block, a more laterally placed needle tip, away from the undersurface of IT, and a reduction in injection volume should be considered. Future studies should focus on comparing the analgesic effects and quadriceps function impairment between PENG block and IPB.

Keywords: PENG block; anterior hip capsule; iliopsoas plane; interfascial plane block; motor-sparing; pericapsular nerve group.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 4

The injectate spread behavior after 5 mL iliopsoas plane block (IPB): Solid arrowed lines represent the routes of spread observed in Nielsen et al.’s IPB volunteer trial [7], while the faded arrowed lines represent the theoretical routes of spread as the injectate volume is increased. Each solid arrowed line is also shown with its respective occurrence frequency observed in the trial [7]. The predominant route of spread (100%) is along the L-shaped iliopsoas plane (IP), comprised of a horizontal fascial plane (i.e., the ligamentous IP) and a vertical raphe between lateral fibers of iliacus (LFI) and iliacus minor (IM) (i.e., the muscular IP), and is colored in green. Lateral fascial plane spread between IM and capsular ligaments of hip toward the gluteus muscles, medial fascial plane spread into the iliopectineal bursa, iliopsoas intramuscular spread along the septum between medial fibers of iliacus (MFI) and LFI, superficial spread along the muscular IP to the anterior surface of iliopsoas complex, and intra-articular spread into hip joint via the bursal-synovium communication were observed in 33%, 28%, 23%, 5%, and 5% of the subjects, respectively. However, definite femoral nerve proper involvement was not readily observed. IT: iliopsoas tendon, PM: psoas major.

Figure 1

The iliopsoas complex and its surrounding structures of a human right hip were illustrated in transverse sections according to the real cadaveric images (right lower panels) at four successive levels (right upper panels) in craniocaudal order: (a) At the level between anterior superior iliac spine (ASIS) and anterior inferior iliac spine (AIIS): The posterolateral wall of iliopsoas plane (IP) is composed entirely of an osseous surface, which is the iliac ala (green solid stroke); (b) At the level of iliopectineal eminence, i.e., the pericapsular nerve group (PENG) block level: Note that as IM emerges, IP starts to divide into a muscular part (green dashed stroke), which is the raphe between IM and lateral fibers of iliacus (LFI), and an osseous part (green solid stroke), which is the iliac corpus; (c) At the level where femoral head dives deep into the acetabular rim, i.e., the iliopsoas plane block (IPB) level: As the capsular ligaments of hip extend inferolaterally from the acetabular rim, the ligamentous IP, which is a potential space between capsular ligament of hip and the iliopsoas complex, gradually replaces the osseous IP as its posterior wall (green solid stroke). And as the IM muscle substance becomes bigger at this level, rendering the muscular IP (green dashed stroke) more vertical, IP becomes L-shaped; (d) At the level where femoral head transits into femoral neck: IP remains L-shaped but the ligamentous IP becomes smaller in area as IM stretches inferomedially, closing up the gap between itself and IT, and inserts into femur just distal to lesser trochanter. At this level, the two divisions of obturator nerve have just left the obturator canal, with the anterior branch traveling inside subpectineal plane (SP) and the posterior branch passing through the obturator externus muscle, on its way to the SP. The most superficial part of the raphe between iliopsoas complex and IM could not be readily distinguished on the cadaveric images and are therefore drawn as a dashed line indicated with question mark. The green arrows indicate the junction between the osseous or ligamentous IP and the muscular IP, and the yellow stars mark the respective final needle tip position of PENG block (b) and IPB (c). Cadaveric images were reconstructed from real cadavers by the Visible Human Project® of National Library of Medicine and excerpted from the VH Dissector with permission from Touch of Life Technologies Inc (www.toltech.net). IT: iliopsoas tendon, MFI: medial fibers of iliacus, PM: psoas major muscle fibers.

Figure 2

Capsular ligaments of hip of the anterior hip capsule and distinction of the osseous and ligamentous iliopsoas plane (IP): (a) Lateral view of the right-sided acetabulum, with femur re-moved, is shown here to demonstrate the proximal attachments of the capsular ligaments of hip of anterior hip capsule and their spatial relationship to the acetabulum and its surrounding iliopubic structures. The attachments of iliofemoral ligament, the capsular fibers, and pubofemoral ligament to the acetabular rim are colored in blue, yellow, and purple, respectively. Both iliofemoral ligament and pubofemoral ligament are distinct thickening of the capsular fibers. The figure was modified from a reconstructed cadaveric image by the Visible Human Project® of National Library of Medicine acquired from the VH Dissector with permission from Touch of Life Technologies Inc (www.toltech.net); (b) In this three-dimensional computed tomography image of the right-sided hip joint reconstructed from a real patient with volume-rendering technique, the osseous IP refers to the wide shallow groove between anterior inferior iliac spine (AIIS) and iliopectineal eminence and its cranial extension on ilium, as demarcated by the arrowed dashed black line. Iliopsoas valley, marked as the dashed red line (also in Figure 2a), is a depression of the anterior acetabular rim that is continuous with the AIIS-iliopectineal eminence concave to allow passage of the iliopsoas complex inferiorly over the femoral head. Capsular ligaments of hip are illustrated as colored bands connecting the acetabular rim and the intertrochanteric line of femur, with the same colors coded as in Figure 2a. The blue-colored iliofemoral ligament has a transverse (lateral) part and a descending (medial) part. The ligamentous IP is demarcated by the dashed white line and refers to the fascial plane between iliopsoas complex and fibers of the capsular ligaments of hip, with iliopsoas tendon (IT, not shown) as its medial border and iliacus minor muscle (IM, not shown) as its lateral border. The yellow stars mark the final needle tip positions of pericapsular nerve group (PENG) block and iliopsoas plane block (IPB).

Figure 3

Flowchart for the selection of studies for the current review. IPB: iliopsoas plane block; PENG: pericapsular nerve group.

Figure 5

Injectate spread in a cadaver after pericapsular nerve group (PENG) block: (a) Injectate spread after 10 mL PENG block is colored in faded green and is overlayed with the faded iliopsoas complex to demonstrate its spatial relationship to the iliacus minor (IM) and iliopsoas tendon (IT). Note the presence of injectate spread deep and medial to IT; (b) Injectate spread after 20 mL PENG block is again colored in faded green and overlayed with the iliopsoas complex. In comparison to 10 mL PENG block, the more extensive spread of a 20 mL PENG block includes an inferomedial extension into the subpectineal plane (SP), from where divisions of the obturator nerve emerge, and a superomedial extension into the lesser pelvis, where the obturator nerve proper traverses intrapelvically towards the obturator canal. The final needle tip position of PENG block is marked as a yellow star deep to IT. The illustrated Figure was made from an image acquired from the VH Dissector with permission from Touch of Life Technologies Inc (www.toltech.net), based on the results of a cadaveric dye injection study by Tran et al. [22]. The original image was reconstructed from real cadaver by the Visible Human Project® of National Library of Medicine. AIIS: anterior inferior iliac spine.

Figure 6

Injectate spread in living human subjects after iliopsoas plane block (IPB): (a–d) The most commonly observed pattern of injectate spread after 5 mL IPB, illustrated as the green-colored area, is superimposed on the four transverse section levels as depicted in Figure 1; (e) The injectate spread is colored in faded green and is overlayed by the iliopsoas complex to demonstrate its spatial relationship to iliacus minor (IM) and iliopsoas tendon (IT). Note that the injectate is confined within a well-defined iliopsoas plane (IP) without the extra-IP spread that is deep and medial to IT as in PENG block (Figure 6). However, there is superficial spread via the muscular IP towards fascia iliaca compartment (FIC) (c,d), potentially reaching femoral nerve proper when given higher volume of injection. The illustrated Figure was made from an image acquired from the VH Dis-sector with permission from Touch of Life Technologies Inc (www.toltech.net), based on the magnetic resonance images by Nielsen et al. [7]. The original image was reconstructed from real cadavers by the Visible Human Project® of National Library of Medicine.

Figure 7

The injectate spread behavior after 20 mL pericapsular nerve group (PENG) block: Solid arrowed lines represent the routes of spread that have been observed in the cadaveric or clinical studies included in this review, while the faded arrowed lines represent theoretical routes of spread that await further evidence. The dashed arrowed line marks the superficial spread via the muscular iliopsoas plane (IP) as in Figure 5. Medial fascial plane (bursal) spread is the most commonly observed route of spread under ultrasound after PENG block (Table 1). Since Iliopectineal bursa lies immediately deep to iliopsoas tendon (IT), it can be easily injected during PENG block. As the bursa ruptures from pressure/volume overload or is punctured by the needle tip, both the anteromedial spread along the anterior surface of psoas major (PM) to involve femoral nerve proper and the posteromedial spread to involve either the obturator nerve proper (intrapelvic) or its divisions (extrapelvic) can occur [22,39]. When iliopectineal bursa is injected, intra-articular spread via the bursal-synovium communication can also occur [38]. Lateral fascial plane spread is the second most commonly observed spread route after PENG block (Table 1), and a further continuation of this lateral spread to the gluteus muscles were shown in another cadaveric study [37].