Fascial plane blocks for postoperative pain management after fast-track total knee arthroplasty: A narrative review

Abstract

Total knee replacement is a common surgical procedure associated with significant postoperative pain, which can delay recovery and increase healthcare costs. Regional anesthesia techniques, including local infiltration analgesia and fascial plane blocks, play a crucial role in multimodal pain management strategies. These approaches aim to enhance pain relief while minimizing opioid use and preserving motor function. This narrative review evaluates the effectiveness and safety of motor-sparing fascial plane blocks for total knee replacement, categorizing techniques based on their anatomical target areas: anterior, posterior, and other approaches. A comprehensive literature search was conducted using databases such as MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials. The search included studies on motor-sparing regional anesthesia techniques for total knee replacement using relevant keywords such as “regional anesthesia,” “peripheral nerve block,” “motor-sparing techniques,” and specific block names. The selection criteria included randomized controlled trials, systematic reviews, meta-analyses, and relevant case studies. The techniques were analyzed based on their effectiveness in pain relief, impact on motor function, and overall contribution to enhanced recovery after total knee replacement. The review highlights that the most evidence-supported technique for anterior knee pain management is the block targeting the adductor canal, which provides effective analgesia while preserving motor function. For posterior compartment pain relief, the infiltration between the popliteal artery and the knee capsule is the preferred approach. Emerging techniques, such as the dual subsartorial block and the para-sartorial compartment block, show promise but require further validation. The review also underscores the importance of integrating different techniques to ensure adequate pain control for both the anterior and posterior compartments, facilitating early mobilization in fast-track recovery protocols. Achieving optimal postoperative pain management after total knee replacement requires a combination of targeted regional anesthesia techniques. Current evidence supports the use of adductor canal block for anterior knee analgesia and the infiltration between the popliteal artery and the knee capsule for posterior pain relief. While newer techniques show potential, further research is needed to validate their efficacy and safety. Future studies should focus on refining fascial plane block strategies to optimize analgesic benefits while minimizing motor impairment, thereby improving functional recovery and reducing the reliance on opioid medications.

Background

Total knee arthroplasty (TKA) is a commonly performed surgical procedure, yet it is often associated with significant postoperative pain, affecting up to 36% of patients. Severe pain can hinder recovery by limiting a patient’s ability to mobilize early and engage in rehabilitation, leading to longer hospital stays and increased healthcare costs. Moreover, inadequate postsurgical pain management may contribute to the development of chronic postsurgical pain.[1] Regional anesthesia, whether administered by the surgeon as local infiltration analgesia (LIA) or by the anesthetist, plays a key role in multimodal analgesia (MMA). It enhances pain control, reduces opioid consumption, and supports functional recovery, enabling patients to follow a fast-track TKA pathway.[2]

LIA has been shown to be effective, with a low incidence of complications, but some surgeons may hesitate to use it due to concerns about infections or vascular or nerve injuries or simply to save operating room time and reduce costs. Additionally, LIA may not be suitable as a rescue technique postoperatively. Moreover, since LIA involves injecting a large volume of local anesthetic around the knee capsule before releasing the tourniquet, there is a risk of local anesthetic systemic toxicity (LAST) when the tourniquet is released.[3] For these reasons, anesthetists have continued to seek long-lasting, motor-sparing regional anesthetic techniques that are easy to perform and reproduce, which could improve patient outcomes and facilitate faster recovery after TKA.

Fascial plane blocks (FPBs), with a few exceptions, are motor-sparing and long-lasting by nature.[4] The effectiveness of FPBs can vary significantly based on several factors, such as the operator’s skill, patient characteristics, and the anesthetic mixture used. The mechanism of action of these blocks involves a local anesthetic effect both on nerve fibers within the fascia and on those that innervate the fascia itself. Additionally, the mechanical effects of the puncture and injection may contribute to its analgesic effect. The local anesthetic also exerts an anti-inflammatory effect on the tissues involved and a systemic effect due to absorption of the drug in the bloodstream. Since FPBs do not target motor nerves primarily, using high concentrations of local anesthetics is unnecessary. However, some FPBs are not truly motor-sparing.

In the context of lower limb anesthesia, examples include fascia iliaca blocks (infra-inguinal and supra-inguinal SIFI) and others discussed later in the text. These techniques can be classified as Virtual Motor-Sparing (VMS) blocks [Table 1] as they do involve motor nerves but achieve differential anesthesia using low concentrations of local anesthetic in larger volumes. While this method is effective, it is not fundamentally different from continuous low-concentration local anesthetic infusion via a perineural catheter. The risk of muscle weakness and patient falls still exists with these techniques.[5]

Table 1.

Virtual Motor-Sparing (VMS) Techniques

Feature	Description
Main Motor-Sensitive Nerves Involvement	Through a fascial plane
Direct Nerve Targeting	No (avoids subepineural injection or epineurium opening) → Reduces nerve injury risk
Injection Volume	High volume → Higher probability of nerve involvement
Local Anesthetic Concentration	Low concentration → Lower probability of muscle weakness but shorter duration
Use of Adjuvants	Yes → Helps in block prolongation
Lower Limb (TKA) Effects	Effective. Muscle movements are preserved without guaranteed full strength → Risk of falls

This narrative review aims to provide a comprehensive list of the motor-sparing FPBs for TKA described in the literature. We cover both well-established, evidence-based techniques as well as the most recent, emerging ones, including those without clinical data but with promising features. Our goal is to give the reader an overview of current knowledge and encourage further research in this area. Given the complexity of knee joint innervation, which can be simplified into two main compartments, anterior and posterior [Figure 1], we have divided the results into three sections: techniques for the anterior compartment, techniques for the posterior compartment, and other relevant techniques. We categorized the techniques based on their evidence and effectiveness, both alone and in combination.

Figure 1.

Primary knee innervation relevant for post-TKA pain management. On the left, the anterior compartment: Green areas indicate the main sensory distribution. For the classic medial parapatellar approach, the nerve to vastus medialis and the saphenous nerve are the key targets for regional anesthesia techniques. On the right, the posterior compartment: The main sensory innervation arises from the articular branches of the sciatic and obturator nerves (Popliteal Plexus, in yellow)

Methods

A comprehensive literature search was conducted using MEDLINE, EMBASE, and the Cochrane Controlled Register of Trials (CENTRAL). To identify all motor-sparing regional anesthesia (RA) techniques for TKA, we used the following keywords and MeSH terms: “Total knee arthroplasty” OR “Total knee replacement” OR “TKA”; “Fast-track”; “ERAS”; “Enhanced recovery”; “Ambulatory TKA”; “Regional anesthesia” OR “Peripheral nerve block” OR “Motor-sparing anesthesia” OR “Multimodal analgesia” OR “Motor-Sparing Nerve Blocks”; “Adductor canal block”; “Femoral triangle block”; “IPACK block” (Infiltration between Popliteal Artery and Capsule of the Knee); “Saphenous nerve block”. Additional keywords related to techniques and outcomes included: “Motor-sparing analgesia”; “Quadriceps-sparing nerve block”; “Functional recovery after TKA”; “Early ambulation after TKA”; “Opioid-sparing analgesia”; “Pain management after TKA”. To ensure a thorough yet targeted search, Boolean operators (AND, OR) were used to optimize the retrieval of relevant studies. Our search strategy aimed to capture a wide range of motor-sparing regional anesthesia techniques for TKA while maintaining a specific focus.

We included various types of publications, such as trials, reviews, meta-analyses, case reports, technical reports, cadaver studies, and letters to the editor, to ensure a comprehensive identification of all FPB techniques described for TKA analgesia.

Results and Discussion

The search resulted in a substantial number of articles covering a wide range of topics. From the title and abstract, we selected the techniques that seemed most relevant to the purpose of this review [Table 2].

Table 2.

List of Published Motor-Sparing FPBs for TKA

Compartment	Techniques	Injection points
Anterior Compartment (including techniques developed to cover both compartments)	- Adductor Canal Block (ACB) (including: femoral triangle block, proximal femoral triangle, distal femoral triangle, true adductor canal, proximal adductor canal, distal adductor canal) Figure 3	Plane between SM and LAM
	- Subsartorial Plexus Block	Plane between the VMM and SM
	- Dual Subsartorial Block	Plane between SM and LAM + Distal Femoral Triangle under the sartorius
	- Distal Subsartorial Compartment Block	The intersection of the SN and the AMT
	- PASC Block	FTB + SPB + above SM
	- TIPS Block	DACB + SPB + distal femoral triangle
Posterior Compartment	- Popliteal Plexus Block (PPB)	Within the distal end of the adductor canal, near the adductor hiatus. The injection is made adjacent to the femoral artery, between the vastus medialis muscle and the great adductor muscle
	- IPACK Block	Distal popliteal fossa, at the level of the femoral condyle, in the space between the popliteal artery and the posterior knee capsule
	- HI-PAC	Proximal AC
	- SPANK	Bony cortex 1 cm anterior to the peak of the adductor tubercle
	- Gastrosoleus Interfascial Plane Block	Fascial plane between the medial gastrocnemius head and the soleus muscles
	- Parasacral Ischial Plane Block	Deep to the piriformis muscle, posteromedial to the ischium
Other Techniques	- Lumbar ESP	Erector spinae plane, landmark transverse process
	- Sacral ESP	Erector spinae plane, landmark intermediate sacral crest
	- Knee PVI	SLGA + SMGA + ILGA + IMGA + IA + IPACK

Adductor Canal Block (ACB), Femoral Triangle Block (FTB), Subsartorial Plexus Block (SPB), Dual Subsartorial Block (DSB), Distal Subsartorial Compartment Block (DSCB), Para-Sartorial Compartments Block (PASCB), Triple Injection Perisartorius Block (TIPS). Popliteal Plexus Block (PPB), Infiltration between the Popliteal Artery and Capsule of the Knee (IPACK), High-Volume Proximal Adductor Canal Block (HI-PAC), Selective Posterior Articular Nerve Knee Block (SPANK). Lumbar Erector Spinae Plane Block (L-ESP), Sacral Erector Spinae Plane Block (S-ESP), Periarticular Vasoconstrictor Infiltration (PVI), Supero-Lateral Genicular Artery (SLGA), Supero-Medial Genicular Artery (SMGA), Infero-Lateral Genicular Artery (ILGA), Infero-Medial Genicular Artery (IMGA), Intraarticular Injection (IA)

For the more commonly utilized procedures, we analyzed available systematic reviews and meta-analyses. For the less frequently used techniques, which had limited or only a single paper published, we examined and commented on all available data.

The results of this search have highlighted several interesting findings, which have allowed the development of a clinical approach based on well-established scientific evidence drawn from multiple second-level studies. At the same time, there is potential for even greater efficacy through alternative, relatively new approaches. Although data are currently unavailable for these techniques, their anatomical foundations suggest that they may be clinically valid and could serve as the basis for future research.

Among the techniques with the strongest supporting evidence, thanks to multiple meta-analyses, the Adductor Canal Block (ACB) and the IPACK block stand out. Following these, the Popliteal Plexus Block (PPB) is supported by four available RCTs. Other techniques are still relatively recent, and insufficient data exist to confirm their validity.

Anterior Compartment Techniques

When discussing ACB, it is important to address the significant confusion in the literature, particularly in studies published before 2016. This confusion arises from the ongoing debate about the differences in efficacy between the ACB and femoral triangle block (FTB), a controversy further fueled by recent anatomical studies by Bendtsen and colleagues.[6,7] These studies have highlighted differences in the involvement of nerve branches relevant to analgesia, depending on the injection site. These distinctions can easily be assessed using ultrasound landmarks and were clearly defined later by a Delphi consensus, which established the following definitions for the two injection sites:[8]

• FTB: Injection in the aponeurotic compartment containing the femoral vessels proximal to the apex of the femoral triangle.

• ACB: Injection in the aponeurotic compartment containing the femoral vessels distal to the apex of the femoral triangle and proximal to the adductor hiatus.

The apex of the femoral triangle is the point where the medial borders of the sartorius and adductor longus muscles cross. Distally to this point, the true adductor canal begins.

Moreover, the true adductor canal, as defined by the consensus, is enclosed by a distinct aponeurotic barrier, the vasto-adductor membrane (VAM), which separates the sartorius and adductor muscles. A true ACB is performed beneath this membrane.

The confusion arises from the fact that the technique referred to as ACB, which did not consider the various possible injection sites, was originally developed with the goal of blocking the main sensory branches of the femoral nerve involved in pain transmission from the knee without affecting the primary motor branches, avoiding risk of falls and improving mobility. However, as will be demonstrated later, each injection site involves different anatomical structures and nerves. In fact, the true adductor canal (true ACB) contains only the saphenous nerve and its infrapatellar branch (which is the primary target of this block) often separates from the main saphenous nerve early and penetrates the VAM at a more proximal level. Another key nerve for knee analgesia is the medial retinacular nerve, a branch of the nerve to vastus medialis (NVM), which consistently runs superficially to the VAM, outside the adductor canal. From this anatomical perspective, an injection placed too distally within the adductor canal, below the VAM, may be inadequate for providing effective analgesia for TKA.

In addition, from the first ultrasound-guided description of the saphenous nerve block in the adductor canal (Manickam, 2009),[9] until Bendtsen’s group study on ultrasound landmarks, the standard surface landmark for placing the ultrasound probe was the mid-thigh, defined as the midpoint between the anterior superior iliac spine (ASIS) and the base of the patella. However, with this probe position, the injection point falls within the femoral triangle rather than the true adductor canal. As a result, most of the literature on ACB from 2009 to 2016 actually describes an FTB rather than a true ACB and this explains the significant clinical efficacy of the block, observed in several studies.

These anatomical clarifications have important implications for refining the technique and understanding its true analgesic mechanisms.

On the other hand, as suggested by Pascarella et al. in 2020,[10] the true adductor canal and the femoral triangle are continuously connected, and an injection in one compartment can result in an injectate spread into the other (as with all fascial plane blocks – FPBs – the anesthetic mixture tends to flow longitudinally along the path of least resistance[4]), meaning that a block performed in the true adductor canal may spread proximally into the femoral triangle, affecting both the NVM and the saphenous nerve, before the emergence of its infrapatellar branch, thereby ensuring optimal analgesia. Similarly, in some cases, the local anesthetic may travel further proximally, potentially reaching the femoral nerve, or distally, toward the adductor hiatus, reaching the popliteal fossa, potentially affecting the sciatic nerve. While these occurrences are rare, they can be clinically significant as they may impair patient mobility and increase the risk of falls.

To minimize these risks while maintaining block efficacy, Jaeger et al. (2015)[11] demonstrated that a 20 mL volume strikes the optimal balance between effective analgesia and excessive spread with unintended motor blockade.

Based on the results of the most recent trials and meta-analyses about ACB/FTB, we can draw the following interesting conclusions:

• For anterior knee pain, a proximal ACB is slightly more effective than a distal ACB in the first 24 hours postsurgery.

• The FTB appears to provide better analgesia than the ACB, but it also increases the risk of spread to the motor components of the femoral nerve, which could lead to a higher risk of falls. For this reason, the proximal ACB emerges as the evidence-based preferred technique, balancing efficacy and safety.[12,13,14]

The aforementioned differences in analgesia and motor blockade observed among various injection sites do not apply to techniques involving continuous infusion via catheter. This finding further supports the continuity between the two compartments. However, catheter placement has not shown any significant advantage over single-shot techniques in terms of analgesia, opioid consumption, or motor blockade.[15,16,17,18] Furthermore, because of the potential risk of accidental catheter dislocation (which is the most reported complication of continuous techniques), a block failure, requiring conversion to systemic analgesia alone, must be considered.[19] Therefore, an ACB catheter is not recommended.

The increasing social and economic pressure, pushing toward an ever-earlier discharge of the growing number of patients undergoing TKA, along with the availability of increasingly advanced ultrasound machines pushed the research toward the development of new fascial plane techniques aimed at achieving more effective analgesia while preserving motor function, further improving functional outcomes and fast recovery.

In 2015, Swenson described the first technique going beyond the saphenous nerve to target additional nerve branches involved in TKA. He introduced the subsartorial plexus block, a technique that, using a special multiorifice needle, aimed to block both the medial retinacular nerve and the infrapatellar branch of the saphenous nerve. It consisted in a single injection, along their course, between the sartorius and vastus medialis muscles, rather than within the adductor canal.[20] This technique appeared promising but was not further developed or widely applied, and no clinical data are available on its efficacy. However, research on these nerve structures continued, and in 2021, Sonawane and colleagues described the dual subsartorial block (DSB).[21] This technique aims to block both the subsartorial plexus for anterior knee analgesia (via an injection in the distal femoral triangle) and the popliteal plexus for posterior knee analgesia (via a second injection in the distal adductor canal). In the same year, the author conducted a pilot study on 15 patients, followed by a randomized trial on 120 patients comparing different anesthetic volumes injected into the two compartments. The study found no significant differences between the groups, likely due to the previously mentioned continuity between these compartments, confirming the effectiveness of a 10–20 mL volume for both injection sites.

While the technique requires two separate injections, it appears promising. However, no comparative data exist against more established techniques, and further randomized trials are needed to validate its effectiveness.[21,22] The same applies to the para-sartorial compartment (PASC) block, a technique developed by Pascarella et al. in 2022.[23] Its goal is to complement a distal femoral triangle block by also blocking the medial and intermediate femorocutaneous nerves (MFCN, IFCN), thereby providing a more comprehensive anterior knee analgesia with improved cutaneous coverage. The block is performed with a single needle entry point and two injections, with part of the anesthetic deposited subsartorially and periarterially and part suprasartorially, where the cutaneous branches emerge. The technique seems interesting, and to validate its effectiveness, other authors have performed and published positive results obtained through an anatomical study and a case series of five patients. However, at present, there are insufficient data to recommend it for routine clinical practice.[23,24,25]

From the evidence examined so far, it is clear that achieving comprehensive postoperative analgesia after TKA requires an approach that integrates three injections: one for the anterior compartment, one for the posterior compartment, and a third for the cutaneous branches. A possible solution could be the combination of a DSB with a suprasartorial injection (or alternatively, a PASC block combined with a distal ACB). This solution was tested by Alabd et al.[26] in 2024 through a randomized controlled trial (RCT) comparing their triple injection peri-sartorius block (TIPS) with the femoral nerve block (FNB) in 80 patients. The results showed that the TIPS block provided significantly better analgesia than the FNB. However, the clinical relevance of this difference did not fully align with its statistical significance as the dynamic VAS scores remained between 2 and 3.5, relatively low pain levels. The most notable finding from this study is that the TIPS block offers analgesia comparable to the FNB while preserving the motor-sparing effect of the ACB.

The technique has been subject of debate, with some arguing that it closely resembles the DSB as the IFCN is already affected in its deeper course by the first injection of the DSB in the femoral triangle. Nonetheless, TIPS may still offer advantages as the suprasartorial injection would involve the IFCN, even in cases of anatomical variability of its course, enhancing the block effectiveness.[26,27,28] Like many other new techniques, current data remain limited, and further studies are needed to validate its efficacy.

In summary, based on the available literature, the most evidence-based, motor-sparing, regional anesthesia technique for anterior knee compartment analgesia after TKA is a single-shot injection of 20 ml of a long-acting local anesthetic at the proximal adductor canal.

To enhance and extend analgesia to the posterior compartment, techniques such as LIA, genicular nerve blocks, or a motor-sparing fascial plane block, specific for the posterior compartment, may be effectively added.

Among emerging techniques, the PASC block, DSB, and TIPS show promise but still lack sufficient supporting evidence. However, with both DSB and TIPS, there remains a risk of unintended anesthetic spread into the popliteal fossa, potentially affecting the sciatic nerve and impairing functional recovery (similar to the risk seen with other VMS techniques). Therefore, careful consideration should be given to the injected volume and the concentration of the local anesthetic used.

When preserving motor function is a priority, a true motor-sparing technique for the posterior compartment such as the popliteal plexus block or IPACK block may be preferable to optimize function and recovery.

Posterior Compartment Techniques

The Popliteal Plexus Block (PPB) was first introduced in 2017 with an anatomical study by Bendtsen’s group, in collaboration with the anatomist Moriggl B. The following year, the same group conducted a feasibility study involving ten patients, which demonstrated significant pain reduction after TKA when the PPB was performed under spinal anesthesia, combined with an FTB.[29,30] In a subsequent publication, Fujino et al.[31] defined the optimal needle placement based on their clinical experience, emphasizing the importance of penetrating the VAM to ensure proper spread toward the adductor hiatus. They also highlighted the ultrasound sign of arterial compression (similar to the “double bubble” sign in the infraclavicular brachial plexus block) as a key indicator of correct execution. Several randomized trials (involving over 250 patients) recently confirmed the efficacy of the block, showing better pain relief and reduced opioid consumption in patients who received the PPB, compared to controls. However, the clinical differences between performing the block or not were less pronounced than the statistical significance of the results.[32,33,34] Similarly, a study by Sakai et al.[35] also demonstrated the noninferiority of the PPB compared to the tibial nerve block in terms of analgesic efficacy while still preserving its motor-sparing characteristics. Although the literature remains limited, there are sufficient data to consider the technique promising. It may eventually complement the IPACK block as an optimal fascial plane technique for the posterior compartment of the knee.

More interestingly, the results highlight how, especially after the prosthetic implant, the sensory innervation of the posterior compartment involved in pain transmission after TKA is less complex than the anterior compartment. Therefore, the role of regional anesthesia techniques for the posterior compartment may not be as crucial as for the anterior compartment [Figure 2]. Consequently, when an effective anterior compartment technique is combined with an adequate multimodal analgesia, the need for additional posterior compartment blocks may be reduced and adding such a block may still lead to statistically significant improvements, even though the clinical benefits remain modest.[36] However, in specific situations, a posterior compartment block may be useful as a rescue technique (which can be performed postoperatively, either proximally or distally to the surgical dressing). Unlikely, the IPACK block, could be necessarily performed before surgery. First described in 2012 by Dr. Sanjay Sinha, it has since become widely adopted and boasts an extensive body of literature, with over 100 published articles. This has resulted in six systematic reviews and meta-analyses, published between 2021 and 2023, all of which consistently confirm its effectiveness in reducing pain, opioid consumption, and improving postoperative performance within the first 24 hours after TKA. The efficacy of the IPACK block is closely tied to its combination with an ACB and a multimodal analgesia regimen.

Figure 2.

Comparison of preoperative and postoperative sensory innervation and pain generator distribution in the two knee compartments. On the left, preoperative state: Green/yellow gradient represents the transition of sensory innervation from anterior to posterior. Pain generators (red stars) are primarily intra- and pericapsular, distributed across both compartments depending on the extent of articular damage. The outer layers are not involved. On the right, postoperative state: Red/orange gradient represents the transition of sensory innervation and pain from anterior to posterior. Intra- and pericapsular pain generators (red stars) have been removed. Most pain generators are now located around the surgical trauma sites and the surgical wound in the outer layers, predominantly on the medial side of the anterior compartment. The nerve to vastus medialis (NVM) and the infrapatellar branch of the saphenous nerve (SN) are the most critical nerves to block

One key takeaway from these studies is the relatively short duration, typically lasting between 12 and 24 hours. However, when compared to the LIA, the IPACK block has shown a longer duration, with some trials indicating reduced opioid consumption for up to 48 hours postoperatively.[37,38,39,40,41,42]

We can hypothesize that higher concentrations of local anesthetics, combined with adjuvants and a vasoconstrictor, could enhance and prolong its efficacy and even though no trials have directly compared the effectiveness of the IPACK block with or without adjuvants, adding dexamethasone to the mixture could potentially amplify the local analgesic effects possibly with a direct anti-inflammatory effect on the injection site (which is close to the surgical site), enhancing the block’s duration beyond what is typically seen with systemic or intrathecal administration.[43,44]

Drawing from current evidence, we conclude that the IPACK block (performed with 15–20 mL of long-acting local anesthetics, potentially combined with adjuvants and a vasoconstrictor) in conjunction with an anterior compartment technique and multimodal analgesia is the preferred strategy for optimal analgesia following TKA.

Several other posterior compartment techniques have been discussed in the literature, though they are supported by very limited data and research, making it difficult to draw firm conclusions. However, these techniques may still be of interest for further research.

The HI-PAC block, described by Sonawane et al. in 2021,[45] closely resembles the second injection of the DSB, but the injection is performed in the proximal adductor canal using high volumes of local anesthetic (30–40 mL of 1% ropivacaine with dexamethasone). The name HI-PAC stands for “HIgh volume - Proximal Adductor Canal.” This technique exploits the continuity between the adductor canal and the femoral triangle as well as between the adductor canal, adductor hiatus, and popliteal fossa [Figure 3].

Figure 3.

Continuity of the adductor canal with the femoral triangle superiorly and the adductor hiatus and popliteal fossa inferiorly. Limited anesthetic volumes injected in the green area (distal femoral triangle/proximal adductor canal) are safe, avoiding both the main trunk of the femoral nerve superiorly and the main trunk of the sciatic nerve inferiorly

The goal is to achieve motor-sparing analgesia for the entire lower limb. However, the large volume of anesthetic and the lower injection site allow the local anesthetic to reach the popliteal fossa and the sciatic nerve, ensuring effective posterior compartment analgesia. To avoid blocking the motor components of the sciatic nerve which may impair early mobilization, making it less ideal in fast-track recovery protocols, the authors suggest using a highly diluted anesthetic mixture (1% ropivacaine combined with dexamethasone) to minimize the motor impairment while extending the duration of the block. This aligns with the concept of VMS techniques, which rely on high volumes of diluted anesthetic to minimize motor block while providing effective analgesia. Despite the theoretical benefits, VMS blocks still target major nerve branches, meaning that even without overt motor block, there is still a risk of muscle weakness, which can increase the risk of falls during early ambulation.

However, when ACB alone results inadequate, being adequately distant from the surgical site, the HI-PAC may be promise as a rescue technique for postoperative pain after TKA; nonetheless, the authors primarily recommend it for surgeries below the knee and its real-world effectiveness remains unproven. No clinical trials have been published to date.[45,46]

Similar to the HI-PAC, Roy et al. in 2018[47] developed another high-volume single-injection technique, called the “4-IN-1 Block”, which targets the saphenous nerve, obturator nerve, NVM, and the sciatic nerve. Compared to the HI-PAC block, the 4-IN-1 block involves a more distal injection at the level where the descending genicular artery branches from the femoral artery, approximately 8–10 cm proximal to the medial femoral condyle. This technique involves a single perivascular injection of local anesthetic (35 mL of 0.2% ropivacaine), which reaches both the adductor canal and popliteal fossa. In a following publication in 2020, Roy et al.[48] modified the technique by adding a smaller injection near the vastus medialis nerve (with the aid of a peripheral nerve stimulator – 0.4–0.5 mA) before performing the second larger perivascular injection. A randomized trial in 2023 demonstrated that this “Modified 4-IN-1 Block” was noninferior to the well-established ACB + IPACK combination for TKA patients. Although promising, the technique should still be categorized among VMS blocks, and its potential for increased risk of falls in fast-track patients cannot be ruled out.[49]

Another interesting development came from Kardash et al. (2016),[50] who noted that after TKA, the analgesic effect of a rescue block for the supero-medial genicular nerve (SMGN) often made blocking other genicular nerves unnecessary. They hypothesized a lateral fascial plane spread and described it as a potential new FPB technique, which they termed the SPANK block (Sensory Posterior Articular Nerves of the Knee). A cadaveric study confirmed that, at the SMGN level, when the needle is positioned slightly posteriorly in a fascial plane superficial to the femoral periosteum, the anesthetic spreads to the lateral compartment, mimicking the pattern of the IPACK block. A trial by Padhy et al.[51] compared the two techniques and found the IPACK to be significantly superior. Despite the limited literature, the SPANK block represents an interesting concept for future research, suggesting the fascial planes surrounding the musculo-tendinous structures of the knee as the main target for future techniques, likewise the gastrosoleus interfascial plane block (GIP), which targets the fascial plane between the soleus muscle and the medial belly of the gastrocnemius muscle. Introduced in 2023 by Abraham et al.,[52] the technique deserves mention. A cadaveric study demonstrated that an injection performed in that plane, 7–8 cm distally from the popliteal crease, resulted in a spread pattern similar to the IPACK block and a pilot study on 22 patients showed comparable results between the two techniques, suggesting the GIP block as a promising alternative.

While more data are needed, this technique appears promising and further supports the idea that fascial planes will increasingly become the primary target for future analgesic approaches. This applies to the techniques specifically designed as FPBs but also to future strategies for indirectly targeting peripheral nerves and nerve plexuses. The prime examples are both the parasacral ischial plane (PIP) block, introduced by Venkataraju in 2019, and the parasacral interfascial plane block, described the same year by Tulgar et al. These two closely related techniques provide an indirect interfascial approach to the sacral plexus, reinforcing the concept that fascial approaches can be safer than direct nerve blocks while remaining equally effective.[53,54,55,56]

Both techniques involve an injection in the fascial plane above the periosteum of the ischial bone, close to the greater sciatic foramen, enabling an indirect block of the proximal sciatic nerve. As with other virtual motor-sparing (VMS) blocks, they may not be the best choice for fast-track TKA. However, the two techniques remain noteworthy as they allow the block to be performed in a supine position and facilitate the placement of a continuous infusion catheter in a more stable, effective, and technically straightforward manner, as demonstrated by Zheng, Ye, and colleagues[57,58]

Beyond the well-established effectiveness of an IPACK block combined with a proximal ACB, using 15–20 ml of a 0.2% to 0.5% long-acting local anesthetic, the posterior compartment blocks contribute to postoperative analgesia management after TKA; however, while this contribution often reaches statistical significance, its clinical impact is generally modest and far less pronounced than that of anterior compartment techniques.

Other Techniques

Among the many ultrasound-guided techniques described, ESP blocks (erector spinae plane blocks), both lumbar and sacral, have been explored for postoperative analgesia in lower limb surgeries. ESP blocks target the paravertebral space, where local anesthetic can spread anteriorly to affect the lumbar or sacral plexuses, offering a virtual motor-sparing effect. However, ESP blocks, more than any other fascial plane block, achieve their effectiveness not only through direct nerve involvement but also via secondary mechanisms such as systemic absorption and the anti-inflammatory effects of local anesthetics 4. Moreover, they are believed to affect the anterior rami of the spinal nerves, nerve root ganglia, and possibly the epidural space (though in a highly diluted portion) ensuring a motor-sparing effect, as demonstrated in some MRI studies.[59] Regarding ESP blocks for TKA, available data remain scarce, consisting mainly of case reports. The lumbar ESP block has shown efficacy in a case of above-knee amputation (Langnas, 2022), while the sacral ESP block has provided effective analgesia following knee arthroplasty, both as a standalone technique (Marrone, 2025) and in combination with ACB (Marrone, 2024). However, high-quality studies are needed to validate these techniques in this clinical setting to establish its clinical validity and suitability.[60,61,62]

Clinically valid and suitable for TKA are the genicular nerve blocks and the LIA, but their description falls outside the scope of this review. On the other hand, a particular variant, introduced by Roques et al.[63] in 2024 as periarticular vasoconstrictor infiltration (PVI), warrants mention for several reasons:

• Unlike LIA, it utilizes supra-periosteal fascial planes, making it comparable to an ultrasound-guided fascial plane block.

• Unlike LIA, it is performed by anesthesiologists rather than surgeons.

• It leverages the vasoconstrictive effect of epinephrine, allowing the procedure to be performed without a tourniquet.

The full technique involves a fascial block targeting the four genicular nerves (near the vessels entering the joint capsule), combined with an IPACK block and an intra-articular/subcutaneous infiltration along the incision line. A total of 60–80 mL of ropivacaine 0.2% or levobupivacaine 0.125%, mixed with epinephrine 1:200,000, is used for the six injections. While the only published study does not provide clinical data, it suggests that PVI’s analgesic efficacy is comparable to LIA. Therefore, from a purely analgesic standpoint, it does not represent a major breakthrough. However, if future studies confirm that it eliminates the need for a tourniquet, the technique could gain widespread adoption. Even in this case, further research is needed.[63]

Conclusions

The available data reinforce key concepts regarding knee innervation and the complexity of regional anesthesia techniques. From this review, we can derive several clinical, anatomical, and conceptual conclusions, as well as potential directions for future research:

• There is a continuous anatomical pathway of fasciae and muscles connecting the femoral triangle, adductor canal, adductor hiatus, and popliteal fossa. Within this continuum, the superficial femoral artery (transitioning into the popliteal artery) serves as a constant landmark, while the main nerve branches, which supply the joint, bones, muscles, tendons, and fasciae, intricately intertwine throughout.

• No single regional anesthesia technique can comprehensively target all these structures with a single injection. Techniques attempting to do so either require multiple needle insertions or rely on high anesthetic volumes that spread via the anatomical continuity, classifying them as virtual motor-sparing (VMS) blocks.

• Complete analgesia for fast-track TKA surgery requires a motor-sparing technique for the anterior compartment combined with a motor-sparing technique for the posterior compartment. However, the sensory innervation of the posterior compartment is less involved in pain transmission than the anterior compartment.

• Based on current evidence, subsartorial techniques collectively referred to as the adductor canal block (ACB) remain the most effective for the anterior compartment. Anatomically, the proximal ACB is the most effective, minimizing the risk of unintentional sciatic or femoral nerve blockade while ensuring reliable coverage of the NVM.

• For the posterior compartment, the IPACK block is currently the most effective technique, while the PPB shows promise.

• VMS blocks carry risks and should be used as rescue techniques or reserved for hospitalized patients who are not intended for early ambulation.

While numerous other ultrasound-guided techniques may prove equally effective, further studies are needed to support their use. Many represent valuable anatomical and research insights but, at present, reflect an ongoing yet unsuccessful effort to develop a single technique that adequately covers both compartments.

Ultimately, this review highlights two major trends in regional anesthesia:

1. The increasing integration of regional techniques into multimodal analgesia protocols aimed at accelerating functional recovery.

2. A growing shift toward fascial plane targets, recognizing their role in acute postsurgical pain generation.

The development of an optimal technique for fast-track TKA remains an ongoing challenge, requiring further research that extends beyond anatomical considerations. Future advancements will likely need to integrate regional anesthesia with other modalities, tailoring approaches to the individual patient characteristics.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.