Do Adductor Canal Blocks Provide Additional Analgesic Benefit to Periarticular Injection Alone for Primary Total Knee Arthroplasty?

Abstract

Background

The added benefit of preoperative, anesthesiologist-performed adductor canal blocks (ACBs) to a modern pain management regimen in total knee arthroplasty (TKA), including multimodal analgesia and periarticular injection (PAI), remains controversial. This study compared opioid consumption and postoperative pain in TKA patients receiving ACB + PAI vs PAI alone.

Methods

This was a single-surgeon retrospective review of patients who underwent unilateral primary TKA over a 2-year period. During year 1, no patients received ACB. During year 2, all patients received ACB. Morphine milligram equivalents, visual analog scale (VAS), and summed pain intensity difference values were compared between both groups over the first 24 hours postoperatively. The final sample included 188 patients: 104 with ACB + PAI and 84 with PAI only.

Results

The mean total morphine milligram equivalents of opioids administered was lower in the ACB + PAI group (31.6 [range: 0-177] vs 42.5 [range: 0-103.5]; P < .01). The ACB + PAI group had lower mean VAS scores (3.1 [range: 0-7.2] vs 4.0 [range: 1.2-6.5]; P < .001). Median maximum VAS pain scores were also lower in the ACB + PAI group (7.0 [interquartile range: 6.0–8.5] vs 8.0 [interquartile range: 7.0–9.0]; P < .001). Similarly, the mean summed pain intensity differ value was lower in the ACB + PAI group (40 [range: 0-118] vs 54 [range: 9-121]; P < .001). These findings remained significant after adjusting for age, sex, body mass index, and American Society of Anesthesiologists class.

Conclusions

The addition of an ACB to PAI was associated with lower postoperative pain values and reduced opioid consumption compared to PAI alone in the first 24 hours postoperatively.

Introduction

Effective postoperative pain management is a critical component of successful recovery following total knee arthroplasty (TKA). Postoperative pain after TKA is often severe and, if inadequately controlled, can hinder early rehabilitation and functional recovery [1]. Patients who experience higher levels of acute postoperative pain following TKA are more likely to develop chronic postsurgical pain at 6 months, even after adjusting for psychological and clinical confounders [2].

Regional anesthesia techniques are a cornerstone of multimodal analgesia for TKA. The adductor canal block (ACB) targets the saphenous nerve in the mid-thigh adductor canal, providing predominantly sensory blockade of the anteromedial knee with minimal impact on quadriceps function [[3], [4], [5]]. Multiple studies have confirmed that an ACB provides postoperative pain relief after TKA that is comparable to complete femoral nerve block, while preserving mobility and reducing the likelihood of falls [6].

Another key analgesic strategy for TKA is periarticular injection (PAI), also known as local infiltration analgesia. PAI is an effective and safe modality for managing postoperative pain in TKA [7]. PAI involves the surgeon infiltrating a cocktail of long-acting local anesthetics into the soft tissues around the knee joint at the time of surgery. This technique directly anesthetizes the surgical site, providing localized pain relief in the immediate postoperative period. PAI has gained popularity because it is simple to perform, has minimal systemic effects, and does not cause motor blockade of major limb muscles, allowing for early mobilization in comparison to femoral nerve block [8]. Studies have demonstrated that PAI significantly reduces postoperative pain with a reduction in nonsteroidal anti-inflammatory drug and opioid consumption, making it a standard in multimodal analgesia protocols in TKA [9,10].

While both ACB and PAI independently improve postoperative pain management, there is ongoing debate about their relative and combined benefits [11]. Some studies suggest that an ACB may provide superior or longer-duration analgesia than local infiltration alone [12]. In contrast, others report that an ACB provides inferior pain relief compared to PAI alone or ACB + PAI [13].

Any intervention that can minimize opioid use while maintaining excellent pain control and allowing early mobilization is highly valuable. Both PAI and ACB fulfill these criteria by providing targeted, localized analgesia with minimal sedation or motor impairment. However, given the resource utilization and procedural risks associated with nerve blocks, it is essential to clarify whether adding ACB to PAI truly confers significant advantages. We hypothesized that the addition of an ACB to PAI would reduce postoperative pain and opioid requirements compared to PAI alone in TKA patients. To investigate this, we conducted a retrospective dual-cohort study comparing postoperative pain scores and opioid consumption in patients who underwent unilateral primary TKA with combined ACB plus PAI vs those who received PAI alone.

Material and methods

Study design and patient sample

Institutional review board approval was obtained at our institution prior to study commencement. This was a retrospective cohort analysis of patients, using medical records review, at a single institution who underwent unilateral primary TKA over a 2-year period. During the first year, patients received PAI alone; during the second year, all patients received PAI + ACB. All other aspects of the standardized perioperative pain protocol remained consistent between groups; no preoperative analgesic regimen was used, but a uniform postoperative protocol was implemented. The PAI cocktail consisted of 60 cc of 0.25% bupivacaine without epinephrine and was standardized across all patients throughout the study. The PAI cocktail was administered after bony resection and prior to trialing in a standardized fashion. A laminar spreader was used to access the posterior joint capsule. The injection was evenly spread throughout the entire joint capsule, femoral and tibial periosteum, and free edges of the arthrotomy. The ACB block consisted of 0.5% ropivacaine, was ultrasound guided, and performed by the same regional anesthesiologists 1 hour prior to the initial surgical incision. All surgeries were performed by a single surgeon utilizing standardized protocols for preoperative assessment and operative technique. Tourniquet use was minimized throughout the study period, consistent with prior evidence that tourniquet use does not significantly impact postoperative pain following primary TKA [14]. The inclusion criteria consisted of patients aged ≥18 who underwent unilateral primary TKA for a diagnosis of primary osteoarthritis using the Stryker Triathlon system with the MAKO robotic platform (Stryker, Mahwah, NJ), received spinal anesthesia, were administered a PAI, and were discharged on postoperative day 1. Only patients who remained in the hospital overnight were included, as their inpatient status allowed for more accurate tracking of opioid utilization compared with relying on at-home recall. The exclusion criteria included same-day discharge and preoperative opioid usage.

Outcomes

Morphine milligram equivalents (MME) values were used to quantify the total amount of opioid analgesic consumed by each patient over the first 24 hours postoperatively, including pain management in the postoperative acute care unit and during formal hospital admission. Opioid administration frequency, drug type, dosage, and route of administration were recorded following surgery. Opioids administered at our institution included: fentanyl intravenous (IV), morphine IV, hydromorphone IV, oxycodone orally (PO), tramadol PO, and hydrocodone PO. Pain was assessed prior to the administration of opioids using the visual analog scale (VAS) pain scores. The sum of pain intensity difference (summed pain intensity difference [SPID]) was used to assess the overall change in pain intensity during the first 24 postoperative hours, reflecting cumulative pain reduction over that period. A raw, nontime weighted-SPID was calculated using VAS pain scores as the mean of the differences between each postoperative score from the baseline.

We grouped patients into 2 cohorts based on analgesic technique administered for their procedure: those who received an ACB (preoperative single-shot anesthesiologist-administered ACB) combined with PAI, and those who received PAI alone. The primary outcome measures included the MME consumed postoperatively, VAS pain scores, and SPID. Other variables of interest collected were sex, age, body mass index (BMI), and American Society of Anesthesiologists (ASA) physical status classification scores, which were extracted from medical records. Age is categorized as <65 years and ≥65 years of age. We also categorized BMI as nonobese (BMI <30 kg/m²) and obese (BMI ≥30 kg/m²).

Data analyses

A priori power analysis was conducted. The study was powered to detect a difference of 10 MME between each group (d = 0.5, alpha = 0.05, power = 0.8), requiring a minimum of 64 per group. Variables were assessed for normality using the Shapiro-Wilk test. Continuous variables were presented as means with ranges or medians and interquartile ranges (IQR) (for non-normally distributed variables). Categorical variables were presented as frequencies and percentages. Comparisons between analgesic groups were performed using chi-square tests for categorical data and independent t tests or the Mann-Whitney U tests for continuous variables. Comparisons of primary outcomes (MME consumption, mean VAS scores, maximum pain scores, and SPID) are presented. The level of statistical significance was set at a P value of <0.05. Additional analyses were performed across demographic factors such as age groups, sex, and BMI. Unadjusted and adjusted regression analyses were used to compare MME consumption and VAS scores between the ACB and PAI groups. Regression coefficients with 95% confidence intervals are reported. All statistical analyses were performed using STATA Version 18.0 (StataCorp LLC, College Station, TX).

There were 504 robotic-assisted primary unilateral TKAs within the study period. The final sample included 188 patients, 104 with ACB vs 84 with PAI only (Table 1). The mean age of patients was 68.7 (range, 18 to 88), with 57% women (n = 108) and 43% men (n = 80). The mean BMI was 31.5 (range, 19.3 to 48) for the ACB group and 32.1 (range, 17.8 to 52.1) for the PAI-only group.

Table 1.

Patient characteristics, postoperative pain, and postoperative narcotics use.

Variables	PAI only (n = 84)	ACB + PAI (n = 104)	Total (n = 188)	P value
Mean age (range)	68 (18 to 84)	69.3 (51 to 88)	68.7 (18 to 88)	.32
Age category (n[%])				.053
<65 years	32 (38.1)	26 (25.0)	58 (30.9)
65+ years	52 (61.9)	78 (75.0)	130 (69.1)
Sex (n[%])				.94
F	48 (57.1)	60 (57.7)	108 (57.4)
M	36 (42.9)	44 (42.3)	80 (42.6)
Mean BMI (range)	32.1 (17.8 to 52.1)	31.5 (19.3 to 48)	31.8 (17.8 to 52.1)	.46
Obesity (n[%])				.081
Nonobese	29 (34.5)	49 (47.1)	78 (41.5)
Obese	55 (65.5)	55 (52.9)	110 (58.5)
ASA classification (n[%])				.043
1	1 (1.2)	0 (0.0)	1 (0.5)
2	56 (66.7)	53 (51.0)	109 (58.0)
3	26 (31.0)	51 (49.0)	77 (41.0)
4	1 (1.2)	0 (0.0)	1 (0.5)
Mean total MME (range)	42.5 (0 to 103.5)	31.6 (0 to 177)	36.5 (0 to 177)	<.01
Mean VAS (range)	4.0 (1.2 to 6.5)	3.1 (0 to 7.2)	3.5 (0 to 7.2)	<.001
Maximum VAS (median [IQR])	8.0 (7.0-9.0)	7.0 (6.0-8.5)	8.0 (6.0-9.0)	<.001
Mean SPID (range)	54 (9 to 121)	40 (0 to 118)	46 (0 to 121)	<.001

P values <0.05 were considered significant.

Results

The mean total MME was significantly lower among patients who received ACB compared to the PAI-only group (31.6 [range: 0 to 177] vs 42.5 [range: 0 to 103.5]; P < .01). The ACB group had significantly lower mean VAS scores compared to the PAI-only group (3.1 [range 0 to 7.2] vs 4.0 [range 1.2 to 6.5]; P < .001). Additionally, the median maximum VAS pain score was significantly reduced in the ACB group (7.0 [IQR: 6.0-8.5] vs 8.0 [IQR: 7.0-9.0]; P < .001). Likewise, the mean SPID was significantly lower in the ACB group compared to the PAI-only group (40 [range 0 to 118] vs 54 [range 9 to 121]; P < .001).

There was no difference between groups in sex, BMI, or age (Table 1). When comparing patients <65 years to those ≥65 years, older patients were more likely to receive an ACB (75.0% [n = 78] vs 25.0% [n = 26], P = .053). Obese patients were more likely to be treated without an ACB (58.5% vs 41.5%). A significantly higher proportion of patients in the ACB group were classified as ASA class 3 compared to those in the PAI-only group (49.0% [n = 51] vs 31.0% [n = 26]), while the PAI-only group had a greater proportion of ASA class 2 patients (66.7% [n = 56] vs 51.0% [n = 53]; P = .043). Additionally, ASA class 1 and 4 were observed only in the PAI-only group, each accounting for 1.2% of that cohort; no patients in the ACB group were classified as ASA 1 or 4 (Table1). Subgroup analysis based on BMI revealed no statistically significant differences in VAS scores or total MME between obese and nonobese patients.

In adjusted regression analyses, after controlling for age, sex, BMI, and ASA class, the ACB group demonstrated a 0.9-point reduction in mean premedication VAS score (0.4 – 1.4-point reduction, P < .001) compared to the PAI group. Similarly, the ACB group showed significantly lower total MME consumption (10.1 lower [2.6 -17.7, P < .01]) than the PAI group. Similar patterns were also observed with maximum pain scores and SPID (Table 2).

Table 2.

Regression analysis of ACB effects.

Outcome variable	Unadjusted β	95% CI	P value	Adjusted βa	95% CI	P value
Mean total MME	−10.9	−18.3 to −3.3	<.01	−10.1	−17.7 to -2.6	<.01
Mean VAS scores	−0.9	1.4 to −0.4	<.001	−0.9	−1.4 to −0.4	<.001
Max VAS score	−1.0	−1.5 to −0.5	<.001	−1.1	−1.6 to −0.6	<.001
SPID	−13.3	−20.0 to −5.93	<.01	−13.6	−21.2 to 5.9	<.01

CI, confidence interval.

^aAdjusted for age, sex, BMI, and ASA class.

Discussion

The addition of an ACB to PAI significantly improved postoperative pain control after TKA. Patients who received combined ACB + PAI on average reported lower pain scores compared to those who received PAI alone. The SPID was lower in the ACB + PAI group, indicating more effective and sustained analgesia in the early postoperative period. Consistent with the improved pain scores, opioid consumption was substantially reduced when ACB was used as an adjunct. The ACB + PAI cohort required fewer opioids than the PAI-only cohort, reflecting a meaningful opioid-sparing effect. In both unadjusted and adjusted analyses, the ACB group demonstrated significantly lower total MME consumption, mean VAS scores, maximum VAS scores, and SPID values, with findings remaining consistent after controlling for age, sex, BMI, and ASA class. It should be noted that the statistically significant reduction in mean VAS scores did not reach previously established thresholds for the minimal clinically important difference (MCID) in TKA patients [15].

Our findings support recent evidence for combining regional nerve blocks with local infiltration techniques for postoperative primary TKA pain management. A 2023 review by Domagalska et al [16] surveyed contemporary analgesic strategies and concluded that the best postoperative pain relief is achieved by combining PAI with a peripheral nerve block, particularly an ACB, due to its potent analgesic effect while sparing motor function. This motor-sparing quality of the ACB makes it an especially attractive adjunct to PAI. A study by Galle et al [17] demonstrated that the combination of ACB + PAI offers superior postoperative pain control compared to either technique alone. While their study reported no immediate differences in pain scores between groups, they did find that patients receiving both ACB and PAI had lower postoperative opioid refill rates and improved early mobilization. These findings align with our results, which demonstrated reduced opioid consumption in the combination ACB + PAI group.

Visser et al [18] examined a large cohort of TKA patients who all received intraoperative PAI, with a subset additionally receiving a continuous ACB. They found that adding a continuous ACB led to substantially decreased opioid consumption on the day of surgery and during hospitalization, without any adverse effect on pain scores, knee range of motion, or length of stay. This parallels our finding; however, we utilized a single-shot preoperative ACB. Likewise, a recent randomized trial compared local infiltration analgesia alone vs a combination of saphenous nerve (adductor canal) block plus iPACK (infiltration between the popliteal artery and capsule of the knee) block, essentially covering both the anterior and posterior knee innervation with nerve blocks [19]. They reported significantly fewer patients with uncontrolled pain in the combined blocks group, lower VAS pain scores postoperatively, and even a slight improvement in knee flexion, as well as earlier hospital discharge, compared to the infiltration-only group [19]. These findings reinforce the concept that comprehensive regional anesthesia can augment the analgesia achieved by local infiltration alone.

It should be noted, however, that not all recent studies have demonstrated large benefits to adding an ACB when a robust multimodal analgesic regimen is already in place. A retrospective review of over 500 TKA patients (all of whom received spinal anesthesia and PAI) found that the addition of an ACB did not significantly improve most early postoperative outcomes, including pain scores, total opioid usage, or length of stay [11]. The only notable difference was a lower incidence of postoperative nausea in the ACB group. The authors concluded that ACB provided little to no added benefit in the context of an established PAI-based analgesic protocol. These findings suggest that high-quality local infiltration can potentially achieve analgesia comparable to that of an ACB in the immediate postoperative period.

The mixed results across studies likely reflect differences in study design and analgesic protocols. Important variables include the constituents of the PAI cocktail and outcome variables of interest. Nevertheless, recent evidence overall favors multimodal approaches. Current reviews concur that combining PAI with peripheral nerve blocks tends to optimize pain control and minimize opioids [16]. Our findings contribute to this literature by specifically confirming the additive value of ACB to a multimodal postoperative pain management protocol.

Improved early pain control, as seen with ACB + PAI, can facilitate early mobilization and can optimize rehabilitation [20]. Patients with lower pain levels are better able to tolerate physical therapy, initiate range of motion exercises, and ambulate sooner after surgery, which later improves postoperative outcomes [1,21]. The motor-sparing property of an ACB means patients maintain the ability to perform straight-leg raises and supported walking even with the nerve block in place [22]. As a result, adding an ACB should not hinder—and in fact likely helps—early mobilization and functional recovery. Our findings align with the goals of Enhanced Recovery After Surgery protocols, which emphasize multimodal analgesia and early ambulation [23]. By reducing pain and avoiding muscle weakness, ACB + PAI can help patients achieve milestones such as walking on the day of surgery or the next morning, which have downstream benefits, including reduced joint stiffness and possibly a lower risk of venous thromboembolism due to early mobility.

Second, the opioid-sparing effect of the ACB has broad implications for patient safety and public health. Patients in the ACB + PAI group required significantly fewer opioids to maintain comfort, which essentially means a lower exposure to opioid-related side effects. In the acute setting, this translates to less postoperative nausea and vomiting, less sedation, and fewer episodes of respiratory depression or confusion, thereby improving the immediate postoperative experience. Our study supports that ACB, as part of a multimodal regimen, can significantly cut down immediate postoperative opioid needs without sacrificing pain relief, thereby enhancing overall recovery quality and reducing opioid dependence.

Additionally, a key safety consideration when combining multiple anesthetic modalities is the total dose of local anesthetic administered. Using a spinal anesthetic, ACB, and a PAI means the patient receives local anesthetic from 3 sources. PAI often involves relatively high volumes of local anesthetic, which can approach toxic systemic levels if the maximum recommended dosage is exceeded [24,25]. In practice, close communication between the surgical and anesthesia teams ensures the total local anesthetic load remains below toxicity thresholds. By managing dosing carefully, the benefits of multimodal analgesia can be achieved safely without predisposing patients to local anesthetic complications.

Limitations

Several potential limitations must be acknowledged when interpreting the results. First, this was a retrospective analysis conducted at a single institution by a single surgeon. Additionally, the surgical technique, anesthetic management, and PAI cocktail, while consistent in our series, may differ elsewhere. Consequently, results might vary with different PAI mixtures or in centers using different rehabilitation protocols. As such, the generalizability of the study may be limited. Another limitation is the subjectivity inherent in pain reporting using VAS scores, which may be influenced by the patient's interpretation or the nursing staff's perception of the patient's pain. Additionally, the 24-hour postoperative measurement window reflects clinical expectations of typical recovery and may introduce selection bias by excluding patients with atypical recovery patterns. Lastly, the clinical meaningfulness of the observed VAS score differences warrants careful interpretation. In adjusted analyses, the ACB group demonstrated a statistically significant 0.9-point reduction in mean VAS score (equivalent to approximately 9 mm on a 100 mm scale). However, we did not include a formal assessment of the MCID. Danoff et al [15] established that the MCID for VAS pain improvement in TKA patients is 22.6 mm, with a minimal detectable change of 16.1 mm. By this benchmark, the observed VAS difference falls below both thresholds and may not represent a change perceptible to patients. This interpretation warrants some caution, as MCID thresholds can vary substantially depending on the statistical method employed, which may affect how surgical benefit is assessed and how many patients are considered to have achieved a meaningful improvement [26].

Conclusions

This retrospective cohort study demonstrated that the addition of an ACB to PAI significantly improved postoperative pain control and reduced opioid consumption within 24 hours following surgery. While statistically significant reductions in mean VAS scores were observed, the magnitude of this difference may not meet established thresholds for clinical meaningfulness. These findings nonetheless add to the growing body of literature supporting ACB combined with PAI as a valuable adjunct in multimodal analgesic protocols.

CRediT authorship contribution statement

Jonathan Brutti: Writing – review & editing, Writing – original draft, Investigation, Formal analysis, Data curation, Conceptualization. Zachary Grand: Writing – review & editing, Writing – original draft, Investigation, Data curation. Chukwuemeka U. Osondu: Writing – review & editing, Project administration, Methodology, Investigation, Formal analysis, Data curation. Robert Birch: Writing – review & editing, Supervision, Methodology, Investigation, Formal analysis, Data curation. Charles M. Lawrie: Writing – review & editing, Visualization, Validation, Supervision, Resources, Investigation, Conceptualization.

Conflicts of interest

C.M. Lawrie is a Zimmer Biomet, Smith and Nephew, Mizuho OSI, Medtronic, Ignite Orthomotion, Ganymed Robotics, and Fios Health consultant and is a AAHKS Fellowship Oversight Committee member and Anterior Hip Foundation president and receives royalties from Zimmer Biomet and owns stock or stock options in Fios Health; all other authors declare no potential conflicts of interest.

For full disclosure statements refer to https://doi.org/10.1016/j.artd.2026.102052.