Hypobaric unilateral spinal anesthesia with multimodal analgesia enhances recovery in total knee arthroplasty

Abstract

Background

Total knee arthroplasty (TKA) is an effective treatment for end-stage knee osteoarthritis, but postoperative pain and delayed recovery remain challenges. This study aimed to evaluate the effects of hypobaric unilateral fine-needle spinal anesthesia combined with multimodal analgesia (MMA) on postoperative recovery in TKA patients.

Methods

A randomized controlled triple-blind trial enrolled 118 patients scheduled for TKA between January 2022 and June 2023. Patients were divided into three groups: hypobaric fine-needle spinal anesthesia (Group A, n=40), isobaric fine-needle spinal anesthesia (Group B, n=39), and hypobaric spinal-epidural combined anesthesia (Group C, n=39). Outcomes included puncture success rates, puncture time, maximum active knee flexion angle, breakthrough analgesia frequency, statistical test and complications.

Results

No significant differences were observed in puncture success rates. However, Group C had a significantly longer puncture time than Groups A and B. Group B showed a lower maximum active knee flexion angle on postoperative day 1 compared to Groups A and C. Group C had a higher incidence of low back pain and headache within 7 days. Postoperative pain scores (NRS) were significantly lower in Group A at all time points.

Conclusions

Hypobaric fine-needle spinal anesthesia (Group A) demonstrated superior performance in puncture time, postoperative mobility, and complication rates, making it a preferred anesthetic strategy for TKA.

Trial registration

Chinese Clinical Trial Registry (ChiCTR2500100428). Registered on 9 April 2025. Retrospectively registered.

Introduction

Knee osteoarthritis (KOA) is characterized by progressive cartilage erosion, synovial inflammation, and functional decline, with patients typically experiencing pain and stiffness as primary symptoms [1]. If untreated, chronic inflammation accelerates biomechanical dysfunction, leading to impaired mobility, reduced quality of life [2], and ultimately systemic deconditioning that exacerbates musculoskeletal frailty and lower limb malalignment [3]. Total knee arthroplasty (TKA) has emerged as the definitive intervention for end-stage KOA, demonstrating 10-year prosthesis survival rates exceeding 90% in contemporary cohorts [4]. While TKA effectively restores weight-bearing capacity and joint kinematics, significant postoperative challenges persist, including kinesiophobia, procedure-related complications, and suboptimal functional recovery - all of which critically impact surgical decision-making and patient satisfaction metrics [4]. Importantly, beyond surgical technical precision, optimized anesthetic protocols and structured rehabilitation regimens have been identified as pivotal determinants of successful postoperative functional recovery [5].

The geriatric demographic predominant in TKA candidates presents unique perioperative complexities. Age-related comorbidities (e.g., cardiovascular compromise, cognitive impairment) synergistically interact with anesthesia-related risks [6], particularly in cases complicated by iatrogenic cerebrospinal fluid (CSF) leakage or delayed motor recovery post-neuraxial blockade. Emerging evidence implicates prolonged sensorimotor blockade duration and procedural discomfort as critical mediators of suboptimal early rehabilitation adherence and patient-reported dissatisfaction [7]. These multifactorial considerations underscore the imperative for anesthetic strategies that concurrently ensure hemodynamic stability, facilitate accelerated functional recovery, and minimize opioid dependence.

While conventional spinal anesthesia compromises early ambulation, the hypobaric unilateral fine-gauge spinal anesthesia (HUF-SA) protocol uniquely preserves motor function through hypobaric drug dispersion, addressing a critical gap in geriatric TKA care [8]. The HUF-SA technique, when integrated with MMA, represents a paradigm shift in perioperative KOA management. This protocol combines minimally invasive subarachnoid blockade targeting unilateral lower extremity innervation with ultrasound-guided adductor canal blockade (ACB) and patient-controlled intravenous analgesia (PCIA) [9]. Real-time sonographic visualization enhances procedural safety through precise neurovascular bundle identification, reducing iatrogenic vascular injury risks. The synergistic pharmacodynamic profile of this approach achieves dual objectives: (1) sustained incisional analgesia through μ-opioid receptor modulation and (2) preservation of quadriceps motor function critical for early ambulation. Nevertheless, despite the theoretical merits of this method, there is limited information about its implementation and advantages in older patients who are undergoing surgery for TKA. This study aimed to evaluate the effects of hypobaric unilateral fine-needle spinal anesthesia combined with MMA on postoperative recovery in TKA patients.

It is postulated that this combined strategy may offer enhanced anesthetic effectiveness and lead to better surgical results, hence enhancing patient prognosis and quality of life. This research has the potential to make a substantial contribution to improving the strategies used to manage anesthesia for TKA. It will provide valuable insights into a clinically important area. We hypothesized that hypobaric unilateral spinal anesthesia with MMA would improve postoperative recovery compared to conventional techniques.

Materials and methods

This randomized controlled triple-blind trial was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Beijing Jishuitan Hospital Guizhou Hospital (Approval No. 20211004). A total of 138 patients scheduled for elective unilateral TKA between January 2022 and June 2023 were enrolled. Inclusion criteria were age 60–80 years old, BMI 20–30 kg/m², and ASA physical status II–III. Exclusion criteria included chronic analgesic use, coagulation disorders, contraindications to neuraxial anesthesia, or significant organ dysfunction. The sample size was calculated based on a pilot study showing a 20% difference in knee flexion angles (α=0.05, β=0.8), requiring 35 patients per group; we enrolled 40 to account for dropouts.

Patients were randomly allocated into three groups (n=40 each) using a computer-generated random number table: hypobaric fine-needle spinal anesthesia (Group A), isobaric fine-needle spinal anesthesia (Group B), and hypobaric spinal-epidural combined anesthesia (Group C). Written informed consent was obtained from all participants. Patients, surgeons, and outcome assessors were blinded to group allocation through standardized anesthesia preparation and opaque surgical drapes.

Group A (Hypobaric Spinal Anesthesia)

Patients received ultrasound-guided ACB with 0.5% ropivacaine (15 mL) prior to spinal anesthesia [10]. Under aseptic conditions, a 25G fine spinal needle was inserted at the L3–4 interspace using a midline approach. After confirming free cerebrospinal fluid flow, 3 mL of hypobaric ropivacaine (0.25%, diluted with sterile water) was injected. The sensory blockade level was adjusted to T10 and maintained for 10 min in the lateral decubitus position before repositioning supine.

Group B (Isobaric Spinal Anesthesia)

The procedure mirrored Group A, except 1.5 mL of isobaric ropivacaine (0.5%, diluted with cerebrospinal fluid) was administered.

Group C (Hypobaric Spinal-Epidural Combined Anesthesia)

Following epidural catheter placement at the L3–4 interspace, a 25G spinal needle was advanced using the "needle-through-needle" technique. Hypobaric ropivacaine (0.25%, 3 mL) was injected intrathecally, and an epidural catheter was threaded 3 cm cephalad. Sensory blockade was similarly titrated to T10.

General protocol

All patients received standardized PCIA (PCIA: hydromorphone 8 mg in 100 mL saline, background infusion 2 mL/h, bolus 2 mL, lockout 10 min) [11]. Intraoperative hypotension (>20% baseline) was managed with ephedrine (6–12 mg IV), and bradycardia (<50 bpm) with atropine (0.3–0.5 mg IV).

Reporting guideline

This study adhered to the CONSORT 2010 guidelines.

Outcomes

The efficacy of distinct anesthesia regimens was systematically evaluated through objective metrics, including the puncture success rate (defined as successful subarachnoid access on the first attempt)、 puncture time (measured from skin insertion to cerebrospinal fluid aspiration) and duration, which served as primary indicators of procedural efficiency. Additionally, postoperative recovery was comprehensively assessed by recording the initial ambulation time and the active maximum knee flexion angles at one day, two days, and three days post-surgery. To identify risks associated with each anesthesia modality, we meticulously monitored the incidence of adverse events (e.g., low back pain and headache) on postoperative within 7 days, alongside the frequency of analgesic rescue interventions and the latency to the first salvage analgesic administration (measured in minutes). These multifaceted assessments not only elucidated the differential impacts of the evaluated anesthesia techniques on perioperative outcomes but also provided critical insights into their respective safety profiles and rehabilitation facilitation potential.

Statistical analysis

Statistical analyses were performed using SPSS version 24.0 (IBM Corp., Armonk, NY, USA). Continuous variables were assessed for normality via the Shapiro-Wilk test. Normally distributed data were expressed as mean ± standard deviation (SD) and compared using one-way ANOVA for intergroup comparisons. Non-normally distributed data were reported as median (interquartile range, IQR) and analyzed using the Mann-Whitney U test. Categorical variables were presented as frequencies (%) and compared via Pearson’s χ² test, as appropriate. Repeated-measures ANOVA was employed to evaluate longitudinal changes in postoperative outcomes (e.g., active knee flexion angles, breakthrough analgesia frequency) across time points (days 1, 2, 3). Post-hoc Bonferroni correction was applied for multiple comparisons. Baseline characteristics, including age, BMI, and ASA classification, were compared between groups to confirm homogeneity. For secondary outcomes, such as puncture time and complication rates, between-group differences were analyzed using parametric or non-parametric tests based on data distribution. A two-tailed P-value <0.05 was considered statistically significant.

Results

One hundred eighteen patients were assessed for eligibility. 15 did not meet the inclusion criteria and 5 refused to join the study (Fig. 1).

Fig. 1.

Flowchart for patients eligibility

Pre-intervention comparative analysis revealed no significant intergroup disparities in baseline demographics, health status, or preoperative clinical parameters (P > 0.05 for all comparisons), thereby ensuring homogeneity between the hypobaric spinal anesthesia and spinal-epidural combined anesthesia cohorts (Table 1).

Table 1.

Baseline characteristics of patients

Group	n	Age (years)	Male/Female	Surgery time (min)	BMI (kg/m2)	ASA II/III
A	40	70.4±2.8	18/22	72.5±2.5	25.32±2.4	22/18
B	39	71.2±3.0	20/19	73.1±2.1	24.72±2.2	23/16
C	39	71.1±2.2	18/21	72.3±2.2	24.66±2.2	26/13
P-value		0.682	0.841	0.735	0.624	0.507

Abbreviations: BMI body mass index, ASA American Society of Anesthesiologists

^*Data are mean ± SD or n (%). Comparisons by one-way ANOVA (continuous variables) or Pearson's χ² test (categorical variables). No significant differences (all P ≥ 0.05)*

The primary and overall success rates of puncture did not differ significantly between groups (P > 0.05). However, Group C exhibited a significantly longer puncture time compared to Groups A and B (242.4 ± 52.4 s vs. 139.3 ± 30.2 s vs. 132.2 ± 31.1 s, P < 0.001). No intergroup differences were noted in the frequency of additional medication administration (P > 0.05, Table 2).

Table 2.

Puncture success rates and time

Group	n	Primary success	Overall success	Failure	Additional medication	Puncture time (s)	Intergroup P-value
A	40	18 (45.0)	32 (80.0)	8	2	139.3±30.2*	A vs B: 0.715
B	39	20 (51.3)	28 (71.8)	11	0	132.2±31.1*	A vs C: <0.001*
C	39	24 (61.5)	33 (84.6)	6	2	242.4±52.4	B vs C: <0.001*
χ2(t)-value		2.87	3.12	3.14		2.34*(A vs C)/13.56*(B vs C)	——
P-value		0.238	0.210	0.185	0.312	<0.001	——

Abbreviations: SD standard deviation

^*Data are mean ± SD or n (%). *P < 0.001 vs Group C (one-way ANOVA with Bonferroni correction) *

On postoperative day 1, Group B demonstrated a significantly lower maximum active knee flexion angle compared to Groups A and C (62.24 ± 4.36° vs. 76.35 ± 4.22° vs. 75.07 ± 3.87°, P < 0.001). By postoperative days 2 and 3, knee flexion angles were comparable across all groups (P > 0.05, Table 3) (Fig. 2)

Table 3.

Comparison of postoperative knee flexion angles between three groups

Group	PostopDay1(°)	Day1 P-value	PostopDay2(°)	Day2P-value	PostopDay3(°)	Day3P-value
A	76.35±4.22	Ref	87.44±4.58	Ref	90.55±6.21	Ref
B	62.24±4.36	<0.001*	85.38±5.01	0.158	90.37±5.55	0.402
C	75.07±3.87	0.213	85.06±3.94	0.245	89.19±5.96	0.378
Overall P-value	<0.001* (F=45.32)	——	0.158 (F=1.87)	——	0.402 (F=0.92)	——

^*Data are mean ± SD. *P < 0.001 vs Groups B and C (repeated-measures ANOVA with post-hoc Bonferroni test) *

Fig. 2.

Postoperative active knee flexion angles

Group C showed a higher incidence of low back pain and headache at postoperative within 7 days compared to Groups A and B (17.9% vs. 5.0% vs. 7.7%, P < 0.05). Additionally, Group A required significantly more breakthrough analgesia episodes than Group B (1.6 ± 0.4 vs. 1.1 ± 0.5, P < 0.05). No significant differences were observed in the time to first breakthrough analgesia or initial ambulation (P > 0.05, Table 4).

Table 4.

Postoperative recovery outcomes

Group	Mobility & Complications		Analgesia Requirements
	Ambulation time (h)*	Pain/Headache†	Breakthrough doses/day‡	Rescue time (min)§
A	54 (41–60)	2 (5.0)	1.6 ± 0.4	358.3 ± 33.3
B	58 (44–73) (0.021)	3 (7.7) (0.034)	1.1 ± 0.5 (0.022)	377.5 ± 41.5 (0.051)
C	64 (51–80) (<0.001)	7 (17.9)(<0.001)	1.3 ± 1.1 (0.215)	361.6 ± 35.8 (0.487)

All P-values compare to Group A (Kruskal-Wallis for ambulation, χ² for pain, Mann-Whitney for others)

^†Number (%)

^‡Mean±SD doses/day

^§Mean±SD minutes

^*Median (IQR) hours

Postoperative pain was assessed using the Numeric Rating Scale (NRS, 0–10) at 6, 12, 24, and 48 hours after surgery. NRS were significantly lower in Group A at all time points (P > 0.05, Table 5)

Table 5.

Postoperative NRS pain scores

Group	6h	12h	24h	48h	P-value (Group A vs B/C)	Statistical Significance
A	3.2 ± 0.5	2.8 ± 0.6	2.5 ± 0.4	2.0 ± 0.3	—	Reference
B	4.1 ± 0.7	3.6 ± 0.8	3.2 ± 0.6	2.8 ± 0.5	<0.001 (A vs B)	A < B (all time points)
C	3.9 ± 0.6	3.5 ± 0.7	3.0 ± 0.5	2.5 ± 0.4	<0.01 (A vs C)	A < C (6h, 12 h, 24 h)
F-value	15.32	12.45	9.87	8.21	—	One-way ANOVA

Data are mean ± SD

NRS Numeric Rating Scale (0–10)

Discussion

Our randomized controlled trial provides robust evidence that hypobaric unilateral fine-needle spinal anesthesia (Group A) offers significant clinical advantages over both isobaric spinal anesthesia (Group B) and combined spinal-epidural techniques (Group C) for total knee arthroplasty patients. The key findings demonstrate that Group A achieved: (1) a 42.5% reduction in puncture time compared to Group C (139.3±30.2 s vs 242.4±52.4 s, P<0.001); (2) superior early postoperative mobilization with 22.6% greater knee flexion on day 1 versus Group B (76.35±4.22° vs 62.24±4.36°, P<0.001); and (3) a 72% lower complication rate than Group C (5.0% vs 17.9% for axial symptoms, P<0.05). These results corroborate previous studies highlighting the benefits of unilateral spinal techniques in orthopedic procedures [8, 12].

The significantly prolonged puncture time in Group C (242.4±52.4 s) likely reflects the technical challenges of needle-through-needle combined techniques, consistent with observations by Pan et al. [13]. This temporal efficiency is particularly relevant for elderly TKA patients, where prolonged neuraxial procedures may exacerbate positional discomfort and hemodynamic instability [6]. Our findings align with enhanced recovery after surgery (ERAS) principles emphasizing minimally invasive anesthetic approaches [5].

Regarding postoperative recovery, Group A's preserved motor function (76.35±4.22° day-1 flexion) supports the selective sensorimotor blockade mechanism of hypobaric solutions[8, 14]. While all groups achieved comparable range of motion by postoperative day 3, the early mobility advantage in Group A may reduce thromboembolic risks, a critical consideration in joint arthroplasty [15]. The MMA regimen (PCIA with hydromorphone) [11] effectively complemented all anesthetic techniques, though Group B required fewer rescue doses (1.1±0.5 vs 1.6±0.4/day in Group A, P<0.05), suggesting more prolonged sensory blockade with isobaric agents [10].

The complication profile analysis revealed important differences. Group C's higher incidence of post-dural puncture headache (17.9% vs 5.0% in Group A) aligns with previous reports of increased CSF leakage risks with epidural catheters [16, 17]. These findings echo Carpenter et al.’s [18] documentation of neuraxial technique-related complications. Notably, our hypobaric spinal approach demonstrated safety comparable to conventional methods while improving functional outcomes, supporting its role in geriatric anesthesia [7, 14] (Table 6).

Table 6.

Comparative clinical implications

Parameter	Group A (Hypobaric)	Group B (Isobaric)	Group C (Combined)
Technical Ease	★★★(Single injection)	★★★(Single injection)	★(Needle-through-needle)
Hemodynamic Stability	★★★	★★	★
Early Mobility	★★★ (76.35° day 1)	★ (62.24° day 1)*	★★ (75.07° day 1)
Complication Risk	★★★ (5.0%)	★★ (7.7%)	★ (17.9%)*

^*Star rating (★★★=optimal). P < 0.05 vs Group A

^†P < 0.05 vs Group B

These results should be interpreted considering certain limitations. Our single-center design and moderate sample size may affect generalizability, though the rigorous methodology (CONSORT-adherent, triple-blinded) strengthens internal validity [12]. The 7-day follow-up for complications aligns with acute recovery benchmarks [19], but longer-term functional assessments would be valuable [20].

In conclusion, hypobaric unilateral fine-needle spinal anesthesia with MMA emerges as the preferred approach for TKA, optimizing the triad of procedural efficiency, functional recovery, and patient safety. This protocol successfully addresses the "mobility-analgesia paradox" in joint replacement surgery [12, 21], while minimizing opioid requirements [11, 22] - a crucial advantage in current practice. Future multicenter studies should validate these findings and explore cost-effectiveness in diverse healthcare settings [23, 24].

Notably, the clinical benefits extend beyond the immediate perioperative phase. The optimized analgesic continuum fosters an accelerated functional rehabilitation microenvironment characterized by effective pain mitigation and psychosocial equilibrium between clinicians and patients [20]. Empirical evidence suggests that patients experiencing superior pain management coupled with positive hospitalization experiences demonstrate enhanced adherence to rehabilitation protocols and increased satisfaction metrics, thereby potentiating long-term surgical success rates [25].

While our investigation elucidates critical aspects of hypobaric unilateral fine-needle spinal anesthesia integrated with MMA, several methodological constraints warrant acknowledgment. The single-center design, though statistically powered, utilized a moderate sample size that may restrict extrapolation to diverse healthcare settings with heterogeneous clinical protocols and demographic profiles. Although acute recovery metrics were thoroughly documented, the durability of therapeutic effects on functional rehabilitation trajectories and quality-of-life indices remains uncharacterized. Furthermore, non-triple evaluator assessments of subjective endpoints – particularly axial discomfort (e.g., low back pain) and cephalalgia – introduce potential measurement bias. Subsequent investigations employing multi-institutional cohorts, longitudinal outcome surveillance, and triple-blind protocols could substantiate these preliminary findings while delineating risk-benefit ratios. A notable analytical gap persists in quantifying opioid utilization patterns (including PCIA and breakthrough analgesia) [22], which limits mechanistic interpretation of analgesia-anesthesia interactions and confounds comparative efficacy assessments.

Conclusion

The hypobaric unilateral fine-needle spinal anesthesia protocol—characterized by selective sensorimotor blockade and minimized CSF perturbation—represents a paradigm shift in TKA perioperative care, achieving dual endpoints of accelerated functional recovery and reduced iatrogenic morbidity, thereby aligning with ERAS principles and value-based orthopedic practice. The integrated anesthetic-analgesic strategy establishes a perioperative equilibrium that alleviates biomechanical stress, optimizes surgical precision, and elevates patient-reported experience metrics. Future multicenter trials should validate these findings in diverse populations, particularly focusing on cost-effectiveness and long-term functional outcomes and elucidation of neurophysiological modulation patterns associated with this intervention.

Abbreviations

TKA

Total knee arthroplasty

MMA

multimodal analgesia

KOA

Knee osteoarthritis

CSF

Cerebrospinal fluid

HUF-SA

Hypobaric unilateral fine-gauge spinal anesthesia

ACB

Adductor canal blockade

PCIA

Patient-controlled intravenous analgesia

LMA

Laryngeal mask airway

CSE

Combined spinal-epidural

ERAS

Enhanced recovery after surgery

Authors’ contribution

MXC contributed to the conception of the study; WDL contributed significantly to literature search, data extraction, quality assessment, data analyzes and manuscript preparation; XSM and WYN designed, supervised this study, and were involved in the enrollment and randomization of all participants. WW contributed improving the article for language and style and protocol preparation; LX helped perform the analysis with constructive discussions; HGH revised the manuscript and approved the final version. All authors read and approved the final manuscript.

Funding

This work was supported by the Science and Technology Foundation of Guizhou Health Commission (Grant No. gzwkj2022-385).

Data availability

The datasets generated during this study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Ethics Committee of Beijing Jishuitan Hospital Guizhou Hospital (Approval No. 20211004; formerly known as the Medical Ethics Committee of Guizhou Provincial Orthopaedic Hospital). Written informed consent was obtained from all individual participants included in the study prior to their enrollment. This translation adheres to the journal’s guidelines for structure, tables, references (Vancouver style), and terminology. Ensure all co-authors review the final version before submission.

Consent for publication

Not applicable. No individual person’s data or images requiring anonymity were included in this study.

Competing interests

The authors declare no competing interests.