Effect of Adding a Biceps Femoris Short Head Block to Adductor Canal Block for Analgesia After Total Knee Arthroplasty

Analgesic Efficacy of Adding a Short Head of the Biceps Femoris Muscle Block to the Adductor Canal Block in Total Knee Arthroplasty: A Prospective, Randomized, Controlled Trial

Total knee arthroplasty (TKA) is frequently associated with moderate to severe postoperative pain, which may delay mobilization, increase opioid consumption, and impair functional recovery. Ultrasound-guided adductor canal block (ACB) is widely used as part of multimodal analgesia because it provides effective analgesia while preserving quadriceps muscle strength. However, ACB alone may provide insufficient analgesia for the posterior aspect of the knee. The biceps femoris short head (BiFeS) block is a novel ultrasound-guided regional anesthesia technique targeting the posterolateral sensory innervation of the knee and may enhance postoperative analgesia when combined with ACB. However, clinical evidence regarding its analgesic efficacy in patients undergoing total knee arthroplasty remains limited. This prospective, randomized, controlled trial aims to compare postoperative analgesia between ultrasound-guided adductor canal block alone and adductor canal block combined with a biceps femoris short head block in adult patients undergoing primary total knee arthroplasty under spinal anesthesia. Participants will be randomly assigned in a 1:1 ratio to receive either ACB alone or combined ACB plus BiFeS block. The primary outcome is cumulative opioid consumption during the first 48 postoperative hours. Secondary outcomes include postoperative pain intensity, time to first analgesic request, quadriceps muscle strength, functional recovery, postoperative recovery quality, postoperative nausea and vomiting, patient and surgeon satisfaction, length of hospital stay, and block-related complications.

Background

Total knee arthroplasty (TKA) is the definitive surgical treatment for end-stage knee osteoarthritis and is one of the most frequently performed orthopedic procedures worldwide. Despite advances in multimodal analgesic strategies, postoperative pain following TKA remains a major clinical challenge. Inadequate pain control may delay early mobilization, impair functional recovery, prolong hospitalization, increase opioid consumption, and reduce patient satisfaction. Therefore, optimization of regional anesthesia techniques continues to be an important component of enhanced recovery protocols after TKA.

Ultrasound-guided adductor canal block (ACB) has become a widely accepted motor-sparing regional analgesic technique for TKA because it provides effective analgesia to the anteromedial aspect of the knee while largely preserving quadriceps muscle strength. Nevertheless, the posterior compartment of the knee receives sensory innervation from branches of the sciatic nerve that are not consistently anesthetized by ACB alone. Consequently, residual posterior knee pain remains a common limitation of this technique.

The ultrasound-guided biceps femoris short head (BiFeS) block is a recently described regional anesthesia technique that targets the posterolateral sensory innervation of the knee through deposition of local anesthetic within the fascial plane adjacent to the short head of the biceps femoris muscle. Anatomical and preliminary clinical investigations suggest that this technique may provide additional analgesic coverage of the posterior knee while preserving motor function. However, evidence regarding its clinical efficacy as an adjunct to ACB in patients undergoing primary TKA remains limited.

Study Objectives

The objective of this study is to determine whether the addition of an ultrasound-guided BiFeS block to a standard ultrasound-guided ACB provides superior postoperative analgesia compared with ultrasound-guided ACB alone in patients undergoing primary unilateral TKA under spinal anesthesia.

Study Design

This is a prospective, single-center, parallel-group, randomized controlled clinical trial. Eligible participants will be randomly assigned in a 1:1 ratio to receive either an ultrasound-guided adductor canal block or an ultrasound-guided adductor canal block combined with a biceps femoris short head block before surgery. All patients underwent total knee arthroplasty under single-shot spinal anesthesia with 15 mg of hyperbaric bupivacaine. No periarticular local infiltration analgesia was performed by the surgical team. Postoperatively, all patients received a standardized multimodal analgesic regimen consisting of intravenous paracetamol (1 g) administered every 8 hours. Rescue analgesia consisted of intravenous tramadol (100 mg), which was administered when the Numeric Rating Scale (NRS) pain score was ≥4.

Outcome Assessment

The primary endpoint is cumulative intravenous morphine consumption (mg) from arrival in the post-anesthesia care unit until 48 hours after surgery. Secondary endpoints include postoperative pain intensity assessed using the Numeric Rating Scale (NRS), time to first rescue analgesic administration, quadriceps muscle strength, functional recovery assessed by the Timed Up and Go test and knee range of motion, quality of postoperative recovery (QoR-15), postoperative nausea and vomiting, patient and surgeon satisfaction, length of hospital stay, and block-related adverse events.

Clinical Significance

This study is designed to provide high-quality evidence regarding the potential clinical benefit of incorporating the BiFeS block into contemporary multimodal analgesic protocols for total knee arthroplasty. If the combined regional analgesic approach demonstrates improved postoperative analgesia while preserving motor function, it may represent an effective strategy to facilitate enhanced recovery after surgery and reduce perioperative opioid requirements.

Inclusion Criteria:

• Scheduled for elective primary unilateral total knee arthroplasty under spinal -anesthesia.
• American Society of Anesthesiologists (ASA) physical status I-III.
• Body mass index (BMI) <40 kg/m².
• Ability to understand the study procedures and provide written informed consent.

Exclusion Criteria:

• Refusal to participate or inability to provide informed consent.
• Body mass index 40 kg/m2 or higher.
• ASA physical status IV or V.
• Known allergy or hypersensitivity to local anesthetics, opioids, or other study -medications.
• Pregnancy or breastfeeding.
• Uncontrolled psychiatric disease or severe anxiety interfering with study participation.
• Pre-existing neuromuscular disease or peripheral neuropathy involving the operative limb.
• Chronic opioid use or opioid dependence.
• Chronic pain syndrome requiring regular analgesic therapy.
• Severe hepatic or renal insufficiency.
• Contraindications to spinal anesthesia or peripheral nerve block, including -coagulopathy, thrombocytopenia, local infection at the injection site, or patient refusal.
• Planned bilateral or revision total knee arthroplasty.