Bladder cancer is one of the most common cancers in older adults. The standard treatment for many bladder tumors is a surgical procedure called transurethral resection of bladder tumor (TUR-BT). During this operation, tumors located on the side wall of the bladder may trigger an involuntary leg movement known as the "obturator reflex." This reflex occurs when electrical stimulation during surgery activates the obturator nerve, causing sudden contraction of the inner thigh (adductor) muscles. Such muscle spasms can lead to serious complications, including incomplete tumor removal or bladder perforation.

To prevent this reflex, anesthesiologists perform an obturator nerve block (ONB), a procedure in which local anesthetic medication is injected around the nerve to temporarily stop its function. With advances in ultrasound technology, different ultrasound-guided techniques have been developed to perform this nerve block more safely and effectively.

There are two commonly used approaches. The first is the interfacial (distal) technique, in which two separate injections are performed to block the anterior and posterior branches of the obturator nerve. The second is the subpectineal (proximal) technique, in which the nerve is blocked with a single injection at a more proximal location, potentially using a smaller amount of local anesthetic.

The purpose of this study was to compare these two ultrasound-guided techniques in patients undergoing TUR-BT surgery. The aim of this study was to compare the effectiveness and safety of the subpectineal and interfacial obturator nerve block techniques in preventing adductor muscle spasm during surgery.

Sixty patients aged between 50 and 80 years who were scheduled for TUR-BT were randomly assigned to receive either the subpectineal or the interfacial obturator nerve block. The main outcome measured was the occurrence and severity of adductor muscle spasm during surgery. Secondary outcomes included the number of needle insertions, duration of anesthesia and surgery, and any complications related to the block.

The hypothesis of this study was that the subpectineal technique would provide comparable effectiveness in preventing adductor muscle spasm compared with the interfacial technique while requiring fewer injections and a lower volume of local anesthetic.

The results of this study may help determine the most effective and practical technique for preventing surgical complications during bladder tumor surgery.

Transurethral resection of bladder tumor (TUR-BT) is the standard diagnostic and therapeutic procedure for non-muscle invasive bladder cancer. During resection of tumors located on the lateral bladder wall, electrical stimulation may activate the obturator nerve, resulting in sudden contraction of the adductor muscles of the thigh. This phenomenon, known as the obturator reflex, may cause incomplete tumor resection, bladder perforation, bleeding, or tumor cell dissemination.

Obturator nerve block (ONB) has been shown to significantly reduce the incidence and severity of adductor muscle spasm during TUR-BT. With the increasing use of ultrasound guidance, several proximal and distal approaches have been described to improve block success and safety profile.

The distal (interfacial) technique requires separate blockade of the anterior and posterior branches of the obturator nerve between the adductor muscle groups. This approach typically involves two injections and a higher total volume of local anesthetic. In contrast, the proximal (subpectineal) technique targets the obturator nerve before its division, allowing a single-injection block performed in the fascial plane between the pectineus and obturator externus muscles.

This prospective, randomized clinical study was conducted to compare the effectiveness of ultrasound-guided subpectineal and interfacial obturator nerve block techniques in patients undergoing TUR-BT. Patients were allocated into two groups using a computer-generated randomization method. All nerve blocks were performed under real-time ultrasound guidance by experienced anesthesiologists.

In the subpectineal approach, a single injection of 10 mL of 0.375% bupivacaine was administered into the fascial plane between the pectineus and obturator externus muscles. In the interfacial approach, 10 mL of 0.375% bupivacaine was injected between the adductor longus and brevis muscles to block the anterior branch, and an additional 10 mL was injected between the adductor brevis and magnus muscles to block the posterior branch.

The study was designed to evaluate whether the proximal subpectineal approach provides comparable prevention of adductor muscle contraction while potentially simplifying the procedure by reducing the number of injections and local anesthetic volume. Safety parameters and perioperative characteristics were also assessed.

Statistical analyses were performed using appropriate comparative tests according to data distribution. A p-value < 0.05 was considered statistically significant.

Inclusion Criteria:

• Patients aged between 50 and 80 years
• Diagnosed with bladder tumor and scheduled for transurethral resection of bladder tumor (TURBT)
• Classified as American Society of Anesthesiologists (ASA) physical status I-III
• Provided written informed consent

Exclusion Criteria:

• Coagulopathy or anticoagulant therapy contraindicating regional anesthesia
• Known allergy to local anesthetics
• Infection at the injection site
• Pre-existing neuromuscular disorder affecting lower extremities
• Severe cardiac, hepatic, or renal dysfunction
• Inability to provide informed consent

Individual participant data will not be publicly shared due to institutional policies and patient confidentiality considerations. Data may be made available upon reasonable request to the corresponding author and subject to approval by the institutional ethics committee.