PATIENT-TAILORED ULTRASOUND-GUIDED LUMBAR PLEXUS BLOCK USING ALTERNATIVE ANATOMICAL LANDMARKS: A PRELIMINARY STUDY

S. Sorrenti¹, M. Ciuffreda¹, E. Pisello¹, C. Pellegrino², A. Monacelli², G. Cucè³, C. Piangatelli¹, D. Galante⁴ | ¹Department of Anesthesiology, Intensive Care and Pain Management, AST Ancona, Fabriano (AN), Italy; ²Department of Anesthesiology, Intensive Care and Pain Management, Marche Polytechnic University, Ancona, Italy; ³Department of Public Health, University of Messina, Italy; ⁴Department of Anesthesiology, Intensive Care and Pain Management, ASL Foggia, Cerignola (FG), Italy

Background and Aims. Lumbar plexus block (LPB) is an advanced regional anesthesia technique that provides reliable blockade of the femoral, obturator, and lateral femoral cutaneous nerves. Despite its effectiveness in lower limb surgery, LPB is performed by relatively few anesthesiologists due to technical difficulty and safety concerns related to deep target structures and the risk of serious complications (e.g., intrathecal spread, renal injury, vascular puncture, and local anesthetic systemic toxicity). Traditional “blind” landmark-based approaches do not account for individual anatomical variability, while fully ultrasound-guided techniques (e.g., Shamrock and Trident) are operator-dependent and often limited in obese or anatomically unfavorable patients. We developed an innovative ultrasound-assisted, patient-tailored LPB protocol combining rapid sonographic identification of the L5 transverse process with alternative anatomical landmarks derived from Traditional Chinese Medicine (1.5 CUN lateral to the interspinous line). The aim of this preliminary study was to evaluate the safety and success rate of this alternative operating protocol in patients undergoing lower limb surgery.
Methods. In this prospective, noninterventional, descriptive observational study, 47 patients (aged 16–86 years) scheduled for elective or emergency lower limb orthopedic surgery received a single-shot LPB (30 mL ropivacaine 2 mg/kg) prior to general or subarachnoid anesthesia. Preoperative data included age, sex, BMI, surgical procedure, 1.5 CUN measurement (converted into centimeters), and sonographic confirmation of L5 transverse process location compared with the Chayen blind approach. Using a low-frequency convex probe, L5 was identified in sagittal and transverse planes, and the depth of the transverse process from skin was measured. The needle entry point was determined at the L5 level with a lateral drift of 1.5 CUN (converted to cm) from the interspinous line. After bone contact, the needle was redirected cranially or laterally and advanced 2–3 cm deeper until a quadriceps twitch was elicited with electrical nerve stimulation (0.2–0.5 mA). A successful block required a patellar twitch, negative aspiration, a positive Raj test, and the absence of injection pain. Complications were systematically recorded.
Results. The overall success rate was 91.49%, independent of age and BMI. More than half of patients (55.32%) were ≥70 years old, and 27.66% were class I obese or higher (maximum BMI 39.4), conditions typically associated with increased technical difficulty. Only 8.51% of blocks failed; subsequent attempts using the traditional Chayen approach were also unsuccessful in these cases. Sonographic evaluation revealed a mismatch between the estimated L5 transverse process position (Chayen approach) and its actual location in 87.23% of patients, indicating the possible inaccuracy of blind landmark techniques. Moreover, the patient-tailored 1.5 CUN measurement corresponded to the fixed 5 cm lateral drift of the Chayen approach in only 12.77% of cases. No major complications were observed, including intrathecal injection, renal injury, vascular damage, hematoma, local anesthetic systemic toxicity, or postoperative nerve deficits. These findings support the safety and reproducibility of the combined ultrasound-assisted and patient-tailored protocol.
Conclusions. This preliminary study describes a novel ultrasound-assisted, patient-tailored LPB protocol integrating rapid sonographic identification of L5 with individualized anatomical landmarks derived from the 1.5 CUN measurement. The approach enhances safety by confirming transverse process location and depth before needle advancement while improving consistency through anthropometrically adapted entry points. This method uses simple, quick sonographic help and electrical nerve stimulation confirmation, unlike deep ultrasound-guided techniques that need a lot of training and may not work well on obese or anatomically difficult patients. Compared with blind Tuffier line-based approaches, the patient-specific CUN measurement allows more accurate paravertebral needle placement. The high success rate and absence of major complications suggest that this “safety-first” protocol may represent a valuable alternative for lumbar plexus block in real-world clinical settings. Larger comparative studies are warranted to further validate its effectiveness and generalizability.