Optimizing injection accuracy for Baxter's nerve entrapment: an ultrasonography-guided approach based on anatomical surface landmarks.

Introduction: The clinical feasibility and applicability of surface landmarks for Baxter nerve entrapment to proximal and distal sites is unclear. This study provides anatomical guidelines for optimal transducer placement using two specific landmarks, the most inferior tip of the medial malleolus (A) and the most protruding posterior tip of the calcaneus (B), to enhance the diagnostic and therapeutic injection efficacy for proximal and distal entrapment sites.

Materials and methods: Eighty-six feet from 45 fresh cadavers (25 male and 20 female) were dissected to determine Baxter's nerve (BN) localization. With A and B as key landmarks, distances (OB, OBN, BBN, and BNx) were measured to accurately localize the nerve. The OB distance was divided into four equal-length quadrants or zones. Twenty feet from 10 fresh cadavers (5 males and 5 females) underwent ultrasonography-guided injection using in-plane and out-of-plane techniques. Two practitioners marked the landmarks to ensure reproducibility and an experienced anesthesiologist administered the injections. The spread of the injected dye was assessed, and statistical analyses were conducted.

Results: Average OB, OBN, BBN, and BNx distances were 50.55 ± 5.83 mm, 7.19 ± 5.85 mm, 43.77 ± 5.31 mm, and 12.13 ± 5.75 mm, respectively. Significant sex-related differences (O to B; B to BN) and notable disparities between the distances on the right and left sides (O to BN; BN to X-axis) were observed. Most of the BN (81.4%) was located in zone 1, representing 25% of the OB length. For entrapment site 1, the in-plane technique achieved a 100% success rate whereas the out-of-plane method achieved an 80% success rate. For entrapment site 2, the out-of-plane approach (90% success) outperformed the in-plane approach (20% success).

Conclusion: Using two specific landmarks provides reliable guidelines for optimal transducer placement during injections targeting compressive neuropathy at proximal and distal entrapment sites.