Pudendal nerve blocks are evolving techniques in the diagnosis and treatment of pelvic floor dysfunction and pain. Existing localization methods are either transvaginal, transrectal or transperineal,(1) traversing the often painful areas; While existing percutaneous transgluteal approaches apply use of fluoroscopic, tomographic or sonographic guidance,(2) impeding office implementation.
Our aim was to develop a percutaneous, transgluteal, anatomical-landmark guided approach for pudendal nerve localization and delivery of injectables.

Formaldehyde-preserved human cadavers were dissected by an expert anatomist to identify the pudendal nerve, anatomical landmarks accessible on surface anatomy, and surrounding structures, including the: coccyx, sacral foramina, pudendal nerve, sacrotuberous ligament (STL), ischial spine (IS), and ischial tuberosity (IT) (Fig 1A). Systematic photos were taken directly above and laterally at a 90° angle using standard rulers for reference. A single observer measured distances and angles using ImageJ® software. Descriptive statistics were applied, and measurements tested for normal distribution using a Shapiro-Wilk test (SAS®).
These measurements were then used to develop a method leading from palpable surface anatomy landmarks to PN localization: First, the tip of the coccyx (point C), ischial tuberosity (point D) and midline, are palpated and marked. Next, measurements are made to draw line BC from the coccyx (C) midline in a cephalad direction; line AB horizontal to line BC; and line AD connecting point A with the ischial tuberosity (D). finally, a line is drawn from point B towards line AD using the ABP angle measurement, to locate the pudendal nerve (P). 
Using the above method, reverse measurements were conducted on previously unmarked cadaveric glutei (Fig 1B). A 22 G (0.7 mm) needle was placed perpendicular to the skin at calculated Point P, the needle was advanced until it crossed a strong fascia presumed to be the STL, and 1 mL of blue dye was injected. Images were taken and measurements between the PN and the needle edge were obtained (Fig 1C).

Seventy-five hemigluteal dissections (48 right, 30 left) were completed on 48 human cadavers. Measurements were obtainable in 72 of 75 dissections (Fig 1A). Average distances of line BC and line AB were 6.5±1.4 cm and 4.8±0.90 cm, respectively. Mean ABP angle was 36 ±8.8°. All measurements exhibited normal distribution, with p-value for Shapiro Wilk test > 0.05.
Reverse measurements were then performed using the mean obtained estimates on 10 previously unmarked hemiglutei (5 right, 5 left), and in all 10 (100%) dissections, the needle traversed the STL, and dye was observed in the targeted Alcock’s canal (Fig 1B). Mean distance between the PN and needle entry into the STL was 1.1±0.7 [range: 0.3-2.9] cm (Fig 1C).

We developed a transgluteal method of pudendal nerve localization and injection, utilizing palpable anatomical landmarks and data derived from multiple systematic cadaveric measurements. We evaluated the accuracy of this method in previously unmarked cadavers and demonstrated injection within 1.1±0.7 cm of the PN.
This method avoids palpation of and needle passage through the referral areas of the pudendal nerve (vulvovaginal, anorectal, perineal regions), which are potential areas of hyperalgesia in patients with pudendal neuralgia.
Utilizing anatomical landmarks, we were able to localize the PN transgluteally without the use of imaging, further simplifying PN block technique and potentially improving patient access to this treatment.
The findings of this cadaver-based feasibility study must be verified in live human patient studies before they can be implemented into routine clinical practice. Future studies will focus on streamlining the measurement method, exploring potential adverse effects of this approach, and comparing its clinical efficacy to current PN block techniques.

Using a large sample of cadaveric measurements, this study demonstrates the feasibility and accuracy of a transgluteal, anatomical landmark-based approach for pudendal nerve injection. Future work will focus on translating this method into use in live human subjects.

Romanzi L. Surgical Techniques: Techniques of Pudendal Nerve Block. The Journal of Sexual Medicine. 2010 May;7(5):1716–9.
Yoon SJ, Gómez-Hoyos J, Márquez-Arabia WH, Martin HD. Pudendal Nerve Neuralgia/Entrapment. In: Martin HD, Gómez-Hoyos J, editors. Posterior Hip Disorders [Internet]. Cham: Springer International Publishing; 2019 [cited 2023 Feb 26]. p. 189–95. Available from: http://link.springer.com/10.1007/978-3-319-78040-5_9

Continence 7S1 (2023) 100928
DOI: 10.1016/j.cont.2023.100928