Anatomy of the pudendal nerve with relationship of the bony landmarks of pelvis Hyung-Jin Mo*, U-Young Lee, Je-Hoon Lee, Seung-Ho Han Department of Anatomy·Catholic Institute for Applied Anatomy, College of Medicine, The Catholic University of Korea * During this study, Hyung-Jin Mo belonged to Department of Anatomy · Catholic Institute for Applied Anatomy, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea. Now, he works in Rebello Clinic. Introduction Result Many surgeons remain unfamiliar with pudendal nerve anatomy and access is difficult without risk of injury to the nerve and its branches. Then, it is necessary to get morphometric data of the pudendal nerve to be able to estimate branching pattern and position of the nerve in consideration of adjacent anatomical landmarks. If the anatomical structure might be described in index form using the metric data of anatomical landmarks, it is possible to standardize a morphology of an anatomical structure. The branching pattern of the pudendal nerve Figure 3. The classification and frequencies in branching pattern of the pudednal nerve according to whether the arising point of its terminal branches is located before or after IT-C. Type V is one of the variations of pudendal nerve which has inferior rectal nerve formed independently from the sacral plexus. IS: ischial spine, C: inferior tip of coccyx, IT: posterior end of ischial tuberosity, 1: inferior rectal nerve, 2: perineal nerve 3: dorsal nerve of penis. Materials and Methods This study investigated the morphometric characteristics about the branching pattern and position of the pudendal nerve in consideration of ischial spine (IS) and the line (IT-C) from posterior end of ischial tuberosity (IT) to inferior tip of coccyx (C). All data acquired from 41 cases of pudendal nerve consisting of 11 male and 10 female cadavers. IT-C IS-PN, IS-IRN Figure 4. The mean distance of IT-C in male and female. There was significant difference between sexes at t-test (P < 0.05). However, the indexes using IT-C in this study had no differences between sexes at t-test (P < 0.05). Figure 5. The mean distance index shows that pudendal nerve run at about medial 1/10 of the IT-C distance from ischial spine. In case of inferior rectal nerve formed independently from sacral plexus, inferior rectal nerve passes at about medial 18/100. of the IT-C distance from ischial spine. IS: ischial spine, C: inferior tip of coccyx, IT: posterior end of ischial tuberosity. Figure 1. Exposure of the pudendal nerve and its branches to describe the pattern and measure the distance or depth of the nerve using anatomical landmarks. PN: pudendal nerve, IS: ischial spine, C: inferior tip of coccyx, IT: posterior end of ischial tuberosity, 1: inferior rectal nerve, 2: perineal nerve 3: dorsal nerve of penis. IT-CIRN, IT-CPrN, IT-CDNP, Dep 1,2,3 Figure 2. Measuring points in this study. Small box of A is magnified in B and C. Large box of A is magnified in D. 'PN' is a midpoint of pudendal nerve on the parallel line to IT-C with same level of ischial spine. If there is inferior rectal nerve formed independently from sacral plexus, 'IRN', a midpoint of inferior rectal nerve on the parallel line to IT-C with same level of ischial spine, is used for measuring the distance from ischial spine. 'BIRN' and 'BDNP' are branching point of inferior rectal nerve and dorsal nerve of penis (clitoris), respectively. 'CIRN','CPrN' and 'CDNP' are crossing points of inferior rectal nerve, perineal nerve and dorsal nerve of penis (clitoris) on the line between IT and C. IS: ischial spine, C: inferior tip of coccyx, IT: posterior end of ischial tuberosity, 1: inferior rectal nerve, 2: perineal nerve 3: dorsal nerve of penis. Dis 1,2 Figure 7. The mean index obtained from the distance from IT-C to branching point of inferior rectal nerve (A) or dorsal nerve penis (clitoris) (B). According to whether the arising point of these branches is located before or after IT-C, mean indexes were calculated differentially. A or B do not show dorsal nerve of penis (clitoris) or inferior rectal nerve, respectively. C: inferior tip of coccyx, IT: posterior end of ischial tuberosity. Figure 6. The mean distance index (A) shows that inferior rectal nerve, perineal nerve and dorsal nerve of penis (clitoris) run at about 4/10, 3/10 and 2/10 point of IT-C from IT, respectively. In the mean depth (B) index, inferior rectal nerve, perineal nerve and dorsal nerve of penis (clitoris) are located below 2-3/10 of the IT-C distance from crossing point of each nerve on IT-C. 'CIRN','CPrN' and 'CDNP' are crossing point of inferior rectal nerve, perineal nerve and dorsal nerve of penis (clitoris) on the line between IT and C. C: inferior tip of coccyx, IT: posterior end of ischial tuberosity. Table 1. Definition of the measurements in this study. Measurements Definition IS-PN Distance from ischial spine to midpoint of pudendal nerve on the parallel line to IT-C with same level of ischial spine IS-IRN Distance from ischial spine to midpoint of inferior rectal nerve on the parallel line to IT-C with same level of ischial spine, in case of inferior rectal nerve formed independently from sacral plexus IT-C Distance between posterior end of ischial tuberosity and inferior tip of coccyx IT-CIRN Distance between posterior end of ischial tuberosity and crossing point of inferior rectal nerve on IT-C line IT-CPrN Distance between posterior end of ischial tuberosity and crossing point of perineal nerve on IT-C line IT-CDNP Distance between posterior end of ischial tuberosity and crossing point of dorsal nerve of penis (clitoris) on IT-C line Dis1 Perpendicular distance from IT-C line, between posterior end of ischial tuberosity and inferior tip of coccyx, to branching point of inferior rectal nerve Dis2 Perpendicular Distance from IT-C line to branching point of dorsal nerve of penis (clitoris) Dep1 Perpendicular depth from crossing point of inferior rectal nerve on IT-C line to inferior rectal nerve Dep2 Perpendicular depth from crossing point of perineal nerve on IT-C line to perineal nerve Dep3 Perpendicular depth from crossing point of dorsal nerve of penis (clitoris) on IT-C line to dorsal nerve of penis (clitoris) Conclusion The positions of the pudendal nerve and its branches were described in form of index that the distance from IS or IT to pudendal nerve or its branches is divided by the distance from IT to C. According to these data, the pudendal nerve runs at 1/10 point of IT-C from IS. The inferior rectal nerve passes at 4/10 point of IT-C from IT and below 2/10 of the IT-C distance. The perineal nerve passes at 3/10 point of IT-C from IT and below 2/10 of the IT-C distance. The dorsal nerve of penis (clitoris) passes at 2/10 point of IT-C from IT and below 2-3/10 of the IT-C distance. These morphometric data of the pudendal nerve are able to estimate branching pattern and position of the nerve by the relationship between this nerve and anatomical landmarks as which ischial spine and the line from ischial tuberosity were used in this study. Therefore, these data are helpful to understand topography of the pudendal nerve in the block or exposure of this nerve. Catholic Institute for Applied Anatomy · Department of Anatomy College of Medicine, The Catholic University of Korea E-mail : hsh@catholic.ac.kr