Materials and Methods
Detailed dissections were performed in 13 unembalmed female cadavers obtained from the Willed Body Program at the University of Texas Southwestern Medical Center in Dallas. This study was exempt from review by the University of Texas Southwestern Medical Center Institutional Review Board in accordance with the Code of Federal Regulations, Title 45. Age, race, height, weight, and cause of death were obtained for all cadavers.
Pudendal nerve dissections were completed bilaterally through a transabdominal (pelvic) and perineal approach. Cadavers were transected above the level of the aortic bifurcation and at midthigh. Each specimen was further transected in the midsagittal plane to facilitate dissection. The peritoneum overlying the sacrum and the fascia covering the piriformis muscles were carefully dissected to expose the lumbosacral trunk (LST) and sacral nerve roots (S1-S5) ( Figure 1 ). The relationship of the superior and inferior gluteal and internal pudendal arteries to the nerve branches as the vessels exited the pelvis were documented. The width of the LST as it crossed over the pelvic brim and the widths of the S1 to S5 nerves 1 cm from the point at which they emerged from the anterior sacral foramina were recorded.
The course of the sacral nerves was followed and their contribution to the formation of the pudendal nerve within the pelvis was documented. The point at which branches of S2, S3, and S4 converged to form the pudendal nerve was labeled and designated the origin of the pudendal nerve. The PN was examined in the following 3 regions: (1) pelvis, (2) dorsal surface of the sacrospinous ligament, and (3) pudendal canal.
Pelvic measurements obtained included the distance from the origin of the PN to the tip of the ischial spine (IS) and the PN width at its origin. When more than 1 branch of the PN was noted within the pelvis, the number and width of the branches were recorded. The distance from the IS to the medial aspect of the S4 foramina was used as a surrogate estimate of the SSL length. The height of the SSL at its midpoint was recorded.
The medial border of the obturator internus muscle within the perineum was exposed by transecting the levator ani muscles medial and parallel to the arcus tendineus fascia pelvis. This permitted inferior and medial access and evaluation of the pudendal canal. The fatty tissue within the ischioanal fossa was removed to expose the IRN, pudendal canal, and other branches of the pudendal nerve as they emerged from the canal.
The length of the pudendal canal was measured from the tip of IS to the point at which the largest PN branch (other than the IRN) emerged. The IRN was identified adjacent to the anus, followed proximally, and its entry into the pudendal canal was documented. The distance from the IS to the point at which the IRN exited the canal was recorded. The width of the IRN was measured as it emerged into the ischioanal fossa.
The SSL was then transected approximately 1 cm medial to its attachment to the IS and the medial cut edge of the ligament was reflected medially to expose the pudendal nerve in this region. Special attention was given to examining the attachments of the pudendal nerve to surrounding connective tissue in all three regions. The mobility or freedom of movement of the nerve in a specific region (pelvic, SSL, pudendal canal) was assessed by applying gentle traction proximal and distal to the area being examined.
Mobility of the nerve was first assessed in the pelvis, then the pudendal canal, and lastly behind the SSL. Displacement of the nerve proximal to the point of traction was interpreted as a positive sign of mobility. Photographs of all dissections were taken for documentation. All measurements were taken twice with a caliper and plastic ruler. Measurements were tabulated and descriptive statistics were used for data analyses and reporting.
Results
Thirteen unembalmed female cadavers (26 hemipelvises) were examined. All cadavers were white, with a median age of 81.7 years (range, 61–95 years). The median body mass index was 18.9 kg/m 2 (range, 13.5–24.9 kg/m 2 ). The most common cause of death was cancer (lung and breast). Dissections and available medical histories revealed no obvious signs of pelvic pathology such as cancer, fractured pelvic bones, or prior trauma.
The widths of the LST, S1-5 nerves, PN, and IRN are shown in the Table . The superior gluteal artery exited the pelvis between the LST and S1 nerves in 69.2% (n = 18) ( Figure 1 ) and above the LST or between the fourth and fifth lumbar nerves in 30.8% (n = 8) ( Figure 2 ) of hemipelvises. The inferior gluteal artery exited the pelvis between S2 or S3 branches in the majority of specimens ( Figure 1 ) but occasionally between S1 and S2 branches ( Figure 2 ). In all specimens, the internal pudendal artery exited lateral to the inferior gluteal artery and in close proximity to the IS ( Figure 2 ). The median length of the SSL was 60.8 mm (range, 52–78.5 mm) and its median height at its midpoint was 20 mm (range, 12.5–24.5 mm).
| Variable | Median width, mm, and range | ||
|---|---|---|---|
| Left side | Right side | Combined | |
| Lumbosacral trunk | 9.0 (6–13.5) | 10.5 (5.3–14.5) | 9.8 (5.3–14.5) |
| Sacral nerves | |||
| S1 | 8.0 (6.5–9.5) | 8.0 (5.5–10) | 8.0 (5.5–10) |
| S2 | 6.0 (4.5–8) | 6.0 (4.8–8) | 6.0 (4.5–8) |
| S3 | 4.0 (3–5) | 4.0 (2.8–6) | 4.0 (2.8–6) |
| S4 | 2.0 (1–4) | 2.0 (1–3) | 2.0 (1–4) |
| S5 a | 1.3 (0.5–2) | 0.5 (0.5–0.5) | 0.8 (0.5–2) |
| Pudendal nerve | 5.0 (2.5–6.3) | 4.3 (2.5–6) | 4.5 (2.5–6.3) |
| Inferior rectal nerve | 3.0 (1–4) | 3.0 (1–4) | 3.0 (1–4) |
In all specimens, the PN was formed from contributions of S2, S3, and S4 nerves ( Figure 1 ). From its point of formation in the pelvis to its division into terminal branches, a single PN trunk was identified in 61.5% (n = 16) of hemi-pelvises ( Figure 3 ). In the remaining hemipelvises (n = 10), multiple PN trunks were identified, 70% (n = 7) within the pelvis or behind the IS and 30% (n = 3) within the pudendal canal.
The median distance from the origin of the PN to the tip of the IS was 27.5 mm (range, 14.5–36.5 mm) on the left and 27.8 mm (range, 19.5–37 mm) on the right side. The pudendal canal was formed by dense connective tissue converging with the medial border of the obturator internus fascia ( Figure 4 ). The median length of the pudendal canal, measured from tip of IS to the point at which the largest terminal PN branch emerged was 40.0 mm (range, 20.5–49 mm) on the left and 40.5 mm (range, 23.5–54.5 mm) on the right side. In all specimens, the PN was fixed by connective tissue to the dorsal surface of the SSL ( Figure 5 ).
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