Despite recent advances in surgical stapling technology, the development of the ideal stapling device for the distal rectum has been slow. The bony confines of the pelvis, especially android pelvises, cause impediments to visibility and access in the distal rectum. The challenges are more pronounced if the dissected rectum is fatty and bulky, and in the presence of a large rectal tumor. Previous studies have revealed that the male gender, shorter distance of the tumor from the anal verge, and narrower pelvic dimensions are associated with longer operative times and worse outcomes in rectal surgery, including anastomotic leak and positive tumor margins [10
An ideal rectal stapler should be easily advanced to the pelvic floor, have excellent ability to hold tissue, accept a wide range of tissue thickness, seal and divide the rectum reliably and safely, and occlude both the proximal and distal ends of the cut bowel. The challenge in designing such a stapler is that a low-profile stapler may have difficulty incorporating the entire rectum within its jaws, or may require several applications resulting in intersecting staple lines susceptible to ischemia. The rectal transection should ideally be perpendicular to the pelvic floor, but to design a stapler that deflects nearly 90 degrees limits its jaw strength and the deployment of a cutting knife.
In this cadaver study, we compared two stapling devices for the rectum that have similar mechanisms in that they have the ability to occlude both ends of the staple line. This is accomplished by the placement of four rows of staples, with a cutting knife in between the second and third rows. This improves on the traditional method of distal rectal division that involves occluding the bowel distal to the tumor with an atraumatic clamp (to limit spillage of stool and liberated tumor cells), stapling the rectum distal to the clamp, and using a long-handled knife deep in the pelvis to divide the bowel under restricted visual access.
We found that the RALC, compared to the CC, could be placed deeper in the pelvis, has improved visualization, is obstructed less by surrounding tissues, and has pelvic access that was superior (rated "excellent" in 38/48 [79%] as opposed to 18/48 [38%] for the CC). This is likely explained by the smaller profile of the RALC 45-mm single-use load and the perpendicular orientation of the jaws in relation to the shaft of the handle. The RALC Single Use Reload's dimensions are 14.6 mm in width, 40.1 mm in height (closed), and 66.5 mm in length, compared with the CC's dimensions of 25.4 mm in width, 95.0 mm in height (closed), and 62.2 mm in length. We also found that the RALC had excellent and equal access to the deep pelvis whether placed coronally or sagittally, but that the CC was best used coronally. The sagittal placement of the CC resulted in poorer ratings for pelvic access compared with its coronal application. In addition, the CC placed in a sagittal configuration clamped the rectum 1.3 cm more proximally than coronally (3.3 versus 2.0 cm from the pelvic floor).
By performing anatomic measurements in the pelvis, we hoped to evaluate what anatomic factor posed the greatest limitation to distal rectal stapling. A prior study by Gu, et al. that utilized magnetic resonance (MR) pelvimetry in rectal cancer surgery demonstrated that failure of a sphincter-preserving procedure was predicted by a shorter distance from the upper pubic bone to the sacrococcyx, longer distance of the sacrococcyx, and excessive curvature of the sacrum [14
]. Another study correlating MR pelvimetry with difficulty of a laparoscopic proctectomy found that a large sagittal pelvic outlet coupled with a narrow transverse intertuberous distance predicted longer operative time [12
]. In our current cadaver study, we found that the stapler distance from the pelvic floor was influenced significantly by the distance between the symphysis pubis and the tip of the coccyx. This anterior-posterior restriction of the pelvic outlet seemed to pose more difficulty than any anatomic measurement in the transverse direction or at the pelvic inlet. This knowledge, we hope, could help in the development of improved stapling devices in the future.
There are limitations of this study. First, there is contraction of the mesorectum in a cadaver compared to a live body, and this simplifies placement of the stapling device both around the rectum and into the pelvis. How these stapling devices would perform in the setting of a bulky mesorectum or large rectal tumor remains unanswered by this study. It is possible that the improved access in the deep pelvis with the RALC would be magnified in live surgery; however, it is also possible that the advantages seen in a cadaver model with the RALC will no longer be appreciated in a more technically difficult setting. Secondly, this study only investigated pelvic access and reach. The devices were clamped onto the distal rectum but not fired in order to maximize the number of applications per cadaver. Thus, one critical aspect of stapler performance-how the devices stapled-could not be assessed. Thirdly, investigator bias could not be eliminated, as it was impossible to blind the surgeon to the technique. Furthermore, this research project was funded by one company and not the other, and the participating surgeons received honoraria for their time. Lastly, it would have been interesting to study the influence of body mass index (BMI) on staple placement. This analysis was not performed, however, since the range of the cadavers' BMI (measured by the supplying company) was narrow; the median BMI (and range) of the cadavers was 24.7 (23.7-25.8) kg/m2.