Optimization of technique for insertion of implants at the supra-acetabular corridor in pelvis and acetabular surgery
OBJECTIVES To determine what anatomic structures are at risk after the application of a subcutaneous anterior pelvic internal fixator (APIF), from an incision over the anterior iliac crest to an incision centered over the pubic symphysis (Pfannenstiel). METHODS A laboratory investigation was performed using 5 fresh, frozen, nonpreserved cadaveric specimens (3 male specimens, 2 female specimens). Dissections were carried out to identify the relationships and proximity between the fixator screw constructs and various anatomic structures, including the (1) lateral femoral cutaneous nerve (LFCN), (2) ilioinguinal nerve (IIN), (3) iliohypogastric nerve (IHN), (4) femoral nerve, (5) femoral artery, (6) femoral vein, (7) genitofemoral nerve; and (8) spermatic cord or round ligament. The mean and range of distance from each of these structures to the implant were measured with calipers. RESULTS Despite variations in pelvic anatomy and width of pelvic brims, precontoured fixators (3.5 locking reconstruction plates) did not violate any pelvic neurovascular structures using this recommended application of an APIF. The spermatic cord was easily avoided as they were directly visualized using our application technique (mean, 0.4 cm, range, 0-2 cm). Abdominal musculature protected the IHN and IIN for most of their course, with the precontoured plates remaining inferior to their course and resting superficial to their branches (IHN mean, 1.5 cm, range, 1.2-1.8 cm and IIN mean, 2.1 cm, range, 0.9-4 cm). The LFCN traveled safely posterior to the inguinal ligament, thus being bridged by the internal spanning fixation without visualized disruption, impingement, or violation (mean, 1.5 cm, range, 0.6-4 cm). Finally, the femoral nerve, artery, and vein collectively demonstrated safe distance from the risk of compression (mean, 2.2 cm, range, 0.8-3.7 cm). CONCLUSIONS The anatomic structures hypothesized to be potentially endangered because of the lack of direct visualization during APIF placement, include the LFCN, IIN, IHN, femoral nerve, femoral artery, and femoral vein. Based upon our anatomic study, APIF, which may be used for treatment augmentation of anterior pelvic ring disruptions, does not place these structures at significant risk. In addition, the reproductive structures (round ligament and spermatic cord) are in direct visualization and can easily be avoided during implant placement.