OTA 2002 Posters

Percutaneous Retrograde Placement of Superior Ramus Screws: A Cadaver Study

Peter C. Krause, MD; Ulises P. Militano, MD; Jose Cancio, MD; Downstate Medical Center, Brooklyn, New York, USA

Purpose: Percutaneous retrograde screw fixation of the superior ramus has been described as a way to stabilize anterior ring disruptions of the pelvis and to treat hypertrophic ramus nonunions. The purpose of this study was to review the safety of this technique by placing cannulated screws under fluoroscopy in cadavers.

Methods: Percutaneous retrograde superior ramus screws were inserted in five cadavers (8 rami) using fluoroscopy. This was accomplished via a stab incision followed by blunt dissection down to the pubic tubercle. Outlet, inlet, and obturator outlet views were obtained to assure the correct starting position for a 2.8-mm guide wire. Fluoroscopy was then used to pass the guide wire, followed by drilling with a 5.0-mm bit, and then placement of a 7.3-mm cannulated screw. The obturator outlet view was used to prevent penetration into the acetabulum and to prevent violation of the superior part of the ramus. The inlet view was used to prevent violation of the anterior and posterior aspects of the ramus. Dissection of the surrounding structures including the joint was performed after screw placement to evaluate the position of the screw and the anatomy placed at risk. The distances from the symphysis, the pelvic brim, and the pubic tubercle to the starting portal were measured.

Results: No occurrences of intraarticular penetration were seen after placement of the screws either under fluoroscopy or during later dissection. No screw penetration was seen out of the ramus. In one cadaver, the size of the ramus was judged to be large enough for the drill bit but not for the screw, and therefore only the drill bit was placed. The entry site for the screw was on the medial and inferior aspect of the pubic tubercle at an average distance from the symphysis of 15.5 mm (range, 10 to 40 mm) and 20.5 mm (range, 12 to 26 mm) from the pelvic brim. The structure most clearly at risk was the spermatic cord (or round ligament), which was an average of 12.5 mm (range, 0 to 30) from the starting portal. One injury of the spermatic cord was noted, associated with a starting portal that was excessively lateral.

Discussion/Conclusion: Retrograde percutaneous screw fixation of the superior ramus can be reliably performed under fluoroscopy using the obturator outlet oblique and inlet views. This technique is potentially useful to avoid extensive surgical dissection, which is associated with increased morbidity, blood loss, and operative time. However, a strictly percutaneous approach clearly should not be performed because of the close proximity of the spermatic cord to the starting portal.