INTERNAL-FIXATION OF THE UNSTABLE ANTERIOR PELVIC RING - A BIOMECHANICAL COMPARISON OF STANDARD PLATING TECHNIQUES AND THE RETROGRADE MEDULLARY SUPERIOR PUBIC RAMUS SCREW

The purpose of this study was to evaluate pubic ramus fracture fixatio n. This biomechanical evaluation compared standard plating techniques with retrograde medullary screw fixation of a superior pubic ramus fra cture in a pelvic fracture model. Six fresh-frozen, cadaveric pelvic s pecimens with a mean age of 79 years were harvested. These specimens w ere physiologically loaded according to the following modifications an d instrumentations: (a) intact; (b) an APC-II unstable pelvic injury, specifically, unilateral superior and inferior rami osteotomies combin ed with ipsilateral anterior sacroiliac (SI) joint, sacrospinous, and sacrotuberous ligamentous disruptions, without fixation; (c) disrupted as in (b) but fixed anteriorly with a l0-hole 3.5-mm reconstruction p late contoured to the superior ramus and secured with four 3.5-mm cort ical screws; (d) disrupted as in (b) but fixed anteriorly with a 10-ho le 3.5-mm reconstruction plate contoured to the superior ramus and sec ured with six 3.5-mm cortical screws; (e) disrupted as in (b) but fixe d anteriorly with a 4.5-mm retrograde medullary superior pubic ramus c ortical screw 80 mm long (medial to the hip joint); and (f) disrupted as in (b) but fixed anteriorly with a 4.5-mm retrograde medullary supe rior pubic ramus cortical screw 130 mm long that was extraarticular an d engaged the lateral iliac cortex cephalad to the ipsilateral hip joi nt. The posterior disruptions of the pelvic ring were not fixed. The A PC-II injury created in this study resulted in significant (p < 0.05) motion at the disrupted rami and the injured SI joint, compared with t he intact pelvic specimen. When compared with the disrupted specimen w ithout fixation, displacement at the superior ramus was significantly (p < 0.05) decreased by all forms of ramus fixation evaluated. Plate f ixation decreased pubic ramus and sacroiliac deflections slightly bett er than retrograde screw fixation did, yet not significantly better. T he number of screws in the plate did not significantly affect displace ment measurements at either the disrupted ramus or the disrupted SI jo int. Similarly, the length of the retrograde ramus screw did not signi ficantly alter displacements at either the injured pubic ramus or the disrupted SI joint. Sacroiliac joint deflections were not significantl y (p < 0.05) decreased by any of the forms of anterior pelvic fixation . Flexion at the disrupted SI joint was slightly, but not significantl y (p < 0.05), decreased with all forms of fixation when compared with the disrupted specimen. The long retrograde screw and the plate with s ix screws decreased flexion slightly, but not significantly, better th an the short retrograde screw and the plate with four screws.