THE HOLDING STRENGTH OF CANNULATED SCREWS COMPARED WITH SOLID CORE SCREWS IN CORTICAL AND CANCELLOUS BONE

The comparative holding strength of cannulated screws (CS) versus soli d core screws (SCS) has not been reported, although differences exist in the respective diameters of their outer thread and pilot drill hole s. Our objectives were to characterize these differences and determine the holding power of CS compared with SCS in cortical and cancellous bone. The dimensions of the Synthes (Paoli, PA) 3.5-mm SCS, 3.5-mm CS, 6.5-mm SCS, and 7.0-mm CS were measured, and the cross-sectional area for thread purchase was calculated. Using adult canine femurs, small- fragment 3.5-mm SCS were inserted in cortical (midshaft) and cancellou s (condyle) bone of one limb, and CS were placed in similar locations in the contralateral limb. The same technique was used for large-fragm ent CS and SCS. Pull-out testing was performed using an MTS machine (M TS Systems, Minneapolis, MN) with axial loads applied at 5 mm/s, and d ata were analyzed to determine the effects of screw type, location, an d size. Differences in CS versus SCS design result in higher cross-sec tional areas available for SCS thread purchase. Yet no significant dif ferences exists between screw types (SCS vs. CS) in either cortical or cancellous bone. In cancellous bone, large-fragment screws required m ore force to pull out than did small screws (p = 0.000). The mean forc e required to pull out small-fragment screws was higher in cortical bo ne than in cancellous bone (p = 0.000). These data suggest that the cl inical decision to use CS versus SCS should not be based on pull-out s trength.