Biomechanical comparison of distal interlocking methods in sheep tibia models, used in fixation of distal tibia shaft fractures with intramedullary nails

There are different types of distally interlocking methods used in intramedullary nailing of tibia fractures. But there is no concensus about the superiority of these methods. With early postoperative weight-bearing, failure of the distal locking screws is an important complication and may cause extra other problems. Contemporarily studies about new distally interlocking methods are still in progress. DSBLS (distally locking bolt screw, TST, Turkey) is a new distally interlocking method which is improved recently. In our study, we compared DSBLS, double screw distally locking and tirple screw distally locking methods againts axial loading forces biomechanically and we aimed to find the most resistant method to axiel loading. 16 pieces of tibia were extracted from sheeps slaughtered for consumption. We osteotomized these tibias 6 cm proximal from tibiotalar joint to make up a transverse fracture model. The proximal portions of tibias were excluded from the study. We divided 16 distal tibia portions into 4 groups. 8 mm solid intramedullary nails were implanted to tibias without reaming and locked distally with different methods in each groups. In we used 2 screws (both in mediolateral position, ZIMED) in group 1, 3 screws (two mediolateral, one anteroposterior position, ORTHOFIX) in group 2, DSBLS (TST) in group 3 and 3 screws with a smaller diameter (two mediolateral, one anteroposterior position, TIPMED) in group 4 for distal interlocking. Axial load was applied to all experimentals by Universal Traction – Distraction Test Machine in CadCam laboratuary, Technical Education Faculty, Kocaeli University. Tests were ended with screw breakage. Force, time and deformation datas were recorded and compared statistically. According to statistic results, resistance to axial loading forces of distally locking bolt screw (DSBLS, group 3) was statistically higher than double (group 1) or triple (group 2, 4) screw distal locking methods. Beside this, resistance to axial laoding forces of triple screw locking method (group 2, 4) was statistically higher than double screw locking method (group 1). When we compared triple screw locking methods, group 2 with larger diameter screws was more resitant than group 4.