The AO Foundation advocates the use of partially threaded lag screws in the fixation of fractures of the medial malleolus. However, their threads often bypass the radiodense physeal scar of the distal tibia, possibly failing to obtain more secure purchase and better compression of the fracture.

We therefore hypothesised that the partially threaded screws commonly used to fix a medial malleolar fracture often provide suboptimal compression as a result of bypassing the physeal scar, and proposed that better compression of the fracture may be achieved with shorter partially threaded screws or fully threaded screws whose threads engage the physeal scar.

We analysed compression at the fracture site in human cadaver medial malleoli treated with either 30 mm or 45 mm long partially threaded screws or 45 mm fully threaded screws. The median compression at the fracture site achieved with 30 mm partially threaded screws (0.95 kg/cm² (interquartile range (IQR) 0.8 to 1.2) and 45 mm fully threaded screws (1.0 kg/cm² (IQR 0.7 to 2.8)) was significantly higher than that achieved with 45 mm partially threaded screws (0.6 kg/cm² (IQR 0.2 to 0.9)) (p = 0.04 and p < 0.001, respectively). The fully threaded screws and the 30mm partially threaded screws were seen to engage the physeal scar under an image intensifier in each case.

The results support the use of 30 mm partially threaded or 45 mm fully threaded screws that engage the physeal scar rather than longer partially threaded screws that do not. A 45 mm fully threaded screw may in practice offer additional benefit over 30 mm partially threaded screws in increasing the thread count in the denser paraphyseal region.

Cite this article: Bone Joint J 2013;95-B:1662–6.

Introduction. Despite costing up to 5X more than a one-third tubular plate (TTP) and no absolute indications, distal fibula locking plates (DFLP) are becoming increasingly popular in the fixation of ankle fractures, particularly in the elderly. We reviewed all our distal fibula fracture fixations, over the course of one year, in order to rationalise DFLP use. Methods. Patient demographics, Weber classification, use of DFLP or TTP and the mode of fixation were recorded. Open fractures and tibial plafond fractures were excluded. Results. 51/84 (61%) of patients had DFLP fixation of their distal fibula fracture, the majority (44/51) of which were for Weber B fractures. The DFLP was used in bridge mode for 12 Weber B fractures and in neutralisation mode for remaining 32. There was a significant difference in age between the DFLP and TTP groups for all fractures (p< 0.005) and for Weber B fractures treated in bridge mode (p=0.036), but not for Weber B fractures treated with a lag screw/ neutralisation plate (p=0.09). Discussion. In 32/44 of our cases, we used the DFLP to neutralise a lag screw. However DFLP are only of mechanical benefit when adequate fracture compression is not obtained either due to fracture comminution or due to osteoperotic bone, often seen in the elderly. All 32 of these Weber B fractures were amenable to a lag screw and were not comminuted. There was also no significant age difference between this group and the group of Weber B fractures that were treated with a lag screw/ neutralisation plate. In these cases therefore, the DFLP did not offer any mechanical advantage. Conclusion. We propose limiting the use of the DFLP to fibula fractures where intra-fragmentary compression cannot adequately be obtained, thus reducing our use by over 60% and significantly reducing our implant costs for such injuries