Background. Bothlimited-contact dynamic compression plate (LC-DCP) and locking compression plate (LCP) systems were designed to provide enhanced bone healing and to improve stability at fracture site. However, implant failure, delayed union, nonunion and instability are still frequently encountered complications. The purpose of this study was to determine the biomechanical characteristics of a novel persistent compression dynamic plate (PCDP) which provides a persistent compression to fracture edges, and to compare the biomechanical properties of such a novel plate with the commonly used LCP. Methods. The novel persistent compression dynamic plate (PCDP) system is composed of a body, an inner compression spring and a distal mobile component. The body (proximal part) contains an adjustable screw and the distal part of the dynamic system can slide inside the body through a special tube. 12 (saw bone) artificial femoral bones were used. Transverse distal shaft fracture was created in all the saw bones at the same level, 6 femurs were fixed using the novel PCDP, whereas the other 6 femurs were fixed using the well-known LCP. All samples had undergone a nondestructive repetitive different forces (axial compression, bending and torsion), to evaluate the biomechanical differences between the two plating systems. Results. Under axial load the mean stiffness value was 439,0 N/mm for the PCDP and 158,9 N/mm for the LCP. There was nosignificant difference in A-P (anteroposterior) ve P-A (posteroanterior) bending stiffness values between PCDP and LCP, P=0.37 and P=0.80 respectively. However LCP provided significantly stiffer fixation in medial and lateral bending tests than PCDP (P=0.037) and (P=0.016), respectively. But no significant difference was detected between the two plating system in the torsional stiffness P=0.15. Conclusion. These results do not show any significant biomechanical difference in the applied torsional and bending stresses between LCP and PCDP. However the remarkably increased persistent compression effect of the PCDP created a considerable stress on fracture edges which may accelerate bone healing. Level of Evidence. Level 5

Introduction and Objective. Plating of geriatric distal femoral fractures with Locking Compression Plate Distal Femur (LCP–DF) often requires augmentation with a supplemental medial plate to achieve sufficient stability allowing early mobilization. However, medial vital structures may be impaired by supplemental medial plating using a straight plate. Therefore, a helically shaped medial plate may be used to avoid damage of these structures. Aim of the current study was to investigate the biomechanical competence of augmented LCP–DF plating using a supplemental straight versus helically shaped medial plate. Materials and Methods. Ten pairs of human cadaveric femora with poor bone quality were assigned pairwise for instrumentation using a lateral anatomical 15-hole LCP–DF combined with a medial 14-hole LCP, the latter being either straight or manually pre-contoured to a 90-degree helical shape. An unstable distal femoral fracture AO/OTA 33–A3 was simulated by means of osteotomies. All specimens were biomechanically tested under non-destructive quasi-static and destructive progressively increasing combined cyclic axial and torsional loading in internal rotation, with monitoring by means of optical motion tracking. Results. Initial axial stiffness and torsional stiffness in internal and external rotation for straight double plating (548.1 ± 134.2 N/mm, 2.69 ± 0.52 Nm/° and 2.69 ± 0.50 Nm/°) was significantly higher versus helical double plating (442.9 ± 133.7 N/mm, 2.07 ± 0.32 Nm/° and 2.16 ± 0.22 Nm/°), p≤0.04. Initial interfragmentary axial displacement and flexural rotation under 500 N static loading were significantly smaller for straight plating (0.11 ± 0.14 mm and 0.21 ± 0.10°) versus helical plating (0.31 ± 0.14 mm and 0.68 ± 0.16°), p<0.01. However, initial varus deformation under this loading remained not significantly different between the two fixation methods (straight: 0.57 ± 0.23°, helical: 0.75 ± 0.34°), p=0.08. During dynamic loading, within the course of the first 4000 cycles the movements of the distal fragment in flexion were significantly bigger for helical over straight plating (1.03 ± 0.33° versus 0.40 ± 0.20°), p<0.01. However, no significant differences were observed between the two fixation methods in terms of varus, internal rotation, axial and shear displacements at the fracture site, and number of cycles to failure. Conclusions. Augmented lateral plating of unstable distal femoral fractures with use of supplemental helically shaped medial plate was associated with more elastic bone-implant construct behavior under static and dynamic loading compared to straight double plating. Both fixation methods resulted in comparable number of cycles to failure. From a biomechanical perspective, the more elastic helical double plating may be considered as useful alternative to straight plating, potentially reducing stress risers at the distal bone-implant interface due to its ameliorated damping capacities

Background. Open reduction and internal fixation using plate osteosynthesis for midshaft clavicle fractures is often associated with hardware prominance. Although clinical studies have suggested a role for the use of thinner 2.7mm plates as a means of increasing cosmetic acceptability this still remains an area of controversy. We investigated the effect of plate size (2.7mm vs. 3.5mm), plate treatment (annealed vs. cold worked) and number of screws on the stiffness and yield point. Methods. Twenty-four synthetic clavicles were randomly divided into four treatment groups - Synthes (Synthes, Paoli, PA) 2.7mm cold-worked calcaneal reconstruction plate with six or eight bicortical screws; 3.5mm LCP reconstruction plate (RP) and 3.5mm LCP pre-contoured superior-anterior clavicle plate (PCSA). After measuring the baseline stiffness of the intact specimens, all clavicles were plated, a wedge-shaped inferior defect was created and testing performed using a cantilever-bending model. Statistical analysis was performed using one-way ANOVA with Tukey's multiple comparison test with significance set at a P value <0.05. Results. The 3.5mm RP construct was significantly stiffer than both of the 2.7mm CR constructs (P < 0.0001). The yield point for the 3.5mm PCSA construct was greater than the other three constructs (P < 0.0001), while the yield point for the 2.7mm CR plate with 6 screws and with 8 screws was higher than the 3.5mm RP construct (P = 0.0002 and P = 0.0023 respectively). The amount of displacement required to reach the yield point was highest for the 2.7mm CR plate with six screws and this was significantly higher than the values for the other three constructs. Conclusion. The 3.5mm plates demonstrated increased bending stiffness compared to the 2.7mm plates. Despite the lower resistance to bending forces, the cold worked 2.7mm plate exhibited a significantly higher yield point and required significantly more superior to inferior displacement to deform

Introduction. In recent years, there has been a growing interest, in many fields of medicine, in the use of bone adhesives that are biodegraded to non-toxic products and resorbed after fulfilling their function in contact with living tissue. Biomechanical properties of newly developed bone glue, such as adhesion to bone and elastic modulus were tested in our study. Material and methods. Newly developed injectable biodegradable “self-setting” bone adhesive prepared from inorganic tricalcium phosphate powder and aqueous solution of organic thermogelling polymers was used for ex-vivo fixing fractured pig femur. Ex-vivo biomechanical tests were performed on 45 fresh pig femurs. Control group consist of 10 healthy bones, tested group was created by 35 bones with artificial fractures in diaphysis – oblique (O) and bending wedge (BW) type of fracture. Tested group were divided to following 4 subgroups (sg); sg1 – O fracture (n=15) glued together with 3 different type of bone adhesives, sg2 BW fracture (n=5) glued together with bone adhesive (n=5); sg3 – BW fracture fixed with locking compression plate (LCP), n=5; sg4 – BW fracture fixed with LCP in combination with bone adhesive. Three-point bending force and shear compression tests were performed on linear electrodynamic test instrument (ElectroPuls E10000, Instron). Femurs from sg1, sg2 and sg4 were tested on Micro-CT before and after biomechanical testing. Results. Shear compression tests in sg1 without amino acids modification showed that it is needed force of 0.5 mPa to recreate fracture, however, modification with amino acids increased glue strength to 3 mPa. Three-point bending force test in sg2 showed reduced force of 250 N to recreate fracture, anyhow in sg4 force needed to initiate the fracture was increased up to 5000 N. Conclusion. Newly developed injectable biodegradable “self- setting” bone adhesive represents new possibility how to fix small bone fragments in comminuted fractures and simultaneous chance how to improve and accelerate bone healing process. Acknowledgement. Project no. AOTEU-R-2016-064 was supported by AOTRAUMA, Switzerland

Introduction. The incidence of distal femoral fractures in the geriatric population is growing and represents the second most common insufficiency fracture of the femur following fractures around the hip joint. Fixation of fractures in patients with poor bone stock and early mobilisation in feeble and polymorbide patients is challenging. Development of a fixation approach for augmentation of conventional LISS (less invasive stabilization system) plating may result in superior long-term clinical outcomes and enhance safe weight bearing. Objectives. The aim of this study was to investigate the biomechanical competence of two different techniques of augmented LISS plating for treatment of osteoporotic fractures of the distal femur in comparison to conventional LISS plating. Materials & methods. Unstable distal femoral fracture AO/OTA 33-A3 was set in artificial femora with low density simulating osteoporotic bone. Three study groups, consisting of 10 specimens each, were created for instrumentation with a 9-hole LISS plate, a LISS plate with an additional 3D-printed polyactide cylindrical intramedullary graft, as well as a LISS plate plus a medial 3.5mm LCP (locking compression plate) - double plating. All specimens were non-destructively tested under axial (20–150N) and torsional (0–4Nm) quasi-static loading. Each construct was tested with two different working length (WL) configurations (long and short) of the LISS plate. Relative movements between the most medial superior and inferior osteotomy aspects were investigated via three-dimensional motion tracking analysis. Results. Interfragmentary displacement along the femur axis (mm) under 150N axial loading was 2.03±0.23/1.65±0.27 for LISS with long/short WL, 0.18±0.06/0.18±0.04 for double plating with long/short WL, and 0.40±0.05/0.30±0.05 for LISS plus graft with long/short WL. Shear interfragmentary displacement (mm) under 4Nm torsional loading in internal rotation was 1.16±0.17/0.92±0.11 for LISS with long/short WL, 0.40±0.10/0.43±0.07 for double plating with long/short WL, and 1.09±0.13/0.82±0.11 for LISS plus graft with long/short WL. Double plating revealed significantly smaller longitudinal and shear displacement compared to the other two techniques for long and short WL, respectively (P≤0.010). In addition, LISS plus graft fixation was with significantly less longitudinal displacement in comparison to conventional LISS plating for long and short WL, respectively (P≤0.001). Long WL resulted in significantly higher longitudinal and shear displacement compared to short WL for LISS and LISS plus graft (P≤0.032), but not for double plating (P=1.000). Conclusion. Intramedullary grafting resulted in significantly increased fracture stability under axial loading in comparison to conventional LISS plating. However, it was not efficient enough to achieve comparable stability to double plating

Summary Statement. Tibia plateau split fracture fixation with two cancellous screws is particularly suitable for non-osteoporotic bone, whereas four cortical lag screws provide a comparable compression in both non-osteoporotic and osteoporotic bone. Angle-stable locking plates maintain the preliminary compression applied by a reduction clamp. Introduction. Interfragmentary compression in tibia plateau split fracture fixation is necessary to maintain anatomical reduction and avoid post-traumatic widening of the plateau. However, its amount depends on the applied fixation technique. The aim of the current study was to quantify the interfragmentary compression generated by a reduction clamp with subsequent angle-stable locking plate fixation in an osteoporotic and non-osteoporotic synthetic human bone model in comparison to cancellous or cortical lag screw fixation. Methods. Adult synthetic human tibiae with hard or soft cancellous bone were osteotomised at the lateral tibia plateau creating a split fracture (AO type 41-B1) and fixed with either two 6.5 mm cancellous, four 3.5 mm cortical lag screws or 3.5 mm LCP proximal lateral tibia plate, preliminary compressed by a reduction clamp (n = 5 per group). Interfragmentary compression was measured by a pressure sensor film after instrumentation. One-way analysis of variance (ANOVA) with Bonferroni post hoc correction was performed for statistical analysis (p < 0.05). Results. Applying a reduction clamp, interfragmentary compression was 0.6 MPa ± 0.1 in non-osteoporotic and osteoporotic bone. The locking plate was able to maintain the compression (0.5 MPa ± 0.1) in non-osteoporotic and osteoporotic bone, but it was significantly lower compared to four cortical lag screws (non-osteoporotic p = 0.01; osteoporotic p = 0.03). Comparing four 3.5 mm cortical lag screws, compression was not significantly different between the non-osteoporotic (1.7 MPa ± 0.7) and osteoporotic bone (1.4 MPa ± 0.5). Two 6.5 mm cancellous lag screws achieved significantly higher compression in non-osteoporotic (2.1 MPa ± 0.6) compared to osteoporotic (0.8 MPa ± 0.2, p = 0.01) bone. Conclusion. Preliminary compression applied by a reduction clamp was maintained by angle-stable locking plates. The two 6.5 mm cancellous screw technique would especially be appropriate for young human non-osteoporotic bone, whereas the four 3.5 mm cortical screw configuration could also be applied in osteoporotic bone

Objectives

This study tests the biomechanical properties of adjacent locked plate constructs in a femur model using Sawbones. Previous studies have described biomechanical behaviour related to inter-device distances. We hypothesise that a smaller lateral inter-plate distance will result in a biomechanically stronger construct, and that addition of an anterior plate will increase the overall strength of the construct.