Objectives. External fixators are the traditional fixation method of choice for contaminated open fractures. However, patient acceptance is low due to the high profile and therefore physical burden of the constructs. An externalised locking compression plate is a low profile alternative. However, the biomechanical differences have not been assessed. The objective of this study was to evaluate the axial and torsional stiffness of the externalised titanium locking compression plate (ET-LCP), the externalised stainless steel locking compression plate (ESS-LCP) and the unilateral external fixator (UEF). Methods. A fracture gap model was created to simulate comminuted mid-shaft tibia fractures using synthetic composite bones. Fifteen constructs were stabilised with ET-LCP, ESS-LCP or UEF (five constructs each). The constructs were loaded under both axial and torsional directions to determine construct stiffness. Results. The mean axial stiffness was very similar for UEF (528 N/mm) and ESS-LCP (525 N/mm), while it was slightly lower for ET-LCP (469 N/mm). One-way analysis of variance (ANOVA) testing in all three groups demonstrated no significant difference (F(2,12) = 2.057, p = 0.171). There was a significant difference in mean torsional stiffness between the UEF (0.512 Nm/degree), the ESS-LCP (0.686 Nm/degree) and the ET-LCP (0.639 Nm/degree), as determined by one-way ANOVA (F(2,12) = 6.204, p = 0.014). A Tukey post hoc test revealed that the torsional stiffness of the ESS-LCP was statistically higher than that of the UEF by 0.174 Nm/degree (p = 0.013). No catastrophic failures were observed. Conclusion. Using the LCP as an external fixator may provide a viable and attractive alternative to the traditional UEF as its lower profile makes it more acceptable to patients, while not compromising on axial and torsional stiffness. Cite this article: B. F. H. Ang, J. Y. Chen, A. K. S. Yew, S. K. Chua, S. M. Chou, S. L. Chia, J. S. B. Koh, T. S. Howe. Externalised locking compression plate as an alternative to the unilateral external fixator: a biomechanical comparative study of axial and torsional stiffness. Bone Joint Res 2017;6:216–223. DOI: 10.1302/2046-3758.64.2000470

Dual plate constructs have become an increasingly common fixation technique for midshaft clavicle fractures and typically involve the use of mini-fragment plates. The goal of this technique is to reduce plate prominence and implant irritation, as these are common reasons for revision surgery. However, limited biomechanical data exist for these lower-profile constructs. The study aim was to compare dual mini-fragment orthogonal plating to traditional small-fragment clavicle plates for biomechanical non-inferiority and to determine if an optimal plate configuration could be identified, using a cadaveric model. Twenty-four cadaveric clavicles were randomized to one of six groups (n=4 per group), stratified by CT-based bone mineral content (BMC). The six different plating configurations compared were: pre-contoured superior or anterior fixation using a single 3.5-mm LC-DC plate, and four different dual-plating constructs utilizing 2.4-mm and 2.7-mm reconstruction or LC-DC plates. The clavicles were plated and then osteotomized to create an inferior butterfly fracture, which was then fixed with a single interfragmentary screw (OTA 15.2B). Axial, torsional, and bending (anterior and superior surface loading) stiffness were determined for each construct through non-destructive cyclic testing, using an MTS 858 Bionix materials testing system. This was followed by a load-to-failure test in three-point superior-surface bending. Kruskal-Wallace H and Mann-Whitney U were used to test for statistical significance. There were no significant differences in BMC (median 7.9 g, range 4.2-13.8 g) for the six groups (p=1.000). For axial stiffness, the two dual-plate constructs with a superior 2.4-mm and anterior 2.7-mm plate (either reconstruction or LC-DC) were significantly stiffer than the other four constructs (p=0.021). For both superior and anterior bending, the superior 2.4-mm and anterior 2.7-mm plate constructs were significantly stiffer when compared to the 3.5-mm superior plate (p=0.043). In addition, a 3.5-mm plate placed anterior was a stiffer construct than a superior 3.5-mm plate (p=0.043). No significant differences were found in torsional stiffness or load-to-failure between the different constructs. Dual plating using mini-fragment plates is biomechanically superior for fixation of midshaft clavicle fractures when compared to a single superior 3.5-mm plate and has similar biomechanical properties to a 3.5-mm plate placed anteriorly. With the exception of axial stiffness, no significant differences were found when different dual plating constructs were compared to each other. However, placing a 2.4-mm plate superiorly in combination with a 2.7-mm plate anteriorly might be the optimal construct, given the biomechanical superiority over the 3.5-mm plate placed superior

Background. Locking internal fixation through a relatively small surgical dissection presents an innovative technique for managing distal tibial extra-articular fractures. The aim of this study is to evaluate the biomechanical properties of one locking internal fixation plate used to treat these injuries. Method. An AO/OTA43-A3 fracture was created in synthetic composite tibiae. Locking internal fixation was achieved with an anatomically pre-contoured medial distal tibial locking plate. Comparisons were made between different screw configurations in holes proximal to the fracture and monocortical versus bicortical fixation. Axial stiffness was measured using a universal materials testing machine. Finite element analysis (FEA) was used to model the elastic deformation of the constructs. Outcome measures were axial stiffness under physiological loading conditions and compression load to failure. Results. A trend towards reduced mean axial stiffness from the bicortical to the monocortical fixation constructs was observed. The physical model demonstrated no difference in measured mean axial stiffness between constructs with all screw holes filled and constructs with 2 screws in the holes closest and furthest from the fracture site. There was a 19% reduction in mean measured axial stiffness between constructs with all holes filled and in constructs with 2 screws in adjacent holes furthest from the fracture site (p<0.05). FEA predicted increased plate deflection and reduced construct axial stiffness with increasing distance of screw placement from the osteotomy site. Conclusion. Axial stiffness of distal tibial extra-articular metaphyseal fractures stabilized by locking internal fixation is dependent upon the configuration of the screw in the plate

Aims. Restoration of proximal medial femoral support is the keystone in the treatment of intertrochanteric fractures. None of the available implants are effective in constructing the medial femoral support. Medial sustainable nail (MSN-II) is a novel cephalomedullary nail designed for this. In this study, biomechanical difference between MSN-II and proximal femoral nail anti-rotation (PFNA-II) was compared to determine whether or not MSN-II can effectively reconstruct the medial femoral support. Methods. A total of 36 synthetic femur models with simulated intertrochanteric fractures without medial support (AO/OTA 31-A2.3) were assigned to two groups with 18 specimens each for stabilization with MSN-II or PFNA-II. Each group was further divided into three subgroups of six specimens according to different experimental conditions respectively as follows: axial loading test; static torsional test; and cyclic loading test. Results. The mean axial stiffness, vertical displacement, and maximum failure load of MSN-II were 258.47 N/mm (SD 42.27), 2.99 mm (SD 0.56), and 4,886 N (SD 525.31), respectively, while those of PFNA-II were 170.28 N/mm (SD 64.63), 4.86 mm (SD 1.66), and 3,870.87 N (SD 552.21), respectively. The mean torsional stiffness and failure torque of MSN-II were 1.72 N m/° (SD 0.61) and 16.54 N m (SD 7.06), respectively, while those of PFNA-II were 0.61 N m/° (SD 0.39) and 6.6 N m (SD 6.65), respectively. The displacement of MSN-II in each cycle point was less than that of PFNA-II in cyclic loading test. Significantly higher stiffness and less displacement were detected in the MSN-II group (p < 0.05). Conclusion. The biomechanical performance of MSN-II was better than that of PFNA-II, suggesting that MSN-II may provide more effective mechanical support in the treatment of unstable intertrochanteric fractures. Cite this article: Bone Joint Res 2020;9(12):840–847

Introduction. The main postoperative complications in fixation of ulna shaft fractures are non-union and implant irritation using currently recommended 3.5-mm locking compression plates. An alternative approach using a combination of two smaller plates in orthogonal configuration has been proposed. The aim of this study was to compare the biomechanical properties of a single 3.5-mm locking compression plate versus double plating using one 2.5-mm and one 2.0-mm mandible plate in a human ulna shaft fracture model. Method. Eight pairs human ulnar specimens with a standardized 10-mm fracture gap were pairwise assigned for instrumentation with either a single 3.5-mm plate placed posteriorly, or for double plating using a 2.5-mm and a 2.0-mm mandible plate placed posteriorly under the flexor muscles and laterally under the extensor muscles. All constructs were initially non-destructively biomechanically tested in axial compression, torsion, and bending, which was followed by cyclic torsional loading to failure. Interfragmentary movements were monitored by means of optical motion tracking. Result. There were no significant differences between the two plating techniques for axial stiffness (p=0.335), torsional stiffness in supination (p=0.462), torsional stiffness in pronation (p=0.307), medio-lateral bending stiffness (p=0.522), and antero-posterior bending stiffness (p=0.143). During cyclic torsional loading over the first 3000 cycles, there were no significant differences between the two plating techniques for shear displacement across the fracture gap, p=0.324. The numbers of cycles until clinically relevant failure of 5° angular deformation were 1366±685 for double plating and 2024±958 for single plating, which was statistically non-significantly different, p>0.05. The constructs treated with both plating techniques failed due to bone breakage at the most distal screw. Conclusion. From a biomechanical perspective double plating of ulna shaft fractures using a 2.5-mm and a 2.0-mm locking mandible plate demonstrated equivalent fixation strength as conventional plating using a single 3.5-mm locking compression plate

Purpose: Cephalomedullary nails rely on a large lag screw that provides fixation into the femoral head. There is an option to statically lock the lag screw (static mode) or to allow the lag screw to move within the nail to compress the intertrochanteric fracture (dynamic mode). The purpose of this study was to compare the biomechanical stiffness of static and dynamic modes for a cephalomedullary nail used to fix an unstable peritrochanteric fracture. Method: Thirty intact synthetic femur specimens (Model #3406, Pacific Research Laboratories, Vashon, WA) were potted into cement blocks distally for testing on an Instron 8874 (Instron, Canton, MA). A long cephalomedullary nail (Long Gamma 3 Nail, Stryker, Mahwah, NJ) was then inserted into each of the femurs. An unstable four-part fracture was created, anatomically reduced, and the cephallomedullary nail was reinserted. Mechanical tests were conducted for axial, lateral, and torsional stiffness with the lag screws in:. static and. dynamic modes. A paired student’s t test was used to compare the 2 modes. Results: The axial stiffness of the cephalomedullary nail was significantly greater (p< 0.01) in the static mode (484.3±80.2N/mm) than in the dynamic mode (424.1±78.0N/mm) (Fig.2A). Similarly, the lateral bending stiffness of the nail was significantly greater (p< 0.01) in the static mode (113.9±8.4N/mm) than in the dynamic mode (109.5±8.8N/mm). The torsional stiffness of the nail was significantly greater (p=0.02) in the dynamic mode (114.5±28.2N/mm) than in the static mode (111.7±27.0N/mm). A post hoc power analysis with & #945;=0.05 and & #946;=0.20 revealed that the paired t test on 30 samples was sufficiently powered to determine a difference in mean axial stiffness of 33.0N/mm (6.8% of static stiffness), a difference in mean lateral bending stiffness of 3.6N/mm (3.2% of static stiffness) and a difference in mean torsional stiffness of 3.4N/mm (3.0% of static stiffness). Conclusion: Our results show that there is a 60N/mm reduction in axial stiffness of the cephalomedullary nail when the lag screw is changed from static to dynamic mode. This represents a 12.4% reduction in axial stiffness with a change from axial to dynamic modes which may be clinically significant. The differences in lateral (4.4N/mm, 3.9%) and torsional (2.8N/mm, 2.4%) are small enough that they are likely not clinically significant. We felt that a difference of greater than 10% in axial stiffness and a difference of greater than 5% in lateral or torsional stiffness would be clinically significant. Our study was adequately powered to detect these differences. Given the significant reduction in axial stiffness with dynamization of the cephalomedullary nail construct, we recommend use of the static mode when treating unstable peritrochanteric fractures with a cephalomedullary nail

Background. Currently about 4–6% of all femur fractures consist of distal femoral fractures. Different methods and implants have been used for the surgical treatment of distal femoral fractures, including intramedullary nails. Retrograde nail. By contrast with antegrade nails, surgical approach or retrograde nailing exposes the knee joint which may lead to tendency of infection and increased knee pain. Present study aims to compare the biomechanical behaviour of distal angular condyler femoral intramedullary nail (DACFIN), retrograde nail and plate fixation. Methods. Fifteen 4th generation Saw bones were used to evaluate the biomechanical differences between the groups (Group 1: Plate fixation, Group 2: Retrograde nailing, Group 3: DACFIN; (n=5)). Biomechanical test was performed by using an electromechanical test device Shimadzu (AG-IS 5kN, Japan). Displacement values were recorded by using a Non-contact Video Extensometer (DVE-101/201, Shimadzu, Japan) during the loading each femur with 5 cycles of 500 N at a rate of 10 N/s to determine axial stiffness. The faliure stiffness was measured by axial load to each constructat a displacement rate of 5 mm/min. Torsional loading applied to all groups in amount of 6 Nm of torque with a velocity of 18 degrees/min. Results. The mean torsion stiffness value of Group 3 (6.33 Nm/degree) was signifacantly higher than Group 1 (1.18 Nm/degree) and Group 2 (2.11Nm/degree), p<0.05). The failure stiffness, Group 3 (1725 N/mm) was significantly higher than Group 1 (1275 N/ mm) and Group 2 (1290 N/mm). However, In axial stiffness, the mean value of Group 2 (2554 N/mm) was higher than Group 3 (1822 N/mm), and signifantly higher than Group 1(468 N/mm), p<0.05). Conclusions. DACFIN is more stiffer than retrograde nail and plate fixation during torsional and failure load conditions. But in axial stiffness retrograde nail was stiffer. DACFIN provide intramedullary femur condyle fracture fixations without open knee joint. Level of evidence. Level 5. Disclosure. Authors declare that there is no conflict of interest related to the present study

Abstract. Several experimental studies derived relationships between density and macroscale material properties of trabecular bone, taking the form E=αρ. β. , where E is Young's modulus, ρ is density, and α and β are constants. Classical structural mechanics demonstrates β can vary between 1 (behaviour of the trabecular lattice is dominated by the axial stiffness of individual trabeculae) and 3 (behaviour is dominated by the bending stiffness of individual trabeculae). The ratio between rods (round trabeculae characterised by radius) and plates (flat trabeculae characterised by thickness) is also believed to govern the macroscale material properties of trabecular bone. To assess feasible ranges of α and β for trabecular bone, and their dependence on rod to plate ratio, 25 virtual samples of trabecular bone were generated as Voronoi lattices. Each 8×8×8mm sample was composed of 320 randomly generated Voronoi cells forming a foam like structure. Edges formed the rod network. Faces formed the plate network. Tissue level Young's modulus was set to 18,000MPa. Relative density was varied: 0.05, 0.1, 0.15, 0.2, 0.25. Rod to plate ratio was varied: 100:0, 75:25, 50:50, 25:75, 0:100. Macroscale Young's modulus was averaged in three orthotropic directions and used to find α and β. Around 14,000 3-noded quadratic beam elements represented rods, with average length of 0.63mm, and around 42,000 8-noded quadratic shell elements represented plates, with average area of 0.10mm. 2. Results for α and β were 3274 and 1.463 for 100% rods, 3646 and 1.067 for 50:50 rods and plates, and 4981 and 1.062 for 100% plates, showing the presence of plates improves the stiffness characteristics of trabecular bone. Work investigating the impact of element based geometry optimisation is ongoing. The work has important implications for the onset of conditions including osteoporosis and osteoarthritis, as well as those designing 3D printed scaffolds and implants

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

Introduction and Objective. Distal femoral fractures are commonly treated with a straight plate fixed to the lateral aspects of both proximal and distal fragments. However, the lateral approach may not always be desirable due to persisting soft-tissue or additional vascular injury necessitating a medial approach. These problems may be overcome by pre-contouring the plate in helically shaped fashion, allowing its distal part to be fixed to the medial aspect of the femoral condyle. The objective of this study was to investigate the biomechanical competence of medial femoral helical plating versus conventional straight lateral plating in an artificial distal femoral fracture model. Materials and Methods. Twelve left artificial femora were instrumented with a 15-hole Locking Compression Plate – Distal Femur (LCP-DF) plate, using either conventional lateral plating technique with the plate left non-contoured, or the medial helical plating technique by pre-contouring the plate to a 180° helical shape and fixing its distal end to the medial femoral condyle (n=6). An unstable extraarticular distal femoral fracture was subsequently simulated by means of an osteotomy gap. All specimens were tested under quasi-static and progressively increasing cyclic axial und torsional loading until failure. Interfragmentary movements were monitored by means of optical motion tracking. Results. Initial axial stiffness was significantly higher for helical (185.6±50.1 N/mm) versus straight (56.0±14.4) plating, p<0.01. However, initial torsional stiffness in internal and external rotation remained not significantly different between the two fixation techniques (helical plating:1.59±0.17 Nm/° and 1.52±0.13 Nm/°; straight plating: 1.50±0.12 Nm/° and 1.43±0.13Nm/°), p≥0.21. Helical plating was associated with significantly higher initial interfragmentary movements under 500 N static compression compared to straight plating in terms of flexion (2.76±1.02° versus 0.87±0.77°) and shear displacement under 6 Nm static rotation in internal (1.23±0.28° versus 0.40±0.42°) and external (1.21±0.40° versus 0.57±0.33°) rotation, p≤0.01. In addition, helical plating demonstrated significantly lower initial varus/valgus deformation than straight plating (4.08±1.49° versus 6.60±0.47°), p<0.01. Within the first 10000 cycles of dynamic loading, helical plating revealed significantly bigger flexural movements and significantly lower varus/valgus deformation versus straight plating, p=0.02. No significant differences were observed between the two fixation techniques in terms of axial and shear displacement, p≥0.76. Cycles to failure was significantly higher for helical plating (13752±1518) compared to straight plating (9727±836), p<0.01. Conclusions. Although helical plating using a pre-contoured LCP-DF was associated with higher shear and flexion movements, it demonstrated improved initial axial stability and resistance against varus/valgus deformation compared to straight lateral plating. Moreover, helical plate constructs demonstrated significantly improved endurance to failure, which may be attributed to the less progressively increasing lever bending moment arm inherent to this novel fixation technique. From a biomechanical perspective, helical plating may be considered as a valid alternative fixation technique to standard straight lateral plating of unstable distal femoral fractures

Introduction: The Taylor Spatial Frame (TSFTM, Smith & Nephew, Memphis) has gained international recognition for the fixation of complex long bone fractures and deformity correction. It’s application with transverse wires can be difficult in some anatomic regions, and fixation of frames with half pins is gaining clinical popularity. Half-pins cause minimal transfixion of the surrounding soft tissues and can be inserted into anatomically safe areas. Aims: This study aimed to compare the stiffness characteristics of a TSF frame fixed with transverse wires to fixation with half pins. Materials and methods: Experiments were carried out in the biomechanics laboratory at Cardiff university. All mechanical testing was performed with a servo-hydraulic test frame (MTS-858 Mini Bionix II®, MTS Corp., Minneapolis). Custom built mounts were used to attach the bone rigidly to one end of the machine and TSF ring to the other. Rings were fixed with 1.8mm transverse wires or hydroxyapatite coated 6.5mm half pins with 45°, 60°, 75° and 90° divergence angles. Bone was loaded with axial load to 400N and torque to 20Nm. Load/displacement curve data were analyzed for slope and displacement. Results: For larger diameter rings (180mm) there was no statistically significant difference in axial stiffness between the transverse wires (with 2 rings) and the half pins (p> 0.05). For 155mm diameter rings half pins provided statistically higher axial stiffness than transverse wires (p= 0.036). Half pins gave significantly more torsional stiffness for both ring diameters when compared to transverse wires (p< 0.05). As in axial stiffness, small diameter rings showed increased stiffness in torsion. There was an increase in axial and torsional stiffness as the divergence angle between the wires or pins increased (p< 0.05). Conclusion and clinical relevance: Half pins provide greater stiffness to TSF frames and allow axial micro-motion as well. This work provides a rationale for clinical decision making in construction of a TSF frame

Summary. Time-lapsed CT offers new opportunities to predict the risk of cement leakage and to evaluate the mechanical effects on a vertebral body by monitoring each incremental injection step in an in-vitro vertebroplasty procedure. Introduction. Vertebroplasty has been shown to reinforce weak vertebral bodies and to prophylactically reduce fracture risks. However, bone cement leakage is a major vertebroplasty related problem which can cause severe complications. Leakage risk can be minimised by injecting less cement into the vertebral body, inevitably compromising the mechanical properties of the augmented bone, as a proper endplate-to-endplate connection of the injected cement is needed to obtain a mechanical benefit. Thus the cement flow in a vertebroplasty procedure requires a better understanding. This study aimed at developing a method to monitor the cement flow in a vertebral body and its mechanical effect. Materials and Methods. Eight fresh frozen human cadaveric vertebrae were prepared for augmentation by performing a bitrans- or bipedicular approach. Following they were XTremeCT-scanned (Scanco, Switzerland) at a nominal resolution of 82µm. A custom made setup enabled to fix the vertebrae in the CT bore (Siemens Emotion6) centrically. Bone cement (Vertecem V+, Synthes GmbH, Switzerland) was injected monopedicularly via a syringe driver (Harvard Apparatus, USA). Injection forces were recorded through a load cell (Type 9211, Kistler Instrumente AG, Switzerland) placed on the driver. Either a custom PEEK cannula or a trocar was inserted into each pedicle of a vertebra to allow artifact-free CT scanning. After each milliliter of injection a CT scan of the vertebra was performed at a nominal resolution of 0.63mm. Subsequently, the CT images were resampled to the original XTremeCT image and the cement cloud was segmented. The image data were then further processed for micro finite element (microFE) modeling (FAIM, Numerics88, Canada). The models were then solved for axial stiffness and Von Mises Stress (VMS) distribution. Finally, the vertebrae underwent a biomechanical quasistatic axial compression test (Mini Bionix II 858, MTS Systems Corp., USA). Results. Endplate-to-endplate connection of the cement was reached in 4 vertebrae. The average volume needed to reach the connection was 5.0±1.2 ml. Cement leakage occurred in all vertebrae, whereby in 4 cases the cement leaked into the spine channel. Each successive cement injection step was characterised with an increase of peak injection forces (16.5±12.7N at 1ml to 70.82±21.14N at 6ml). With respect to axial stiffness the mechanical tests and the microFE models correlated well (R. 2. = 0.778). Analyzing the top 100 VMS an elevated stress concentration between the endplate and the cement was observed unless the endplate was in direct contact with the cement. Conclusion. Cement flow can be monitored precisely at each injection step using the time-lapsed CT approach. Combined with microFE modeling the mechanical properties of the augmented bone can be evaluated for different incremental cement volumes injected. Our results suggest augmenting the bone until an endplate-to-endplate connection is established as otherwise partial filling would increase the risk of failure in the trabecular bone structure. This is in close agreement to other studies

The reduction for unstable femoral intertrochanteric fracture should be extramedullary, which means that the proximal fragment protrudes for the distal fragment. However, only few articles have compared extramedullary and intramedullary reductions in a biomechanical study. Thus, we created unstable femoral intertrochanteric fracture models using imitational bone (extramedullary and intramedullary groups, each with 12 cases) and evaluated their biomechanical stabilities. The fracture type was 31-A2 according to the AO-OTA Classification of Fractures and Dislocations and greatly lacked bone on the posterior side. We performed compression examination and evaluated stiffness. The implant used for fixation was TFNA (DePuy Synthes). We applied axial compression with 20 adduction in the standing position. Statistical analysis was performed using the Mann-Whitney U test. No significant difference in initial loading force was found between the two groups. However, the axial stiffness of the extramedullary bone showed a significant increase (p < 0.05) in high loading force (800–1000 N). This means that the stability of the extramedullary reduction was superior to that of the intramedullary reduction in terms of high loading force in the standing position. We suggest that antero-medial bony buttress is important for unstable femoral intertrochanteric fractures. These data indicate that extramedullary reduction and fixation for unstable femoral intertrochanteric fractures increase stability

Purpose: Minimizing tip-apex distance (TAD) has been shown to reduce clinical failure of extramedullary sliding hip screws used to fix peritrochanteric fractures. There is debate regarding the optimal position of the lag screw in the femoral head when a cephalomedullary nail is used to treat a peritrochanteric fracture. Some authors suggest the TAD should be minimized as with an extramedullary sliding hip screw, while others suggest the lag screw should be placed inferior within the femoral head. The primary goal of this study was to determine which of 5 possible lag screw positions in the femoral head provides greatest mechanical stiffness and/or load-to-failure for an unstable peritrochanteric fracture treated with a cepha-clomedullary nail. The secondary goal was to determine if there is a linear correlation between implant-femur mechanical stiffness and/or load to failure (dependent variables) with a series of five radiographic measurements (independent variables) of distance from the lag screw tip to the femoral head apex. Method: Long Gamma 3 Nails (Stryker, Mahwah, NJ) were inserted into 30 left synthetic femurs (Pacific Research Laboratories, Vashon, WA). An unstable four-part fracture was created, anatomically reduced, and repaired using one of 5 lag screw placements in the femoral head:. superior (n=6),. inferior (n=6),. anterior (n=6),. posterior (n=6),. central (n=6). All specimens were radiographed in the anterioposterior and lateral planes, and radiographic measurements including TAD and a calcar referenced tip-apex distance (CalTAD) were calculated. All specimens were tested for axial, lateral, and torsional stiffness, and then loaded-to-failure in the axial position using an Instron 8874 (Canton, MA). ANOVA was used to compare means of the five treatment groups. Linear regression analysis was used to compare stiffness and load-to-failure (dependant variables) with radiographic measurements (independent variables). A post hoc power analysis was performed. Results: The inferior lag screw position had significantly greater mean axial stiffness than superior (p< 0.01), anterior (p=0.02) and posterior (p=0.04) positions. Analysis revealed significantly less mean torsional stiffness for the superior lag screw position compared to other lag screw positions (p< 0.01 all 4 pairings). No statistical differences were noted for lateral stiffness. Superior and central lag screw positions had significantly greater mean load-to-failure than anterior (p< 0.01 and p=0.02) and posterior (p< 0.01 and p=0.05) positions. There were significant negative linear correlations between stiffness tests with CalTAD, and load-to-failure with TAD. Power was greater than 95% for axial stiffness, torsional stiffness and load-to-failure tests. Conclusion: Position of the lag screw in the femoral head affects the biomechanical properties of the implant-femur construct. Central placement of the lag screw with minimization of TAD may provide the best combination of stiffness and load-to-failure

Minimizing tip-apex distance has been shown to reduce clinical failure of sliding hip screws used to fix peritro-chanteric fractures. The purpose of this study was to determine if such a relationship exists for the position of the lag screw in the femoral head using a cephalomedullary device. Methods: Thirty intact synthetic femur specimens (Model #3406, Pacific Research Laboratories, Vashon, WA) were potted into cement blocks distally for testing on an Instron 8874 (Instron, Canton, MA). A long cephalomedullary nail (Long Gamma 3 Nail, Stryker, Mahwah, NJ) was inserted into each of the femurs. An unstable four-part fracture was created, anatomically reduced, and repaired using one of 5 lag screw placements in the femoral head:. Superior (N=6),. Inferior (N=6),. Anterior (N=6),. Posterior (N=6),. Central (N=6). Mechanical tests were repeated for axial, lateral and torsional stiffness. All specimens were radiographed in the anterioposterior and lateral planes and tip-apex (TAD) distance was calculated. A calcar referenced tip-apex distance (CalTAD) was also calculated. ANOVA was used to compare means of the five treatment groups. Linear regression analysis was used to compare axial, lateral and torsional stiffness (dependant variables) to both TAD and CalTAD (independent variables). Results: ANOVA testing proved that the mean axial (p< 0.01) and torsional stiffness (p< 0.01) between the 5 groups was significantly different, but lateral stiffness was not statistically different (p=0.494). Post hoc analysis showed that the inferior lag screw position provided significantly higher mean axial stiffness (568.14±66.9N/ mm) than superior (428.0±45.6N/mm; p< 0.01), anterior (443.2±45.4N/mm; p=0.02) and posterior (456.7±69.3N/ mm; p=0.04) lag screw positions. There was no significant difference in mean axial stiffness between inferior (568.14±66.9N/mm) and central (525.4±81.7N/mm) lag screw positions (p=0.77). Post hoc analysis revealed significantly less mean torsional stiffness for the superior lag screw position compared to other lag screw positions (p< 0.01 all 4 pairings). There were no significant correlations between TAD and axial (r=−0.33, p=0.08), lateral (r=−0.22, p=0.24) or torsional (r=0.08, p=0.69) stiffness. There were significant correlations between CalTAD and axial (r=−0.66, p< 0.01), lateral (r=−0.38, p=0.04) and torsional (r=−0.38, p=0.04) stiffness. Discussion: Our results suggest that placement of the lag screw inferiorly in the femoral head when using a cephalomedullary nail to treat an unstable peritrochanteric fracture results in the stiffest construct in axial and torsional biomechanical testing. A simple radiographic measurement, CalTAD, provides an intraoperative method of determining optimal cephalomedullary nail lag screw position to achieve greatest construct stiffness

Purpose: Endoprosthetic reconstruction of the distal femur is the preferred approach for patients undergoing resection of bone sarcomas. The traditional How-medica Modular Resection System, using a press-fit stem (HMRS or Kotz prosthesis, Stryker Orthopaedics, Mahwah, New Jersey, USA) has shown good long-term clinical success, but has also been known to incur complications such as stem fracture. The Restoration stem, as a part of the new Global Modular Resection System (GMRS, Stryker Orthopaedics, Mahwah, NJ, USA), is currently proposed for this same application. This stem has a different geometry and provides the advantage of decreased risk of fracture of the component. The goal of this study was to compare the HMRS and Restoration press-fit stems in terms of initial mechanical stability. Methods: Six matching pairs fresh frozen adult femora were obtained and prepared using a flexible canal reamer and fitted with either a Restoration or HMRS press-fit stem distally. All constructs were mechanically tested in axial compression, lateral bending, and torsion to obtain mechanical stiffness. Torque-to-failure was finally performed to determine the offset force required to clinically fail the specimen by either incurring damage to the femur, the stem, or the femur-stem interface. Results: Restoration press-fit stems results were: axial stiffness (average=1871.1 N/mm, SD=431.2), lateral stiffness (average=508.0 N/mm, SD=179.6), and torsional stiffness (average=262.3 N/mm, SD=53.2). HMRS stems achieved comparable levels: axial stiffness (average=1867.9 N/mm, SD=392.0), lateral bending stiffness (average=468.5 N/mm, SD=115.3), and torsional stiffness (average=234.9 N/mm, SD=62.4). For torque-to-failure, the applied offset forces on Restoration (average=876.3 N, SD=449.6) and HMRS (aver-age=690.5 N, SD=142.0) stems were similar. There were no statistical differences in performance between the two stem types regarding axial compression (p=0.97), lateral bending (p=0.45), or torsional stiffnesses (p=0.07). Moreover, no differences were detected between the groups when tested in torque-to-failure (p=0.37). The mechanism of torsional failure for all specimens was “spinning” (i.e. surface sliding) at the femur-stem interface. No significant damage was detected to any bones or stem devices. Conclusions: These results suggest that the Restoration and HMRS press-fit stems may be equivalent clinically in the immediate post-operative situation. Funding: Commerical funding Funding Parties: Stryker Orthopaedics

Introduction: Distraction osteogenesis has been used as a method of generating new bone in limb lengthening and deformity realignment; and is achieved in our unit though the use of the Sheffield Ring Fixator. The development of soft tissue tension creates an entirely different mechanical environment, and can often result in severe complications during treatment. Fixators must therefore be able to resist these forces. Furthermore, biomechanical modelling is very different from fracture and bone gap simulation. The model developed in this study intended to look at linear distraction, i.e. lengthening. Aims: To create a mechanical model that simulates the soft tissue effects during lengthening with an external fixator. To obtain a synthetic material with similar passive tensile properties to that measured in lengthened soft tissue. To measure the effect of tensioned synthetic soft tissue on osteotomy motion and multi-planar stiffness during cyclic loading. Materials and Methods: A standard two 150mm ring frame was mounted on an acrylic rod, with a centrally placed osteotomy gap of 75mm. One ring was fixed with wires and the other with screws. An inter-fragmentary motion device was attached across the osteotomy, to measure axial, angular and shear deformation with both axial and off-axis loading. Soft tissue tension was simulated with the use of neoprene rubber sheeting, attached to the nylon rod by Jubilee clips, with a gap anteriorly or medially. Extensive tensile testing was performed to determine the visco-elastic behaviour of the rubber, which showed it to be consistent and reliable. Tension of a similar magnitude to lengthened muscle (35–125N) was achieved, and could be accurately predicted for certain distraction lengths. The stiffness of the frame was calculated from osteotomy motion with various distraction lengths both with the rubber attached and without. Results: Tension in the soft tissues summates with the force applied in loading, with the effect of increasing the axial stiffness of the fixator by up to 70N, with a directly proportional relationship. It also acts as a restraint for shear and angulatory motion. In anterior and lateral loading positions however, the angulation stiffness remains low; this is thought to be due to the unequal distribution of soft tissues around the bony column, as seen in vivo. The stiffness of the frame is lowered by increasing the distance between rings; this effect can be counteracted by soft tissue tension in axial stiffness, but less so for angular and shear. Conclusions: We conclude that osteotomy stability is dependent on soft tissue tension, and the magnitude of tension greatly alters the stiffness characteristics of the external fixator. This study highlights the important role of soft tissue tension in biomechanical modelling and clinical limb lengthening, and has exciting ramifications for future orthopaedic models

Three Cannulated Screws (3CS), Dynamic Hip Screw (DHS) with antirotation screw (DHS–Screw) or with a Blade (DHS–Blade) are the gold standards for fixation of unstable femoral neck fractures. Compared to 3CS, both DHS systems require larger skin incision with more extensive soft tissue dissection while providing the benefit of superior stability. The newly designed Femoral Neck System (FNS) for dynamic fixation combines the advantages of angular stability with a less invasive surgical technique. The aim of this study is to evaluate the biomechanical performance of FNS in comparison to established methods for fixation of the femoral neck in a human cadaveric model. Twenty pairs of fresh–frozen human cadaveric femora were instrumented with either DHS–Screw, DHS–Blade, 3CS or FNS. A reduced unstable femoral neck fracture 70° Pauwels III, AO/OTA31–B2.3 was simulated with 30° distal and 15° posterior wedges. Cyclic axial loading was applied in 16° adduction, starting at 500N and with progressive peak force increase of 0.1N/cycle until construct failure. Relative interfragmentary movements were evaluated with motion tracking. Highest axial stiffness was observed for FNS (748.9 ± 66.8 N/mm), followed by DHS–Screw (688.8 ± 44.2 N/mm), DHS–Blade (629.1 ± 31.4 N/mm) and 3CS (584.1 ± 47.2 N/mm) with no statistical significances between the implant constructs. Cycles until 15 mm leg shortening were comparable for DHS–Screw (20542 ± 2488), DHS–Blade (19161 ± 1264) and FNS (17372 ± 947), and significantly higher than 3CS (7293 ± 850), p<0.001. Similarly, cycles until 15 mm femoral neck shortening were comparable between DHS–Screw (20846 ± 2446), DHS–Blade (18974 ± 1344) and FNS (18171 ± 818), and significantly higher than 3CS (8039 ± 838), p<0.001. From a biomechanical point of view, the Femoral Neck System is a valid alternative to treat unstable femoral neck fractures, representing the advantages of a minimal invasive angle–stable implant for dynamic fixation with comparable stability to the two DHS systems with blade or screw, and superior to Three Cannulated Screws

Unstable distal tibia fractures are challenging injuries requiring surgical treatment. Intramedullary nails are frequently used; however, distal fragment fixation problems may arise, leading to delayed healing, malunion or nonunion. Recently, a novel angle-stable locking nail design has been developed that maintains the principle of relative construct stability, but introduces improvements expected to reduce nail toggling, screw migration and secondary loss of reduction, without the requirement for additional intraoperative procedures. The aim of this study was to investigate the biomechanical competence of a novel angle-stable intramedullary nail concept for treatment of unstable distal tibia fractures, compared to a conventional nail in a human cadaveric model under dynamic loading. Ten pairs of fresh-frozen human cadaveric tibiae with a simulated AO/OTA 42-A3.1 fracture were assigned to 2 groups for reamed intramedullary nailing using either a conventional (non-angle-stable) Expert Tibia Nail with 3 distal screws (Group 1) or the novel Tibia Nail Advanced system with 2 distal angle-stable locking low-profile screws (Group 2). The specimens were biomechanically tested under conditions including quasi-static and progressively increasing combined cyclic axial and torsional loading in internal rotation until failure of the bone-implant construct, with monitoring by means of motion tracking. Initial axial construct stiffness, although being higher in Group 2, did not significantly differ between the 2 nail systems, p=0.29. In contrast, initial torsional construct stiffness was significantly higher in Group 2 compared to Group 1, p=0.04. Initial nail toggling of the distal tibia fragment in varus and flexion was lower in Group 2 compared to Group 1, being significant in flexion, p=0.91 and p=0.03, respectively. After 5000 cycles, interfragmentary movements in terms of varus, flexion, internal rotation, axial displacement and shear displacement at the fracture site were all lower in Group 2 compared to Group 1, with flexion and shear displacement being significant, p=0.14, p=0.04, p=0.25, p=0.11 and p=0.04, respectively. Cycles to failure until both interfragmentary 5° varus and 5° flexion were significantly higher in Group 2 compared to Group 1, p=0.04. From a biomechanical perspective, the novel angle-stable intramedullary nail concept has the potential of achieving a higher initial axial and torsional relative stability and maintaining it with a better resistance towards loss of reduction under dynamic loading, while reducing the number of distal locking screws, compared to conventional locking in intramedullary nailed unstable distal tibia fractures

Open reduction and internal fixation of proximal humerus fractures with angular stable plates is, beside antegrade nailing of the humerus, a standard procedure. A retrograde nail has been developed to avoid penetrating the rotator cuff and to avoid opening the fracture side during osteosynthesis. The aim of our biomechanical study was to evaluate if retrograde nailing of proximal humerus fractures is as stable as locking plate osteosynthesis. The biomechanical properties of 2 implants were tested in 11 human fresh frozen cadaveric humeri pairs. The Retron Nail® and the Philos® plate were implanted after osteotomy. All specimens were suspected to axial and torque load for 1000 cycles in a servo pneumatic testing apparatus. The Philos® plate had greater torsion stiffness than the Retron® nail, but we found no significance. The Retron® nail had greater axial stiffness but our findings were not statistically significant. Our study showed, that there are no significant differences between a retrograde nail and locking plate osteosynthesis for proximal humerus fractures concerning axial and torsion deformities. Therefore the retrograde nail is a suitable alternative for fixation of proximal humerus fracture