Interfragmentary Motion Research Articles

HELICAL VERSUS STRAIGHT PLATING OF PROXIMAL THIRD HUMERAL SHAFT FRACTURES - A BIOMECHANICAL STUDY

Proximal humeral shaft fractures are commonly treated with long straight locking plates endangering the radial nerve distally. The aim of this study was to investigate the biomechanical competence in a human cadaveric bone model of 90°-helical PHILOS plates versus conventional straight PHILOS plates in proximal third comminuted humeral shaft fractures.Eight pairs of humeral cadaveric humeri were instrumented using either a long 90°-helical plate (group1) or a straight long PHILOS plate (group2). An unstable proximal humeral shaft fracture was simulated by means of an osteotomy maintaining a gap of 5cm. All specimens were tested under quasi-static loading in axial compression, internal and external rotation as well as bending in 4 directions. Subsequently, progressively increasing internal rotational loading until failure was applied and interfragmentary movements were monitored by means of optical motion tracking.Flexion/extension deformation (°) in group1 was (2.00±1.77) and (0.88±1.12) in group2, p=0.003. Varus/valgus deformation (°) was (6.14±1.58) in group1 and (6.16±0.73) in group2, p=0.976. Shear (mm) and displacement (°) under torsional load were (1.40±0.63 and 8.96±0.46) in group1 and (1.12±0.61 and 9.02±0.48) in group2, p≥0.390. However, during cyclic testing shear and torsional displacements and torsion were both significantly higher in group 1, p≤0.038. Cycles to catastrophic failure were (9960±1967) in group1 and (9234±1566) in group2, p=0.24.Although 90°-helical plating was associated with improved resistance against varus/valgus deformation, it demonstrated lower resistance to flexion/extension and internal rotation as well as higher flexion/extension, torsional and shear movements compared to straight plates. From a biomechanical perspective, 90°-helical plates performed inferior compared to straight plates and alternative helical plate designs with lower twist should be investigated in future paired cadaveric studies.

ANTERIOR VARIABLE-ANGLE LOCKED PLATING VERSUS TENSION BAND WIRING OF SIMPLE AND COMPLEX PATELLA FRACTURES: A BIOMECHANICAL STUDY

Treatment of simple and complex patella fractures represents a challenging clinical problem. Controversy exists regarding the most appropriate fixation method. Tension band wiring, aiming to convert the pulling forces on the anterior aspect of the patella into compression forces across the fracture site, is the standard of care, however, it is associated with high complication rates. Recently, anterior variable-angle locking plates have been developed for treatment of simple and comminuted patella fractures. The aim of this study was to investigate the biomechanical performance of the novel anterior variable-angle locking plates versus tension band wiring used for fixation of simple and complex patella fractures.Sixteen pairs of human cadaveric knees were used to simulate either two-part transverse simple AO/OTA 34-C1 or five-part complex AO/OTA 34-C3 patella fractures by means of osteotomies, with each fracture model created in eight pairs. The complex fracture pattern was characterized with a medial and a lateral proximal fragment, together with an inferomedial, an inferolateral and an inferior fragment mimicking comminution around the distal patellar pole. The specimens with simple fractures were pairwise assigned for fixation with either tension band wiring through two parallel cannulated screws, or an anterior variable-angle locking core plate. The knees with complex fractures were pairwise treated with either tension band wiring through two parallel cannulated screws plus circumferential cerclage wiring, or an anterior variable-angle locking three-hole plate. Each specimen was tested over 5000 cycles by pulling on the quadriceps tendon, simulating active knee extension and passive knee flexion within the range from 90° flexion to full knee extension. Interfragmentary movements were captured by motion tracking.For both fracture types, the articular displacements, measured between the proximal and distal fragments at the central aspect of the patella between 1000 and 5000 cycles, together with the relative rotations of these fragments around the mediolateral axis were all significantly smaller following the anterior variable-angle locked plating compared with the tension band wiring, p < 0.01From a biomechanical perspective, anterior locked plating of both simple and complex patella fractures provides superior construct stability versus tension band wiring.

Biomechanical study of internal fixation methods for femoral neck fractures based on Pauwels angle.

Objective: To select the most appropriate internal fixation method based on the Pauwels angle, in order to provide a new concept for clinical accurate treatment of femoral neck fractures (FNFs). Methods: FNFs models of Pauwels ; ; ; were created respectively. For Pauwels ≤ , 1, 2 and 3 Cannulated Compression Screws (CCS) and Porous Tantalum Screws (PTS) were used to fix the fracture for the models. For Pauwels , 3CCS and Medial Buttress Plate (MBP) combined with 1, 2 and 3CCS were used to fix the fracture. Based on the results of the finite element (FE) analysis, the biomechanical properties of each model were compared by analyzing and evaluating the following four parameters: maximal stress of the bone (MBS), maximal stress of the implants (MIS), maximal displacement of bone (MBD), interfragmentary motion (IFM). Results: At Pauwels , the larger parameters were found in 1CCS, which was 94.8MPa (MBS), 307.7MPa (MIS), 0.86mm (MBD) and 0.36mm (IFM). In 2CCS group, the parameters were 86.1MPa (MBS), 254.4MPa (MIS), 0.73mm (MBD) and 0.27mm (IFM), which were similar to those of PTS. At Pauwels ; , with the increase of the number of used CCS, accordingly, the parameters decreased. Particularly, the MIS (Pauwels ) of 1CCS was 1,195.3 MPa, but the other were less than the yield range of the materials. At Pauwels , the MBS of 3CCS group was 128.6 Mpa, which had the risk of failure. In 2CCS + MBP group, the parameters were 124.2MPa (MBS), 602.5MPa (MIS), 0.75mm (MBD) and 0.48mm (IFM), The model stability was significantly enhanced after adding MBP. Conclusion: Pauwels type Ⅰ (< ) fractures can reduce the number of CCS, and PTS is an appropriate alternative treatment. For Pauwels type Ⅱ fractures ( ), the 3CCS fixation method is still recommended. For Pauwels type Ⅲ fractures (> ), it is recommended to add MBP to the medial femoral neck and combine with 2CCS to establish a satisfactory fracture healing environment.

Translated article] Comparative biomechanical study of two configurations of cemented screws in a simulated proximal humerus fracture fixed with locking plate

IntroductionScrew tip augmentation with bone cement for fixation of osteoporotic proximal humerus fractures seems to improve stability and to decrease the rate of complications related to implant failure. However, the optimal augmentation combinations are unknown. The aim of this study was to assess the relative stability of two augmentations combinations under axial compression load in a simulated proximal humerus fractures fixed with locking plate. Material and methodsA surgical neck osteotomy was created in five pairs of embalmed humeri with a mean age of 74 years (range 46–93 years), secured with a stainless-steel locking-compression plate. In each pair of humeri, on the right humerus were cemented the screws A and E, and in the contralateral side were cemented screws B and D of the locking plate. The specimens were first tested cyclically in axial compression for 6000 cycles to evaluate interfragmentary motion (dynamic study). At the end of the cycling test, the specimens were loaded in compression force simulating varus bending with increasing load magnitude until failure of the construct (static study). ResultsThere were no significant differences in interfragmentary motion between the two configurations of cemented screws in the dynamic study (p=0.463). When tested to failure, the configuration of cemented screws in lines B and D demonstrated higher compression load to failure (2218N vs. 2105, p=0.901) and higher stiffness (125N/mm vs. 106N/mm, p=0.672). However, no statistically significant differences were reported in any of these variables. ConclusionsIn simulated proximal humerus fractures, the configuration of the cemented screws does not influence the implant stability when a low-energy cyclical load is applied. Cementing the screws in rows B and D provides similar strength to the previously proposed cemented screws configuration and could avoid complications observed in clinical studies.

Biomechanical analysis of helical versus straight plating of proximal third humeral shaft fractures.

Proximal humeral shaft fractures are surgically challenging and plate osteosynthesis with a long straight plate is one operative treatment option in these patients although endangering the radial nerve distally. Helical plates potentially avoid the radial nerve by twisting around the humeral shaft. Aim of the study was to investigate in a human cadaveric model the biomechanical competence of helical plates versus straight lateral plates used for fixation of proximal third comminuted humeral shaft fractures. Eight pairs of humeral cadaveric humeri were instrumented using either a long 90°-helical plate (Group1) or a straight long PHILOS plate (Group2). An unstable proximal humeral shaft fracture was simulated by means of a 5cm osteotomy gap. All specimens were tested under quasi-static loading in axial compression, internal and external rotation, and bending in four directions. Subsequently, progressively increasing cyclic loading in internal rotation until failure was applied and interfragmentary movements were monitored by motion tracking. During static testing flexion/extension deformation in Group1 was significantly higher, however, varus/valgus deformation as well as shear and torsional displacement under torsional load remained statistically indifferent between both groups. During cyclic testing shear and torsional displacements were both significantly higher in Group1 compared to Group 2. However, cycles to catastrophic failure remained statistically indifferent between the groups. From a biomechanical perspective, although 90°-helical plating is associated with higher initial stability against varus/valgus collapse and comparable endurance under dynamic loading, it demonstrates lower resistance to flexion/extension and internal rotation with bigger shear interfragmentary displacements versus straight lateral plating and, therefore, cannot be considered as its real alternative. Alternative helical plate designs should be investigated in the future.

Cerclage Wiring Improves Biomechanical Stability in Distal Tibia Spiral Fractures Treated by Intramedullary Nailing

Partial weight-bearing after operatively treated fractures has been the standard of care over the past decades. Recent studies report on better rehabilitation and faster return to daily life in case of immediate weight-bearing as tolerated. To allow early weight-bearing, osteosynthesis needs to provide sufficient mechanical stability. The purpose of this study was to investigate the stabilizing benefits of additive cerclage wiring in combination with intramedullary nailing of distal tibia fractures. In 14 synthetic tibiae, a reproducible distal spiral fracture was treated by intramedullary nailing. In half of the samples, the fracture was further stabilized by additional cerclage wiring. Under clinically relevant partial and full weight-bearing loads the samples were biomechanically tested and axial construct stiffness as well as interfragmentary movements were assessed. Subsequently, a 5 mm fracture gap was created to simulate insufficient reduction, and tests were repeated. Intramedullary nails offer already high axial stability. Thus, axial construct stiffness cannot be significantly enhanced by an additive cerclage (2858 ± 958 N/mm NailOnly vs. 3727 ± 793 N/mm Nail + Cable; p = 0.089). Under full weight-bearing loads, additive cerclage wiring in well-reduced fractures significantly reduced shear (p = 0.002) and torsional movements (p = 0.013) and showed similar low movements as under partial weight-bearing (shear 0.3 mm, p = 0.073; torsion 1.1°, p = 0.085). In contrast, additional cerclage had no stabilizing effect in large fracture gaps. In well-reduced spiral fractures of the distal tibia, the construct stability of intramedullary nailing can be further increased by additional cerclage wiring. From a biomechanical point of view, augmentation of the primary implant reduced shear movement sufficiently to allow immediate weight-bearing as tolerated. Especially, elderly patients would benefit from early post-operative mobilization, which allows for accelerated rehabilitation and a faster return to daily activities.

Estudio biomecánico comparativo de dos configuraciones de tornillos cementados en una fractura simulada de húmero proximal fijada con placa y tornillos bloqueados

IntroductionScrew tip augmentation with bone cement for fixation of osteoporotic proximal humerus fractures seems to improve stability and to decrease the rate of complications related to implant failure. However, the optimal augmentation combinations are unknown. The aim of this study was to assess the relative stability of two augmentations combinations under axial compression load in a simulated proximal humerus fractures fixed with locking plate. Material and methodsA surgical neck osteotomy was created in five pairs of embalmed humeri with a mean age of 74 years (range 46–93 years), secured with a stainless-steel locking-compression plate. In each pair of humeri, on the right humerus were cemented the screws A and E, and in the contralateral side were cemented screws B and D of the locking plate. The specimens were first tested cyclically in axial compression for 6,000 cycles to evaluate interfragmentary motion (dynamic study). At the end of the cycling test, the specimens were loaded in compression force simulating varus bending with increasing load magnitude until failure of the construct (static study). ResultsThere were no significant differences in interfragmentary motion between the two configurations of cemented screws in the dynamic study (p=0.463). When tested to failure, the configuration of cemented screws in lines B and D demonstrated higher compression load to failure (2218N vs. 2105, p=0.901) and higher stiffness (125N/mm vs. 106N/mm, p=0.672). However, no statistically significant differences were reported in any of these variables. ConclusionsIn simulated proximal humerus fractures, the configuration of the cemented screws does not influence the implant stability when a low-energy cyclical load is applied. Cementing the screws in rows B and D provides similar strength to the previously proposed cemented screws configuration and could avoid complications observed in clinical studies.

The effects of mechanical instability on PDGF mediated inflammatory response at early stage of fracture healing under diabetic condition

Background and ObjectiveMechanical stability plays an important role in fracture healing process. Excessive interfragmentary movement will continuously damage the tissue and newly formed capillaries at the fracture site, which leads to overproduction of platelet-derived growth factor (PDGF) that attracts more macrophages into fracture callus, ultimately persistent and enhanced inflammatory response happens. For diabetic condition, the impact of mechanical instability of fracture site on inflammatory response could be further compliciated and the relevant research in this field is relatively limited. MethodsBuilding on previous experimental studies, this study presents a numerical model consisting of a system of reactive-transport equations representing the transport as well as interactions of different cells and cytokines within the fracture callus. The model is initially validated by available experimental data, and then implemented to investigate the role of mechanical stability of fracture site in inflammatory response during early stage of healing. It is assumed that there is an increased release of PDGF due to the rupture of blood vessels resulting from mechanical instability, which leads to increased production of inflammatory cytokines (i.e., TNF-α). The bone healing process under three different conditions were investigated, i.e., mechanically stable condition with normal inflammatory response (Control, Case 1), mechanically unstable condition with normal inflammatory response (Case 2) and mechanically unstable condition with diabetes (Case 3). ResultsMechanical instability can promote the macrophage infiltration and thus induce an enhanced and prolonged inflammatory response, which could impede the MSCs proliferation during the early fracture healing stage (e.g., compared with the control condition, the MSCs concentration in unstable fracture with normal inflammatory response can be reduced by 3.2% and 5.2% on day 2 and day 10 post-fracture, respectively). Under diabetic condition, the mechanical instability of fracture site could lead to a significant increase of TNF-α concentration in fracture callus (Case 3) in comparison to control (Case 1) (e.g., three-fold increase in TNF-α concentration compared to control). In addition, the results show that the mechanical instability affects the cell differentiation and proliferation in fracture callus in a spatially dependent manner, e.g., for diabetic fracture patients, the mechanical instability could potentially decrease the concentration of MSCs, osteoblasts and chondrocytes by around 39%, 30% and 29% in cortical callus, respectively, in comparison to control. ConclusionThe mechanical instability together with diabetic condition can significantly affect the natural resolution of inflammation during early stage of healing by turning acute inflammation into chronic inflammation which is characterized by a continuously upregulated TNF-α pathway.

The ideal site of cement application in cement augmented sacroiliac screw fixation: the biomechanical perspective

PurposeTo compare construct stability of cement augmented sacroiliac screws using two different cementation sites in a biomechanical fragility fracture model of the pelvis.MethodsA fracture model with an incomplete fracture of the sacral ala and complete fracture of the anterior pelvic ring mimicking a FFP IIB fragility fracture of the pelvis was established in five fresh frozen human cadaveric pelvises. Sacral fracture stabilization was achieved with bilateral 7.3 mm fully threaded sacroiliac screws. Cement augmentation was performed at the tip of the screw (body of S1; Group A) on one side, and at the midshaft of the screw (sacral ala; Group B) on the contralateral side. Biomechanical testing was conducted separately on both sides comprising cyclic loading of axial forces transferred through the tested hemipelvis from L5 to the ipsilateral acetabulum. Combined angular displacement in flexion and internal rotation (“gap angle”), angular displacement of the ilium in relation to the screw (“screw tilt ilium”), and screw tip cutout were evaluated.ResultsRelative interfragmentary movements were associated with significantly higher values in group A versus group B for “gap angle” (2.4° vs. 1.4°; p < 0.001), and for “screw tilt ilium” (3.3° vs. 1.4°; p < 0.001), respectively. No significant difference was indicated for screw tip cutout between the two groups (0.6 mm [Group A] vs. 0.8 mm [Group B]; p = 0.376).ConclusionThe present study demonstrated less fragment and screw displacements in a FFP IIB fracture model under physiologic cyclic loading by cement augmentation of sacroiliac screws at the level of the lateral mass compared to the center of vertebral body of S1.

Low-cost locally manufacturable unilateral imperial external fixator for low- and middle-income countries.

Treating open fractures in long bones can be challenging and if not performed properly can lead to poor outcomes such as mal/non-union, deformity, and amputation. One of the most common methods of treating these fracture types is temporary external fixation followed by definitive fixation. The shortage of high-quality affordable external fixators is a long-recognised need, particularly in Low- and Middle-Income Countries (LMICs). This research aimed to develop a low-cost device that can be manufactured locally to international standards. This can provide surge capacity for conflict zones or in response to unpredictable incidents and situations. The fixator presented here and developed by us, the Imperial external fixator, was tested on femur and tibia specimens under 100 cycles of 100 N compression-tension and the results were compared with those of the Stryker Hoffmann 3 frame. The Imperial device was stiffer than the Stryker Hoffmann 3 with a lower median interfragmentary motion (of 0.94 vs. 1.48 mm). The low-cost, easy to use, relatively lightweight, and easy to manufacture (since minimum skillset and basic workshop equipment and materials are needed) device can address a critical shortage and need in LMICs particularly in conflict-affected regions with unpredictable demand and supply. The device is currently being piloted in three countries for road traffic accidents, gunshot wounds and other conflict trauma-including blast cohorts.

Comparative Analysis of Uncoupled Mode Approximations for Molecular Thermochemistry and Kinetics.

The accurate prediction of thermochemistry and kinetic parameters is an important task for reaction modeling. Unfortunately, the commonly used harmonic oscillator model is often not accurate enough due to the absence of anharmonic effects. In this work, we improve the representation of an anharmonic potential energy surface (PES) using uncoupled mode (UM) approximations, which model the full-dimensional PES as a sum of one-dimensional potentials of each mode. We systematically analyze different PES sampling schemes and coordinate systems for constructing the one-dimensional potentials, and benchmark the performance of UM methods on data sets of molecular thermochemistry and kinetic properties. The results show that the accuracy of the UM approach strongly depends on how the one-dimensional potentials are defined. If one-dimensional potentials are constructed by sampling along normal mode directions (UM-N) or along the directions that minimize intermode coupling (E- and E'-optimized), the accuracies of the predicted properties are not significantly improved compared to the harmonic oscillator model. However, significant improvements can be achieved by sampling the torsional modes separately from the vibrational modes (UM-T and UM-VT). In this work, three types of coordinate systems are examined, including redundant internal coordinates (RIC), hybrid internal coordinates (HIC), and translation-rotation-internal coordinates (TRIC). The HIC and TRIC coordinate systems can outperform RIC since transition state species may contain large-amplitude interfragmentary motions that regular internal coordinates can not describe adequately. Among all the methods we examined, the activation energies and pre-exponential factors calculated using UM-VT with either TRIC or HIC best agree with the reference values. Since UM-VT requires only a number of additional single point energy calculations for each independent mode, the scaling of computational costs of UM-VT is the same as that of the standard harmonic oscillator model, making UM-VT an appealing way of calculating the thermochemistry and kinetic properties for large-size systems.

Optimal design and biomechanical analysis of sandwich composite metal locking screws for far cortical locking constructs.

In the interests of more flexible and less stiff bridge constructs to stimulate bone healing, the technique of far cortical locking has been designed to improve locked plating constructs in terms of stress concentration, stress shielding, and inhibition of issues around fracture healing. However, far cortical locking screws currently lack objective designs and anti-fatigue designs. This study investigates an optimization algorithm to form a special locking screw composed of various metals, which can theoretically achieve the maintenance of the excellent mechanical properties of far cortical locking constructs in terms of fracture internal fixation, while maintaining the biomechanical safety and fatigue resistance of the structure. The numerical results of our study indicate that the maximum von Mises stress of the optimized construct is less than the allowable stress of the material under each working condition while still achieving sufficient parallel interfragmentary motion. Numerical analysis of high cycle fatigue indicates that the optimized construct increases the safety factor to five. A high cycle fatigue test and defect analysis indicates that the sandwich locking constructs have better fatigue resistance. We conclude that the sandwich locking construct theoretically maintains its biomechanical safety and fatigue resistance while also maintaining excellent mechanical properties for fracture internal fixation.

Finite element analysis for better evaluation of rib fractures: A pilot study.

Modeling rib fracture stability is challenging. Computer-generated finite element analysis (FEA) is an option for assessment of chest wall stability (CWS). The objective is to explore FEA as a means to assess CWS, hypothesizing it is a reliable approach to better understand rib fracture pathophysiology. Thoracic anatomy was generated from standardized skeletal models with internal/external organs, soft tissue and muscles using Digital Imaging and Communications in Medicine data. Material properties were assigned to bone, cartilage, skin and viscera. Simulation was performed using ANSYS Workbench (2020 R2, Canonsburg, PA). Meshing the model was completed identifying 1.3 and 2.1 million elements and nodes. An implicit solver was used for a linear/static FEA with all bony contacts identified and applied. All material behavior was modeled as isotropic/linear elastic. Six load cases were evaluated from a musculoskeletal AnyBody model; forward flexion, right/left lateral bending, right/left axial rotation and 5-kg weight arm lifting. Standard application points, directions of muscle forces, and joint positions were applied. Ten fracture cases (unilateral and bilateral) were defined and 66 model variations were simulated. Forty-three points were applied to each rib in the mid/anterior axillary lines to assess thoracic stability. Three assessment criteria were used to quantify thoracic motion: normalized mean absolute error, normalized root mean square error, and normalized interfragmentary motion. All three analyses demonstrated similar findings that rib fracture deformation and loss of CWS was highest for left/right axial rotation. Increased number of ribs fracture demonstrated more fracture deformation and more loss of CWS compared with a flail chest segment involving less ribs. A single rib fracture is associated with ~3% loss of CWS. Normalized interfragmentary motion deformation can increases by 230%. Chest wall stability can decrease by over 50% depending on fracture patterns. Finite element analysis is a promising technology for analyzing CWS. Future studies need to focus on clinical relevance and application of this technology. Diagnostic Tests or Criteria; Level IV.

Forgivingness of an Anteromedially Positioned Small Locked Plate for High Tibial Osteotomy in Case of Overcorrection and Lateral Hinge Fracture.

High tibial osteotomy (HTO) represents a sensible treatment option for patients with moderate unicondylar osteoarthritis of the knee and extraarticular malalignment. The possibility of a continuously variable correction setting and a surgical approach low in complications has meant that the medial opening osteotomy has prevailed over the past decades. The objective of the present study was to determine whether anteromedially positioned small plates are nevertheless forgiving under biomechanically unfavourable conditions (overcorrection and lateral hinge fracture). In this study, a simulated HTO was performed on composite tibiae with a 10-mm wedge and fixed-angle anteromedial osteosynthesis with a small implant. Force was applied axially in a neutral mechanical axis, a slight and a marked overcorrection into valgus, with and without a lateral hinge fracture in each case. At the same time, a physiological gait with a dual-peak force profile and a peak load of 2.4 kN was simulated. Interfragmentary motion and rigidity were determined. The rigidity of the osteosynthesis increased over the cycles investigated. A slight overcorrection into valgus led to the lowest interfragmentary motion, compared with pronounced valgisation and neutral alignment. A lateral hinge fracture led to a significant decrease in rigidity and increase in interfragmentary motion. However, in no case was the limit of 1 mm interfragmentary motion critical for osteotomy healing exceeded. The degree of correction of the leg axis, and the presence of a lateral hinge fracture, have an influence on rigidity and interfragmentary motion. From a mechanically neutral axis ranging up to pronounced overcorrection, the implant investigated offers sufficient stability to allow healing of the osteotomy, even if a lateral hinge fracture is present.

Comminuted intraarticular calcaneal fractures: Multiplanar VA locked plating and interlocked nailing incorporate longitudinal strut and provide superior stability – a biomechanical cadaveric study

Treatment of comminuted intraarticular calcaneal fractures remains controversial and challenging. The aim of this study was to investigate the biomechanical performance of three different methods for fixation of such fractures. Comminuted calcaneal fractures, including Sanders III AB fracture of the posterior facet and Kinner II B fracture of the calcaneocuboid joint (CCJ) articular calcaneal surface, were created in 18 human cadaveric lower legs by osteotomizing. The ankle joint, medial soft tissues and midtarsal bones along with their ligaments were preserved. The specimens were randomized to three groups for fixation with either (1) 2.7 mm variable-angle locking lateral calcaneal plate (Group 1), (2) 2.7 mm variable-angle locking anterolateral calcaneal plate in combination with one 4.5 mm and one 6.5 mm cannulated screws (Group 2), or (3) interlocking calcaneal nail with 3.5 mm screws in combination with three separate 4.0 mm cannulated screws (Group 3). All specimens were biomechanically tested to failure under axial loading in midstance foot position. Each test commenced with a quasi-static compression ramp from 50 to 200 N, followed by progressively increasing cyclic loading at 2 Hz. Starting from 200 N, the peak load of each cycle increased at a rate of 0.2 N/cycle. Interfragmentary movements were captured by motion tracking. In addition, mediolateral X-rays were taken every 250 cycles with a triggered C-arm. Böhler angle after 5000 cycles (1200 N peak load) increased significantly more in Group 1 compared to both other groups (P ≤ 0.020). Varus deformation of 10° between the calcaneal tuberosity and the lateral calcaneal fragments was reached at significantly lower number of cycles in Group 1 compared the other groups (P ≤ 0.017). Both cycles to 10° plantar gapping between the anterior process and the calcaneal tuberosity fragments, and 2 mm displacement at the CCJ articular calcaneal surface revealed no significant differences among the groups (P ≥ 0.773). From a biomechanical perspective, treatment of comminuted intraarticular calcaneal fractures using anterolateral variable-angle locking plate with additional longitudinal screws or interlocked nail in combination with separate transversal screws provides superior stability as opposed to lateral variable-angle locked plating only.

Spatial Bridge Locking Fixator versus Traditional Locking Plates in Treating AO/OTA 32-A3.2 Fracture: Finite Element Analysis and Biomechanical Evaluation.

ObjectiveTo compare the biomechanical behaviors of the spatial bridge locking fixator (SBLF), single locking plate (SP), and double locking plate (DP) for AO/OTA 32‐A3.2 fractures using finite element analysis and biomechanical tests.MethodsAxial loading of 700 N was conducted on the AO/OTA 32‐A3.2 model via finite element analysis. The von Mises stress and the interfragmentary movement (IFM) were comparatively analyzed in the three configurations above. On the mechanical tester, axial and torsional loading of 30 synthetic femurs (five specimens of each configuration for each test at random) was performed, and the interfragmentary movement, torsion angle, stiffness, and ultimate load were recorded and analyzed.ResultsThe finite element analysis (FEA) results showed that the von Mises stress of the spatial bridge locking fixator (SBLF) was lower than that of the single locking plate (SP) and higher than that of the double locking plate (DP). At 700 N, the axial IFMs were 0.15–0.38 mm (SBLF), 0.03–0.84 mm (SP), and 0.02–0.07 mm (DP). The biomechanical experiment indicated that the axial interfragmentary movements (IFMs) were 0.44 ± 0.23 mm (SBLF), 1.02 ± 0.40 mm (SP), and 0.07 ± 0.07 mm (DP) (p < 0.001). The axial IFM of the SBLF group had the highest probability (79.26%) of falling within the ideal range (0.2–0.8 mm), and the SP and DP groups had probabilities of 27.10% and 3.14%, respectively. The axial stiffness in the SBLF group (1586 ± 130 N/mm) was significantly lower than that in the DP group (10,264 ± 2671 N/mm) (p < 0.001) but greater than that in the SP group (725 ± 178 N/mm) (p = 0.396). The range of axial loads to ultimate failure was 3385–4527 N (SBLF), 3377–4664 N (SP), and 3780–4804 N (DP). The shear motion of the fracture end was 0.35 ± 0.14 mm (SBLF), 0.16 ± 0.10 mm (SP), and 0.08 ± 0.04 mm (DP) (p < 0.001). The torsional stiffness was 1.68 ± 0.14 Nm/degree (SBLF), 2.32 ± 0.29 Nm/degree (SP) (SBLF&SP, p < 0.001), and 3.53 ± 0.73 Nm/degree (DP) (SBLF&DP, p < 0.001).ConclusionsThe SBLF structure may exhibit a better biomechanical performance compared with the SP and DP in providing the best quantity and more symmetrical interfragmentary movement for AO/OTA 32‐A3.2 fractures.

The addition of cerclage wiring does not improve proximal bicortical fixation of locking plates for Type C periprosthetic fractures in synthetic humeri

BackgroundTreatment of proximal humerus periprosthetic fractures is challenging. It remains difficult to achieve robust fixation of the proximal fragment to the locking plate using cerclage wiring and/or unicortical screws. Use of polyaxial tangentially directed bicortical locking screws increases screw purchase, but it is unclear if this option provides robust fixation. This biomechanical study compares fixation of constructs using cerclage wires, bicortical locking screws, and a hybrid method utilizing both methods. MethodsUncemented humeral stems were implanted into synthetic humeri and Type C periprosthetic fractures were simulated with a 1 cm transverse osteotomy. Distal ends of locking plates were secured with bicortical non-locking screws. The proximal ends were supported by either isolated cerclage wires, polyaxial locking screws, or a hybrid combination of both (n = 6 for each group). A universal test frame was used for non-destructive torsion and cyclic axial compression tests. 3-D motion tracking was employed to determine stiffnesses and relative interfragmentary motions. FindingsIsolated screw constructs showed significantly increased resistance against torsional movement, bending, and shear, (p < 0.05) in comparison to cerclage constructs. The hybrid construct provided no significant changes in stability over the isolated screw construct. InterpretationAddition of cerclage wires in this synthetic bone model of Type C periprosthetic humerus fractures did not add significant stability to proximal bicortical locking plate fixation. Considering risks of tissue stripping and nerve injury, usage of cerclage wires in a similar clinical setting should be chosen carefully, especially when bicortical fixation around the prosthetic stem can be achieved.

Biomechanical design of a new percutaneous locked plate for comminuted proximal tibia fractures

Comminuted proximal tibia fractures are an ongoing surgical challenge. This “proof of concept” study is the first step in designing a new percutaneous plate for this injury under toe-touch weight-bearing as prescribed after surgery. Finite element simulations generated design curves for overall stiffness, bone and implant stress, and interfragmentary motion using 3 fixations (no, 1, or 2 “kickstand” (KS) screws across the fracture gap) over a range of plate elastic moduli (EP = 5 to 200 GPa). Combining well-established optimization criteria to enhance callus formation (i.e. 0.2 mm ≤ axial interfragmentary motion ≤ 1 mm; shear / axial interfragmentary motion ratio < 1.6), lessen stress shielding (i.e. bone stress under the proposed plate > bone stress under a traditional titanium or steel plate), and reduce steel screw breakage (i.e. screw max stress < ultimate tensile stress of steel) resulted in plate design recommendations: 172.6 ≤ EP < 200 GPa (no KS screw), 79.8 ≤ EP < 100 GPa (1 KS screw), and 4.9 ≤ EP < 100 GPa (2 KS screws). A prototype plate could be made from materials currently used or proposed for orthopaedics, such as polymers, fiber-reinforced polymers, fiber metal laminates, metal foams, or shape memory alloys.

Percutaneous fixation of intraarticular joint-depression calcaneal fractures with different screw configurations - a biomechanical human cadaveric analysis.

The aim of this study was to assess the biomechanical performance of different screw configurations for fixation of Sanders type II B joint-depression calcaneal fractures. Fifteen human cadaveric lower limbs were amputated and Sanders II B fractures were simulated. The specimens were randomized to three groups for fixation with different screw configurations. The calcanei in Group 1 were treated with two parallel longitudinal screws, entering superiorly the Achilles tendon insertion, and two screws fixing the intraarticular posterior facet fracture line. In Group 2 two screws entered the tuberosity inferiorly to the Achilles tendon insertion and two transverse screws fixed the posterior facet. In Group 3 two screws were inserted along the bone axis, one transverse screw fixed the posterior facet and one oblique screw was inserted from the posteroplantar part of the tuberosity supporting the posterolateral part of the posterior facet. All specimens were biomechanically tested to failure under progressively increasing cyclic loading. Initial stiffness did not differ significantly between the groups, P = 0.152. Cycles to 2mm plantar movement were significantly higher in both Group 1 (15,847 ± 5250) and Group 3 (13,323 ± 4363) compared with Group 2 (4875 ± 3480), P ≤ 0.048. No intraarticular displacement was observed in any group during testing. From a biomechanical perspective, posterior facet support by means of buttress or superiorly inserted longitudinal screws results in less plantar movement between the calcaneal tuberosity and the anterior fragments. Inferiorly inserted longitudinal screws are associated with bigger interfragmentary movements.

Current concepts in fracture healing: temporal dynamization and applications for additive manufacturing.

Objectives:Current surgical fracture treatment paradigms, which use rigid metallic constructs to heal bones, provide reasonable clinical outcomes; however, they do not leverage recent advances in our understanding of bone healing and mechanotransduction throughout bone healing. The objective of this review was to investigate the efficacy and potential clinical applicability of surgical techniques and implants that deliberately introduce interfragmentary motion throughout the healing process.Methods:The authors searched PubMed and Google Scholar databases for articles reporting on fracture repair using dynamic locking plates, dynamized surgical techniques, and reverse dynamization. Data collection also included assessment of additively manufactured (AM) implants that provide dynamic mechanical behaviors.Results:Forty articles were included for final review. It was found that accelerated rates of fracture healing can be achieved with staged 2-part surgeries or dynamic implant designs. Temporal dynamization, where static fixation of bones is followed by the introduction of micromotion and controlled loading, has been shown to improve callus volume and accelerate the healing response. Reverse dynamization, where micromotion is encouraged during early callus formation and arrested later, may represent a significant advance for the treatment of critical defect injuries. Advances in AM techniques will likely provide the ability to create high-resolution implants capable of dynamized and reverse dynamized modalities.Conclusions:There is no one-size-fits-all approach to optimization of fracture healing. However, it has been clearly demonstrated that fracture treatment can be enhanced by systematically altering the construct stiffness throughout the different phases of healing, which may be achieved with AM implant designs.