Fixation Stiffness Research Articles

Mechanism research of elastic fixation promoting fracture healing based on proteomics and fracture microenvironment.

This study aimed to demonstrate the promoting effect of elastic fixation on fracture, and further explore its mechanism at the gene and protein expression levels. A closed tibial fracture model was established using 12 male Japanese white rabbits, and divided into elastic and stiff fixation groups based on different fixation methods. Two weeks after the operation, a radiograph and pathological examination of callus tissue were used to evaluate fracture healing. Then, the differentially expressed proteins (DEPs) were examined in the callus using proteomics. Finally, in vitro cell experiments were conducted to investigate hub proteins involved in this process. Mean callus volume was larger in the elastic fixation group (1,755 mm3 (standard error of the mean (SEM) 297)) than in the stiff fixation group (258 mm3 (SEM 65)). Pathological observation found that the expression levels of osterix (OSX), collagen, type I, alpha 1 (COL1α1), and alkaline phosphatase (ALP) in the callus of the elastic fixation group were higher than those of the stiff fixation group. The protein sequence of the callus revealed 199 DEPs, 124 of which were highly expressed in the elastic fixation group. In the in vitro study, it was observed that a stress of 200 g led to upregulation of thrombospondin 1 (THBS1) and osteoglycin (OGN) expression in bone marrow mesenchymal stem cells (BMSCs). Additionally, these genes were found to be upregulated during the osteogenic differentiation process of the BMSCs. Elastic fixation can promote fracture healing and osteoblast differentiation in callus, and the ability of elastic fixation to promote osteogenic differentiation of BMSCs may be achieved by upregulating genes such as THBS1 and OGN.

The infraacetabular screw - anatomy, radiology, biomechanics and clinics.

Acetabular fracture surgery follows the primary aim of anatomic reduction and rigid stable fixation of the fracture. Infraacetabular screws (IAS) allow for an increased stability of the acetabular fixation by closing the periacetabular fixation frame without requiring an additional posterior approach. The osseous screw corridor for infraacetabular screws use the transition zone between the acetabular ring and the obturator ring. The infraacetabular screw corridor (IAC) shows a double-cone shape with an isthmus located near the acetabular fovea. The iliopectineal eminence (IE) is mainly used as a clinical landmark for the intraoperative assessment of the entry point of IAS. The inlet view, the combined obturator oblique outlet view and a 1/3 iliac oblique outlet view may be used for the intraoperative radiological assessment for both the entry point and the screw trajectory of IAS. Several biomechanical studies have shown that IAS increase the stiffness of the internal fixation. Scientific proof for an improved clinical outcome is still missing.

Comparative Biomechanical Study of Fragment-Specific Plates and Headless Screws for Radial Styloid and Lunate Facet Fixation in Distal Radius Fracture Evaluated in a Synthetic Composite

To evaluate the compressive stiffness (ability to resist compression under an applied load) of fragment-specific plate and headless screw fixation for radial styloid and volar lunate facet fractures in a synthetic composite distal radius. A simulated radial styloid fracture (AO type B1.1) and simulated volar lunate facet fracture (AO type B3.3) were created in synthetic composite distal radii and fixed with a fragment-specific plate (FSP) using a radial styloid or lunate facet plate or with two- or three-headless screws (2HS, 3HS), creating 6 fixation models: B1.1/FSP, B1.1/2HS, B1.1/3HS, B3.3/FSP, B3.3/2HS, and B3.3/3HS. Compressive stiffness of fixation constructs under initial static load, cyclic load, and final static load was investigated. Nonaxial loadings, including shearing and rotation, were not evaluated. Regarding AO type B1.1, the mean stiffness of the B1.1/FSP construct was not significantly different from the intact radius, and the mean stiffness was greatest in the B1.1/3HS and lowest in the B1.1/2HS construct. For AO type B3.3, the mean stiffness of the B3.3/3HS construct was not significantly different from the intact radius, and the mean stiffness of the B3.3/FSP and B3.3/2HS construct was greatest and lowest, respectively. Minimal differences in stiffness between initial and final static loads confirmed that there was no evidence of failure implant under cyclic compressive loads. Fragment-specific plates and two- or three-headless screw fixation maintained mechanical stability through compressive cyclic loading for radial styloid and volar lunate facet fractures. The FSPs and three-headless screws fixations provided superior stiffness over the two-headless screws fixation. There was no articular fracture failure in all fixation constructs with initial static compression, cyclic loading, and final compression. Fragment-specific plates and headless screws can both be considered as adequate fixation for radial styloid and volar lunate facet fractures.

Structural design and evaluation of bone remodeling effect of fracture internal fixation implants with time-varying stiffness

The stiffness of an ideal fracture internal fixation implant should have a time-varying performance, so that the fracture can generate reasonable mechanical stimulation at different healing stages, and biodegradable materials meet this performance. A topology optimization design method for composite structures of fracture internal fixation implants with time-varying stiffness is proposed, considering the time-dependent degradation process of materials. Using relative density and degradation residual rate to describe the distribution and degradation state of two materials with different degradation rates and elastic modulus, a coupled mathematical model of degradation simulation mechanical analysis was established. Biomaterial composite structures were designed based on variable density method to exhibit time-varying stiffness characteristics. Taking the bone plate used for the treatment of tibial fractures as an example, a composite structure bone plate with time-varying stiffness characteristics was designed using the proposed method. The optimization results showed that material 1 with high stiffness formed a columnar support structure, while material 2 with low stiffness was distributed at the degradation boundary and inside. Using a bone remodeling simulation model, the optimized bone plates were evaluated. After 11 months of remodeling, the average elastic modulus of callus using degradable time-varying stiffness plates, titanium alloy plates, and stainless steel plates were 8 634 MPa, 8 521 MPa, and 8 412 MPa, respectively, indicating that the use of degradable time-varying stiffness plates would result in better remodeling effects on the callus.

Biomechanical Consequences of Proximal Screw Placement in Minimally Invasive Surgery for Hallux Valgus Correction

Hallux valgus is one of the most common surgically corrected forefoot deformities. Studies evaluating clinical outcomes of minimally invasive chevron and akin (MICA) procedure have shown shorter operation time, faster recovery, and smaller scars compared to the open approach. Previous biomechanical cadaveric studies have largely focused on the open approach with minimal on MICA. To our knowledge, no studies have compared different proximal screw placements in MICA which can either be three-point fixation or intramedullary. This study aims to compare the biomechanical properties of fixation between these 2 techniques in MICA. Six matched pairs of human fresh frozen cadaveric feet were randomized to either 3-point fixation or intramedullary groups. Both procedures were performed by a single fellowship-trained orthopedic foot and ankle surgeon. Using a material testing machine, each specimen underwent 1000 cycles of plantar-to-dorsal uniaxial loads from 0 to 31 N in cantilever configuration while monitoring bending stiffness and distal fragment dorsal angulation. They were then subjected to load until failure at a compression rate of 10 mm/min. Specimens from both groups tolerated the walking fatigue test. Mean bending stiffness of 3-point fixation was 84% higher than intramedullary constructs (p = .002). Mean dorsal angulation of intramedullary was thrice that of 3-point fixation constructs (p = .008). Mean load to failure of 3-point fixation was 30% higher than intramedullary constructs (p = .001). Three-point fixation provide superior biomechanical stability compared to intramedullary proximal screw placement. The surgical technique using 3-point proximal screw fixation can offer robust fixation and lead to better clinical outcomes.

Effect of geometrical design variables on implantation configuration and fixation stiffness of titling bone anchors: A parametric finite element study

The mechanical interaction of a tilting anchor and cancellous bones of various densities was simulated using finite element modeling. The model enjoyed a sophisticated representation of the bone, as an elasto-plastic material with large deformation capability. The anchor's tilting action during implantation phase, as well as its fixation stiffness during pull-out test, were predicted by the model and a parametric study was performed to investigate the effects of the anchor's distal width and corner fillet radius, on these measures. The model predictions were validated against the results of an experimental test on ovine humerus specimens. The model could reasonably reproduce the tilting action of the anchor during the implantation phase. Comparison of the model predictions with the experimental results revealed similar trends during both the implantation and the pull-out phases, but smaller displacement magnitudes (end points: 1.4 vs. 2.1 mm and 4.6 vs. 5.2 mm, respectively). The results of the parametric study indicated substantial increase in the fixation stiffness with increasing bone density. Reducing the distal width and increasing the fillet radius improved the anchor's implantation configuration and fixation stiffness in low-density bones. For high-density bone applications, however, a larger distal width was favored for improving the fixation stiffness.

Biomechanical evaluation of a fixation technique with a modified hemicerclage for tibial tuberosity transposition: an ex vivo cadaveric study.

(1) To determine stiffness, load at failure, and mode of failure of a novel fixation method with a tension modified-hemicerclage (MH) for tibial tuberosity transposition, and (2) to compare the biomechanical properties of this novel fixation technique to 2 pins (2Pins) and 2 pins and tension band wire fixation (2Pins + TBW). Thirty cadaveric stifles from dogs between 5.2 and 13.1 kg were assigned to 3 treatment groups: Group 1: fixation technique with MH; Group 2: 2Pins; Group 3: 2Pins + TBW. Biomechanical testing was performed with the tibia positioned at an angle of 135° relative to vertical position. Tensile force was applied to the patellar ligament until catastrophic failure was observed. The mode of failure, the load at failure, and the stiffness were compared among treatment groups. The mean stiffness of the novel fixation (38.1 N/mm 7.1) and the 2Pins + TBW (40.2 N/mm 9.3) were greater than the 2Pins (26.7 N/mm 6.7). There was no significant difference between the novel fixation technique and 2Pins + TBW in stiffness and maximum load to failure. The 2Pins (284.3 N 70.5) failed at a significantly lower load than the tension modified-hemicerclage (555.7 N 225.9 N) and 2Pins + TBW (715.3 N 339.8 N). A fixation technique using a modified hemicerclage had the same strength and stiffness as the 2Pins + TBW and was stronger and stiffer than the 2 Pins technique in a cadaveric model.

Latarjet procedure: biomechanical evaluation of 2-screw coracoid fixation

Coracoid nonunion is a relevant complication following the Latarjet procedure and is influenced by multiple factors, including the method of graft fixation. The purpose of this study was to evaluate and characterize the biomechanical properties of various two-screw fixation constructs used for coracoid graft fixation in the Latarjet procedure. Forty model scapulae (Sawbones Inc., Vashon, WA, USA) were used for this study. A 15% anterior inferior glenoid bone defect was created. The coracoid was osteotomized at the juncture of the vertical and horizontal aspects, transferred to the anterior-inferior edge of the glenoid, and fixed with either two 3.5mm fully threaded cannulated cortical screws, two 3.5mm fully threaded solid cortical screws, two 3.5mm partially threaded cannulated screws, or two 4.5mm partially threaded malleolar screws (MS). Biomechanical testing was performed with an Instron material testing machine (Instron Corp., Norwood, MA, USA) by applying loads to the lateral aspect of the transferred coracoid graft. The constructs were preconditioned with nondestructive cyclical loading (0N-20N) to determine construct stiffness. After 100 cycles of dynamic loading, the construct was loaded to failure to determine ultimate failure load, yield displacement, and mode of failure. All failures were associated with plastic deformation of the screws and coracoid graft fracture. There was a significantly lower initial stiffness for partially threaded cannulated screws compared to MS (186±49.3N/mm vs. 280±65.5N/mm, P=.01) but no significant differences among the other constructs. There was no difference in ultimate failure load (P=.18) or yield displacement (P=.05) among constructs. Two screw coracoid fixation of the coracoid in a simulated classic Latarjet procedure with 3.5mm fully threaded cortical and cannulated screws is comparable to 4.5mm MS in strength, stiffness, and displacement at failure. On the other hand, partially threaded 3.5mm cannulated screws provide inferior fixation stiffness and could potentially affect clinical outcomes.

The Effect of Supplementary Staple Fixation on Biomechanical Properties of Soft Tissue Graft Tibial Fixation in Anterior Cruciate Ligament Reconstruction.

This study aimed to test and compare the biomechanical properties of three tibial fixation methods of anterior cruciate ligament (ACL) tendon grafts under cyclic load and load-to-failure testing in the bovine proximal tibiae, comprising (1) staple fixation alone, (2) interference screw fixation alone, and (3) interference screw fixation with a supplementary staple. Twenty-four bovine tibiae used in the study were divided into three groups (eight proximal tibiae in each group) based on tibial fixation methods of ACL tendon grafts: group A (a spiked ligament staple alone), group B (a cannulated interference screw alone), and group C (a cannulated interference screw with a supplementary staple). Each graft fixation was exposed to cyclic loading conditions. Significant differences were determined in failure load among the three groups (p = 0.008). The mean failure load was significantly higher in group B (717.04 ± 218.51 N) than in group A (308.03 ± 17.22 N) (p = 0.006). No significant differences were observed among the groups regarding axial stiffness (p = 0.442). Cyclic displacement differed significantly among the three groups (p = 0.005). In pairwise comparisons, the mean cyclic displacement was significantly higher in group A (8.22 ± 3.24 mm) compared with group C (1.49 ± 0.41 mm) (p = 0.005). Failure displacement varied considerably among the groups (p = 0.037). Although group B (15.53 ± 6.43 mm) exhibited a greater mean failure displacement than both group A (4.9 ± 0.75 mm) and group C (8.84 ± 4.65 mm), these differences did not reach statistical significance (p = 0.602 and p = 0.329, respectively). Interference screw fixation alone and supplementary staple fixation have biomechanically similar characteristics in terms of initial strength and stiffness of tibial ACL soft tissue graft fixation. Regardless of staple use, an interference screw with the same diameter as the tibial tunnel can ensure sufficient tensile strength in tibial ACL graft fixation.

Efficacy of poller screw in addition to lag screw in the treatment of intertrochanteric fractures with proximal femoral nail: a biomechanical evaluation.

The most common type of failure in treating intertrochanteric fractures with proximal femoral nails is cut-out due to varus collapse. We aim to evaluate the effect of the poller screw applied to the proximal fragment and the lag screw on varus collapse and stability in intertrochanteric fractures. An unstable intertrochanteric fracture model without medial support was simulated in 20 synthetic femur models. In the poller screw group, in addition to the lag screw, pole screws were applied to the proximal fragment superior and inferior to the lag screw. In the progressive cyclic loading test, starting from 100 N, the loading was increased by 50 N in each cycle, and the test was continued until the maximum load at which failure occurred as a result of conditioning cycles and progressive cyclic loading tests, stiffness, type of failure, force at failure, lag screw displacement, and varus collapse were recorded. The average stiffness was found to be 124.705 N/mm in the poller screw group and 102.77 N/mm in the control group (P < 0.001). The maximum load to failure was 1897.10 N in the poller screw group and 1475.20 N in the control group (P < 0.001). The average displacement of the lag screw within the femoral head was 0.85mm in the poller screw group and 3.60mm in the control group (P < 0.001). As a result, it has been shown that poller screws applied around the lag screw increase fixation stiffness and reduce varus collapse.

A Review of the Impacts of Implant Stiffness on Fracture Healing

The bone healing process is influenced by various physiological factors. Fracture fixation traditionally relied on rigid metallic implants. However, excessively rigid constructs can lead to complications, necessitating revision surgery. This review focuses on approaches to improve bone healing by introducing adequate interfragmentary movement (IFM) at the fracture site. IFM promotes secondary fracture healing and callus formation. Studies suggest that rigid fixation may impair fracture healing by inhibiting callus formation and causing stress shielding. Titanium alloy locking plates have been shown to be biomechanically superior to stainless steel. Flexible fixation and techniques to regulate implant stiffness are crucial for managing fractures with bridge plating. Materials with a lower Young’s modulus balance biomechanical properties. A novel TiNbSn alloy with a low Young’s modulus has been developed to address stress shielding issues. It is effective in promoting osteosynthesis, bone healing, and superior mechanical properties compared with materials with higher Young’s moduli. The enhanced formation of bone and callus associated with TiNbSn alloy suggests its promise for use in fracture treatment plates. Understanding the biomechanics of fracture healing, optimizing fixation stiffness, and exploring innovative materials like TiNbSn alloys, are crucial for advancing approaches to accelerate and enhance bone healing.

Biomechanical analysis of combi-hole locking compression plate during fracture healing: A numerical study of screw configuration.

Locking compression plates (LCPs) have become a widely used option for treating femur bone fractures. However, the optimal screw configuration with combi-holes remains a subject of debate. The study aims to create a time-dependent finite element (FE) model to assess the impacts of different screw configurations on LCP fixation stiffness and healing efficiency across four healing stages during a complete fracture healing process. To simulate the healing process, we integrated a time-dependent callus formation mechanism into a FE model of the LCP with combi-holes. Three screw configuration parameters, namely working length, screw number, and screw position, were investigated. Increasing the working length negatively affected axial stiffness and healing efficiency (p < 0.001), while screw number or position had no significant impact (p > 0.01). The time-dependent model displayed a moderate correlation with the conventional time-independent model for axial stiffness and healing efficiency (ρ ≥ 0.733, p ≤ 0.025). The highest healing efficiency (95.2%) was observed in screw configuration C125 during the 4-8-week period. The results provide insights into managing fractures using LCPs with combi-holes over an extended duration. Under axial compressive loading conditions, the use of the C125 screw configuration can enhance callus formation during the 4-12-week period for transverse fractures. When employing the C12345 configuration, it becomes crucial to avoid overconstraint during the 4-8-week period.

Unilateral external fixator and its biomechanical effects in treating different types of femoral fracture: A finite element study with experimental validated model

Previous works had successfully demonstrated the clinical effectiveness of unilateral external fixator in treating various types of fracture, ranging from the simple type, such as oblique and transverse fractures, to complex fractures. However, literature that investigated its biomechanical analyses to further justify its efficacy is limited. Therefore, this paper aimed to analyse the stability of unilateral external fixator for treating different types of fracture, including the simple oblique, AO32C3 comminuted, and 20 mm gap transverse fracture. These fractures were reconstructed at the distal diaphysis of the femoral bone and computationally analysed through the finite element method under the stance phase condition. Findings showed a decrease in the fixation stiffness in large gap fracture (645.2 Nmm-1 for oblique and comminuted, while 23.4 Nmm-1 for the gap fracture), which resulted in higher displacement, IFM and stress distribution at the pin bone interface. These unfavourable conditions could consequently increase the risk of delayed union, pin loosening and infection, as well as implant failure. Nevertheless, the stress observed on the fracture surfaces was relatively low and in controlled amount, indicating that bone unity is still allowable in all models. Briefly, the unilateral fixation may provide desirable results in smaller fracture gap, but its usage in larger gap fracture might be alarming. These findings could serve as a guide and insight for surgeons and researchers, especially on the biomechanical stability of fixation in different fracture types and how will it affect bone unity.

Biomechanics of internal fixation in Hoffa fractures – A comparison of four different constructs

ObjectiveCompare the biomechanical effectiveness of four different bone-implant constructs in preventing fracture displacement under axial loading. MethodsTwenty artificial femora had a standardized coronally oriented fracture of the lateral femoral condyle, representing a Hoffa fracture classified as a Letenneur type I. Four different fixation constructs were applied to the synthetic bones for biomechanical testing. The constructs consisted of a posterolateral (PL) buttressing locking plate in conjunction with two cannulated lag screws inserted from posterior to anterior (PA) – Group 1; Two cannulated screws inserted from anterior to posterior (AP) without plating– Group 2; A posterolateral (PL) buttressing locking plate in isolation – Group 3; and a combination of two lag screws from anterior to posterior (AP) in addition to a horizontal one-third tubular locking plate – Group 4. An axial load was applied to the fracture site with a constant displacement speed of 20 mm/min, and the test was interrupted when a secondary displacement was detected determining a fixation failure. We recorded the maximum applied force and the maximum fracture displacement values. ResultsGroup 1 demonstrated the highest overall bone-implant axial stiffness with the lowest secondary displacement under loading. Groups 3 and 4 showed equivalent mechanical behavior. Group 2 presented the lowest mechanical stiffness to axial loading. The combination of the one-third tubular locking plate with anterior-to-posterior lag screws (Group 4) resulted in 302 % increase in fixation stiffness when compared to anterior-to-posterior lag screws only (Group 2). ConclusionsThis study confirms the mechanical superiority of having a plate applied parallel to the main fracture plane in the setting of coronally oriented femoral condyle fractures. The addition of a horizontal plate, perpendicular to the main fracture plane, significantly increased the resistance to shearing forces at the fracture site when compared to constructs adopting just cannulated screws. Level of evidenceBiomechanical study

Which of 51 Plate Designs Can Most Stably Fixate the Fragments in a Fracture of the Mandibular Condyle Base?

In the surgical treatment of the most common fracture of the mandible, which is a fracture of the condylar base, a great choice of different plate shapes is observed. The aim of this study was to determine which shape gives the greatest fixation stiffness. To ensure homogeneity in comparison, tests were performed on polyurethane models divided at the level of the condylar base fracture and each were fixed with 51 plates. The plates were cut from a 1 mm thick grade 23 titanium sheet. The models were then loaded and the force required for 1 mm of fracture displacement was recorded. It was noted that in addition to osteosynthesis from two simple plates, there were also two dedicated single plates with similar rigidity. Among the large number of described designs of plates, there is considerable variation in terms of the stability of the fixation performed with them. The proposed Mechanical Excellence Factor allows a pre-evaluation of the expected rigidity of fixation with a given plate shape without the need for a loading experiment. The authors expect this to be helpful for surgeons in the application of relevant plates, as well for inventors of new plates for the osteosynthesis of basal fractures in mandibular condyle.

SIMULATING BIORESORBABLE LATTICE STRUCTURES TO ENABLE TIME-DEPENDENT STIFFNESS IN FRACTURE FIXATION DEVICES

AbstractAdditive manufacture (AM) enables a greatly increased design freedom owing to its ability to manufacture otherwise difficult or impossible geometries. However, design creativity can often present itself as a barrier to realising the advantages that AM could offer. In this study the use of AM, bioresorbable materials and lattice design is considered as a method of satisfying contradicting design requirements during fracture healing. Often, immediately after a fracture high stiffness fixation is required; contradictingly during the remodelling phase high stiffness can inhibit bone healing. This study proposes the use of a bioresorbable body centred cubic (BCC) or face centred cubic (FCC) lattice structure to meet the need for tailored variation in implant stiffness over time. To reduce computational expense of lattice modelling a method is outlined, including the use of homogenisation. Results show homogenised representations perform within 5.2% and 1.4% for BCC and FCC unit cells respectively, with a 95% reduction in computational expense. Using resorption rates from the literature, time-dependent change in unit cell geometry was also modelled, showing the way in which a decrease in stiffness over time could be achieved.

Effects of dynamization timing and degree on bone healing of different fracture types.

Dynamization, i.e., increasing interfragmentary movement (IFM) by reducing fixation stiffness from a rigid to a more flexible state, has been successfully used in clinical practice to promote fracture healing. However, it remains unclear how dynamization timing and degree affect bone healing of different fracture types. Finite element models of tibial fractures based on the OTA/AO classification (Simple: A1-Spiral, A2-Oblique, A3-Transverse; Wedge: B2-Spiral, B3-Fragmented; Complex: C2-Segment, C3-Irregular), in combination with fuzzy logic-based mechano-regulatory tissue differentiation algorithms, were used to simulate the healing process when dynamization of varied degrees (dynamization coefficient or DC = 0-0.9; 0.9 represents 90% reduction in the fixation stiffness relative to a rigid fixation) were applied at different time points after fracture. The fuzzy logic-based algorithms have been validated with a preclinical animal model. The results showed that the healing responses of type A fractures were more sensitive to the changes in dynamization degree and timing comparing with type B or C fractures. Additionally, the optimal dynamization regime for each fracture type was different. For type A fractures, a moderate dynamization degree (e.g., DC = 0.5) applied after week 1 promoted the recovery of biomechanical integrity. For type B and C fractures, the effective dynamization included a greater dynamization degree (DC=0.7) applied after week 2. Our results further demonstrated that the fracture morphology affected interfragmentary strain environments within the callus, leading to varied healing results for different fracture types. These results suggest that the effects of dynamization are highly dependent of the fracture types. Therefore, specific dynamization strategies should be chosen for different fracture types to achieve optimal healing outcomes. This article is protected by copyright. All rights reserved.

Biomechanical Evaluation of Temporomandibular Joint Reconstruction Using Individual TMJ Prosthesis Combined with a Fibular Free Flap in a Pediatric Patient.

The main aim of this study was to perform a complex biomechanical analysis for a custom-designed temporomandibular joint (TMJ) prosthesis in combination with a fibular free flap in a pediatric case. Numerical simulations in seven variants of loads were carried out on 3D models obtained based on CT images of a 15-year-old patient in whom it was necessary to reconstruct the temporal-mandibular joints with the use of a fibula autograft. The implant model was designed based on the patient's geometry. Experimental tests on a manufactured personalized implant were carried out on the MTS Insight testing machine. Two methods of fixing the implant to the bone were analyzed-using three or five bone screws. The greatest stress was located on the top of the head of the prosthesis. The stress on the prosthesis with the five-screw configuration was lower than in the prosthesis with the three-screw configuration. The peak load analysis shows that the samples with the five-screw configuration have a lower deviation (10.88, 0.97, and 32.80%) than the groups with the three-screw configuration (57.89 and 41.10%). However, in the group with the five-screw configuration, the fixation stiffness was relatively lower (a higher value of peak load by displacement of 171.78 and 86.46 N/mm) than in the group with the three-screw configuration (where the peak load by displacement was 52.93, 60.06, and 78.92 N/mm). Based on the experimental and numerical studies performed, it could be stated that the screw configuration is crucial for biomechanical analysis. The results obtained may be an indication for surgeons, especially during planning personalized reconstruction procedures.

Biomechanical comparison of one pin versus two pin fixation in a canine tibial tuberosity avulsion fracture model.

To determine whether one larger or two smaller diameter pins used for tibial tuberosity avulsion fracture (TTAF) stabilization provides greater axial tensile strength and stiffness when subjected to monotonic mechanical load to failure in normal skeletally mature canine cadavers. Paired ex vivo biomechanical study. Eleven pairs of adult cadaveric dog tibias. Twenty-two tibias from 11 dogs were collected to model a TTAF. Each limb of a pair was randomly assigned a one or two-pin fixation. Tibias were subjected to monotonic, axial load to failure. Fixation stiffness, strength, and pin insertion angles were analyzed with parametric testing. Significance was set at p < .05. The mean strength of the single-pin fixation was 426.2 ± 50.5 N compared to two-pin fixation at 639.2 ± 173.5 N (p = .003). The mean stiffness of the single-pin fixation was 57.3 ± 18.7 N/mm and the two-pin fixation was 71.7 ± 20.5 N/mm (p = .029). The normalized ratio between one and two-pin fixation had a mean stiffness of 68% ± 25.8% and strength of 82.8% ± 24.6%. In an ex vivo cadaveric TTAF model, vertically aligned two-pin fixation offers greater strength and stiffness when compared to a single-pin fixation. When repairing TTAF, surgeons should aim to apply two vertically aligned pins rather than a single pin for greater strength and stiffness.

Will the adjustment of insertional pedicle screw positions affect the risk of adjacent segment diseases biomechanically? An in-silico study.

The fixation-induced biomechanical deterioration will increase the risk of adjacent segment diseases (ASD) after lumbar interbody fusion with Bilateral pedicle screw (BPS) fixation. The accurate adjustment of insertional pedicle screw positions is possible, and published studies have reported its mechanical effects. However, no studies clarified that adjusting insertional screw positions would affect the postoperative biomechanical environment and the risk of ASD. The objective of this study was to identify this issue and provide theoretical references for the optimization of insertional pedicle screw position selections. The oblique lumbar interbody fusion fixed by BPS with different insertional positions has been simulated in the L4-L5 segment of our previously constructed and validated lumbosacral model. Biomechanical indicators related to ASD have been computed and recorded under flexion, extension, bending, and axial rotation loading conditions. The change of screw insertional positions has more apparent biomechanical effects on the cranial than the caudal segment. Positive collections can be observed between the reduction of the fixation length and the alleviation of motility compensation and stress concentration on facet cartilages. By contrast, no pronounced tendency of stress distribution on the intervertebral discs can be observed with the change of screw positions. Reducing the fixation stiffness by adjusting the insertional screw positions could alleviate the biomechanical deterioration and be an effective method to reduce the risk of ASD caused by BPS.