Biomechanical comparison of conventional and optimised locking plates for the fixation of intraarticular calcaneal fractures: a finite element analysis

Biomechanical role of bone grafting for calcaneal fracture fixation in the presence of bone defect: A finite element analysis

BACKGROUND

The purpose of this study was to compare the biomechanical stress and stability of calcaneal fixations with and without bone defect, before and after bone grafting, through a computational approach.

METHODS

A finite element model of foot-ankle complex was reconstructed, impoverished with a Sanders III calcaneal fracture without bone defect and with moderate and severe bone defects. Plate fixations with and without bone grafting were introduced with walking stance simulated. The stress and fragment displacement of the calcaneus were evaluated.

FINDINGS

Moderate and severe defect increased the calcaneus stress by 16.11% and 32.51%, respectively and subsequently decreased by 10.76% and 20.78% after bone grafting. The total displacement was increased by 3.99% and 24.26%, respectively by moderate and severe defect, while that of posterior joint facet displacement was 86.66% and 104.44%. The former was decreased by 25.73% and 35.96% after grafting, while that of the latter was reduced by 88.09% and 84.78% for moderate and severe defect, respectively.

INTERPRETATION

Our finite element prediction supported that bone grafting for fixation could enhance the stability and reduce the risk of secondary stress fracture in cases of bone defect in calcaneal fracture.

Biomechanical characteristics of Sanders type II and III calcaneal fractures fixed by open reduction and internal fixation and percutaneous minimally invasive fixation

BACKGROUND

This work investigated the differences in the biomechanical properties of open reduction and internal fixation (ORIF) and percutaneous minimally invasive fixation (PMIF) for the fixation of calcaneal fractures (Sanders type II and III calcaneal fractures as examples) through finite element analysis.

METHODS

Based on CT images of the human foot and ankle, according to the principle of three-point fixation, namely the sustentaculum tali, the anterior process and the calcaneal tuberosity were fixed. Three-dimensional finite element models of Sanders type II and III calcaneal fractures fixed by ORIF and PMIF were established. The proximal surfaces of the tibia, fibula and soft tissue were constrained, and ground reaction force and Achilles tendon force loads were added to simulate balanced standing.

RESULTS

The maximum stress was 80.54, 211.59 and 113.88 MPa for the calcaneus, screws and plates in the ORIF group and 70.02 and 209.46 MPa for the calcaneus and screws in the PMIF group, respectively; the maximum displacement was 0.26, 0.21 and 0.12 mm for the calcaneus, screws and plates in the ORIF group and 0.20 and 0.14 mm for the calcaneus and screws in the PMIF group, respectively. The values obtained from the simulation were within the permissible stress and elastic deformation range of the materials used in the model, and there was no significant stress concentration. The maximum stress and displacement of the calcaneus and implants were slightly lower in the PMIF group than in the ORIF group when fixing Sanders type II and III calcaneal fractures.

CONCLUSIONS

This study may provide a reference for optimising the design of implants, the development of individualised preoperative plans and the choice of clinical surgical approach.

Topology optimization of embracing fixator considering bone remodeling to mitigate stress shielding effect

The embracing fixator is one of the widely used internal fixation implants for bone fracture treatment. However, the stress shielding effect, a stress imbalance between the implant and bone caused by the mismatch in mechanical properties between them, is a significant and critical issue that may lead to treatment failure. Thus, it is of great importance to design the implant with an appropriate stiffness which can mitigate the stress shielding effect and provide the most favorable mechanical environment for bone healing and remodeling. To this end, a time-dependent topology optimization algorithm considering bone remodeling is proposed to optimize an embracing fixator used in the tibia fracture treatment. The change of callus density over time is simulated based on a bone remodeling model, and the callus density after a period of bone remodeling is selected to be the design objective to maximize. The design constraints include volume and the compliance of the whole fixation system. Meanwhile, the influence of the constraints on the regularity of material distribution of the optimized result is also studied. Besides, to test the effectiveness of the consideration of the bone remodeling in the embracing fixator design, a topology optimization concerning the minimization of the compliance of the entire system is also performed to make a comparison. Finally, the safety performance of optimized results considering bone remodeling is also verified by static analysis.

Finite element analyses of three minimally invasive fixation techniques for treating Sanders type II intra-articular calcaneal fractures

BACKGROUND AND OBJECTIVE

Calcaneal Sanders type II or III fractures are highly disabling with significant burden. Surgical treatment modalities include open reduction and internal fixation (ORIF) techniques and a variety of minimally invasive surgical (MIS) approaches. ORIF techniques are associated with complications and traditional MIS techniques need extensive intraoperative fluoroscopic procedures. The present study aims to investigate the effects of three different minimally invasive internal fixation (MIIF) techniques used to treat Sanders type II intra-articular calcaneal fractures using finite element analyses.

METHODS

A 64-row spiral computed tomography scan was used to observe the calcaneus of a healthy adult. The scanning data were imported into Mimics in a DICOM format. Using a new model of a Sanders type II-B intra-articular calcaneal fracture, three minimally invasive techniques were simulated. Technique A involved fixation using an isolated minimally invasive locking plate; Technique B used a minimally invasive locking plate with one medial support screw; and Technique C simulated a screw fixation technique using four 4.0-mm screws. After simulating a 640-N load on the subtalar facet, the maximum displacement and von Mises stress of fragments and implants were recorded to evaluate the biomechanical stability of different fixation techniques using finite element analyses.

RESULTS

After stress loading, the maximum displacements of the fragments and implants were located at the sustentaculum tali and the tip of sustentaculum tali screw, respectively, in the three techniques; however, among the three techniques, Technique B had better results for displacement of both. The maximum von Mises stress on the fragments was < 56 Mpa, and stress on the implants using the three techniques was less than the yield strength, with Technique C having the least stress.

CONCLUSION

All three techniques were successful in providing a stable fixation for Sanders type II intra-articular calcaneal fractures, while the minimally invasive calcaneal locking plate with medial support screw fixation approach exhibited greater stability, leading to improved enhancement for the facet fragment; however, screw fixation dispersed the stress more effectively than the other two techniques.

3D mapping of intra-articular calcaneal fractures

To determine the pattern of intra-articular calcaneal fractures (ICFs) by a three-dimensional (3D) mapping and determine whether there were consistent fracture patterns and comminution zones. In this study, 67 patients with ICFS by CT scan were included. The calcaneal fractures fragments in CT were multiplanar reconstructed and virtual reduced. 3D heat mapping was subsequently created by graphically superimposing all fracture lines onto a standard calcaneal template. The cohort included 26 (38.8%) left calcaneal fractures, 27 (40.30%) right calcaneal fractures, and 14 (20.9%) cases with bilateral fractures. Comminuted fractures accounted for 92.5%. Sagittal 3D mapping shows that the fracture line is mainly concentrated at the critical angle of Gissane and extending rear to the posterior of the tuberosity of the lateral wall and the anterior of the medial process of the calcaneus tuberosity but with more significant variation in the medial wall. The average angle of fracture lines concerning the long calcaneal axis (LCA) was 29.1° and 19.2° in the lateral and medial walls. Axial 3D mapping shows that fracture lines were primarily concentrated in the anterior area to the posterior joint facet and extending along the rear joint facet and calcaneus sulcus to the posteriorly of the tuberosity. The mean angle of fracture lines concerning the LAC was 11° in the axial wall. Our data provided elucidated that ICFs have consistent characteristic fracture patterns and comminution zones. This study provides visual guidelines for understanding fracture morphology, which may assist with fracture classification, preoperative planning, development of fixation concepts.

Biomechanical Comparison of Conventional Plate and the C-Nail® System for the Treatment of Displaced Intra-Articular Calcaneal Fractures: A Finite Element Analysis

The C-Nail® system is a novel intramedullary fixation method for displaced intra-articular calcaneal fractures. The aim of this study was to evaluate the biomechanical performance of the C-Nail® system and compare it with conventional plate fixation for the treatment of displaced intra-articular calcaneal fractures using finite element analysis. The geometry of a Sanders type-IIB fracture was constructed using the computer-aided design software Ansys SpaceClaim. The C-Nail® system (Medin, Nové Mesto n. Morave, Czech Republic) and the calcaneal locking plate (Auxein Inc., 35 Doral, Florida) and screws were designed according to the manufacturer specifications. Vertical loading of 350 N and 700 N were applied to the subtalar joint surfaces to simulate partial weight bearing and full weight bearing. Construct stiffness, total deformation, and von Mises stress were assessed. The maximum stress on the C-Nail® system was lower compared with the plate (110 MPa vs. 360 MPa). At the bone level the stress was found to have higher values in the case of the plate compared to the C-Nail® system. The study suggests that the C-Nail® system can provide sufficient stability, making it a viable option for the treatment of displaced intra-articular calcaneal fractures.

Biomechanical Analysis of a Novel Double-Point Fixation Method for Displaced Intra-Articular Calcaneal Fractures

The development of minimally invasive procedures and implant materials has improved the fixation strength of implants and is less traumatic in surgery. The purpose of this study was to propose a novel “double-point fixation” for calcaneal fractures and compare its biomechanical stability with the traditional “three-point fixation.” A three-dimensional finite element foot model with a Sanders type IIIAB calcaneal fracture was developed based on clinical images comprising bones, plantar fascia, ligaments, and encapsulated soft tissue. Double-point and three-point fixation resembled the surgical procedure with a volar distal radius plate and calcaneal locking plate, respectively. The stress distribution, fracture displacement, and change of the Böhler angle and Gissane’s angle were estimated by a walking simulation using the model, and the predictions between the double-point and three-point fixation were compared at heel-strike, midstance, and push-off instants. Double-point fixation demonstrated lower bone stress (103.3 vs. 199.4 MPa), but higher implant stress (1,084.0 vs. 577.9 MPa). The model displacement of double-point fixation was higher than that of three-point fixation (3.68 vs. 2.53 mm). The displacement of the posterior joint facet (0.127 vs. 0.150 mm) and the changes of the Böhler angle (0.9° vs. 1.4°) and Gissane’s angle (0.7° vs. 0.9°) in double-point fixation were comparably lower. Double-point fixation by volar distal radius plates demonstrated sufficient and favorable fixation stability and a lower risk of postoperative stress fracture, which may potentially serve as a new fixation modality for the treatment of displaced intra-articular calcaneal fractures.

Optimal Design and Biomechanical Analysis of a Biomimetic Lightweight Design Plate for Distal Tibial Fractures: A Finite Element Analysis

The treatment of fractures of the distal tibia can be problematic due to the insubstantial soft-tissue covering this part of the anatomy. This study investigates a novel strategy for minimally invasive plate osteosynthesis of distal tibia fractures called bionic lightweight design plating. Following the structure of the animal trabecular bone, we utilized topological mathematical methods to redesign the material layout of the internal fixation device to fulfill the desired lightweight design within given boundary conditions. The results showed that this method can maintain the same stability of the construct as the original plate after a reduction in the original volume by 30%, and the differences in strain energy of plates and maximum node displacement of constructs between the constructs [RP construct vs. LP construct] were not statistically significant (p > 0.05). In the safety assessment of the constructs, the peak stress of plates between constructs was found to not be statistically significantly different under a doubled physiological load (p > 0.05). The average stress of the plates’ elements exceeding the allowable stress was analyzed, and no statistically significant differences were found between the two constructs under axial compression stress conditions (p > 0.05). The average stress of the plates’ elements in the redesigned plating construct under torsional stress conditions was 3.08% less than that of the locked plating construct (p < 0.05). Under the double physiological load condition, 89% of the elements of the plate in the redesigned plating construct and 85% of the elements of the plate in the locked plating construct were lower than the maximum safe stress of the plate, which was 410 MPa (secondary allowable stresses). That reminds us the topology optimization offer a possible way to improve the capacity of soft tissue protection while ensuring the safety of the RP construct by reducing the volume of the implants.

Biomechanical comparisons of different diagonal screw designs in a novel embedded calcaneal slide plate

BACKGROUND

Medial displacement calcaneal osteotomy (MDCO) is frequently used for the surgical correction of flatfoot. This study aims to investigate the biomechanical effect of the different diagonal screw design on a novel-designed embedded calcaneal plate for MDCO using finite element analysis (FEA), mechanical test and digital image correlation (DIC) measurement.

METHODS

Four groups according to the varied implanted plate were set as control group (Group 1), non-diagonal screw (Group 2), one-diagonal screw (Group 3), and two-diagonal screws groups (Group 4). For FEA, A 450 N load was applied to on the anterior process of the calcaneus from top to bottom. Observational indices included the stress on the cortical and cancellous bone of the calcaneus surrounding the implant, the plate itself as well as screws, and the displacement of the overall structure. In addition, this study also used in vitro biomechanics test to investigate the stiffness of the structure after implantation, and used DIC to observe the displacement of the calcaneus structure after external force.

RESULTS

Under a simulated load in FEA, there are significant overall instability and high stress concentration on the calcaneal surrounding host bone and the plate/screws system, respectively, in group 2 compared with other groups. Regard to the mechanical testing with DIC system, significant increased rotation stability, maximum force and stiffness with the addition of diagonal screws. In comparison to Group 2, the increase of 112% and 157% in maximum force as well as 104% and 176% in stiffness were found in Group 3 and 4, respectively.

CONCLUSION

For reducing stress concentration and enhancing overall stability, more than one-diagonal screw design is recommended and two-diagonal screws design will be superior. This study provided biomechanical references for further calcaneal implants design to prevent clinical failure after MDCO.

The advances of topology optimization techniques in orthopedic implants: A review

Metal implants are widely used in the treatment of orthopedic diseases. However, owing to the mismatched elastic modulus of the bone and implants, stress shielding often occurs clinically which can result in failure of the implant or fractures around the implant. Topology optimization (TO) is a technique that can provide more efficient material distribution according to the objective function under the special load and boundary conditions. Several researchers have paid close attention to TO for optimal design of orthopedic implants. Thanks to the development of additive manufacturing (AM), the complex structure of the TO design can be fabricated. This article mainly focuses on the current stage of TO technique with respect to the global layout and hierarchical structure in orthopedic implants. In each aspect, diverse implants in different orthopedic fields related to TO design are discussed. The characteristics of implants, methods of TO, validation methods of the newly designed implants, and limitations of current research have been summarized. The review concludes with future challenges and directions for research. Wang TO design of global layout and local structure of implants in diverse fields of orthopedic.

Biomechanical evaluation of a novel mandibular distraction osteogenesis protocol: an in-vitro validation and the practical use of the method

The aim of this study was to optimize and experimentally validate the certain parameters affecting the operation success of Mandibular Distraction Osteogenesis (MDO). According to FEA results, the displacement of the samples showed 28.5% reduction as only the osteotomy line was separately optimized, and 64.2% less displacement was determined when the osteotomy line and the screw configuration were optimized together. In consistent with the FEA results, the samples showed 62% and 84.5% fewer displacement values, respectively. As a result, the MDO protocol suggested, which is validated by both numerical and experimental studies, offers promising outcomes for operation success.

Impact of surgical procedures on soft tissue microcirculation in calcaneal fractures: A prospective longitudinal cohort study

PURPOSE

Wound healing complications are a major concern after open reduction and internal fixation (ORIF) in patients with calcaneal fractures. Microcirculation is known to play a key role in bone and soft tissue healing. The present study aimed to characterize and contrast the dynamics of changes in microcirculation comparing two different surgical procedures: A) ORIF and B) a minimally invasive approach (MIA).

METHODS

Blood flow (BF[AU]), oxygen saturation (sO₂[%]) and relative amount of haemoglobin (rHb[AU]) were measured at two depths (2 mm and 8 mm) non-invasively by spectrophotometry (Micro-Lightguide O2C®, LEA Medizintechnik, Giessen, Germany) before surgery and every 24 h after surgery for a duration of six days. A linear mixed model (LMM) was used to analyse longitudinal data and repeated measurements.

RESULTS

Nineteen patients (44 years, range 21.9-71.0 years) were enrolled in the study. Surgical treatment consisted of ORIF (n = =15) and MIA (n = =9). The postoperative BF and sO₂ at the 2 mm and 8 mm depths were higher in the ORIF group (BF: p < 0.001, p = =0.003; sO₂: p = =0.001, p = =0.011). The BF at the 2 mm and 8 mm depths increased after surgery (2 mm: p = =0.003, 8 mm: p = =0.001) in both groups. This increase did not correlate with the surgical technique. sO₂ and rHb values at the 8 mm depth decreased after surgery (sO₂: p = =0.008, rHb: p < 0.001) in both groups, whereas sO₂ at the 2 mm depth increased after surgery (p = =0.003). Furthermore, the surgical technique correlated with the postsurgical course of sO₂ values at the 2 mm depth (p = =0.042).

CONCLUSIONS

The spectrophotometry results were in line with the generally accepted phases of soft tissue wound healing. Postsurgical changes in microcirculation are predominantly independent of surgical techniques and may be primarily determined by wound and fracture healing. Future studies should focus on the potential of spectrophotometry to monitor wound healing after surgery. Moreover, studies with longer observation periods are needed in order to examine the changes in microcirculation during all wound-healing phases.

Comparison and predictive factors analysis for efficacy and safety of Kirschner wire, anatomical plate fixation and cannulated screw in treating patients with open calcaneal fractures

This study aimed to compare the efficacy and safety among Kirschner wire, anatomical plate fixation and cannulated screw treatments in patients with open calcaneal fractures, and to explore the predictive factors for treatment response and complication occurrence.The 142 open calcaneal fracture patients were enrolled in this study, who received fixation procedures of Kirschner wire, anatomical plate fixation or cannulated screw on demand. Treatment efficacy was assessed by AOFAS score and occurrence of complications was recorded.No difference of AOFAS score was observed among Kirschner wire, anatomical plate fixation and cannulated screw groups (P = .792), and the numbers of patients with excellent, good, medium, and poor AOFAS score in Kirschner wire group were 16 (16.2%), 42 (42.4%), 32 (32.3%), and 9 (9.1%), which in anatomical plate fixation group were 4 (16.7%), 11 (45.8%), 7 (29.2%), and (8.3%), and in cannulated screw group were 1 (5.3%), 10 (52.6%), 6 (31.6%), and 2 (10.5%), respectively. No difference of total complication occurrence (P = .709) or specific complications including skin graft (P = .419), flap graft (P = .229), deep infection (P = .644) or amputation (P = .428) was discovered among 3 groups. Logistic regression analysis revealed that fixation options did not affect treatment response and complication occurrence (all P > .05), while higher Gustilo type correlates with decreased treatment response (P < .001) and elevated complication occurrence (P < .001) independently.Kirschner wire, anatomical plate fixation, and cannulated screw are equally efficient and tolerated in treating patients with open calcaneal fractures, and higher Gustilo type correlates with decreased treatment response and increased complication occurrence independently.

Intra-articular calcaneal fractures. Do locking plates keep the reduction better than conventional plates?

INTRODUCTION

Since the development of locking plates, calcaneal fractures have been considered ideal for this type of fixation, due to the need to maintain the height of the subastragaline joint after depression fractures in a location where bone quality tends to be poor. However, there are no comparative studies that support the theoretical superiority of these plates over conventional plates. The aim of this study was to compare the results of intraarticular calcaneal fractures treated using locking plates vs. conventional plates in terms of radiological reduction, complications and number of reinterventions.

MATERIAL AND METHODS

We designed a comparative study of calcaneal fractures operated in our centre using the "L" approach. Two groups were established: group B, comprising 15 patients operated between 2010 and 2015 with calcaneal locking plates, and group A, comprising a stratified random sample of 23 patients taken from a historical cohort of 90 patients operated in our centre between 1997 and 2007 using conventional calcaneal plates. Demographic data were recorded (age, sex, diabetes mellitus, smoking) and data relating to the fracture (type of fracture according to Sander's classification system, complications, presurgical delay). To evaluate loss of reduction, varus angulation of the calcaneus (measured from the axial view), Böhler's angle and Gissane's angle were assessed radiographically. These angles were measured preoperatively, immediately postoperatively, and at the end of follow-up. Finally, we recorded complications and the number of reinterventions.

RESULTS

There were no differences in terms of age, sex or fracture type between the 2 groups. There was greater loss of varus angulation in group A, 0.6 vs. 0.41°, and there was greater reduction in Böhler's angle in group A, 3.79 vs. 2.6°, while Gissane's angle decreased more in group B, 4.13 vs. 2.52°. There were no significant differences in the proportion of complications and reinterventions between the 2 groups.

CONCLUSION

In our study we observed no significant differences between the 2 groups in terms of radiological reduction, complications or number of reinterventions. However, we did observe a greater loss of reduction of Böhler's angle in the patients who were operated using conventional plates.

Biomechanical considerations in the design of patient-specific fixation plates for the distal radius

Use of patient-specific fixation plates is promising in corrective osteotomy of the distal radius. So far, custom plates were mostly shaped to closely fit onto the bone surface and ensure accurate positioning of bone segments, however, without considering the biomechanical needs for bone healing. In this study, we investigated how custom plates can be optimized to stimulate callus formation under daily loading conditions. We calculated implant stress distributions, axial screw forces, and interfragmentary strains via finite element analysis (FEA) and compared these parameters for a corrective distal radius osteotomy model fixated by standard and custom plates. We then evaluated these parameters in a modified custom plate design with alternative screw configuration, plate size, and thickness on 5 radii models. Compared to initial design, in the modified custom plate, the maximum stress was reduced, especially under torsional load (- 31%). Under bending load, implants with 1.9-mm thickness induced an average strain (median = 2.14%, IQR = 0.2) in the recommended range (2-10%) to promote callus formation. Optimizing the plate shape, width, and thickness in order to keep the fixation stable while guaranteeing sufficient strain to enhance callus formation can be considered as a design criteria for future, less invasive, custom distal radius plates. Graphical abstract ᅟ.