Micromotion at the Fracture Site After Tibial Nailing With Four Unreamed Small-Diameter Nails—A Biomechanical Study Using a Distal Tibia Fracture Model

Finite element analysis and clinical evaluation of cross locking external fixator configuration for distal third tibia fracture

External fixators have been used effectively in damage control orthopaedic and open fractures management of various bones. It is well known that stability of external fixators is greatly influenced by its construct. Various rules have been documented to influence the stiffness and stability of external fixators. In this study, two clinical cases treated with a novel concept of cross self-locking rods external fixation construct were being described, coupled with biomechanical analysis of its stability in comparison with other constructs by using finite element study. These novel self-locking rods configuration proven improve strength by applying the same numbers of rod and pin with the delta frame construct in clinical practice. A validated three-dimensional (3D) model of the bone from a previous study was used and external fixator were designed via computer-aided design (CAD) modelling software, Solidworks. A 1500 N load representing the axial load compression during weight bearing was applied to the tibia with the distal segment of the fracture site secured without any movement. The clinical results showed bone healing process with both cases achieving bone union within the acceptable time. The results of the finite element study shows that the double cross self-locking rods construct had better stability since it showed optimum magnitude in relative micromotion (0.18 mm), lowest stress at the fracture site (189 MPa), displacement of fixator (13.4 mm), and stress at the fixator (687 MPa). In conclusion, double cross self-locking design could provide optimum stability of the external fixator construct by providing better stress distribution at the bone and external fixator, minimize displacement and micromotion at fracture fragments.

Computational analysis of the biomechanical stability of internal fixation of the lateral tibial plateau fracture: A mechanical stability study

The selection of internal fixation as the primary fixation modality for the patient is one of the challenges for the surgeon treating the patient in question. A model of the lateral tibial plateau fracture was established. Three different configurations of internal fixators namely L bone plate, T bone plate, and screw-washer were analyzed. Three stages after surgery were simulated to assess the displacement of bone plates, screws, washers, and the stress shielding ratio in the fracture area.At three stages after surgery, the T bone plate showed better stability for patients during rehabilitation compared with the remaining two schemes, and the screw-washer scheme was the least stable due to the larger internal fixation displacement and stress shielding ratio in the fracture area. In contrast, the L bone plate scheme showed better stability in the early stages after surgery but was second only to the screw-washer scheme in the middle and late stages after surgery. The T bone plate showed better stability and became a new selection for surgeons to treat related patients. At three stages after surgery, the T bone plate has better biomechanical stability compared to the L bone plate and screw-washer schemes.

Biomechanical evaluation of combined proximal tibial osteotomy for varus knee osteoarthritis implanted novel designed plate system: Finite element analysis

BACKGROUND

Combined proximal tibial osteotomy (CPTO) is an innovative and effective procedure for correcting varus knee osteoarthritis (VKOA) with intra- and extra-articular deformity. Here, we designed a novel internal fixation plate system for CPTO and assessed the biomechanical strength of the bone-implant.

METHODS

Our newly designed CPTO internal fixation plate system included a specialized plate shape, combination holes, locking screw holes, screw position, and size of fixation. The biomechanical performance of this plate system in CPTO treatment was compared via finite element analysis (FEA) to traditional Tomofix devices implanted in the opening-wedge high tibial osteotomy (OWHTO), tibial condylar valgus osteotomy (TCVO), and CPTO.

RESULTS

The tibial wedge stiffness and displacement after CPTO implantation of the novel internal plate fixation increased by 9.6%, which was -65% higher than the CPTO with the Tomofix system. The average stress of the bone, plate, and screws in the CPTO implanted the novel designed plate system compared to the Tomofix system decreased by 12.7%, 1.9%, and 20.3 %, respectively. The device maximum stress and wedge stiffness after CPTO with the novel plate system versus traditional OWHTO and TCVO with the Tomofix system were 255.7 MPa, 204 MPa, 130.4 MPa, and 678.9 N/mm, 660.3 N/mm, 1626.0 N/mm, respectively.

CONCLUSIONS

The novel internal fixation plate system usage during CPTO exhibited similar bone-implant biomechanical strength, compared to OWHTO, but with enhanced construct stability.

Biomechanical Performance of BoneHelix® Compared with Elastic Stable Intramedullary Nailing (ESIN) in a Pediatric Tibia Fracture Model

Tibial shaft fractures are common injuries in the pediatric and adolescent populations. Elastic stable intramedullary nailing (ESIN) is the treatment of choice for cases that require surgical stabilization. A new intramedullary device, BoneHelix^® (BH), may be an alternative for use with fractures that cannot be satisfactorily stabilized with ESIN. This study aimed to assess the biomechanical performance of BH compared with ESIN in a porcine tibia fracture model, observing cyclic fatigue and load to failure. Computed tomography was used to monitor the implant position and to rule out unintended damage. No implant or bone failure occurred during the fatigue testing. An increase in the cumulative plastic displacement was observed in both test groups over the loading cycles applied. Both implant–bone constructs displayed a trend toward closure of the osteotomy gap. During the load-to-failure test, the average loads at failure in specimens instrumented with ESIN and BH were 5364 N (±723) and 4350 N (±893), respectively, which were not statistically significant (p = 0.11). The values of both groups were two to three times higher than the estimated maximal load (2000 N) during physiological weight bearing. The biomechanical results thus indicate equivalent performance and stability by the implants tested.

Biomechanical evaluation of three different configurations of external fixators for treating distal third tibia fracture: Finite element analysis in axial, bending and torsion load

External fixators have been widely used in treating open fractures and have produced excellent outcomes, as they could successfully heal bones. The stability of external fixators lies greatly in their construction. Factors that associated with the stability of the external fixators includes stress, displacement, and relative micromotion. Three-dimensional (3D) models of bone and external fixators were constructed by using 3D modelling software, namely Materialise and SolidWorks, respectively. Three different configurations of external fixators namely Model 1, Model 2, and Model 3 were analysed. Three load cases were simulated to assess the abovementioned factors at the bone, specifically at the fracture site and at the external fixator. Findings showed that the double-cross configuration (Model 3) was the most promising in axial, bending, and torsion load cases as compared to the other two configurations. The no-cross configuration (Model 1) had the highest risk of complication due to high stress, relative micromotion, and displacement in the bending and torsion load cases. On the other hand, the single-cross configuration (Model 2) had the highest risk of complication when applied with axial load. In conclusion, the double-cross locking construct (Model 3) showed the biggest potential to be a new option for medical surgeons in treating patients associated with bone fracture. This new double-cross locking construct showed superior biomechanical stability as compared to single-cross and no-cross configurations in the axial, bending, and torsion load cases.

Distal Locking Screws for Intramedullary Nailing of Tibial Fractures

Recently introduced tibial intramedullary nails allow a number of distal screws to be used to reduce the incidence of malalignment and loss of fixation of distal metaphyseal fractures. However, the number of screws and the type of screw configuration to be used remains obscure. This biomechanical study was performed to address this question. Thirty-six Expert tibial nails (Synthes, Oberdorf, Switzerland) were introduced in composite bone models. The models were divided into 4 groups with different distal locking configurations ranging from 2 to 4 screws. A 7-mm gap osteotomy was performed 72 mm from the tibial plafond to simulate a 42-C3 unstable distal tibial fracture. Each group was divided in 3 subgroups and underwent nondestructive biomechanical testing in axial compression, coronal bending, and axial torsion. The passive construct stiffness was measured and statistically analyzed with one-way analysis of variance. Although some differences were noted between the stiffness of each group, these were not statistically significant in compression (P=.105), bending (P=.801), external rotation (P=.246), and internal rotation (P=.370). This in vitro study showed that, when using the Expert tibial nail for unstable distal tibial fractures, the classic configuration of 2 parallel distal screws could provide the necessary stability under partial weight-bearing conditions.

Early weight-bearing in operatively fixed ankle fractures: a systematic review

BACKGROUND

Ankle fractures are among the most common lower limb fractures and they can cause significant detrimental effects on quality of life and work.

OBJECTIVE

The objective of the review was to evaluate if there is any advantage of early weight-bearing after open reduction and internal fixation of the ankle.

METHODS

Electronic databases, reference lists of included studies and relevant systematic reviews were searched for randomized and non-randomized controlled trials in adults comparing early and late weight-bearing after open reduction and internal fixation of the ankle. The search was inclusive up to February 2012.

RESULTS

Nine studies comprising 555 subjects were included for review. There were significantly better outcomes for improved early dorsiflexion, time to full weight-bearing, early return to previous work and shorter hospital stay (patient<60 years of age) in the early weight-bearing group.

CONCLUSION

The evidence base contained many methodological limitations and was generally poor, and so any conclusion drawn from the research must be done so with caution. The literature suggests that early weight-bearing may allow for quicker rehabilitation and earlier return to work. Future studies should focus on randomized controlled trials with narrow range of clinically useful outcome measures and consistent immobilization strategy between experimental groups.

The primary stability of angle-stable versus conventional locked intramedullary nails

PURPOSE

The aim of this study was to compare the initial biomechanical characteristics of the angle-stable locking system for intramedullary nails using the new biodegradable sleeve with conventional locking in the treatment of unstable distal tibial fractures.

METHODS

Eight pairs of fresh, frozen porcine tibiae were used for this study. The expert tibial nail (Synthes) was equipped with either conventional locking screws (CL) or the angle-stable locking system (AS). This system consists of a special ASLS screw with a biodegradable sleeve. For this investigation distal tibias (5.5 cm) were used and the nails were locked with three screws in both groups. Biomechanical testing included non-destructive torsional and axial loading.

RESULTS

The AS group showed a significantly higher torsional stiffness (70%) compared to the CL group. The range of motion was 0.5 times smaller for the AS constructs. The neutral zone was eight times higher in the CL group (p < 0.001). In axial loading the AS group also showed a 10% higher axial stiffness and a 12% lower range of motion (p < 0.001).

CONCLUSION

The angle-stable locking system (ASLS) using a special screw and sleeve locking for intramedullary nails provides a significantly higher primary stability. The differences determined in this study may have clinical relevance particularly for torsional loads. For the new biodegradable angle-stable sleeve we found a comparable stability to the PEEK-based sleeve system. This system has the potential to decrease complications such as secondary loss of reduction and mal-/non-union.

Biomechanical Characterization of an Osteoporotic Artificial Bone Model for the Distal Femur

The treatment of osteoporotic distal femur fractures is still an unsolved problem of trauma surgery. The poor bone stock often leads to secondary loss of reduction and implant failure. Therefore, the development of new implants and their biomechanical testing is essential. In a previous study, we developed and initially characterized an artificial osteoporotic bone model of the distal femur. This follow-up study was performed to characterize this model in a biomechanical comparison. We investigated two different artificial bones: five foam cortical shell (Sawbones) and 10 custom-made artificial femoral condyles. Additionally, eight human femora were used for comparison. For biomechanical testing, two intramedullary nails (distal femur nail (DFN) and supracondylar nail (SCN)) were cyclically axial loaded in an AO 33 C2 unstable distal femoral fracture model. In our testing, the artificial bone showed a decrease in the axial stiffness of 27% for the SCN and 28% for the DFN compared to the human results. Also the number of cycles for a deformation of 2.5 mm was reduced by 55% (SCN) and 62% (DFN). This decrease was homogenous and caused by the relative high bone mineral density of the human specimen used. The modes of failure showed no difference between the artificial and human bones. Our customized artificial bone provides suitable results. In relation to the human bones classified as mildly osteoporotic, we assume that the biomechanical properties match to serve as an osteoporotic bone. Yet, we suggest to check transferability of the results with human material.