A Biomechanical Comparison of Conventional versus an Anatomic Plate and Compression Bolts for Fixation of Intra-articular Calcaneal Fractures

The purpose of this study was to compare the biomechanical stability obtained by using our technique featured an anatomical plate and compression bolts versus that of the conventional anatomic plate and cancellous screws in the fixation of intraarticular calcaneal fractures.Eighteen fresh frozen lower limbs of cadavers were used to create a reproductive Sanders type-Ⅲ calcaneal fracture model by using osteotomy.The calcaneus fractures were randomly selected to be fixed either using our anatomical plate and compression bolts or conventional anatomic plate and cancellous screws.Reduction of fracture was evaluated through X radiographs.Each calcaneus was successively loaded at a frequency of 1 Hz for 1000 cycles through the talus using an increasing axial force 20 N to 200 N and 20 N to 700 N,representing the partial weight bearing and full weight bearing,respectively,and then the specimens were loaded to failure.Data extracted from the mechanical testing machine were recorded and used to test for difference in the results with the Wilcoxon signed rank test.No significant difference was found between our fixation technique and conventional technique in displacement during 20-200 N cyclic loading(P=0.06),while the anatomical plate and compression bolts showed a great lower irreversible deformation during 20-700 N cyclic loading(P=0.008).The load achieved at loss of fixation of the constructs for the two groups had significant difference:anatomic plate and compression bolts at 3839.6±152.4 N and anatomic plate and cancellous screws at 3087.3±58.9 N(P=0.008).There was no significant difference between the ultimate displacements.Our technique featured anatomical plate and compression bolts for calcaneus fracture fixation was demonstrated to provide biomechanical stability as good as or better than the conventional anatomic plate and cancellous screws under the axial loading.The study supports the mechanical viability of using our plate and compression bolts for the fixation of calcaneal fracture.

Design Improvements and Validation of a Novel Fully 3D Printed Analogue Lumbar Spine Motion Segment

Spine biomechanical testing methods in the past few decades have not evolved beyond employing either cadaveric studies or finite element modeling techniques.However,both these approaches may have inherent cost and time limitations.Cadaveric studies are the present gold standard for spinal implant design and regulatory approval,but they introduce significant variability in measurements across patients,often requiring large sample sizes.Finite element modeling demands considerable expertise and can be computationally expensive when complex geometry and material nonlinearity are introduced.Validated analogue spine models could complement these traditional methods as a low-cost and high-fidelity alternative.A fully 3D printable L-S1 analogue spine model with ligaments is developed and validated in this research.Rotational stiffness of the model under pure bending loading in flexion-extension,Lateral Bending(LB)and Axial Rotation(AR)is evaluated and compared against historical ex vivo and in silico models.Additionally,the effect of interspinous,intertransverse ligaments and the Thoracolumbar Fascia(TLF)on spinal stiffness is evaluated by systematic construction of the model.In flexion,model Range of Motion(ROM)was 12.92±0.11°(ex vivo:16.58°,in silico:12.96°)at 7.5Nm.In LB,average ROM was 13.67±0.12°at 7.5 Nm(ex vivo:15.21±1.89°,in silico:15.49±0.23°).Similarly,in AR,average ROM was 17.69±2.12°at 7.5Nm(ex vivo:14.12±0.31°,in silico:15.91±0.28°).The addition of interspinous and intertransverse ligaments increased both flexion and LB stiffnesses by approximately 5%.Addition of TLF showed increase in flexion and AR stiffnesses by 29%and 24%,respectively.This novel model can reproduce physiological ROMs with high repeatability and could be a useful open-source tool in spine biomechanics.