Finite Element Analysis of Unilateral versus Bipedicular Bone-Filling Mesh Container for the Management of Osteoporotic Compression Fractures

Biomechanical behaviour of a novel bone cement screw in the minimally invasive treatment of Kummell's disease: a finite element study

OBJECTIVE

To investigate and evaluate the biomechanical behaviour of a novel bone cement screw in the minimally invasive treatment of Kummell's disease (KD) by finite element (FE) analysis.

METHODS

A validated finite element model of healthy adult thoracolumbar vertebrae T12-L2 was given the osteoporotic material properties and the part of the middle bone tissue of the L1 vertebral body was removed to make it wedge-shaped. Based on these, FE model of KD was established. The FE model of KD was repaired and treated with three options: pure percutaneous vertebroplasty (Model A), novel unilateral cement screw placement (Model B), novel bilateral cement screw placement (Model C). Range of motion (ROM), maximum Von-Mises stress of T12 inferior endplate and bone cement, relative displacement of bone cement, and stress distribution of bone cement screws of three postoperative models and intact model in flexion and extension, as well as lateral bending and rotation were analyzed and compared.

RESULTS

The relative displacements of bone cement of Model B and C were similar in all actions studied, and both were smaller than that of Model A. The minimum value of relative displacement of bone cement is 0.0733 mm in the right axial rotation of Model B. The maximum Von-Mises stress in T12 lower endplate and bone cement was in Model C. The maximum Von-Mises stress of bone cement screws in Model C was less than that in Model B, and it was the most substantial in right axial rotation, which is 34%. There was no substantial difference in ROM of the three models.

CONCLUSION

The novel bone cement screw can effectively reduce the relative displacement of bone cement by improving the stability of local cement. Among them, novel unilateral cement screw placement can obtain better fixation effect, and the impact on the biomechanical environment of vertebral body is less than that of novel bilateral cement screw placement, which provides a reference for minimally invasive treatment of KD in clinical practice.

Biomechanical evaluation of percutaneous anterograde and retrograde screw implantation for superior ramus pubis fractures: a finite element analysis

OBJECTIVE

To evaluate the biomechanical characteristics of percutaneous anterograde and retrograde screw implantation for superior ramus pubis fractures.

METHODS

Mimics software was used to reconstruct the normal pelvis. 3-Matic software was used to establish a model for superior ramus pubis fracture, and percutaneous anterograde/retrograde screw implantation was used to simulate the treatment of a superior ramus pubis fracture. After material assignment by Mimics software, Ansys software simulated the force of a standing position with a 600 N load on an S1 vertebral endplate and then compared the mechanical stability.

RESULTS

After simulating the fracture at five points, the effect of anterograde and retrograde screw implantation on the displacement and stress of the pelvis and the left pubic bone were found to be similar. When anterograde screw implantation was used, screw displacement at each point was 1.10 mm, 1.04 mm, 1.10 mm, 1.10 mm, and 1.07 mm; the stress at each point was 14.95 MPa, 11.50 MPa, 18.60 MPa, 18.07 MPa, and 18.37 MPa. When retrograde screw implantation was used, screw displacement at each point was 0.62 mm, 0.62 mm, 0.70 mm, 0.76 mm, and 0.87 mm; and the stress at each point was 5.13 MPa, 4.03 MPa, 6.61 MPa, 9.74 MPa, and 11.55 MPa respectively.

CONCLUSIONS

When assessing the treatment of superior ramus pubis fractures from a biomechanical perspective, we found that if the distance between the fracture line and the insertion point is less than 70 mm, it is recommended to use retrograde screw implantation.

A 20-Year Review of Biomechanical Experimental Studies on Spine Implants Used for Percutaneous Surgical Repair of Vertebral Compression Fractures

A vertebral compression fracture (VCF) is an injury to a vertebra of the spine affecting the cortical walls and/or middle cancellous section. The most common risk factor for a VCF is osteoporosis, thus predisposing the elderly and postmenopausal women to this injury. Clinical consequences include loss of vertebral height, kyphotic deformity, altered stance, back pain, reduced mobility, reduced abdominal space, and reduced thoracic space, as well as early mortality. To restore vertebral mechanical stability, overall spine function, and patient quality of life, the original percutaneous surgical intervention has been vertebroplasty, whereby bone cement is injected into the affected vertebra. Because vertebroplasty cannot fully restore vertebral height, newer surgical techniques have been developed, such as kyphoplasty, stents, jacks, coils, and cubes. But, relatively few studies have experimentally assessed the biomechanical performance of these newer procedures. This article reviews over 20 years of scientific literature that has experimentally evaluated the biomechanics of percutaneous VCF repair methods. Specifically, this article describes the basic operating principles of the repair methods, the study protocols used to experimentally assess their biomechanical performance, and the actual biomechanical data measured, as well as giving a number of recommendations for future research directions.