Ultra-high-molecular-weight Polyethylene (UHMWPE) Wing Method for Strong Cranioplasty.

We developed a new cranioplasty method that utilizes artificial bone made of ultra-high-molecular-weight polyethylene, with a wedge-shaped edge (UHMWPE Wing). This study shows the methods and data of case series and finite element analyses with the UHMWPE Wing. A circumferential wing was preoperatively designed for a custom-made artificial bone made of UHMWPE to achieve high fixed power and to minimize the usage of cranial implants. Here, we present 4 years of follow-up data and finite element analyses for patients treated with the UHMWPE Wing between February 2015 and February 2019. Eighteen consecutive patients underwent cranioplasty using our UHMWPE Wing design. There were no postoperative adverse events in 17 of the patients for at least 18 months. One case of hydrocephalus experienced screw loosening and graft uplift due to shunt malfunction. Placement of a ventriculo-peritoneal shunt immediately returned the artificial bone to normal position. Finite element analyses revealed that a model using the UHMWPE Wing had the highest withstand load and lowest deformation. This is the first report on the UHMWPE Wing method. This method may enable clinicians to minimize dead space and achieve high strength in cranioplasty.

Biomechanical analysis of the mechanism of elbow fracture-dislocations by compression force.

Fracture-dislocations of the coronoid and olecranon were produced experimentally, and their onset mechanisms were analyzed to clarify the effects of compression force on the coronoid and olecranon. The study used two-dimensional finite element method (2D-FEM) simulations and static loading experiments. The latter applied axial force distally to 40 cadaveric elbows. Posterior fracture-dislocations occurred between 15 degrees of extension and 30 degrees of flexion, anterior or posterior fracture-dislocations at 60 degrees, and only anterior fracture-dislocations at 90 degrees. Injuries were mainly to anterior or posterior support structures. The 2D-FEM simulations showed that the stress concentration areas moved from the coronoid process to the olecranon as position changed from extension to flexion. The very high frequency of concurrent fracture-dislocations of radial head or neck in the current study indicated that the radial head may also function as a stabilizer in the anterior support system.

Analysis of stress distribution in the humeroradial joint.

Stress distribution in the humeroradial joint was analyzed with pressure-sensitive film, a tactile sensor, and by the three-dimensional finite element method. Fifteen cadaveric elbows with minimal osteoarthritic changes were loaded perpendicular to the articular surface of the radial head in the full pronation, supination, and neutral positions from 0 degrees to 90 degrees. Finite element analysis of stress distribution in the joint was based on a model of the same conditions. The patterns of stress distribution were similar with all three analysis methods. High stress was concentrated laterally in supination, and medially in the neutral and pronation positions. The results of the analyses closely resembled those found in some studies of the pathophysiology of degenerative changes in the humeroradial joint.