Challenge

The orthopedic industry has come to achieve many technological healthcare milestones in which prosthesis and implants are designed with a minimal invasive approach and considering patient´s comfort. However, there are still some functional considerations that need to be made for developing safe and structurally stable devices. In the case of transpedicular screws, the most common faults are fractures due to stress concentration leading to the need of removing the implant.

Solution

For minimizing stress concentration in the surface of the screw, Bioana proposal consists in a redesign of the conventional geometry of the screw aiming to redistribute stress homogeneously within its body. The shaft approach pretends to insert more firmly to the bone adapting its configuration from a straight section to a conical shape ending.

Results

We performed a finite element analysis of the screw design iterations inside the L4 vertebra using cortical and spongy bone material to assess the grip, deformation and stress concentration in the devices due to the movement of the column. The screw has a rotating head for easy handling of the surgeon and a mechanical stop to limit the introduction of the implant to the vertebral pedicles. The analysis was performed simulating daily activities of an 80 kg person including standing up, walking, climbing upstairs and sitting down involving displacement and momentum applied to the body of the screw. The FEA analysis of the designed assembly showed that the resultant stress value is below the yield strength of the Ti6Al4V material, avoiding its permanent deformation. Design Patent Pending MX/a/2015/000701.

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