As reported by Orthopedics Today, April 16, 2008.

Filling Cortical Defects After Hardware Removal May Reduce Re-fracture Risk

SAN FRANCISCO — Using polylactic acid screws to fill the cortical defects that result from the removal of internal fixation hardware can decrease the stress-riser phenomenon associated with such defects, reducing the risk of re-fracture, according to a biomechanical study presented here.

Joseph P. DeAngelis, M.D., and colleagues at the University of Connecticut Medical School in Farmington, Conn., evaluated how uni-cortical and bi-cortical filling affected cortical defects both biomechanically and using finite element analysis (FEA). They displayed their findings in a poster at the American Academy of Orthopaedic Surgeons 75th Annual Meeting.

In the first part of the study, the researchers created bi-cortical defects in six paired cadaveric radii and ulnae. They then divided the specimens into two groups based on whether the defects were filled with polylactic acid screws (Arthrex), according to the study.

"All specimens were tested in torsion to determine their torsional rigidity and load to failure," the study authors wrote.

In the second part of the study, the researchers used an FEA model for bone in torsion, which was designed to recreate the biomechanical model. This simulation examined specimens under three conditions, including empty bi-cortical defects, bi-cortical defects that had been filled with a bi-cortical peg and bi-cortical defects that had been filled with separate uni-cortical plugs, according to the study.

In the biomechanical evaluation, the investigators found that specimens with screw-filled bi-cortical defects had significantly higher torsional rigidity and lower loads to failure.

Also, "In a FEA model, filling a bi-cortical defect with a bi-cortical peg dramatically changes the stress distribution within the construct, reducing both surface stress distribution and stress concentration," the authors wrote.

"Uni-cortical filling of a bi-cortical defect results in a normal distribution of surface stress while decreasing the stress concentration at a cortical defect," they noted.

For more information:

  • DeAngelis JP, McLaughlin J, Obopilwe E, et al. Empty screw holes after hardware removal: Solving the stress riser phenomenon. Poster P463. Presented at the American Academy of Orthopaedic Surgeons 75th Annual Meeting. March 5-9, 2008. San Francisco.