Biomechanical testing of alloplastic PMMA cranioplasty materials

Alloplastic cranioplasty techniques using polymethylmethacrylate (PMMA) are a common method of restoring lost cranial bone. Numerous compositions of PMMA exist for this application, using either intraoperatively cured solid compositions or preoperatively fabricated porous custom implants. Although all of these PMMA materials feel solid by palpation, the amount of cranial protection that they provide has never been precisely evaluated. Whether differences exist between the differing PMMA cranioplasty materials likewise is unknown. An impact resistance test was performed on uniform-size blocks of differing PMMA materials of representative cranial thickness using American Society of Testing and Materials (ASTM) method D 3029-78. Based on mean failure weights of 3.9 lb (Cranioplast), 4.2 lb (Cranioplexx), and 4.0 lb (HTR polymer), all of these materials are comparatively the same in impact resistance. Precured porous PMMA, despite having 30% to 40% less material, offered no less impact resistance. Based on projections to cranial bone, PMMA materials appear to offer protection similar to that of native osseous tissue.