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A biomechanical analysis of the orbitozygomatic complex in human cadavers: examination of load sharing and failure
1Division of Plastic Surgery, Sunnybrook Health Science Centre, University of Toronto, Canada.
Abstract:
The orbitozygomatic complex (OZC) and zygomatic arch act as key buttresses in the restoration of midfacial projection and width in the treatment of panfacial fractures, yet little is known about the biomechanical and deformational forces placed on this region under applied load conditions. The aims of this project were (1) to study the stress-force relationships and load sharing of the intact human OZC under subfailure loads, (2) to assess load sharing and breaking strength of the OZC when intact and after four-point miniplate fixation with either titanium (1.2 and 1.7 mm) or bioresorbable (1.5 and 2.0 mm) systems, and (3) to analyze failure patterns. Using the MTS machine, fresh frozen human skulls stripped of soft tissue underwent loading with subfailure and failure forces directed in a standard fashion. Electrical resistance gauges applied directly to local and remote bony buttresses demonstrated temporary deformation at local (zygomatic arch, lateral and inferior orbital rim) and remote (supraorbital rim) buttresses under subfailure loading conditions. Breaking strength of the OZC (N = 10) measured before and after four-point application of 1.2- or 1.7-mm titanium or 1.5- or 2.0-mm bioresorbable miniplates demonstrated a significant (p < 0.05) decrease compared with intact controls. Surprisingly, the 2.0-mm bioresorbable miniplate construct provided only 13% of the intact breaking strength of the OZC compared with 39% for the 1.7-mm titanium system (p < 0.05). Plate bending or breakage was responsible for failure of the OZC following rigid fixation. Biomechanical testing of the OZC demonstrates (1) load sharing at regional and remote bony buttresses, (2) significant decreases in breaking strength following miniplate fixation, and (3) deformation of miniplates as a primary cause of failure under load conditions. Data generated from this project may be useful with regard to optimizing fixation of the OZC in the context and treatment of panfacial fractures.
