Cyclic loading effects on craniofacial strain and sutural growth in pigs.

Abstract

Current craniofacial growth modification devices use static forces, but cyclic forces are believed by some to be more effective. The latter have not been evaluated in large animal models, and it is not known how such forces are transmitted to distant parts of the skull. In this study, we aimed to (1) develop a portable loading system capable of delivering reliable cyclic loads to the porcine nasofrontal suture (NFS), (2) explore strain transmission to distant sutures, and (3) characterize the sutural growth effects in a small pilot study. After we validated the device, cyclic (2.5Hz) tensile loads were applied unilaterally to the NFS of 6 abattoir pig heads, with strain gauges on multiple sutures. Similar loading was applied to 3-month-old live pigs (Sus scrofa, n=4 and 1 sham) 30minutes per day for 5days. These animals received fluorescent markers of mineralization on loading days 1 and 3. Suture strains were recorded on day 5. Histomorphometric analysis quantified suture width and mineral apposition rate. A wearable loading system was developed to produce an average of +900 microstrain at the targeted NFS. Substantial strains were seen at the contralateral NFS and midline sutures, but bone strains were low. Strain patterns were similar exvivo and invivo, with the latter generally having higher magnitudes. Preliminary evidence demonstrates wider sutures with higher mineral apposition rates in the loaded sutures. Daily spurts of cyclic load caused sutural strain throughout the skull. This regimen most likely enhances sutural growth and may be therapeutically useful.