Cyclic Loading Effects on Craniofacial Strain and Sutural Growth in Pigs

Abstract

Background: Current craniofacial growth modification devices utilize static forces to modulate sutural growth. Although effective, the application of continuous static forces over several months is not efficient. Evidence on the effects of these orthopedic forces on distant parts of the skull is also lacking. Purpose: 1. To develop a loading system capable of reliably delivering cyclic loads to the nasofrontal suture (NFS), 2. To explore strain transmission resulting from cyclic loading of the NFS both ex vivo and in vivo and 3. To characterize the effects of cyclic loading on sutural growth. Methods: Tensile loads cycling at 2.5 Hz were applied to one NFS of abattoir pig heads (n=6) instrumented with strain gages. Similar loading was applied to 3-month old live pigs (Sus scrofa, n=4 and 1 sham) 30 minutes/day for 5 days. Strains were recorded on day 5. Quantitative computerized histomorphometric analysis was performed to compare suture widths and mineral apposition rate (MAR) with controls. Results: The loading system proved capable of producing a consistent load output and, strains of desired frequency, magnitude and polarity at the loaded NFS. Ex vivo, only the loaded NFS showed significant tensile strain (+898 µɛ) while the non-loaded NFS experienced smaller tensile strain (+660 µɛ). Internasal sutures experienced strain magnitudes <200 µɛ of varying polarity. Generally small (<100 µɛ) tensile and compressive strains were registered at the interfrontal and coronal sutures respectively. Nasal and frontal bone principal strains were also low (<100 µɛ). In vivo, live pigs showed a much higher NFS strain (+1543 µɛ) and notable coronal suture strain (-764 µɛ). Preliminary evidence indicates cyclic loading increased MAR (33 µm/day in n=2 loaded vs 11 µm/day in n=5 control) and suture width (355 µm vs 184 µm) of the targeted NFS, suggesting increased suture growth. Conclusions: Daily spurts of cyclic load increased strain transmission in the skull, perhaps by loosening the sutures. The regime likely has a positive effect on suture growth and may be therapeutically useful.