Rigid fixation and strain patterns in the pig zygomatic arch and suture.
OBJECTIVE
In orthognathic surgery, rigid fixation is routinely used to hold together bone fragments that may experience heavy force from attached masticatory muscles. Internal fixation plates are assumed to hold bony parts rigidly, but the mobility at such sites subjected to normal masticatory function has not been measured. The purpose of this study was to investigate in vivo the degree to which a linear plate immobilizes separated bones, specifically sutures.


METHODS
Three female miniature pigs (Sus scrofa) had 1.3-mm Synthes titanium plates placed across the suture in the zygomatic arch. Foil strain gauges were used to record load deformation in the zygomatic and squamosal (temporal) bones and across the vertical and horizontal parts of the suture. Strain was recorded in vivo during mastication and in anesthetized pigs with electrical stimulation of masticatory muscles.


RESULTS
Strain at the suture was not reduced from normal levels. The plate induced increases in strain within the bones, but the changes were slight.


CONCLUSIONS
The results indicate that linear "rigid fixation" does not immobilize sutures.
Freeman
J A
JA
Department of Orthodontics, University of Washington, Seattle 98195-7446, USA.
Teng
S
S
Herring
S W
SW
D000818:Animals; D001732:Bite Force; D001860:Bone Plates; D003393:Cranial Sutures / Q000502:physiology* / Q000601:surgery; D004576:Electromyography; D005260:Female; D007103:Immobilization / Q000502:physiology*; D008409:Mastication; D008410:Masticatory Muscles / Q000502:physiology; D013314:Stress, Mechanical; D013552:Swine; D013556:Swine, Miniature; D013701:Temporal Bone / Q000502:physiology / Q000601:surgery; D015050:Zygoma / Q000502:physiology / Q000601:surgery*