Cranial vault expansion: a comparison of magnetic coupled distraction to traditional surgical repositioning

We compared the effectiveness of transcutaneously activated magnetic distraction of an osteotomized cranial bone flap to surgical repositioning of the flap with immediate, rigid internal fixation. Thirty immature rabbits were studied. All 30 rabbits underwent complete circumferential osteotomies of both parietal bones and postoperatively all were fitted with head frames. The rabbits were divided into 4 groups. The experimental magnetic distraction group consisted of 10 animals (group 1). In these rabbits magnets were secured to both parietal bones and magnets of opposite polarity were placed in the headframes. Each morning, the magnets in the head-frames were moved 0.25 mm farther away from the skull; this continued for 20 days for a total setback of 5 mm. Five animals served as the magnetic distraction controls; in these animals magnets were placed on the parietal bones but none were attached to the headframes (group 2). The experimental surgical repositioning group consisted of 10 rabbits (group 3). In each the parietal bones were elevated and fixed 5 mm above the rest of the skull using vitallium mesh and screws. Five rabbits made up the surgical respositioning control group (group 4). In these animals, parietal osteotomies were performed but the bones were secured to the skull in their original positions using hardware identical to that used in the experimental group. Six weeks later all of the animals were sacrificed. Two significant differences were identified between the experimental groups: (1) the cranial contours of the animals in the magnetic distraction group were rounded while those of the surgically repositioned group were acutely angled; (2) the osteotomies in rabbits in the magnetic distraction group were essentially completely ossified while in rabbits in the surgically repositioned group there were obvious gaps at the osteotomy sites that were filled with fibrous tissue. These conclusions support the potential utility of magnetically activated distraction as an alternative to current methods of cranial vault remodeling.