Spring-Assisted Cranioplasty Alters the Growth Vectors of Adjacent Cranial Sutures

Expansile cranial springs are used to treat selected cases of sagittal synostosis. After sagittal suturectomy, springs are placed perpendicular to the line of the synostosis. Normal growth across the coronal suture is approximately perpendicular to the suture line. To allow cranial expansion in the parietal direction, it is hypothesized that the normal growth vectors across the coronal sutures are altered. Ten New Zealand White rabbits underwent suturectomy of the midline posterior frontal suture followed by insertion of an expansile spring. Radiologic markers were placed on either side of the normal coronal sutures (n = 20) perpendicular to the released suture. Serial radiology was performed up to 7 weeks. Growth vectors across the coronal suture were compared with those of 10 control rabbits. Dorsal cranial expansion was predominantly in an anterolateral direction in controls. The normal growth vector across the coronal suture occurred at an angle of -1 degree to the midline. A spring altered this growth vector to 63 degrees. Over 7 weeks, the cranial width increased 5.1 mm in rabbits with springs compared with 0.2 mm in the control group (p < 0.01). The increase in cranial length across the coronal suture was 1.82 mm in controls and 0.93 mm in rabbits with springs (p = 0.019). Application of a spring across a midline cranial suture alters the growth vector of the normal adjacent sutures. The spring greatly increases cranial width at the expense of some of the normal increase in cranial length over this period. This would be beneficial in correcting the cranial index in sagittal synostosis.