The thickness of parietal bones in a New Zealand sample of cadaveric skulls in relation to calvarial bone graft, 2007-2011

Abstract

Objectives: (1) To evaluate the average thickness of the parietal bones in a New Zealand European sample of cadaveric skulls; (2) to construct a thickness map of the parietal bone; and (3) to identify the ideal site(s) for calvarial bone graft harvest using the parietal bone.

Study Design: Twenty-five wet cranial vaults (fifty parietal bones) of New Zealand European origin were obtained from the Department of Anatomy at the University of Otago, New Zealand.

A total number of 3887 points (average of 78 points per bone) in 135 equivalent locations throughout the specimens were measured for its thickness using an electronic calliper. Statistical analysis was performed using a software system R. Analyses to identify the ideal harvest sites were conducted so that they fit features of ideal harvest site described in the literature as: 6 mm of minimum thickness; and 2 cm way from the midline.

Results: The overall average thickness was 6.69 mm with a standard error of 0.22 mm. The average thickness at different locations ranged from 2.85 mm to 6.93 mm. The report also observed a progressive thickening of the parietal bone in both medial and posterior directions. A thickness map clearly demonstrated regions with varying thickness of the parietal bone in its different regions.

Of all 135 locations, a significant proportion - forty-seven locations (34.5%) - had an average thickness greater than 6 mm. The proportion was also high – twenty-seven locations (20%) - after excluding the locations within 2 cm from the midline. However, a frequency of encountering bone with an actual thickness less than 6 mm was also high at 20.6% in this region. The frequency was reduced to 13% in locations with an average thickness greater than 6.5 mm. However, only a very limited number of locations (3/135 = 2%) had an average thickness greater than 6.5 mm in our study sample after excluding the locations within 2 cm from the mid-sagittal plane.

Conclusions: Parietal bone thickness in our study sample is similar to that of other ethnicities reported in the literature.

The ideal calvarial bone graft sites that safely meet the recommendations were found to be scarce in this study.

Further research to validate or update the current recommendations for the ideal sites of calvarial bone harvest sites including pre-operative imaging modalities is recommended.