3D Computer graphical anatomy study of the femur: a basis for a new nail design

Current intramedullary nails with a radius of curvature (ROC) of 1500-2000 mm sometimes cause distal anterior cortical encroachment. Furthermore, clinical data indicate that the proximal nail end is too long for some Asian patients. The objective of our study was to develop a comprehensive 3D measurement protocol that measures both the anatomy of the canal and the proximal region. The protocol was used to obtain measurements from Caucasian and Asian (Japanese and Thai) specimens.

A total of 90 3D bone models representative of hip fracture patients were reconstructed from CT data. RapidForm 2006 was used to generate the reference geometries required for determining radius and angulation of shaft antecurvature as well as measurements of the proximal anatomy. Multiple linear regression analyses were used to determine the relative contribution of height, age, ethnicity, gender, and body side on the total variance.

The mean ROC in the natural 3D antecurvature plane was 885 mm overall, 974 mm in Caucasians and 787 mm in Asians. Height, age, ethnicity, gender, and body side significantly predicted ROC (R = 0.53, p = 0.000). The mean values of anteversion measurements for Asians (Japanese: 22.1°; Thai: 22.7°) were significantly larger than those of the Caucasians (14.5°; p = 0.001). There was virtually no difference (p = 0.186) between the measurements pertaining to the length of the proximal nail end between Caucasian and Asian samples. There was no significant difference between the mean neck-to-shaft angles (Caucasian: 126°; Japanese: 128.2°; Thai: 125.7°; p = 0.198 for Asians vs Caucasians).

The developed comprehensive anatomical 3D measurement protocol could serve as standardised approach for anthropometric studies in the future. Our data suggest that the ROC of current nail designs should be reduced from between 1500 and 2000 to 1000 mm to achieve an improved fit for the investigated population.