Effects of ethnicity on proximal femoral intramedullary nail protrusion-a 3D computer graphical analysis

Antegrade nailing of proximal femur or femoral shaft fractures is a proven treatment with good to excellent results. Nonetheless, clinical evidence from Asia indicates that proximal femur nails can be too proud at the greater trochanter (GT) causing irritation for some Asian patients. This study aimed to identify any significant differences in proximal nail misfit for a set of Asian and Caucasian femora.

Two nails (Gamma3, TFNA) were virtually inserted into 63 femoral 3D models (28 Japanese, 4 Thai, 31 Caucasian). In AP, the entry point was 4° lateral for Gamma3 and 5° for TFNA; laterally the same location was used for both. Insertion depth was controlled by aligning the lag screw centre head. The distance of the nail end from the GT was measured at five (medial, lateral, anterior, posterior and centre) reference points (RPs). The correlation between GT height, CCD angle and proximal nail distance to GT was analysed.

There was no significant difference between either nail (p = 1.0). The TFNA was overall less prominent than the Gamma3, and significantly less prominent at all RPs except lateral. The Asian femora were 3.76 (p = 0.016) times more likely to have the nail protruding proximally. The Asian subjects were shorter (p < 0.05) than the Caucasians. Their GT height was slightly shorter and CCD angles larger compared to Caucasian (Asian: 41.1 mm, 128.1°, Caucasian: 42.2 mm, 126.4°), but the differences were not significant (p = 0.36). Stature, GT height and CCD angle significantly correlated with nail distance to GT.

This study illustrated a significantly increased incidence of proximal nail protrusion in Asian compared to Caucasian femora, corroborating clinical findings. The combination of shorter stature and GT height and a larger CCD angle in Asians likely contributes to this difference.