Mismatch of the short straight cephalomedullary nail (PFNA-II) with the anterior bow of the Femur in an Asian population.

OBJECTIVES

The aims of this study were to evaluate the morphologic discrepancies between the short straight proximal femoral nail antirotation-Asian version (PFNA-II) and the anterior bow of the femur in Chinese patients and to propose a further design modification.

DESIGN

Retrospective study.

SETTING

Level I academic trauma center.

PATIENTS/PARTICIPANTS: A consecutive 158 cases (35 men and 123 women with mean age of 77.2 years) with unstable per/intertrochanteric fractures (AO/OTA 31 A2 and A3) treated by PFNA-II from August 2008 to December 2010 participated in this study.

INTERVENTION

Nailing of PFNA-II.

MAIN OUTCOME MEASUREMENTS

The nail tip position was classified to a 5-grade scale on postoperative lateral radiographs of the femur. The distance between the nail axis and the canal axis at the tip level was measured. The degree of the theoretical bent curvature and its corresponding radius were calculated, assuming that the anterior protrusive nail tip was placed back to the central canal axis.

RESULTS

The distal tip of PFNA-II was located anterior to the femur canal central axis in 118 cases (74.7%), of which 55 cases abutted against the anterior cortex (contact between nail and internal cortex) (34.8%). With longer nails, the abutment occurred more often and was more prominent. For nail lengths of 170, 200, and 240 mm, the theoretical distance to replace the nail tip to the central canal axis was 1.42 ± 0.18, 1.77 ± 0.39, and 2.46 ± 0.20 mm, respectively; the corresponding bent curvature angle was 2.51 ± 2.40, 2.13 ± 1.65, and 2.09 ± 0.98 degrees, respectively; and the bent curvature radius was 1483 ± 818, 2329 ± 1293, and 3710 ± 1957 mm, respectively.

CONCLUSIONS

There is a mismatch between the current short straight PFNA-II and the anterior bow of the femur in the Chinese population. In light of the documented complications and technical problems related to this mismatch, further modifications with an anterior bow are proposed.