A biomechanical evaluation of proximal femoral nail antirotation with respect to helical blade position in femoral head: A cadaveric study

Abstract

Objective: Despite new developments in the management of osteoporotic fractures, complications like screw cutout are still found in the fixation of proximal femur fractures even with biomechanically proven better implants like proximal femoral nail antirotation (PFNA). The purpose of this cadaveric study was to investigate the biomechanical stability of this device in relation to two common positions (center-center and inferior-center) of the helical blade in the femoral head in unstable trochanteric fractures.

Materials and methods: Eight pairs of human cadaveric femurs were used; in one group [center-center (C-C) group], the helical blade of PFNA was fixed randomly in central position both in anteroposterior and lateral view, whereas in the other group it was fixed in inferior one-third position in anteroposterior and in central position in lateral view [inferior-center (I-C) group]. Unstable intertrochanteric fracture was created and each specimen was loaded cyclically till load to failure

Results: Angular and rotational displacements were significantly higher within the C-C group compared to the I-C group in both unloaded and loaded condition. Loading to failure was higher in the I-C group compared to the C-C group. No statistical significance was found for this parameter. Correlations between tip apex distance, cyclic loading which lead to femoral head displacement, and ultimate load to failure showed a significant positive relationship.

Conclusion: The I-C group was superior to the C-C group and provided better biomechanical stability for angular and rotational displacement. This study would be a stimulus for further experimental studies with larger number specimens and complex loading protocols at multicentres.

Keywords: Biomechanical study; PFNA; cadaveric study; helical blade position; unstable trochanteric fracture.

Figure 1

Osteotomy of cadaveric proximal femur as proposed by Krischak et al. showing an unstable trochanteric fracture in (a) anterior view and (b) posterior view

Figure 2

Anteroposterior and lateral radiograph of PFNA fixation in I-C group (a and b) and C-C group (c and d), respectively

Figure 3

Biomechanical experimental model for three-dimensional motion analysis of the femoral head: (a) Attachment of metal markers and fixation of jig for the experimental model and (b) establishment of experimental environment for stereophotogrammetry

Figure 4

Flow diagram for the assessment of three-dimensional motion of the femoral head using stereophotogrammetry