Does bone compaction around the helical blade of a proximal femoral nail anti-rotation (PFNA) decrease the risk of cut-out?: A subject-specific computational study

Abstract

Objectives: Because of the contradictory body of evidence related to the potential benefits of helical blades in trochanteric fracture fixation, we studied the effect of bone compaction resulting from the insertion of a proximal femoral nail anti-rotation (PFNA).

Methods: We developed a subject-specific computational model of a trochanteric fracture (31-A2 in the AO classification) with lack of medial support and varied the bone density to account for variability in bone properties among hip fracture patients.

Results: We show that for a bone density corresponding to 100% of the bone density of the cadaveric femur, there does not seem to be any advantage in using a PFNA with respect to the risk of blade cut-out. On the other hand, in a more osteoporotic femoral head characterised by a density corresponding to 75% of the initial bone density, local bone compaction around the helical blade provides additional bone purchase, thereby decreasing the risk of cut-out, as quantified by the volume of bone susceptible to yielding.

Conclusions: Our findings indicate benefits of using a PFNA over an intramedullary nail with a conventional lag screw and suggest that any clinical trial reporting surgical outcomes regarding the use of helical blades should include a measure of the femoral head bone density as a covariable.

Keywords: Cadaveric bone; Cut-out; Finite element analysis; Osteosynthesis; PFNA; Trochanteric fracture.

Fig. 1

Diagram showing the calculation of the intrusion distance of the medial fragment into the fracture complex: defined as the ratio of the length of the medial wedge in the anteroposterior view (AB) to the length of the fracture line (AC) and expressed as a percentage ([AB/AC] × 100).

Fig. 2

Diagrams showing the minimum (compressive) principal strains plotted in percent with a yield strain cut-off value of -0.9%. Grey regions have strains below -0.9% and are at higher risk of being involved in blade cut-out.

Fig. 3

Bar chart showing the volume of bone susceptible to yielding calculated by using a yield strain cut-off value of -0.9% for minimum principal strains. The higher this volume, the greater the risk of blade cut-out.