The central collinear start point in femoral reconstruction nailing decreases ultimate failure load of the femoral neck: a cadaveric biomechanics study

Abstract

Objectives: To compare the ultimate and relative failure loads of the femoral neck after insertion of a reconstruction nail through either the central collinear start point or the piriformis start point.

Methods: Twelve bilateral cadaveric femur pairs were assigned to either the central collinear (CC) group or the piriformis fossa (PF) group with an effort to match age distribution, sex, and bone mineral density between the 2 groups. All left femora were used as the surgical specimen, and all right femora were used as their respective intact controls. After insertion of a femoral reconstruction nail through the assigned starting point, each surgical femur underwent axial loading in line with the mechanical axis on a servohydraulic mechanical testing system until the ultimate failure load at the femoral neck was recorded.

Results: The ratio of the surgical femora ultimate failure load to the control failure load was 0.628 (SD = 0.072) for the CC group and 0.895 (SD = 0.064) for the PF group. A linear mixed effects model that used control versus CC versus PF group as the main effect and bone mineral density as a covariate yielded significant differences in ultimate failure load between intact controls and the CC surgical femora (P < 0.001) and between CC and PF surgical femora (P = 0.002). However, the model found no significant differences between the intact controls and the PF surgical femora (P = 0.597).

Conclusions: The central collinear start point reduces the ultimate failure load of the femoral neck compared with the intact femur and the piriformis fossa start point despite testing the instrumented femora with a femoral reconstruction nail including 2 femoral neck screws in place. However, there is no significant decrease in ultimate failure load with the piriformis fossa start point compared with the intact femur.

Keywords: biomechanics; central collinear; femoral reconstruction nailing; piriformis fossa.

Figure 1.

Comparison of (A) piriformis fossa versus (B) central collinear start points with inserted reconstruction nail.

Figure 2.

Anterior-posterior and lateral views of the proximal femur with a reconstruction nail placed from the (A) piriformis fossa start point and (B) the central collinear start point.

Figure 3.

Setup configuration of a surgical femur on the servohydraulic mechanical testing system.

Figure 4.

Relative failure load of central collinear and piriformis fossa groups compared with intact controls.

Figure 5.

Oblique subcapital/transcervical fracture orientation of a control femur after failure load testing.

Figure 6.

Single type of failure noted with central collinear start points: basicervical through the start point.

Figure 7.

Two types of failures noted with piriformis fossa start points: (A) basicervical through the start point and (B) oblique subcapital/transcervical not involving the start point.