A biomechanical evaluation of femoroplasty under simulated fall conditions

Abstract

Objectives: To test the hypotheses that, compared with controls: 1) femoroplasty (the injection of bone cement into the proximal femur in an attempt to prevent fragility fracture) increases the yield and ultimate loads, yield and ultimate energies, and stiffness of the proximal osteoporotic femur in a simulated fall model; and 2) the manner in which the cement distributes in the proximal femur affects the extent to which those mechanical properties are altered.

Methods: In 10 pairs of osteoporotic human cadaveric femora, we injected one femur of each pair with 40 to 50 mL of polymethylmethacrylate bone cement; the noninjected femur served as the control. The filling percentage was calculated in four anatomic regions of the femur: head, neck, trochanter, and subtrochanter. All specimens were biomechanically tested in a configuration that simulated a fall on the greater trochanter. Student t test, linear regression, and multinomial logistic regression statistical analyses were conducted where appropriate with significant difference defined as P < 0.05.

Results: Femoroplasty significantly increased yield load (22.0%), ultimate load (37.3%), yield energy (79.6%), and ultimate energy (154%) relative to matched controls but did not significantly change stiffness (-10.9%). There was a strong (r = 0.7) correlation between yield load and filling percentage in the femoral neck.

Conclusions: This study showed that 1) femoroplasty significantly increased fracture load and energy to fracture when osteoporotic femora were loaded in simulated fall conditions, and 2) cement filling in the femoral neck may have an important role in the extent to which femoroplasty affects mechanical strength of the proximal femur.

FIGURE 1

Representative anteroposterior view of a computed tomography scan slice showing an augmented specimen with bone cement (left) and a control specimen (right).

FIGURE 2

Anteroposterior view of the proximal femur in the 4 designated regions: head (1), neck (2), trochanter (3), and subtrochanter (4).

FIGURE 3

Experimental testing set-up simulating a fall on the greater trochanter using a materials testing machine (MTS Bionix 858 Test System, MTS, Eden Prairie, Minnesota). Specimens were positioned so that the axis of the femoral shaft was rotated 10 degrees below a horizontal plane parallel to the MTS table and the shaft was rotated internally 15 degrees.

FIGURE 4

Representative force-versus-displacement plot used to determine loads and calculate energies. Data shown are yield (a) and ultimate (b) loads for the femoroplasty specimens, and yield (c) and ultimate (d) loads for the control specimens.

FIGURE 5

Anteroposterior view of a computed tomography scan slice showing a subtrochanteric fracture of a femoroplasty specimen (left) and an intertrochanteric fracture in a control specimen (right).