Optimal parameters and Biomechanical analysis of the lightbulb technique for osteonecrosis of the femoral head: a finite element analysis

Abstract

Background: The lightbulb technique (LBT) is a common surgical procedure for treating peri-collapse osteonecrosis of the femoral head (ONFH). However, the drilling parameters and biomechanics of the technique have not been analyzed. The aim of this study was to optimize the biomechanical stability of the LBT by finite element (FE) analysis to guide intraoperative and postoperative schemes.

Methods: FE models were established based on computed tomography images of a healthy adult, including three different degrees of necrotic lesion (60°, 100°, 115°), drilling locations (points C and L) and diameters (1.0 cm, 1.5 cm). The stress of the drilling entrance area, superior and inferior edges of the femoral neck, and bone flap was evaluated under three different loads at 0.5 times body weight (0.5 BW, standing on two feet), 2.75 BW (standing on one foot), and 4 BW (walking with the middle foot on the ground).

Results: The stress of the superior and inferior edges of femoral neck, entrance, and bone flap increased as drilling diameter increased. The maximum Von Mises stress of proximal femur does not exceed its yield strength with diameter of 1.0 cm, except for diameter of 1.5 cm. The stress of entrance area and bone flap cortex at point L were higher than those at point C with same diameter. Moreover, the stress of femoral neck and entrance area decreased as the range of lesions increased, except for bone flap cortex. Furthermore, the maximum Von Mises stress of proximal femur did not exceed its yield strength with patients standing on one or both feet and walking process (4BW) with drilling diameter of 1.0 cm at points C or L after surgery, except for diameter of 1.5 cm. Meanwhile, the angles reaching to the coronal plane and transverse plane of weight-bearing area through point L with diameter of 1.0 cm were smaller than those through point C.

Conclusions: The optimal parameters of LBT can be selected with a diameter of 1.0 cm at point L. Patients can load partial weight to stimulate the healing of the necrotic area after surgery, but avoid beyond middle foot weight during walking.

Keywords: Finite element analysis; Hip preserving; Lightbulb technique; Optimal parameters; Osteonecrosis of femoral head.

Fig. 1

Drilling entrance of anterior femoral head-neck junction (The anterior midpoint of the femoral head-neck junction was defined as central point (point C), and the its proximal 5 mm was defined as lateral point (point L))

Fig. 2

Construction of lightbulb technique models with different lesions, diameters, and entrance (Note: Red line was the width of head-neck junction, and its center was the entrance to point C, and its proximal 5 mm was defined as point L. Yellow, red, and green part were filled by cancellous bone, cortical bone of the flap, cancellous bone of the flap, respectively)

Fig. 3

The model of osteonecrosis of the femoral head using finite element analysis. (a) Mesh of the femur; (b) Boundary condition and force load of femur models; (c) Stress distribution of femur and interest points of femoral neck

Fig. 4

Maximum Von Mises stress of entrance area in different models under 4BW load

Fig. 5

Maximum Von Mises stress of bone flap cortex in different models under 4BW load

Fig. 6

Von Mises stresses of the femoral neck. (a) Von Mises stresses of each point on superior and inferior edges of the femoral neck; (b) Comparison of the mean von Mises stresses in different models under 4BW load

Fig. 7

Maximum Von Mises stress values of the femur under three different loads

Fig. 8

The angles reaching to the weight-bearing area of femoral head necrosis through points C (a) and L (b); (c) Comparison of the coronal and transverse plane angles through points C and L (Note: The coronal angle was defined as between the drilling channel and the midline of the femoral neck in the coronal plane. The transverse angle was defined as between the drilling channel and horizontal plane)