Biomechanical study on parallel cannulated compression screw combined with medial buttress plate fixation and F-type cannulated compression screw fixation in Pauwels III femoral neck fracture：A finite element analysis

Abstract

Objectives: Pauwels III fracture is a kind of femoral neck fractures, in which the angle of the fracture line in the coronal plane and the upper edge of the acetabulum is more than 50°. Internal fixation for the treatment of femoral neck fractures is largely performed by cannulated compression screw (CCS), dynamic hip screw, or locking plate. This study aims to compare the biomechanical properties of parallel CCS combined with medial buttress plate fixation and F-type CCS fixation in the treatment of Pauwels III femoral neck fracture by finite element modeling and to determinate the most suitable procedure for such fractures.

Methods: A 52-year-old male volunteer, 176 cm in height and 72 kg in weight, with no history of hip joint, was selected. X-ray and CT examination confirmed that the morphology and bone condition of the right hip of the volunteer were normal. A simulation model of Pauwels III femoral neck fracture was established from the collected CT data of the right proximal femur of the volunteer by the finite element method. Four internal fixations were developed to treat the finite element model: Three CCSs in an inverted triangular parallel configuration combined with medial buttress plate model served as Group A, 2 CCSs in a vertical parallel configuration combined with medial buttress plate model served as Group B, 2 CCSs in a horizontal parallel configuration combined with medial buttress model served as Group C, and the "F" shaped CCS model served as Group D. The distribution of stress, the peak stress, the distribution and maximum of displacement of internal fixations and fracture ends in different models were evaluated.

Results: For Groups A, B, C, and D, the peak stresses on the internal fixation were 362.74, 586.84, 558.25, and 208.66 mPa, respectively, all of which occurred near the fractures and the stress distribution in Group D was the most uniform. The maximum displacements of internal fixations in Groups A, B, C, and D were 0.39, 0.45, 0.44, and 0.41 mm, respectively; the peak stresses on the fracture ends were 70.62, 98.48, 55.84, and 65.39 mPa, respectively, all of which were concentrated on the base of femoral neck and lateral cortex of the femoral shaft, and the stresses of Groups C and D were more evenly distributed than those of Groups A and B. The maximum displacements of fracture ends in Groups A, B, C, and D were 0.44, 0.52, 0.50, and 0.44 mm, respectively.

Conclusions: The biomechanical stability of F-type CCS fixation is similar to that of 3 CCSs in an inverted triangular parallel configuration combined with medial buttress plate, with a better dispersion of stress. F-type CCS fixation may be a well option for the treatment of femoral neck fracture of Pauwels III.

Keywords: cannulated compression screw; femoral neck fractures; finite element analysis; internal fixation of fracture; medial buttress plate.

图1

Mimics软件重建的股骨近端三维模型 Figure 1 Construction of 3D model for proximal femur via Mimics software A: Coronal view of cortical bone; B: Horizontal view of cortical bone; C: Axial view of cortical bone; D: Three-dimensional model of cortical bone; E: Coronal view of trabecular bone; F: Horizontal view of trabecular bone; G: Axial view of trabecular bone; H: Three-dimensional model of trabecular bone.

图2

Geomagic软件精确拟合后的股骨近端曲面模型 Figure 2 Surface model of proximal femur via Geomagic software A: Model of cortical bone; B: Model of trabecular bone; C: Model of cortical bone and cancellous bone assembled.

图3

4种不同内植物固定Pauwels III型股骨颈骨折的几何建模 Figure 3 Construction of geometric models for 4 fixation methods for Pauwels III femoral neck fracture A and B: Front view (A) and top view (B) of three CCS in an inverted triangular parallel configuration combined with medial buttress plate model (Group A); C and D: Front view (C) and top view (D) of two CCS in a vertical parallel configuration combined with medial buttress plate model (Group B); E and F: Front view (E) and top view (F) of two CCS in a horizontal parallel configuration combined with medial buttress model (Group C); G and H: Front view (G) and top view (H) of “F” shaped CCS model (Group D).

图4

模型中的接触设置 Figure 4 Contact property of model Contact properties between cortical bone and trabecular bone (A), CCS and cortical bone (B), CCS and trabecular bone (C), and cortical screw and third tube plate (D) were simulated as bonded.

图5

边界条件及载荷的设置 Figure 5 Boundary conditions and loading force settings A: Freedom of all nodes at the distal end of the femur was set to zero. B: A preload of 600 N force was applied vertically on the head of femur.

图6

4种不同固定方式治疗Pauwels III型股骨颈骨折模型中内植物的应力分布 Figure 6 Stress distribution of fixators in 4 internal fixation models for Pauwels III femoral neck fracture A: Inverted triangular parallel CCS + medial plate models; B: Vertical parallel CCS + medial plate models; C: Horizontal parallel CCS + medial plate models; D: F-type CCS models

图7

4种不同固定方式治疗Pauwels III型股骨颈骨折模型中内植物的位移分布 Figure 7 Displacement distribution cloud charts of fixators in 4 internal fixation models for Pauwels III femoral neck fracture A: Inverted triangular parallel CCS + medial plate models; B: Vertical parallel CCS + medial plate models; C: Horizontal parallel CCS + medial plate models; D: F-type CCS models.

图8

4种不同内植物固定Pauwels III型股骨颈骨折模型中骨折端的应力分布 Figure 8 Stress distribution of fracture end in 4 internal fixation models for femoral neck fracture A and B: Stress distribution of femoral head (A) and femoral shaft (B) in inverted triangular parallel CCS + medial plate model; C and D: Stress distribution of femoral head (C) and femoral shaft (D) in vertical parallel CCS + medial plate model; E and F: Stress distribution of femoral head (E) and femoral shaft (F) in horizontal parallel CCS + medial plate model; G and H: Stress distribution of femoral head (G) and femoral shaft (H) in F-type CCS model.

图9

4种不同内植物固定Pauwels III型股骨颈骨折模型中骨折端的位移分布 Figure 9 Displacement distribution cloud charts of femurs in 4 internal fixation models for femoral neck fracture A and B: Displacement distribution offemoral head (A) and femoral shaft (B) in inverted triangular parallel CCS + medial plate model; C and D: Displacement distribution of femoral head (C) and femoral shaft (D) in vertical parallel CCS + medial plate model; E and F: Displacement distribution of femoral head (E) and femoral shaft (F) in horizontal parallel CCS + medial plate model; G and H: Displacement distribution of femoral head (G) and femoral shaft (H) in F-type CCS model.