Supracondylar humerus fracture (SCHF) is one of the commonest elbow fractures in children. It is common injury for children with age from four to fourteen. In current study, the finite element technique is used to evaluate two techniques, namely, parallel and crossed K-wire fixation for treatment of SCHF, using K-wire fixation.
The humerus bone is the upper arm bone that connects the shoulder, by articulating the humeral head with the glenoid of the scapula, to the elbow by articulating the testal humerus with the ulna and radius, as shown in Figure
Humerus bone in human arm.
Accurate reduction and stable fixation are needed to avoid posthealing complication, namely, deformity and limitations of movements. These fractures most often require surgical treatment unless the bones are held in proper position. Sometimes surgeons want to know which alternative they should give preference, for the benefits of the patients. Fixation of unstable SCHF in children by two K-wires is the treatment of the choice by many surgeons (Figure
Crossing K-wires fixation treatment techniques adopted by orthopedic surgeons for distal humerus fracture treatment, (a) anterior-posterior view; (b) lateral view.
These K-wires can be parallel from lateral side or crossing from medial and lateral sides.
In present work, surgeon’s treatment of SCHF using K-wire fixation (distal humerus type) is modeled, analyzed, and evaluated.
The research role is to gather information from CT scan and X-ray developed in KKU hospital. Based on these obtained X-ray and CT scan for particular patient, a CAD solid model can be developed. The developed CAD solid model is to be coupled with the finite-element analysis to study the strength of different injury treatments adopted by orthopedic surgeons that suit that particular patient.
The solid model and finite element models were generated using the
In the beginning, a data file of the FE model was generated using
The X-ray and CT scan were obtained from KKU Hospital for humerus bone. The X-ray was obtained for two perpendicular projections. The X-ray image is imported as rusted image to AutoCAD program to measure the outer dimensions and to obtain the 2D geometry of CT scan at different levels. Next, the 2D drawing is imported to GID program and joined to complete the 3D solid model.
The solid model mainly consists of three main parts or three volumes, see Figures
Solid model of humerus bone fracture treatment with parallel K-wires.
Solid model of humerus bone fracture treatment with crossed K-wires.
The mid-part of the solid model is divided into two main parts: the external (cortical bone) part with wall thickness of 2 mm which is the harder and high strength bone, and internal (Cancellous bone) which has lower strength and hardness compared to cortical bone, see Figure
Main parts of mid-solid model of humerus bone.
Constrain conditions along three directions are assigned on the top surfaces of humerus bone as shown in Figure
Assigned material properties on the developed solid model.
Group | Part | Material | Young modulus (MPa) | Poisson's ratio |
---|---|---|---|---|
1 | Top bone | Cortical bone | 0.29 | |
2 | Bottom bone | Cortical bone | 0.29 | |
3 | Mid-external bone | Cortical bone | 0.29 | |
4 | Mid-internal bone | Cancellous bone | 0.29 | |
5 | K-wire 4 mm diameter | Nickel-chrome alloy | 0.29 |
Assigned constrain and loading conditions on the developed solid models.
Two main finite element meshes were generated for modeling parallel K-wire fixation treatment model and the other for crossing K-wire fixation model. The finite element (FE) meshes were generated using 4-node tetrahedral elements, see Figure
Number of nodes and elements used to generate the two finite element meshes.
Model | Number of nodes | Number of elements |
---|---|---|
Parallel K-wire fixation treatment model | 4907 | 21387 |
Crossing K-wire fixation treatment model | 5660 | 25044 |
Generated finite element meshes for parallel and crossed K-wire fixation treatment models.
Furthermore, as shown in Figure
Four wire frame models to model the two types fracture areas.
Both peak normal principal stresses and Von-Misses stresses are reported at the two selected crack areas, see Figures
Predicted normal principal stress contours
Predicted normal principal stress contours
Summary of the FE results for top and bottom crack positions are shown in Tables
Summary of FE results for top crack area.
FE Results for different loading conditions | ||||||
Lateral | Lateral | Lateral | ||||
Parallel K-wire fixation | Crossing K-wire fixation | Parallel K-wire fixation | Crossing K-wire fixation | Parallel K-wire fixation | Crossing K-wire fixation | |
2.54 | 0.26 | 1.87 | 1.21 | 2.04 | 1.44 | |
0.71 | −0.001 | −0.72 | −0.46 | 0.41 | 0.06 | |
−0.17 | −0.74 | 0.87 | −0.67 | 0.1 | −0.09 | |
Summery of FE results for bottom crack area.
Results for different loading conditions | ||||||
Lateral | Lateral | Lateral | ||||
Parallel K-wire fixation | Crossing K-wire fixation | Parallel K-wire fixation | Crossing K-wire fixation | Parallel K-wire fixation | Crossing K-wire fixation | |
1.28 | 0.44 | 0.81 | 1.95 | 0.03 | 2.68 | |
0.33 | 0.04 | −0.03 | 0.30 | −0.25 | 2.12 | |
−0.86 | −1.28 | −0.77 | −0.35 | −0.87 | −5.23 | |
Predicted peak Von-Misses stresses for the three loading conditions for parallel and crossing K-wire fixation models, at top crack position.
Predicted peak Von-Misses stresses for the three loading conditions of parallel and crossing K-wire fixation techniques at the bottom crack position.
Figure
On the other hand, Figure
There are two types of treatment techniques commonly used for supracondylar humerus fracture in children. These treatments cover inserting crossing two K-wires or parallel key-wires fixation techniques. The present work showed that crossing K-wire fixation technique is beneficial for top fracture position, while parallel K-wire fixation technique is beneficial for bottom fracture position.
The authors would like to acknowledge King Abdulaziz City for Science and Technology for the financial support of the project At-28-2.