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Lateral closing wedge osteotomy is a treatment for Kienbock’s disease. It is one of the most frequently used treatment options, which has been reported with relatively good long-term results. However, the results about the treatment are still controversial in some literatures and some key mechanisms are still not clear. The objective of the cur-rent study was to study the biomedical mechanism of the treatment. A finite element model was developed based on the geometry of carpal bones. Various situations in-cluding inclination angle changes by cutting the radial with 0?, 5?, 10? and 15? osteot-omy angles were studied. The effectiveness of the treatment was also studied for the carpal structure with abnormal positions of the lunate bone. The results show that the effectiveness of the stress reduction with the angle depends on many situations such as the initial morphology of the carpal structure.

The lunate bone is a carpal bone in the human hand. Kienbock’s disease is the osteonecrosis of the lunate bone [

As for the treatment of the Kienbock’s disease, many surgical options have been reported including ulna lengthening or radial shortening, capitate shortening, lunate resection, and radial wedge osteotomy [

Based on the literature review, it seems that there is no consistent conclusion on the effectiveness of the osteotomy treatment and on the optimum angle of the wedge that should be cut on the radial bone. Therefore, the objective of the current work is to study how the stress distribution changes on the lunate bone and the surrounding cartilages with the radial inclination. Finite element models were developed in the study to demonstrate how the stress distributions were affected by various factors.

To obtain the full field solution of the stress distribution of the lunate bone, two-di- mensional finite element models were developed using software ANSYS [

To simplify the extremely complicated carpal joint structure, only the scaphoid, lunate, ulna and radius bones were used in the model and the lunate bone contacts with radius and ulna bones with cartilages. It was believed the abnormal radial inclination, uncovering of the lunate, and the relative position of the lunate could be the factors that lead to the disease [

For all the models, cartilages were assumed to be bonded between the contact surfaces of the four bones. Fixed boundary conditions were applied at the bottom of radius and ulna bones to constrain the model. Forces of 40N and 60N were applied in the downward direction on the top of the scaphoid and lunate bone, respectively. The lunate, radius, ulna, and scaphoid bones were simulated as homogenous elastic cancellous material with Young’s modulus of 18,000 MPa and Poisson’s ratio of 0.2 [

As the minimum principal stress detonates the maximum value of the compression stress under the compression load in the models, the minimum principal stress was compared for model 1 with osteotomy (wedge cut) angles of 0˚ (control model), 5˚, 10˚ and 15˚. The stress distributions of model 1 are shown in Figures 4(a)-(d) and for model 2 Figures 5(a)-(d). The stress distributions of models 3 are shown in

While it can be seen that stress distribution changes with different osteotomy angles and shift distance in Figures 4-6, the stress values were compared for the stresses at different locations to demonstrate the effect.

Compared to model 1 which is for the carpal structure of a person without the disease, the stress values of model 2 at corresponding points are much higher than the control model. For point 3 in model 2, before the surgery, the stress is 139.7% of the control, which decreases with the angle. They are 125.6% at 5˚, 104.7% at 10˚, and 105.8% at 15˚.

That is, the stress reaches minimum at 10˚. For point 5 in model 2, the stress value keeps decreasing with the angle from 120.8% at 0˚ to 104.9% at 15˚. As the lunate bone shifts 1.5 mm, the stress values are much higher than the control one for the two points. The 187.9% and 140.6% of the control at point 3 and 5, respectively, as the lunate shift for 1.5 mm. While as it shifts further, the value become smaller, but most values are still higher than the control.

As stated in [

The radial closing wedge osteotomy surgery intends to reduce the load on lunate. The

clinical results showed the treatment was effective [

The current study still made the effort to resolve the debate and looked into the biomedical mechanism of the treatment. The results showed that the effectiveness of the stress reduction with the angle depends on many situations such as the initial morphology of the carpal structure. For example, in model 1, the stress changes with the angle, but not very significant. However, if started with the initial position of the lunate in model 2, the stress is much higher than the control, which is 139.7% of the control. The stress value decreases greatly with the angle to 104.7% at 10˚ for point 3. Stress value at point 5 reduces from 120.8% at 0˚ to 104.9%, which is not as significant as point 3. It should be pointed out that in the previous studies [

There are some limitations of the current study that should be mentioned herein. For the material properties of the bone and cartilage, they were assumed to be homogenous elastic. While these properties were obtained from other literatures [

Yang, G., Partridge, K.A., Abdel-Mohti, A., McMullen, A.J. and Shen, H. (2016) Finite Element Analysis of Osteotomy Treatment for Kienbock’s Disease. J. Biomedical Science and Engineering, 9, 161-170. http://dx.doi.org/10.4236/jbise.2016.910B021