Biomechanical effect of the configuration of screw hole style on locking plate fixation in proximal humerus fracture with a simulated gap: A finite element analysis

Ya-Kui Zhang; Hung-Wen Wei; Kang-Ping Lin; Wen-Chuan Chen; Cheng-Lun Tsai; Kun-Jhih Lin

doi:10.1016/j.injury.2016.02.028

Biomechanical effect of the configuration of screw hole style on locking plate fixation in proximal humerus fracture with a simulated gap: A finite element analysis

Injury. 2016 Jun;47(6):1191-5. doi: 10.1016/j.injury.2016.02.028. Epub 2016 Mar 7.

Authors

Ya-Kui Zhang¹, Hung-Wen Wei², Kang-Ping Lin³, Wen-Chuan Chen⁴, Cheng-Lun Tsai⁵, Kun-Jhih Lin⁶

Affiliations

¹ Department of Orthopaedics Tongzhou Luhe Teaching Hospital, Capital Medical University, Beijing, China.
² Department of Physical Therapy and Assistive Technology, National Yang-Ming University, Taipei, Taiwan; Translation Technology Center for Medical Device, Chung Yuan Christian University, Taoyuan, Taiwan.
³ Department of Electrical Engineering, Chung Yuan Christian University, Taoyuan, Taiwan; Translation Technology Center for Medical Device, Chung Yuan Christian University, Taoyuan, Taiwan.
⁴ Translation Technology Center for Medical Device, Chung Yuan Christian University, Taoyuan, Taiwan.
⁵ Department of Biomedical Engineering, Chung Yuan Christian University, Taoyuan, Taiwan; Translation Technology Center for Medical Device, Chung Yuan Christian University, Taoyuan, Taiwan.
⁶ Department of Electrical Engineering, Chung Yuan Christian University, Taoyuan, Taiwan; Translation Technology Center for Medical Device, Chung Yuan Christian University, Taoyuan, Taiwan. Electronic address: kjlin2009@gmail.com.

PMID: 26975793
DOI: 10.1016/j.injury.2016.02.028

Abstract

Background: Locking plate fixation for proximal humeral fractures is a commonly used device. Recently, plate breakages were continuously reported that the implants all have a mixture of holes allowing placement of both locking and non-locking screws (so-called combi plates). In commercialized proximal humeral plates, there still are two screw hole styles included "locking and dynamic holes separated" and "locking hole only" configurations. It is important to understand the biomechanical effect of different screw hole style on the stress distribution in bone plate.

Methods: Finite element method was employed to conduct a computational investigation. Three proximal humeral plate models with different screw hole configurations were reconstructed depended upon an identical commercialized implant. A three-dimensional model of a humerus was created using process of thresholding based on the grayscale values of the CT scanning of an intact humerus. A "virtual" subcapital osteotomy was performed. Simulations were performed under an increasing axial load. The von Mises stresses around the screw holes of the plate shaft, the construct stiffness and the directional displacement within the fracture gap were calculated for comparison.

Results: The mean value of the peak von Mises stresses around the screw holes in the plate shaft was the highest for combi hole design while it was smallest for the locking and dynamic holes separated design. The stiffness of the plate-bone construct was 15% higher in the locking screw only design (132.6N/mm) compared with the combi design (115.0N/mm), and it was 4% higher than the combi design for the locking and dynamic holes separated design (119.5N/mm). The displacement within the fracture gap was greatest in the combi hole design, whereas it was smallest for the locking hole only design.

Conclusions: The computed results provide a possible explanation for the breakages of combi plates revealed in clinical reports. The locking and dynamic holes separated design may be a better configuration to reduce the risk of plate fracture.

Keywords: Bone fracture; Combi-hole; Finite element method; Plate breakage; Stress concentration.

MeSH terms

Biomechanical Phenomena
Bone Plates
Bone Screws
Finite Element Analysis
Fracture Fixation, Internal / instrumentation
Fracture Fixation, Internal / methods*
Humans
Humerus / anatomy & histology
Humerus / surgery*
Imaging, Three-Dimensional*
Male
Materials Testing / methods*
Middle Aged
Shoulder Fractures / diagnostic imaging
Shoulder Fractures / pathology
Shoulder Fractures / surgery*
Stress, Mechanical
Tomography, X-Ray Computed