title: Biomechanical properties of orthogonal plate configuration versus parallel plate configuration using the same locking plate system for intra-articular distal humeral fractures under radial or ulnar column axial load.
abstract: BACKGROUND
  Previous reports have questioned whether an orthogonal or parallel configuration is superior for distal humeral articular fractures. In previous clinical and biomechanical studies, implant failure of the posterolateral plate has been reported with orthogonal configurations; however, the reason for screw loosening in the posterolateral plate is unclear. The purpose of this study was to evaluate biomechanical properties and to clarify the causes of posterolateral plate loosening using a humeral fracture model under axial compression on the radial or ulnar column separately. And we changed only the plate set up: parallel or orthogonal.
  
  
  METHODS
  We used artificial bone to create an Association for the Study of Internal Fixation type 13-C2.3 intra-articular fracture model with a 1-cm supracondylar gap. We used an anatomically-preshaped distal humerus locking compression plate system (Synthes GmbH, Solothurn, Switzerland). Although this is originally an orthogonal plate system, we designed a mediolateral parallel configuration to use the contralateral medial plate instead of the posterolateral plate in the system. We calculated the stiffness of the radial and ulnar columns and anterior movement of the condylar fragment in the lateral view.
  
  
  RESULTS
  The parallel configuration was superior to the orthogonal configuration regarding the stiffness of the radial column axial compression. There were significant differences between the two configurations regarding anterior movement of the capitellum during axial loading of the radial column.
  
  
  CONCLUSIONS
  The posterolateral plate tended to bend anteriorly under axial compression compared with the medial or lateral plate. We believe that in the orthogonal configuration axial compression induced more anterior displacement of the capitellum than the trochlea, which eventually induced secondary fragment or screw dislocation on the posterolateral plate, or nonunion at the supracondylar level. In the parallel configuration, anterior movement of the capitellum or trochlea was restricted because of the angular stability of the plate and locking screws in the condyle.
  
  
  CONCLUSIONS
  The posterolateral plate tended to bend anteriorly under axial compression of the radial column in the orthogonal configuration, which led to secondary displacement of the posterolateral plate and eventual screw loosening.
authors: Department of Orthopedic Surgery, Juntendo University Urayasu Hospital, Chiba, Japan.
authors: Toshiya
authors: T
authors: Kudo
authors: Department of Orthopedic Surgery, Juntendo University Urayasu Hospital, Chiba, Japan. Electronic address: hara.a@juntendo-urayasu.jp.
authors: Akira
authors: A
authors: Hara
authors: Department of Mechanical Engineering, Juntendo University Shizuoka Hospital, Shizuoka, Japan.
authors: Hideaki
authors: H
authors: Iwase
authors: Department of Orthopedic Surgery, Juntendo University Urayasu Hospital, Chiba, Japan.
authors: Satoshi
authors: S
authors: Ichihara
authors: Department of Orthopedic Surgery, Juntendo University, Tokyo, Japan.
authors: Masashi
authors: M
authors: Nagao
authors: Department of Orthopedic Surgery, Juntendo University Urayasu Hospital, Chiba, Japan.
authors: Yuichiro
authors: Y
authors: Maruyama
authors: Department of Orthopedic Surgery, Juntendo University, Tokyo, Japan.
authors: Kazuo
authors: K
authors: Kaneko
mesh_terms: D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D004551:Elbow Joint / Q000503:physiopathology*; D005593:Fracture Fixation, Internal; D006801:Humans; D006810:Humeral Fractures / Q000503:physiopathology*; D057072:Intra-Articular Fractures / Q000503:physiopathology*; D008422:Materials Testing; D008953:Models, Anatomic; D013314:Stress, Mechanical
keywords: Artificial bone; Comminuted intra-articular distal humerus fracture; Distal humeral plate; Radial column; Ulnar column