Pediatric supracondylar humerus fractures: effect of bone-implant interface conditions on fracture stability.

Abstract

Closed reduction and percutaneous fixation with Kirschner wires (KWs) is the standard of care of pediatric supra-condylar humerus fractures (SCHFs). Failure modes leading to loss of reduction are not clear and have not been quantified. Multiple factors may weaken the KW-bone interface bonding conditions. To the best of our knowledge, the possible effect of this decrease on different KW configurations and fracture stability has never been studied. To investigate the effect of bone-KW friction conditions on SCHF post-operative mechanical stability and to formulate clinical guidelines for KW configuration under different conditions. Finite element-based model of a fixated SCHF was used to simulate structure stability for two lateral divergent versus crossed lateral and medial KW configurations under varying KW-bone friction conditions. Finite element simulations demonstrated that crossed KWs provide superior stability compared with the divergent configuration when KW-bone bonding is compromised. When KW-bone bonding conditions are adequate, crossed and divergent KW configurations provide similar, sufficient fracture stability. Under normal bone-implant interface conditions, the two diverging lateral KW configuration offers satisfactory mechanical stability and may be the preferred choice of SCHF fixation. When KW-bone bonding is suboptimal, as when one or more of the lateral KWs are re-drilled, addition of a medial KW should be considered in order to improve stability despite risk to ulnar nerve.