Pediatric supracondylar humerus fractures: effect of bone-implant interface conditions on fracture stability
Ron Lamdan1, Meir Liebergall2, Amit Gefen3
1Pediatric Orthopedics, Hadassah University Hospital, P.O.B. 12000, Jerusalem, Israel.
Insights
For pediatric humerus fractures, crossed Kirschner wires (KWs) offer better stability than divergent KWs if the bone-wire bond weakens. Adequate bonding ensures stability with either configuration.
Area of Science:
- Orthopedic surgery
- Biomechanical engineering
- Pediatric orthopedics
Background:
- Pediatric supra-condylar humerus fractures (SCHFs) are commonly treated with Kirschner wires (KWs).
- Failure modes and the impact of bone-KW interface conditions on fracture stability are not well understood.
- The effect of reduced bone-KW friction on KW configurations and fracture stability has not been previously investigated.
Purpose of the Study:
- To assess the influence of bone-KW friction on the mechanical stability of pediatric SCHFs post-fixation.
- To develop clinical recommendations for optimal KW configurations based on varying friction conditions.
Main Methods:
- A finite element model simulating a fixated pediatric SCHF was utilized.
- Simulations evaluated stability for divergent and crossed KW configurations under varied friction levels.
- Bone-KW friction conditions were systematically altered to mimic different scenarios.
Main Results:
- Crossed KW configurations demonstrated superior stability over divergent KWs when bone-KW bonding was compromised.
- Sufficient fracture stability was achieved with both crossed and divergent KW configurations under adequate bone-KW bonding conditions.
- Finite element analysis quantified the mechanical performance differences between configurations.
Conclusions:
- The divergent KW configuration provides adequate mechanical stability for SCHFs under normal bone-implant interface conditions.
- In cases of suboptimal bone-KW bonding (e.g., after re-drilling), incorporating a medial KW with crossed configurations enhances stability.
- Clinical guidelines suggest considering crossed KWs when fixation integrity may be compromised, balancing stability against potential ulnar nerve risks.
Background:
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.
Purpose:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
