Biomechanical analysis of crossed pinning construct in supracondylar fracture of humerus : does the point of crossing matter?

Abstract

This is the first biomechanical study that compare the stability of various location of crossing point in crossed pinning K-wiring construct for the treatment of paediatric Supracondylar Humerus Fracture (SCHF). The main aim of this study was to compare the stability of various location of crossing point in crossed pinning K-wiring construct. The other aim of this study is to compare the biomechanical stability between crossed pinning K-wire construct with the three-lateral divergent K-wiring construct. Thirty synthetic humeri were osteotomized at mid olecranon fossa, anatomically reduced and pinned using two 1.6 mm Kirschner wires in five different constructs namely centre crossing point, medial crossing point, lateral crossing point, superior crossing point and lateral divergent K-wire construct. Six samples were prepared for each construct and were tested for extension, flexion, valgus, varus, internal rotation and external rotation forces. For crossed pinning K-wire construct, centre crossing point were noted to be the stiffest construct both in linear forces and rotational forces (48.6960 N/mm; 0.385 Nmm/degree) compared to lateral crossing point (41.335 N/mm; 0.380 Nmm/degree), superior crossing point (43.5952; 0.380 Nmm/degree) and medial crossing point (47.6235 N/mm ; 0.265 Nmm/degree). Despite centre crossing point is verified to be the stiffest construct, lateral crossing point and superior crossing point showed no significant statistical difference when compare to centre crossing point both in linear force and rotational force. In the other hand, medial crossing point showed no statistically significant difference in term of linear force, however showed statistically significant difference in term of rotational force when compare to centre crossing point. Comparison between crossed pinning K-wire construct and lateral divergent had showed that crossed pinning construct was noted to be more stable compared to lateral divergent construct both in linear and rotational force. There was no statistically significant difference in rotational stability and statistically significance difference in linear stability when comparing between these two constructs. From this analysis, we can recommend that, if the crossed pinning construct was chosen to be the treatment option for the treatment of SCHF, the surgeon should aim for centre crossing point as it is the most stable construct. However, if lateral crossing point and superior crossing point are obtained during the initial attempt of fixation, we can recommend that the fixation can be accepted, and no revision of the K-wire is required as the stability of these construct were comparable and no significant difference when compare to the centre crossing point. Another recommendation that can be derived from this study is for the treating surgeon to try to avoid medial crossing point as it is significantly less stable in term of rotational force when compare to centre crossing point.