Purpose: This study examines the structural performance of different devices for the fixation of supracondylar femoral ‘T’-type intra-articular fractures.
Methods: A finite element model was developed to examine three commonly used devices for fixation of ‘T’-type unstable fractures of the distal femur:-
a retrograde distal femoral nail with condylar bolts and multi-planar locking screws,
a retrograde nail with two parallel distal screws, and
a dynamic condylar screw and plate construct.
The distal femoral geometry was been taken from the BEL repository. The bone was aligned with the mechanical axis and a compressive load of 2000N and separately a torsion load of 10Nm were applied. A fracture was introduced by removing a transverse 15mm slice of material and a saggital slice of 1mm thickness.
The FE model examined whether any of the constructs was markedly stiffer than any other.
Results: Both intra-medullary nail constructs were stiffer than the DCS, with the nail with condylar bolts and multi-planar screws being stiffer than the nail with only two parallel distal locking screws. The nail with condylar bolts did, however, produce significant levels of stress within the bone before any axial load was applied – particularly in the region adjacent to the end washers. Under torsion, the nail constructs were always more effective than the side plate construct.
Conclusions: This FE model demonstrates that fixation of supracondylar femoral ‘T’-type fractures is mechanically superior with retrograde nails rather than DCS constructs. Fixation with a retrograde nail with condylar bolts plus multiplanar screws gives the stiffest fixation. High stresses are seen around the condylar bolts, but if the bone quality is adequate then the additional stiffness achieved is significant. These results support the clinical use of intra-medullary nails with compression bolts and multi-planar screws for the fixation of this type of fracture.
