Objectives

We aimed to further evaluate the biomechanical characteristics of two locking screws versus three standard bicortical screws in synthetic models of normal and osteoporotic bone.

Aims: Loss of distal þxation occurs with this the blade plate, especially in the setting of a very distal femur fracture and/or in osteoporotic bone. The LISS (Less Invasive Stabilization System) provides a þxation construct for supracondylar/intracondylar distal femoral fractures, with features including submuscular þxation and percutaneous placement of self-drilling unicortical þxed angled screws. The purpose of this study was to evaluate the biomechanical characteristics of the LISS versus the angled blade plate in an osteoporotic human cadaveric femoral model. Methods: Twenty-four matched pairs of fresh frozen human femora were utilized. Three groups of eight pairs each were tested to failure in one-time axial loading, one-time torsional loading and cyclical axial loading. A fracture model was created to simulate an AO 33–A3 fracture. Results: The average axial load to failure was 34% higher for the LISS compared with the blade plate (p = 0.03). All 8 LISS constructs failed by plastic deformation of the implant only, while 3/8 blade plates failed by loss of distal þxation. The blade plate had a 47% higher torsional moment to failure (p= 0.05). Permanent deformation after cyclical axial loading was signiþcantly lower for the LISS (p = 0.01). Conclusions: Of signiþcant interest is potential loss of þxation in catastrophic loading of a supracondylar femoral fracture þxation construct. In conclusion, biomechanical testing of the LISS demonstrates in comparison to the blade plate: (1) superior þxation of the distal femoral Ç block È in axial loading, (2) lower torsional strength, and (3) less permanent deformation in cyclical axial loading. The results further indicate that one-time axial loading of the LISS þxation construct will ultimately result in þxator plastic deformation, rather than screw pullout.