Abstract
Introduction
The most common treatment options for fixation of osteoporotic distal femur fractures are retrograde nails and locking plates. There are proponents of more elastic titanium plates as well as more rigid steel plates; No clear superiority of one over the other has been established. We aimed to evaluate the mechanical differences between stainless steel and titanium locking plates in the fixation of distal femur fractures in osteoporotic bone. We hypothesized that due to its higher elasticity titanium locking plates can absorb more energy and are therefore less likely to “cut” into the bone compared to stainless steel locking plates resulting in improved metaphyseal osteoporotic fracture fixation.
Methods
We used eight matched pairs of osteoporotic fresh-frozen human cadaveric femurs (age >70 years, all female). Within each pair we randomized one femur to be fitted with a Less Invasive Stabilization System (LISS-Titanium locking plate) and one with a Distal Locking Condylar Plate (DLCP-Stainless steel locking plate).
A fracture model simulating an AO 33-A3 fracture was created (extraarticular comminuted fracture) and specimens were subsequently subjected to step-wise cyclic axial loading to failure. We used an advanced three dimensional tracking system (Polhemus Fastrak) to monitor the movement of the distal fragment relative to the real time distal plate position allowing us to evaluate distal implant cut-out.
Results
During cyclic testing, seven of the eight pairs of matched femurs, the DLCP failed before the LISS plate (p=0.03). All constructs were able to withstand cyclical loading up to 800N. The overall plastic deformation as measured by the displacement of the Instron crosshead experienced by the titanium plate constructs was significantly lower compared to the stainless steel plate construct: The plastic deformation of the LISS plates was 39% lower compared to the Locking Condylar plates after cycle testing at 400 Newtons and 70% lower at 800N. Furthermore during the 800N cycle testing the LISS plating system showed a significantly lower rate of plastic deformation not only for the entire bone-implant construct, but also between the plate and the distal fragment than the locking condylar plate (=less distal implant cut-out).
Conclusions
The use of a more advanced three dimensional tracking system, fresh-frozen osteoporotic matched human specimen and the ability to test all constructs to failure allowed us a more thorough comparison of titanium versus stainless steel implants compared to previous studies. The titanium locking plates provided an overall superior fixation of osteoporotic distal femur fractures with less distal implant cut-out, a better elastic recoil, and a slower rate of residual plastic deformation.
