Biomechanical evaluation of the docking nail concept for periprosthetic fracture fixation (Docknail)

This study was performed to compare in biomechanical aspects common plate osteosynthesis with the concept of a slotted docking nail on the prosthetic tip as stabilization for periprosthetic fractures type Rorabeck II after cemented total knee arthroplasty and type Vancouver B1 after cemented total hip arthroplasty. It was the aim to analyze bare implant characteristics of plates and nails in torsional, medio-lateral bending and axial stiffness depending on size and material selection before insertion in the constructs. Especially the influence of the nail size for a most stable nail-tip stability was of our interest. As with lacking bony support in unstable fracture patterns the implants stability is decisive to bridge the fracture zone until fracture healing occurs, we created an osteotomy gap for the biomechanical construct comparison after total knee arthroplasty. The constructs with plate osteosynthesis and the ones with docking-nails were confronted in interfragmentary movement, in cycles to failure, failure load and failure mode in the aim to reveal the osteosynthetic treatment with highest construct stability. It was hypothesized that nail constructs for type Rorabeck II fractures would obtain higher stability due to the intramedullary support in the unstable fracture simulation. In contrast, for the biomechanical analysis of periprosthetic fracture stabilization for type Vancouver B1 after total hip arthroplasty, the comparison of both groups was done in simulated stable fracture patterns. The aspects of constructs mediolateral bending, axial and torsional stiffness were analyzed and cycles to failure have been performed to determine failure load and mode. It was hypothesized, that plate osteosynthesis with added bicortically anchored plates around the prosthetic tip and supporting cortical abutment would obtain a higher stability in simulated stable periprosthetic fractures type Vancouver B1 than a docking-nail concept.