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Paul R. Kuzyk, MD, FRCSC, MSc,

AAOS Now

Published 5/1/2016
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Mark Crawford

Periprosthetic Femur Fracture Fixation

OREF grant recipient tests which treatment methods are most effective
More than 300,000 total knee arthroplasty (TKA) procedures are performed every year in the United States. With seniors living longer and staying more active, the number of these procedures is expected to double over the next decade. Unfortunately, that means that postoperative complications—especially periprosthetic femur fractures that occur around knee implants—will be of increasing concern.

What's the best way to treat distal femur fractures that occur above a well-fixed femoral component for a total knee arthroplasty? Intramedullary nailing and locked plating are two of the most common methods, but there are currently no randomized controlled trials that compare their effectiveness.

In 2012, assistant professor at the University of Toronto and lower extremity reconstructive surgeon at Mount Sinai Hospital, received an Orthopaedic Research and Education Foundation (OREF)/Zimmer Young Investigator Grant to conduct a biomechanical study comparing three different treatment options.

"Using composite osteoporotic femur models," said Dr. Kuzyk, "we studied the biomechanical properties of established techniques for fixation of these fractures—retrograde intramedullary nail and locking plate—as well as a novel technique using a variable angle locking plate with an intramedullary fibular allograft.

"Our results will provide information on the structural stability of three different management modalities under various loading patterns, which should help orthopaedic surgeons select the best fixation for their patients, and minimize complications and revisions," he added.

Force measurement
To compare techniques, Dr. Kuzyk and his research team used 15 large-sized (485-mm) fourth-generation composite femurs that simulate osteoporotic human bone. Composite femurs were used to ensure consistent material properties.

The researchers placed the femoral component of a knee prosthetic on the distal femurs, created a fracture just above the component, and then repaired the fractures using one of three treatment methods:

  • retrograde intramedullary nail
  • polyaxial locking plate
  • intramedullary fibular strut allograft with polyaxial locking plate

They compared the constructs on an Instron mechanical testing machine. Each sample was statically loaded in axial compression, torsion, and cantilever bending. The team calculated load displacement curves, load to failure, energy to failure, mode of failure, and stiffness (Fig. 1).

"The Instron machine allowed us to place a specific force on the construct and then measure how much the whole construct displaced or changed," said Dr. Kuzyk. "It gave us an idea of how stiff everything was. This allowed us to compare the three groups to see which treatment option delivered the best results in terms of stability."

Best treatment
Early results suggest the intramedullary nail was the stiffest construct in axial loading, but the least stiff in rotation.

"The polyaxial locking plate offered the best combination of axial and rotational stiffness," Dr. Kuzyk explained. "The intramedullary fibular graft did not improve the stiffness of the polyaxial locking plate construct."

Paul R. Kuzyk, MD, FRCSC, MSc,
Fig. 1 Instron machine with a femur fixed using a variable angle locking plate that was cyclically loaded to failure.
Courtesy of Paul R. Kuzyk, MD, FRCSC, MSc
Fig. 2 Matched cadaveric femurs. (l-r) The left femur was fixed using a variable angle locking plate and the right femur was fixed using a retrograde nail.
Courtesy of Paul R. Kuzyk, MD, FRCSC, MSc

The study does contain several limitations: femoral neck fractures were encountered in the axial quasi-static load-to-failure tests. The fracturing was probably related to increased strains in the proximal femur, while the shaft and distal femur are supported by the hardware (intramedullary nail or locking plate).

"This finding implies that retrograde intramedullary nails and polyaxial locking plates are able to resist loads greater than normal physiologic load," said Dr. Kuzyk.

Although the synthetic femurs allow for reduced inter-specimen variability, their biomechanical properties are not identical to real bone; therefore, the two best groups from this study, the polyaxial locking plate and the intramedullary nail, were tested using paired cadaveric femurs (Fig. 2).

"The polyaxial locking plates were placed in the left femurs and the intramedullary nails were placed in the right femurs," Dr. Kuzyk said. "This study also suggests that the intramedullary nail provides the greatest resistance to axial applied forces."

Investing in orthopaedics
According to Dr. Kuzyk, the study could not have been conducted without the funding he received from OREF.

"Without the OREF grant, we would not have had the funding for the specific type of sawbones we used for the study," he explained. "Although Zimmer donated some of the implants, we had to purchase some of those as well and the OREF grant helped us do that."

Dr. Kuzyk is grateful that OREF has grants for researchers who are just beginning their careers.

"New orthopaedic surgeon investigators have a lot to do—develop clinical practices, help teach residents, put together a lab, and find funding for it, all of which is very difficult. OREF's grant program for new investigators is very important," he said.

Dr. Kuzyk believes that high-level research is the only way to advance orthopaedics. The year after he received his grant, he volunteered as a reviewer for OREF resident research proposals and said that OREF's peer review process is well done.

"OREF has been very successful in terms of selecting research studies that are likely to be successful and make a difference in clinical decision making. If we're going to invest in terms of furthering orthopaedics, then OREF is definitely a great resource to support," he said.

Mark Crawford is a contributing writer for OREF. He can be reached at communications@oref.org