Periprosthetic fracture plate

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This is a joint project between Medical Engineering and Orthopaedics, Hull Royal Infirmary (Hull and East Yorkshire Hospitals NHS Trust). The project was funded by the Department of Health through a MedLINK grant.

It is currently estimated that over 800,000 total hip replacement operations are performed every year world-wide, with over 40,000 procedures carried in the United Kingdom alone. Furthermore, the number of knee replacements is rapidly approaching that of hip replacements and the number of hip fractures may rise as high as 120,000 per year in the UK within 20 years, half of which will be replaced by hemi-arthroplasty. Thus, the number of total joint replacements or hemi-arthroplasties undertaken per annum in the UK may conservatively be estimated to be 140,000 by the next century, and nearly 3 million in the Western world. It is possible therefore, that over the next decade the total number of patients in the UK with a total joint replacement or hemi-arthroplasty may be more than 1 million and possibly 25 million in the Western world. Periprosthetic fracture typically occurs in 0.1% of replacements, which equates to possibly 2-3000 cases each year for this condition in the UK alone.

X-ray of a periprosthetic 
fracture of the femur


The nature of the fracture makes it a difficult complication to treat. The treatment options depend on the stability of the prosthesis, patient condition, fracture pattern and bone condition, but will involve one of the following, most of which have a number of serious short-comings:

  • exchange prosthesis
    - cemented
    - uncemented

  • plating
    - held in place with cables or wires
    - held in place with screws
    - held in place with prongs crimped onto the bone

  • circlage wiring

  • removal of implant and intermedullary nailing

  • traction with cast bracing

  • combination of the above.

If the prosthesis is loose and the patient is fit enough, the optimal treatment is revision arthroplasty. Unfortunately however, the majority are elderly and unfit for this complex major surgery, which can be a difficult procedure, technically and physiologically, for the surgeon and patient respectively. The revision total hip replacement or knee replacement may or may not be cemented. With a cemented revision the cement will invariably be forced in to the fracture site which will impede union and be a problem in the longer term. With an uncemented exchange prosthesis two possible options exist - impaction bone grafting and locking designs of prostheses. In both cases up to 3 to 4 months are required before the implants become weight-sharing rather than weight-bearing, and the patient must mobilise non weight-bearing until then. This limitation is problematic because the majority of patients that suffer from periprosthetic fractures are elderly and will be difficult to mobilise non-weight bearing.

The most common method used to fix fractures is by a longitudinal support plate and screws (eg AO plate and Bridge Plate (DePuy)), but in patients with total joint replacement there is a significant risk with this technique of damaging the cement mantle and/or the bone-cement or bone-implant interface, possibly resulting in loosening of the implant. There are plates which avoid the use of screws and make use of circlage devices instead (eg Cable Ready System (Zimmer) and Partridge plate). However, anycirclage device around the femoral shaft acts as a tourniquet restricting the periosteal circulation and may ultimately lead to delayed or non-union of the fracture. A different approach is used with the Mennen plate which does not use screws, but has prongs down its length that are crimped into the bone to provide support for the fracture. However, while the Mennen plate has proved to be successful on some smaller bones, it has frequently been shown to be inadequate on the femur, primarily because it provides negligible flexural and torsional support at the fracture site, as illustrated below. Clearly there are problems and limitations associated with all these support plate methods, but there is a significant number of patients, with limited expectations and demands and where early mobilisation is important, and for whom a suitable plate may still be the most expedient solution to this problem.

typical failure of
a Mennen plate

Removal of the prosthesis and replacement with an intermedullary nail in elderly patients is not an optimal solution as it will lead to early incapacity because of the extra effort required to move and function without a truly functional articulating joint. Finally, the extended bed rest required for traction leads to very high risks of morbidity in elderly patients due to pressure sores, chest  infections and difficulty in nursing, and is not recommended.

A new fracture plate A new fracture plate is being developed which uses prongs to secure the bone but with additional proximal and distal fixation providing enhanced support for the fracture together with compression of the fracture site, encouraging union and early mobilisation. (Patents: GB 9724322.4, EU 98309364.2). The plate is manufactured from titanium and is designed so that the prongs generate a positive clamping on the bone, but with sufficient flexibility to allow the prongs to be positioned around the femur. The figure below shows a schematic of the new fracture plate.

schematic of the
new fracture plate

As part of the work, a detailed finite element model of the plate has been developed in position on a fractured femur, which is being used to optimise the plate design. The plots below show a close up of the plate and femur, and a more detailed model of an individual prong, which was used to optimise the prong dimensions.

finite element model of the plate
in position on a femur

finite element model of a prong and 
bending moment stress distribution

The plate has now been manufactured and tested successfully on composite laboratory femurs (Sawbones), and its performance compared to that of other commercial methods of managing periprosthetic fractures. The results are due to be published soon