Biomechanical analysis using infrared thermography of a traditional metal plate versus a carbon fibre/epoxy plate for Vancouver B1 femur fractures

Abstract

Traditional high-stiffness metal plates for Vancouver B1 femur shaft fractures below the tip of a hip implant can cause stress shielding, bone resorption, and implant loosening. This is the first study to compare the biomechanics of a traditional metal plate versus a low-stiffness carbon fibre/epoxy composite plate for this injury. A total hip replacement was implanted in two previously validated intact artificial femurs. Femurs were fitted with either a metal or composite plate and had a 5 mm fracture gap created to simulate a Vancouver B1 shaft fracture. Femurs were cyclically loaded using 5 Hz at 7° of adduction with an average axial load of 800 N (range = 400-1200 N). Overall mechanical stiffnesses and femur and plate thermographic stresses were obtained. Femur/metal plate stiffness (698 N/mm) was only 12% higher than femur/composite plate stiffness (625 N/mm). The femur with the composite plate had 22.7% higher combined average stress compared to the femur with the metal plate, having specific differences of 29.5% (anterior view), 33.9% (posterior view), 1.0% (medial view), and 26.4% (lateral view). The composite plate itself had an average 21.1% reduction in stress compared to the metal plate. The composite plate reduced stress shielding, yet provided adequate stiffness.

Stress analysis of a carbon fiber-reinforced epoxy plate with a hole undergoing tension: A comparison of finite element analysis, strain gages, and infrared thermography

“…The IR thermography camera employed was a Silver 420 (FLIR Systems Canada, Burlington, ON, Canada), as done previously by the authors (Figures 1(a) and 2). 9,13–16 It had the following features: an image resolution of 1 MPa; an image size of 320 × 256 pixels; a built-in auto focusing 27 mm lens; and a 5 Hz to 170 Hz frame rate. It senses surface temperature changes on an object's surface due to its cyclic motion at a fixed frequency to which the IR camera has been synchronized; this is referred to as “lock-in.” The IR camera requires a minimum loading frequency of 3 to 5 Hz to achieve a cyclic temperature gradient that will produce reasonable stress map images.…”

“…One reason is that stainless steel and titanium have a long established history of use for orthopaedic implants, although there is a growing interest in composite materials whose properties can be tailor-made in order to more closely match the mechanical behavior of host bone. 9–18 For instance, stress analysis has been done using IR thermography, strain gages, and/or FEA for a carbon fiber/polyamide 12 total hip implant, 9,10 a metal total hip implant inserted into a glass fiber/epoxy synthetic femur, 11 and a glass fiber/epoxy synthetic femur on its own. 12,13 Similarly, for bone fracture plates made from composite materials, a few studies employed IR thermography and FEA to assess unwanted “stress shielding” (i.e.…”

“…understressing) of underlying host bone or to examine the composite's cyclic fatigue properties. [14][15][16] However, these studies did not comprehensively examine the stress field around the screw holes of the composite bone fracture plate using IR thermography, strain gages, or FEA, which is important since screw holes are stress concentration zones that could undergo failure.…”

“…First, to the authors' knowledge, this study is the first to determine the details of the stress field of a standard carbon fiber/epoxy plate with a center hole under both static and dynamic tensile loads using a three-way comparison of FEA, strain gages, and IR thermography; this may help establish which method(s) is the most reliable for studying composite plates. Second, this study is part of a unique ongoing effort by some of the authors [14][15][16][17][18] to evaluate previously fabricated composite materials for industrial applications (e.g. carbon fiber/epoxy) and/or to create a new generation of composite materials (e.g.…”

Development of a composite intramedullary nail for treating femoral shaft fractures

“…Several studies showed increased bone stress with the use of composite bone plates through computer simulations or ex-vivo testing [88][89][90][91]. Kim et al [92] used the finite element method to examine the fracture gap strain distribution in a fractured tibia fixed with five different composite bone plates, and compare it to that in a fractured tibia fixed with a stainless steel plate.…”