  Aseptic loosening, or loss of implant fixation, is a common complication
following total joint replacement. Revision surgeries cost the healthcare
system over $8 billion annually in the US. Despite the prevalence of aseptic
loosening, timely and accurate detection remains a challenge because
traditional imaging modalities such as plain radiographs struggle to reliably
detect the early stages of implant loosening. Motivated by this challenge, we
present a novel approach for in vivo monitoring and failure detection of
cemented joint replacements. Poly(methyl methacrylate) (PMMA) bone cement is
modified with low volume fractions of chopped carbon fiber (CF) to impart
piezoresistive-based self-sensing. Electrical impedance tomography (EIT) is
then used to detect and monitor load-induced deformation and fracture of
CF/PMMA in a phantom tank. We therefore show that EIT indeed is able to adeptly
detect loading force on a prosthetic surrogate, distinguish between increasing
load magnitudes, detect failure of implant fixation, and even distinguish
between cement cracking and cement de-bonding. Because EIT is a low-cost,
physiologically benign, and potentially real-time imaging modality, the
feasibility study herein presented has potential to transform the standard of
care for post-operative monitoring of implant conditions. Beyond clinical
relevance, this technique could positively impact orthopedic researchers by
providing, via in vivo monitoring, insight into the factors that initiate
aseptic loosening.
