Analysis: with hip fractures and replacements on the rise, what can be done to prevent complicated, costly and painful second surgeries?
According to the Irish Hip Fracture Database, 3,666 hip fracture cases in patients aged 60 years and over were performed in Ireland in 2020. This accounts for 99% of all hip fracture cases in Ireland. Given how the overall quality of life is improving for the general population, it is only expected that there will be a projected increase in hip fracture surgeries.
Hip fractures tend to occur in patients between 60 and 80 years, with 90% of hip replacement surgeries resulting from osteoarthritis, and in individuals who partake in high-impact sports. Typically, the patient would have to return after 15 years for a revision surgery to fix or replace the hip implant from the first surgery. This second surgery can be complicated, costly, time-consuming and painful for the patient.
So why do implants fail and need to be replaced? There are two main reasons for implant failure from a materials scientist perspective. The most common cause is poor bonding of the implant with bone, a phenomenon where the implant is loosened from its initial position over time.
From ABC7, animation created for the Lanier law firm in the US to show normal hip anatomy, hip replacements, how implants can fail and how ions circulate in the body
Bone fixation is a major research concern in implant technology, where a number of approaches have been tested. For example, bone-bonding can be improved by roughening the implant surface, such that the surface can interlock with protrusions on the surface of bone. This approach reduces friction and minimises corrosion products and wear-and-tear debris from accumulating at the bone/implant interface.
It is imperative that a suitable material is used for the implant. Metal-on-metal implants tend to release toxic metal ions, and plastic tends to wear out quickly. Other than mechanically (or chemically) roughening the implant surface to improve bone fixation, the surface can be coated with materials that can stimulate bone production.
Studies show that magnesium deficiency can result in bone mass loss and skeletal weakness, which can lead to bone-related complications such as osteoporosis. To accelerate the bone-healing process, researchers are developing ways to incorporate magnesium into the implant coating, and modifying it to release magnesium ions at a controlled rate at the bone fracture site.
The most common problem is poor bonding of the implant with bone, where the implant is loosened from its initial position over time
The second most common issue associated with implant failure is that the implant surface is prone to bacterial infection during and after the initial surgery. This could be due to improper handling of surgical tools, improper sterilisation techniques or even the patients themselves harbouring opportunistic pathogens.
To prevent bacterial infection from occurring, it is routine to administer antibiotics to the patient before, during and after the surgery. However, this strategy is risky as the over-use of antibiotics has led to antibiotic resistance, where bacteria have adapted resistance to antibiotics that were once effective on them.
A major concern related to antibiotic resistance is the mechanism at which bacteria form biofilms on the implant surface. Biofilms consist of a matrix within which bacteria stick to one another and on the implant surface. Biofilms are extremely difficult to eradicate and the patient must often return for additional surgeries or treatments to address this implant-associated infection.
A popular approach to prevent initial bacterial attachment and subsequent infection is to coat the biomedical implant surface with an antibacterial coating. Such coatings can be active or passive. Active coatings involve the release of antibacterial agents, such as antibiotics, over a short period of time, at the proximate area of the fracture. These coatings are preferred for instances where the fracture is expected to heal quickly.
Passive coatings are typically preferred for fractures that are expected to heal in the long-term. Instead of releasing antibacterial agents at the fracture site, the coating itself is designed to prevent bacteria attaching to the implant surface and prevent biofilm formation.
Developing preliminary materials with the potential to become biomedical implants not only considers issues with bone fixation and bacterial infection, but also the materials' response with the body. A host of viable solutions have been proposed the last few years. Some are taking advantage of strong metal alloys for mechanical strength and coating them with corrosion-resistant, antibacterial coatings. An exciting research approach also includes the development of "bioresorbable" magnesium alloy implants. Such implants are designed to dissolve at the fracture site while releasing magnesium ions which promote bone growth and accelerated healing rate.
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
