The encounter is going exceptionally well with Ms. Thomas. Then the inevitable question comes up.
“Dr. Goldberg, how long will my hip last?” she asks.
“How long are you going to last?” I reply cautiously, evading the question.
She responds without hesitation, “I hope to live to 100.”
“Then your hip should last one day past you!”
The answer has met her test of my confidence and knowledge, but is it the truth?
Unfortunately, the answer is a decisive YES…. and a decisive NO.
As with all things in medicine, the answer to how long a hip replacement will last is quite grey and never black and white. By its very nature, the question itself is trying to ask, “What are the failure mechanisms of a total hip replacement, and what are my chances of getting them?”
“How Long Will My Hip Last?” A Historical Perspective
This is great news! They don’t wear out!
There was an era where hip replacement implants failed at a relatively predictable rate due to a linear wear property of the utilized materials. You may recall the advice to “Wait as long as possible to have it because it’s only good for 10 years.” That advice was alluding to the predictable failure of the plastic by “wearing out” through a predictable number of cycles occurring over a set number of years.
Fortunately, the orthopedic industry has largely solved the wear properties of the materials we currently use. Since 1998, we have consistently utilized plastics (called polyethylene) treated by specific chemical and mechanical processes that make them relatively resistant to wear regardless of their thickness.
This should be great news!
They don’t wear out!
However, it exposes other causes of failure that used to exist, although infrequent compared to poly wear. These failure mechanisms are rare but still occur…and, of course, the answer is more complicated than just what these modes of failure are and what is there incidence is. But I will try to simplify them as best we can.
Modes of Hip Replacement Failure
First, without getting too scientific, I’ll try to explain the current modes of failure and the incidence of failure. Next, I’ll elucidate the differences in these failure modes and how they apply to my patients and humans as biologically diverse beings.
Many studies look at failure mechanisms, including registry data from other countries.
For this blog, I want to highlight the revision rates between 2 different approaches – Anterior and Posterior. As you likely know, there are several approaches to performing a hip replacement. In the United States, the two most common are Anterior and Posterior. Angerame and his colleagues analyzed almost 7,000 patients in their center. They found that the overall revision rate was 1.5%, regardless of approach. The reasons were:
- Femoral component loosening
- Acetabular component loosening
- Fracture
- Infection
- Instability
- Other
Notice that wear is no longer a failure mode. Perhaps more importantly, however, it should be noted that the failure mechanisms were different in the 2 groups. For example, Femoral Component Loosening (FCL) was more common in the Anterior group. At the same time, Instability and Fracture were more common in the Posterior patients.
So, the natural question is, if Anterior Approach is so excellent regarding early outcomes, then why do hips fail at the same rate, and what is the issue with the different modes of failure? The answer to these is complex as well. First, the Anterior approach exposes a previously rare failure mechanism – Femoral Component Loosening.
FCL, or Aseptic Femoral Failure, is a complicated failure mechanism that I truthfully have yet to understand as it is multifactorial in etiology. With Anterior Approach, patients have been freed of traditional rehabilitation with prolonged use of walking aids, positional restrictions, and therapy. However, there is always a price. In this case, it is a violation of the Principle of Osseointegration.
For a hip rOeplacement to be durable, the implants must incorporate into the skeleton of the patient. This “Osseointegration” depends on the implant’s surface, shape, and type of metal. It also depends on the patient’s bone morphology.
It turns out that our human skeletons are changing over time, particularly in the hip. Unfortunately, this change is not necessarily for the better because, in this case, it exposes the failure of the orthopedic industry to “keep up” with these changes and design implants that won’t fail via FCL.
Our Bones are Changing
Larry Dorr, MD, categorized the shape of femur bones in 1993 with his Dorr Classification System. In his study, he found there were 3 types of femurs – Dorr A, Dorr B, and Dorr C. Furthermore, they all existed roughly equally (33%) throughout the population.
Fast forward 30 years, and it turns out that 56% of us are Dorr A, 39% Dorr B, and only 5% are Dorr C.
In truth, it is more complicated than just Dorr A, B, C. The Dorr classification is made from a simple 2-dimensional x-ray. Our bones have a changing 3-dimensional morphology (shape) that must be accommodated. Osseointegration depends upon getting the right surface of the right metal to Cortical bone.
Implants, unfortunately, are not necessarily designed to maximize the internal contact of cortical bone. Most implants are a simple geometric shape – a rectangle or cone. The hope is that there is enough cortical contact to allow the implant to osseointegrate.
The truth is, now they simply are not contacting enough cortical bone.
Our bones are indeed changing.
Why? No one truly knows, but I suspect it is our diet. It is foolish to me to see the incidence of diabetes, obesity, heart disease, etc., steadily increase without believing that there will not be some effect on our musculoskeletal system.
However, what cannot be denied is the fact that the combination of our changing anatomy, our hastened recovery protocols, with relatively stagnant implant shapes has exposed a new failure mechanism for hip replacement. The studies show that FCL predominantly occurs in patients with Dorr A bone.
The “Failure-prone” Patients
So traditional implants with speedy recovery protocols in patients with Dorr A bone are the recipe for potential failure. I have traditional implants. I perform Anterior Approach with its enhanced recovery protocol. Over 50% of my patients have Dorr A bone. These patients encompass a large part of my practice.
These are the patients whom I pay extra attention to make sure I get them right. They make me a better surgeon for all my patients.
When I trained in the late 1990s, we learned basically to use one implant for all of our patients, and they worked from an Osseointegration perspective. Now, with Anterior approach broach-only techniques, surgeons must be wiser in choosing the correct implants/techniques/rehab protocols to avoid FCL. One thing is for sure: the rehab protocols are here to stay. Keeping patients in the hospital for a week and on walkers for six weeks is no longer acceptable. Thus, the onus is upon us as surgeons and industry to choose the correct implant/technique for a particular patient.
I’m not alluding to the Anterior vs. Posterior approach; I’m alluding to surgical fixation techniques such as cementation or “ream-and-broach” that surgeons can do to optimize the chance for successful results. I’m also referring to stem choices provided by the industry. Obviously, the perfect implant would be an implant custom ‘printed’ to a patient’s anatomy to fit perfectly within the bone. While I predict it will occur in the future (companies are working on the concept), it is not prevalent yet.
Recognizing this dilemma, I use seven different implants and three different techniques to implant my patients. Why do I have this complexity, you might ask? Because there are many patients before you that I have tried and failed with.
A wise surgeon evaluates their results frequently and seeks to constantly improve their techniques/care pathways to ensure their patients achieve the best possible results. I learn from mistakes. I have studied and learned to be a better surgeon to help modify the things I can change. After all, I can’t really change that are bones are changing!
I hope this helps clarify the question, “how long will my hip last?”
I have spent the last decade trying to figure it out myself, so I’m happy to discuss it further in the office anytime you want. It’s my passion.
And by the way, when FCL does occur, it does not necessarily mean revision surgery. However, if it does, I have learned how to fix it and how to give you the hip replacement you deserve – pain-free, functional, and durable – for “1 day past you”!
