The University of Southampton

Author: Agata Szubska

Hip replacement – the past, and the future.

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Recently I have had the privilege to come to Prof. Douglas Dunlops’ clinic, where I have gained a lot of understanding on orthopaedic surgery. One thing that interested me the most was looking at the development and evolution of hip replacement strategies, and where it can lead us in the future, hence why I have decided to write this blog.

From the beginning

Sir John Charnley was the first to research and develop total hip replacements. He aimed to create a total hip replacement using a synthetic substance between the femur head and the socket, instead of using the natural synovial fluid. After failed attempts with PTFE, Charnley eventually used Ultra-high-molecular-weight polyethylene (UHMWPE) for the first time in 1962. After five years of observing his patients Charnley announced the method as safe, allowing other surgeons to use his patented design and officially making the first functionally total hip replacement. After Charnley’s patent lapsed over 100 kinds of hips were licences, one of them being the EXETER. Its success arose from its tapered stem, allowing it to be easily popped out and replaced, but even-though 92% of them last over 30 years, hip prosthetics still seem to fail.

Less history, more science

Prof. Douglas Dunlop gave me a lot of insight on all the reasons why hip replacements fail, but one that stood out to be the most and seemed to reoccur was corrosion. The same way the natural femoral head of the hip joint erodes with time, the synthetic joint can cause wear and tear of the cartilage, leading to the formation of a shallow socket and osteolysis. On top of that, physical shearing forces slowly remove the protective film on the metal surface, and any taper interference will corrode the metal further.

Prof. Dunlop also showed me an x-ray of an elderly patient who had undergone multiple hip replacement surgeries. The shallow socket of the patient caused by hip displasia required for the the prosthetic to be ‘screwed’ into place along with cement loosening. Each time the stem was replaced, the femur had to be reamed, increasing the risk of fracture, prosthetic loosening and infection. This patient had a 3M Capital hip, which prompted the national joint registry due to its poor performance. At the time, the Southampton General hospital was also using a CPT Zimmer brand prosthetic with a fracture rate of 3.4%, giving them a low rating on the registry. In order to overcome this issue, Prof. Dunlop, alongside researchers at Southampton University came up with a solution.

The future of prosthetics

35 years ago, another patient at Southampton General had a similar issue. Her prosthetic migrated and became loose, leaving behind a gap in the bone. In 2003, bone graft from the bone bank was used, but eventually that also failed as screws loosened and the femoral head migrated. It was clear to me that any other attempt at revision would also be unsuccessful, but Prof. Dunlop told me about a new cutting edge technology that has the potential to change prosthesis for ever.

To overcome this issue, 3D custom implants were used, and held in place using stem cells. Not only is the shape of the implant a precise shape for the patient, but the stem cells act as a ‘glue’, allowing for bone formation and encouraging regeneration of the surface layer of damaged cartilage. The removal of old prosthetics may leave behind scar tissue, therefore stem cells may be the only solution to a patient where biology has failed. Upon further reading I have discovered that Dr. Daniel Wiznia of Yale University has developed a similar approach, and deduced that stem cells are a credible strategy and have considerable potential in the future of prosthesis.

Moving away from monoblock stems and exchanging them for a stem with an exchangeable ceramic head seemed to me like a very impactful advancement, but after hearing about the use of 3D printing and stem cells, it has become clear to me that scientists are not done there. It is fascinating to see how the approaches to prosthesis have changed in the last 60 years, and leaves us to think where it can lead us in the future. By writing this blog I aim to show just how fast science is progressing and how successfully scientists are coming up with solutions to clinical problems.

I got the opportunity to listen to Prof. Dunlop talk about his work
Source of information on Sir John Charnley

Hip Replacement 101- and all that could go wrong.

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I have recently had the opportunity to meet a very successful surgeon who specialises in Hip replacement and trauma surgery. Prof. Douglas Dunlop was kind enough to invite me to his clinic where a one hour conversation inspired me to write this blog. He gave me a lot of insight about hip replacement surgery and with that, exactly what could go wrong.

Initially Prof. Dunlop showed me a couple images of hip replacement x-rays, such as the exemplar. One in particular was an image of an anonymous patient, an elderly male who had undergone multiple hip replacement surgeries. Prof. Dunlop and I have discussed why more than one surgery was needed, which leads me to talk about Hip replacement, and it’s potential risks. It might be miss-leading for me to use that title considering it’s impossible to write about every setback, but I will aim to discuss the ones I have learned about.

Going back to the patient. Initially the male had a 3M Capital hip, which due to poor performance lead to revision. Prof. Dunlop explained that the femoral head of the implant became loose in the joint along with the cement holding it together. The friction exerted on the socket lead to osteolysis and screws were needed to keep the implant in the shallow socket. I will not be going into a lot of detail on the 3M Capital hip, but upon further research I have stumbled upon a risk assessment document. It pinpointed that revision was more common in males, and the findings from the report were conclusive; the 3M Capital hips had higher revision rates than other commonly used prosthesis. In addition, with each round of surgery, the hip stem needed to get larger. To make room for a new implant, the femur needs to be reamed. This in turn sacrificed the bone, increasing the risk of fracture, along with loosening of the prosthesis or infection.

Why do hips fail?

I was surprised to hear that the patient had over 3 hip replacement surgeries. On that note its very important to not only think about the failure of the prosthesis, but also why they are initially needed.

In our discussion, Prof. Dunlop identified the two most common causes of surgery in his patients; arthritis and hip dysplasia.

Hip dysplasia is a medical condition where the hip socket does not fully cover the femoral head. This in turn creates a very shallow socket, which is very susceptible to osteolysis. Friction damages the labrum that lines the joint and can lead to hip labral tear, causing pain and discomfort. Arthritis gives rise to similar symptoms and can have multiple causes.

(MORE) problems with prosthetics.

Wear and tear has a honorary mention on this blog. It seems to be one of the leading culprits for hip surgery, damaging not only the bone, but the implant itself. Below is a list of a couple other things that could go wrong:

  • Loosening – causes pain and can lead to an inflammatory response
  • Dislocation of the prosthetic
  • Tendonitis – inflammation and injury of tendons
  • Fractures – example of stiffer hips made of cobalt chrome with 3.4% fracture rate and CPT (Zimmer brand) previously used at Southampton General with a high fracture rate.

Prof. Dunlop also highlighted that often a ceramic head is used in combination with a metal stem for the prosthetic. Many surgeons are now moving away from monoblock prosthetics as the acetabular component cannot be changed.

Where to go from there?

Hip prosthesis may lead to a lot of uncertainty, but just like any other invasive procedure it comes with risks and benefits. I once met a lovely woman called Anne; she has had both her knees and one hip replaced, and yet she has no complaints. In fact she said that the surgery was “life changing”. It allowed her to carry out day to day activities at the age of 87!

Despite ‘all that could go wrong’, it is very important not to overshadow all the benefits that come with prosthesis. The risks can be analysed, prompting researchers and surgeons to develop more successful treatment options and prosthetic joints with less complications. It is fascinating to see what the future of prosthesis may hold!

A large review study demonstrated that hip replacements last 25 years in approximately only 58% of patients.

Centeno-Schultz clinic
For more on Prof. Douglas Dunlop