Hip and Knee Replacement Surgery...The evidence

There has been much media coverage about whether hip or, especially, knee replacement surgery is better for patients or not. There is no doubt that replacing an arthritic hip or knee joint at an appropriate time leads to a significant improvement in the patient’s quality of life. Function is restored and pain relief achieved. Hundreds of studies have shown the clinical outcome improvements provided surgery is done at the correct time.

Patients should always try non-operative therapies first but a time will be reached when these treatments no longer control pain and their function deteriorates. Pain at rest and at night or severe mobility restrictions is an indicator of end stage disease. Osteoarthritis of the hip and knee is not reversible and, at some point, surgery may need serious consideration.

There are many misconceptions about joint replacement.

  1. When to have a joint replacement?
  2. Are you too young or too old for a replacement?
  3. How long will the replacement last?
  4. What type of replacement is best?
  5. Is one surgical approach better than another?

Hip and knee replacement surgery is well-established, and we can now look back over 50 years and evaluate what works best. Remember, not every new product is better (for example, the DePuy ASR metal on metal hip was a new shiny product that ended in huge number of failures and revisions within five years).

Australia has an outstanding National Joint Registry (aoanjrr.sahmri.com), which tracks every joint replaced in this country from every hospital. This registry has collected data for the past 20 years, and the yearly reports produced have changed Orthopaedic practice for the better with the revision burden dropping due to surgeons choosing implants that work better.

The take home message and most important factor in any joint replacement surgery is for the patient or referring professional to choose the right surgeon. Studies have demonstrated that surgeon experience and skill is a major factor in determining the success of the replaced joint. Higher volume surgeons usually have better outcomes.

Hip replacement

Question: When to have a hip replacement?
Answer: When non-operative therapy no longer controls pain and activities of daily living are affected.

Question: Are you too young or too old for a hip replacement?
Answer: Studies have now shown that hip replacement surgery in the elderly and in the young patient (when clinically indicated) have outstanding results.

Hip Replacement in >80 years old

Outcomes depend on comorbidities. Clearly the more unwell the patient the higher the mortality risk. I always get a Specialist Geriatric Physician consultation prior to considering hip replacement surgery in the elderly.

Remember that the happiest patients are elderly patients who have had their hip (or knee) replaced, lose their pain and become independent and mobile again. One of my ‘stars’ was a 97 year old lady who could not walk or sleep due to pain, had her hip replaced, and lived to 105, pain free and smiling. Don’t give up on our elderly patients…at least get them evaluated.

Hip Replacement in the <50 year old and <20 year old

Joint registry studies are showing excellent outcomes in the young patient needing a THR. There is actually no difference in the revision rate in a patient under 50 or under 20. Modern day implants with tried and tested bearings are working well. A well performed operation using a tried and tested implant has only an 8% -10% revision rate for any reason 20 years post implantation.

Put another way, most patients needing a hip replacement in 2020 may well never need another operation. Laboratory data suggests that younger patients with modern bearing surfaces may have their hip last 30 to 40 years or more. Time will tell clinically, but things look very promising.

Birmingham Hip Resurfacing in young males (<55) is still an outstanding option in those males wanting to remain sportingly active with no difference in revision rates compared to young males with standard hip implants.

The take home message with hip replacement surgery is that WHATEVER AGE, if clinically appropriate, hip replacements have outstanding outcomes and the old saying of waiting until you are old should no longer apply.

Question: What type of hip replacement is best?
Answer: This is a guide only and each patient's individual needs are taken into account before a final implant and approach decision is made.

Patients over the age of 75 usually have a cemented stem with an uncemented socket and highly cross linked polyethelene liner. A metal or ceramic head is used. This hip should last a lifetime.

Patients between 60-75 usually have an uncemented stem (or cemented stem if bone quality poor) and socket with a ceramic on highly cross-linked polyethelene liner. This hip should last a lifetime.

Patients under 60 usually have an uncemented stem and socket with a ceramic on ceramic liner. This hip may or may not last a life time and follow up every 10 years is important.

Males under the age of 55 who are active, and who have excellent bone quality, are candidates for a Birmingham hip resurfacing. However, we discuss the pros and cons of resurfacing versus a total hip replacement with a ceramic bearing according to the patient’s individual circumstances.

Question: Is one surgical approach better than another?
Answer: All approaches work. My preferred approach (90%) is the minimally invasive Direct Anterior approach (DA). This is purely for short-term gain. Studies have shown that the DA approach may afford a quicker short-term recovery without the need for hip precautions. Patients can usually drive within 7-10 days.

Some patients are not suitable for this approach due to anatomical abnormalities, morbid obesity, or other complicating factors. Rest assured, however, that by 6-12 months all approaches function equally well. It is more important to have the surgery done properly by experienced surgeons to achieve good outcomes no matter what approach is used.

Knee replacement

Question: When to have a knee replacement?
Answer: Unlike hip replacement, knee replacement outcomes are not quite as good and recovery is definitely longer. The literature reports an 85% satisfaction rate in knee replacements, however, the outcomes are always better when the clinical decision to operate is made at the correct time. Mild arthritic changes should not have knee replacement surgery.

Physiotherapy and weight loss plays a major role in managing patients with knee arthritis and should be strongly encouraged as a first line treatment. The obesity epidemic is leading to more young patients presenting for knee replacements. Unlike hip replacements, younger patients (under 50) having knee replacement surgery have higher revision rates and it is always best to delay a knee replacement until a patient reaches 60+, if possible. There are, of course, exceptions.

Countless studies support the significant improvement in pain relief with physiotherapy and weight loss as a first line treatment for knee arthritis. All the injections (such as steroid, PRP, viscosuplimentaion and stem cells) do not stop the progression of the disease. They may provide temporary pain relief only.

Question: Are you too young or too old for a knee replacement?
Answer: Just like with hips, older age should not be a deterrent and the patient should get a proper evaluation.
Younger age knee arthritis is a real problem. Knee replacement surgery in younger patients have higher failure rates and should be delayed for as long as practical. Patients may be suitable for a Tibial (or sometimes Femoral) osteotomy that in the right patient can improve pain and function.

Question: What type of knee replacement is best?
Answer: There are many manufacturers of knee replacements. They all however have the same basic principal of a Femoral and Tibial component made out of either titanium or chrome cobalt and a polythelene insert that acts as the new articular cartilage (shock absorber). Knee replacements can be cruciate retaining (CR) where the posterior cruciate is retained, or cruciate substituting (PS) where the PCL is removed. There are also newer constrained inserts such as the ball and socket medial pivot variety as well as mobile bearing inserts. There is no clear evidence to suggest which design of a knee replacement is better.

All insert types work well with very little difference in the revision rate. The key is the surgical procedure that achieves a well-balanced and aligned replacement. Patients should not get too focused on the type of bearing but, rather, on the experience of the surgeon doing the surgery and the importance of post-operative physiotherapy exercises.

Question: Is Computer Navigation and Robotic Surgery better?
Answer: There is currently no clinical evidence that fancy robots or computer navigation is improving patient outcomes in knee replacement surgery over age 65. There have been some reports that in the younger patient computer navigation, to improve alignment and balance, may be beneficial but further studies are required to verify this.


Surgeons who perform high volumes of joint replacement are likely to choose correct implants with tried and tested designs, that are implanted with due skill and care, which provide the patient with a successful hip or knee replacement that is likely to last 25 years or more…a lifetime for the majority of patients.

Michael Solomon
Updated April 2020