Getting yourself ready for a Knee Replacement : What actually helps
A knee replacement is one of the most reliable operations in modern medicine.
Most people end up with far less pain and a knee they can trust again. But
roughly one in five patients report dissatisfaction with the result.¹
Persistent pain, stiffness and incomplete return of function are the usual
reasons.
Some of what determines which group you land in is out of your hands. Some of
it isn’t. The weeks before surgery are a real opportunity, and most people
don’t use them.
A word on the evidence first. Much of what follows comes from studies showing
that people with a particular problem, such as low vitamin D, anaemia or
ongoing opioid use, tend to do worse. That is not the same as proving that
fixing the problem fixes the outcome. For a few items here the trial evidence
is strong. For most of them it is only suggestive. I have said which is which
as I go along.
THE THINGS WITH THE STRONGEST EVIDENCE
If you smoke, stopping is the highest value thing you can do
Smoking impairs wound healing and tissue oxygenation and raises infection
risk. Unlike most items on this list, this one has proper randomised evidence
behind it. A trial in Danish hip and knee replacement patients found that
those given cessation counselling and nicotine replacement before surgery had
substantially fewer postoperative complications than controls.²
The practical question is how long you need. Reviews of the arthroplasty
literature suggest that starting about four weeks before surgery is enough to
produce a meaningful reduction in complications, and that longer is better.³ ⁴
Ask your GP about nicotine replacement or a stop smoking service. Willpower
alone has poor odds. Supported quitting works considerably better.
If you drink heavily, cut back
This gets discussed less often, but the evidence is reasonable. A Cochrane
review found that intensive alcohol cessation programmes lasting four to eight
weeks before surgery probably reduce postoperative complications in people
drinking at risky levels, defined as more than about 21 units a week.⁵ The
effects of heavy drinking on immune function and clotting are largely
reversible within a few weeks of stopping.
If you are taking opioids, talk about weaning before you talk about surgery
This is the item most often missing from patient information, and it matters.
Around a quarter of people come to joint replacement already taking opioids.⁶
Compared with opioid naive patients they report worse pain and function scores
after surgery,⁶ ⁷ have longer hospital stays,⁸ need more manipulations under
anaesthetic for stiffness, and are far more likely to still be taking opioids
months later.⁹
This is not a moral point and it is not your fault. You were prescribed them
for a painful knee. The difficulty is that opioids change how your nervous
system processes pain, which blunts the benefit of an operation designed to
relieve pain. If you can reduce or come off them beforehand, with your GP’s
help and a proper tapering plan, the operation is more likely to give you what
you want from it. Do not stop abruptly on your own.
Get your diabetes under control
Diabetes roughly doubles the risk of joint infection and wound problems.¹⁰
Where exactly the threshold sits is still debated. One multicentre study put
the inflection for infection risk at an HbA1c of about 7.7%.¹¹ A large 2025
analysis argued that HbA1c is a fairly blunt predictor,¹² and shorter term
markers such as fructosamine may predict complications better.¹⁰ ¹³
What this means in practice: aim for good control, expect your team to check,
and start early. HbA1c reflects roughly three months of blood sugar, so this
is not a fortnight’s work.
Check for anaemia
About one in five people coming for elective hip or knee replacement is
anaemic,¹⁴ and most of that is iron deficiency. Anaemia going in means a
higher chance of transfusion, and is associated with longer stays and more
complications.¹⁵
Treating it beforehand with iron reduces transfusion rates and length of stay,
although the authors of the relevant meta-analysis are clear that high quality
randomised trials are still lacking.¹⁶ Ask for a full blood count and iron
studies. Iron deficiency also has causes worth investigating in their own
right.
MUSCLE AND NUTRITION
Build strength before you lose it
Your quadriceps starts wasting almost immediately after surgery, and
quadriceps strength is a strong predictor of functional independence in older
adults.¹⁷ The stronger you go in, the more you have in reserve.
Prehab is often oversold, though, and the evidence is mixed. A 2022 meta-
analysis found low to very low certainty evidence that prehabilitation
improves knee function before surgery and for up to three months afterwards,
with no significant difference by six to twelve months.¹⁸ A large multicentre
randomised trial found no benefit from multidisciplinary prehabilitation on
functional independence or activity limitation.¹⁹ A 2025 meta-analysis of 21
trials found reduced pain at one, three and six months but no effect on length
of stay.²⁰
So it is worth doing, likely to make the early weeks easier and less painful,
and unlikely to change where you end up in a year. The early weeks are the
hard part, so that is still worth having. Ask for a physiotherapy programme.
Straight leg raises, seated knee extensions, sit to stands and stationary
cycling are the workhorses.
Eat more protein than you think you need
Surgery drives your body into a catabolic state where tissue is broken down.
Protein is what you rebuild with, and most older adults under eat it even
before you add an operation. Spread it across meals rather than loading it all
into dinner.
Essential amino acid (EAA) supplements have better trial evidence than most
things in this area. A double blind randomised trial in knee replacement
patients found that EAA supplementation preserved quadriceps muscle mass,
reduced pain and shortened time to recovery of daily activities,²¹ with
strength and volume gains still present at two years.²² A trial in frail older
women having hip replacement found EAA plus physiotherapy beat physiotherapy
alone for hip and knee strength.²³ A meta-analysis of 12 trials reported
improved patient reported outcomes and no adverse events.²⁴
The trials are small and this is not standard care everywhere. It is cheap and
safe, though, so it is worth asking about, particularly if you are older or
already losing muscle.
VITAMINS AND MINERALS WORTH CHECKING
Vitamin D
This is the best studied of them. Somewhere between 13 and 63% of people
coming for joint replacement are deficient,²⁵ and deficiency is linked to
longer hospital stays, more stiffness needing manipulation under anaesthetic,
higher infection rates and poorer function scores.²⁵ ²⁶ A systematic review
and meta-analysis in knee replacement specifically found deficiency associated
with worse outcomes and improvement after supplementation.²⁷ A large cohort
study found fewer complications and superficial wound infections in patients
given vitamin D before surgery.²⁸
Two caveats. That meta-analysis pooled only three studies for its main
quantitative finding, and most of the included studies were retrospective, so
the case is suggestive rather than settled. And no study has established the
right dose for everyone.²⁷
Ask for a blood test (25-hydroxyvitamin D) and let your doctor prescribe
according to the result. Do not self prescribe large doses. Excess vitamin D
can cause high calcium and kidney stones.²⁹ One useful quirk to know about:
levels measured after surgery are unreliable, because the inflammatory
response distorts the result.³⁰ Get tested beforehand.
The supporting cast
Vitamin C. A randomised trial in 110 knee replacement patients found reduced
inflammatory markers, lower pain scores and better early mobility.³¹ It may
reduce complex regional pain syndrome, though the strongest meta-analytic
evidence for that is in wrist fracture rather than knee replacement, so
applying it here is an extrapolation.³² Caution if you have had oxalate kidney
stones.³³
Magnesium. Needed to activate vitamin D, so being low blunts the response to
supplementing it.³⁴ It also has analgesic properties in knee replacement.³⁵
Caution in advanced kidney disease.
Zinc. Low levels are linked to delayed wound healing.³⁶ Only worth
supplementing if you are deficient, since prolonged high doses cause copper
deficiency.³⁷
Diosmin and hesperidin (MPFF). This one is for swelling after surgery rather
than before it, but the evidence is better than you might expect. A
multicentre randomised trial of 330 patients found reduced calf, thigh and
knee swelling and less pain on movement,³⁸ and a second trial of 176 patients
found better knee flexion and less nausea.³⁹ Worth raising with your surgeon.
The sensible approach throughout is to test, correct what is low, and avoid
taking a scattergun of high dose supplements on spec.
WEIGHT
Losing weight reduces joint loading and lowers some surgical risks, and many
units have BMI thresholds. Rapid weight loss before surgery has a downside
that gets discussed far too little, though. A meaningful proportion of what
you lose quickly is muscle, which is precisely what you need in order to
recover.²⁵
If you are taking a GLP-1 medication (Ozempic, Wegovy, Mounjaro and similar),
tell your surgeon and anaesthetist early. These drugs slow stomach emptying,
which affects fasting instructions and aspiration risk, and anaesthetic bodies
have published conflicting guidance on how to manage them around surgery.²⁵ ⁴⁰
Your team needs to know.
Whatever you are doing to lose weight, keep protein high, keep training, and
avoid crash dieting into an operation.
YOUR HEAD MATTERS AS MUCH AS YOUR KNEE
Most patient leaflets skip this, and the evidence for it is stronger than for
several of the supplements above.
In a Swedish registry study of 8,745 patients, self reported anxiety or
depression more than doubled the risk of dissatisfaction one year after knee
replacement, even among patients whose pain and function had objectively
improved.⁴¹ Pain catastrophising, meaning a tendency to ruminate on and
magnify pain, independently predicts chronic pain after joint replacement, as
does preoperative psychological distress.⁴² ⁴³ Unmet expectations are among
the strongest predictors of dissatisfaction.⁴⁴
Two things follow from this. First, if you have untreated anxiety or
depression, treat it as part of your surgical preparation rather than as
something separate from the operation. There is encouraging news here too,
since several studies find that depressive symptoms often improve after joint
replacement, and that people with depression gain as much functional
improvement as anyone else.⁴⁵
Second, get your expectations calibrated. Ask your surgeon directly what this
knee will let you do and what it will not. Most replaced knees do not feel
like the one you had at thirty. Knowing that in advance protects you from
feeling that the operation failed when it did not.
PRACTICAL MATTERS IN THE LAST FEW WEEKS
Fasting. Many units now give a carbohydrate drink two to three hours before
surgery instead of nil by mouth from midnight. It reduces the insulin
resistance that surgery triggers and you will feel considerably better. A
randomised trial in patients with type 2 diabetes found lower insulin
resistance and less preoperative hunger, with no aspiration events.⁴⁶ Follow
your own unit’s instructions.
Skin and nose. Many units screen for Staphylococcus aureus carriage and give
carriers a short course of nasal ointment and antiseptic body wash before
surgery. The evidence base is largely observational rather than randomised,
but the treatment is low risk and appears to reduce staph surgical site
infections.⁴⁷ ⁴⁸ If your unit offers it, complete the full course properly.
Teeth. Advice on this has changed, so it is worth being precise. Getting
active dental infection treated before an elective joint replacement remains
sensible. The once standard practice of routine antibiotics before dental
procedures after joint replacement is no longer well supported, however. A
meta-analysis of over 157,000 patients found no significant reduction in joint
infection,⁴⁹ and the 2024 AAOS guideline now states that routine prophylaxis
may not reduce the risk.⁵⁰ Discuss it with your surgeon rather than assuming
either way.
Set the house up. Clear trip hazards, put daily items at waist height, arrange
a raised toilet seat if you need one, stock the freezer, and sort out who is
helping in the first fortnight. You will not want to be problem solving on day
three.
WHAT TO ASK AT YOUR PRE-OP APPOINTMENT
- Can I have my vitamin D level checked and corrected?
- Can you check my full blood count and iron studies?
- Is there a prehab physiotherapy programme I can start now?
- Should I take a protein or essential amino acid supplement, and which one?
- If you are on opioids: can we make a plan to reduce these before surgery?
- If you are diabetic: what HbA1c are you aiming for, and how long do I have?
- What are your eating and drinking instructions, and do you use a
carbohydrate drink? - If you are on a GLP-1 drug: how should I manage it around surgery?
- Do you screen for staph carriage?
- Realistically, what will this knee let me do at six weeks, six months and
a year?
IN SHORT
The strongest evidence sits with the least glamorous items. Stop smoking, cut
the alcohol, reduce opioids, control blood sugar, treat anaemia, look after
your mental health. The supplements are cheap and low risk and probably help
at the margins, but they are not where most of the benefit lies.
You will not determine the outcome single handedly, and the surgery and the
surgeon matter more. You can arrive in better shape than you otherwise would
have, though, and that shows up in how the first three months feel.
This is general information, not medical advice. Your medications and your
kidney, liver and heart function all change what is appropriate, particularly
around supplements. Talk to your surgeon, GP or pre-assessment team before
starting or stopping anything.
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