The stiffness that takes a while to shake off each morning. The ache after a long sit. The knee that complains more some weeks than others. You've filed it under age, or that old injury, and you've probably been told the same.
Age is a poor explanation. Your other knee is the same age. When researchers examined about 2,400 American skeletons, knee arthritis turned up in 16% of modern people and only 6% of those from the early industrial era. Among prehistoric hunter-gatherers and early farmers, it was 8%. Allow for how old they were and what they weighed, and it was still 2.1 times as common. The authors concluded that knee arthritis is more preventable than we assume.
So something else is going on, and some of it is within reach. None of this regrows worn cartilage. But why it hurts, and why it hurts you more than the next person, have better answers than "you're getting on".
Where the pain comes from
Cartilage has no nerves and no blood vessels. It can wear away and feel nothing at all. So the ache has to come from what's around it, and the bone underneath is a prime suspect, as bone has pain fibres of its own. In 401 people with knee arthritis, swollen patches in the bone marrow showed up in 77.5% of those with painful knees and 30% of those without.
That's why a joint can be far from "worn out" and still hurt, and why it's worth asking what's irritating the tissue around it, and not only how much cartilage you have left.
The scan and the ache
Here's where it gets odd. Of people with knee pain, between 15 and 76% had arthritis on an X-ray, depending on the study. Of people with arthritis on an X-ray, between 15 and 81% had pain. Two people can carry the same picture and live very different lives.
That doesn't make the damage imaginary. When researchers compared each person's painful knee with their other knee, which takes everything else about that person out of the sum, damage was strongly linked to pain. So the wear counts. What differs between people is everything else they bring to it, and that's the part you can work on.
It's also why a scan may not be the next step. NICE, which writes the UK's health guidelines, says osteoarthritis can be diagnosed without imaging if you're 45 or over, your pain comes with activity, and any morning stiffness lasts no longer than 30 minutes. It advises against routine imaging unless something doesn't fit.
What's behind it
Inflammation is part of the answer. Background inflammation tends to climb slowly with age, which has earned it the name inflammaging. But age isn't the only thing feeding it, and here's what the rest of the list looks like.
Genes. These count, and I won't pretend otherwise. In 250 pairs of female twins, genes accounted for 39 to 65% of the variation in arthritis of the hand and knee, even allowing for age and weight. But genes don't change much in a century, and knee arthritis has doubled since the mid-20th century.
Old injuries. A review found that a knee ligament or cartilage injury raises the risk of knee arthritis 4 to 6 times. So if you've torn something, the rehab is no optional extra.
Weight. In 142 older adults with knee arthritis, each pound lost took about four pounds of load off the knee at every step, and you take thousands of steps a day. It isn't only mechanics. In a study of 1.7 million people, arthritis of the hand ran at 2.6 cases a year per 1,000 at a normal weight and 4.0 with more serious obesity, and your hands carry no extra weight at all. Unless you've been walking on them.
Food. In a small pilot trial of older adults with knee arthritis, 12 weeks of low-carb eating reduced pain more than a low-fat diet or their usual food, and it lowered a marker of oxidative stress. It's a pilot, so it's a lead. I'd still start there: meat, fish and eggs, and a lot less sugar and refined flour. Why Seed Oils Are Wrecking Your Health has the case against the fats, so cook in animal fat, such as , instead. Why Your Anti-Inflammatory Diet Isn't Helping Your Joints, linked below, has what cartilage is built from.
The gut. This one is early but interesting. In a large Dutch population study, repeated in 867 more adults, more Streptococcus in the gut went with more knee pain, and the link seemed to run through inflammation in the joint itself. It doesn't show that the bacteria cause the pain, and there's no treatment to buy from it.
Sleep and stress. When 18 volunteers were randomly assigned to 8 or 4 hours a night, the short sleepers' levels of an inflammatory marker, IL-6, went up after 10 days, and the higher it went, the more pain they reported. The Stress-Sleep Vicious Cycle: How to Break It has how the two feed each other.
Too little movement. Resting a sore joint feels right, and the evidence says otherwise. Across 44 trials with 3,537 people with knee arthritis, exercise took about 12 points off pain, on a 100-point scale where those who didn't exercise scored 44. Jim Johnson's has simple exercises to start with, and a is an inexpensive way to add load at home. Your joint may hurt more at first, and NICE says to expect that, as regular exercise pays off in the long term.
It needn't be much, either. Among 1,564 adults aged 49 or over with joint symptoms, those reaching about 55 minutes of moderate to vigorous activity a week were far less likely to lose mobility over four years, 3% against 24%. It's an observational finding, but it's a small number. What Your Workouts Are Doing to Your Joints has how to load a joint without flaring it, and What Keeps Some People's Joints Working Into Their 80s, linked below, has the everyday habits. If you've already spent a fortune on capsules, Your Joint Supplements Aren't the Problem takes them one at a time.
Reading the signal
Which of these matters most to you is individual, and the way to find out is cheap. Time your morning stiffness for a couple of weeks. Change one thing, then watch the trend, and ignore any single morning.
The reason to measure is that everything seems to work. Across 215 trials with 41,392 people with arthritis, on average 75% of the pain relief came from the context of treatment, such as expectation and attention, and not from the treatment's specific action. It ranged from 47% for steroid injections to 91% for washing out the joint. So your neighbour's capsule may well have helped, and the capsule may have had little to do with it.
Keep an eye on two things while you're at it. NHS guidance says stiffness from osteoarthritis usually wears off within 30 minutes of getting up, so stiffness that drags on past that deserves a check, as it can point to rheumatoid arthritis. And a joint that turns suddenly hot, red, swollen and very painful, often the big toe, can be gout, which needs treating promptly. Talk to a qualified health professional about either.
Can your knee predict rain?
Probably not, though it's not entirely mad. Among 1.5 million older Americans, visits for joint or back pain were no more common on rainy days, and the tiny difference ran the other way. Yet when 2,658 people logged their pain in a phone app for 15 months, there was a modest link with humidity, pressure and wind. So your knee may know something, but it's a poor forecaster. Your own record against what you ate and did will tell you far more.
Surgery and pills
Treatment has its place here, and it's worth knowing what's been tested. In one trial, 180 people with knee arthritis had keyhole surgery on the joint or a fake operation, with cuts in the skin and nothing done inside. Two years on, those who had the real surgery reported no less pain and no better function. The fake operation came with real scars and the same results.
Joint replacement is different, and it does work. In a trial of 100 people who qualified for a new knee, those who had one improved by about twice as much at 12 months as those given exercise, education and diet advice alone, with 32.5 points against 16. They also had four times as many serious complications, 24 against 6, and only 26% of the non-surgical group had gone on to have the operation by then.
Injections deserve a word too. In a two-year trial, 140 people with knee arthritis had a steroid or a salt-water injection every three months. The steroid group lost about twice as much cartilage, 0.21 mm against 0.10 mm, and their pain was no better.
NICE puts therapeutic exercise and weight at the core of treating osteoarthritis, and it says paracetamol shouldn't be offered routinely. For knee arthritis it recommends offering an anti-inflammatory gel, and it says to use any drug at the lowest effective dose for the shortest possible time. It also says there's no strong evidence for glucosamine. So use whatever helps with the pain, under proper advice, and work on what's behind it at the same time.
What your joints are telling you
The ache is information as well as a nuisance. Some of it comes from wear you can't undo. A good part of it comes from what you weigh, what you eat, how you sleep and how much you move, and that part hasn't finished its say.
None of it is fast. What tends to improve is comfort, function and how much the joint intrudes on an ordinary day. The stiffness you time tomorrow morning is free, and it's a better guide to whether any of this is working than anything you could buy.
Looking for the daily habits? What Keeps Some People's Joints Working Into Their 80s — the movement, food, weight and sleep habits that keep joints working.
Wondering what to eat? Why Your Anti-Inflammatory Diet Isn't Helping Your Joints — what cartilage is built from, and the eating changes that reach the joint.
Know someone who's been told it's just their age? Send them this, and ask how their other knee is.
Disclaimer: This article is general information. Joint pain can have serious causes, so talk to a qualified health professional about new or worsening symptoms and before changing any treatment, and promptly about a joint that turns hot, red and swollen.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
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