Knee pain, decade by decade.

Ask a room of people in their late forties and early fifties whether their knees hurt on most days, and about one in three will say yes. Ask a room of people over 75, and more than half will. The figures come from the Johnston County Osteoarthritis Project in North Carolina, which put one plain question to about 3,000 adults aged 45 and over: "On most days, do you have pain, aching, or stiffness in your knee?"¹

The answers rose steadily with every age band: 34.2% between 45 and 54, 42.6% between 55 and 64, 49.0% between 65 and 74, and 56.6% at 75 and over.¹ What changes from decade to decade is how often it comes with damage to the joint, who carries most of it, and how much of it was ever inevitable.

The forties and fifties: earlier than most people think

The Global Burden of Disease study notes that osteoarthritis most often appears after the age of 40, and that it becomes steeply more common with every decade after that.² In the United States, researchers estimated that nearly 2 million people with symptomatic knee osteoarthritis were younger than 45, and another 6 million were between 45 and 65. More than half of everyone with the condition was under 65.³

In Johnston County, 14.9% of people aged 45 to 54 already had osteoarthritis visible on an X-ray, and 7.3% had both the X-ray changes and knee symptoms, the combination researchers call symptomatic knee osteoarthritis.¹

The sixties, seventies and beyond: the steep part of the curve

From the mid fifties onwards the picture on the X-ray changes quickly. Radiographic knee osteoarthritis rose from 26.2% at 55 to 64, to 36.1% at 65 to 74, and 49.9% at 75 and over. Symptomatic disease was more than four times as common at 75 and over as at 45 to 54: 32.8% against 7.3%.¹ The Framingham study, which X-rayed more than 1,400 older adults in Massachusetts, found the same slope: 27% of those under 70 had radiographic knee osteoarthritis, against 44% of those aged 80 and over.⁴ Among adults aged 70 and over, osteoarthritis is the seventh leading cause of years lived with disability worldwide.²

Symptomatic knee osteoarthritis by age

Share of adults with knee symptoms on most days plus osteoarthritis on X-ray, Johnston County Osteoarthritis Project, 1991 to 1997

45 to 547.3%

55 to 6416.3%

65 to 7420.8%

75 and over32.8%

Source: Jordan et al., Journal of Rheumatology (2007), Table 2, weighted prevalence

Yet an X-ray and a sore knee are not the same thing. Worn-looking joints can be painless, and painful knees can look ordinary, a mismatch we explore in our piece on what the X-ray does not show.

Why the numbers climb

Part of the answer is the tissue itself. A review in Nature Reviews Rheumatology describes how ageing pushes cartilage cells towards a proinflammatory, catabolic state, with more breakdown and poorer repair of damaged tissue. The same review stresses that ageing and osteoarthritis are closely linked but independent processes.⁵ Getting older raises the risk, but age alone does not explain the disease.

Muscle matters too: weaker quadriceps, the muscles at the front of the thigh, are linked to a higher risk of painful knee osteoarthritis, as we describe in our piece on the muscle that guards the knee.

Weight works slowly, over decades. In Framingham, women whose body mass index fell by two units or more, about 5 kg, over the ten years before their examination had roughly half the odds of developing symptomatic knee osteoarthritis.⁶

Old injuries keep their own calendar. Across 53 studies and about a million participants, an anterior cruciate ligament injury was associated with about four times the odds of later knee osteoarthritis, and a meniscal injury with about six times the odds.⁷ The people in those studies were, on average, in their late twenties and thirties when they were hurt.

Why women overtake men

In the US national survey NHANES III, 42.1% of women aged 60 and over had radiographic knee osteoarthritis, compared with 31.2% of men, and women were about twice as likely to have the most severe grades (12.9% against 6.5%).⁸ A meta-analysis of population studies reached a similar conclusion: women, particularly those aged 55 and over, tend to have more severe knee osteoarthritis than men.⁹

The timing has drawn attention to menopause. A 2022 review notes that osteoarthritis becomes significantly more common in women than in men after the age of 50, and that knee and hip disease rise quickly from menopausal age, around 50, to about 75. It also found the evidence on hormone therapy mixed, and whether oestrogen protects the joint remains unclear.¹⁰ In Framingham, the rise with age was driven mainly by a marked increase in new cases among women.⁴ By 75 the gap is wide: in Johnston County, 64.3% of white women that age reported knee symptoms, against 38.0% of white men.¹

What is normal, and what is not

It is tempting to read these curves as destiny. Two findings argue against it. In US national surveys, the prevalence of knee pain among white adults aged 60 to 74 rose by about 65% between 1974 and 1994, even after adjusting for age and body mass index; in Framingham, symptomatic knee osteoarthritis roughly doubled in women and tripled in men over 20 years, while X-ray osteoarthritis did not.¹¹ Something other than birthdays was changing.

The second finding comes from bones. Researchers who examined skeletons spanning thousands of years found knee osteoarthritis in 16% of the post-industrial sample, against 6% in the early industrial one. After controlling for age and body mass index, prevalence in the modern group was still 2.1 times higher than in the early industrial one, and the authors concluded that the disease is "more preventable than is commonly assumed."¹²

The rise is real, but it is a population average, not a forecast for any one knee. Strength, weight and injury history are all linked to it, and the evidence on what helps once pain has started is covered in our piece on knee osteoarthritis. Those later decades are the years Veema is designed around. Whether a powered exoskeleton can help people through them is a question only studies with older adults can answer.

These figures describe the need. They are not results or claims about Veema.

Sources

1. Jordan et al., Journal of Rheumatology (2007): Johnston County Osteoarthritis Project, about 3,000 adults aged 45+: knee symptoms 34.2%, 42.6%, 49.0%, 56.6%; radiographic knee OA 14.9%, 26.2%, 36.1%, 49.9%; symptomatic knee OA 7.3%, 16.3%, 20.8%, 32.8% (ages 45 to 54, 55 to 64, 65 to 74, 75+); knee symptoms at 75+ 64.3% in white women vs 38.0% in white men; symptom question wording.
2. GBD 2021 Osteoarthritis Collaborators, Lancet Rheumatology (2023): Osteoarthritis most frequently occurs after age 40 with prevalence rising steeply with age; seventh ranked cause of YLDs in adults aged 70 and older.
3. Deshpande et al., Arthritis Care and Research (2016): Nearly 2 million US cases of symptomatic knee OA in adults under 45 and 6 million more aged 45 to 65; more than half of all cases under 65.
4. Felson et al., Arthritis and Rheumatism (1987): Framingham: 1,424 radiographed, aged 63 to 94; radiographic knee OA 27% under 70 vs 44% at 80+; age-related increase driven by a marked age-associated rise in OA incidence in women.
5. Loeser, Collins and Diekman, Nature Reviews Rheumatology (2016): Ageing promotes a proinflammatory, catabolic state in joint tissue with poorer repair; ageing and OA are closely linked but independent processes (no numbers used).
6. Felson et al., Annals of Internal Medicine (1992): Framingham women: a BMI decrease of 2 units or more (about 5.1 kg) over 10 years lowered the odds of symptomatic knee OA by 50% (OR 0.46).
7. Poulsen et al., British Journal of Sports Medicine (2019): 53 studies, about 1 million participants; ACL injury OR 4.2 and meniscal injury OR 6.3 for knee OA; mean age at injury 28 (ACL) and 38 (meniscal) years.
8. Dillon et al., Journal of Rheumatology (2006): NHANES III, adults 60+: radiographic knee OA 42.1% in women vs 31.2% in men; Kellgren-Lawrence grade 3 to 4 changes 12.9% vs 6.5%.
9. Srikanth et al., Osteoarthritis and Cartilage (2005): Meta-analysis: women, especially those aged 55 and older, tend to have more severe knee OA than men (no numbers used).
10. Mei et al., Frontiers in Rehabilitation Sciences (2022): OA incidence and prevalence significantly greater in women than men after age 50; knee and hip OA rise rapidly from menopausal age (around 50) to 75; evidence on hormone therapy mixed and oestrogen effect unclear.
11. Nguyen et al., Annals of Internal Medicine (2011): NHANES non-Hispanic white adults aged 60 to 74: age- and BMI-adjusted knee pain prevalence rose about 65% from 1974 to 1994; Framingham knee pain and symptomatic knee OA roughly doubled in women and tripled in men over 20 years; radiographic OA did not increase.
12. Wallace et al., PNAS (2017): Skeletal samples: knee OA 16% post-industrial vs 6% early industrial; 2.1-fold higher after controlling for age and BMI; OA "more preventable than is commonly assumed".