Risk IV: Bones, Joints, and Wearing Out

Part IV of the Risks series. Parts I through III covered cardiovascular disease, cancer, and neurodegenerative disease.

The short version

• This one is about function, and function is what people actually mean when they say "healthy." The first three parts covered what kills you. This one covers what takes your capability first, and then, by way of a fall and a hip fracture, kills you anyway.

• The account closes early. Peak bone mass is set by around age 30. After that you are managing withdrawals, and women make the largest ones in the years around menopause. This is an article for 25-year-olds as much as 65-year-olds.

• The patient is not the image, and effort beats repair. Most of the money goes to scans and procedures on the back end. Most of the result comes from what you load, what you eat, and what you weigh for the decades before.

When patients tell me they want to be healthy long term, they almost never mean a lab value. They mean they want to be on the floor with their grandchildren at 75 and able to get back up. They want to travel, carry their own bag, and do the things that make the trip worth taking. Health, as most people actually use the word, is function.

Function is also the most taken-for-granted thing you own. Most people never push themselves hard enough to notice it slipping. If you don't regularly stress the body, there is nothing to tell you that the ceiling has been coming down an inch a year.

The stakes are larger than they look. Low back pain is the leading cause of disability in this country. Chronic musculoskeletal pain is how a lot of people end up on years of anti-inflammatories, with the stomach, kidney, and blood pressure costs that come with them, and it is how a lot of people met opioids. About one in four adults over 65 falls each year. One in two women and up to one in four men over 50 will have an osteoporotic fracture. Falls are the leading cause of injury death after 65, and a hip fracture after 65 carries roughly 20% to 30% one-year mortality. In practice, the hip fracture is very often the beginning of the end.

The frame is the same one as the rest of this series, adjusted for the tissue. Build on the front end, measure in the middle, repair on the back end.

The nest egg

The analogy I use with patients is retirement savings. Cardiovascular fitness, muscle, and bone are a nest egg. Aging is going to take withdrawals whether you approve them or not. Hormones decline, muscle mass drops, bone thins. The size of the account when the withdrawals begin determines how long you stay functional.

The depressing part, and I watch it land on people's faces, is how early the contribution window closes. Peak bone mass is reached by about 30, a little earlier in women than in men. Most of it is built in the teenage years and early twenties. Muscle mass and power start a slow slide in the thirties. So the biggest determinants of your hip at 80 are what you did at 15: whether you ate enough, whether you jumped and sprinted and lifted, whether you were under-fueled through puberty in a sport that rewarded being light.

For women, the largest single withdrawal comes in the years around menopause, when estrogen falls and bone loss accelerates.

None of that means the account is frozen after 30. You can still contribute at 50 and at 70. An untrained system improves at any age. The deposits are just smaller, which is an argument for starting now and not an argument for giving up.

What actually wears a joint out

"Wearing out" is in the title because that is how people talk about it. It is mostly the wrong model. A joint is not a brake pad.

Articular cartilage has no blood supply. It is fed by movement, by the compression and release that pushes fluid in and out of the tissue. The line you hear all over the musculoskeletal world is that movement is life, and for cartilage that is close to literal. The best data I know on this is in runners. Recreational runners have less hip and knee arthritis than sedentary people, on the order of 3.5% versus 10%. Competitive, high-volume runners are the ones who run higher, around 13%.

That second number is the honest half of the story. Three things reliably produce arthritis over time: volume without adequate recovery, excess body weight, and prior joint injury with cartilage damage. Excess weight works through more than load. Arthritis of the hand tracks with obesity, and nobody walks on their hands.

There is a fourth thing that I see constantly and that gets very little attention: muscular imbalances that were ignored for twenty years. In highly active people they surface in the thirties. In everyone else, the forties and fifties. The joint was never the original problem. It is where the bill was sent.

Where the money goes

Same pattern as cancer. The dollars go to repair on the back end, and the results come from the front.

In musculoskeletal care, active treatment almost always beats passive treatment. Active means the patient has to do work. Passive means something is done to the patient, and surgery is the most passive treatment there is. For several of the most common operations, the trials are humbling. Arthroscopic surgery for a degenerative meniscal tear performed no better than sham surgery. The common shoulder decompression procedure performed no better than a placebo operation. In a lot of these conditions, physical therapy alone lands in the same place.

I want to be fair to the surgeons, the same way I was fair to the oncologists. A displaced fracture needs fixing. A full-thickness tendon tear that will otherwise cost you strength permanently needs repair, and I've had one repaired myself. Hip replacement, when it is indicated, is one of the best operations in medicine for pain and quality of life. The problem is not surgery. It is surgery as a substitute for the work.

The other thing to understand is that the patient is not the image. In studies of people with no back pain at all, disc degeneration shows up on MRI in about a third of 20-year-olds and nearly all 80-year-olds. The relationship between what the picture shows and how much the person hurts is weak. An MRI of a joint that doesn't bother you is a very efficient way to acquire a diagnosis you didn't need.

What's worth measuring

In the clinic we already measure most of this. Body composition tells us skeletal muscle mass. Grip strength is the cheap proxy for whole-body strength. VO2 max covers cardiovascular reserve. Those are three of the five measurements on the Health Score Card.

Then there are the tests that cost nothing. Get up off the floor without using your hands. Stand on one leg. Count how many times you can rise from a chair in thirty seconds. Stand up, walk ten feet, turn around, and sit back down, on a clock. Be clear about what these measure. They are not fitness tests. They mark the minimum level of function required to live independently. Passing them at 45 is not an achievement. Failing one is a finding.

The gap is bone. I said in the Score Card article that body composition testing can't see bone density, and it can't. The guideline is a DEXA scan for women at 65, and earlier for postmenopausal women with risk factors. If you've been on long-term steroids, you're thin, you went through menopause early, osteoporosis runs in your family, or you broke a bone falling from standing height, you should not be waiting for 65.

What you do with the answer

Prevention here is not complicated. Maintain a healthy body weight. Lift regularly. Do regular cardiovascular work. I cannot emphasize enough how many different systems exercise acts on at once, and the payoff is not deferred to the end of your life. It shows up in the decades before, as energy and as a general sense of being well.

Protein is where I think the largest gap sits between the official number and what the body actually needs. My working estimate is one gram per pound of lean body mass per day. The recommended dietary allowance comes out to roughly half of that for most people, because it was set as the minimum to prevent deficiency, not as the amount that drives muscle protein synthesis. If you are past midlife and trying to hold on to muscle, the minimum is not the target.

Total calories matter too, at both ends. Under-eating through puberty costs bone that cannot be fully bought back later. Under-eating while training hard does a version of the same thing at any age.

Train balance and power on purpose. Those are the qualities that go first, and power is what catches you when your foot slips. Strength you can't express quickly doesn't prevent a fall.

On hormones, I'll give the careful version. In women, estrogen has real fracture data. In the Women's Health Initiative it reduced hip fractures by about a third, and it is approved for preventing osteoporosis. What we don't have are head-to-head trials showing it beats the standard bone medications, so I treat bone as one good reason among several to have the conversation in the menopause window and not as a standalone prescription. In men, testosterone improves bone density on a scan, but the largest trial we have found more fractures in the treated group, not fewer. A better scan is not the same thing as a bone that doesn't break.

GLP-1s cut both ways here. Losing weight unloads the joints, and semaglutide has trial data showing a meaningful reduction in knee arthritis pain. But a real share of the weight lost on these drugs is lean mass, and bone tends to follow muscle. I covered this last week. The drug without protein and lifting trades one risk for another.

What's in your control

Not in your control. Your age, your sex, your genetics, and the knee you tore up at 19.

In your control. It is the list you have now seen four times. Eat enough whole food, with enough protein in it. Hold a healthy body weight. Lift and do your cardiovascular work. Sleep.

I'd apologize for the repetition, except the repetition is the finding. The same short list lowers your risk of a heart attack, of cancer, of dementia, and of a broken hip. There is no joint-specific secret.

Three things to do

1. Get down on the floor tonight and stand back up without using your hands. Then stand on one leg for thirty seconds on each side. If either one is harder than you expected, you've just found out something an MRI would not have told you.

2. Lift something heavy twice a week and count your protein for one week. Most people are doing neither. Aim for roughly a gram of protein per pound of lean body mass, and scale the loading to where you are today, not where you were in college.

3. Find out whether you need a bone density scan before 65. Long-term steroids, a thin frame, early menopause, a family history of osteoporosis, or a fracture from a standing-height fall all move the date up. Bring it to your next visit.

Next in this series: Risks V — Alcohol and the Other Substances.