Hip Osteoarthritis: What Wears Out and How It Leads to Replacement

Hip osteoarthritis is the slow wearing away of the smooth cartilage that lines the ball and socket of the hip joint, until the bone underneath is left to rub against bone, and it is the single most common reason a hip is eventually replaced. I did not know any of that the first time my groin ached on a flat pavement. I thought I had pulled something. It took two years and a worn-out right hip for me to understand what was actually happening inside the joint, so this is the plain version no one handed me at the start.

What the hip joint is, and what wears out

The hip is a ball-and-socket joint: the rounded top of the thigh bone (the femoral head) sits inside a cup in the pelvis (the acetabulum). Both surfaces are coated in articular cartilage, a slick, gristly layer a few millimetres thick that lets the joint glide almost without friction. In osteoarthritis that cartilage thins and frays ¹.

It is not only the cartilage. As the surface breaks down, the bone underneath thickens and hardens, the joint lining can become inflamed, and the body lays down small bony outgrowths called osteophytes around the rim ². The old phrase “wear and tear” makes it sound passive, like a tyre going bald. It is closer to an active, untidy repair process that does not quite keep up with the damage.

Osteoarthritis is common. The World Health Organization estimates that hundreds of millions of people live with osteoarthritis worldwide, and the hip and knee are among the joints most often affected ¹.

The symptoms, and how they creep up on you

The first thing most people notice is pain felt deep in the groin or the front of the thigh, not on the bony outer side. Mine came on with walking and twisting, and for a long time it eased the moment I sat down. Early arthritis pain is mechanical: worse with weight-bearing, better with rest ².

Then the quieter symptoms arrive. Stiffness after sitting still, so the first few steps out of a chair are the worst. A morning stiffness that loosens within about half an hour, which is one of the features that separates osteoarthritis from inflammatory arthritis ². A range of movement that shrinks so gradually you barely register it, until one day you cannot reach the foot to put on a sock. For me the tell was sleep: the ache started waking me, and pain at night is one of the things that pushes a worn hip from nuisance towards a real problem.

What actually causes it

There is rarely one cause. The biggest risk factors are increasing age, being female, a family history of osteoarthritis, being overweight (which loads the joint), previous injury to the hip, and abnormal joint shape from birth or childhood, such as hip dysplasia or impingement ¹. The hip is most commonly replaced in people aged 60 to 80, though plenty of younger and older people develop it too.

Knowing the cause does not change the joint that is already worn, but it explains the two levers you do have some control over: keeping body weight down to reduce load, and staying active to keep the joint nourished and the muscles around it strong.

How it is diagnosed

Diagnosis is mostly clinical: your account of the pain, plus an examination where a clinician checks how far the hip moves and which movements reproduce the pain. An X-ray supports it, showing the classic signs of narrowed joint space (the gap where cartilage used to be), bony spurs, and hardened bone ².

One thing surprised me and is worth knowing: the X-ray and the pain do not always agree. Some people have alarming-looking joints and modest symptoms, and some have severe pain with milder-looking films. Treatment follows how you feel and function, not the scan alone ³. Blood tests are not used to diagnose osteoarthritis, though they may be done to rule out inflammatory types of arthritis.

How a worn joint reaches replacement

Surgery is the end of a road, not the start of one. International guidance is consistent that first-line care for hip osteoarthritis is non-surgical and is offered to everyone: education, structured exercise, and weight management, with pain relief layered on as needed ³. Exercise in particular has good evidence behind it: a Cochrane review found that land-based exercise reduces hip pain and improves function, with benefits lasting for months after a programme ⁴. Counter-intuitive, when every step hurts, but the joint does better moving than resting.

You can read more on the alternatives to hip replacement and on the signs it is time for a hip replacement, because that judgement deserves its own space.

Replacement enters the conversation when pain and loss of function persist despite a genuine effort at those measures, and when the limits on daily life and sleep have become hard to live with. There is no single number on a scan that flips the switch. In my case it was the accumulation: the limp, the broken nights, the walk I had quietly given up. When the worn joint finally is replaced, total hip replacement surgery swaps the worn ball and socket for an artificial ball, stem, and socket, and it is one of the most effective operations in modern medicine for relieving arthritis pain. That, though, is a later chapter. This one is simply about understanding the joint that brought you here.

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General information, not medical advice. Hip pain has several causes, and the right path depends on your own joint and circumstances; please see a qualified clinician for diagnosis and treatment.