I was disappointed when George Carter came to see me. To be honest, I was annoyed. He was complaining bitterly about his right knee. He insisted that something had to be done, but there was nothing much to see.

I had always thought George was a robust individual, a man who would grit his teeth in a difficult situation. He’d been a policeman and then a security guard. He done building work in his spare time. He’d played rugby until he was thirty-two years old. He’d shrugged off a broken nose and two fractured ribs. He’d treated his kidney stone, said to be the cause of one of the worst pains you can get, with indifference.

George was sixty-eight years old. His knee had been causing him problems for just over six months and was slowly getting worse. It was painful when walking. It was stiff if he had been sitting for a long period. Getting up from his chair was uncomfortable. He had noticed some swelling. At times, the knee felt as if it might give way, but it never had. It didn’t lock. Although his various activities had no doubt caused a degree of trauma, George could not remember any specific, knee injury.

George’s knee was slightly swollen. I thought there was some thickening of the bone around the margins of the joint. You could also feel that there was fluid inside the joint. The ligaments appeared to be intact. There was a good range of movement. George could bend and straighten his knee without pain. If you placed the palm of your hand on his kneecap (patella) when he did this, you could feel crepitus. Crepitus is a grinding or crunching sensation. It is a common finding in osteoarthritis but often occurs in fairly normal knees. George also had some muscle wasting of his right thigh.

As far as I could tell, George’s pain was due to mild osteoarthritis.

I arranged an x-ray which confirmed the diagnosis. George came to see me for the results. I explained that I did not think his arthritis was bad enough for surgery. It might actually improve in time rather than get worse. Although he was not very overweight, losing weight would probably help. Would he like to join a supervised exercise class in the leisure centre or go swimming? I explained that both of these options would be good for his joints.

He wasn’t interested. He was adamant that he needed to see a specialist. He did not want to wait and see how things progressed. Reluctantly, I agreed to the referral. Equally reluctantly, George agreed to have physiotherapy: he was only willing to do this because I had pointed out that he would have to wait between six and twelve months for the appointment with the specialist.

‘I suppose it’s something to do in the meantime,’ he said grumpily. He wasn’t too happy about having to wait for so long, but there wasn’t much that could be done about it.

George saw Mr Alistair Wilson, the orthopaedic surgeon, about a year later. I was surprised to hear that he had been put on the waiting list for a new knee. Things must have deteriorated since I saw him.

George waited patiently for a further twelve months then came back to see me. He had had enough. His mobility was even worse despite stronger painkillers. He wanted me to chase up his operation.

I don’t like writing letters to expedite appointments or operations, not unless something unexpected has happened or there has been a drastic change. It does not seem fair to other patients. After all, you had to have very bad arthritis to get on the waiting list in the first place. How do you decide if one person’s circumstances are worse than anyone else’s? I looked at George. He was miserable. To be fair, he was limping badly now and using a walking stick.

‘Let’s check this knee again,’ I said. ‘If I am going to write to Mr Wilson, I would like to reassess it.’

George took his shoes and trousers off and got onto the couch.

At first glance, the knee looked very similar to what I remembered from before. The swelling did not seem any worse. He could bend it fully and straighten it almost completely.

‘It doesn’t seem very different to me, George. It is slightly worse, but I still think you’ve got mild osteoarthritis. I really don’t think you need a knee replacement.’

‘It’s awful, doctor. I can hardly walk. I can’t even get to the village shop. You’ve got to do something.’

I smiled sympathetically. ‘I don’t know, George. Have you been doing those exercises?’

‘They’re too painful.’

I noticed that George was lying with his right leg raised up slightly at the hip: it was at an angle of about ten degrees. His knee was bent so that his foot rested on the couch. I frowned. ‘Put your leg down flat for me,’ I said.

He tried to force the leg down. He groaned. ‘It won’t go flat. It hurts.’

‘Try harder!’

He tried again. ‘It hurts too much. I can lift it up a bit, but it won’t go down.’

I stared at George’s leg. I swallowed uncomfortably. It looked as if he had a fixed flexion deformity of his hip. He could not straighten it completely. This meant that George almost certainly had arthritis of his hip: severe arthritis.

Several factors may restrict the movement of a joint and contribute to a fixed flexion deformity in osteoarthritis. These include bony abnormalities (bone thickening or bony protuberances), scarring (fibrosis) of the joint capsule, muscle shortening (contractures) as a result of reduced mobility and pain.

‘Let me have a look,’ I muttered. I applied as much downward pressure to his thigh as I could without hurting him. The leg definitely would not move. It felt like there was a mechanical block. I shook my head.

The remainder of my examination revealed further evidence of arthritic change. The range of motion of his hip joint was severely restricted. He could hardly bring the leg out sideways. I twisted his thigh to rotate the head of the thigh bone in the joint socket. It barely budged. It grated and felt uncomfortable. George groaned again.

‘It’s your hip, George,’ I said. ‘That’s been the problem all along. The mild arthritis in your knee is a red herring.’

‘Yes, I realise that, now,’ he said. ‘I could tell that the hip wasn’t in good shape when you were examining it.’ He looked at me. ‘I haven’t had any pain there at all. Even the specialist thought it was my knee.’

‘I should have checked your hip in the beginning,’ I said. ‘I’m sorry. I thought you were making a bit of a fuss.’

He laughed. ‘That was two years ago, doctor.’

‘I know, but I think there would have been evidence of significant arthritis in the hip, even then. It’s pretty bad now.’

I arranged for an x-ray and wrote an urgent letter to Mr Wilson. A few months later, George had his hip replacement. He came to see me afterwards, once he could drive again. He felt much better. His pain had completely gone and his mobility was improving. There was a big smile on his face.

I was rather embarrassed to have been caught out like this. Hip pain is usually felt in the groin area, in the front. The groin is right over the joint itself. The pain sometimes travels down the thigh as far as the knee. Occasionally, in patients like George, the pain is only felt in the knee and not the hip. This is unusual.

As a student, I was repeatedly told that, if a patient is complaining of pain in one joint, it is very important to check adjacent joints and other nearby structures. Pain from arthritis in the neck can be felt in the shoulder. Pain from the lumbar spine may be referred into the hip or down the leg. Sciatica might only be felt in the foot.

Sometimes, the connection is less obvious. The intense ache of a heart attack might be felt in the jaw and not the chest. The first sign of lung cancer could be a painful shoulder. Pancreatic cancer can cause persistent back pain.

During all the time that I was in practice, a painful hip joint masquerading as a knee problem was the most common example of this type of medical subterfuge that I came across.

The second patient that I want to mention is Mrs Elizabeth Southgate. She was a slightly more unusual example of referred hip pain. I remembered being called out to see her one cold, autumn afternoon. She had fallen in the garden, onto the concrete path and could not move. Her daughter had tried to help her up, but she was in too much pain.

As a general rule, if an elderly lady has fallen, injured her leg and cannot move, there is a good chance that she has fractured her hip. This is less likely in men as thinning and weakness of the bones due to osteoporosis is not such a common occurrence.

When I asked specifically, Mrs Southgate told me that there was no pain in her hip. It was fine. It was her knee that was painful. She was sure she had broken one of the bones. It felt awful.

I could not examine her properly. Any attempt to move her leg, even by a few millimetres, was agony. The knee was tender to touch, but there was no swelling, bruising or deformity.

I explained that I still thought that she had fractured her hip. Mrs Southgate wasn’t convinced. She reiterated that she had had no pain there at all.

While I called the ambulance, Sally Southgate got her mother more blankets and a hot water bottle. We didn’t want her to get too cold.

As it turned out, Mrs Southgate had indeed fractured her hip. The x-rays of her knee were normal. She had surgery the next day and made a good recovery.

Mrs Southgate was the only patient I ever saw with a hip fracture that had caused knee pain but no hip pain.

OSTEOARTHRITIS

Osteoarthritis is extremely common. The hip and knee joints are frequently affected. An analysis [1] of data from the Global Burden of Disease Survey, published in 2025, estimated that, over a thirty-year period, just under 8% of the global population suffered from osteoarthritis. They noted that knee was the most commonly affected joint. A separate analysis of data from the same survey [2] showed that global age-standardised prevalence of knee osteoarthritis was 3.8% and hip osteoarthritis was 0.85%.

The hip is a ball and socket joint. The ball consists of the rounded, upper end of the thigh bone (femur). The socket (acetabulum) is a cup shaped indentation in the pelvis. Within the joint, the surfaces of the ball and socket are each covered with articular cartilage.

The knee joint is a hinge joint where the lower end of the thigh bone rests on the upper end of the shin bone (tibia). The kneecap is positioned in front of the joint. It protects the joint and ensures that the muscles and tendons remain correctly positioned when the knee is moved. Like the hip, the joint surfaces are covered with articular cartilage. The less stable structure of the knee means that it is more reliant on the ligaments and muscles to maintain its integrity.

Articular cartilage acts as a shock absorber and provides a smooth surface so that the bones can glide easily over each other when the joint is moved. Most joints are enclosed by a strong, protective capsule. The joint capsule is lined by synovial membrane. This produces synovial fluid which lubricates the inside of the joint.

For many years, it was thought that osteoarthritis was due to simple wear and tear. We now know that it is a biological process that involves low grade inflammation along with active destruction of articular cartilage.

The cartilage inside our joints is subject to all sorts of knocks and jolts. Cartilage cells (chondrocytes) are constantly repairing and refining it: they patch up small defects and smooth out bumps or other irregularities. They build new cartilage and break down and remove damaged cartilage.

It is thought that, in osteoarthritis, the maintenance of articular cartilage goes wrong. We do not know how this is triggered. Cartilage cells produce increased amounts of the chemicals (enzymes) that break down cartilage. Their repair processes cannot keep up. As a result, the articular cartilage becomes thin and eroded. Underlying bone may be exposed. Areas of bone close to joints are damaged. Bone tissue becomes thickened (sclerosis). Bony protuberances may develop. Cysts may occur just beneath the surface of the bone. In severe cases, the bones and the joints themselves become deformed.

The changes of osteoarthritis lead to pain, stiffness and a reduced range of movement of the affected joints.

It is important to remember that osteoarthritis in a joint does not always become progressively worse. The destruction of cartilage can settle and may improve.

Our joints receive a lot of support from the nearby ligaments and muscles. Exercise to strengthen these can improve joint function. Even the symptoms of severe osteoarthritis can be improved to some extent by the correct sort of exercises.

It is hoped that, in future, treatments will be developed that either prevent the breakdown of articular cartilage in the first place or help repair and replace cartilage that has been damaged or lost.

REFERENCES

1. Xie X, Zhang K, Li Y, et al. Global, regional, and national burden of osteoarthritis from 1990 to 2021 and projections to 2035: A cross-sectional study for the Global Burden of Disease Study 2021. PLoS One. 2025;20(5):e0324296. Published 2025 May 27. doi:10.1371/journal.pone.0324296
2. Cross M, Smith E, Hoy D, et al. The global burden of hip and knee osteoarthritis: estimates from the global burden of disease 2010 study. Ann Rheum Dis. 2014;73(7):1323-1330. doi:10.1136/annrheumdis-2013-204763