Septic arthritis

Septic arthritis is a bacterial infection inside a joint. Two things set it apart from other joint pain: it usually affects one joint only, and it comes on fast — over hours or a day or two, not over weeks. It is a medical emergency and needs to be treated as one. The bacteria and the inflammation they trigger dissolve joint cartilage within days, and lost cartilage does not grow back. At the same time, septic arthritis responds well to treatment, provided the person gets to hospital straight away rather than after a week of watching the joint.

Why this cannot wait until Monday

The inside of a healthy joint is sterile and has no way of defending itself against microbes. As soon as bacteria get in, inflammatory cells pour in after them, and the joint fluid turns into a mixture of enzymes that eats away at cartilage. This starts on the first day. Within a few days some of the damage is already permanent: even once the infection has been cured, the joint may stay stiff, sore under load and less mobile than before.

The second reason for urgency is the microbe itself. It travels from the joint into the bloodstream, and septic arthritis often comes together with sepsis, which is life-threatening in its own right.

Hence a simple rule: a hot, swollen, almost immovable joint that got that way in a day or two means going to hospital today, not booking an appointment for later in the week. This cannot be managed at home under any circumstances. The joint has to be punctured with a needle, fluid taken for analysis, the pus drained, and intravenous antibiotics started at the same time. None of those steps can be done outside hospital.

What an infected joint looks like

The picture is usually hard to miss:

• severe constant pain, present even at complete rest and turning sharp with the slightest movement;
• the joint is swollen and the skin over it is hot and often red;
• movement is almost impossible: the person holds the leg or arm in one position and will not let anyone touch it;
• inability to put weight on the leg if the knee, hip or ankle is involved;
• fever, shivering, aching and a general sense of being seriously unwell.

The knee is affected most often, then the hip, shoulder, ankle and wrist. As a rule only one joint is involved. If several become inflamed at once and the person is clearly unwell, the situation is no less urgent — more often it means the infection arrived through the bloodstream.

Call an ambulance (in Spain, Italy, Portugal, Poland and Ukraine the single number is 112) if the painful joint is joined by confusion, rapid breathing, extreme weakness, shivering, mottled or greyish skin, or passing very little urine. These are signs of sepsis.

When there is no fever but there is arthritis

This is the commonest reason people arrive late. Infection is expected to come with a temperature, so if the thermometer reads 36.9 the person decides they have simply strained the joint and takes a painkiller. Fever may in fact be absent altogether:

• in older people, in whom serious infection often runs without a temperature and shows up instead as confusion, unusual drowsiness, weakness or refusing food;
• in anyone on immunosuppressive treatment for rheumatoid arthritis, psoriasis, inflammatory bowel disease, an organ transplant or chemotherapy;
• in anyone already taking steroids or anti-inflammatory painkillers for another reason: these blunt both fever and pain, and the redness looks milder than it is;
• in people with diabetes or chronic kidney disease.

So the thing to go by is the joint, not the thermometer. One joint that has become hot, swollen and immovable within a day is reason enough to go to hospital, even with a normal temperature and even if you otherwise feel tolerable.

Where the infection comes from and who is more at risk

There are only three routes. Most often the blood carries bacteria in from another focus — the skin, the urinary tract, the lungs, an infected tooth. Less often they enter directly through a wound, a bite, a deep graze, a joint injection or joint surgery. Very rarely the infection spreads across from neighbouring bone.

The risk is higher in people:

• with rheumatoid arthritis or other inflammatory joint disease — the danger here is twofold, from the disease and from its treatment, and above all because the joint already hurts, so the change gets put down to a flare;
• with a joint replacement, or recent joint surgery or an injection into the joint;
• with a weakened immune system, diabetes or severe liver or kidney disease;
• of older age;
• with ulcers, wounds or infected skin lesions, particularly on the feet;
• who inject drugs.

Gonorrhoea is a story of its own. In young sexually active people the gonococcus sometimes travels beyond the genitals and causes inflammation of joints and tendons together with a sparse skin rash. It looks milder than classic septic arthritis and treats well, but finding the cause is still a job for a doctor.

"It looks like gout" is not a reason to wait

A gout attack, other crystal deposits in a joint and septic arthritis all look the same: one joint, hot, red, sharply painful, sometimes with a temperature. Telling them apart by examination and blood tests is not possible. The uric acid level does not help: during an acute attack it is often normal, and someone with years of gout can have an infected joint as well, because one does not rule out the other.

The only way to settle it is to take fluid out of the joint: it is examined under the microscope for crystals and sent for culture. So if the attack is worse than usual, has struck a joint other than the usual one, comes with shivering, or is not responding to the medicine that always worked, it needs sorting out in hospital the same day rather than by increasing the dose at home.

An artificial joint is a separate matter

Infection of a replaced joint behaves differently and is treated differently. The early kind, in the first weeks after the operation, shows in the wound: it weeps, reddens, the edges pull apart, discharge appears. The late kind, months or years on, often runs without fever — the joint simply stops feeling like your own: it aches constantly, hurts from the first steps and at night rather than only under load, and may feel loose. Any other focus in the body, from a tooth to a urinary infection, can seed a prosthesis.

Antibiotics alone almost never cure it: the bacteria live as a film on the surface of the implant, where the drug does not reach. Surgery is usually needed — a recent infection means washing out the joint and exchanging the removable parts, while a long-standing one means taking the prosthesis out and putting a new one in, in one or two stages. That is why timing matters so much here: the sooner, the better the chance of keeping the implant. With any new pain, swelling or redness around an artificial joint, contact the surgeon who operated rather than waiting for a scheduled review.

In a child: not putting weight on the leg

In children the hip is the joint most often affected, and it is harder to spot: it sits deep, and from the outside there is neither swelling nor redness to see. You have to go by behaviour:

• the child has stopped putting weight on the leg, is limping, or wants to be carried;
• lies with the leg held in one fixed position, slightly bent and turned outwards, and screams if anyone tries to straighten or rotate it;
• in a baby, the leg moves less than the other one and there is crying during changing and nappy changes;
• fever, listlessness, refusing food and drink.

A child who refuses to put weight on a leg must be seen by a doctor the same day — this rule has no exceptions. There is a similar and far more harmless condition, a temporary inflammation of the hip after a recent cold, which settles on its own within days. But telling the two apart is for doctors, with blood tests and an ultrasound scan of the joint, and until then the worst case is assumed.

What happens in hospital

The first step is to aspirate the joint: the fluid goes for culture and microscopy, and its appearance alone already tells the doctor a great deal. Intravenous antibiotics are started immediately afterwards, without waiting for the culture, aimed at the likeliest organisms; once the culture is back, treatment is narrowed down. In parallel the joint is cleared out, by repeated aspirations, by washout through an arthroscope, or by open surgery if there is a lot of pus or the joint is hard to reach.

Antibiotics into a vein usually continue for a few days or up to two weeks, after which they are switched to tablets for several weeks more. The course has to be finished even once the pain has gone and everything seems over: a partly treated bone and joint infection comes back, and it is harder to treat the second time. As the inflammation settles, careful movement of the joint begins, because movement is part of the treatment — an immobilised joint scars up and loses range quickly.

Online consultation

On this topic an online appointment is useful for one thing above all: answering quickly whether you should be going to hospital now or can safely watch and wait. The Oladoctor doctor will ask how fast it all started, what exactly is happening to the joint and what conditions and medicines are in the background, then say plainly whether this looks like joint infection and where to go. This is a case where the consultation does not replace a hands-on examination but stops you losing a day to doubt. Online is also a good place to sort out the aftermath: how to take the prescribed course, what to do about pain, when to load the joint again, and what to do if it swells up once more after discharge. If the description suggests you need emergency care, you will be told so straight away.

This material is for information only and does not replace medical advice.