Knee osteoarthritis: symptoms, treatment and when surgery is considered

The knee is where the thigh bone and shin bone meet, with the kneecap at the front. The bone ends are covered in smooth cartilage, and two rings of tougher cartilage called menisci help spread weight across the joint. Arthritis UK explains that in osteoarthritis the joint's ability to repair itself becomes less effective, the cartilage thins and roughens, and bony spurs called osteophytes can form, so the joint moves less smoothly.

NICE Clinical Knowledge Summaries frames osteoarthritis as a disorder of the whole joint with cartilage loss, remodelling of nearby bone, osteophytes and mild inflammation of the joint lining. It is a long-term condition, but the NHS stresses that it does not necessarily get worse over time and can sometimes gradually improve.

NICE guidance sets out a step-by-step approach. The core treatments are therapeutic exercise and, where appropriate, weight management, supported by information and support. Medicines are added alongside these rather than instead of them, and surgery is reserved for people whose symptoms are substantially affecting their quality of life despite non-surgical care.

The sections below cover each step in more detail. The table summarises the order in which NICE and Arthritis UK describe the options.

Arthritis UK describes pain, either all around the knee or in one place, stiffness or difficulty moving it, creaking or grating sounds, leg weakness and a feeling that the knee gives way. Swelling may be hard, from bony spurs, or soft, when the joint makes extra fluid, sometimes called water on the knee.

Symptoms usually fluctuate with good and bad days. They tend to be worse at the end of the day or when moving the knee, for instance on stairs or rising from a chair, and better with rest. Morning stiffness is usually brief, rarely lasting more than half an hour. Some people have pain that wakes them at night, and Arthritis UK notes that the amount of pain does not always match the amount of change in the joint.

NICE CKS also describes flares, defined as a sudden, sustained increase in symptoms for at least 24 hours that is worse than usual and typically lasts 3 to 8 days. Complications can include a change in joint shape, a Baker's cyst behind the knee and changes in walking that load the hips or back.

No single cause explains knee osteoarthritis. The NHS lists age, joint injury, family history, obesity, other joint conditions such as rheumatoid arthritis or gout, and being a woman as factors that raise the risk. Arthritis UK names being overweight, inherited genes, previous knee injury and other joint conditions, and says it is most common in women over 50.

The load on the knee matters. The NHS says being obese puts excess strain on weight-bearing joints such as the knees and hips, and Arthritis UK reports that weight issues are linked to symptoms in nearly 1 in 4 people with knee pain. The NHS also says exercise or a job that puts frequent strain on joints, so that they bear an excessive load, can increase the risk.

NICE guideline NG226 recommends diagnosing osteoarthritis clinically, without imaging, in people who are 45 or over with activity-related joint pain and either no morning stiffness or stiffness that lasts no more than 30 minutes. Imaging is not used routinely unless there are atypical features or features that suggest another diagnosis.

NICE defines atypical features as recent trauma, prolonged morning stiffness, rapid worsening or deformity, a hot swollen joint, or concerns about infection or cancer. In those cases NICE CKS suggests a joint X-ray, and the NHS says X-rays or blood tests are used mainly to rule out other causes such as rheumatoid arthritis or a fracture. A scan showing wear does not by itself predict how much pain someone has.

NICE says the core treatments are therapeutic exercise and, where appropriate, weight management, supported by information. It tells clinicians to offer exercise tailored to the person, such as local muscle strengthening and general aerobic fitness, and to consider supervised sessions. It also advises explaining that pain may rise at first, but regular, consistent exercise benefits the joints in the long run.

For people living with overweight or obesity NICE advises that any weight loss is likely to be beneficial and that losing 10% of body weight is likely to be better than 5%. Arthritis UK suggests swimming or water-based exercise and walking, pacing activities, wearing shoes with thick soles, using a walking stick in the opposite hand, and using a handrail on stairs. NICE says to consider walking aids for lower-limb osteoarthritis but not to offer insoles, braces or supports routinely unless there is joint instability and exercise has not worked.

NICE advises that medicines are used alongside exercise, at the lowest effective dose for the shortest time. For knee osteoarthritis it says to offer a topical NSAID gel or cream first. If topical treatment is ineffective or unsuitable, an oral NSAID can be considered with a stomach-protecting medicine, taking account of risks to the stomach, kidneys, liver and heart.

The guideline is cautious about other options: it says not to routinely offer paracetamol or weak opioids, that paracetamol has no strong evidence of benefit, and not to offer glucosamine or strong opioids. NHS pages still mention capsaicin cream for hands and knees when topical NSAIDs have not helped, and say steroid injections can ease pain for several weeks or months. NICE puts that at 2 to 10 weeks and suggests injections only when other treatments are ineffective or unsuitable, or to support exercise. NICE also says not to offer hyaluronan injections, which Arthritis UK notes are not generally available on the NHS.

NICE says to consider referral for joint replacement when symptoms such as pain, stiffness, reduced function or progressive deformity are substantially affecting quality of life and non-surgical management has been ineffective or unsuitable. Referral should rest on clinical assessment rather than a numerical severity score, and people should not be excluded because of age, sex, smoking, other conditions or a high BMI, although NICE says the risks can vary with those factors.

Arthritis UK says up to 8 in 10 knee replacements could last as long as 25 years, while noting that surgery carries risks that the surgeon will explain. Keyhole washout is not usually offered for knee osteoarthritis unless there are clear mechanical problems such as locking. NICE CKS suggests an orthopaedic referral if non-surgical care has failed after 3 months or if there is diagnostic uncertainty or sudden worsening.

On the NHS, care typically begins with a GP or a self-referral musculoskeletal service, then a physiotherapist-led programme, and an orthopaedic opinion if that has not worked. NICE CKS describes a local multidisciplinary musculoskeletal team that can provide manual therapy, aids and devices, injections and structured education.

Some people choose a private physiotherapist or orthopaedic surgeon to shorten the wait. The clinical threshold for surgery should not change: ask what has been tried, what the realistic benefit is, and the specific risks for you.