Knee pain

What your diagnosis means

Knees get a lot of attention. We notice them on the stairs, kneeling in the garden, getting up from a low sofa or halfway round a Saturday parkrun. And when a knee starts to hurt, the labels come thick and fast: arthritis, a torn cartilage, runner's knee, tendonitis, a sprain.

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Many people I meet have been given more than one of these over the years, often without much explanation. So let me take you through what each common knee diagnosis means.

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A quick tour of the knee

The knee is essentially a hinge between the thigh bone (femur) and the shin bone (tibia), with the kneecap (patella) sliding in a groove at the front. The bone ends are covered in smooth cartilage, and sitting between them are two C-shaped pads of rubbery cartilage called the menisci. Four main ligaments hold the joint together: two inside the knee, the anterior and posterior cruciate ligaments (ACL and PCL), and one on each side, the medial and lateral collateral ligaments (MCL and LCL). At the front, the quadriceps tendon attaches to the top of the kneecap and the patellar tendon runs from the kneecap to the shin.

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Knee osteoarthritis

Knee Osteoarthritis is the most common arthritis label for knees, especially in people over 45. The diagnosis describes the smooth cartilage thinning and changing, along with changes in the bone underneath and sometimes small bony growths around the joint. You'll often hear it called 'wear and tear'. People given this label commonly describe stiffness and aching, sometimes in both knees, and occasionally a grating or crackling feeling when the knee moves. A GP can diagnose it from your age and symptoms, without needing an X-ray.

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Meniscus tear

When people say they've 'torn a cartilage', they usually mean a meniscus tear. The menisci act as shock absorbers and help the knee stay stable, and a tear describes a split in one of them. There are two broad types. A traumatic tear tends to happen with a sudden twist while your weight is on the knee, which is common in sport. A degenerative tear comes on gradually, with no clear injury, and is more commonly seen in adults from about 35 onwards. People given this label sometimes describe the knee catching, clicking, locking or giving way.

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Patellofemoral pain (runner's knee)

Patellofemoral pain describes discomfort at the front of the knee, around or behind the kneecap, where it glides over the thigh bone. You may also have heard it called runner's knee, anterior knee pain or chondromalacia patellae. Despite the nickname, it isn't limited to runners. It's one of the most common knee labels, in active and less active people of any age.

People given this diagnosis often describe aching on the stairs (especially going down), when squatting or kneeling, or after sitting for a long time, such as in the cinema. A grinding sound (crepitus) is common with this label.

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Tendinopathy

As with other joints, 'tendinopathy' describes a tendon that is painful or not coping as well as usual with what it's being asked to do. In the knee, the label usually refers to the patellar tendon, between the kneecap and the shin, and you may hear it called 'jumper's knee' because it's often linked with running and jumping sports. Less commonly, it refers to the quadriceps tendon just above the kneecap.

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Ligament sprain

A sprain is a stretched or torn ligament, usually after a twist, a sudden change of direction or a knock. Sprains are often graded from mild (stretched) to severe (completely torn). In the knee, the MCL on the inner side is commonly involved when the knee is pushed inwards. An ACL injury tends to happen with a twist or pivot, sometimes with a popping sound, and people often describe the knee feeling unstable or giving way afterwards.

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These labels describe what a scan or examination shows. They don't explain why pain persists and for many people the nervous system is an important part of the picture.

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Where arthritis fits

Many people assume that a painful knee in midlife must be arthritis, when the label they've been given is actually one of the musculoskeletal ones above. If you'd like to understand more about arthritis read my page on what arthritis means.