Knee Osteoarthritis — Symptoms, Examination and X-rays

Part of The Joint Replacement Guide — Phase 1: Understanding Your Condition · Article 3 of 42 · Knee

Key Points

  • Knee OA most commonly affects the inner (medial) side of the knee first, often linked to a bow-legged (varus) alignment.
  • Pain, swelling, stiffness and a grinding or grating sensation (crepitus) are the classic features.
  • The knee has three separate compartments, and which ones are affected influences treatment options, including whether a partial or total knee replacement may be suitable.
  • Weight-bearing X-rays are more informative than X-rays taken lying down, because they show how the joint behaves under load.
  • As with the hip, X-ray severity does not always match symptom severity.

Typical Symptoms of Knee Osteoarthritis

Knee OA typically presents with pain that is worse with activity and improves with rest, though as the condition progresses pain can occur at rest and disturb sleep. Common features include:

  • Pain localised to the inner (medial), outer (lateral), or front (patellofemoral) part of the knee, depending on which compartment is most affected.
  • Stiffness after periods of rest, easing with movement.
  • Swelling, sometimes with a visible or palpable effusion (fluid within the joint).
  • A grinding, grating or crackling sensation (crepitus) with movement.
  • A feeling of the knee “giving way”, particularly on stairs or uneven ground — usually due to weakness or pain inhibition rather than true ligament instability.
  • Difficulty with kneeling, squatting, and descending stairs, which tend to be affected earlier and more severely than ascending.

How We Examine the Knee

We assess your gait and overall leg alignment first — knee OA is strongly associated with varus (bow-legged) alignment when the medial compartment is affected, and valgus (knock-kneed) alignment when the lateral compartment predominates. On the couch, we check for an effusion, assess range of movement (a flexion contracture, where the knee cannot fully straighten, is common in more advanced disease), feel for tenderness along the joint line, and test the ligaments to make sure there isn’t an additional element of instability. We also examine the patellofemoral joint specifically, as anterior knee pain and difficulty on stairs can point to this compartment being the main driver of symptoms. Where the story is unclear, tests such as McMurray’s test help assess for an associated meniscal tear, which frequently coexists with OA.

X-rays and Imaging

Standard views include a weight-bearing AP X-ray (taken standing, which shows true joint space narrowing far better than a view taken lying down), a lateral view, and a skyline or patellofemoral view to assess the joint behind the kneecap. As with the hip, we look for joint space narrowing, osteophytes, subchondral sclerosis and cysts, and grade severity using the Kellgren-Lawrence system.

A key difference from the hip is that the knee has three separate compartments — medial, lateral and patellofemoral — and OA can affect one, two, or all three. This matters practically: someone with isolated medial compartment OA and an intact anterior cruciate ligament may be a candidate for a partial (unicompartmental) knee replacement rather than a total knee replacement, which is a smaller operation with a faster recovery, though not everyone is suitable and the decision depends on several factors covered elsewhere in this guide.

In More Depth

The relationship between alignment and OA progression works in both directions — malalignment increases load through the affected compartment and accelerates cartilage loss, and as that compartment narrows further, the malalignment itself tends to worsen, creating a self-reinforcing cycle. This is one of the reasons some surgeons monitor alignment over time rather than relying on a single X-ray, and why long-leg alignment films (showing the whole leg from hip to ankle) are sometimes requested when planning surgery, particularly if significant deformity correction is anticipated.

It’s also worth understanding that meniscal tears are extremely common findings alongside knee OA, particularly degenerative tears that occur as part of the same ageing process rather than a discrete injury. In this context, meniscal surgery (arthroscopy) generally does not improve OA symptoms and is not routinely recommended for degenerative tears found alongside established OA — a point that sometimes surprises patients who expect “cleaning out” the knee to help, but which is well supported by trial evidence and reflected in national guidance.

This article is general information and does not replace individual clinical advice. If you are concerned about your symptoms, please speak to your GP or a specialist.

Sources

  • NICE guideline NG226 — Osteoarthritis in over 16s: diagnosis and management (2022)
  • British Association for Surgery of the Knee (BASK) patient resources
  • Royal College of Radiologists — imaging guidance for suspected osteoarthritis
  • Cochrane Database of Systematic Reviews — arthroscopic meniscal surgery in degenerative knee disease

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