When It Is Not OA — Other Causes of Hip and Knee Pain

Part of The Joint Replacement Guide — Phase 1: Understanding Your Condition · Article 5 of 42 · Hip & Knee

Key Points

  • Not all hip or knee pain in adults is osteoarthritis, even when someone is in the typical age group for OA.
  • Inflammatory arthritis, avascular necrosis, and referred pain from other structures are among the important alternative diagnoses.
  • Getting the right diagnosis matters because the treatment can be very different — some conditions need urgent attention, others need a rheumatologist rather than an orthopaedic surgeon.
  • Certain “red flag” features should prompt urgent assessment rather than routine referral.

Osteoarthritis is by far the most common cause of hip and knee pain in adults, but it isn’t the only one, and part of a thorough assessment is making sure the diagnosis is actually correct before treatment — surgical or otherwise — is planned. This article covers the main alternative causes worth knowing about.

Inflammatory Arthritis

Conditions such as rheumatoid arthritis, psoriatic arthritis, and crystal arthropathies (gout and pseudogout) can all affect the hip and knee. Inflammatory arthritis tends to behave differently from OA — morning stiffness is often prolonged, lasting more than an hour rather than easing within thirty minutes, and there may be associated joint swelling, warmth, and systemic symptoms such as fatigue. Blood tests often (though not always) show raised inflammatory markers. Because these conditions are managed very differently from OA — usually led by a rheumatologist using disease-modifying medication rather than by an orthopaedic surgeon — recognising the pattern matters, and joint replacement surgery, if eventually needed, is planned alongside the rheumatology team rather than instead of it.

Avascular Necrosis (AVN)

Avascular necrosis occurs when the blood supply to part of a bone — most often the femoral head at the hip — is disrupted, causing that area of bone to die and eventually collapse. Risk factors include long-term steroid use, excess alcohol intake, previous trauma, and certain blood disorders such as sickle cell disease, though in some cases no clear cause is found. AVN often affects younger patients than typical OA, and can progress more quickly. It can look different from OA on imaging, particularly in its early stages, and an MRI scan is often needed to make the diagnosis before changes are visible on a plain X-ray.

Post-Traumatic Arthritis

A previous fracture involving the joint surface, or significant ligament or cartilage injury, can lead to arthritis years or even decades later, even if the original injury healed well and caused no problems for a long time. This is essentially OA with a clear precipitating cause, and it can affect much younger patients than typical age-related OA — something worth mentioning to your surgeon if you have a relevant injury history.

Referred Pain

Pain doesn’t always come from where it’s felt. Hip pain can sometimes originate from the lumbar spine — conditions such as lumbar radiculopathy or spinal stenosis can cause pain radiating into the buttock, thigh, and even the groin. Conversely, as covered in the previous article, hip joint pathology very commonly presents as knee pain. This is why a thorough assessment for either joint typically includes examination of the joint above and below, and sometimes the spine, rather than focusing solely on the joint you’re describing symptoms in.

Soft Tissue Mimics

A number of soft tissue conditions around the hip and knee can mimic joint pain. Greater trochanteric pain syndrome (bursitis or gluteal tendinopathy) causes pain over the outer, bony point of the hip, which is a different pattern from the groin pain typical of hip joint OA, and is managed very differently — usually with physiotherapy and activity modification rather than joint replacement. Around the knee, conditions such as pes anserine bursitis (pain on the inner side, just below the joint line) and iliotibial band syndrome (pain on the outer side, particularly with activity) can be mistaken for OA if not carefully examined for.

Red Flags — When to Seek Urgent Assessment

Most hip and knee pain, including OA, is not an emergency. However, certain features should prompt more urgent medical assessment rather than a routine referral:

  • A hot, red, swollen joint with fever — this can indicate septic arthritis, a joint infection that needs same-day assessment.
  • Sudden, severe pain with inability to weight-bear, particularly after a fall — this may indicate a fracture.
  • Unexplained weight loss, or a history of cancer, alongside new joint or bone pain.
  • Pain that is constant, worsening, and not relieved by rest or position, particularly at night.

If any of these apply to you, please seek urgent medical attention rather than waiting for a routine outpatient appointment.

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, or seek urgent care if any red flag features apply to you.

Sources

  • NICE guideline NG100 — Rheumatoid arthritis in adults: management
  • NICE guideline NG226 — Osteoarthritis in over 16s: diagnosis and management (2022)
  • British Orthopaedic Association — patient resources on hip and knee pain
  • NHS.uk — septic arthritis and avascular necrosis patient information

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