Red flags for knee pain: when to seek professional help

Knee pain is a common complaint among Australians of all ages, from active teenagers to older adults managing osteoarthritis. While many cases of knee discomfort are benign and respond well to rest or physiotherapy, some symptoms may indicate a more serious underlying issue. These are known as red flags – warning signs that suggest the need for urgent medical assessment.

In this blog, we’ll explore the key red flags for knee pain, explain why they matter, and help you understand when it’s time to seek professional help. Whether you’re a weekend warrior, a tradie, or simply someone who wants to stay active, recognising these signs early can make all the difference.

What are red flags in knee pain?

Red flags are clinical indicators that suggest a potentially serious pathology. In physiotherapy, identifying these signs is crucial to ensure timely referral to a GP, orthopaedic specialist, or emergency care when needed.

According to Australian clinical guidelines and expert consensus, red flags for knee pain include:

1. Persistent or severe pain

• Unbearable discomfort that makes walking difficult.
• Constant ache that doesn’t improve with rest or standard treatment.
• Night-time pain that disrupts sleep.

Persistent pain may indicate structural damage, underlying inflammatory conditions such as rheumatoid arthritis, infection, or advanced joint degeneration and should not be ignored (1).

2. Swelling and inflammation

• Noticeable puffiness or fluid build-up around the knee.
• Warmth to the touch, or redness.
• Restricted movement due to swelling.

Swelling or inflammation can be present in conditions such as septic arthritis, or acute injury. If swelling is accompanied by fever or malaise, urgent medical evaluation is essential (1).

3. Changes in appearance or structure

• Visible deformities, such as abnormal bumps or misalignment.
• Discolouration of the skin around the knee.
• Sudden onset of fluid accumulation.

Structural changes can be signs of fractures, ligament ruptures, or tumours. These require imaging and specialist input (1).

4. Mechanical symptoms

• Locking of the knee joint, where it gets stuck during movement.
• Popping or crunching sounds, especially if accompanied by pain.
• Instability or a “wobbly” feeling, which may indicate ligament damage or meniscal tears.

Mechanical symptoms often suggest internal derangement (damage to the structures within the joint) of the knee and may require surgical intervention (1).

5. Neurological or systemic signs

• Numbness or tingling in the leg or foot.
• Sudden weakness or inability to bear weight.
• Fever, chills, or unexplained weight loss.

These signs may be associated with nerve compression, infection, or systemic illness such as cancer or deep vein thrombosis (DVT) (1,2).

When should you see a physiotherapist or GP?

If you’re experiencing any of the red flags listed above, it’s important to seek professional help promptly. A physiotherapist can perform a thorough musculoskeletal assessment and refer you for further investigations if needed.

You should see a GP or physiotherapist immediately if:

• Your knee pain is severe and sudden.
• You notice swelling, redness, or warmth.
• You cannot fully bend or straighten your knee.
• You experience instability or locking.
• You have systemic symptoms like fever or fatigue.

In cases of trauma, deformity, or suspected fracture, head straight to your local emergency department.

Common conditions associated with red flags

Some of the serious conditions that may present with red flags include:

• Septic arthritis – a joint infection requiring urgent antibiotics and drainage.
• Ligament ruptures – such as ACL (anterior cruciate ligament) rupture.
• Meniscal tears – especially if locking or clicking is present.
• Osteonecrosis – spontaneous bone death, often seen in older adults.
• Tumours or metastases – rare but serious causes of knee pain.
• DVT (deep vein thrombosis) or vascular disease – presenting with swelling, warmth, and pain in the calf or knee (1,2).

How physiotherapy for knee can help

For non-emergency knee pain, physiotherapy remains one of the most effective treatments. Your physio will:

• Conduct a detailed assessment.
• Identify any red or yellow flags.
• Develop a personalised rehabilitation plan.
• Refer you to a GP or specialist if needed.

Early intervention can prevent complications, improve mobility, and reduce the need for surgery.

Address your knee pain today

Knee pain is common, but not all pain is created equal. Recognising red flags is essential for protecting your long-term joint health. If you’re unsure whether your symptoms are serious, it’s always better to err on the side of caution and seek professional advice.

At our Lifecare clinics, we’re here to help you stay active, pain-free, and informed. Book an appointment today if you’re experiencing knee pain that concerns you.

References

• Clinical Reference MSK. Red Flags – Knee | Lower Limb [Internet]. ClinRef; [cited 2025 Sep 19]. Available from: https://clinref.com/red-flags/red-flags-knee-lower-limb/
• . Physiopedia. Understanding Red Flags in Patellofemoral Pain [Internet]. Physiopedia; [cited 2025 Sep 19]. Available from: https://www.physio-pedia.com/Understanding_Red_Flags_in_Patellofemoral_Pain