Why Does My Knee Hurt?

Understanding Knee Pain: Common Causes and Clinical Reasoning

Knee pain is a common clinical complaint, presenting in both active individuals and sedentary populations. Causes can vary widely from degenerative joint diseases to traumatic injuries. This article outlines the most common causes of knee pain and provides a structured clinical approach to diagnosis, with references from recent evidence-based guidelines and peer-reviewed literature.

Common Causes of Knee Pain

1. Osteoarthritis (OA)

Osteoarthritis is the most common form of arthritis and a leading cause of disability in adults over 50 [1]. It involves progressive degeneration of articular cartilage, leading to joint pain, stiffness, and functional limitation.

“Osteoarthritis is characterised by joint pain and stiffness that typically worsens with activity and improves with rest” [1].

2. Patellofemoral Pain Syndrome (PFPS)

Often referred to as “runner’s knee,” PFPS is prevalent in young adults and athletes. It is typically caused by abnormal patellar tracking or overuse and presents with anterior knee pain aggravated by climbing stairs or squatting [2].

“Patellofemoral pain is one of the most frequent causes of anterior knee pain in adolescents and young adults” [2].

3. Meniscal Tears

Meniscal tears result from trauma or degeneration, especially in older adults. They often cause joint line pain, swelling, and mechanical symptoms like locking or clicking [3].

“Degenerative meniscal tears are highly prevalent among middle-aged and older adults and may not always require surgical intervention” [3].

4. Ligament Injuries

The anterior cruciate ligament (ACL) and medial collateral ligament (MCL) are commonly injured in athletic populations. ACL injuries are frequently associated with a "popping" sound at injury and subsequent joint instability [4].

“ACL injury is a significant concern in pivoting sports and often requires surgical reconstruction in active individuals” [4].

5. Bursitis

Prepatellar and pes anserine bursitis involve inflammation of the bursa and are commonly caused by repetitive motion or prolonged pressure [5]. Pain is usually localised and worsens with activity or direct pressure.

“Knee bursitis presents with localised swelling and tenderness, typically without intra-articular involvement” [5].

6. Tendinopathy

Patellar tendinopathy, or “jumper’s knee,” is common in athletes engaged in jumping sports. It presents with focal pain over the inferior pole of the patella [6].

“Patellar tendinopathy is characterised by activity-related anterior knee pain and is best managed with eccentric exercise rehabilitation” [6].

7. Inflammatory Arthritis

Rheumatoid arthritis and other autoimmune conditions can cause synovial inflammation, leading to chronic knee pain, swelling, and morning stiffness [7].

“Early recognition and treatment of inflammatory arthritis are crucial to prevent joint destruction” [7].

8. Referred Pain

Referred knee pain may originate from the hip, spine, or sacroiliac joints. Careful history and examination are required to avoid misdiagnosis [8].

“Not all knee pain originates from the knee joint; lumbar spine or hip pathologies should be considered” [8].

Diagnostic Approach

Clinicians typically follow a structured pathway:

History: Characterise pain onset (sudden vs gradual), nature (sharp, dull), mechanical symptoms, systemic signs.
Age & Trauma: Consider degenerative vs traumatic causes based on age and activity.
Physical Examination: Inspect gait, joint alignment, swelling, range of motion, and perform special tests.
Imaging: X-ray for degenerative changes; MRI for soft tissue evaluation; ultrasound for effusions and bursitis.
Laboratory Tests: Inflammatory markers, autoimmune screening (e.g. RF, anti-CCP) when systemic disease is suspected.
Referral: Consider orthopaedic or rheumatology referral for persistent, severe, or systemic cases.

Conclusion

Knee pain has a wide differential diagnosis, and a thorough history, physical examination, and targeted investigations are key to diagnosis. Understanding age-related and mechanism-specific causes allows for effective, evidence-based management.

References (Vancouver Style)

National Institute for Health and Care Excellence. Osteoarthritis in over 16s: diagnosis and management. NICE guideline [NG226]. London: NICE; 2022. Available from: https://www.nice.org.uk/guidance/ng226
Willy RW, Hoglund LT, Barton CJ, Bolgla LA, Scalzitti DA, Logerstedt DS, et al. Patellofemoral pain: Clinical practice guidelines linked to the International Classification of Functioning, Disability, and Health. J Orthop Sports Phys Ther. 2019;49(9):CPG1–CPG95.
Katz JN, Brophy RH, Chaisson CE, De Chaves L, Cole BJ, Dahm DL, et al. Surgery versus physical therapy for a meniscal tear and osteoarthritis. N Engl J Med. 2013;368(18):1675–84.
Moksnes H, Engebretsen L, Risberg MA. Management of anterior cruciate ligament injuries in skeletally immature individuals. J Orthop Sports Phys Ther. 2012;42(3):172–82.
Akkaya S, Akkaya N, Gungor HR, Atalay NS, Sahin F, Kucukdurmaz F. The effectiveness of physical therapy in patients with prepatellar bursitis: a prospective randomized controlled study. Clin Rheumatol. 2016;35(1):169–75.
Van Ark M, Zwerver J, Van den Akker-Scheek I. Injection treatments for patellar tendinopathy. Br J Sports Med. 2011;45(13):1068–76.
Smolen JS, Aletaha D, Barton A, Burmester GR, Emery P, Firestein GS, et al. Rheumatoid arthritis. Nat Rev Dis Primers. 2018;4(1):18001.
Reid DC. The myth of referred pain in knee disorders. Clin J Sport Med. 1992;2(2):109–12.

Disclaimer:
This content is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you may have about your health or a medical condition.

Never disregard professional advice or delay seeking it because of something you have read or seen here.

The creators of this content accept no responsibility for any injury, loss, or damage arising from reliance on the information provided.

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