Knee Pain: Causes, Treatment, and When to See a Doctor

## Overview Knee pain is one of the most common musculoskeletal complaints in primary care, affecting an estimated 25% of adults and accounting for nearly 4 million primary-care visits annually in the United States alone (PMID:22006937). It can originate from any structure in or around the knee joint — bone, cartilage, menisci, ligaments, tendons, bursae, or the surrounding muscles and nerves. The ICD-10 codes most frequently used for unspecified knee pain are **M25.561** (right knee) and **M25.562** (left knee). People search for information on knee pain because it directly affects mobility, independence, and quality of life. Whether caused by an acute sports injury, gradual wear-and-tear osteoarthritis, or an inflammatory condition, knee pain can range from a mild, self-limiting nuisance to a debilitating problem requiring surgical intervention. Understanding the potential causes, knowing when to seek care, and being aware of safe self-management strategies are essential first steps. > **Important:** This article is for general educational purposes and does not replace individualized medical advice. Always consult a qualified healthcare professional for diagnosis and treatment of knee pain. --- ## Common Causes Knee pain can be broadly grouped into mechanical/degenerative, inflammatory, traumatic, and referred categories. The following are ranked roughly by how often they present in clinical practice. ### 1. Osteoarthritis (OA) The single most common cause of chronic knee pain in adults over 50. OA involves progressive degradation of articular cartilage, subchondral bone remodeling, and low-grade synovial inflammation. Risk factors include age, obesity, prior joint injury, and genetic predisposition. A 2011 population-based study found that symptomatic knee OA prevalence rose from approximately 16% to 33% over two decades (PMID:22006937). ### 2. Patellofemoral Pain Syndrome (PFPS) The most common cause of anterior knee pain in younger and physically active individuals, affecting up to 23% of the general population at some point. The pathophysiology involves abnormal patellar tracking, quadriceps imbalance, and increased patellofemoral joint stress (PMID:27247250). ### 3. Meniscal Tears The menisci are C-shaped fibrocartilaginous structures that absorb shock and stabilize the knee. Acute tears typically result from twisting injuries in younger patients; degenerative tears are common in middle-aged and older adults and frequently coexist with OA. ### 4. Ligament Injuries - **Anterior cruciate ligament (ACL)** — often from pivoting sports; presents with a "pop," rapid swelling, and instability. - **Medial collateral ligament (MCL)** — usually from a valgus force; medial tenderness and laxity. - **Posterior cruciate ligament (PCL)** and **lateral collateral ligament (LCL)** — less common, often from high-energy trauma. ### 5. Tendinopathy - **Patellar tendinopathy ("jumper's knee")** — overuse injury at the inferior pole of the patella. - **Iliotibial band syndrome** — lateral knee pain common in runners and cyclists. ### 6. Bursitis Inflammation of the bursae around the knee. **Prepatellar bursitis** ("housemaid's knee") results from prolonged kneeling; **pes anserine bursitis** causes medial knee pain, often in overweight women with OA. ### 7. Inflammatory Arthritis Rheumatoid arthritis, gout, pseudogout (calcium pyrophosphate deposition disease), and reactive arthritis can all present with knee pain, swelling, warmth, and stiffness. ### 8. Referred Pain Hip pathology (e.g., hip OA, slipped capital femoral epiphysis in adolescents) can refer pain to the knee. Lumbar radiculopathy (L3–L4) may also present as anterior knee pain. --- ## RED FLAGS Seek **immediate medical attention** (emergency department or call emergency services) if knee pain is accompanied by any of the following: - **Acute, severe swelling** within minutes to hours of injury (suggests hemarthrosis — possible ACL rupture or fracture) - **Visible deformity or inability to bear weight** after trauma (possible fracture or dislocation) - **Locked knee** — inability to fully extend or flex the joint (possible displaced meniscal tear or loose body) - **Signs of infection:** hot, red, markedly swollen joint with fever or chills (possible septic arthritis — a surgical emergency) - **Pulselessness, pallor, or numbness below the knee** after injury (possible vascular compromise — especially with knee dislocation) - **Rapid-onset severe pain with redness and swelling without trauma**, particularly in patients on anticoagulants (possible hemarthrosis or crystal arthropathy requiring urgent evaluation) - **Systemic symptoms** such as unexplained weight loss, night pain unrelated to activity, or persistent fever (may indicate malignancy or systemic infection) - **Calf swelling, warmth, and pain** in addition to knee pain (may indicate deep vein thrombosis) --- ## Self-Care at Home Many causes of knee pain — particularly mild sprains, overuse syndromes, and early OA — respond well to conservative, non-pharmacological management. The following strategies are supported by clinical evidence. ### RICE Protocol (Acute Injuries, First 48–72 Hours) - **Rest:** Relative rest — avoid aggravating activities but maintain gentle range-of-motion. - **Ice:** Apply a cold pack wrapped in a towel for 15–20 minutes every 2–3 hours. - **Compression:** An elastic bandage may reduce swelling. - **Elevation:** Keep the leg elevated above heart level when possible. ### Exercise and Physical Activity Exercise is the single most effective non-pharmacological intervention for knee OA. A Cochrane review of 54 trials found that land-based therapeutic exercise provides short-term benefit in pain reduction and physical function comparable to that of NSAIDs (PMID:25461849). Key approaches include: - **Quadriceps strengthening** — straight-leg raises, wall sits, terminal knee extensions - **Low-impact aerobic exercise** — walking, swimming, cycling - **Flexibility and range-of-motion exercises** — gentle stretching of the hamstrings, quadriceps, and iliotibial band - **Balance and proprioception training** — single-leg stands, wobble board exercises The 2019 ACR/AF guidelines strongly recommend exercise as a core treatment for knee OA (PMID:31908163). ### Weight Management Every 1 kg of body weight lost reduces the load on the knee joint by approximately 4 kg during walking. Weight loss of ≥5% of body weight is associated with clinically meaningful improvements in pain and function in knee OA. ### Supportive Devices - **Knee braces or sleeves** — may provide proprioceptive feedback and mild stability. - **Appropriate footwear** — cushioned, supportive shoes; avoid high heels. - **Walking aids** — a cane used in the contralateral hand can reduce knee joint load by up to 20%. ### Topical Therapies (Non-Drug) - **Heat packs** for chronic stiffness (avoid in acute inflammation). - **Cold therapy** for acute flare-ups. --- ## OTC Medications That Help Over-the-counter medications can provide meaningful short-term relief for mild-to-moderate knee pain. Always read labels and consult a pharmacist or clinician if you have underlying conditions. | Class | Example | Typical Adult Dose | Notes | |---|---|---|---| | **Oral NSAIDs** | Ibuprofen (Advil, Motrin) | 200–400 mg every 4–6 h (max 1200 mg/day OTC) | Effective for inflammatory and OA pain. Avoid with active peptic ulcer disease, CKD (eGFR <30), or significant cardiovascular disease. A 2017 network meta-analysis found all NSAIDs superior to acetaminophen for OA pain (PMID:28699595). | | **Oral NSAIDs** | Naproxen sodium (Aleve) | 220 mg every 8–12 h (max 660 mg/day OTC) | Longer half-life; may be preferred for sustained pain. Same GI, renal, and CV precautions as ibuprofen. | | **Acetaminophen (paracetamol)** | Tylenol | 500–1000 mg every 4–6 h (max 3000 mg/day for chronic use; 4000 mg absolute max) | Modest analgesic effect for OA; generally safer GI profile than NSAIDs. **Caution in liver disease and with alcohol use.** No anti-inflammatory properties. | | **Topical NSAIDs** | Diclofenac sodium 1% gel (Voltaren Arthritis Pain) | Apply 4 g to knee 4 times daily | Recommended as first-line in OARSI 2019 guidelines for knee OA (PMID:31278997). Significantly lower systemic absorption and GI risk versus oral NSAIDs. | | **Topical counterirritants** | Menthol/camphor (Biofreeze, Icy Hot) | Apply to intact skin 3–4 times daily | Provide temporary relief via gate-control theory. Avoid on broken skin or with heating pads. | | **Oral supplements** | Glucosamine sulfate / Chondroitin sulfate | Glucosamine 1500 mg/day; Chondroitin 800–1200 mg/day | Evidence is mixed. Some trials suggest modest benefit for knee OA; the 2019 ACR/AF guidelines conditionally recommend against use due to inconsistent data (PMID:31908163). Generally safe; discuss with clinician. | > **Note:** Avoid combining multiple oral NSAIDs. Using an oral NSAID together with a topical NSAID is generally not recommended due to cumulative systemic exposure. --- ## Prescription Options When OTC measures and self-care prove insufficient, a clinician may consider the following prescription therapies. These are typically prescribed by a primary-care physician, rheumatologist, orthopedic surgeon, or sports-medicine specialist. | Class | Examples | Indication | Notes | |---|---|---|---| | **Prescription-strength oral NSAIDs** | Meloxicam 7.5–15 mg/day; Celecoxib 100–200 mg/day | OA, inflammatory arthritis, chronic pain | Celecoxib (COX-2 selective) may have a lower GI risk profile. Monitor renal function and blood pressure. | | **Intra-articular corticosteroid injections** | Triamcinolone acetonide 40 mg; Methylprednisolone acetate 40–80 mg | Acute OA flare, inflammatory effusion | Generally limited to 3–4 injections per joint per year. Provides weeks to months of relief. OARSI 2019 conditionally recommends for knee OA (PMID:31278997). | | **Hyaluronic acid (viscosupplementation)** | Hylan G-F 20 (Synvisc); Sodium hyaluronate (Euflexxa) | Knee OA inadequately responsive to other therapy | Injected intra-articularly. Evidence is mixed; the 2019 ACR/AF guidelines conditionally recommend against, though OARSI guidelines conditionally recommend. May benefit select patients. | | **Duloxetine** | Cymbalta 60 mg/day | Chronic knee OA pain, especially with comorbid depression or neuropathic component | SNRI; FDA-approved for chronic musculoskeletal pain. Side effects include nausea, dizziness, and dry mouth. | | **Tramadol** | Tramadol 50–100 mg every 4–6 h (max 400 mg/day) | Moderate-to-severe OA pain not responsive to other agents | Weak opioid; risk of dependence, serotonin syndrome, and seizures. The 2019 ACR/AF guidelines conditionally recommend against (PMID:31908163). Use with caution and for short duration. | | **Disease-modifying agents (inflammatory arthritis)** | Methotrexate, sulfasalazine, biologics (adalimumab, etanercept) | Rheumatoid arthritis, psoriatic arthritis | Prescribed and monitored by rheumatologist. Not used for OA. | | **Colchicine / Urate-lowering therapy** | Colchicine 0.5 mg BID; Allopurinol; Febuxostat | Gout, pseudogout | Colchicine for acute flares; allopurinol/febuxostat for long-term urate reduction in gout. | ### Surgical Options (When Conservative Treatment Fails) - **Arthroscopic surgery** — primarily for mechanical symptoms (locking, loose bodies); evidence does not support routine arthroscopy for OA alone. - **Osteotomy** — realignment procedure for younger patients with unicompartmental OA. - **Partial knee replacement (unicompartmental)** — for isolated medial or lateral compartment disease. - **Total knee arthroplasty (TKA)** — definitive treatment for end-stage knee OA. Over 700,000 TKAs are performed annually in the U.S. with 10-year survival rates exceeding 95%. --- ## Lab Tests Typically Ordered The diagnosis of knee pain is primarily clinical and imaging-based, but laboratory tests are important when systemic, inflammatory, or infectious causes are suspected. | Test | Rationale | |---|---| | **Complete blood count (CBC)** | Screen for infection (elevated WBC), anemia of chronic disease in inflammatory arthritis. [More info →](/tests/complete-blood-count) | | **Erythrocyte sedimentation rate (ESR)** | Non-specific marker of inflammation; elevated in RA, infection, and malignancy. [More info →](/tests/erythrocyte-sedimentation-rate) | | **C-reactive protein (CRP)** | Acute-phase reactant; useful for monitoring inflammatory activity. [More info →](/tests/c-reactive-protein) | | **Rheumatoid factor (RF) and Anti-CCP antibodies** | Ordered when rheumatoid arthritis is suspected. Anti-CCP is more specific. [More info →](/tests/rheumatoid-factor) | | **Serum uric acid** | Supports diagnosis of gout when elevated, though normal levels do not exclude acute gout. [More info →](/tests/uric-acid) | | **Synovial fluid analysis (arthrocentesis)** | Critical for differentiating septic arthritis (WBC >50,000/μL, positive culture), crystal arthropathy (monosodium urate or calcium pyrophosphate crystals), and inflammatory vs. non-inflammatory effusions. | | **ANA (antinuclear antibody)** | May be ordered when systemic lupus erythematosus or other connective tissue disease is suspected. [More info →](/tests/antinuclear-antibody) | | **X-ray (weight-bearing AP, lateral, sunrise views)** | First-line imaging for suspected OA, fracture, or alignment issues. Hallmarks of OA include joint-space narrowing, osteophytes, subchondral sclerosis. | | **MRI** | Gold standard for soft-tissue evaluation — meniscal tears, ligament injuries, cartilage defects, bone marrow edema. | --- ## Special Populations ### Children and Adolescents Knee pain in the pediatric population has a distinct differential diagnosis: - **Osgood-Schlatter disease** — traction apophysitis of the tibial tubercle; common in adolescents during growth spurts. - **Sinding-Larsen-Johansson syndrome** — similar mechanism at the inferior pole of the patella. - **Juvenile idiopathic arthritis (JIA)** — the most common chronic rheumatic disease of childhood; a swollen, warm knee without clear trauma warrants referral to pediatric rheumatology. - **Referred hip pain** — always examine the hip in a child presenting with knee pain. Slipped capital femoral epiphysis (SCFE) and Legg-Calvé-Perthes disease can present as knee pain. **Medication considerations in children:** - Ibuprofen and naproxen are commonly used NSAIDs in pediatrics, but **dosing must be weight-based and determined by a pediatrician**. Do not use adult doses in children. - **Aspirin is contraindicated in children under 16** due to the risk of Reye syndrome. - Acetaminophen is generally safe at weight-based doses determined by a clinician. ### Pregnancy Knee pain may increase during pregnancy due to weight gain, ligamentous laxity from relaxin, and altered biomechanics. - **Acetaminophen** is generally considered the first-line analgesic in pregnancy (previously FDA Category B; now evaluated under the PLLR framework). Use the lowest effective dose for the shortest duration. - **NSAIDs** should generally be avoided, especially after 20 weeks of gestation. The FDA issued a Drug Safety Communication in 2020 warning that NSAID use at ≥20 weeks can cause fetal renal dysfunction and oligohydramnios. NSAIDs are **contraindicated in the third trimester** due to the risk of premature closure of the ductus arteriosus. - **Non-pharmacological approaches** (ice, gentle exercise, supportive braces) are preferred. - Corticosteroid injections may be considered in select cases after risk–benefit discussion with the treating obstetrician. ### Elderly - OA is the predominant cause of knee pain in older adults. - **NSAIDs carry increased risks** in the elderly: GI bleeding, renal impairment, cardiovascular events, and drug interactions (especially with anticoagulants, antihypertensives, and diuretics). Topical NSAIDs are generally preferred over oral formulations. - **Acetaminophen** is often first-line, but hepatic function should be considered; maximum chronic dose is generally capped at 2000–3000 mg/day in frail elderly. - **Fall risk:** Knee pain and instability contribute to falls. Assess gait and balance; consider physical therapy and assistive devices. - **Opioids** should generally be avoided or used only as a last resort due to heightened sensitivity, fall risk, cognitive effects, and constipation. ### Athletes - Overuse injuries (PFPS, IT band syndrome, patellar tendinopathy) are extremely common. - **Activity modification** — not complete rest — is key. Cross-training helps maintain fitness while offloading the knee. - **Biomechanical assessment** by a sports physiotherapist may identify modifiable risk factors (e.g., hip weakness, overpronation). - **Return-to-sport protocols** after ligament injuries (especially ACL reconstruction) should follow evidence-based criteria, including quadriceps strength symmetry ≥90% and successful completion of sport-specific functional tests. - NSAIDs may be used short-term for acute injuries but should generally be avoided in the first 48 hours of soft-tissue injuries, as inflammation is part of the early healing response. --- ## When to Escalate Use the following guide to determine the urgency of medical evaluation: ### Same-Day GP or Primary-Care Appointment - Persistent knee pain lasting more than 2–3 weeks despite self-care - Mild-to-moderate swelling without trauma - Gradual worsening of pain that interferes with daily activities - Knee pain with a known history of OA that is no longer controlled by usual measures - New clicking, catching, or giving-way sensations ### Urgent Care (Within 24–48 Hours) - Moderate swelling after injury with ability to bear weight - Inability to fully straighten or bend the knee - Knee pain with low-grade fever or mild redness - Acute gout-like presentation (sudden, severe pain with redness and warmth) in a patient with a history of gout ### Emergency Department (Immediately) - Knee trauma with inability to bear weight (Ottawa Knee Rules suggest X-ray is needed) - Suspected fracture or dislocation — visible deformity, severe pain - Acute, hot, swollen joint with high fever — **suspect septic arthritis until proven otherwise** - Signs of vascular compromise — absent distal pulses, pale or cool limb - Rapid, massive swelling immediately after injury (hemarthrosis) > **Ottawa Knee Rules:** An X-ray is indicated after acute knee injury if the patient is ≥55 years old, has isolated patellar tenderness, has fibular head tenderness, cannot flex the knee to 90°, or cannot bear weight for 4 steps immediately and in the emergency department. These validated rules have a sensitivity approaching 99% for fractures. --- ## References [1] Nguyen US, Zhang Y, Zhu Y, et al. Increasing prevalence of knee pain and symptomatic knee osteoarthritis: survey and cohort data. *Ann Intern Med.* 2011;155(11):725-732. PMID:22006937. [2] Crossley KM, Stefanik JJ, Selfe J, et al. 2016 Patellofemoral pain consensus statement from the 4th International Patellofemoral Pain Research Retreat. *Br J Sports Med.* 2016;50(14):839-843. PMID:27247250. [3] da Costa BR, Reichenbach S, Keller N, et al. Effectiveness of non-steroidal anti-inflammatory drugs for the treatment of pain in knee and hip osteoarthritis: a network meta-analysis. *Lancet.* 2017;390(10090):e21-e33. PMID:28699595. [4] Bannuru RR, Osani MC, Vaysbrot EE, et al. OARSI guidelines for the non-surgical management of knee, hip, and polyarticular osteoarthritis. *Osteoarthritis Cartilage.* 2019;27(11):1578-1589. PMID:31278997. 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Available at: https://www.fda.gov/drugs/drug-safety-and-availability. --- *Last reviewed: April 2026. This article is for informational purposes only and does not constitute medical advice. Consult a licensed healthcare provider for diagnosis and treatment decisions.*