Knee Pain — Causes, Diagnosis, and Treatment

Author: Dr. Zeljko Kojadinovic, MD, PhD – Neurosurgeon and Pain Management Specialist

Last medically reviewed: June 7, 2026

Epidemiology and Common Misconceptions

Knee pain is among the top three musculoskeletal complaints in adults, affecting up to 25% of people over 50.
However, radiographic osteoarthritis (OA) is found in far more individuals than those who report pain — only about half of those with X-ray evidence of OA actually have symptoms.
Conversely, many patients with disabling pain have normal or near-normal imaging because the source is extra-articular (bursae, tendons, or muscle attachments).
This mismatch explains why so many ineffective surgeries are performed based solely on imaging.

Distribution of Pain Sources

Knee pain may originate from structures located inside the joint capsule (intra-articular) or from soft tissues outside the capsule (extra-articular). In clinical practice, roughly 50–60% of painful knees are intra-articular in origin, and 40–50% are extra-articular. Distinguishing between the two is crucial, since their mechanisms, treatment, and prognosis differ completely.

Intra-articular sources

Pain arising from inside the joint capsule reflects irritation or injury of structures such as:

• Articular cartilage, which undergoes degenerative wear in osteoarthritis, leading to loss of the smooth gliding surface between the femur and tibia.
• Menisci, two crescent-shaped fibrocartilaginous pads that act as shock absorbers between the femur and tibia. Degeneration or tearing disrupts joint congruence and causes mechanical irritation of the joint lining.
• Synovial membrane, which lines the inner surface of the joint capsule, is a thin, vascular tissue that produces the lubricating synovial fluid necessary for smooth cartilage movement. When irritated by cartilage wear debris, crystal deposits (such as urate or calcium pyrophosphate), or chemical by-products of degeneration, it becomes inflamed — a condition known as synovitis. The inflamed membrane thickens and secretes excess fluid, leading to joint effusion, swelling, and stiffness even when X-rays appear normal.
• Cruciate ligaments (anterior and posterior), which stabilize forward and backward translation (sliding motion) of the tibia beneath the femur. Partial or complete rupture leads to abnormal joint motion and secondary inflammation.
• Less frequent intra-articular pain generators include plica irritation (redundant synovial folds that become inflamed) and loose bodies of cartilage or bone moving freely inside the joint space.

Overall, intra-articular pain reflects structural damage, inflammation, or mechanical instability within the joint itself.

Extra-articular sources

Extra-articular pain often comes from surrounding soft tissues rather than the joint itself. Pain from outside the capsule arises from the supporting tendons, ligaments, bursae, and fat pads that stabilize or move the joint:

• Collateral ligaments (medial and lateral) provide side-to-side stability and may be strained or inflamed after overload or trauma.
• Tendons of the quadriceps and patellar mechanisms may develop microtears and degeneration (tendinopathy) from repetitive stress.
• Bursae — small fluid-filled sacs that reduce friction — can become inflamed (bursitis). Common sites include the prepatellar bursa (in front of the kneecap), the infrapatellar bursa (below it), and the pes anserine bursa (inner side of the upper shin), which often coexists with arthritis.
• Collateral ligament injuries cause pain and tenderness on either the inner (medial) or outer (lateral) side of the knee, often after sudden twisting or side impact. Mild sprains produce sharp pain when the knee bends sideways, while more significant injuries can lead to swelling and a feeling of instability.
• Hoffa’s fat pad, located just beneath the patellar tendon, can become inflamed or fibrotic after repetitive compression or direct trauma.
• Iliotibial (IT) band friction at the lateral femoral condyle produces irritation of the underlying tissue due to repetitive flexion and extension.
• In the posterior (popliteal) region, extra-articular pain may originate from strain of the gastrocnemius or hamstring tendons, rupture of a Baker’s cyst, or entrapment of the tibial or peroneal nerve.
  Vascular problems such as popliteal artery entrapment or superficial thrombophlebitis can occasionally mimic musculoskeletal pain.

In some patients, apparent knee pain is referred from the hip or lumbar spine, despite normal imaging of the knee itself.

Understanding whether the lesion is intra- or extra-articular is essential: true intra-articular damage (e.g., meniscal tear, cruciate injury, advanced OA) may require surgical intervention, while most extra-articular conditions respond well to conservative or image-guided treatment.

Image- Complex knee anatomy

Image: Inflamed knee bursae. While treatment is generally successful, they can be a source of severe knee pain and mobility issues for years before a proper diagnosis.

Symptoms of Knee Pain

Clinical presentation depends on the underlying anatomical source.

Symptoms from Intraarticular Causes

Pain is usually deep and diffuse, felt “inside the joint,” and aggravated by weight bearing, climbing stairs, or prolonged walking.

• In osteoarthritis, pain is dull and mechanical, with stiffness, swelling, and crepitus (crackling) during motion.
• Meniscal tears cause sharp, localized joint-line pain (inner or outer), sometimes with catching, locking, or a sense of giving way.
• Synovitis or chondral lesions lead to persistent swelling, warmth, and a feeling of fullness even when X-rays are normal.
• Cruciate injuries cause deep pain and a sense of instability, especially when pivoting or descending stairs.
• Occasional stabbing pain may occur when a plica fold or loose body gets trapped during movement.

Symptoms from Extraarticular Causes

Pain is typically well localized, reproducible by palpation or specific movement, and related to the tendon, bursa, or ligament involved.

• Pes anserine bursitis causes tenderness on the inner upper shin, sometimes radiating upward.
• IT-band friction produces lateral knee pain that worsens with repetitive bending.
• Patellar or quadriceps tendinopathy leads to pain above or below the kneecap, aggravated by climbing, running, or squatting.
• Hoffa’s fat pad inflammation produces burning or pressure-like anterior pain beneath the kneecap.
• Posterior knee pain (popliteal area) may stem from muscle strain, Baker’s cyst, or nerve irritation, often described as deep tightness behind the knee.
• Referred pain from the hip or lumbar spine mimics knee pain but is associated with normal knee motion and imaging.

In summary, intra-articular pain tends to be deep, aching, and diffuse, while extra-articular pain is superficial, focal, and movement-related. Correct localization of the pain generator is the key to effective treatment.

Diagnostic Approach — Why Imaging Alone Is Not Enough

Plain radiographs detect joint-space narrowing, osteophytes, and sclerosis — but these are not reliable predictors of pain.
Accurate diagnosis integrates:

• Focused physical exam: palpation of specific tender zones, patellar tracking, gait, and dynamic pain tests.
• Ultrasound: reveals soft-tissue causes (bursitis, tendinopathy, fluid) and allows guided diagnostic injections.
• MRI: indicated when intra-articular pathology (such as a meniscal tear or cartilage defect) is suspected, or when conservative therapy fails. It may also suggest extra-articular abnormalities, but it cannot reliably differentiate the true pain generator — unlike a focused clinical examination, ultrasound assessment, or navigated diagnostic blocks. MRI can show structural changes that appear significant but do not actually explain the pain.
• Diagnostic blocks: selective injections (pes anserine, IT-band, intra-articular) to confirm the pain generator.

Treatment of Knee Pain

Most patients improve without surgery once the true pain source is identified and treated.

Medication & local therapy — Short courses of NSAIDs for acute inflammation. When pain is localized, ultrasound-guided injections of long-acting corticosteroids or platelet-rich plasma (PRP) can be placed precisely into the affected bursa, tendon sheath, or joint space.

Physiotherapy — A structured program aimed at restoring quadriceps and gluteal control, correcting load distribution, and improving flexibility.
Key principles include gradual strengthening, avoidance of deep squats or stairs during flares, and activation of hip abductors to offload the knee.

Interventional Pain Knee Procedures

• For extra-articular pain: ultrasound-guided lavage or aspiration of inflamed bursae, or peritendinous hydrodissection.
• For intra-articular pathology: diagnostic or therapeutic intra-articular injections, viscosupplementation, or radiofrequency ablation (RFA) of genicular nerves when standard therapy fails.

Surgery —

• Arthroscopy is not recommended for degenerative knee disease without mechanical locking; large meta-analyses show minimal benefit beyond physiotherapy. Partial meniscectomy or chondroplasty is reserved for true mechanical lesions verified clinically and on MRI.
• Total knee arthroplasty (TKA) is indicated for advanced OA with major cartilage loss and severe limitation of movement.
• Genicular nerve RFA provides pain relief for about 6–12 months in patients who are poor surgical candidates or awaiting arthroplasty. The procedure interrupts sensory fibers transmitting pain from the joint capsule and subchondral bone, primarily through the superior medial, superior lateral, and inferior medial genicular nerves.
  However, it does not act on extra-articular pain sources — such as tendons, bursae, or small nerve branches around the knee — which often remain symptomatic even after a technically successful RFA. If you have undergone genicular denervation but your knee pain persists, it may originate from these extra-articular structures, which are not influenced by RFA and can often be identified through a targeted clinical or ultrasound-guided evaluation.

Only about 10–15% of all chronic knee pain cases ultimately require surgical or nerve-ablative procedures.
The remaining majority can be successfully managed with a combination of conservative therapy (activity modification, medications, targeted physical therapy) and image-guided management — which includes ultrasound-guided diagnosis and precise local treatments such as perineural injections, hydrodissection, or tendon and bursal procedures that directly target the actual pain source.

Online pain consultation for regional pain in detail

Schematic explanation of the video consultation for regional pain

Answers to questions about the process and success of video consultations for regional pain

There are several common reasons for poor therapeutic outcomes in the treatment of chronic pain, which are often seen in patients with regional pain.

Artificial intelligence can also support the process by analyzing complex pain syndromes in fibromyalgia, but clinical expertise remains essential.

Why Knee Pain Does Not Improve Despite Treatment

Many patients continue to experience knee pain despite undergoing standard treatments such as medication, physiotherapy, or injections.

In a large number of cases, this is not because treatment options are ineffective, but because the dominant pain source has not been clearly identified. Imaging findings such as cartilage degeneration, meniscal changes, or mild osteoarthritis are common, but they often do not fully explain the intensity or pattern of symptoms.

Pain may persist when treatment is directed at structural findings rather than the true functional pain generator, or when contributing factors — such as altered biomechanics, muscle imbalance, joint overload, or systemic influences — are not addressed. As a result, even well-applied therapies may fail to achieve lasting improvement.

Treatment of Contributing Factors in Knee Pain

Effective treatment of knee pain always begins with identifying the primary pain generator — the specific structure responsible for symptoms (such as intra-articular pathology including cartilage or meniscus, pes anserine bursa, patellar or quadriceps tendon, iliotibial band, or small nerve branches around the knee).

However, in many patients, pain persists not only because of the local problem, but because additional contributing factors are not recognized or adequately addressed. These factors rarely act as the sole cause of pain, but they can maintain irritation, delay recovery, and reduce the effectiveness of otherwise appropriate treatment.

For that reason, successful management of knee pain requires not only treating the primary structure, but also understanding the broader mechanical and systemic context.

What contributing factors may play a role in knee pain?

• Repetitive loading and mechanical overload — Walking, stairs, squatting, or prolonged standing can continuously stress the same structures, especially in degenerative conditions.
• Lower limb alignment and biomechanics — Varus/valgus alignment, altered gait, or poor load distribution increase stress on specific compartments of the knee.
• Muscle imbalance and reduced joint stability — Weak quadriceps, gluteal muscles, or poor neuromuscular control lead to overload of tendons, bursae, or joint surfaces.
• Hip and core dysfunction — Poor hip control (especially abductors) shifts load toward the knee and contributes to persistent symptoms.
• Metabolic factors, pro-inflammatory diet and low-grade inflammation — Obesity, insulin resistance, and chronic inflammation increase joint stress and pain sensitivity.
• Nutritional deficiencies — Low vitamin D, B12, or other micronutrients may impair tissue recovery.
• Sleep disturbances and chronic pain cycle — Poor sleep increases pain sensitivity and delays healing.
• Central sensitization — The nervous system amplifies pain signals even when structural damage is limited.
• Reduced activity and deconditioning — Avoidance of movement leads to weakness and further joint overload.
• Medications and previous treatments — Certain medications such as statins, long-term use of pain medications, corticosteroids, or medications that cause excessive sedation may contribute to muscle or tendon-related pain, reduce tissue quality, or alter pain perception. Previous treatments, including repeated injections or incomplete rehabilitation, may also maintain symptoms if the underlying mechanism was not fully addressed.
• Other medical conditions and comorbidities — Conditions such as autoimmune diseases, thyroid disorders, diabetes, or chronic inflammatory states may increase pain sensitivity, affect tendon and joint structures, and reduce the response to otherwise appropriate treatment.
• Vitamin-related factors — Both deficiencies and excesses of certain vitamins (particularly vitamin B6) may contribute to nerve-related symptoms, burning pain, or altered sensitivity around the knee.
• Tissue quality and degeneration — Age-related changes, reduced blood supply, or repeated micro-injuries may impair tendon healing and increase vulnerability to persistent pain, even when mechanical factors are partially corrected.

Why this matters in practice

In many cases, treatment fails because the primary pain generator is not correctly identified, and therapy is directed only at contributing factors such as exercise, posture, or lifestyle changes. Conversely, even when the main structural cause is treated, failure to recognize and address contributing factors often leads to only partial or temporary improvement.

The most effective approach is a carefully selected combination of treatment that addresses both the primary pain generator and the contributing mechanical, functional, and systemic factors. In contrast, an inadequate or incomplete combination — even when it includes individually effective methods — is a common reason for suboptimal or short-lasting results.

This approach significantly increases the likelihood of long-term improvement and reduces the need for repeated injections or surgery.

In practice, many patients try to address contributing factors on their own — for example through exercise programs, posture correction, anti-inflammatory diet, supplements (vitamin D, magnesium, glucosamine, chondroitin), or supportive methods.

While these approaches can be helpful, they rarely lead to lasting improvement if the primary pain generator is not clearly identified and treated. On the other hand, even well-targeted medical treatment may fail if all contributing factors are not recognized and corrected.

Many patients reading this recognize that they have already tried one part of this approach — but not the complete strategy. This is one of the most common reasons why otherwise well-treated knee pain becomes chronic.

Prognosis and Long-Term Outlook

When the pain source is accurately localized and treated, most patients experience substantial and sustained improvement.
Persistent relief after a guided injection or successful physiotherapy usually predicts durable recovery and reduced need for surgery.

FAQ About Persistent Knee Pain