Definition
Knee osteoarthritis is a progressive degenerative condition of the knee joint. To varying degrees, it combines changes to the articular cartilage, changes in the subchondral bone, osteophyte formation, inflammation of the synovial membrane, meniscal changes and, sometimes, a joint effusion.
It can affect the medial tibiofemoral compartment, the lateral tibiofemoral compartment, the patellofemoral joint, or several compartments at the same time. In runners, it can be particularly troublesome because running subjects the knee to thousands of loading cycles on every run.
One key point must be stressed from the outset: knee osteoarthritis seen on X-ray is not necessarily painful, and conversely, significant pain can be present with relatively modest radiographic abnormalities. There is therefore an imperfect correlation between the radiological picture, pain and the ability to run. Management must be guided above all by symptoms and function, and not by the appearance of the X-ray alone.
Anatomy
Articular cartilage covers the bone ends of the knee, notably the femoral condyles, the tibial plateau and the articular surface of the kneecap. It provides low friction between the joint surfaces, distribution of stress, a degree of load absorption and smooth knee movement. Unlike other tissues, articular cartilage has a limited capacity for spontaneous repair.
It would, however, be wrong to see osteoarthritis as simple “mechanical wear”. Knee osteoarthritis is a disease of the whole joint, jointly involving the cartilage, subchondral bone, synovium, menisci, ligaments and periarticular muscles.
The knee consists of two functionally linked joints. The tibiofemoral joint mainly allows flexion, extension and some rotation when the knee is bent. The patellofemoral joint allows the kneecap to glide in the femoral trochlea and plays a major role in transmitting the forces of the quadriceps.
The distribution of stress varies considerably depending on the activity: walking, running, stairs, squats and downhill sections therefore do not load the knee in the same way.
🔍 Click on the image to enlarge it
Epidemiology
“Does running wear out your knees?” is probably one of the most frequent questions among runners, and the current answer is much more nuanced than the classic “running wears out your cartilage”.
The available data do not show that recreational running is associated with a higher prevalence of knee osteoarthritis compared with non-runners. A 2023 meta-analysis of more than 12,000 participants found no significant difference in the prevalence of knee osteoarthritis according to weekly running volume. Another recent systematic review also found no significant short-term radiographic or symptomatic worsening in runners.
In people over 50 who already had knee osteoarthritis, self-selected running was not associated with greater radiographic progression and was even associated with a higher likelihood of pain improvement.
Nevertheless, recreational running must be distinguished from very high training volumes, a history of trauma, after-effects of meniscal surgery, ligament injuries, axial deformities, obesity and repeated episodes of overload: running is therefore probably not the sole cause of knee osteoarthritis in runners.
Causes & risk factors
Knee osteoarthritis is multifactorial: the risk increases with age, but osteoarthritis is not an inevitable consequence of ageing.
History of trauma
This is a major factor in secondary knee osteoarthritis, particularly ACL rupture, meniscal injury, intra-articular fracture, chronic instability or meniscal surgery.
Meniscectomy
Losing part of the meniscus changes the distribution of stress within the affected compartment and can promote the progression of osteoarthritis.
Overweight and obesity
Body weight increases the mechanical stress placed on the knee, but the effect is not purely mechanical: adipose tissue is also involved in metabolic and inflammatory processes. Weight loss, when needed, can significantly improve pain and function; the OARSI guidelines list weight management among the core interventions in knee osteoarthritis.
Axial deformities
Marked genu varum or genu valgum can increase the stress on one compartment of the knee.
Muscle weakness
Reduced strength in the quadriceps and hip muscles can reduce the functional capacity of the lower limb.
Why can running become painful?
A joint with osteoarthritis has a load capacity that may be reduced. When the load imposed temporarily exceeds this capacity, a painful flare-up can occur — particularly when returning after several weeks off, after a sudden increase in mileage or elevation gain, a change of terrain, marathon preparation, several intense sessions close together, a loss of muscle strength, weight gain or a general decrease in physical activity. It is therefore more relevant to speak of load tolerance than of simple mechanical wear.
Symptoms
The presentation varies considerably from one patient to another.
Mechanical pain
Pain is generally brought on by prolonged walking, running, stairs, downhill sections, squats and repeated effort. It is usually relieved by rest.
Stiffness
Stiffness may appear on waking, after a period of sitting, after a car journey or after a long session. Morning stiffness is generally relatively short-lived; prolonged stiffness should prompt consideration of other diagnoses, particularly inflammatory ones.
Swelling
An effusion may appear after significant activity. It may be intermittent.
Cracking
Crepitus or cracking is common in osteoarthritis. However, it is not a sign of worsening: a knee that cracks without pain generally does not require any specific treatment.
Feeling of weakness
Some patients describe a feeling of weakness, difficulty on stairs or a sensation of the knee giving way. In such cases, a quadriceps deficit or true ligament instability should be looked for in particular.
Location of pain
Medial tibiofemoral osteoarthritis causes pain on the inner compartment of the knee, which is particularly troublesome during prolonged walking, running, downhill sections or single-leg weight-bearing efforts. Lateral tibiofemoral osteoarthritis causes pain on the outer compartment, sometimes associated with a valgus deformity. Patellofemoral osteoarthritis presents as anterior pain, often brought on by stairs, going downhill, squatting, prolonged sitting or running with significant knee flexion. Finally, several areas may be painful at the same time in diffuse forms.
Clinical examination
The examination looks at the precise location of the pain, range of motion, any effusion, axial deformity, muscle strength, ligament stability, patellar mobility, patellofemoral pain and overall muscle condition. The patellar tap (ballottement) test can be used to confirm an effusion; a recurrent effusion must be taken into account when adjusting load. In terms of mobility, the examiner looks in particular for loss of extension, reduced flexion or pain at end-range flexion — a progressive loss of extension can have a major impact on running.
Functional assessment of the runner
The examination should not be limited to the knee. It is useful to observe the double-leg and single-leg squat, the step-down, stepping up and down a step, single-leg balance, double-leg and single-leg jumps, and overall control of the lower limb. In particular, the examiner assesses pelvic control, hip stability, knee control, ankle mobility, quadriceps strength, gluteal strength and landing quality, in order to identify the capacities that currently limit sporting activity.
Radiographic severity and functional severity
Radiological severity and functional severity must be distinguished. Radiographic knee osteoarthritis with few symptoms results in occasional pain, good walking capacity, running that is still possible and little functional limitation. Conversely, an advanced, disabling form causes significant pain, major limitation of daily activities, a marked reduction in walking distance and a significant loss of function. Between these two extremes, discomfort when running, stiffness after exercise and reduced tolerance to training volume gradually set in. The radiological stage alone is therefore never enough to determine management.
Further tests
Plain X-rays (± weight-bearing)
First-line investigation to confirm and characterise knee osteoarthritis: looks for joint space narrowing, osteophytes, subchondral sclerosis, subchondral cysts (geodes), deformity and involvement of one or more compartments. When possible, weight-bearing X-rays are particularly useful because they assess the knee under its usual mechanical conditions.
MRI
Generally not needed to diagnose typical knee osteoarthritis. It can nevertheless be useful in cases of atypical symptoms, when the X-ray does not adequately explain the pain, when a significant meniscal or osteochondral lesion, a stress fracture or an associated ligament condition is suspected, or before joint-preserving surgery. It can show cartilage abnormalities well before radiographic signs appear, but an abnormality on MRI is not necessarily responsible for the pain.
Differential diagnoses
Meniscal injury
Pain often triggered by twisting or squatting, sometimes with a feeling of locking or catching in the joint; it can perfectly well coexist with knee osteoarthritis without being the only explanation.
Patellofemoral pain syndrome / patellar or quadriceps tendinopathy
Anterior pain, but more focal — over the tendon or the femoral trochlea — than the diffuse pain of patellofemoral osteoarthritis, and it can occur without any associated radiographic abnormality.
Iliotibial band syndrome
Lateral knee pain, typically triggered after a certain amount of running time, centred on the lateral femoral condyle rather than on the whole lateral compartment.
Pes anserinus bursitis / popliteus tendinopathy
Medial or posteromedial pain, generally lower and more focal than the pain of medial tibiofemoral osteoarthritis.
Stress fracture / osteochondral lesion
Pain that comes on gradually with exercise, sometimes with no clear correlate on plain X-rays; an MRI is needed to confirm or rule it out.
Popliteal cyst / ligament injury
Swelling at the back of the knee or a clear feeling of instability, to be distinguished from a simple osteoarthritic effusion or a feeling of weakness linked to a quadriceps deficit.
Classification
Grade 1 (Kellgren-Lawrence)
Doubtful or minimal radiographic signs.
Grade 2 (Kellgren-Lawrence)
Definite osteophytes, with possible slight joint space narrowing.
Grade 3 (Kellgren-Lawrence)
Multiple osteophytes, definite joint space narrowing and associated bone changes.
Grade 4 (Kellgren-Lawrence)
Marked or complete joint space narrowing, large osteophytes, sclerosis and bone deformity. However, this high radiographic grade does not perfectly predict pain: a grade 4 knee can be relatively painless, whereas a grade 2 knee can be very symptomatic.
Treatment
Understanding the principle of treatment
Knee osteoarthritis is a chronic disease: there is currently no treatment that can reliably reverse established osteoarthritis. However, it is entirely possible to reduce pain, improve strength and mobility, improve function, return to sport, reduce disability and maintain independence. International guidelines place therapeutic exercise, physical activity and, when needed, weight management at the forefront of management.
Phase 1 – Controlling the painful flare-up (the 24-hour rule)
During a flare-up, the aim is not necessarily to stop all activity, but to temporarily reduce the irritating stresses: cut back on mileage, speed, elevation gain, downhill sections, interval training, technical trail running or the frequency of closely spaced sessions, while keeping up, where possible, suitable walking, cycling, swimming, elliptical training and strengthening work. Activity must be adapted to the knee's tolerance.
A useful practical rule is to observe how the knee reacts after activity. A session is generally acceptable if pain remains mild to moderate, does not gradually worsen during exercise, the knee does not swell significantly and symptoms return to their usual level within 24 hours. If pain or swelling is still clearly increased the next day, the load was probably too high and should be temporarily reduced in duration, intensity, frequency or elevation gain. This approach helps avoid the classic cycle: pain → complete rest → muscle loss → overly abrupt return → new flare-up.
Phase 2 – Restoring mobility
Good mobility is important for running. As regards extension, the aim is to regain full or near-full extension (for example, heel resting on a support with the knee unsupported, holding the extension for progressively longer). Flexion is worked on gradually through heel slides, cycling, active mobilisation or squats within a comfortable range — never aiming for aggressive mobilisation.
Phases 3–4 – Strengthening the quadriceps and posterior chain
The quadriceps is a key element of management: isometric contractions, terminal extension work against progressive resistance, partial squats then gradually deeper ones, leg press (double-leg then single-leg), controlled step-ups and step-downs, with a gradually increasing load. The aim is not simply to "work the muscle" but to restore a genuine capacity to produce force.
The programme should also include strengthening of the posterior chain: glutes, hamstrings, calves and hip muscles, for example through glute bridges, hip thrusts, deadlifts, leg curls, hip abduction or calf raises. This overall strengthening improves the lower limb's ability to handle the stresses of running.
Phases 5–6 – Single-leg and plyometric work
As running is a succession of single-leg supports, it is worth working on single-leg balance, single-leg squats, step-downs, forward lunges, lateral lunges and single-leg calf raises, gradually increasing the difficulty through load, speed, range of motion, instability or multidirectional movements.
For runners wishing to return to regular running, jump training is particularly valuable, with a progression from weight transfer to small double-leg hops, jumps on the spot, single-leg hops, bounds, then changes of direction and running-specific exercises. The aim is to gradually reaccustom the knee to impacts.
Return to running and training adjustments
There is no universal mileage suitable for all patients with osteoarthritis: the return must be individualised. One possible progression is to start with brisk walking, then alternate running and walking (for example 1 min running / 2 min walking, repeated several times), before gradually increasing running time, then distance, then reintroducing elevation gain and finally speed — one parameter at a time.
The 10% rule (increasing running volume by 10% per week) can be a simple guide, but it should not be considered a universal medical rule: in a patient with osteoarthritis, progression should instead be determined by the starting level, symptoms, strength, age, weight, medical history, type of osteoarthritis and the knee's response to previous sessions.
Several adjustments can improve tolerance rather than imposing a complete ban: temporarily reducing mileage, reducing downhill running (often particularly symptomatic), avoiding very intense sessions, splitting the session into two shorter runs, or changing the terrain by starting on even, flat and predictable ground before gradually reintroducing elevation gain, trails and technical terrain.
A slight increase in cadence can reduce some of the mechanical stress on the knee in some runners, although there is no universal "perfect technique": a change in technique is only worthwhile if it reduces symptoms, improves comfort, is easily reproducible and does not cause pain elsewhere. Likewise, there is no single shoe that treats knee osteoarthritis, but a comfortable shoe that suits the foot, is sufficiently stable and is appropriate for the terrain can improve comfort; sudden changes of shoes or a major change in drop should be avoided during a symptomatic phase and introduced gradually.
Complementary treatments
Weight loss
In an overweight runner, weight loss can have a major effect on pain, function, walking capacity and exercise tolerance. The OARSI guidelines consider weight loss an essential component of treatment in overweight or obese patients: a loss of at least 5%, and ideally more where possible, can provide clinical benefit. In runners, however, the aim is not to reach a minimal weight: a weight-loss strategy must not lead to an energy deficit, muscle loss, fatigue, reduced performance or inadequate recovery.
Paracetamol
Its effectiveness in knee osteoarthritis is limited, but it can be used in certain situations.
Oral NSAIDs
Non-steroidal anti-inflammatory drugs can be effective during painful flare-ups. They must be used taking into account age, kidney function, gastrointestinal risk, cardiovascular risk and other medications.
Topical NSAIDs
Can be particularly useful when pain is localised to the knee. The American College of Rheumatology guidelines strongly recommend topical NSAIDs for knee osteoarthritis.
Corticosteroid injection
An intra-articular corticosteroid injection may be offered in the event of a significant painful or inflammatory flare-up and can provide short-term improvement, but it does not rebuild cartilage. It should be part of an overall strategy that includes temporary load reduction, strengthening and a gradual return to activity. International guidelines recognise a role for intra-articular corticosteroid injections in symptomatic knee osteoarthritis.
Hyaluronic acid
Hyaluronic acid injections are still used in certain contexts. However, international guidelines are not unanimous and the level of evidence for their clinical benefit varies: they should not be presented as a treatment capable of "regenerating" cartilage.
PRP (platelet-rich plasma)
Increasingly used in knee osteoarthritis, particularly in active patients. The data suggest a potential benefit for pain and function in some patients, but protocols are highly heterogeneous and the optimal indications are not fully defined. The 2024 European ESSKA-ORBIT consensus considers it an option that may be discussed in some cases of symptomatic, non-end-stage knee osteoarthritis, while stressing the need for better standardisation of products and protocols. It should be presented as a potential symptomatic treatment, not as proven cartilage regeneration.
Stem cells and regenerative medicine
A very active field of research, but one that should not be presented as a treatment that can currently reliably rebuild an osteoarthritic joint. Recent ESSKA consensus statements stress that the data remain insufficient and heterogeneous for many indications: particular caution is needed with promises of "cartilage regeneration", "curing osteoarthritis" or "joint reconstruction".
Surgery
Surgery is generally not indicated simply because an X-ray shows osteoarthritis. It is considered when pain is significant, functional limitation is major, properly conducted conservative treatment is insufficient, or quality of life is severely affected.
Total knee replacement may be considered for advanced, disabling knee osteoarthritis. It generally brings a major improvement in pain, function and quality of life, but it does not necessarily mean the end of all physical activity.
Can you run with a knee replacement?
The question must be considered on an individual basis. Low-impact activities — cycling, swimming, walking, hiking, the elliptical trainer — are generally preferred. Running is more controversial: in some selected patients, a return to running may be considered after full recovery, but it is generally not the priority goal after total knee arthroplasty. A discussion with the surgeon and the rehabilitation specialist is essential.
Recovery time
Knee osteoarthritis progresses very differently from one person to another: some people remain only mildly symptomatic for a long time despite significant radiographic abnormalities, while others have severe painful flare-ups despite radiologically moderate osteoarthritis. There is therefore no single recovery time, as there would be for an acute injury: the aim is not necessarily to make the radiographic findings disappear, but to maintain low pain, high strength, good mobility, sufficient load capacity and regular physical activity.
During an occasional painful flare-up, the 24-hour rule makes it possible to adjust the load session by session; most flare-ups improve within a few days to a few weeks when the load is adjusted in time. OARSI notes in particular that imaging abnormalities do not accurately predict how symptoms will evolve.
Prevention
It is not possible to prevent all cases of knee osteoarthritis, but several factors can be optimised.
Maintaining regular physical activity is essential: inactivity is not a prevention strategy. It is also important to maintain good muscle strength, particularly in the quadriceps, glutes, hamstrings and calves, and to avoid sudden changes in load — the body adapts gradually.
Preventing ligament ruptures and major meniscal injuries may be of long-term benefit for the risk of secondary knee osteoarthritis. Weight control, when needed, is one of the most important modifiable factors. Finally, keeping variety — alternating running, strengthening, cycling, swimming and hiking — helps maintain excellent physical fitness while modulating joint stress.
Frequently asked questions
Can you run with knee osteoarthritis?
Does running accelerate osteoarthritis?
Is it better to walk rather than run?
Is cycling recommended?
Should you do strength training?
Are squats dangerous?
Can you do trail running with knee osteoarthritis?
Can knee osteoarthritis go away?
Can cartilage regenerate?
When should you see a surgeon?
Can you train for a marathon with knee osteoarthritis?
Is cracking in the knee a cause for concern?
Common mistakes
Stopping running completely as soon as knee osteoarthritis is diagnosed, even though recreational running has not been shown to systematically accelerate osteoarthritis.
Avoiding all impacts for fear of wearing down the cartilage further, even though exercise is one of the fundamental treatments for knee osteoarthritis.
Resting excessively in the belief that "the more I rest, the better my knee will be", even though excessive rest leads to loss of strength, deconditioning and increased sensitivity when returning to activity.
Limiting muscle strengthening to the quadriceps alone, even though the programme should cover the whole lower limb.
Believing that radiographic severity directly determines the intensity of pain, even though this relationship is imperfect.
Interpreting cracking in the knee as a sign of cartilage destruction, even though these joint noises are common and cannot on their own be used to judge how the osteoarthritis is progressing.
Permanently banning squats, even though they can be gradually reintroduced with an appropriate range of motion and load.
Believing that an injection solves the problem for good, even though it may temporarily reduce symptoms but does not replace long-term work.
Key points — Institut Basque du Coureur
Knee osteoarthritis is not a life sentence that means you must stop running. In runners, we need to move away from the simplistic model of "damaged cartilage = no running": knee osteoarthritis is a disease of the whole joint, and its radiographic severity does not necessarily match the intensity of the pain. Management is based above all on appropriate physical activity, muscle strengthening, restoring mobility, gradual load management, weight control when needed, training adjustments and symptomatic treatment during flare-ups. Recreational running has not been shown to cause a systematic acceleration of osteoarthritis; the available data are rather reassuring, including in some patients who already have knee osteoarthritis. The right goal is not to protect an osteoarthritic knee from all stress indefinitely, but to gradually restore its capacity to withstand the stresses the runner wants to place on it.
- Dhillon J, Kraeutler MJ, Belk JW, Scillia AJ, McCarty EC, Ansah-Twum J, et al. Effects of Running on the Development of Knee Osteoarthritis: An Updated Systematic Review at Short-Term Follow-up. Orthop J Sports Med. 2023;11(3):23259671231152900.
- Burfield M, Sayers M, Buhmann R. The association between running volume and knee osteoarthritis prevalence: A systematic review and meta-analysis. Phys Ther Sport. 2023;61:1-10.
- Lo GH, Musa SM, Driban JB, et al. Running does not increase symptoms or structural progression in people with knee osteoarthritis: data from the Osteoarthritis Initiative. Clin Rheumatol. 2018.
- Timmins KA, Leech RD, Batt ME, Edwards KL. Running and Knee Osteoarthritis: A Systematic Review and Meta-analysis. Am J Sports Med. 2017;45(6):1447-1457.
- Coburn SL, Crossley KM, Kemp JL, Warden SJ, West TJ, Bruder AM, et al. Is running good or bad for your knees? A systematic review and meta-analysis of cartilage morphology and composition changes in the tibiofemoral and patellofemoral joints. Osteoarthritis Cartilage. 2023;31(2):144-157.
- Holden MA, Hattle M, Runhaar J, Riley RD, Healey EL, Quicke J, et al. Moderators of the effect of therapeutic exercise for knee and hip osteoarthritis: a systematic review and individual participant data meta-analysis. Lancet Rheumatol. 2023;5(7):e386-e400.
- Kolasinski SL, Neogi T, Hochberg MC, et al. 2019 American College of Rheumatology/Arthritis Foundation Guideline for the Management of Osteoarthritis of the Hand, Hip, and Knee. Arthritis Rheumatol. 2020;72(2):220-233.
- 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.
- Laver L, Filardo G, Sconfienza LM, et al. The use of injectable orthobiologics for knee osteoarthritis: A European ESSKA-ORBIT consensus. Part 1—Blood-derived products (platelet-rich plasma). Knee Surg Sports Traumatol Arthrosc. 2024.
- de Girolamo L, et al. The use of injectable orthobiologics for knee osteoarthritis: A formal ESSKA-ORBIT consensus. Part 2—Cell-based therapy. Knee Surg Sports Traumatol Arthrosc. 2025.
- Glinski T, et al. Impact of Running on the Risk and Progression of Knee Osteoarthritis: A Review of Current Evidence. Clin Sci (Lond). 2026.
Similar injuries
Pes anserinus tendinopathy
Inflammation of the tendons that insert on the inner side of the tibia (sartorius, gracilis, semitendinosus), causing pain on the inner side of the knee.
Patellofemoral pain syndrome
Anterior knee pain caused by poor patellar tracking, accounting for 25 to 40% of knee injuries in runners.
Quadriceps tendinopathy
Inflammation of the quadriceps tendon above the kneecap, a common overuse injury when training is increased too quickly.