Previous changes

July 2017 — reviewed. A literature search was conducted in June 2017 to identify evidence-based guidelines, UK policy, systematic reviews, and key randomized controlled trials published since the last revision of the topic. Sections on risk factors and prognosis have been added to Background information. The recommendations on assessment and management of knee pain have been amended in line with current evidence.

November 2010 to March 2011 — this is a new CKS topic. The evidence base has been reviewed in detail, and recommendations are clearly justified and transparently linked to the supporting evidence.

New evidence

Evidence-based guidelines

No new evidence-based guidelines since 1 July 2022.

HTAs (Health Technology Assessments)

No new HTAs since 1 July 2022.

Economic appraisals

No new economic appraisals relevant to England since 1 July 2022.

Systematic reviews and meta-analyses

No new systematic reviews published since 1 July 2022.

Primary evidence

No new primary evidence which reaches the CKS threshold for inclusion published since 1 July 2022.

New policies

No new national policies or guidelines since 1 July 2022.

New safety alerts

No new safety alerts since 1 July 2022.

Changes in product availability

No changes in product availability since 1 July 2022.

Basis for recommendation

Recommendations on important features in the patient history are based on the clinical features of underlying causes of knee pain and recommendations from a textbook [Bowden, 2010], the National Institute for Health and Care Excellence (NICE) guideline Osteoarthritis: care and management [NICE, 2020b] and a review article [Calmbach and Hutchens, 2003a].

The information that persistent pain or pain that occurs at rest or at night suggests a tumour, inflammatory arthritis, or severe osteoarthritis is based on the National Institute for Health and Care Excellence (NICE) guideline Osteoarthritis: care and management [NICE, 2020b] the Royal College of Surgeons commissioning guide for painful osteoarthritis of the knee [Royal College of Surgeons, 2013], the UK guidelines for the management of bone sarcomas [Gerrand, 2016], and the European Society for Medical Oncology (ESMO) guideline on bone sarcomas [ESMO, 2021].

The information on acute joint swelling in the presence or absence of trauma is based on expert opinion from a review article [Calmbach and Hutchens, 2003b] and a textbook [Bowden, 2010].

The statement that crepitus, snapping and clicking are of limited value in identifying the cause of knee pain, and that a loud pop may represent ligamentous or meniscal injury is based on a narrative review [Song, 2018], BMJ Best Practice topics [BMJ Best Practice, 2019a; BMJ Best Practice, 2021a], and expert opinion from CKS reviewers.

The recommendation to use the Ottawa knee rule is based on the National Institute for Health and Care Excellence (NICE) guideline Fractures (non-complex): assessment and management [NICE, 2016].

The statement 'a history of an injury does not exclude the possibility of a bone sarcoma' is in line with the UK guidelines for the management of bone sarcomas [Gerrand, 2016].

What are the likely causes of knee pain by age group?

• Children and adolescents (<18 years of age)
  • Patellofemoral pain (usually adolescents).
  • Osgood-Schlatter's disease.
  • Referred pain from hip (such as Perthes' disease or slipped capital femoral epiphysis).
  • Joint hypermobility syndrome.
  • Growing pains.
  • Pattelar subluxation/instability.
  • Osteochondritis dissecans.
  • Septic arthritis. 
  • Tumours.
  • Pattelar tendonitis. 
  • Bipartite patella. 
  • Henoch-Schonlein purpura. 
• Younger adults (18-50 years of age)
  • Patellofemoral pain (usually adolescents).
  • Trauma (cruciate and collateral ligament sprains, meniscal tears).
  • Joint hypermobility syndrome.
  • Bursitis.
  • Inflammatory arthritis.
  • Septic arthritis.
  • Early osteoarthritis (previous injury).
  • Plicae.
  • Iliotibial band syndrome.
• Older adults (>50 years of age)
  • Osteoarthritis. 
  • Gout and pseudogout.
  • Baker's cyst.
  • Referred pain from osteoarthritis of the hip. 
  • Degenerative meniscal tear. 
  • Septic arthritis. 
  • Secondary tumours.
• Note: Many of the conditions can occur in other age groups (for example, septic arthritis can occur at any age). Conditions are allocated to the age group in which they most commonly occur. 

[Calmbach and Hutchens, 2003b]

What are the likely causes of knee pain by anatomical site?

• Anterior knee pain may be caused by:
  • Patellar subluxation or dislocation.
  • Osgood-Schlatter disease.
  • Patellar tendonitis.
  • Patellofemoral pain syndrome.
  • Patellar or quadriceps tendon rupture.
  • Patellofemoral joint arthritis.
• Medial knee pain may be caused by:
  • Medial collateral ligament sprain.
  • Medial meniscal tear.
  • Pes anserine bursitis.
  • Medial plica syndrome.
  • Medial compartment arthritis.
• Lateral knee pain may be caused by:
  • Lateral collateral ligament sprain.
  • Lateral meniscal tear.
  • Iliotibial band tendonitis.
  • Lateral compartment arthritis.
• Posterior knee pain may be caused by:
  • Baker's cyst.
  • Posterior cruciate ligament injury.
  • Posterior horn meniscal tears.

[Calmbach and Hutchens, 2003b; BMJ Best Practice, 2022a]

How are the specific diagnostic knee tests performed?

Versus Arthritis have produced a video of a knee examination, which includes some of the specific knee examination tests.

The provocative knee tests are difficult to visualise from written description and are better understood watched. Tests which may be helpful for those who are confident/experienced in performing them include the following:

Basis for recommendation

General knee examination recommendations are based on expert opinion in review articles [Calmbach and Hutchens, 2003a; Fanelli, 2011], a BMJ Best Practice review [BMJ Best Practice, 2022a] and a textbook [Bowden, 2010].

The recommendation to use the Ottawa knee rules in people over 2 years of age with knee injuries is in line with the National Institute for Health and Care Excellence guideline Assessment and management of non-complex fractures [NICE, 2016] and is based on diagnostic accuracy studies.

Assess for ligament tears and laxity 

Recommendations are based on the Oxford Handbook of Orthopaedics [Bowden, 2010] and a BMJ Best Practice review [BMJ Best Practice, 2022a].

• A comprehensive overview of meta-analyses and systematic reviews concluded that the Lachman test is the only test able to rule in or out a knee disorder [Decary, 2017]. The Lachman test was found to be an accurate test to rule in or out an anterior cruciate ligament injury [Decary, 2017], although another systematic review found it to have decreased sensitivity, particularly for partial ruptures [Leblanc, 2015].
• Expert opinion is that using a combination of tests may be more accurate [Swain, 2014; Decary, 2017; Kopf, 2020].
• The statement that specific tests for meniscal injury have poor diagnostic accuracy, particularly in non-specialist settings is based on expert opinion in review articles [Hegedus et al, 2007; Buchbinder, 2015; Bhan, 2020], and systematic reviews [Smith, 2015; Decary, 2017; Kopf, 2020]. For this reason, CKS does not recommend their use. 

Specific diagnostic knee tests information

Specific diagnostic knee tests information is derived from expert opinion in review articles [Rossi, 2011; Bunt, 2018a; BMJ Best Practice, 2022a] a textbook [Bowden, 2010], and the educational websites linked in the text.

Basis for recommendation

The recommendation to use the Ottawa knee rule in people over 2 years of age is based on the National Institute for Health and Care Excellence (NICE) guideline Fractures (non-complex): assessment and management [NICE, 2016]. The use of the Ottawa knee rule is also recommended in a review article [Bunt, 2018a], a BMJ Best Practice review[BMJ Best Practice, 2022a]  and further supported by systematic reviews and meta-analyses [Decary, 2017; Sims, 2020].

Basis for recommendation

Recommendations for investigations are based on expert opinion in review articles [Bunt, 2018a; BMJ Best Practice, 2022a], and on local NHS pathways [Leeds Adult Knee Pathway, 2015; East and North Hertfordshire CCG Knee pain pathway, 2019; Sussex MSK Partnership, 2019; NHS Coventry and Warwickshire ICB, 2021].

What are the signs and symptoms of serious pathology that may cause knee pain?

• Infection (septic arthritis or osteomyelitis)
  • Redness, swelling, heat, and reduced movement of the knee, especially if:
    • Rapid onset.
    • Movement is severely restricted, with pain associated with any attempt at movement.
    • Only one joint is affected, although in up to a fifth of people with septic arthritis, more than one joint is affected.
    • Knee pain is severe or, in people with pre-existing joint disease (for example rheumatoid arthritis and osteoarthritis), out of proportion to the usual symptoms.
    • Difficulty weight bearing, particularly in children, who may present with a limp.
    • Fever is present (although the absence of fever does not exclude septic arthritis); the person is systematically unwell.
    • There are risk factors for infection: recent joint surgery/corticosteroid injection, prosthetic joint, other joint disease, rheumatoid arthritis, history of open fracture, previous orthopaedic surgery, intravenous drug use, immunosuppression (for example diabetes, use of long-term corticosteroids, alcoholism), or adjacent discharging sinus, skin infection or ulceration.
• Tumour — see the CKS topics on Bone and soft tissue sarcoma, Childhood cancers and Haematological cancers.
  • Persistent, non-mechanical bone pain.
  • Pain at night or at rest.
  • Unexplained weight loss.
  • Previous cancer.
  • Hard, localised mass adjacent to the knee.
    • Swelling may not be present until late in the disease.
  • Unexplained lump, increasing in size.
  • Sudden onset of pain (may indicate a pathological fracture, but can also occur in osteonecrosis).
• Inflammatory polyarthritis — see also the CKS topic on Rheumatoid arthritis.
  • Persistent synovitis, indicated by:
    • Pain that is worse at rest or during periods of inactivity.
    • Joint swelling, tenderness, and warmth — giving a 'boggy' feel on palpation.
    • Stiffness in the morning and after inactivity that lasts more than 15-30 minutes.
  • Children may present with a limp.
  • Synovitis affecting more than one joint — symmetrical synovitis of the small joints of the hands and feet is typical in rheumatoid arthritis.
  • A history of psoriasis, inflammatory bowel disease, recent infection (for example diarrhoeal illness or genitourinary infection), uveitis, episcleritis, scleritis and other ocular conditions associated with inflammatory arthritis.
  • In an otherwise well child with swollen joint(s) and no clear history of trauma, the most likely diagnosis is juvenile idiopathic arthritis.

Which other non-traumatic problems can cause knee pain?

Patellofemoral pain

• Most commonly presents in teenage years or in young adulthood but can occur in active people at any age.
• Symptoms:
  • Anterior knee pain, often behind the patella, that is:
    • Diffuse and aching.
    • Gradual in onset.
    • Aggravated by ascending or descending stairs, squatting, running or long periods of sitting (or rising or straightening the knee after sitting).
  • Some people may report a sensation of 'giving way'. This is not true instability, which occurs in meniscal or ligamentous injury.
  • There may be reported crepitus and/or stiffness.
• Signs: 
  • Diagnosis of patellofemoral pain is clinical, and other causes of knee pain should be excluded.
  • There is no definitive clinical test for diagnosis but the best available test is anterior knee pain reproduced on squatting.
  • Additionally there may be tenderness when palpating the patellar edges.
  • Diagnosis is based on the typical history, reproduction of pain on squatting and exclusion of other pathology.

Knee osteoarthritis

• Symptoms:
  • Activity-related, persistent pain.
  • Stiffness in the morning or after inactivity lasting 30 minutes or less.
  • Impaired function.
• Signs:
  • Crepitus.
  • Painful or restricted movement.
  • Bony enlargement.
• The guideline on osteoarthritis from the National Institute for Health and Care Excellence (NICE) states that osteoarthritis may be diagnosed clinically if a person:
  • Is aged 45 years or more
  • Has activity-related joint pain, and
  • Has either no morning joint-related stiffness or morning stiffness that lasts no longer than 30 minutes.
• For further information on making a diagnosis and management of knee osteoarthritis, see the CKS topic on Osteoarthritis.

Referred pain

• Consider referred pain, particularly in children, and particularly when examination of the knee itself is normal. Examination for knee pain should include examination of hips, ankles and spine, particularly in children. 
• Causes include:
  • Referred pain from the hip in a child (see the CKS topic on Acute childhood limp) such as:
    • Slipped capital femoral epiphysis.
    • Septic arthritis of the hip.
    • Transient synovitis of the hip (irritable hip, reactive arthritis).
    • Perthes' disease (idiopathic avascular necrosis or osteonecrosis of the femoral epiphysis).
    • Juvenile idiopathic arthritis of the hip.
  • Osteoarthritis of the hip — see the CKS topic on Osteoarthritis.
  • Lumbar radiculopathy — see the CKS topic on Sciatica (lumbar radiculopathy).

Osgood-Schlatter's disease

• Osgood-Schlatter's disease is an osteochondrosis with traction apophysitis affecting the extensor mechanism of the knee.
• It is typically associated with growth spurts, most commonly between the ages of 10 and 15, and more common in boys than girls.
• Symptoms:
  • Gradual onset knee pain during adolescence localised to the tibial tuberosity.
  • Typically unilateral, but bilateral in up to 30% of people.
  • Relieved by rest and made worse by activity and mild local pressure. 
• Signs:
  • Tenderness and swelling over the tibial tuberosity.
  • Pain provoked by resisted knee extension.
• Sinding-Larsen-Johansson syndrome is a similar osteochondrosis affecting the inferior pole of the patella.
• For further information on making a diagnosis and management, see the CKS topic on Osgood-Schlatter disease.

Bursitis

There are four bursae associated with the knee joint; supra-patellar, infra-patellar, pes anserine and pre-patellar. Prepatellar bursitis is the most common bursitis in the knee. Bursitis may be acute (relating to trauma, infection, or crystalline joint disease such as gout) or chronic (associated with inflammatory arthropathies or repetitive pressure or overuse).

• Pre-patellar bursitis:
  • Symptoms:
    • Anterior knee swelling that may be accompanied by anterior knee pain usually with direct pressure or activity.
    • There may be a history of preceding trauma, repetitive friction or pressure (for example kneeling, hence the term "housemaid's knee"), or bursal disease (from previous traumatic bursitis, rheumatoid arthritis, or gout).
  • Signs:
    • Localised, fluctuant swelling over the patella.
  • It may be difficult to differentiate between septic and non-septic bursitis on clinical grounds.
    • Suspect if significant erythema, warmth or tenderness, or systemic signs.
  • For further information, see the CKS topic on Pre-patellar bursitis.
• Infra-patellar bursitis presents with anterior knee pain, and is difficult to distinguish from patellar tendonitis. Bursae may be superficial or deep. It may also be associated with prolonged kneeling. There is usually localised tenderness of the distal patellar tendon.
• Pes anserine bursitis:
  • Inflammation of the pes anserine bursa, at the anteromedial aspect of the proximal tibia. 
  • Symptoms:
    • Medial or anteromedial knee pain, worse on repetitive flexion and extension.
  • Signs:
    • Tenderness over the medial knee, just posterior and distal to the medial joint line.
    • There may be slight swelling at the insertion of the medial hamstring muscles, but there is no joint effusion.
    • Valgus stress or resisted knee flexion may reproduce the pain.

Gout and pseudogout

• Typical presentation is acute onset (<24 hours) of severe pain, swelling and tenderness of the joint.
  • These features are not specific to gout or pseudogout, and may also occur with septic or reactive arthritis.
  • If the person presents with a short history of a hot, swollen, tender knee joint with restriction of movement, immediately refer them to a specialist within hospital who has the expertise to aspirate the joint to exclude septic arthritis.
• Tophi may be present.
• For more information, see the CKS topic on Gout.

Degenerative meniscal tear

• Meniscal tears can occur in association with a degenerative process and without a traumatic injury, usually in middle-aged or older people. 
• Symptoms:
  • Symptoms are non-specific and may be hard to distinguish from the osteoarthritis which is commonly associated.
  • Gradual onset of recurring localised knee pain, medially or laterally. The medial meniscus is more commonly involved.
  • There may be catching or locking, particularly on squatting or twisting movement.
  • There may be a history of the knee giving way.
• Signs:
  • There is joint line tenderness medially or laterally.
  • There may be a loss of full extension.
  • There may be palpable or audible clicking.

Baker's Cyst

• Symptoms:
  • Popliteal swelling.
  • Posterior knee aching or stiffness.
  • Acute rupture or dissection may present with pain and calf swelling.
• Signs:
  • Posteromedial fullness and/or tenderness.
  • Cyst is firm in knee extension and soft in flexion.
  • Signs of rupture:
    • Discolouration in the calf, beneath one of the malleoli or on the dorsum of the foot.
    • Calf swelling.
• For further information, see the CKS topic on Baker's cyst.
• If a ruptured Baker's cyst cannot be distinguished from a deep vein thrombosis on the basis of the history and examination, see the CKS topic on Deep vein thrombosis.

Patellar tendonitis

• Patellar tendonitis (jumper's knee) occurs most commonly in athletes who are involved in sports which involve jumping (repetitive loading of the tendon), such as basketball or volleyball. It may also occur in teenage boys, particularly during a growth spurt.
• Symptoms:
  • Anterior knee pain, usually present for several months and aggravated by running, walking downstairs, and jumping.
  • Stiffness.
• Signs:
  • Tender patellar tendon. (Palpable tenderness at the inferior pole of the patella.)
  • Pain reproduced by resisted knee extension.
  • There may be localised thickening, or nodules, but there is no joint effusion.

Osteochondritis dissecans

• Osteochondritis dissecans is a relatively common, idiopathic condition affecting the subchondral bone and articular cartilage. It generally affects growing adolescents, but can affect adults. 
• Symptoms:
  • Presentation is variable but the person will usually report vague knee pain, worse with exercise.
  • They may describe locking, catching or giving way.
  • Symptoms are usually unilateral but are bilateral in up to 25% of cases.
• Signs:
  • There may be quadriceps weakness and (disuse) atrophy, focal bony tenderness, a small knee effusion, and limitation of knee extension. 
• Offer X-rays of both knees if suspected, although not all lesions will be detected on X-rays.
  • Ensure that the request form states that osteochondritis dissecans is suspected so that correct views are taken.

Patellar subluxation

• Most common in teenage girls.
• Symptoms:
  • Recurrent episodes of a sensation of the patella 'giving way'.
  • The person may also complain of anterior knee pain, locking, catching sensations, and recurrent mild swelling.
• Signs:
  • Tenderness over the medial patellofemoral ligament.
  • Positive patellar apprehension test (patellar apprehension elicited by subluxing the patella laterally).
  • There may be a mild effusion.
• 'Atraumatic' dislocation can occur in an anatomically abnormal knee without, or with a minimal, direct blow to the patella.  Abnormalities will usually also be revealed on examination of the other knee. For information on patellar dislocation, see Other traumatic causes.

Iliotibial band syndrome

• Occurs most commonly in people who undertake activities involving repetitive knee flexion, such as running and cycling.
• Symptoms:
  • Lateral knee pain.
  • Usually aggravated by activity. Initially, the pain is felt late in or after completion of activity, but as it progresses, it occurs earlier during activity.
  • An objective 'clicking' or 'clunking' sounds may be heard during some movements
• Signs:
  • Tenderness to the lateral knee, typically 2–3 cm superior to the joint line.
  • An objective 'clicking' or 'clunking' sound may be heard during examination of the knee.
  • There is no joint effusion.

'Growing pains'

• Occur in young children 3–12 years of age.
• Symptoms:
  • Poorly localised aches and pains in the lower limbs, usually in the calves, shins, anterior thighs and popliteal fossa, and not exclusively in joints.
  • Bilateral and symmetrical symptoms.
  • Pains only occur at night, and are not present in the day, after waking. Children may be woken by leg pain.
  • There is no limp and no limitation of physical activities, and the child has normal motor development.
  • Systematically well.
• Signs:
  • Physical examination is normal apart from possible joint hypermobility.
• For further information about growing pains, see the CKS topic Developmental rheumatology in children.

Other causes

• Bipartite patella is usually asymptomatic (and discovered as an incidental finding on X-ray), but may present with anterior knee pain during adolescence, usually related to repetitive or rigorous sporting activity, and more common in males.
  • Pain is associated with knee extension and squatting.
  • On examination, there is tenderness over the location of the bipartite patella, most commonly the upper outer quadrant.
  • If pain is severe, refer the person to a physiotherapist for treatment with activity modification advice, a brace, and exercises. Surgery is occasionally required if symptoms persist.
• Infrapatellar fat pad inflammation/impingement:
  • Impingement of the infrapatellar fat pad between the patella and the femoral condyle may result from direct blow or impact injury, or an acute hyperextension injury. Inflammation may be associated with chronic irritation from patellar tendinopathy, patellofemoral syndrome or recurrent synovitis.
  • The person usually has anterior or inferior knee pain worse on knee extension, kneeling, or with prolonged standing. They may report a painful catching sensation.
  • On examination, there is infrapatellar swelling and tenderness.
  • The inferior pole of the patella may be posteriorly displaced.
  • Diagnosis is usually made on MRI scan.
• Osteonecrosis of the knee is usually idiopathic, and most commonly occurs in the medial femoral condyle and in women older than 60 years of age. It may also be secondary, due to known causes of disrupted blood supply (including trauma, surgery or medical conditions.)
  • It presents with sudden, spontaneous, severe pain in the medial part of the knee. 
  • The pain is usually worse at night and on weight-bearing.
  • On examination there is localised tenderness medially. There may be a small effusion. Range of movement is usually relatively unaffected.
• Plicae are embryonic membranous remnants which may become inflamed and impinged.
  • The medial plica is most commonly involved.
  • May present acutely after increase of usual activity.
  • Most commonly there is medial or anterior knee pain; there may be catching, clicking or snapping during flexion and extension.
  • Pain may be worsened by running, climbing stairs, squatting or sitting with legs flexed for long periods of time.
  • On examination, there may be medial joint line tenderness, and nodularity may be felt on the anterior medial joint. There may be a palpable thickened band. There is usually no joint effusion.
• Complex regional pain syndrome may be precipitated by a relatively minor musculoskeletal injury or surgery, and when it occurs in the knee, is often associated with patellofemoral joint abnormality. Pathophysiology is not well understood. It occurs in adults and children.
  • Continuous pain, allodynia or hyperalgesia, out of proportion to clinical findings or original event, is suggestive of this diagnosis.
  • There may also be knee joint swelling, as well as sweating and abnormalities of skin temperature and colour.
  • There may be motor change such as loss of range of movement, weakness, tremor or dystonia.
  • There may be changes to hair/nails/skin (trophic change).
  • Guidelines about this condition from the Royal College of Physicians offer a diagnostic check list for GPs in Appendix 4.
• Joint hypermobility syndrome is a condition involving generalised joint laxity with associated musculoskeletal symptoms.
  • Symptoms are variable. Joint pain, especially of the knee or ankle, is usually after activity but can become constant in adulthood. Other symptoms include susceptibility to soft tissue injury, joint instability, and tiredness.
  • Signs may include pain on joint movement. Effusions may occur. Clinically significant tenderness or inflammation are not present. Specific signs of hypermobility depend on the joint affected.
  • Diagnosis can be made by calculating a Beighton score and using the Brighton criteria.
  • There is clinical overlap with the hypermobility type of Ehlers-Danlos syndrome and other connective tissue disorders.
  • For more information on joint hypermobility syndrome, see the CKS topic Developmental rheumatology in children.
• Henoch–Schönlein purpura is a systemic vasculitis that mainly affects children 3-15 years of age. Peak incidence of 6 years of age. 90% of cases occur in children under the age of 10, but it may also affect adults.
  • Clinical features include a palpable purpuric rash (usually on the legs and buttocks), arthritis (usually of the knees and ankles), and/or abdominal pain.
  • Symptoms often follow a respiratory tract infection, can occur over days or weeks, and in any sequence.
  • Renal complications occur in 40-50% of patients and range from isolated haematuria or proteinuria, to progressive glomerulonephritis.
  • 75% have joint involvement, arthralgia or arthritis, and in 15% it may present before the rash. Knees and ankles are the joints commonly affected. Joint involvement is usually transient and not destructive.
  • Other diagnoses, in particular meningococcal septicaemia, should be considered.  See the CKS topic on Non-blanching rash or meningococcal septicaemia.

Basis for recommendation

Red flags

• Red flags for infection are derived from joint UK guidelines for the management of a hot, swollen joint in adults [Coakley, 2006], a commissioning guide produced by the Royal College of Surgeons (RCS) [Royal College of Surgeons, 2013], European recommendations for the diagnosis and initial management of patients with acute or recent onset swelling of the knee [Landewé et al, 2010] and expert review articles [Bunt, 2018a; Colson, 2018; BMJ Best Practice, 2021b].
• Red flags for a tumour are based on the National Institute for Health and Care Excellence (NICE) guidelines Suspected cancer: recognition and referral [NICE, 2021a], the Royal College of Surgeons commissioning guide for painful osteoarthritis of the knee [Royal College of Surgeons, 2013], the UK guidelines for the management of bone sarcomas [Gerrand, 2016], and the European Society for Medical Oncology (ESMO) guideline on bone sarcomas[ESMO, 2021]. The presenting features of pathological fracture are derived from expert opinion from a BMJ Best Practice review on long bone fracture [BMJ Best Practice, 2022b].
• Red flags for inflammatory arthritis are based on the NICE guideline Rheumatoid arthritis: national clinical guideline for management and treatment in adults [NICE, 2020c], the NICE guideline Osteoarthritis: care and management [NICE, 2020b]and guidelines on the diagnosis and management of juvenile idiopathic arthritis by the Royal Australian College of General Practitioners [RACGP, 2009].
  • The statement that in an otherwise well child with swollen joint(s) the most likely diagnosis is juvenile idiopathic arthritis (JIA) is based on the Scottish guideline on JIA in children [NHSGGC, 2019].  

Other non-traumatic causes

• Patellofemoral pain information is derived from a consensus statement from the 4th international patellofemoral pain research retreat, and guidelines from the American Physical Therapy Association [Crossley, 2016; Willy, 2019].
• Knee osteoarthritis information is derived from clinical guidelines on osteoarthritis from NICE [NICE, 2020b] and the European League Against Rheumatism (EULAR) [Zhang, 2010], and a commissioning guide produced by the RCS [Royal College of Surgeons, 2013].
• The information that knee pain may be the result of referred pain from other joints is derived from expert opinion from a textbook [Bowden, 2010] and expert opinions in review articles [Calmbach and Hutchens, 2003b; Dibra, 2017].
• Osgood-Schlatter's disease information is based on expert opinion from a BMJ Best Practice review [BMJ Best Practice, 2019b] and review articles [Atanda et al, 2011; Weiler, 2011].
• Bursitis information is based on a BMJ Best Practice review [BMJ, 2019] and expert opinion in review articles [Calmbach and Hutchens, 2003b; Bunt, 2018a; Rishor-Olney, 2022].
• Gout information is based on evidence-based recommendations for the management of gout produced by the European League Against Rheumatism (EULAR) [Richette, 2017] and American College of Rheumatology/EULAR gout classification criteria [Neogi, 2015].
• Degenerative meniscal tears information that meniscal tears is derived from expert opinion in review articles [Calmbach and Hutchens, 2003b; Howell, 2014; Buchbinder, 2015; Bunt, 2018a], and background information in a Cochrane review [O'Connor, 2022].
• Baker's cyst information is based on expert opinion in review articles [Herman, 2014; Frush, 2015].
• Patellar tendonitis information is based on expert opinion in review articles [Calmbach and Hutchens, 2003b; Bunt, 2018a; Challoumas, 2021].
• Osteochondritis dissecans information is dbased on clinical guidelines produced by the American Academy of Orthopaedic Surgeons [Chambers, 2011], expert opinion in review articles [Calmbach and Hutchens, 2003b; Houghton, 2007] and a BMJ Best Practice review [BMJ Best Practice, 2022c].
• Patellar subluxation information is mainly based on expert opinion in review articles [Calmbach and Hutchens, 2003b; Houghton, 2007; Bunt, 2018a] and a textbook [Bulstrode, 2011].
• Iliotibial band syndrome information is derived from expert opinion in review articles [Calmbach and Hutchens, 2003a; Strauss, 2011; Bunt, 2018a; Jiménez Díaz, 2020] and a BMJ Best Practice review [BMJ Best Practice, 2022d].
• Growing pains information is based on expert opinion in review articles [Lehman, 2017; Kanta, 2019].
• Bipartite patella information is based on expert opinion in review articles [Houghton, 2007; Atesok, 2008; Hong, 2014].
• Fat pad impingement information is based on expert opinion in review articles [Houghton, 2007; Hong, 2014; Genin, 2017].  
• Osteonecrosis of the knee information is derived from expert opinion in review articles [Karim, 2015; Young, 2022].
• Plicae information is based on expert opinion in review articles  [Houghton, 2007; Hong, 2014; Bunt, 2018a].
• Complex regional pain syndrome information is based on expert opinion from review articles [Dowd, 2007; van Bussel, 2014; Misidou, 2019], and on guidelines from the Royal College of Physicians [Royal College of Physicians, 2018].
• Joint hypermobility syndrome information is based on expert opinion in review articles [Syx, 2017; Ross and Grahame, 2011]. The information regarding consensus on diagnosis, management and guidelines comes from a 2020 statement from the British Society for Rheumatology [BSR, 2020].
• Henoch-Schonlein Purpura information is based on expert opinion in review articles [Reamy et al, 2009; Roache-Robinson, 2022].

What are the signs and symptoms of serious pathology that may cause knee pain?

• Fracture
  • Symptoms:
    • The mechanism of injury may be direct trauma/blow or a fall.
    • The patient is usually unable to weight bear.
  • Signs:
    • Joint deformity or shortening, and swelling.
    • Severe pain on movement and limited movement.
    • Neurovascular injury may be present.
  • See Ottawa knee rule.
  • Pathological fracture following a less significant stress should prompt investigation for malignancy.
• Anterior cruciate ligament (ACL) injury
  • Symptoms:
    • Mechanism of injury is typically sudden deceleration, stopping, or change of direction with a fixed foot, or forceful hyperextension.
    • A sudden, painful popping sensation or audible pop noise.
    • Significant, rapid swelling (haemarthrosis) within one to two hours of injury.
    • Inability to return to full activity.
    • May occur in isolation or in combination with other internal knee injuries (such as avulsion fractures).
  • Signs:
    • Lateral knee and joint line tenderness.
    • The Lachman test is often positive.
    • An anterior drawer or pivot shift test may be positive. The pivot shift test may be more useful when assessment is not made directly after the injury.
    • Diagnostic accuracy of the specific tests in non-specialist hands may be low.
• Posterior cruciate ligament (PCL) injury
  • Symptoms:
    • The mechanism of injury is typically a direct blow to the proximal tibia with the knee in flexion, or a hyperextension injury. Usually there is a history of high energy trauma, such as a road traffic accident (dashboard injury) or sports injury.
    • If only the PCL is injured (in the absence of injury to the posterolateral complex), the person may be relatively asymptomatic immediately after the injury.
    • There may be posterior pain (or pain on kneeling), although the person may complain of anterior pain with a chronic PCL injury.
    • May occur in isolation or in combination with other internal knee injuries. PCL injury is commonly associated with posterolateral corner injury.
  • Signs:
    • Mild effusion and reduced range of knee flexion may be present.
    • The posterior drawer test will often be positive, and the posterior sag test may be positive. The quadriceps active test is another test which may be used for diagnosis.
• Patellar dislocation
  • First-time traumatic patellar dislocation often occurs in association with ligament injuries and fractures.
  • Symptoms:
    • The mechanism of injury is usually a direct blow to the medial or lateral aspect of the knee.
    • Spontaneous relocation often occurs but some present still dislocated.
  • Signs:
    • The patella may be clearly dislocated (lying medial or lateral to the joint).
    • There is usually acute swelling due to intra-articular effusion (If there is haemarthrosis suspected from aspiration, this suggests possible fracture.)
    • There is usually tenderness along the medial edge of the patella.
    • There is usually a positive apprehension test (anxiety and/or resistance when the examiner attempts to move the patella laterally with the patient lying supine with the knee flexed to 30°.)
  • 'Atraumatic' dislocation can occur in an anatomically abnormal knee without, or with a minimal, direct blow to the patella.  Abnormalities will usually also be revealed on examination of the other knee.
  • Recurrent dislocations and persistent anterior knee symptoms can occur following a first-time patellar dislocation.
• Quadriceps or patellar tendon rupture
  • Quadriceps tendon rupture occurs mostly in people older than 45 years of age (most commonly people 45–60 years of age), whereas patellar tendon rupture occurs mostly in people younger than 45 years of age.
  • More common in men.
  • Symptoms:
    • Usually occurs during sporting activity or after a fall, but can also occur spontaneously owing to underlying disease.
    • Sudden onset of anterior knee pain.
  • Signs:
    • Inability to straight leg raise or extend the knee.
    • Change in height of the patella. There is usually visible deformity with the patella migrated proximally in patellar tendon rupture, and distally in quadriceps tendon rupture.
    • A palpable gap in the patellar or quadriceps tendon (although this may be difficult to detect owing to overlying haematoma).

What are the other potential traumatic causes?

• Meniscal injury or degenerative tear
  • Symptoms:
    • The mechanism of injury is typically twisting or pivoting. Meniscal tears can also occur in association with a degenerative process.
    • Symptoms are variable depending on the location and severity of the tear and associated injury/pathology.
    • The person may describe various symptoms including pain, locking, catching, clicking and the knee giving way.
    • Pain is usually well localised over the anteromedial or anterolateral joint line.
    • Swelling usually occurs. The volume of swelling is mild to moderate, and occurs several hours after the injury. Over the following weeks, there may be recurrent swelling.
  • Signs:
    • There may be an effusion, joint line tenderness, and a block to full extension or flexion.
    • Clinical tests such as McMurray, Thessaly and Apley tests have poor diagnostic accuracy, particularly in primary care settings.
• Medial collateral ligament injury
  • This is the most ligament most commonly injured in the knee. 
  • Symptoms:
    • The mechanism of injury may be a direct blow to the lateral aspect of the knee, or a twisting injury, most often during sport.
    • Medial knee pain.
    • The person may be able to walk.
    • Medial collateral ligament injuries often occur in association with cruciate and meniscal injuries, which should be excluded.
  • Signs:
    • Tenderness along the course of the ligament.
    • There may be effusion.
    • There is often a positive valgus stress test. (Valgus pressure is applied to the knee in full extension and at 30° flexion - there is pain, laxity or medial joint gapping/opening in a positive test.) 
• Lateral collateral ligament injury
  • A lateral collateral ligament injury is less common than a medial collateral ligament injury. 
  • Injury to the lateral collateral ligament can occur in combination with other posterolateral complex structures including the peroneal nerve. A careful neurovascular assessment is required.
  • Symptoms:
    • The mechanism of injury may be a direct blow to the medial aspect of the knee, or other varus stress.
    • There is usually acute onset of lateral knee pain and cessation of activities.
  • Signs:
    • There is tenderness over the lateral collateral ligament (at the lateral joint line).
    • There is swelling of the knee.
    • Instability or pain on varus stress test.
      • Varus stress applied to the knee in full extension and 30° flexion.
    • There may be paraesthesia or weakness of the lateral lower limb.

Basis for recommendation

Red flags

• Fracture information is based on expert opinion in a BMJ Best Practice review [BMJ Best Practice, 2022a].
  • The recommendation to investigate for malignancy in cases of pathological fracture is derived from expert opinion in a BMJ Best Practice review [BMJ Best Practice, 2022b].
  • The recommendation to use the Ottawa knee rule in people over 2 years of age is based on the National Institute for Health and Care Excellence (NICE) guideline Fractures (non-complex): assessment and management [NICE, 2016]. The use of the Ottawa knee rule is also recommended in a review article [Bunt, 2018a], a BMJ Best Practice review [BMJ Best Practice, 2022a]  and further supported by systematic reviews and meta-analyses [Decary, 2017; Sims, 2020].
• Anterior cruciate ligament (ACL) injury information is mostly derived from expert opinion from a BMJ Best Practice review [BMJ Best Practice, 2021a] as well as expert opinion in review articles [Bunt, 2018b; Farha, 2021].
  • A comprehensive overview of meta-analyses and systematic reviews [Decary, 2017] concluded that the Lachman test is the most accurate test to diagnose an ACL disorder, although another systematic review [Leblanc, 2015] found it to have decreased sensitivity, particularly for partial ruptures. Studies generally included orthopaedic surgeon examiner findings. The test may not be as accurate when performed by non-specialists.
  • The anterior draw test is less sensitive and specific [BMJ Best Practice, 2022a]  [Decary, 2017; Bunt, 2018a].
  • Although some systematic reviews demonstrate that the pivot shift test exhibits high specificity, others are less conclusive, and it is difficult to perform and unfamiliar to most primary care professionals [Scholten et al, 2003; Leblanc, 2015].
  • The general statement about poor diagnostic accuracy in the hands of non-specialists is derived from systematic reviews and review articles [Scholten et al, 2003; Leblanc, 2015; Bunt, 2018a]  [Allott, 2022].
• Posterior cruciate ligament injury (PCL) information is based on review articles [Rosenthal, 2012; Bunt, 2018a; Winkler, 2021; BMJ Best Practice, 2022a].
  • The posterior draw test is the most specific and sensitive test for evaluation of suspected PCL injuries, with the posterior sag test being less specific [Rosenthal, 2012].
• Suspected first time-patellar dislocation information is based on expert opinion in review articles [Hong, 2014; Duthon, 2016; Bunt, 2018a], a BMJ Best Practice review [BMJ Best Practice, 2022e] and a textbook [Bulstrode, 2011].
• Quadriceps or patellar tendon rupture information is based on expert opinion in a review article [Ibouniq, 2016] and a BMJ Best Practice review [BMJ Best Practice, 2022a].

Other causes

• Meniscal injury or degenerative tear information is based on expert opinion in review articles [Buchbinder, 2015; Bhan, 2020; Raj, 2022] and a BMJ Best Practice review [BMJ Best Practice, 2020].
• Medial collateral ligament injury information is based on a BMJ Best Practice review [BMJ Best Practice, 2019a], a textbook [Bowden, 2010] , and review articles [Andrews, 2017; Bunt, 2018a; Naqvi, 2022].
• Lateral collateral ligament injury information is based on a textbook [Bowden, 2010], and expert opinion in review articles [Calmbach and Hutchens, 2003b; Crespo, 2015; Bunt, 2018a; Yaras, 2022].

When do I refer a person with knee pain urgently for immediate specialist assessment?

• Refer for immediate specialist assessment if:
  • Septic arthritis is suspected or cannot be excluded.
  • Slipped capital femoral epiphysis is suspected.
  • Fracture cannot be excluded.
  • There is any evidence of neurovascular damage following trauma (including loss of sensation or weakness in the lower leg or foot, absence or asymmetry of pedal pulses, or compartment syndrome).
  • Quadriceps or patellar tendon rupture is suspected.
  • First-time traumatic patellar dislocation is suspected, or a recurrent dislocation is associated with moderate or severe swelling.
  • There is severe soft tissue injury with gross instability.
    • Discuss with a specialist as there may be an appropriate alternative available locally (see below).
• Consider referral for immediate assessment if:
  • A child presents with a limp, depending on clinical features - see the CKS topic Acute childhood limp for detailed guidance.
  • Henoch-Schönlein purpura is suspected - seek specialist advice.
• Depending on local arrangements, refer to an accident and emergency department, fracture clinic or acute knee clinic if:
  • A significant soft tissue injury is suspected in a person with acute knee pain following trauma, due to:
    • A sensation of a 'pop' or 'snap'.
    • Effusion, with rapid or gradual onset of swelling.
    • Inability to complete the activity.
    • Instability.
    • Locking.
    • Giving way.
    • Difficulty weight bearing.
• If unsure of the appropriate referral pathway, seek specialist advice.

When do I refer a person with knee pain?

• Refer urgently (to be seen within 2 weeks of referral) to an appropriate specialist if a tumour is suspected.
• Refer any person with suspected persistent synovitis of undetermined cause to a rheumatologist to assess for inflammatory polyarthritis.
  • Refer urgently (usually to be seen within 2 weeks) if any of the following are present:
    • The small joints of the hand or feet are affected.
    • More than one joint is affected.
    • There has been a delay of 3 months or longer between symptom onset and seeking medical help.
  • Refer urgently to a paediatric rheumatologist if a child or young person presents with suspected juvenile idiopathic arthritis. Discuss immediate management with the on-call rheumatologist at the same time as making the referral.
• Refer urgently to an orthopaedic surgeon any person suspected of having osteonecrosis of the knee.
• Depending on local pathways and services, refer for further assessment and/or advice to an integrated musculoskeletal service or orthopaedic surgeon if there is:
  • Persisting knee pain or other symptoms for more than six weeks.
  • A suspected degenerative meniscal tear.
  • Symptomatic bipartite patella.
  • Fat pad impingement/inflammation.
  • Plicae syndrome.
  • Osteochondritis dissecans.
  • Recurrent patellar dislocation/subluxation.
  • Patellofemoral pain syndrome, particularly if not improved after 6 weeks of conservative management.
  • Iliotibial band syndrome.
• Appropriately focused imaging is in most cases better performed as part of this further specialised assessment. Note that direct access to MRI scan may be available depending on local arrangements, for people with knee pain meeting locally-defined criteria.
• Refer to an appropriate specialist if complex regional pain syndrome is suspected for confirmation of diagnosis, to rule out ongoing pathology or other causes, and for symptom control and rehabilitation.
  • This may be to an orthopaedic surgeon if pain is secondary to trauma/surgery, or to an appropriate secondary care physician such as a rheumatologist, neurologist or pain specialist if there was no preceding trauma.
  • If complex regional pain syndrome is confirmed, referral to a specialist pain service is recommended.
• If the diagnosis is uncertain, consider referring to an appropriate specialist (for example a rheumatologist, orthopaedic surgeon, sports physician, or other musculoskeletal specialist).
• For when to refer to a specialist for the specific conditions, see the CKS topics on:
  • Osteoarthritis.
  • Pre-patellar bursitis.
  • Gout.
  • Baker's cyst.
  • Osgood-Schlatter disease.
  • Rheumatoid arthritis.
  • Acute childhood limp.