Key points

  • Always take a thorough history, examine the affected knee(s) and consider whether or not any further investigations are needed to make a diagnosis.
  • Apply Ottawa rules to determine if diagnostic X-rays are necessary for suspected fractures – preferably including weight-bearing image requests in your referral – and review them before devising a care plan.
  • Remember that every care plan must be based on a diagnosis (eg, fracture) and that most uncomplicated acute knee pain will resolve with simple conservative measures.
  • Review the patient on several occasions, if needed, to assess progress.
  • Avoid unnecessary further investigation.
  • Be mindful that MRI does not provide additional useful information in most cases of knee injury, especially when degenerative joint disease is evident on plain X-ray (eg, it often reveals incidental findings that are unrelated to the patient’s pain).
  • Recognise that surgical procedures (eg, arthroscopy) have a very limited role in the treatment of acute knee pain at any age, but especially when patients are middle-aged or older.

History and a physical exam are usually sufficient

Knee pain is a common symptom among middle-aged or older people and one that often prompts them to visit their GPs. 1-6

There are many causes of acute knee pain.2 In the majority of cases, history-taking and an appropriately targeted physical examination of the affected joint(s) may be all that is required to establish a diagnosis.2,7-10 Indeed, RACGP guidelines report that thorough examination of the knee can be as accurate as MRI in identifying ACL tears or meniscal injury.9

Be mindful that middle-aged and older patients presenting with acute knee injuries are very likely to have coexisting degenerative joint disease, which may (or may not) be causing or contributing to their acute knee pain.4,5,11,12 Osteoarthritis (OA), for example, is very common among middle-aged and older people.1,3,6

Moreover, OA of the knee is frequently associated with degenerative changes in other tissues within the affected knee and often coexists with other knee pathology (eg, meniscal abnormalities, ligament tears, bursitis, inflammatory arthropathies).12-16 Meniscal degeneration is especially prevalent among people with OA, but is usually not the cause of the patient’s symptoms.12,13,15,17-19


Diagnosing acute knee pain 2,9,20

History

  • Ask about the mechanism and early features of injury.
  • Ask about any  previous injuries.

Physical examination

  • Conduct relevant physical tests (eg, assess range of motion, check for presence of an effusion, perform ligament laxity tests and tests for meniscal tear).

Further investigations (if findings are likely to change management)

  • Apply Ottawa Knee Rules to determine whether radiography is warranted for suspected fractures.

Meniscal damage is not always clinically relevant

Degenerative meniscal injury is common among middle-aged and older people. It often accompanies knee OA and/or coexists with degenerative changes in other knee joint structures.12-15

However:

  • meniscal abnormalities (eg, tears) may not be the underlying cause of acute knee pain5,12,14-17 and most authors have reported a negligible correlation between MRI-detected meniscal tears and pain (Figure 1).14,16,17,21
  • specific interventions to treat a suspected meniscal tear are unlikely to be warranted if a patient's pain or other symptoms are due to damage elsewhere in the knee.14-16

Suspected or apparent meniscal abnormalities may be completely unrelated to a patient's acute knee pain, especially if he/she has coexistent OA.

Prevalence of meniscal tears among middle-aged and elderly people with radiographic osteoarthritis

Data based on 167 ambulatory subjects aged 50–90 years with radiographic evidence of osteoarthritis; selection was not made on the basis of knee or other joint problems. Integrity of the menisci in the right knee was assessed using MRI. Radiographic evidence of osteoarthritis was considered present if the Kellgren–Lawrence grade was 2 or higher.14


The role of diagnostic imaging

If the cause of a middle-aged patient's acute knee pain remains uncertain, or if an adequate trial (eg, 6–8 weeks) of conservative treatment interventions has failed to sufficiently relieve symptoms, further investigations may be warranted, if the findings are likely to alter the treatment strategy. 7,10

Apply the Ottawa Knee Rules to guide referral for X-rays for suspected fractures, preferably with weight-bearing knee X-rays (several views).2,5,7,10 Ultrasound has a very limited role in the assessment of the knee and is not recommended for evaluation of acute knee pain. 9,22

More advanced imaging options include MRI and CT scanning.

MRI is rarely indicated, as it is an expensive investigation that is generally not recommended for the routine assessment of acute knee pain (although it may be indicated if/when there is a history of true 'knee locking' or of the knee 'giving way').8,22 CT scans are indicated if there is a complex fracture involving the knee.23 Neither MRI nor CT scanning have any role to play in the primary investigation of suspected knee OA.7

Diagnostic knee MRI – when is it needed?

Consider using …
  • after an appropriate period of conservative management (approx. 6–8 weeks), when there is doubt about the diagnosis following history/examination.a,9,22
  • when the level of patient disability after 6–8 weeks is such that surgery is being considered as part of a shared decision-making approach.9
  • when the presence of other complex or unusual pathology is suspected (eg, a tumour in or around the joint).22
Avoid
  • when comprehensive history and examination does not suggest cruciate or collateral ligament or meniscal injury.9,22
  • when surgical intervention is not being considered.9
  • when degenerative joint disease is evident on plain X-rays (NOTE: MRI does not provide additional useful information in this situation).22

a For example: In cases of true 'knee locking', where there is a 'mechanical block' that prevents a full range of movement; or when there appears to be mechanical instability, causing the knee to buckle or give way.24

Is MRI scanning being overused?

Accumulating evidence suggests that use of MRI as a diagnostic tool is often unwarranted in the management of patients who present with acute knee pain.5,25,26 For example, the authors of one retrospective study found that:

  • 90% of 100 knee MRIs ordered by a group of 32 GPs (for 100 consecutive patients aged ≥ 40 years) had resulted in either no change in their treatment plan or a referral to a specialist.5
  • 88 of these 100 knee MRIs had been unnecessary, in the opinion of orthopaedic specialists, because, in these cases, it had been possible to make the diagnosis via history, physical examination and/or X-rays alone.5
In another retrospective study, orthopaedic specialists found that – among a cohort of 112 patients with radiographically detectable degenerative joint disease – approximately 60% of previously obtained knee MRIs had been of minimal or no use in helping the treating clinician make a correct diagnosis or select the most appropriate treatment option.26

Before ordering MRI

  • Ask: Is the result likely to change the treatment plan?9
  • Manage patient expectations 3,8,26
  • Discuss the expected value of the investigation you are about to order with the patient (the extent to which it is likely to help you make a correct diagnosis, or alter the recommended treatment strategy).
  • Clearly explain why you have chosen to order (or not to order) an MRI scan.
  • Consider referral to or consultation with relevant specialist when appropriate.7

Incidental MRI findings can be a potential distraction

It's important to remember when managing middle-aged or older patients who present with acute knee pain, that MRI will often yield incidental findings – age-related degenerative lesions of cartilage, menisci or other tissues – that are clinically insignificant, and have nothing to do with a patient's presenting symptoms.5,8,11,14-17,26

  • MRI frequently reveals apparent meniscal signal changes that are reported as abnormalities or tears, as incidental findings, often in asymptomatic knees and also when there is no radiographic evidence of osteoarthritis (OA).11,12,14-17,21,27
  • In one study, use of MRI revealed lesions in the knee joints of approximately 90% of middle-aged and elderly people whose knee radiographs did not demonstrate any features of OA, regardless of whether they reported pain.9,11
  • MRI may even suggest the presence of a meniscal tear when there is no tear at all.8,28
Authors have noted that incidental MRI findings clearly have the potential to confound GPs' diagnoses and treatment plans.5,26 Crucially, such findings may lead to further investigation and/or intervention (such as arthroscopy) that may be unnecessary (if the finding is unrelated to a patient's symptoms) and, in some cases, even detrimental. For example, an arthroscopy procedure could lead to damage of surrounding tissues, an increased risk of developing infection, deep vein thrombosis and/or other complications.12,29


Managing acute knee pain

There is no convincing evidence that surgical management is likely to be better than use of conservative measures as first-line treatment for acute knee pain in middle-aged or older individuals.12,15,30-34

  • Not all meniscal and ACL tears require surgery (low-grade injuries respond well to conservative therapies).9
  • At least one group of study investigators has recommended that clinicians adopt a 'wait-and-see' approach when managing traumatic knee disorders, after finding that the vast majority of patients report clinically relevant recovery, regardless of whether MRI reveals a meniscal tear, ligament lesion or no identifiable damage at all.35
In addition, recently published data do not support the use of arthroscopic surgery as a treatment for middle-aged or older patients with knee pain and degenerative joint disease (± radiographic signs of OA).12,36

When seeking to treat symptoms of degenerative joint disease in middle-aged patients, GPs are advised always to initiate conservative, non-surgical interventions as first-line therapy (eg, weight loss interventions, appropriate exercise regimens, physiotherapy, use of simple analgesics,b,3,8,30 In each case, the effectiveness of prescribed or recommended interventions should be periodically reviewed, over several weeks, or even months, to determine whether the patient's treatment plan needs to be adjusted.

b Unless arthroscopy/surgical interventions definitely indicated, for example, evidence of loose bodies or mechanical symptoms, such as locking, giving way or catching, or some other serious underlying disorder.

Advice for patients and clinicians

The 4 Ms for patients 3,37

  1. Modify lifestyle (eg, reduce weight, increase or change exercise).
  2. Minimise loads on the knee.
  3. Maintain strength of muscles that move and support the knee joint (by performing simple, appropriate exercises).
  4. Medicate with simple over-the-counter analgesics (eg, paracetamol).

Advice for clinicians

  • Manage the patient's expectations – explain the likely cause(s) of pain, the rationale for performing specific investigations (eg, MRI) and the aims of specific treatments or interventions.
  • Favour simple conservative interventions whenever possible, ensuring that sufficient time is allowed for them to work.
  • Recognise that surgical procedures (eg, arthroscopy) have a limited role in the management of acute knee pain in middle-aged or older patients and may cause irreversible side effects. Only recommend when definitely indicated.
  • Periodically review the effectiveness of interventions and reconsider management strategy, or refer, if symptoms persist.

Expert reviewer

Dr John North

Senior Visiting Orthopaedic Surgeon
Princess Alexandra and Mt Isa Hospitals, Queensland
Past president, Australian Orthopaedic Association

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