Clinical guidance for MRI referral

MRI of the knee

MBS item description

MRI - scan of knee following acute knee trauma, after referral by a medical practitioner (other than a specialist or consultant physician), for a patient 16 to 49 years with:

  • inability to extend the knee suggesting the possibility of acute meniscal tear; or
  • clinical findings suggesting acute anterior cruciate ligament tear (R) (Contrast)

Key information

  • MRI of the knee joint can lead to improved health outcomes by reducing (or eliminating) the need for diagnostic arthroscopy.
  • In the majority of cases, clinical examination is as good as MRI for diagnosis.
  • If a diagnosis is clear on clinical exam, confirmation with MRI is not routinely warranted.
  • There is a role for MRI when the diagnosis is unclear and the level of patient disability/pain is such that surgery is being considered.
  • Not all meniscal and anterior cruciate ligament (ACL) tears require surgery – low-grade injuries respond well to conservative therapies.
The recommendation is supported by fair evidence (consistent results from multiple studies, but with some risk of bias).

MRI is indicated in the assessment of ACL injuries, but is not always necessary if the clinical diagnosis is clear

The recommendation is supported by fair evidence (consistent results from multiple studies, but with some risk of bias).

MRI is indicated for assessment of meniscal tears, but is not always necessary if a clear clinical diagnosis of meniscal tear has been made

The recommendation is supported by fair evidence (consistent results from multiple studies, but with some risk of bias).

Use MRI particularly in situations where there is doubt about diagnosis or patient management

The recommendation is supported by expert opinion only, based on level 4 evidence in the text, and the expertise within the multidisciplinary team.

Do not use MRI for the diagnosis of isolated medial collateral ligament injuries, except where there is concern about alternative pathology or if symptoms fail to settle after 6–8 weeks

Grade: None given

Further testing is not immediately needed in patients with knee injury who have negative physical examination findings, although close follow-up is required

Acute knee presentations are diagnosed by history, physical examination and plain X-ray (where indicated for suspected bony injury). Urgent further imaging is rarely indicated. Re-examination after a period of conservative management is recommended and at that time further imaging may be considered if it is likely to alter ongoing management.

ACL injury


Patients may report a popping sensation, or a sensation that the knee ‘came apart’, during sudden deceleration, stopping or change of direction (with a fixed foot, or hyperextension or posteroanterior force to the tibia). People engaged in sport at the time typically need to be helped from the field. There may be significant swelling within a few hours of the injury.52

Physical examination

The acute swelling that can accompany injuries may make the initial physical examination difficult. If a fracture is unlikely, a repeat examination in 1–2 weeks is recommended.53

Tests for ACL injury include the Lachman test, the pivot shift test and anterior drawer sign. The Lachman test, when correctly performed, is the most validated test for diagnosing ACL integrity and further imaging (with MRI) is unnecessary.53,54

Meniscal injury


Meniscal injuries typically occur during twisting or pivoting, and there may be no or minimal force required to cause a tear in middle-aged and older people. Patients may describe locking and/or catching of the knee, although these are not specific for meniscal injuries. Swelling is usually mild to moderate and takes hours (up to 36) to appear. The swelling may recur during the weeks following the injury.52

Physical examination

There may be an effusion, joint line tenderness and a block to full extension.52 Tests for meniscal injury include the Thessaly test (pain on twisting on the knee while standing with it bent at 5 and 20 degrees of flexion), the Apley test, joint line tenderness and McMurray test. The Thessaly test at 20 degrees of knee flexion can be used safely and effectively as a first-line screening test for the diagnosis of both medial and lateral meniscal tears.55 Combined findings from the history and physical examination are more clinically helpful than any one examination manoeuvre alone, and a thorough examination can be as accurate as MRI.53,56


The Ottawa Knee Rules are highly sensitive for identifying knee fractures and should be used to determine which patients with acute knee injury require radiography.51,57 X-rays are not indicated for soft tissue injury assessment of the knee.

Table 2.11

Table 2.11

The Ottawa knee rules


Ultrasound is not recommended for evaluation of menisci or cruciate ligament injuries.49


MRI is the imaging of choice for internal knee derangement.51 However, its use should be confined to more doubtful, difficult and complex knee injuries.56

Imaging issues, benefits and risks

Clinical examination, when combined with MRI, provides the most accurate non-invasive source of information currently available for pathological findings in the menisci and the ACL.58<

When comparing MRI and diagnostic arthroscopy for ACL and meniscal tears, MRI is superior and offers the health benefit of avoiding invasive surgery.50 In one study, almost half of patients presenting with an acutely locked knee had their management changed from surgical to conservative based on MRI findings.51

However, careful evaluation by an experienced examiner identifies patients with surgically treatable meniscus and ACL tears with equal (or better) reliability than MRI.50,53,54

The ACL can regain continuity after partial or complete rupture.59 Hence, the relative efficacy of surgical reconstruction and rehabilitation for the short-term and long-term outcomes after ACL rupture is debated. Results of a 2013 randomised controlled trial encourage doctors to consider rehabilitation as a primary treatment option following an acute ACL tear in young adults.60

MRI studies have higher false positive than false negative results.54,58 MRI shows lesions in the knee joint in most (almost 90%) middle-aged and elderly people in whom knee radiographs do not show any features of osteoarthritis, regardless of pain.61

MRI has been shown to have a false positive rate of 65% for identifying medial meniscal tears and 43% for lateral meniscus tears when compared with surgical findings.62

MRI of the knee is often performed in cases where a diagnosis is uncertain, and abnormal findings, such as meniscal tears, could be suspected to be the cause of the symptoms. However, incidental meniscal findings are common on MRI within the general population. For example in one study, 19% of women aged 50–59 years and 56% of men aged 70–90 years had asymptomatic meniscal injuries on MRI. Meniscal findings have been shown to increase with age.63 Additionally, no conclusion can be drawn about the natural course of meniscal injury seen at MRI imaging.59 A period of conservative management and re-evaluation is warranted in most cases.

MRI is not effective at detecting all forms of injury of the knee. For example:

  • radial meniscal injuries are difficult to visualise on MRI and account for a large number of tears missed by MRI58
  • MRI is not the most reliable tool for diagnosing recurrent meniscal tears, detecting only 66% compared with 88% with arthrography58
  • the accuracy of MRI decreases in patients with multiple injuries.64

MRI is the method of choice for the non-invasive diagnosis of meniscal and ACL tears. Despite the high performance of this method, some cases are challenging and the criteria described in the literature are not sufficient to reach a diagnosis.65

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