Acute ankle and knee injuries: Limited role for imaging

Imaging – including X-rays, ultrasound and MRI – has a role to play in the diagnosis of acute ankle and knee injuries. However current evidence and guidelines show that this role is limited.

Most acute ankle and knee injuries of the type that present to primary care and are seen by GPs can be accurately diagnosed following a patient history and physical examination alone. Imaging is only useful in specific situations. 

Acute ankle and knee injuries in primary care

Acute ankle and knee injuries make up a considerable proportion of the 24 million encounters in Australian general practice at which at least one musculoskeletal problem was managed. For instance, a 2014 BEACH report found that of all sprains/strains (excluding the back) managed by GPs, about 20% were located in the ankle and 5% in the knee. 

Ankle and knee fractures: X-rays

The rate of ankle and knee fractures in Australian general practice is not known. However, research shows that ankle (and mid-foot) fractures make up only around 15% of acute ankle injuries and knee fractures less than 7% of acute knee injury presentations in hospital emergency settings. Rather than routinely referring acute ankle and knee injuries for X-rays, it is recommended to use the:

• Ottawa Ankle Rules (OAR) to indicate a fracture of the lateral and medial malleolus of the ankle, navicular or base of 5th metatarsal is present. 
• Ottawa Knee Rules (OKR) to indicate a fracture of the patella or head of the fibula is present.

Meta-analyses have found that the Ottawa Rules are nearly 100% sensitive (most people with a fracture would not be missed) and reduce unnecessary X-rays. Ankle and knee soft tissue injuries

The rates in Australian general practice of specific acute soft tissue injuries of the ankle and knee are also not known. According to overseas studies, ankle sprains are the most common injury in sport (11% to 15%) while tears to the anterior cruciate ligament (ACL) and menisci are the most common acute knee injuries in sport. 

MBS items are available for GPs when making an ultrasound referral to help diagnose acute ankle sprains and MRI referrals for ACL and meniscal tears.

Practice points for primary health care nurses

• Reassure patients that most acute ankle and knee injuries can be accurately diagnosed following a history and physical examination by an experienced examiner.
• Recognise that imaging (X-rays, ultrasound and MRI) is only useful in limited situations, and unnecessary imaging may lead to potential harms.
• Provide conservative management including RICE and no HARM during the initial management of acute ankle and knee soft tissue injuries, particularly when a physical examination is not possible due to pain and swelling.

Evidence and guidelines: Ultrasound and MRI

The evidence shows that the diagnostic accuracy of a patient history and physical examination by an experienced examiner is the same as, if not better than, ankle ultrasound or knee MRI. 

No Australian or international guidelines recommend the routine use of ultrasound for acute ankle injuries. The 2013 RACGP Clinical guidance for MRI referral recommend a referral for knee MRI only if there is doubt about diagnosis and if confirming a diagnosis will change management (see Table 1). 

Table 1: Indications and considerations for imaging

Inappropriate imaging

Unnecessary referral for imaging of acute ankle and knee injuries may lead to possible harms. For example, not following the Ottawa Rules can result in unnecessary exposure to radiation from X-rays. Asymptomatic meniscal tears, present in adults of all ages, may be found on MRI. These findings may lead to harms such as a cascade of unnecessary treatments, including surgery, and patients avoiding exercises and normal activities of daily living due to fear of further injury resulting in limited restoration of normal knee function. 

Management

RICE (rest, ice, compression, elevation) and no HARM (see Figure 1) are recommended as the initial management of acute injuries such as ankle sprains and ACL and meniscal tears. 

It should be noted that pain and swelling soon after an acute injury may reduce an examiner’s ability to conduct a physical examination. In this situation, the above management is provided until a physical examination can be performed. 

For an ankle sprain this is usually around four days after injury and one to two weeks after injury for ACL tears, where severe swelling often appears within hours. Swelling due to meniscal tears, which is usually moderate and takes up to 36 hours to appear, should not impact on a physical examination. 

Figure 1: Initial conservative management for acute injuries

Want more information?

A new health professional program on ankle and knee imaging – developed by NPS MedicineWise in conjunction with musculoskeletal experts and in line with Australian College of Nursing Choosing Wisely Australia® recommendations – provides health professionals with an update on the latest imaging recommendations for the type of acute knee and ankle injuries that are commonly seen in general practice. 

Resources include:

• NPS MedicineWise case study: www.nps.org.au/ankle-knee-case-study
• NPS MedicineWise acute ankle and knee injuries patient action plan: www.nps.org.au/ankle-kneeimaging-action-plan
• NPS MedicineWise ankle and knee videos: www.nps.org.au/scrivito/physical-examination-of-acute-ankle-and-knee-injuries-8508d0c1755fafcb
• Choosing Wisely Australia – find out which tests, treatments and procedures you should question: www.choosingwisely.org.au

For a fully referenced version of this article please contact editor@apna.asn.au

NPS MedicineWise
NPS MedicineWise is an independent, not-for-profit and evidence-based organisation working across Australia and throughout the Asia-Pacific region to positively change the attitudes and behaviours which exist around the use of medicines and
medical tests, so that consumers and health professionals are equipped to make the best decisions when it counts.

Source: Primary Times Autumn 2017 (Volume 17, Issue 1)