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Orthopaedic update on knee injuries

In the fifth of our six-part series, orthopaedic surgeons Mr Alister Hart and Mr Dinesh Nathwani outline management of the most common knee injuries that present to GPs. Article also includes video clips on ways to diagnose knee problems

In the fifth of our six-part series, orthopaedic surgeons Mr Alister Hart and Mr Dinesh Nathwani outline management of the most common knee injuries that present to GPs. Article also includes video clips on ways to diagnose knee problems

Knee injuries, or their aftermath, present quite often to the GP. This article covers many of the common problems – but not major high-energy injuries such as open fractures, multiple ligament injuries and compartment syndrome, which would be managed in A&E. Instead, we will concentrate on medium- and low-energy injuries, such as sporting injuries or those arising from activities of daily living.

With any injury, the differential diagnosis includes damage to the following structures:

• cartilage

• meniscus

• anterior cruciate ligament (ACL)

• medial collateral ligament (MCL)

• lateral collateral ligament (LCL)

• iliotibial (IT) band

• patella tendon.

History

The two most relevant features in the history are: first, whether the injury was high- or low-energy and, second, the presence of swelling either immediately or within six hours.

Symptoms resulting from a low-energy injury – for example, ‘I stood up after crouching down while gardening, and felt a sudden give in the knee' – suggest a meniscal injury.

By contrast, medium-energy injuries – such as ‘I attempted a sliding tackle after sprinting and violently twisted my knee' – may cause an ACL or peripheral meniscal tear. But note that many ACL injuries do not involve contact with another player and ACL injuries are commonly associated with other internal derangements.

41236451Immediate swelling suggests a haemarthrosis caused by damage to structures within the knee capsule with a good blood supply – such as intra-articular fracture, ACL tear or peripheral meniscus injury.

We recommend urgent referral within 24 hours of knees that swell within six hours of injury. Ideally, there should be a dialogue with the on-call team who can make necessary arrangements for the patient to be seen either that day or in the next available fracture or acute knee clinic.

When referred, all such knees require plain X-ray, including a horizontal beam lateral view to determine whether there is a lipohaemarthrosis – fat and blood in the joint that indicates an intra-articular fracture.

Further details of the injury are also important. A twist might suggest a meniscal tear. An associated ‘crack' or ‘pop' is characteristic of an ACL injury. The inability to weight bear, walk, ski or continue to play football implies a significant injury.

Locking and giving way are signs that there is mechanical derangement inside the knee, such as a meniscal tear, loose cartilage body or ACL rupture.

41236452But these symptoms can be present after low-energy injuries as a result of pain, muscle inhibition and general lack of confidence in an injured knee, often secondary to capsule irritation.

Without swelling, it is generally safe for these knees to be assessed by an orthopaedic surgeon at six weeks post-injury.

Patients presenting late often give a history of trauma and the symptoms above if questioned carefully. Locking, localised joint tenderness and pain on squatting are good clues to a chronic or subacute meniscal injury.

Similarly, an ACL injury often presents late, having been cleared in casualty with a diagnosis of no fracture and ‘soft tissue sprain'. Symptomatic ACL deficiencies that are chronic often present with apprehension, or giving way when changing direction acutely or on walking downstairs.

Also, bear in mind that it's common for arthritic knees to suddenly become painful, perhaps precipitated by a minor injury.

Examination

Limp

Most acutely injured knees cause limping for at least a week. Limping beyond three weeks usually requires a specialist opinion.

Effusion

The most important clinical sign is the presence or absence of an effusion. If this developed within six hours of injury, a haemarthrosis is likely and the patient should be referred to a specialist within 24 hours.

Tenderness

Localising the tenderness to an anatomical structure will greatly assist in diagnosis – such as the femoral insertion of the MCL, medial joint line for a medial meniscal tear, lateral joint line for lateral meniscal tear, patella tendon and IT band, and so on.

Stability testing

Swelling and pain make tests for instability difficult in an acutely injured knee. It is important to rule out an MCL injury with valgus stress testing because this injury will require early treatment, usually in the form of bracing. ACL injuries may be apparent with a Lachman's test, but swelling and pain can cause a false negative test, especially in the acute setting. Most knee surgeons accept that stability testing in the acutely injured knee is often difficult and unreliable.

Straight leg raising

Remember to rule out acute extensor mechanism ruptures. A simple straight leg raise will often pick up tears of the quadriceps muscle or patellar tendon. Quadriceps muscle ruptures are often missed in the early stages because of the patient's ability to weight bear and compensate for the injury. An extensor lag or inability to perform a straight leg raise are good clues to an extensor mechanism disruption together with a palpable defect in the muscle and these patients should be referred within 24 hours.

Investigations

If you're considering plain X-rays, ultrasound or MRI to assist diagnosis of an acutely injured knee, referral to an orthopaedic surgeon is advisable. Recommended views are: AP and lateral weight-bearing, Rosenberg (PA view with the knee flexed at 45°) and a patella skyline.

Treatment

Acute meniscal tears that present with locked knees – an inability to fully extend the knee – should be referred early as a locked knee usually represents a significant bucket handle tear of a medial or lateral meniscus. If seen early, there is a good chance the meniscus can be salvaged with current arthroscopic techniques.

Knees that are not locked but have positive meniscal provocation tests should have an MRI scan and be referred for surgical treatment, in which case a specialist opinion can be delayed for six to eight weeks.

41236453Other causes of a locked knee include loose body formation. Again, if acute, it may be that the patient has sustained an acute chondral fracture, in which case early surgical intervention may allow surgical repair rather than removal.

Acute anterior cruciate ruptures usually require a period of time – six weeks – to allow the range of movement to return prior to consideration of reconstruction unless there is also a locked bucket handle meniscal tear. In such cases referral within 24 hours allows for an urgent MRI scan and either single-stage ACL reconstruction and meniscal repair or, if the range of movement is severely restricted and the knee still very swollen, staged surgery. This means the meniscus can be repaired urgently and a brace applied to protect the repair, followed by reconstructive surgery within six weeks.

If a referral has been made, treatment while waiting for the appointment is largely dependent on the severity of the injury. However, the common advice would be to apply ice, rest the limb and elevate to reduce the acute swelling.

Mr Alister Hart and Mr Dinesh Nathwani are consultant orthopaedic surgeons at The London Clinic

See also www.precisionsurgery.co.uk or call 020 7224 0326

Case 1 Case 2 Case 3 Locking and giving way are signs there may be mechanical derangement such as a meniscus tear Meniscal tear Knee Exam: Valgus Stress Test Video Knee Exam: Valgus Stress Test

Lachman's Test Lachman's Test

Straight leg raise Straight leg raise

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