Knee problems, part one

The essentials

- Hip pathology may frequently present as knee pain.

- If septic arthritis is suspected, urgent referral is essential.

- Anterior knee pain is common but responds to non-surgical measures.

- Some people remain active despite anterior cruciate ligament rupture.

- More than a third of meniscal injuries are due to sporting activity.

1. Examination and investigation of the knee

This week's article deals with problems likely to be encountered in the younger patient.

When presented with a knee problem, simple observation of the knee is helpful. Study the patient's gait, and then look at the knee for swelling and synovial thickening. Note any scars, and the position of the patella.

There may be deformity, such as a flexion deformity or genu varus or valgum.

Palpation and movements

Check the four quadrants of the patella, and test for patellar apprehension.

Examine the patellar tendon, the joint line, the femoral condyles, and the collateral ligament insertions. Check to see if there is an effusion.

Test the range of flexion and extension, both active and passive. The ability to squat and perform straight leg raising should be assessed.

Observe the tracking of the patella during movement of the joint. Hip pathology may frequently present with knee pain. In women of childbearing age, knee pain can be caused by intra-pelvic pathology.

Specific tests

Lachman's test is an anterior draw sign, carried out at 20 deg of flexion, to detect anterior cruciate ligament injury. Also check for pivot shift and the effects of varus and valgus stress. McMurray's test is performed to detect meniscal injury.

The patient lies supine while the examiner rotates the foot fully outward as the knee is slowly extended. A painful click suggests a tear of the medial meniscus.

Investigations

Screening blood tests will rarely show any abnormality in patients with traumatic pathology, but a raised ESR, abnormal RA latex and autoantibodies may help distinguish the inflammatory arthropathies from other causes of pain and swelling. Urate levels may be raised in gout.

Anterior-posterior and lateral knee X-rays with weight-bearing views should be done. In anterior knee pain, consider skyline views of the patella.

This may demonstrate patellar tilt or overhang. Asking for notch views may help define loose bodies. Aspiration of an effusion may be of help, but a patient with an obvious tense effusion would usually need referral to a rheumatologist or an orthopaedic surgeon.

An MRI can give excellent views of the knee architecture, and is often performed as a diagnostic aid or to help plan surgery. However, it has been said that more than 85 per cent of knee problems can be diagnosed on the history and examination alone.

KEY POINTS

- Simple observation of the knee can give useful information.

- Anterior-posterior and lateral knee X-rays while weight bearing can be helpful.

- Blood tests may help indicate an inflammatory cause of knee pain.

- Aspiration of an effusion may help diagnosis, but consider referral, especially in the young.

- An MRI scan can help diagnosis.

2. Mechanical symptoms

The knee is a common source of problems in young adults, whether they are physically active or sedentary, and it is often difficult to identify the definitive source of a problem.

Locking of the knee

True locking of the knee occurs when it will not fully extend. It is often useful to make a comparison with the normal knee. The healthy young knee will often hyperextend by about five degrees. A locked knee can still flex easily, but the last 10 degrees or so of extension are lost.

Attempts to extend the knee may be resisted by pain inhibition, or by a mechanical block such as a bucket handle meniscal tear that has prolapsed into the joint, a loose body or a large effusion.

Patients may describe episodes of 'locking', 'jamming' or 'sticking', which may resolve by performing some manoeuvre to jiggle the knee out straight.

The situation can be confused in patients who experience intermittent subluxation of the patella, or have a pivot shift from an anterior cruciate ligament (ACL) tear, because they may describe similar sensations. A persistently locked knee from an injury is likely to need surgery.

Swelling

A detectable knee effusion is a sensitive sign for the presence of pathology, but is non-specific. A patient who develops an effusion within two hours of an acute injury has a 75 per cent chance of an ACL tear. Most of the remaining 25 per cent will have a meniscal tear or an intra-articular fracture. If a capsular tear has also occurred, the haemarthrosis or effusion may disperse into the surrounding tissues.

Delayed swelling until one or two days after an injury is more likely to be a meniscal tear. Swelling usually resolves over two to three weeks, but may recur when sport is attempted again.

Aspirating a knee under aseptic conditions will distinguish a haemarthrosis from a simple effusion. Microscopy, culture and examination for crystals will help identify inflammatory arthritides.

If the knee is hot, red, and painful with an effusion, a septic arthritis must be excluded. Urgent referral is necessary if this is suspected.

Any skin infection is a contraindication to aspiration, because the needle may transfer bacteria from the skin into the knee joint causing a septic arthritis.

Giving way

Actual giving way, or a feeling that this might happen, is a common mechanical symptom. Ligamentous instability, patellar subluxation and pain inhibition may cause the knee to collapse suddenly.

A feeling of instability (as opposed to pain) on going down stairs or turning corners may indicate an ACL injury.

Pain

The location of pain may give a clue to the pathology, but is not reliable.

Pain at rest or at night may indicate an inflammatory cause. Pain on descending stairs is often patello-femoral in origin.

KEY POINTS

- A persistently locking knee following injury is likely to need surgery.

- An effusion is a sensitive sign for the presence of pathology.

- Do not aspirate the joint in the presence of skin infection.

- Giving way, or the feeling that this may happen is a common mechanical symptom.

3. Anterior knee pain

Anterior knee pain refers to a collection of problems at the front of the knee. It is probably the most common knee problem in young people in primary care. It is frequently the result of common inherent anatomical factors.

Patients describe pain in the front of the knee or deep in the knee, and will often place the palm of their hand over the kneecap when describing it. Pain is often worse after prolonged sitting or using the stairs. Swelling is not usually a feature.

Nature has ensured that the articular cartilage on the back of the patella is the thickest in the human body. This is because huge forces (up to six times body weight) are transmitted across the patello-femoral (PF) joint, especially during squatting. In a small group of patients, severe debilitating anterior knee pain may follow a direct blow to the knee.

Symptoms and signs

Symptoms may be caused by anatomical misalignment, muscular imbalance or overuse. Previous patella fracture or dislocation predisposes to PF joint degeneration. Observation of the alignment of the limb with respect to the presence of flat feet, varus or valgus knees or 'squinting' patellae (patellae that point towards each other when the patient stands erect) may alert you to the underlying problem. Patients who are keen at sports and have patellar tendon pain or pain at the inferior pole of the patella may have overuse tendonitis. This is often worse after playing their sport.

Normally, the patella should move medially and laterally by about one-third of its width. Patients with PF pain may have little medial movement, with tight lateral structures causing excessive pressure on the lateral facet during knee flexion. A patellar apprehension test may be present.

Skyline views on X-ray may show PF degeneration, tilt or overhang, but maltracking may not be demonstrated on still images. Even patients with severe symptoms may have apparently normal X-rays. Chondromalacia patellae is often used as a 'catch-all' phrase, but is no longer widely used. It is best reserved for those patients with demonstrable chondral degeneration.

Treatment

Anterior knee pain can be particularly difficult to treat, but 90 per cent of patients should respond to simple non-surgical measures to control their symptoms. Physiotherapy to specifically strengthen and control the medial part of the quadriceps mechanism may help to redress a functional imbalance. Strapping or taping, flexibility exercises, activity modification and addressing any contributing foot deformities should be considered.

Surgery should be reserved for patients who have failed conservative treatment, and who are unable to put up with their symptoms. There are a number of possible options, including lateral release, medial advancement and tibial tuberosity transfer. Patients must be warned that they may be worse after the surgery, and rehabilitation can take many months.

KEY POINTS

- Anterior knee pain is often the result of common inherent anatomical factors.

- Swelling is not usually a feature.

- Patients with severe symptoms may have apparently normal X-rays.

- 'Squinting' patellae suggest an underlying problem in anterior knee pain.

- Physiotherapy to improve medial quadriceps function is valuable.

4. The anterior cruciate ligament

More has been written about the anterior cruciate ligament (ACL) than any other ligament in the body. Rupture is common in men and women who play sport.

There are a number of mechanisms of injury, but the patient usually experiences a pop or click during the injury, followed by immediate swelling and inability to continue. A young footballer typically describes a twist in his knee, getting sudden pain, and the joint swelling up as he is carried off.

This initial swelling is mostly blood. When the onset of swelling is less dramatic, it is mostly synovial fluid.

This history suggests a 75 per cent chance of an ACL rupture. Other causes of sudden bleeding include a meniscal tear, an intra-articular fracture, a synovial tear, patella subluxation or dislocation, or rarely, a posterior cruciate ligament tear. The worst scenario consists of a combination of ACL rupture, medial meniscal tear and medial collateral rupture - the so-called 'O'Donoghue's miserable triad'.

Treatment of ACL rupture

Immediately after the injury, aspiration reveals blood, and removal eases the pain. The presence of fat globules on the surface of the aspirated blood usually indicates an intra-articular fracture. Most tears are within the ligament, but a large flake of bone may be avulsed, especially in adolescents.

People vary in their ability to live without an ACL. Some are crippled, yet some, depending on the sport, continue to play professionally. Chronic ACL deficiency predisposes to further knee injuries. Patients can be divided into three groups. About one third of them experience no problems or instability and are able to return to their pre-injury sport. Another third experience instability only when attempting to do sport, and such patients are usually advised either to modify their activity, or have ACL reconstruction.

A final third experience recurrent episodes of giving way and definitely require ACL reconstruction. In the initial stages patients would usually be offered intensive physiotherapy, before any decision about surgery is made.

Reconstructing the ACL

With a skilled surgeon, the results of reconstructing the ACL are excellent.

The procedure is now carried out using an autogenous hamstring tendon graft or a bone-patellar tendon-bone graft. Specific expertise is required.

It can be performed arthroscopically, or at open surgery. Patients need to be highly motivated, because the procedure must be followed by prolonged physiotherapy.

Undisciplined and poorly motivated patients are not good candidates.

Middle-aged people with a sedentary lifestyle probably do not benefit from ACL reconstruction.

KEY POINTS

- ACL rupture is common in men and women who play sport.

- A twisted knee, followed by sudden pain and swelling suggests ACL rupture.

- People vary in their ability to live without an ACL.

- Autogenous human tissue grafting is now the repair method of choice.

5. Meniscal injuries

More than a third of meniscal injuries occur as a result of sporting activities, and soccer accounts for about two thirds of these. The usual mechanism involves a rotational force applied to a flexed knee. Getting out of a car is a common cause. As patients become older, degenerate tears can occur with minimal force, but produce the same mechanical symptoms.

Following the initial tear, there may be rapid or gradual swelling. There will also usually be a loss of about 20 deg of extension. The symptoms may resolve, but intermittent clicking or locking returns later. The knee gives way or swells intermittently when sport is attempted.

Examination and treatment

There may be little to find on examination, although joint line tenderness is the most sensitive feature. McMurray's and Apley's tests are not highly sensitive or specific.

Patients may be offered treatment on the history and symptoms alone, but an MRI scan should confirm the diagnosis.

Surgery to the menisci has a chequered history in orthopaedics. It used to be standard practice to remove a torn meniscus entirely through an open incision, because the menisci were thought to serve no useful purpose, and locking was prevented. This view has been reversed, as the menisci are now known to play an important function in distributing body weight across the articular cartilage, and premature removal can precipitate joint degeneration.

The proof of this is the number of patients now coming to knee replacement who have had total menisectomies in the past.

Current treatment is to resect small flaps of menisci, and repair larger peripheral tears or detachments, preserving as much meniscus as possible in the hope that the knee will not rapidly degenerate.

KEY POINTS

- Playing soccer accounts for many meniscal injuries.

- These occur when a rotational force is applied to a flexed knee.

- Joint line tenderness is the most sensitive feature on examination.

- Removal of the entire cartilage is now avoided because it leads to early joint degeneration.

FURTHER RESOURCES

Further reading

Primary Care Orthopaedics by Steven Cutts, Alison Edwards and Ryan Price, published by the RCGP.

Websites

See Medicine on the Web, page 46.

Previously in Clinical Review

You can print an A4 copy of any Clinical Review published in the past year by logging on to GPonline.com. Recent issues have covered:

- Gastro-oesophageal reflux disease (June 9)

- Dealing with long-term illness (26 May)

- Ovarian cancer (19 May) NEXT WEEK: Knee problems part two, by Mr Steven Cutts.

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