The basics - Knee pain

Knee pain is a common presentation that usually can be easily categorised, as Dr Louise Warburton explains.

There are three main categories of knee problems that a GP is likely to see.

In the young athletic population and the middle-aged athlete, knee injuries related to sports and exercise will be the most common reason for presentation.

In young to middle-aged females, anterior knee pain will be common.

From middle age to the elderly, osteoarthritis (OA) will be a common reason to consult.

Knee injuries fall into two categories: meniscal injuries and ligament tears.

A torn meniscus can be viewed by arthroscopy  (Photo: dr p marazzi/science photo library )

Meniscal injuries
The knee contains the medial and lateral menisci (cartilages), which act to lubricate and facilitate rotation of the femoral condyles upon the tibia. They also act as shock absorbers.

It is relatively easy to tear a meniscus if the knee is subjected to a shearing force while the foot is anchored on the ground, for example when football studs are worn.

The patient will be aware of pain within the knee, but may carry on playing. Once the game is finished, the knee may swell and cause pain.

Sometimes the knee will lock. This is classically due to a piece of cartilage breaking off and sticking between the articular surfaces. An acutely locked knee that will not straighten is an orthopaedic emergency.

More commonly, the patient will be able to play again after a few days, but the knee will swell and be painful after activity.

When the patient presents, take a good history as the nature of the injury will often give the diagnosis.

On examination, there may be a small effusion. Look carefully for quadriceps wasting, which can happen very soon after the injury.

Ask the patient to squat; this will be painful with a torn meniscus. Squatting on one leg may be even more difficult.

Walking on the haunches with knees bent (duck waddling) is painful with posterior meniscal tears.

The Thessaly test is done standing barefoot, first on the normal, healthy leg. The patient holds the examiner's hands for balance. The patient bends the knee of the standing leg five degrees and rotates the knee and body in and out three times.

The test is repeated with the knee flexed 20 degrees. Then the test is done on the involved or injured leg.

Patients with a meniscal tear feel pain or discomfort along the joint line on the side of the tear. They may have a feeling of locking or catching.

The classical McMurray test is also a test for meniscal tears. For this, the patient is supine and the affected knee is flexed and extended with the foot in medially and laterally rotated positions. This aims to catch the meniscus between the femoral condyles and tibia and will elicit pain.

It is very important to watch the patient's face carefully, as apprehension should be noted. The test must be performed very carefully after this point is reached. Diagnosis is confirmed by MRI.

Simple tears are usually treated with physiotherapy, as they tend to heal. Large tears or bucket-handle tears - where a circular circumferential tear in the meniscus happens, and the flap flicks over and can lock between the articular surfaces -often have to be treated with arthroscopy.

Ligament tears
The cruciate ligaments are torn by significant force applied to the tibia, usually pushing it sideways and away from the femur, as in a heavy football tackle. The player will often feel a 'pop' within the joint. The knee will swell immediately and further play is impossible.

Lesser tears may be sustained by falls or slipping.

Laxity of the tibia on the femur, with the patient supine, is the typical finding. The anterior and posterior drawer tests involve 'drawing' the tibia anterior and posterior on the femur. Lachmann's test is similar, but with the knee partly flexed.

Diagnosis is again by MRI scanning. Repair is only undertaken in footballers and professional athletes.

Torn ligament results in swelling

Osteoarthritis
Knee OA can affect up to 15 per cent of the older population and presents with pain and stiffness. Risk factors are occupational (common in farmers), previous injury (ligament tears and meniscal removals all predispose to OA) and genetic causes.

Diagnosis is on history and examination. Nocturnal pain suggests severe OA. Examination findings include quadriceps wasting and osteophyte formation along the joint line, which can be palpated.

Larger osteophytes cause remodelling of the joint surfaces, so that the size of the knee increases and bony projections can be easily palpated. Sometimes there will be an effusion.

A warm joint should raise suspicions of an inflammatory arthritis or gout. X-ray will confirm the findings.

Functional impairment can be assessed using the Oxford knee questionnaire.1

Management includes weight loss and exercise such as swimming. Core stability exercises such as yoga and pilates are particularly useful.

Patients should not be referred for arthroscopic lavage and debridement unless there is a clear history of mechanical locking - not gelling, 'giving way' or X-ray evidence of loose bodies.

Paracetamol should be considered for pain relief in addition to core treatment.

Paracetamol and/or topical NSAIDs should be considered ahead of use of oral NSAIDs, COX-2 inhibitors or opioids.

Referral for joint replacement surgery should be considered in patients with OA with joint symptoms that have a substantial impact on their quality of life and are refractory to non-surgical treatment.

Corticosteroids and local anaesthetic injection into the joint can be effective treatment for pain relief.

Patellofemoral pain
Patellofemoral pain (anterior knee pain) is common in young females; there is a continuum into OA of the patellofemoral joint (PFJ). Patellofemoral pain is also common in OA knee.

The pain is due to lateral displacement of patella during walking or running and imbalance of medial to lateral quadriceps strength.

It is more common with increased femoral anteversion, knee valgus (increased Q angle), increased tibial rotation, subtalar pronation and inadequate flexibility. Patella position is also important, as is degree of patellar movement.

Treatment of patellofemoral pain involves immediate reduction of pain. Reduce load on the PFJ with better training shoes, insoles, and a more sympathetic running surface. Quads training is also beneficial.

Taping of the patella improves the recruitment and contraction of fibres in vastus medialis oblique with relation to vastus lateralis, in the quadriceps muscle. Once the taping is discontinued, improved recruitment continues.

  • Dr Warburton is a GPSI in rheumatology in Ironbridge, Shropshire References

1. Dawson J, et al. Questionnaire on the perceptions of patients about total knee replacement. J Bone Joint Surg Br 1998; 80(1): 63-9. www.orthopaedicscore.com/scorepages/oxford_knee_score.html

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