Knee Assessment (History and Examination)

The knee is a very vulnerable joint. Stability is maintained by 4 ligaments and the muscles around the joint. It carries the weight of the body. It is extremely susceptible to sports injuries and other accidents. It is susceptible to osteoarthritis and knee joint replacements now outnumber hip joint replacements. History and examination can give a good assessment of the knee to guide treatment or further investigations.

When a patient complains of a painful knee the initial differential diagnosis is wide but a good history will rapidly reduce this and examination should confirm the diagnosis. Special investigations may still be required.

• Was onset gradual or acute? (OA comes on over years)
• If acute was there trauma?
• What exactly happened in the trauma?
• Was there any sound? (A "popping" sound suggests rupture of a ligament)
• Did the knee swell immediately, gradually or not at all? (Rapid swelling suggests haemarthrosis, gradual may be an effusion)
• Does the knee lock? (Suggesting a loose body, usually cartilage)
• Does the knee give way? (Instability or muscle weakness)
• Has the patient attended A&E? (May have been x-rayed to exclude fracture)
• If injury occurred in sport or an accident get a precise history of the mechanism. Was there a direct blow causing vulgus or varus stress? Was there a twisting motion?

Get the patient to lie comfortably on the couch. Pain or apprehension will make examination difficult and unrewarding.

Look at the patient

• A pyrexial and unwell patient may have septic arthritis.
• Look at the joint.
  • Is it swollen?
  • Is it red?
  • Is it hot?
• Is there muscle wasting? Compare with other side.

Check for fluid.

This is unnecessary if swelling is gross but a patella tap may be elicited if more than 30-40ml of fluid is present. Press down on the patella and the patella will be felt to move down to touch the underlying bone. In the absence of a patella tap a small effusion can be shown by massage of any fluid from the medial to the lateral part of the joint and then pushing it back. A positive sign is the obvious movement of fluid.

Tenderness

Joint line tenderness and locking or blocked motion are characteristic of meniscal tears. Tenderness above and below the joint line is more suggestive of collateral ligament damage.

Range of Movement

Full range of movement is from 3° of hyperextension to 140° of flexion. ie for the heel to touch the buttock. For most daily activities one needs 115° of flexion (compare with other side if necessary). Clicking knees are common and not significant.

Stability

There are a number of techniques to check the integrity of the ligaments. They all involve slight flexion of the joint and the intention to get the muscles around the knee to relax.

• To assess the medial collateral ligament (MCL) get the patient to bend the knee by about 10° and push on the lateral side of the joint to stress the ligament whilst holding the lower leg steady. More than minimal movement is abnormal.
• Do the same pushing on the medial side to assess the lateral collateral ligament (LCL).
• Cruciate ligaments are tested with the knee flexed to 90° and relaxation is essential. The foot is placed on couch with the examiner sitting on it to anchor the tibia.
  • The anterior drawer test can be performed. Interlock the fingers behind the knee clasping the sides of the leg between the thumbs with each tip on a femoral condyle. With the quadriceps relaxed, assess anteroposterior movement of tibia on the femur. Normal is around 0.5cm. The anterior cruciate ligament prevents anterior glide; the posterior prevents posterior glide. Excessive glide in one direction suggests damage to the relevant ligament. Compare knees. Examination should also be performed in 15-20° of flexion
  • Lachman's test is a more sensitive test to determine if symptoms are really due to cruciate ligament damage. It can be asymptomatic. It is the 'pivot shift test'. Flex the knee, then put it in valgus. Now extend it. If the anterior cruciate is ruptured, the knee jumps smartly forwards. This is often hard to elicit, unless the patient is very relaxed or under general anaesthesia.

Other Tests

• If appropriate, test for crepitus, usually suggesting osteoarthritis but it is also found in chondromalacia patellae. Place the left hand over the knee and with the right hand grasp the ankle and flex and extend the knee. A grating sensation is a positive sign.
• Testing for damage to the menisci is controversial. The McMurray's rotation test is in the textbooks. The knee is flexed, the tibia laterally rotated on the femur, then the knee is extended. It is now considered an unreliable way of detecting pedunculated tears of menisci and is not recommended because it causes excessive pain and the test may aggravate any cartilage tear. The squat test tries to produce meniscal symptoms by performing repetitions of a full squat with the feet and legs alternately internally and externally rotated as the squat is performed (lateral and medial menisci respectively).
• The apprehension test in chondromalacia patellae involves forced hyperextension of the knee whilst pushing laterally on the patella. Pain or a feeling of subluxation is a positive sign.

Gait

Always remember to assess gait.

• If the knee is tense and swollen or if pain or apprehension causes the muscles to be tight, the signs for inadequacy of the ligaments may show false negatives. It may be possible to demonstrate such signs after aspiration of the joint but often they take days or weeks to develop.
• Nowadays, torn menisci may be diagnosed by MRI scan or arthroscopy without risking further damage to the cartilage.
• If the cause of pain in the knee is not obvious, check for flat feet (pes planus). Fallen arches cause hyperpronation of the ankle and valgus deformity of the knees. This also causes malalignment of the pull of the patella tendon. Correction of flat feet may solve several problems that may not seem immediately to be relevant.
• If there is little or nothing abnormal to find despite the history, examine the hip and seek another source for the pain. The hip as a cause of knee pain is common in children.

Aspiration of a swollen joint can be both diagnostic and therapeutic. Effusion predisposes to muscle wasting and so aspiration may reduce this although fluid may rapidly re-form. Using aseptic technique, infiltrate the skin and subcutaneous tissues with a little lignocaine and then insert a wide bore needle attached to a large syringe. Withdraw as much fluid as possible.

• If the fluid is purulent send some for culture.
• If gout or pseudogout is suspected ask for examination for bi-refringent crystals
• If the fluid becomes more blood-stained as more is withdrawn this is probably due to trauma from the needle.
• If frank blood is aspirated after trauma, leave a bottle of it to stand for a while. If a fatty layer floats on the surface this is from bone marrow and so a fracture has occurred.
• If the cause is thought to be arthritis it may be beneficial to inject some steroid with local anaesthetic before withdrawing the needle.
• X-ray may reveal fracture of any of the bones or the calcium pyrophosphate crystals of pseudogout.

Damage to cartilage or ligaments can be demonstrated by MRI or arthroscopy. A Health Technology Assessment concluded that the use of MRI in patients presenting at DGHs with chronic knee problems in whom arthroscopy was being considered did not increase NHS costs overall, was not associated with significantly worse outcomes and avoided surgery in a significant proportion of patients.¹ However, some orthopaedic surgeons still argue that arthroscopy is minimally invasive and if something needs treatment, it can be undertaken immediately instead of putting the patient on the waiting list for arthroscopy. The question of whether or not GPs should have direct access to MRI of the knee or if such requests should come only from an orthopaedic specialist is currently being assessed in the DAMASK trial.²