The
knee
General
Watch a patient walking first before starting examination of the lower
limb.
Look
also from in front or behind to see whether the knees are aligned in the
sagittal plane. Varus knees (or bow legs) have clear space visible between the
knees when the ankles are together. It is not uncommon to see slight varus in
males, a normal variant. Severe varus is commonly seen in osteoarthritis which
commonly attacks the medial compartment of the knee first, as the arthritis
destroys the joint which then collapses.
Valgus
knees tend to brush together as the patient walks even though the ankles may be
wide apart. This deformity is commonly seen in rheumatoid arthritis, which
attacks the lateral side of the knee first and leads to collapse there.
Look
Expose the legs fully including thighs (rolled up trousers is not
enough).
Skin
Check for redness, scars and lacerations. (Do not forget the back of the
knee.)
Soft
tissue
Swelling. Look for an effusion in the knee. The dimple on the medial
side of the knee will be lost compared with the other side if there is an
effusion.
Wasting.
Vastus medialis can be clearly seen if the patient is asked to force their knees
into hyperextension. This muscle wastes within days of a knee injury, and will
fail to bulge when contracted, compared with the other side.
Bone
Check for knock-knee, bow legs, fixed flexion and for the position of
patella (Fig. 20.9).
Fixed flexion is the position of comfort in the knee and tends to
develop secondary to any acute infection or inflammation.
The
patella almost always dislocates laterally (Fig. 20.10). If not reduced it may
remain jammed outside the lateral femoral condyle.
Feel
Skin
Temperature. Inflammation of the knee will produce a knee hot to the
touch compared with the other side.
Sensation.
Damage to nerves at or around the knee will produce disturbance of sensation
distally. The same examination as described in the section on ‘The foot and
ankle’ should therefore be performed.
Soft
tissue
Swelling. Check for a knee effusion, using either a patella tap, cross
fluctuation or a stroke test.
Stroke
test. With the patient lying supine, empty the medial side of the knee joint by
stroking any fluid up into the suprapatella pouch. Then watching the medial side
of the knee carefully, stroke down the front of the thigh squeezing any fluid
lying in the suprapatella pouch back into the medial side of the knee. As the
fluid returns the dimple on the medial side of the knee pops out (Fig.
20.11).
The margin of the synovium can most easily be felt on the medial side
above the patella. It can be rolled under your fingers, but is only palpable if
the synovium is thickened.
Baker’s
cyst. This is an outpouching of the synovium through a defect in the capsule
posteriorly. It can be difficult to feel. As soon as the knee is flexed the cyst
disappears, but reappears in full extension. It is associated with
osteoarthritis of the knee. The patient will guide your fingers to the lump if
you are having difficulty finding it.
Circulation.
The distal pulses and capillary filling should be checked in the same way as
examination of the foot.
The margins of the patella, the femoral condyles and the margins of the
tibial plateau are all easy to feel as they are subcutaneous. The underside of
the patella may be tender if there is synovitis of the knee when the inflammed
synovium is compressed against the bone.
The inferior pole of the patella is tender if there is tendonitis of the
patella tendon origin (jumper’s knee).
The
fat pad beneath the patella tendon is tender in Hoffa’s syndrome, an
inflammation commonly brought on by sudden forced hyperextension of the knee.
The
tibial tubercle is enlarged and tender when the insertion of the patella tendon
is inflammed (Osgood—Schlatter’s syndrome), a common condition in athletic
adolescents.
A
tear in the meniscus may produce tenderness at the joint line margin over the
area of the tear.
Move
Active
Flexion. The knee should be able to flex until the heel touches the
buttock. Loss of flexion can be measured by the number of centimetres that the
heel stops short of the buttock, rather than by actually measuring the angle of
the knee. Comparison with the other side gives a sensitive guide to loss of
range of movement.
Extension.
The patient should be asked to force their knee into the bed. Most knees
hyperextend at least by a few degrees.
Passive
Flexion. The knee can be bent up passively, but be sure to watch the
patient’s face, especially if you push the knee beyond the active range of
flexion. It may be limited because of pain.
Extension.
With the patient lying supine and relaxed the feet can be raised off the bed by
lifting under the heels. Any loss of extension will be visible because one knee
will remain higher (in fixed flexion) than the other.
In
posterior ligamentous damage to the knee (as may occur in a hyperextension
injury) the knee may hyperextend excessively. In this case the abnormal limb
will be lower than the other.
Lag
test. A subtle test for quadriceps weakness is to ask the patient to lift their
leg 10 cm off the bed. Most patients can do this and, indeed, even if the
quadriceps mechanism is completely ruptured this manoeuvre is still possible
because the patient uses the lateral retinaculum to lock the knee in extension.
The patient is then asked to bend the knee 200 and straighten it, again with the
leg still in the air (Fig. 20.12). The patient will not be able to return the
knee to its original extension if the quadriceps muscle is weak. This loss of
flexion is not a fixed flexion deformity (they have already demonstrated that
the knee will extend); it is caused by weakness in the quadriceps and is known a
‘quads lag’.
Stability
Collateral ligaments. The integrity of the collateral ligaments can only
be tested when the knee is slightly flexed. In full
Cruciate
ligaments. The anterior is the cruciate ligament most commonly injured.
History.
The patient is commonly twisting on a flexed knee and the foot jams on the
ground. There is often a loud crack and the knee swells immediately (with
blood). If the injury occurs during sport the patient cannot play on and is
usually carried off. The injury maybe accompanied by a torn meniscus or, indeed,
the instability may subsequently cause a torn meniscus. If the quadriceps are
allowed to waste (as they will without treatment) the knee will be unstable
giving way on turns and swelling up each time this occurs. If the meniscus is
also torn the knee may lock intermittently (become jammed in flexion).
The
posterior cruciate has a completely different mechanism of injury. It can occur
either as a result of a hyperextension injury, or if the tibia is driven
backwards with the knee in flexion (the dashboard injury).
There
are several tests for cruciate disruption but one simple method is as follows.
The patient lies supine with both knees bent up to a right angle and the feet
resting on the bed. The examiner looks from the side to see whether one tibial
tubercle is lying further back than the other. If the tubercle
The
pivot shift test. This test relies on the fact that an anterior cruciate
deficient knee frequently has some rotatory instability in extension. In this
position the femoral condyles rolling on the tibia do not control rotation well.
With the patient lying supine and the examiner sitting at the patient’s foot
facing up the bed, one hand is used to lift the leg off the bed by the ankle and
to rotate the tibia inwards on the femur. The examiner’s other hand presses
against the lateral side of the knee pushing it into valgus, so that the lateral
femoral condyle is engaged firmly with the tibial plateau. This hand now gently
pushes the knee into flexion (Fig. 20.15). If there is anterior cruciate
instability the knee starts to
Patella
apprehension.
History. Patients who have lax ligaments (are double-jointed) are much
more susceptible to dislocation of the patella. The dislocation commonly occurs
during a twisting manoeuvre on a flexed knee and if the knee cap relocates
immediately the injury can closely mimic the history of an anterior cruciate
rupture. The knee swells at once (with blood) and the patient is unable to walk
on it. If the patella stays out the patient may claim that they saw a lump on
the medial side of the knee. This is in fact the medial femoral condyle (the
patient assumes that the patella indicates the position of the knee).
Examination of a knee which has recently had a dislocated patella is very
difficult as the knee is stiff, swollen and very painful. However, patients who
dislocate a patella have frequently previously dislocated the other patella and
the patella apprehension test can be performed on the opposite knee.