The
knee
The knee does not feature prominently in children’s orthopaedics,
but commonly poses problems in adolescents with anterior knee pain otherwise
known as chondromalacia patellae. Subluxation and dislocation of the patella may
also start to cause problems at this age. In the young adult problems with the
knee are exceptionally important. All contact sports and high demand sports,
such as skiing, produce a rich crop of sports injuries. Rheumatoid arthritis
affects the knee in the later stages just as it affects the hip, and in the
elderly osteoarthritis of the knee is as common as osteoarthritis of the hip,
and within the next few years total knee replacement may become as common an
operation as total hip replacement. Certainly, it is already quite as
successful.
History
of knee injury
The history of an accident can be divided into three types:
acute extrinsic, the patient was struck on the knee; acute intrinsic,
something snapped or gave way in the knee; and chronic, where the onset was
gradual and not related to any specific event. Each of these kinds of history is
related to a completely different diagnosis (Table
23.8).
Acute extrinsic
Tibial plateau fracture
Acute intrinsic Torn mensiscus, dislocated patella, torn ligaments
Chronic
Anterior knee pain, Osgood—Schlatter disease,
jumpers knee, plica,
arthritis
Investigation
for torn meniscus
A torn meniscus only shows up on X-ray if dye is used (an arthrogram —
see Fig. 23.27). It also shows up very well on MRI. The investigation of choice
is therefore MRI. If, however, the history is absolutely clear of mechanical
locking, then arthroscopy is the investigation of choice, as it is going to be
necessary anyway and it allows treatment to be undertaken at the same
time. If, however, the diagnosis is in doubt than a noninvasive investigation
such as MRI is the first line of investigation, the only problem being that
interpretation of the MRI can be difficult and there is an incidence of false
positives.
Osteochrondritis
of the knee
A small flake fracture of the articular surface of the knee is also
possible after a twisting injury. The presentation is very similar to a torn
meniscus and plain X-rays may miss the diagnosis unless the defect is
silhouetted in one of the views. Both MRI and CT scan are used in making the
diagnosis, but arthroscopy can miss it because unless the whole of the articular
surface is carefully probed the actual defect may be invisible from the surface
and systematic probing of the whole articular surface will be needed to find the
actual defect. If the fragment is small and breaks away into the joint it may
cause mechanical locking and needs to he removed. If it is large then an attempt
should be made to replace it using a recessed screw, buried pins or some
kind of bone glue. If it is not felt to be possible to replace the fragment some
people drill the base of the defect to stimulate healing by providing a blood
supply to the damaged area, but the cartilage will only be replaced by
fibrocartilage which has poor wear properties.
Ruptured
anterior cruciate ligament
This is an epidemic in modern sport. It occurs when a very high twisting
force is applied to the bent knee. If contact sports did not allow the use of
studs on boots the injury would probably almost disappear. It is only when the
foot is fixed firmly to the ground and the body continues to twist fast on it
that the injury is inevitable. The patient often hears a loud crack in the knee
and collapses. They cannot play on
Aspiration
of the joint will produce a dramatic reduction of pain. If there are fat
globules in the aspirate then a fracture must be suspected as marrow has escaped
into the joint (Fig. 23.28).
Treatment
of the ruptured anterior cruciate ligament
In the child the anterior cruciate avulses with a fragment of bone. It
is relatively simple to fix this fragment back into the tibia either with a bone
screw or with sutures passed through to the front of the tibia. In the adult the
anterior cruciate tears its central part, where there is no capacity to heal.
This does not necessarily mean that surgery to substitute the ligament is
required. In a significant number of patients intense physiotherapy rebuilds the
control of the knee to levels where the absence of an anterior cruciate does not
hamper performance. In other patients whose performance is compromised by an
anterior cruciate deficient knee it is a perfectly valid option for the patient
decide to modify their lifestyle to cope with their disability. For example,
they may decide that the time has come to give up contact sport. It is only
after these first two options have been exhausted that the possibility of
performing surgery to substitute for the anterior cruciate ligament should even
be considered. Even then the surgery is complex, the rehabilitation is difficult
and there is no evidence in the long term that functionally the knee maintains
any greater stability, or that reconstruction protects the knee from
osteoarthritis. There is also now good evidence that some of the synthetic
ligaments used are not
As
the ligament does not heal, the alternatives are either to realign the
structures outside the knee to prevent the instability caused by anterior
cruciate deficiency or a second possibility is to take a ligament from elsewhere
in the patient and route it through the track of the anterior cruciate to recreate
the function of the ligament. A third option is to put in a synthetic ligament.
A ligamentous augmentation device (LAD) is a synthetic ligament which in itself
is not strong or elastic enough to undertake the function of an anterior
cruciate but combined with tendon material from the patient is supposed to
perform this function.
Extra-articular repair
The Macintosh operation involves reefing the lateral dynamic structures
of the knee. It pulls back on the lateral tibial plateau in flexion in an
attempt to stop it sliding forward in a uncontrolled way (the pivot shift),
which makes the knee so unstable in twisting and turning.
lntra-articular
repair
Intra-articular repairs can be performed either through the arthroscope
or open. The Jone’s repair involves freeing the proximal end of the middle
third of the patella tendon and rerouting this tendon through the knee along the
line of the anterior cruciate. Semitendinosus tendon can be used in a similar
way or a synthetic tendon can be inserted. The key issue surgically is to make
sure that the origin and insertion of this new ligament are in the correct place
to allow free movement of the knee without undue laxity.
Posterior
cruciate
A posterior cruciate tear is commonly associated with a hyperextension
injury and disruption of the posterior structures of the knee (Fig.
23.29).
Treatment of the knee in a plaster usually allows the posterior capsule to heal
up. There is then little functional disability despite the fact that the
posterior cruciate does not heal.
Rupture
of the medial collateral ligament
Ruptures of the medial collateral ligament occur when the leg is forced
into valgus usually by a blow on the outside of the leg. With moderate trauma
there is usually only a tear of the short cruciate ligament. If the force is
greater then the medial collateral ligament disrupts. The knee is grossly
unstable when stressed into valgus. If on
Anterior
knee pain — chondromalacia patellae
This condition tends to start in the teens and is more common in girls
than in boys. It may follow an injury to the knee, particularly a dislocation of
the kneecap. The patient gives a history that they have pain on stairs,
particularly going down stairs when the knee may actually feel unsafe. They also
experience severe pain when sitting for any length of time. When they try to
move after the knee has been still for a while the pain may be so severe that
the knee feels locked. This is not true mechanical locking. It seems to be more
to do with synovial inflammation. On examination, there may be some quadriceps
wasting, there is not usually an effusion but there is tenderness if the
synovium around the patella is pressed against the patella itself. This is
sometimes confused with tenderness beneath the patella; it is the synovium
caught between your finger and the patella that is causing the pain as there are
no nerve fibres under the patella itself.
Management
There is no proven treatment for this condition, but because its
severity fluctuates it is a diagnosis which has attracted all sorts of unusual
therapies. There is little doubt that pain killers and nonsteroidal
anti-inflammatory drugs make little or no difference to the pain. Strapping and
tubigrip can actually make the pain worse, and there is no evidence that
avoiding activities which make the pain worse makes any difference to the
natural history of the condition. The use of crutches, plaster cylinders and
even wheelchairs merely seems to confirm the child in the role of an invalid.
There is always quadriceps inhibition and eventually wasting, so exercises to
build up the quadriceps, particularly the vastus medialis, should be encouraged.
Unfortunately, these exercises can be quite painful, but if the child is
encouraged to contract the muscles isometrically (without moving the knee) the
pain can be minimised. There are several surgical
operations described for this condition but there is no evidence that
any of them do any good and some of them certainly make the condition worse, so
they should be avoided.
Dislocating
kneecap
It is most common to see a patient who has had a previous dislocation.
The kneecap normally relocates itself, but if it has not the patient can be
given nitrous oxide. When the knee is straightened the patella will relocate.
Immediately after a dislocation the patient will have a quadriceps lag and
should therefore be protected with a back slab and crutches. Physiotherapy
should be started at once. If there have been recurrent dislocations, then
swelling may be minimal but quadriceps wasting may be marked. It is then even
more important to arrange physiotherapy to build up the muscles around the knee
if further dislocations are to be avoided.
Surgery
for the dislocated patella (Fig. 23.30) should only be undertaken as a last
resort. If the patient has built up the quadriceps well but the kneecap is still
unstable then initially a soft-tissue realignment of the patella should be
considered by performing a lateral release. This involves dividing the lateral
retinaculum of the patella so that the pull on the patella is more medial.
Dislocation
of the knee
In high-energy accidents the knee can be dislocated. The tibia is driven
backwards and dislocates posteriorly. The key feature in this injury is that
there is a high risk of neurovascular injury. The pulses to the foot must be
intact before and after relocation, and even if they return great care must be
taken that a compartment syndrome does not develop. The knee can then be treated
in a plaster for 6 weeks with active quadriceps exercises.
Fractured
patella
There are two types of fractured patella. The first is a direct blow to
the patella, which tends to shatter the patella into
Management
of the communited undisplaced fracture
There is often an open wound over the patella and this needs cleaning.
If it is contaminated it should be left open for delayed primary closure. It is
unlikely that the patella can be reconstructed when it is in a large number of
fragments, and therefore the choice is either to treat the patella as a ‘bag
of bones’ (simply mobilised without any attempt at reduction) or to excise it.
The patella acts as a fulcrum for the quadriceps tendon and a stabiliser, so if
it is excised the knee may subsequently be weaker and less stable. However, if
it is moblised early as a ‘bag of bones’ the articular surface may be
smoothed but will never be truly congruent and early oesteoarthritis in the
patellofemoral joint is inevitable.
Management
of the displaced transverse fracture of the patella (avulsion)
The fracture can be managed in exactly the same way as an olecranon
fracture with wires passed through the patella and a figure-of-eight tension
band passed around the outside of the patella. The load of the quadriceps
passing through the patella and down the patella tendon into the tibial tubercle
serves to compress the fracture provided that the outer cortex is held together
with a tension band (Fig. 23.31). The patient is mobilised with partial
weight-bearing until the fracture is healed. The pins and wires are then removed
as otherwise they cause skin irritation.
Tibial
plateau fractures
Tibial plateau fractures occur in the elderly when the knee is forced
into varus or valgus and the osteoporotic bone fails before the ligaments.
Fracture can also occur in the young adult but are then associated with very
high-energy injuries which may also have damaged the ligaments and caused
fractures elsewhere. The pattern of fracture of the plateau depends on the
direction of the force exerted. If the knee was forced into valgus then there
tends to be a depressed fracture of the lateral plateau; if the knee is forced
into varus then, similarly, the medial plateau will be fractured. If there is an
axial force then both plateaux may be damaged. A check should always be made on
the contralateral side of the fracture for ligamentous disruption as the
compressed side will have acted as a fulcrum for the load to come on to the
opposite ligament. There are two main types of tibial plateau fracture. The
first is a vertical cleft fracture where a whole
Management
of vertical shear fractures
If the fracture is a pure vertical shear fracture with displacement of
more than 2 mm then the fragment needs to be exposed, elevated, and fixed back
with a buttress plate and lag screws across the knee. Early partial
weight-bearing and mobilisation can then be started.
Management
of depressed fractures
In these cases the joint may need to be opened so that the fragments can
be elevated under direct vision. The incision should be extended down beside the
tibia and a small window opened in the cortex into which a punch can be
introduced. The fragments can then be elevated from inside the bone and the
cavity packed with bone graft. If there is combined vertical shear fracture then
this can be fixed with a buttress plate (Fig. 23.32). Most of the load to the
knee goes through the medial side so a fracture of the lateral plateau may only
need protecting with a cast brace to prevent the knee going into valgus, but a
fracture of the medial plateau should be nonweight-bearing for some weeks.
Rheumatoid
arthritis of the knee
Rheumatoid arthritis commonly affects the knee, but the diagnosis is
simple as it is one of the later joints to be affected. In the first instance
the problem is pain and swelling secondary to an aggressive synovitis. At this
stage medical treatment, nonsteroidal anti-inflammatory drugs, pain killers,
splints and physiotherapy are the best choice. Synovectomy can be performed
chemically using short acting radioisotopes. Surgical synovectomy can also be
performed through an arthroscope. This is technically difficult because of the
florid synovitis and should only be undertaken if there is still a good range of
movement and the articular surfaces are well preserved. In the later stages of
rheumatoid arthritis there is severe arthritis in the lateral compartment with a
contracture of the lateral structures of the knee, producing external rotation
of the tibia and a fixed flexion deformity. Total knee replacement is now the
operation of choice but this may need to be combined with a careful soft-tissue
release to obtain a stable straight knee.
Management
of osteoarthritis of the knee
Osteoarthritis of the knee may be idiopathic or secondary to trauma. The
disease may affect all three compartments of the knee: the patellofemoral joint
as well as both the medial and lateral compartments of the knee, but its main
effect appears to be on the medial compartment. Initially the patient may
present with pain on walking. Weight-bearing X-rays may show slight narrowing of
the medial joint space. If medical treatment and physiotherapy are no longer
controlling the symptoms and there appears to be a major inflammatory element
to the disease then an arthroscopic washout should be considered. It is not
known how this operation works but it can give considerable relief of pain in
the short term. A valgus osteotomy may help to transfer the weight-bearing
away from the medial compartment and more equally into the medial lateral
compartment. This is only suitable if the lateral compartment shows no sign of
arthritis on X-ray, the knee is stable and there is a good range of movement (at
least 900).
The degree of yams (Fig. 23.33) should be measured carefully on long leg
X-rays. The size of wedge which needs to be removed from the tibia should then
be calculated with the aim of putting the knee in neutral or very slightly into
valgus. At operation a laterally based wedge is removed from tibia just below
the joint surface leaving the medial cortex intact to stabilise the osteotomy.
An alternative procedure is the ‘dome osteotomy’, where a series of drill
holes in the shape of an arch is drilled through from the front of the tibia to
the back and then joined using a sharp osteotome. The distal tibia can then be
rotated in the dome to correct the alignment of the knee. As with the wedge
osteotomy, the new position can then be held using a long leg plaster. Care must
be taken in either operation to avoid damaging the vessels immediately behind
the knee, which lie very close to the bone especially if the knee is extended.
These procedures are therefore best all performed with the knee well flexed.
Knee
replacement
Most knee replacements are total condylar knee replacements (Fig.
23.34). The femoral component replaces both femoral condyles and there is a
tibial plateau component which covers the tibia. An optional extra is a
resurfacing component for the back of the patella. Unicompartmental knee
replacements are available, but unicompartmental arthritis is not that common,
and technically these implants can be difficult to insert.
Operative
technique for total condylar knee replacement
The patient is placed supine on the table. It is not necessary to use a
tourniquet although many people do. The risk of causing vascular damage,
especially in the elderly, outweighs any possible advantages in obtaining a
blood-free field. A long midline anterior incision should be made from 10 cm
above the patella to 3 cm below the tibial tubercle. This incision can be curved
slightly medially. The incision is carried down to the patella and patella
tendon without undercutting the edges. The medial margin of the patella tendon
and of the patella is now exposed and the incision carried on through this
tissue to the knee joint. Above the patella the incision is brought round to the
midline of the patella and then extended vertically up the quadriceps muscle in
the midline for 10 cm above the knee. The patella is turned upside down and
dislocated laterally and the knee flexed up to 90 degree .Any bleeding in the wound edges should now stop so that a tourniquet
would now serve no further useful function. The fat pad and menisci are excised
and a jig is placed on the femur. The jig should be sized so that the femoral
component will be the same size as the condyles it is replacing.
Having
checked that rotation is correct the anterior and posterior cuts should then be
made on the femur. Very little of the anterior condyles should be removed. Each
fragment of the posterior condyle should be about the size of a thumb nail and
no thicker than the thickness of the replacement metal component. The tibial jig
should now be applied. Two types of jig are available. One is fitted on a rod
passed down the medulla of the tibia and relies on the tibial shaft anatomy
being normal and the entry hole being in the centre of the tibia. The second
type of jig (extramedullary jigging) relies on the surgeon clipping the jig to
the tibia and achieving the correct alignment by eye. This second system relies
more on the surgeon’s skill and expertise, and tends to be used more by
experienced knee surgeons who may wish to make allowances for abnormal anatomy.
The cut on the tibia should only remove as much tibia as is needed to make room
for the thickness of the thinnest of the tibial components. If there is a defect
in either the medial or the lateral plateau no attempt should be made to remove
the defect by cutting lower, as the defect can be filled with cement or, indeed,
with special components that can be fitted to the implant. The gap between the
cut top of the tibia and the posterior cut of the femur should be measured with
the knee in 90 degree of
flexion using the spacers provided on the instrument tray. This gap measured
will include the thickness of the tibial component and of the femoral component.
With
the knee now extended, and using the same spacer, a mark should be made on the
femur so that the distal cut of the femur is made at a height that will keep the
components in the same amount of tension through flexion and extension. If,
however, it is found that it is difficult to get the distal tibia in the correct
alignment to the femur in extension (70 degreeof
valgus) then a soft tissue release may need to be carried out on either the
medial or lateral collateral ligaments. The lateral ligament is best released
from the femur; the medial side can be released from both femur and tibia until
the knee is in correct alignment in extension. A similar amount of bone should
then be cut from the femoral condyles as the thickness of the metal of the
components, allowing for any defects in the femur caused by osteoarthritis.
The distal cut in the femur should now be carried out using a jig to ensure that
it is at the correct angle to the anterior and posterior cuts. The corners are
trimmed where necessary, and a trial femoral component can be fitted to test
against a trial tibial component. Iris now possible to see whether the cuts have
been put in the right place and whether the tension of the knee in both flexion
and extension is correct. On good designs the tension in flexion should be
slightly less than in extension to allow rotation of the tibia on the femur in
flexion. If the alignment and tension are good then the components can be
cemented into place. There is no evidence that resurfacing the back of the
patella makes any difference to the long term outcome, and the complications of
this thin implant are well described. Nevertheless, the patellofemoral joint is
clearly a potential source of pain and some surgeons argue that it should be
replaced.
The
patella is reduced and a single tacking suture put in to hold the medial
retinaculum to the patella. A check is then made that the patella
Complications
of total knee replacement
Total knee replacement is subject to wound breakdown if care is not
taken with the anterior incision. If the wound does break down then the knee
replacement is likely to become infected.
Tourniquet
damage is well described, especially in the elderly. The tourniquet may fracture
atherosclerotic plaques in the femoral vessels and, if left on too long, may
cause nerve damage. If tourniquet time is more than 1 hour in the elderly, the
tourniquet should probably be released and then reinflated after 10 minutes.
Tourniquets
can also cause burns if alcohol-based skin preparation solution is allowed to
seep down into the tourniquet padding (Fig. 23.35).
Damage
to the vessels behind the knee can be avoided by making the cuts on the tibia
with the knee flexed and being very careful not to let the saw cut too deep.
The
retractor on the lateral side of the knee must be used with care if damage to
the lateral popliteal nerve is to be avoided.
If
the knee is put in too loose it may be unstable and require bracing.
The
infection risk of total knee replacements is around the same as total hip
replacements, somewhere below 2
The
incidence of deep vein thrombosis after total knee replacement appears to be
high, but few of these cases produce any clinical symptoms. The overall death
rate after total knee replacement is low (less than I per cent, and the death
rate from pulmonary embolus even lower). There is, therefore, no evidence to
support the use of thromboprophylaxis in total knee replacement, either chemical
or mechanical.
Some
total knee replacements fail to mobilise quickly particularly if physiotherapy
resources are not good or the patient lacks motivation. After 2 weeks a
manipulation under anaesthetic may need to be performed to release any adhesions.
This must be done with great care to avoid breaking the femur.
Total
knee replacement does not produce immediate relief of pain but if severe pain
persists the possibility of aseptic or septic loosening must be considered. The
joint should be aspirated and fluid sent for culture. If a trial of antibiotics
does produce relief of pain then the diagnosis of septic loosening is most
likely and a revision should be considered.
Aseptic
loosening of total knee replacements probably occurs in a similar way to the
hip, with particulate wear stimulating an inflammatory response. Special
implants are available for revision but tissue should be sent at the time of
surgery for histology and bacteriology. The problems of wound healing after a
revision are considerably increased, as is the risk of infection and stiffness.