X-RAY OF KNEE JOINT
X-ray Knee Joint A/P View
. Knee AP
Region: knee
joint, proximal tibia,
proximal fibula,
distal femur
Pathology: ligament
injury, fracture, chondromalacia, degenerative joint disease and arthritis
of knee
joint
SID: 100 cm (40
inches)
Central Ray: perpendicular
beam directed at the point 1 cm (0.4 inches) inferior to the apex of patella
Respiration: unrelated
Position
1. The patient should be placed a supine position or in a sitting
position with no rotation of pelvis and
leg fully extended.
2. Place major axis of leg and knee on the vertical axis of the image receptor
(IR) and rotate the leg about 5° internally to show true antero-posterior
projection image.
Collimation: Include
distal portion of femur and
proximal portion of tibia and fibula.
Evaluation
1. Knee joint should not be overlapped.
2. The medial portion of the head of fibula should
overlap in tibial
direction.
3. Overlapping of patella should
be shown above the femur shadow.
kVp-60, mAs-8
Tip
1. When it cannot make parallel with IR, project with 5°~7°
cephalad heading 1 cm below the end of patella.
X-ray Knee Joint Lateral View
Knee Lateral
Region: knee
joint, proximal tibia,
proximal fibula,
distal femur
Pathology: ligament injury, fracture, chondromalacia,
degenerative joint disease and arthritis of knee
joint
SID: 100 cm (40
inches)
Central Ray: beam
directed at the knee
joint with 5~7˚ cephalic angulation
Respiration: unrelated
Position
1. The patient is placed in a lateral decubitus position.
2. Flex the nonfilming leg and place the leg in front.
3. While flexing the filming knee 20°~30°, place bilateral condyles of femur perpendicularly
to image receptor (IR).
Collimation
Include distal portion of femur and
proximal portion of tibia and fibula.
Evaluation
1. Femoral
condyles should be overlapped.
2. Overlapping of femoral
condyles should be seen in intercondylar
eminence of knee
joint.
3. Patella is
observed from the true lateral side and the space in the patellofemoral
joint should be seen without overlap.
kVp-62, mAs-8
Tip
1. According to changes in angles in flexion of Knee Lateral
Projection, capacity of joint cavity changes; severity of ligament injury can
be examined.
Anatomy Knee joint.
The knee joint is a hinge type synovial
joint, which mainly allows for flexion and extension (and a small degree of medial
and lateral rotation). It is formed by articulations between the patella, femur
and tibia.
In this article, we shall examine the anatomy of the knee
joint – its articulating surfaces, ligaments and neurovascular supply.
Fig 1 – The femur, tibia and patella of the knee joint.
Articulating Surfaces
The knee joint consists of two articulations – tibiofemoral
and patellofemoral. The joint surfaces are lined with hyaline cartilage
and are enclosed within a single joint cavity.
Tibiofemoral – medial and lateral condyles of the femur
articulate with the tibial condyles. It is the weight-bearing component of the
knee joint.
Patellofemoral – anterior aspect of the distal femur
articulates with the patella. It allows the tendon of the quadriceps femoris
(knee extensor) to be inserted directly over the knee – increasing the
efficiency of the muscle.
As the patella is both formed and resides within the quadriceps
femoris tendon, it provides a fulcrum to increase power of the knee extensor
and serves as a stabilising structure that reduces frictional forces placed on
femoral condyles.
Fig 2 – More detailed view of the bony surfaces. The
inferior surface of the femur and superior surface of the tibia is shown.
Neurovascular Supply
The blood supply to the knee joint is through the genicular
anastomoses around the knee, which are supplied by the genicular branches
of the femoral and popliteal arteries.
The nerve supply, according to Hilton’s law, is by the
nerves which supply the muscles which cross the joint. These are the femoral,
tibial and common fibular nerves.
Menisci
The medial and lateral menisci are fibrocartilage structures
in the knee that serve two functions:
To deepen the articular surface of the tibia, thus
increasing stability of the joint.
To act as shock absorbers by increasing surface area
to further dissipate forces.
They are C shaped and attached at both ends to the intercondylar area
of the tibia.
In addition to the intercondylar attachment, the medial
meniscus is fixed to the tibial collateral ligament and the joint capsule.
Damage to the tibial collateral ligament usually results in a medial meniscal
tear.
The lateral meniscus is smaller and does not have
any extra attachments, rendering it fairly mobile.
Fig 3 – Posterior view of the knee joint, with the joint
capsule removed. Note the close relationship of the tibial collateral ligament,
and the medial meniscus
Fig 4 – The menisci of the knee joint. Superior surface of
the tibia
Bursae
A bursa is synovial fluid filled sac, found between moving
structures in a joint – with the aim of reducing wear and tear on those
structures. There are four bursae found in the knee joint:
Suprapatellar bursa – an extension of the synovial
cavity of the knee, located between the quadriceps femoris and the femur.
Prepatellar bursa – found between the apex of the
patella and the skin.
Infrapatellar bursa – split into deep and superficial.
The deep bursa lies between the tibia and the patella ligament. The superficial
lies between the patella ligament and the skin.
Semimembranosus bursa – located posteriorly in the knee
joint, between the semimembranosus muscle and the medial head of the
gastrocnemius.
Fig 5 – Sagittal view of the knee joint, showing the major
bursae.
Ligaments
The major ligaments in the knee joint are:
Patellar ligament – a continuation of the quadriceps
femoris tendon distal to the patella. It attaches to the tibial tuberosity.
Collateral ligaments – two strap-like ligaments.
They act to stabilise the hinge motion of the knee, preventing excessive medial
or lateral movement
Tibial (medial) collateral ligament – wide and flat
ligament, found on the medial side of the joint. Proximally, it attaches to the
medial epicondyle of the femur, distally it attaches to the medial condyle of
the tibia.
Fibular (lateral) collateral ligament – thinner and rounder
than the tibial collateral, this attaches proximally to the lateral epicondyle
of the femur, distally it attaches to a depression on the lateral surface of
the fibular head.
Cruciate Ligaments – these two ligaments connect the
femur and the tibia. In doing so, they cross each other, hence the term
‘cruciate’ (Latin for like a cross)
Anterior cruciate ligament – attaches at the
anterior intercondylar region of the tibia where it blends with the medial
meniscus. It ascends posteriorly to attach to the femur in the intercondylar
fossa. It prevents anterior dislocation of the tibia onto the femur.
Posterior cruciate ligament – attaches at the
posterior intercondylar region of the tibia and ascends anteriorly to attach to
the anteromedial femoral condyle. It prevents posterior dislocation of the
tibia onto the femur.
Fig 6 – Anterior view of the knee joint, showing some of the
major ligaments. The patella ligament is situated on the anterior aspect of the
knee joint, and is not visible is this diagram.
Movements
There are four main movements that the knee joint permits:
Extension: Produced by the quadriceps femoris, which
inserts into the tibial tuberosity.
Flexion: Produced by the hamstrings, gracilis, sartorius and
popliteus.
Lateral rotation: Produced by the biceps femoris.
Medial rotation: Produced by five muscles; semimembranosus,
semitendinosus, gracilis, sartorius and popliteus.
NB: Lateral and medial rotation can only occur when the knee
is flexed (if the knee is not flexed, the medial/lateral rotation occurs at the
hip joint).
Clinical Relevance: Injury to the Knee Joint
Collateral Ligaments
Injury to the collateral ligaments is the most common
pathology affecting the knee joint. It is caused by a force being applied to
the side of the knee when the foot is placed on the ground.
Damage to the collateral ligaments can be assessed by asking
the patient to medially rotate and laterally rotate the leg. Pain on
medial rotation indicates damage to the medial ligament, pain on lateral
rotation indicates damage to the lateral ligament.
If the medial collateral ligament is damaged, it is more
than likely that the medial meniscus is torn, due to their attachment.
Cruciate Ligaments
The anterior cruciate ligament (ACL) can be torn by hyperextension of
the knee joint, or by the application of a large force to the back of the knee
with the joint partly flexed. To test for this, you can perform an
anterior drawer test, where you attempt to pull the tibia forwards, if it
moves, the ligament has been torn.
The most common mechanism of posterior cruciate ligament
(PCL) damage is the ‘dashboard injury’. This occurs when the knee is flexed,
and a large force is applied to the shins, pushing the tibia posteriorly. This
is often seen in car accidents, where the knee hits the dashboard. The
posterior cruciate ligament can also be torn by hyperextension of the knee
joint, or by damage to the upper part of the tibial tuberosity.
To test for PCL damage, perform the posterior draw test.
This is where the clinician holds the knee in flexed position, and pushes the
tibia posteriorly. If there is movement, the ligament has been torn.
Bursitis
Friction between the skin and the patella cause the
prepatellar bursa to become inflamed, producing a swelling on the anterior side
of the knee. This is known as housemaid’s knee.
Similarly, friction between the skin and tibia can cause the
infrapatellar bursae to become inflamed, resulting in what is known as clergyman’s
knee (classically caused by clergymen kneeling on hard surfaces
during prayer).
Unhappy Triad (Blown Knee)
As the medial collateral ligament is attached to the medial meniscus, damage to either can affect both structure’s functions. A lateral force to an extended knee, such as a rugby tackle, can rupture the medial collateral ligament, damaging the medial meniscus in the process. The ACL is also affected, which completes the ‘unhappy triad’.
