The Anatomy of Knee Joint

Structure, Ligaments, Bursae, Movements & Clinical anatomy of the Knee Joint

Complexity of joint due to fusion of 3 joints:
a. Lateral femorotibial
b. Medial femorotibial
c. Femoropatellar

Type of Joint:
Compound synovial joint involving:
a. 2 condylar joints between condyles of femur and tibia
b. Saddle joint between the femur and the patella

Articular Surfaces:
a. The condyles of the femur
b. Patella
c. The condyles of the tibia
The condyles of femur articulate with the tibial condyles below and behind, and with the patella in front.

Ligaments:

Ligaments of Knee Joint

 

a. Fibrous capsule
b. Ligamentum patellae
c. Tibial collateral or lateral ligament
d. Fibular collateral or medial ligament
e. Oblique popliteal ligament
f. Arcuate popliteal ligament
g. Cruciate ligaments : Anterior and Posterior
h. Meniscus : Lateral and Medial
i. Transverse ligament

a. Fibrous capsule:
Attachment on femur:
Anteriorly: Thin and deficient where it is replaced by quadriceps femoris, the patella and the ligamentum patellae.
Posteriorly: Attached to intercondylar line
Laterally: Encloses the origin of popliteus

Attachment on tibia:
Anteriorly: Descends downwards along the margins of the condyles to the tibial tuberosity
Posteriorly: Attached to intercondylar ridge
Posterolaterally: There is a gap behind the lateral condyle for passage of the tendon of the popliteus.

Parts of the capsule:
Coronary ligament: The part of the capsule between the menisci and the tibia
Short lateral ligamnet: Extends from lateral epicondyle to the femur

Openings:

  1. To suprapatellar bursa
  2. To exit of the tendon of the popliteus

 

b. Ligamentum patellae:
It is attached above to the margins and apex of patella, and below to the upper part of tibial tuberosity.

c. Tibial Collateral or Medial Ligament:
Superiorly, it is attached to the medial epicondyle of the femur. Inferiorly it divides into anterior and posterior parts. The anterior(superficial) part is separated from the capsule by one or two bursae. it is attached to the medial border and the medial surface of the shaft of the tibia. The posterior (deep) part of the ligament is short and blends with the capsule and withe the medial meniscus.
Morphologically, the tibial collateral ligament represents the degenerated tendon of the adductor magnus muscle.

d. Fibular Collateral or Lateral Ligament:
It extends from the lateral epicondyle of the femur to the lateral surface of the head of the fibula. It is separated from the lateral meniscus by the tendon of the popliteus and by the capsule. It is embraced by the two heads of the biceps femoris inferiorly.
Morphologically, it represents the femoral attachment of the peroneus longus.

e. Oblique popliteal ligament:
It is the expansion from the tendon of the semimembranosus. It runs upwards and laterally from the medial tibial condyle, blends with the posterior surface of capsule and is attached to the intercondylar line and lateral condyle of the femur. It reinforces the joint on posterior aspect.

f. Arcuate popliteal ligament:
It extends fromthe posterior aspect of the head of the fibula, passes superomiedially over the tendon of popliteus and attaches to intercondylar area of the tibia.

g. Cruciate ligaments:
They are the union between tibia and femur, to maintain anteroposterior and rotatory stability of knee joint. They lie at the center of joint and cross each other like letter “X”.

Anterior cruciate ligament: Begins from anterior part of intercondylar area of tibia, runs upwards, backwards and laterally and is attached to the medial surface of lateral condyle of femur.
It is slacked when flexion and taut when extension of knee occurs preventing the posterior displacement of the femur on the tibia and hyper extension of the knee joint.

Posterior cruciate ligament: Begins from the posterior part of the intercondylar area of tibia, runs upwards, forwards and medially and is attached to the lateral surface of the medial femoral condyle. It taut during flexion of the knee joint which prevents hyperflexion of knee joint.

These are supplied by middle genicular vessels and nerves (branches of obturator, femoral, tibial and common fibular nerves).

h. Menisci or Semilunar cartilages:
They are 2 crescent shaped fibrocartilaginous discs that deepen the articular surfaces of the condyles of the tibia and partially divide the joint cavity into upper and lower compartments. It has 2 ends, 2 borders and 2 surfaces. The upper surface is concave for articulatiob with the femur while the lower surface is flate and rests on the periphery of condyles of tibia.

Medial meniscus: Larger with open “C” configuration (nearly semicircular)
Lateral meniscus: Closed “C” configuration (nearly circular)

Functions of menisci:
1. Makes the articular surfaces more congruent
2. Serve as shock absorbers
3. Lubricates the joint cavity
4. Giver rise to proprioceptive impulses (sensory function due to nerve supply)

i. Transverse ligament:
It connects the anterior ends of the medial and lateral mensici.

Synovial Membrane:
It lines the capsule, except posteriorly where it is reflected forwards by the cruciate ligaments. It is absent from the patella. Above the patella is prolonged as the suprapatellar bursa. Below the patella it covers the deep surface of the infrapatellar fat.

Bursae Around the Knee:
As many as 13 bursae have been described around the knee – 4 anterior, 4 lateral and 5 medial. They absorb shock and prevent friction in the joint. They are listed below:

Anterior:
1. Subcutaneous prepatellar bursa
2. Subcutaneous infrapatellar
3. Deep infrapatellar
4. Suprapatellar

Lateral:
1. Bursa deep to the lateral head of the gastrocnemius
2. Bursa between the fibular collateral ligament and the biceps femoris
3. Bursa between the fibular colleteral ligament and the tendon of the popliteus
4. A bursa between the tendon of the popliteus and the lateral condyle of the tibia

Medially:
1. Bursa deep to the medial head of the gastrocnemius
2. Anserine bursa
3. Bursa deep to tibial collateral ligament
4. Bursa deep to the semi membranosus
5. Occasionally a bursa is present between the tendons of the semimembranosus and the semitendinosus.

Blood supply:

Blood supply of knee joint

 

1. 5 genicular branches of the popliteal artery
2. Descending branch of femoral artery
3. Descending branch of the lateral circumflex femoral artery
4. 2 recurrent branches of the anterior tibial artery
5. 2 Circumflex fibular branch of the posterior tibial artery

Nerve supply:
1. Femoral nerve to the vasti
2. Sciatic nerve genicular branch
3. Obturator nerve, through its posterior division

Movements at the Knee Joint:
a. Flexion: Muscles involved are biceps femoris, semitendinosus, semimembranosus, gracilis, sartorius, popliteus.
b. Extension: Muscles involved are quadriceps femoris and tensor fasciae latae.
c. Medial rotation: Muscles involved are popliteus, semimembranosus, semitendinosus, sartorisus, gracilis.
d. Lateral rotation: Muscle ivolved is biceps femoris

Locking and Unlocking of the Knee joint:

Locking occurs as a result of medial rotation of the femur during the last stage of extension. It allows the knee to remain in the position of full extension as in standing without much muscular effort. It is produced by quadricep femoris.

Unlocking is the reversal of locking i.e. lateral rotation of the femur. A locked knee joint can be flexed only after it is unlocked. Unlocking is brought about by the action of popliteus muscle.

Clinical Anatomy:
1. It is a weak joint. It is stabilized by cruciate ligaments, collateral ligaments, iliotibial tract, etc.

2. Deformities:

a. Genu valgum or Knock knee: Abnormally abducted leg
b. Genu varum or Bow knee: Abnormally adducted leg (like in rickets)

3. Diseases:

a. Osteoarthritis
b. Infections (swelling and collection of fluids in the joint cavity)

4. Injuries:
a. Injury of medial menisci: The medial meniscus is more vulnerable to injury than the lateral because of its fixity to the tibial collateral ligament and because of greater excursion during rotatory movements. The lateral meniscus is protected by the popliteus which pulls it backwards so that it is not crushed between the articular surfaces.

b. Injuriy to anterior cruciate ligament (Anterior dislocation of tibia) is more common than that of the posterior (Posterior dislocation of tibia).

c. Injuries to collateral ligaments due to severe abduction and adduction strains.

2 Comments
  1. June 3, 2010
  2. October 18, 2012

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