Popliteal fossa & knee joint

Question 1

Popliteal fossa:
* Borders
* Floor
* Roof
* Contents

Answer 1

• Borders - lateral border of semimembranosus and semitendinosus (superomedial), medial border of biceps femoris (superolateral), lateral border of medial head of gastrocnemius (inferomedial), medial border of lateral head of gastrocnemius (inferolateral).
• Floor - popliteal surface of femur, capsule of knee joint reinforced by oblique popiteal ligament and popliteus muscle covered by its fascia.
• Roof - fascia lata.
• Contents - popliteal artery, popliteal vein, tibial and common peroneal parts of sciatic nerves, popliteal lymph nodes, popliteal fat pad.

Question 2

Popliteus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 2

• Origin - lateral condyle of the femur and the posterior horn of the lateral meniscus, via a strong tendon called the popliteus tendon.
• Insertion - tibia just proximal to the soleal line but below the tibial condyles.
• Nerve supply - tibial nerve (L4, 5, S1)
• Action - assists in knee flexion and its function is decided according to the position of the lower extremity i.e. weight-bearing or non weight-bearing, as it is a primary internal rotator of the tibia in a non weight-bearing position. In open chain kinematics, it rotates tibia medially. In close chain kinematics, it laterally rotates femur in the initial phase of knee flexion.

Question 3

What type of joint is the knee joint?

Answer 3

• The knee joint is a synovial joint, the largest in the body.
• It is a modified hinge joint; in addition to flexion and extension a small amount of rotation of the leg is possible in the flexed position of the knee.
• It is a compound joint that includes two condylar joints between the femur and the tibia and a sellar (saddle) joint between the patella and the femur, the former being partly divided by menisci.

Question 4

Describe the articular surfaces of the knee.

Answer 4

• The lateral and medial articular surfaces of the femur and tibia are asymmetrical.
• The distal surface of the medial condyle of the femur is narrower and more curved than that of the lateral condyle.
• The lateral tibial articular surface is almost circular, the medial is oval with a longer anteroposterior axis, and these differences are reflected in the shapes of the menisci.
• The articular surface of the patella is divided by a vertical ridge into a large lateral and a small medial surface; the latter is further subdivided by a faint vertical ridge into two smaller areas.
• The large lateral area articulates with the lateral condyle of the femur in extension and flexion.
• In extension the area next to it is in contact with the medial femoral condyle and the most medial area does not articulate with the femur.
• In flexion this surface is in contact with the medial condyle and the middle area is opposite the intercondylar notch of the femur.

Question 5

Describe the femoral components of the knee capsule.

Answer 5

• The capsule of the knee joint is attached posteriorly to the proximal margins of the femoral condyles and the intercondylar fossa.
• Medially the capsule is attached to the articular margin of the femur, but laterally the attachment is proximal to the groove for the popliteus tendon.
• Anteriorly the capsule blends with the patellar retinacula and is attached to the sides of the patellar ligament (tendon) and patella.
• The capsule is deficient above the level of the patella, permitting the suprapatellar bursa to be in full communication with the joint.

Question 6

Describe the tibial components of the knee capsule.

Answer 6

• Posteriorly on the tibia the capsule is attached to the margins of the tibial condyles, and in the intercondylar area to the distal edge of the groove for the posterior cruciate ligament.
• The attachment to the lateral condyle is interrupted by an aperture for the passage of the popliteus tendon.
• On the sides, the capsule is attached to the margins of the tibial condyles, and laterally to the head of the fibula as well.
• A thickening of the capsule on the medial side is a deep component of the tibial collateral ligament and is firmly attached to the medial meniscus.
• On its deep aspect the capsule has weak attachments to the rims of both menisci, the coronary ligaments, which connect them to the tibia.
• Anteriorly the line of attachment on the tibia of the fused capsule and patellar retinacula inclines distally from the medial and lateral condyles to the tibial tuberosity.

Question 7

Describe the tibial collateral ligament of the knee.

Answer 7

• The tibial collateral ligament (medial ligament) is a flat, triangular band attached above to the medial femoral epicondyle, just distal to the adductor tubercle, and attached below to the upper part of the medial surface of the tibia.
• Its anterior margin, which forms the vertical base of the triangle, is free except at its attached extremities.
• The posterior apex of the triangular ligament blends with the capsule and is thereby attached to the medial meniscus.
• Above its distal attachment the ligament is crossed by the tendons of sartorius, gracilis and semitendinosus with a bursa interposed.
• The medial inferior genicular vessels and nerve and the anterior expansion of the semimembranosus tendon are deep to the distal part of the ligament with another bursa intervening.

Question 8

Describe the fibular collateral ligament of the knee.

Answer 8

• The fibular collateral ligament (lateral ligament) is cord-like and is attached proximally to the lateral epicondyle, below the attachment of the lateral head of gastrocnemius and above that of the tendon of popliteus.
• Its distal attachment is to the head of the fibula overlapped by the tendon of biceps femoris, a bursa intervening between them. * The ligament is not attached to the capsule and has no connection with the lateral meniscus.
• A bursa lies between the ligament and the capsule, and the tendon of popliteus lies deep to the capsule here.
• The lateral inferior genicular vessels and nerve run deep to the distal part of the ligament.

Question 9

Describe the oblique popliteal ligament of the knee.

Answer 9

The oblique popliteal ligament is an expansion from the tendon of semimembranosus that blends with the capsule at the back of the joint and ascends laterally to the intercondylar fossa and lateral femoral condyle. The popliteal artery lies on it, and genicular vessels and nerves penetrate it.

Question 10

Describe the arcuate popliteal ligament of the knee.

Answer 10

The arcuate popliteal ligament is a Y-shaped thickening of posterior capsular fibres. The stem of the Y is attached to the head of the fibula. The medial limb arches over the tendon of popliteus to the posterior edge of the tibial intercondylar area. Some popliteus mus-cle fibres are attached to it. The lateral limb ascends to the lateral femoral condyle with the popliteus tendon.

Question 11

Outline the anterior cruciate ligament of the knee.

Answer 11

• The cruciate ligaments are a pair of very strong ligaments connecting tibia to femur.
• They lie within the capsule of the knee joint, but not within the synovial membrane.
• It is as though they had been herniated into the synovial membrane from behind, so that they are covered by synovial membrane on their front and sides but not posteriorly.
• The anterior cruciate ligament is attached to the anterior part of the tibial plateau between the attachments of the anterior horns of the medial and lateral menisci.
• The ligament ascends posterolaterally, twisting on itself, and is attached to the posteromedial aspect of the lateral femoral condyle.

Question 12

Outline the posterior cruciate ligament of the knee.

Answer 12

• The posterior cruciate ligament is stronger, shorter and broader, and less oblique.
• It is attached to a smooth impression on the posterior part of the tibial intercondylar area which extends to the uppermost part of the posterior surface of the tibia.
• The ligament ascends anteromedially and is attached to the anterolateral aspect of the medial femoral condyle.
• The cruciate ligaments cross each other like the limbs of the letter X, the anterior ligament lying mainly anterolateral to the posterior ligament.

Question 13

Outline the medial meniscus of the knee.

Answer 13

• The menisci (formerly called semilunar cartilages) are crescentic discs of fibrocartilage comprising mainly collagenous fibrous tissue that lie on and are attached to the tibial plateau.
• They are triangular in cross-section, being thicker at their convex periphery.
• Their distal surfaces are flat, while their proximal surfaces are concave and articulate with the convex femoral condyles.
• The menisci are mainly avascular but their peripheral zone is vascularized by capillaries from the capsule.
• The medial meniscus is almost a semicircle and is broader posteriorly. Its anterior horn is attached to the intercondylar area in front of the anterior cruciate ligament, while the posterior horn is similarly attached in front of the posterior cruciate ligament.
• The medial meniscus is firmly attached to the capsule and the tibial collateral ligament.

Question 14

Outline the lateral meniscus of the knee.

Answer 14

• The lateral meniscus is about four-fifths of a circle and is of uniform width.
• Its anterior horn is attached in front of the intercondylar eminence of the tibia, behind the anterior cruciate ligament with which it partly blends. * The posterior horn is attached behind the intercondylar eminence, in front of the posterior horn of the medial meniscus.
• From the posterior convexity of the lateral meniscus fibrous bands pass upwards and medially to the medial femoral condyle, in front of and behind the posterior cruciate ligament. These are the anterior and posterior meniscofemoral ligaments.
• More medially some fibres of the popliteus muscle are attached to the posterior convexity of the lateral meniscus.
• The transverse ligament is a variable band that connects the anterior convexity of the lateral meniscus to the anterior horn of the medial meniscus.

Question 15

Outline the nerve supply of the knee

Answer 15

The joint is supplied from:
* Femoral nerve through its branches to the three vasti.
* Sciatic nerve by the genicular branches of its tibial and common peroneal components.
* Obturator nerve by the twig from its posterior division, which accompanies the femoral artery through the gap in the adductor magnus into the popliteal fossa.

During arthroscopy it must be remembered that, although local anaesthesia affects the overlying skin, the cruciate ligaments remain sensitive (tibial nerve). The horns of the menisci are innervated but their central parts are devoid of sensory fibres.