L7: The Thigh and Knee

Question 1

What are the key nerves of the lumbosacral plexus?

Answer 1

• The iliohypogastric nerve
• Ilioinguinal nerve
• Genitofemoral nerve
• Lateral cutaneous nerve of the thigh
• Femoral nerve (L2-L4)
• Obturator nerve (L2-L4)
• The lumbosacral trunk

Question 2

What are the major terminal nerves of the lumbosacral trunk?

Answer 2

The lumbosacral trunk makes a connection with the sacral plexus - outflow from S1-3. It receives from L4-L5.

Major nerves from this region include:

• Sciatic Nerve (L4-S3) - The sciatic nerve though looks like one nerve is made of two parts the tibial part (innervates muscles in the posterior aspect and the foot) and the common fibular nerve (from the lateral thigh).
• Superior Gluteal (L4-S1) - supplies the gluteus maxmius and minimus
• Inferior Gluteal (L5-S2) - supplies the gluteus maximus

Question 3

Why is the femur angled?

Answer 3

The femur is the bone of the thigh. The distal femur articulates with eth tibial at the knee. The femur is angled slightly obliquely returning the weight of the body to the midline.

Question 4

What are the bony landmarks of the mid and distal femur?

Answer 4

The shaft is the tubular long part. Posteriorly is two ridges called the medial and lateral lips of the linea aspera. These are important for muscle attachments. Towards the distal end posteriorly are the supracondylar lines. We also have medial and lateral epicondyles. Between them is the intercondylar notch.

On the anterior surfae is the adductor tubercle is a sight of attachment for muscles. The smooth surface is the patellar surface for the articulation of the patella (knee cap).

Question 5

What are the bony landmarks of the proximal tibia and fibia?

Answer 5

The fibula does not participate at the knee joint but an important attachment site for one of the posterior thigh muscles. The tibia lies medially in the leg and the fibula lies laterally.

The tibial tuberosity is a bony protrusion, it is the attachment for tendons in the anterior thigh. There are sharp anterior borders on the tibia which can be palpated. There is not a lot of subcutaneous tissue here.

On the posterior tibia we can see a flattened area in the tibia. These are the tibial plateaus. They articulate with the femoral condyles and help with congruency. There is a raised region of bone between the plateaus called the intercondylar tubercles.

The soleal line is an important site of attachment for a muscle. It is a line on the posterior tibia. Between these bones in life we have a strong interosseous membrane. It also has small apertures which allow for the passage of structures and vessels to allow pass from the anterior to posterior compartment.

Question 6

How is the knee stabilised?

Answer 6

Stability of the knee is important. It is an incongruent joint - the flat plateaus and the rounded condyles is not a good fit. This is achieved by:

- Surrounding muscles  
- Menisci (cartilage) 
- Ligaments inside intra-articular) and outside (extra-articular) the joint

Question 7

What is the menisci? What is it’s role?

Answer 7

The menisci are crescent shaped regions of fibrocartilage. The tibial plateaus are deepened by the medial and lateral menisci. They are thick at the lateral aspects and thinner at the medial aspect. They help to:

- Increase congruency  
- Distribute weight evenly   
- Shock absorption  
- Assist in the locking mechanism

Question 8

When is the knee joint most stable?

Answer 8

There is more congruency in extension as there is more of the condyles in contact with the plateaus. In flexion, there is less of the femoral condyles in contact with the proximal tibia. Injuries are more likely to occur in flexion.

Question 9

What are collateral ligaments?

Answer 9

These are the fibular (lateral collateral ligament) and tibial ligaments. These are extra-articular ligaments. Here we are looking laterally at the right knee.

Lateral collateral ligament - fibular:

- Cord like band not attached to the meniscus  
- Stabilises the knee and prevents adduction of the leg at the knee  

Tibial ligament

- This is a flat band  
- Attached to the medial meniscus. Therefore when we get injuries to one of these structures, we often get an injury to the other 
- This prevents abduction of the leg at the knee

Question 10

What are the cruciate ligaments?

Answer 10

These are ligaments inside the joint. Common in young people playing sport such as skiing or football. There is an anterior and posterior cruciate ligament (ACL) and (PCL).

The ACL:

- Important to prevent anterior displacement of the tibia on the femur 
- Prevents hyperextension  
- Injury occurs when the knee is hyperextended or force is applied anteriorly. Also seen in twisting ligaments of the knee 

The PCL:

- Prevents posterior dislocation of the tibia on the femur  
- Prevents hyperflexion 
- Main stabiliser of the flexed knee when weight bearing on a flexed knee e.g. walking downhill.  
- Can be injured when landing on the tibial tuberosity with the knee in flexion

Question 11

How are the muscles in the thigh seperated?

Answer 11

These compartments are separated by fascial septae and enclosed by a fibrous sleeve called the fasica lata. Some muscles of the thigh also cross the hip joint and cause movement at the hip.

Question 12

How are extensors and flexors of the knee joint organised?

Answer 12

Extensors: Anterior compartemnt
Flexors: Posterior compartment

Question 13

Name the muscles, their function and attachments of the anterior thigh.

Answer 13

Pectineus -lie on the floor off the femoral triangle. Flexes and adducts the hip.

Iliopsoas - is the major flexor of the hip - inserts on the lesser trochanter of the femur. Forms the floor of the femoral triangle

Sartorious - attaches from the ASIS to the medial tibia. Flexes the hip, laterally rotates the hip and flexes the knee. It is a ribbon or band like that takes an oblique course. It doesn’t perform any of the actions very strongly, acts alongside other muscles.

Tensor fascia lata - This muscle is part of the gluteal group. In the anterior aspect of the thigh inserts into the iliotibial tract - the thickening of the fascia lata on the thigh. It inserts on the lateral side of the tibia. It can contribute to flexion (not a strong flexor). It is important as a stabiliser due to its attachment.

The Quads:
Vastus Lateralis - originates from the greater trochanter and linea aspera. This is the lateral thigh. On the distal femur the linea aspera were the raised ridges on the lateral posterior femur.

Vastus Medialis - Has an attachment proximally to the intertrochanteric line and linea aspera - deep to rectus femoris.

Vastus Intermedius - originates from the anterior tibia converging down onto the tibia. Has an attachment to the linea aspera. Extensor.

Rectus Femoris - This is a straight muscle (rectus). Originates from the AIIS. Most anterior muscle of the quad. It also flexes the hip.

All 4 muscles converge onto the quadriceps tendon. This tendon crosses over the patella and merges with the patella tendon together which they attach to the tibial tuberosity.

Question 14

What are the boundaries of the femoral triangle?

Answer 14

Superior boundary - formed by the inguinal ligament

The medial boundary - formed by adductor longus

The lateral boundary - formed by sartorius

Question 15

At what point does the great saphenous vein drain into the femoral vein?

Answer 15

The point at which it drains into the femoral vein is known as the saphenofemoral junction. Inserts through the femoral ring.

Question 16

Name the muscles, their function and attachments of the medial thigh.

Answer 16

Adductor group:

- Adductor brevis (blue) - body of the pubis and inferior ramus to pectineal line and linea aspera. Insertion point is on the posterior aspect of the femur.  
- Adductor longus (pink)- originates from the body of the pubic bone and inserts on the middle third of the linea aspera. 

These therefore pull the femur towards the midline

- Adductor magnus - this is a deeper muscle - has two parts to it.  

Others:

- Gracilus (purple) inserts on the tibia from the body and inferior ramus. Since it courses the knee it can weakly flex the knee.     - Obturator externus - deeper muscle. Arises from the margins of the obturator foremen and obturator membrane and inserts in the trochanteric fossa. Acts to externally rotates the femur when the hip is extended, but when the hip is flexed it actually abducts the thigh.

Question 17

What is the innervation of the medial thigh?

Answer 17

Obtrurator nerve (L2-L4)

Question 18

What is the innervation of the anterior thigh?

Answer 18

Femoral nerve (L2-L4)

Question 19

Name the muscles, their function and attachments of the posterior thigh.

Answer 19

The Hamstrings:

These muscles are made up of the:

Semimembranosus Lies medially. Attaches on the posterior aspect of the medial tibial condyle. 

Semitendinosus - Lies medially on the posterior thigh and inserts on the medial aspect of the superior tibia. It has a long thin tendon in comparison at the distal point. 

Biceps femoris - on the lateral aspect. It has two parts - a long head and a short head. The long head from the tibial tuberosity and the short head arises from the linea aspera. This means the long head can flex the knee but does not extend the hip. It is innervated by the common fibular nerve. The long head can act as a hamstring and extend the hip. The muscle has dual innervation. The long head is innervated by the tibial nerve.

Question 20

Name the boundaries of the popliteal fossa.

Answer 20

• Semitendinosus and Semimembranosus medially and superiorly
  
  • The biceps femoris supralateral
  • Inferiorly is the muscle of the posterior aspect of the calf - Gastrocnemius

Question 21

What is the innervation of the posterior thigh?

Answer 21

Innervated by the tibial nerve a divisor of the sciatic nerve

Question 22

How does rotation of the knee occur?

Answer 22

We have a small muscle called popliteus. As the joint approaches full extension the femur undergoes a few degrees of rotation of medial rotation of the tibia. This is called locking of the knee. This makes sure the knee is in a very stable position and therefore the thigh muscles can relax. When we want to flex the knee, this rotation muscle be first undone - Popliteus undergoes the unlocking. It causes a little bit of lateral rotation of the femur so the hamstring muscles can allow flexion.

Question 23

Describe the blood supply to the thigh.

Answer 23

The femoral artery supplies predominantly the anterior compartment of the thigh. The profunda femoris branch travels through the thigh supplies the thigh itself. The femoral goes through into the popliteal fossa. The profunda femoris give off perforating branches that travel through the holes in adductor magnus into the posterior thigh and supply the hamstrings.

Question 24

Describe the blood supply to the knee.

Answer 24

Anastomoses around the knee are formed by the branches from the femoral, popliteal and posterior tibial arteries. The posterior tibial artery is the continuation into the posterior leg of the popliteal artery.

Question 25

What is Genu vanum?

Answer 25

The alignment between the oblique femur and the proximal tibia is important so we can get even distribution. In abnormal alignment we can therefore get an abnormal load on one side of the knee. In a condition called Genu vanum (Genu = knee) we get abnormal loading of the medial aspect of the knee leading to abnormal wearing and tearing on that aspect of the knee. This can lead to the tibia being adducted with respect to the femur - “bow legged appearance”.

Question 26

What is Genu valgum?

Answer 26

In Genu valgum we get abnormal alignment of the knee and bones in the lower limb leading to abnormal wear and tear in the lateral condyl. The tibia is abducted with respect to the femur.

Question 27

What is the “unhappy triad?”

Answer 27

Commonly seen due to excessive twisting of the flexed knee (when the knee is most unstable) or blow to the lateral side of the extended knee can lead to:

1. Tears in the tibial collateral ligament which is attached to … 
2. Medial meniscus which is also attached to … 
3. ACL which can also tear

Question 28

What are meniscal tears?

Answer 28

There is displacement of the cartilage which can become trapped during the knee movements leading to pain and locking. Damage is associated with the development of osteoarthritis and so they would develop this at a much younger age than you would normally see. Treatment is by repair and resection. They have a fairly poor blood supply and so do not heal very well.

Question 29

What are the different types of bursitis?

Answer 29

The Bursae are fluid filled sacs that are closely associated with joints are areas of friction to reduce friction. There is multiple around the joint. The pre-patellar bursa lies anterior to the patella. The deep and superficial infrapatellar bursa lie inferior to the patella. There is a suprapatellar bursa lying deep and superior to the patella. In bursitis around the knee joint we can get swelling. The look depends on which bursa is affected.

Question 30

What are the two parts of adductor magnus?

Answer 30

1. Adductor part comes from the inferior pubic ramus from the gluteal tuberosity ridge on the posterior aspect of the femur) and linea aspera. Innervated by the obturator nerve.
   
   2. Hamstring part Originates from the ischial tuberosity to the adductor tubercle and so innervates the by tibial nerve (light blue line). Acts as an extensor of the hip. Acts as an hamstring. When it contracts it extend the hip.

Question 31

What is the adductor hiatus?

Answer 31

Passage way through for the femoral artery and vein into the popliteal fossa. The arch way formed by the adductor and hamstring parts of the muscle.

Question 32

Why are ovarian masses associated with medial thigh pain?

Answer 32

The obturator nerve exists the pelvis through the obturator foremen. It overlies adductor brevis. Inside the pelvis it runs on the lateral wall of the pelvis and so can be contracted by pelvic and ovarian masses. Compression therefore is associated with sign and symptoms in the medial compartment of the leg.