Case 24- bone

Question 1

Bone- intramembranous

Answer 1

Intramembranous- connective tissue membrane to bone
• Condensation of mesenchyme forms bone blastema
• Osteoblast and osteoclast activity
• Formation of flat bone from a membranous mesenchyme template
• E.g. skull bones, mandible, clavicle

Question 2

Intramembranous ossification (1)

Answer 2

1. Mesenchymal cells form membrane and differentiate into osteoblasts
2. Ossification centre forms in membrane where osteoblasts start to form
3. Osteoblasts secrete osteoid collagen
4. Forms mineralised bone matrix in spicules (spike-like) from osteoid and hydroxypaptite
5. Osteoblasts trapped in bone matrix become osteocytes

Question 3

Intramembranous ossification (2)

Answer 3

6. Blood vessels form inbetween the boney spicules
7. Osteoid laid down between spicules, which fuse and form trabeculae of woven bone
8. Mesenchyme lines up and forms the periosteum (outer layer)
9. Woven bone forms collar, then is remodelled into Haversian bone
   - Trabeculae persist internally, compact bone is on the outside

Question 4

Intramembranous ossification- histology (first half)

Answer 4

• Intramembranous bone formation occurs within ‘membranes’ of condensed, primitive mesenchymal tissue.
• Mesenchymal cells differentiate into osteoblasts which begin synthesis and secretion of osteoid at multiple centres of ossification; mineralisation of osteoid follows closely.
• The osteoblasts are arranged into Ossification centres which release Osteoid which mineralises into a woven bone spicule, some of the osteoblasts are trapped within the spicule they then develop into osteocytes
• As osteoid is laid down, osteoblasts are trapped in lacunae to become osteocytes and their fine cytoplasmic extensions shrink to form the fine processes contained within the canaliculi.

Question 5

Intramembranous ossification (second half)

Answer 5

• Osteoprogenitor cells at the surface of the centres of ossification undergo mitotic division to produce further osteoblasts which lay down more bone.
• Progressive bone formation results in the fusion of adjacent ossification centres to form bone which is spongy in gross appearance.
• Collagen fibres of developing bone are randomly arranged in interlacing bundles
• The woven bone then undergoes progressive remodelling into lamellar bone by osteoclastic reabsorption and osteoblastic deposition to form mature compact or trabecular bone.
• The primitive mesenchyme remaining in the network of developing bone differentiates into bone marrow.

Question 6

Intramembranous ossification summary

Answer 6

1. Mesenchyme condensations form and an ossification centre develops.
2. Osteoprogenitor cells differentiate into osteoblasts and surround the newly formed capillaries.
3. Osteoblasts secrete osteoid and mineralisation occurs.
4. Fusion of adjacent ossification centres occur and eventually the woven bone is converted into lamellar bone
5. The mesenchyme which is not undergoing ossification forms the endosteum (inner layer of bone) and periosteum (outer layer of bone)

Question 7

Bone- Endochondral

Answer 7

Endochondral- cartilage to bone
• Formation of bone from a cartilage template
• Most bones form this way
• Involves chondrocytes and bone cells
• The hyaline cartilage on the ends of bones is left over from this process
• Hyaline cartilage is the template of long bones
• Osteoprogenitor cells of the perichondrium form the periosteal collar, the ossification centre forms in the middle of the long bone
• Hyaline cartilage is generated from mesenchymal cells, and is deposited into the shape of future bones

Question 8

Endochondral ossification (1)

Answer 8

• Chondroblasts form perichondrium and then periosteum (outer boundary). The periosteum is formed from the perichondrium and osteoblasts. Forms around the superficial surface of the bone
• Formation of bone collar around the diaphysis (shaft of bone). This bone collar will eventually become the periosteum (outer layer of bone)
• The bone collar prevents adequate diffusion of nutrients and oxygen into the cartilage. This causes the chondrocytes to release osteocalcin and alkaline phosphate and subsequently die
• Chondrocyte proliferation increases length of template
• Cavitation of cartilage template
• Primary ossification centre forms in cavity (diaphysis). Mineralisation occurs as the bone forms and blood vessels enter the cavity

Question 9

Hyaline cartilage

Answer 9

Generated from mesenchymal cells, deposited in the shape of future bone

Question 10

Endochondral ossification (2)

Answer 10

• Calcium deposited in cartilage matrix in primary ossification centre and chondrocytes proliferate further, mineralisation spreads along the length of the bone shaft
• Increases bone length and width through chondrocyte proliferation
• Capilaries penetrate periosteum and grow into diaphysis, important for bone marrow formation
• Secondary ossification centres are established in epiphyses, epiphyseal growth plates form which increase the bone length

Question 10

Endochondral ossification (2)

Answer 10

• Calcium deposited in cartilage matrix in primary ossification centre and chondrocytes proliferate further, mineralisation spreads along the length of the bone shaft
• Increases bone length and width through chondrocyte proliferation
• Capilaries penetrate periosteum and grow into diaphysis, important for bone marrow formation
• Secondary ossification centres are established in epiphyses, epiphyseal growth plates form which increase the bone length

Question 11

Endochondral ossification (3)

Answer 11

• Osteoblasts form in primary ossification centre
• Osteoblasts secrete osteoid bone matrix (trabecular bone)
• Osteoid is mineralised
• Trabecular bone fuses with collar
• Hyaline cartilage remains only in epiphyseal plate region and the articular surfaces
• Secondary ossification centre completely ossifies the epiphyses
• The epiphyseal plate disappears and your left with articular cartilage on each end

Question 12

What does the bony collar form

Answer 12

The bony collar forms the periosteum, get mineralisation in the centre at the diaphysis. The mineralisation spreads till you are left with just the articular cartilage. During the process we get increase in width and length and penetration of blood vessels

Question 12

What does the bony collar form

Answer 12

The bony collar forms the periosteum, get mineralisation in the centre at the diaphysis. The mineralisation spreads till you are left with just the articular cartilage. During the process we get increase in width and length and penetration of blood vessels

Question 13

When does endochondral ossification form

Answer 13

Endochondral ossification after birth
• At birth the secondary ossification centre begins to form within the epiphyses
•Bone replaces cartilage except at the articular margins and at the growth plates (the junction between the epiphysis and diaphysis in long bones)
• Epiphyseal plates begin to fuse which stops bone growing in length
• The epiphyseal plates close and skeletal maturity and final stature is achieved

Question 14

Structure of the lower limb

Answer 14

The lower limb can be divided into the gluteal region, the thigh, the knee, the leg, the ankle and the foot. The thigh and the leg are compartmentalised, each compartment having its own muscle that perform group functions and its own distinct nerve and blood supplies

Question 15

What type of joint is the knee joint

Answer 15

• Weight bearing joint- bones, ligaments, muscle/tendons
• Synovial joint- contains articular cartilage which lines the bone, capsule which surrounds the joint, synovial membrane (lines the capsule and non-articular surfaces) and synovial fluid which is released from the synovial membrane, bursae

Question 16

Knee joint

Answer 16

• A modified hinge joint- allows for flexion and extensions
• Bones- Femur, Tibia, Patella
• Knee joint does not fibula
• Largest synovial joint

Question 17

Knee joint articulations

Answer 17

1) Single joint cavity contains three articulations
2) Patello-femoral joint= femur with patella
3) Tibio-femoral joint= two condyles of the femur with the plateau of the tibia. Weightbearing part of the joint. Two joints between the Tibia and the femur. The lateral condyle of the femur articulates with the lateral condyle of the tibia and the medial condyle of the tibia articulates with the medial condyle of the femur

Question 18

Patella-femoral joint

Answer 18

• Patello-femoral joint= saddle joint
• The patella is imbedded within the Quadriceps femoris tendon and provides a lever for the Quadriceps femoris muscles to work which is the main extensor of the knee joint. The 4 heads of the muscle unite to form the Quadriceps tendon. Inferior to the Patella it forms the Patella ligament which attaches to the tibial tuberosityy
• Provides mechanical advantage to quadriceps femoris

Question 19

Knee joint capsule

Answer 19

• Posterior and sides= capsule attaches to the articular margins of the femur and tibia, the aperture for the passage of the popliteus tendon from the popliteus muscle to attach laterally to the femur
• Anterior- is lacking in the back and is replaced by the quadriceps tendon, the Patella and the Patella ligament
• Superior view- the capsule is attached to the articular surface of the tibia. The synovial membrane lines the capsule. The synovial membrane from the posterior surface reflects anteriorly into the intercondylar area. Tibial condyles, gap in fibrous capsule for popliteus tendon

Question 20

Synovial membrane

Answer 20

Lines the non-articular areas. Attaches to the periphery of the articular cartilage covering the femoral and tibial condyles and edges of the menisci. The menisci and synovial fluid in the knee joint allow for weight bearing and allow for smooth articulation of the tibia with the femur, also acts as a shock absorber.

Question 21

The synovial cavity- knee

Answer 21

The synovial cavity is full of synovial fluid, posterior to the Patella the synovial cavity extends superiorly behind the quadriceps tendon to form a Suprapatellar bursae. The muscle deep to it is the vastus intermedius muscle which retracts the bursae during extension

Question 22

The Bursae

Answer 22

The Bursae act as cushioning pads and help to reduce friction. If you overuse them they can get inflamed. The deep infrapatellar bursa is deep to the patellar ligament. The Superficial infrapatellar bursa is superficial to the Patellar. The Pre-patellar bursa is in front of the Patella

Question 23

Nerve damage which affects knee flexion and extension

Answer 23

Knee extension will be affected if the femoral nerve is injured as it supplies the quadriceps muscle in the anterior (extensor) compartment of the thigh.
Knee flexion will be affected if the sciatic nerve is injured as it supplies hamstrings and short head of biceps muscles in the posterior (flexor) compartment of the thigh.

Question 24

Muscles of the thigh- knee joint

Answer 24

1) Anterior compartment- extensors (4 muscles)
2) Vastus lateralis
3) Vastus medialis
4) Vastus intermedius
5) Rectus femoralis
6) The 4 muscles unite to form the Quadriceps tendon and continues inferior to the Patella as the Patella ligament which is attached to the tibial tuberosity. It crosses the knee joint anteriorly and causes extension of the leg at the knee. All other muscles and joints cross the knee posterior
7) The 4 muscles form the quadriceps femoralis

Question 25

Vastus medialis and Vastus lateralis

Answer 25

• Vastus lateralis- laterally on the thigh. Attaches to the lateral lip of the linea aspera, the line of attachment continues upwards to the greater trochanter
• Vastus medialis- medially on the thigh. Posteriorly it attaches to the medial lip of the linea aspera and at the top it attached to the intertrochanteric line. It arises from the posterior aspect and then wraps around the femur to go anteriorly and joint with the tendon of the vastus intermedius

Question 26

Vastus intermedius and rectus femoralis

Answer 26

• Vastus intermedius- between the vastus medialis and vastus lateralis. Arises from the anterolateral aspect of the femur
• Rectus femoralis- attaches to the Anterior Inferior Iliac spine and the Ileum superior to the acetabulum. Only Quadriceps muscle which crosses the hip joint so it acts on the hip joint

Question 26

Vastus intermedius and rectus femoralis

Answer 26

• Vastus intermedius- between the vastus medialis and vastus lateralis. Arises from the anterolateral aspect of the femur
• Rectus femoralis- attaches to the Anterior Inferior Iliac spine and the Ileum superior to the acetabulum. Only Quadriceps muscle which crosses the hip joint so it acts on the hip joint

Question 27

Muscles of the knee joint- flexors

Answer 27

1) 4 muscles, 3 of which are hamstrings. Posterior compartment of the thigh
2) Short and long head of the biceps femoralis
3) Semimembranosus
4) Semitendinosis
5) Gracilis and Sartorius
6) The Iliacus and Psoas major cross the hip anteriorly and insert on the lesser trochanter of the femur, flex the hip joint
7) Cross the knee joint posteriorly and will flex the knee

Question 28

Hamstring muscles

Answer 28

Long head of biceps femoralis, Semimembranosus and Semitendinosus. The common proximal attachment is to the Ischial tuberosity, they cross the hip joint so they act on the hip joint. Extensors of the hip joint

Question 29

Bicep femoralis

Answer 29

• The short and long head of the bicep femoris unite to form the bicep tendon which is attached to the fibula. The Semimembranosus and Semitendinosus muscle is attached to the Tibia
• The Biceps femoralis forms the superolateral boundary of the popliteal fossa. The Semimembraneous and Semitendinosus ligament form the superomedial boundary. The popliteal fossa is on the posterior aspect of the knee

Question 29

Bicep femoralis

Answer 29

• The short and long head of the bicep femoris unite to form the bicep tendon which is attached to the fibula. The Semimembranosus and Semitendinosus muscle is attached to the Tibia
• The Biceps femoralis forms the superolateral boundary of the popliteal fossa. The Semimembraneous and Semitendinosus ligament form the superomedial boundary. The popliteal fossa is on the posterior aspect of the knee

Question 29

Bicep femoralis

Answer 29

• The short and long head of the bicep femoris unite to form the bicep tendon which is attached to the fibula. The Semimembranosus and Semitendinosus muscle is attached to the Tibia
• The Biceps femoralis forms the superolateral boundary of the popliteal fossa. The Semimembraneous and Semitendinosus ligament form the superomedial boundary. The popliteal fossa is on the posterior aspect of the knee

Question 30

Knee flexors- Gracilis and Sartorius

Answer 30

1) The Gracilis and Sartorius muscle which cross the knee joint and insert with the semi-tendinous ligament to the anteromedial surface of the posterior tibia.
2) They act as guide rope muscles as they attach to three different parts of the hip bone. Gracilis attaches to the pubis, Semi-tendinousus to the Ischium and Sartorius to the Ileum.
3) The Sartorius muscle cross the hip joint anteriorly and crosses the knee joint posteriorly.
4) One of the longest muscles in the body, travels obliquely across from lateral to medial in the posterior compartment of the thigh and inserts on the anteromedial surface of the tibia with the gracilis and Semitendinosus muscle.
5) The sartorius forms the lateral boundary of the triangular depression which is inferior to the inguinal ligament. The Abductor longus muscle forms the other border of the femoral triangle

Question 31

Other muscles which cross the knee joint

Answer 31

• Medial and lateral head of the gastrocnemius, the lateral head is attached to the lateral condyle of the femur, medial head is attached to the medial condyle of the femur. Cross the knee joint posteriorly and will flex the knee joint.
• The Quadriceps and Patilla ligament cross the knee joint anteriorly and the extend the knee

Question 32

Flexion and Extension of the knee joint

Answer 32

Flexion= 120-150, limited by leg against posterior thigh
Extension= 5-10, uses quadriceps femoris muscle

Question 33

The different articulations of the knee joint

Answer 33

Distal part of the femur with the medial and lateral epicondyle, the tibial plateaus (medial and lateral) along with patella. The articular surface of the tibia forms the tibial plateau. The articular surface of the Patella forms the Patella-femural joint
The femoral condyles articulates with the patella. A fracture of the Patellar is more common through the body. A bipartite (2 heads) patella is more common through the side

Question 34

Boundaries of the Popliteal fossa

Answer 34

• Floor- popliteal surface of the femur (superiorly), joint capsule of the knee joint, oblique popliteal ligament, popliteal muscle covered by its fascia (inferiorly).
• Inferomedially- the medial head of gastrocnemius
• Inferolaterally- the lateral head of gastrocnemius and plantaris
• Superomedially- the semimembranosus and semitendinosus
• Superolaterally- the biceps femoris
• Roof- skin and popliteal fascia

Question 35

Contents of the Popliteal fossa

Answer 35

• Popliteal artery and its branches
• Popliteal vein receives small saphenous vein
• Tibial nerve and medial rural nerve
• Common peroneal nerve and lateral rural nerve
• Popliteal lymph nodes

Question 36

The femur

Answer 36

The strongest and heaviest bone of the body, it transmits body weight from the hip bone to the tibia when the person is standing

Question 37

Parts of the femur

Answer 37

Proximal part- Head, neck and two trochanters (greater and lesser) which give attachment to some muscles. The head of the femur and acetabulum in the pelvic bone form the hip joint.
The body (or shaft) of the femur- has the linea aspera, a ridge where numerous muscles of the thigh insert

Question 38

Distal part of the femur

Answer 38

• Forms the knee joint with the tibia and patella.
• The two condyles are slightly prominent anteriorly and are separated by the patellar surface. Posteriorly they project more and form a deep notch (the interchondylar fossa of the femur).
• The patellar surface articulates with the patella and the condyles of the femur articulates with the condyles of the tibia to form the knee joint.

Question 39

Development of the lower limb

Answer 39

• Both upper and lower limbs undergo torsion around their long axes but in opposite directions
• The medial rotation and permanent pronation cause the foot to become orientated with the great toe on the medial side and the knee (unlike the joints superior to it) and the joints inferior to the knee i.e. IP joints of toes extends anteriorly and flexes posteriorly. You are able to flex the elbow anteriorly but the knee bends or flexes posteriorly. All the joints superior to the knee flex anteriorly and extend posteriorly

Question 40

Compartments of the lower limb

Answer 40

• The deep fascia encloses the large thigh and leg muscles.
• It gives rise to intermuscular septa which form three unyielding fascial compartments.
• There is an anterior and posterior compartment, in the thigh there is a medial compartment and a lateral compartment in the leg.
• Anterior compartments are extensors, in the thigh it causes knee extension (hip flexion) and in the leg it causes dorsiflexion of the foot which extends the ankle. The extensor muscles cross the knee anteriorly
• The posterior compartment are flexors which cause flexion of the knee and flexion/plantarflexion of the ankle, flexors cross the knee joint posteriorly
• The medial compartment in the thigh cause Hip adduction and the lateral compartment muscles in the leg cause eversion.

Question 41

The thigh

Answer 41

The thigh contains the femur
The thigh covers the area between the inguinal ligament and the knee joint anteriorly: the posterior thigh is below the gluteal fold to the knee
The muscles of the thigh are divided into anterior, posterior and medial compartments. The walls of these compartments are formed by the fascia lata and three fascial intermuscular septa that arise from its deep aspect and attach to the linea aspera of the femur.

Question 42

Innervated by the muscles of the thigh

Answer 42

The muscles are innervated by femoral, sciatic and obturator nerves, all of which arise from the lumbosacral plexus.

1. The muscles in the anterior/ extensor compartment are mainly hip flexors and knee extensors. Femoral nerve is the nerve of the extensor compartment and hence innervates the muscles (except psoas major).
2. The muscles in the posterior/ flexor compartment are hip extensors and knee flexors. Sciatic nerve is the nerve of the flexor compartment and innervates the muscles.
3. The muscles in the medial compartment are mainly hip adductor muscles. Obturator nerve is the nerve of the medial compartment and innervates the muscles

Question 43

The main blood supply to the thigh

Answer 43

The main blood supply is femoral artery and vein (Anterior compartment), its deep artery of the thigh branch with veins accompanying it (Posterior compartment) and obturator artery (Medial Compartment).

Question 44

Muscles in the different compartments

Answer 44

•Muscles of the anterior compartment= Psoas major, Iliacus, Vastus medialis, Vastus intermedius, Vastus lateralis, Rectus femoralis, Sartorius
• Muscles of the medial compartment= Gracilis, Pectineus, Obturator externus (gluteal region muscle), Adductor longus, Adductorbrevis, Adductor magnus
• Muscles of the posterior compartment= Biceps femoris, Semitendinosus, Semimembranosus
The femoral triangle- a subfascial area in the upper anterior aspect of the thigh

Question 45

Femoral triangle boundaries

Answer 45

• The lateral, medial and superior boundaries are formed by the Sartorius muscle, Adductor longus muscle and Inguinal ligament respectively. [SAIL]
• The muscular floor of the femoral triangle is formed (laterally to medially) by the iliopsoas, pectineus, and adductor longus muscles.

Question 46

Contents of the femoral sheath

Answer 46

The femoral vein, artery and nerve are within the triangle. The great sapherous vein empties into the femoral vein

Question 46

Contents of the femoral sheath

Answer 46

The femoral vein, artery and nerve are within the triangle. The great sapherous vein empties into the femoral vein

Question 47

The femoral sheath

Answer 47

The femoral sheath is formed by an inferior prolongation of transversalis and iliopsoas fascia from the abdomen and does not enclose the femoral nerve. It allows the femoral artery and vein to glide deep to the inguinal ligament during movements of the hip joint.

Question 48

The compartments of the femoral sheath

Answer 48

• Lateral compartment for the femoral artery.
• Intermediate compartment for the femoral vein.
• Medial compartment, which is the femoral canal contains lymph nodes and fat.