TBL7 - Bones of Thigh and Leg

Question 1

What are lower limb bones and hip bones derived from? What is different about the morphogenesis of the upper and lower limbs?

Answer 1

1) Like the shoulder and upper limb, the hip bones and bones of the lower limb are formed by chondroblasts and osteoblasts of the parietal layer of lateral plate mesoderm
2) Development of the upper and lower limbs is similar except that morphogenesis of the lower limb is approximately 1 to 2 days behind that of the upper limb
3) Also, during the seventh week of gestation, the limbs rotate in opposite directions. The upper limb rotates 90° laterally, so that the extensor muscles lie on the lateral and posterior surface, and the thumbs lie laterally, whereas the lower limb rotates approximately 90 degrees medially, placing the extensor muscles on the anterior surface and the big toe medially

Question 2

What supports body weight?

Answer 2

1) Body weight is transferred from the vertebral column through the sacro-iliac joints (divided and directed laterally to the sacrum and via the sacroiliac joints to the thick portions of the bilateral ilia) to the pelvic girdle
2) Rami of the pubis are joined centrally at the pubic symphysis to stabilize the weight-bearing sacrum and ilia
3) From the pelvic girdle, body weight is transferred through the hip joints to the femurs (L. femora)
4) While standing, the weight of the upper body is transmitted to the heads and necks of the femurs

Question 3

What 3 bones form the hip bone? What do these 3 bones also contribute to?

Answer 3

1) Fusion of the ilium, pubis, and ischium forms the hip bone
2) Portions of all three bones contribute to the acetabulum that articulates with the head of the femur to form the hip joint

Question 4

What three ligaments reinforce the joint capsule at the hip? In what fashion do these ligaments travel from the hip bones to the femur? What about these ligaments increases or decreases joint stability and mobility?

Answer 4

1) The iliofemoral, pubofemoral, and ischiofemoral ligaments reinforce the joint capsule at the hip
2) The ligaments pass in a spiral fashion from the hip bones to the femur and envision extension of the femur winds them more tightly thus increasing joint stability but restricting extension to 10-20⁰ beyond the vertical position
3) Flexion of the femur unwinds the ligaments and joint mobility is increased allowing flexion to ≥ 90⁰ beyond vertical

Question 5

What results from the weakness of the ischiofemoral ligament? How are overabduction and hyperextension of the hip joint are prevented?

Answer 5

1) Posteriorly is the ischiofemoral ligament, which arises from the ischial part of the acetabular rim, is the weakest of the three ligaments. This causes hip dislocations most commonly in a posterior direction
2) Said to be the body’s strongest ligament, the iliofemoral ligament (located anteriorly & superiorly) specifically prevents hyperextension of the hip joint during standing by screwing the femoral head into the acetabulum
3) Anteriorly and inferiorly is the pubofemoral ligament, which blends with the medial part of the iliofemoral ligament, and tightens during both extension and abduction of the hip joint. The pubofemoral ligament prevents overabduction of the hip joint

Question 6

Describe the relationship between the iliac fossa and crest. What is the function of the anterior superior and inferior iliac spines?

Answer 6

1) The thin iliac fossa is below the thickened superior border of the fossa, which forms the iliac crest
2) The anterior superior iliac spine (ASIS) and anterior inferior iliac spine are attachment sites for tendons of the anterior thigh muscles

Question 7

What are avulsion fractures of the hip bone?

Answer 7

1) Avulsion fractures of the hip bone may occur during sports that require sudden acceleration or deceleration forces, such as sprinting or kicking in football, soccer, hurdle jumping, basketball, and martial arts
2) A small part of bone with a piece of a tendon or ligament attached is “avulsed” (torn away)
3) Avulsion fractures occur where muscles are attached: anterior superior and inferior iliac spines, ischial tuberosities, and ischiopubic rami

Question 8

What is the ilium continuous with? Describe the location of the pubis, ischial spine, ischial tuberosity, and ischiopubic ramus. What do the ischium and pubis form the border of?

Answer 8

1) The ilium is continuous posteriorly with the body of the ischium and anteriorly with the superior ramus of the pubis
2) The ischium and pubis form the border of the obturator foramen

Question 9

Recognize the head, neck, and greater and lesser trochanters of the femur. On the posterior aspect of the shaft, locate the linea aspera and recognize the lateral and medial epicondyles and condyles on the distal femur

Answer 9

Use figure to view these parts

Question 10

How do spiral fractures and comminuted fractures of the femur differ?

Answer 10

1) Fractures of the greater trochanter and femoral shaft usually result from direct trauma (direct blows sustained by the bone resulting from falls or being hit) and are most common during the more active years
2) A spiral fracture of the femoral shaft may occur, resulting in foreshortening as the fragments override
3) The fracture may be comminuted (broken into several
pieces) , with the fragments displaced in various directions as a result of muscle pull and depending on the level of the fracture

Question 11

Locate the medial and lateral condyles, shaft, tibial tuberosity, and medial malleolus of the tibia. What is the function of the knee joint?

Answer 11

The knee joint, which is formed by articulation of the femoral and tibial condyles, enables flexion and extension of the leg

Question 12

Locate the head, neck, shaft, and lateral malleolus of the fibula

Answer 12

Use figure to view these parts

Question 13

What causes Osgood-Schlatter disease and what are its symptoms?

Answer 13

Disruption of the epiphysial plate at the tibial tuberosity may cause inflammation of the tuberosity and chronic recurring pain during adolescence (Osgood-Schlatter disease), especially in young athletes

Question 14

What is the function of having obliquity of the femur in the thigh and verticality of the tibia in the leg?

Answer 14

The angle of inclination enables femoral obliquity, which places the knee joints inferior to the sacrum; thus, the center of gravity returns to the vertical axes of the supporting legs and feet

Question 15

What occurs to the angle of the femur as one ages? What does this cause?

Answer 15

1) The angle of inclination of the femur diminishes (becomes more acute) with aging
2) Thus, increased strain on the neck of the femur makes its fracture more common in the elderly

Question 16

What are the lateral and medial menisci?

Answer 16

1) Observe the incongruence of the articular surfaces at the knee joint
2) The lateral and medial menisci are incomplete rings of dense connective tissue partially covering the articular surface of the tibial condyles

Question 17

What is the most stable position of the knee joint?

Answer 17

The most stable position of the knee joint is the erect, extended position when contact of the articular surfaces is maximized and the primary ligaments of the knee are taut

Question 18

What does the lateral (fibular) collateral ligament (LCL) attach to?

Answer 18

The cord-like lateral (fibular) collateral ligament (LCL) attaches the lateral epicondyle of the femur to the fibular head

Question 19

What does the medial (tibial) collateral ligament (MCL) attach to?

Answer 19

The strong, flat medial (tibial) collateral ligament (MCL) attaches the medial epicondyle of the femur to the superomedial surface of the tibia

Question 20

What separates the lateral meniscus from the LCL? What is noticeable about the medial meniscus and MCL?

Answer 20

1) The tendon of the popliteus muscle separates the lateral meniscus and LCL
2) The medial meniscus is attached to the MCL; thus, the medial meniscus and MCL are commonly torn during contact sports

Question 21

What does the combined structure of the ACL and PCL look like?

Answer 21

In the center of the knee joint, the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) cross each other obliquely like the letter X

Question 22

Where does the PCL attach? What is its function?

Answer 22

1) The stronger PCL arises from the posterior intercondylar area of the tibia and attaches anteriorly to the medial condyle of the femur
2) Thus, the PCL prevents anterior displacement of the femur on the tibia and hyperflexion of the leg

Question 23

Where does the ACL attach? What is its function?

Answer 23

1) The weaker ACL arises from the anterior intercondylar area of the tibia and attaches posteriorly to the lateral condyle of the femur
2) Thus, the ACL prevents posterior displacement of the femur on the tibia and hyperextension of the leg

Question 24

How can twisting of the flexed knee create the “unhappy triad” injury?

Answer 24

1) The firm attachment of the TCL to the medial meniscus is of considerable clinical significance because tearing of this ligament frequently results in concomitant tearing of the medial meniscus. The injury is frequently caused by a blow to the lateral side of the extended knee, or excessive lateral twisting of the flexed knee that disrupts the TCL and concomitantly tears and/or detaches the medial meniscus from the joint capsule
2) The ACL, which serves as a pivot for rotatory movements of the knee, and is taut during flexion, may also tear subsequent to the rupture of the TCL, creating an “unhappy triad” of knee injuries

Question 25

What are the anterior and posterior drawer signs?

Answer 25

1) ACL rupture causes the free tibia to slide anteriorly under the fixed femur, known as the anterior drawer sign; it is tested clinically via the Lachman test
2) PCL ruptures allow the free tibia to slide posteriorly under the fixed femur, known as the posterior drawer sign

Question 26

What is the sliding area of the joint formed by? What is the function of the menisci?

Answer 26

1) The sliding area of the joint is formed by articular cartilage i.e., hyaline cartilage lacking a perichondrium
2) The meniscus projecting into the synovial cavity provides shock absorption and load distribution for the knee joint

Question 27

What is the joint capsule of the knee made of? Where are these joint capsules found?

Answer 27

1) The joint capsule is lined by the synovial membrane, which consists of simple cuboidal epithelium that produces synovial fluid for lubrication of the articular surfaces
2) Synovial cavities, synovial membranes, and articular cartilage characterize all joints of the upper and lower limbs

Question 28

What is the pathogenesis of osteoarthritis, the most common form of arthritis?

Answer 28

1) Osteoarthritis, the most common form of arthritis, is a major cause of long-term disability in adults in North America
2) It is primarily a disease of articular cartilage, its hallmarks being extracellular matrix degradation and altered chondrocyte metabolism
3) Loss of cartilage leads to bone-on-bone contact in synovial joints with rapid deterioration of movement and function