Lower Limb Bones

EXTREMITY ANATOMY

Bones of the Lower Limb

  • The lower extremity is specialized for:
    • Locomotion
    • Supporting body weight
    • Maintenance of balance
  • Major bones include:
    • Os coxae (Hip bone)
    • Femur (Thigh bone)
    • Tibia (Shin bone)
    • Fibula (Lateral bone of the leg)
    • Patella (Kneecap)
    • Tarsals (Ankle bones)
    • Metatarsals (Foot bones)
    • Phalanges (Toe bones)

Lower Extremity Development

  • The lower extremity undergoes a developmental process similar to that of the upper extremity (UE).
  • The lower extremity rotates medially (pronation) such that the great toe is positioned medially.
  • This torsion is incomplete at birth; infants can easily oppose the soles of their feet without difficulty.
  • Rotation reaches completion with the mastery of bipedal ambulation, emphasizing the importance of walking in development.

Lower Extremity Regions

  • Key regions include:
    • Gluteal Region:
    • Contains gluteal muscles.
    • Includes hip joint.
    • Composed of pelvis elements (ilium, ischium, pubis).
    • Thigh:
    • Contains the femur.
    • Includes knee details (distal femur, patella, proximal tibia and fibula).
    • Popliteal Fossa:
    • Space behind the knee joint.
    • Leg:
    • Comprises tibia and fibula.
    • Encompasses calf region.
    • Ankle (Talocrural Region):
    • Joint between the leg and foot.
    • Foot:
    • Comprises tarsus (group of bones in the ankle), metatarsus, and phalanges.

Sesamoid Bones of the Foot

  • The most common sesamoid bone is found in the flexor hallucis brevis tendon at the metatarsophalangeal joint of digit I (the big toe).

Weight Transfer through the Lower Limb

  • Body weight is transferred as follows:
    • From the spine through the sacroiliac (SI) joints to the pelvic girdle.
    • Through the hip joints to the femurs.
    • From the femur to the knee.
    • From the knee through the ankle to the talus and then through the foot to the ground.

Os Coxae (Hip Bone)

  • Composed of three parts:
    • Ilium
    • Ischium
    • Pubis
  • United by tri-radiate cartilage.
  • Fusion begins at ages 15-17 years and completes at 20-25 years.
Os Coxae - Ilium
  • Forms the superior part of the hip and acetabulum.
  • The medial portion consists of thick columns for weight-bearing.
  • The lateral portion is thinner (known as the ala), providing attachment sites for lower extremity muscles.
  • Key features include:
    • Anterior Superior Iliac Spine (ASIS)
    • Anterior Inferior Iliac Spine (AIIS)
    • Tubercle of the Iliac Crest
    • Posterior Superior Gluteal Line
    • Posterior Inferior Gluteal Line
    • Iliac Fossa for iliacus muscles attachment.
    • Greater Sciatic Notch
    • Body of Ilium joins the pubis and ischium forming the acetabulum.
Os Coxae - Ischium
  • Forms the posterior inferior part of the acetabulum and hip bone.
  • Key features include:
    • Body (joins the ilium and superior ramus of the pubis to form the acetabulum).
    • Ramus (joins the inferior ramus of the pubis, forming ischiopubic ramus).
    • Ischial spine, ischial tuberosity, and lesser sciatic notch serving as a trochlea for muscles emerging from the pelvis.
Os Coxae - Pubis
  • Key features include:
    • Superior ramus
    • Inferior ramus
    • Pubic symphysis (joined at the midline).
    • Pubic crest.
Os Coxae in Anatomical Position
  • Anterior superior iliac spine and anterior superior pubis are aligned vertically.
  • The symphysial surface is vertical.
  • Acetabulum faces inferolaterally, with the acetabular notch directed inferiorly.
Obturator Foramen
  • Bounded by the pubis, ischium, and their rami.
  • Closed by the obturator membrane, except for the obturator canal.
Acetabulum
  • Articulates with the head of the femur.
  • Formed by all three bones of the hip (ilium, ischium, pubis).
  • Features include:
    • Incomplete inferior margin.
    • Acetabular notch and transverse acetabular ligament.
    • Acetabular fossa is a superior extension of the acetabulum floor.
    • The lunate surface of the acetabulum is the actual articular surface for the femur.

Differences in Pelvic Structure by Gender

  • Female pelvis:
    • Larger pelvic outlet (> 90º).
    • Sacrum tilted back.
    • Ilia spread wider.
  • Male pelvis:
    • Smaller pelvic outlet (< 90º).
    • Sacrum tilted forward.
    • Ilia are closer together.
  • Note the inter-ischial spine distance and angle as additional distinctions.

Femur

  • The longest and heaviest bone in the body.
  • Length equals approximately 1/4th of overall height.
  • Head is approximately 2/3rds of a sphere and covered with hyaline cartilage.
  • Fovea Capitis: A pit for the round ligament.
  • Major features include:
    • Greater Trochanter: Lateral and superior; serves as attachment for abductors and rotators.
    • Intertrochanteric Line: A line between greater and lesser trochanters.
    • Lesser Trochanter: Medial and inferior; extends medially from the junction of the neck and shaft, serves as attachment for iliopsoas (primary thigh flexor).
Additional Features of the Femur
  • Quadrate Tubercle and Intertrochanteric Crest.
  • Neck: Trapezoidal in shape, critical for the angle of inclination.
  • Shaft: Slightly bowed anteriorly.
  • Linea Aspera: Has medial and lateral lips, providing attachment for adductors, as well as:
    • Gluteal Tuberosity
    • Pectineal Line
    • Medial and Lateral Supracondylar Lines
    • Adductor Tubercle
    • Intercondylar Fossa
    • Medial and Lateral Condyles
    • Medial and Lateral Epicondyles
Angles of the Femur
  • Angle of Inclination: Ranges from 115° to 140°, larger in females and greatest at birth, diminishing with age; influences femur mobility.
  • Angle of Declination (Torsion Angle): Angle between the head/neck and the angle of the femoral condyles, measuring 7° in males, 12° in females.

Patella

  • The patella is a sesamoid bone that forms within the patellar tendon.
  • Structure includes:
    • Base: Superior border.
    • Apex: Inferior border.
    • Articular Surface: Covered by cartilage.

Tibia

  • The second largest bone in the body, primarily responsible for weight-bearing.
  • Articulates with:
    • Femur at the medial and lateral condyles.
    • Talus (ankle joint).
    • Fibula (articular facet at the head and notch at the inferior fibula).
  • Forms the medial malleolus (inner ankle bone).
  • Contains a soleal line on its posterior surface.
  • The interosseous membrane connects the tibia and fibula.

Fibula

  • Located posterior-lateral to the tibia.
  • Functions as an attachment site for muscles.
  • Forms the lateral malleolus (outer ankle bone).
  • Positioned 1 cm distal to the medial malleolus.
  • Both tibia and fibula are permanently in a pronated position (the great toe is medial compared to the lateral thumb in the hand).

Ankle - Tarsus

  • The tarsus is formed by seven bones:
    • Talus: Articulates with the leg bones and the navicular bone; features head, neck, and body; the trochlea grips by the malleoli, supporting body weight, distributing weight between the calcaneus and forefoot, with no muscular or tendinous attachments.
    • Calcaneus: Positioned between the talus and cuboid; provides support through the talar shelf; the medial calcaneal tuberosity is a weight-bearing prominence; lateral and anterior aspects also present weight-bearing prominence; fibular trochlea for tendon passage.
    • Cuboid Bone: Located in the foot.
    • Navicular Bone: Positioned between the talus and cuneiforms; navicular tuberosity allows tendon attachment; part of the longitudinal arch of the foot.
    • Cuneiform Bones: Comprised of medial, intermediate, and lateral cuneiforms, each articulating with the navicular.
    • Metatarsals: Five long bones in the foot.
    • Phalanges: Toe bones, including proximal, middle, and distal phalanges.