Bones and Bony Landmarks of the Lower Extremity: Study Notes

Bones and Bony Landmarks of the Lower Extremity

Functional and Structural Features

The lower extremity bones possess distinct projections, depressions, and openings that serve as attachment points for muscles and ligaments, form joints, or allow passage of nerves and blood vessels. Understanding these features is essential for identifying bones and their functions.

• Projections (Muscle/Ligament Attachment):

  • Crest: Narrow ridge (e.g., iliac crest).

  • Epicondyle: Raised area above condyle.

  • Linea aspera: Less prominent ridge.

  • Spine: Sharp, slender projection.

  • Trochanter: Large, blunt projection (femur).

  • Tubercle: Small, rounded projection.

  • Tuberosity: Large, rounded projection (e.g., tibial tuberosity).

• Projections (Form Joints):

  • Condyle: Rounded articular projection.

  • Facet: Smooth, flat surface.

  • Ramus: Armlike bar of bone.

• Depressions & Openings:

  • Fissure: Narrow slit.

  • Foramen: Round opening (e.g., obturator foramen).

  • Fossa: Shallow depression (e.g., iliac fossa).

  • Meatus: Canal-like passage.

  • Notch: Indentation at edge.

  • Sinus: Cavity within bone.

Major Bones and Landmarks of the Lower Extremity

Pelvic Girdle (Coxal Bone)

The pelvic girdle supports the trunk and connects the lower limbs to the axial skeleton. Each coxal bone is composed of three fused bones: the Ilium, Ischium, and Pubis.

• Ilium:

  • Anterior Superior Iliac Spine (ASIS): Palpable, used for side identification.

  • Posterior Superior Iliac Spine (PSIS): Near sacroiliac joint.

  • Iliac Crest: Superior border, site of muscle attachment.

  • Iliac Fossa: Smooth concave surface on medial side.

  • Greater Sciatic Notch: Large notch below the PSIS.

  • Sacroiliac Articulating Surface: Articulates with sacrum.

• Ischium:

  • Ischial Tuberosity: Weight-bearing when sitting; muscle attachment.

  • Lesser Sciatic Notch: Below ischial spine.

• Pubis:

  • Superior Ramus: Connects to ilium.

  • Inferior Ramus: Connects to ischium.

  • Obturator Foramen: Large opening for nerves/vessels.

• Male vs. Female Pelvis:

  • Male: Narrower, deeper, heart-shaped pelvic inlet.

  • Female: Wider, shallower, round pelvic inlet for childbirth.

Sacrum

• Sacroiliac Articulating Surface: Articulates with ilium.

• Location: Between two coxal bones, above coccyx.

Femur

The femur is the longest and strongest bone in the body, forming the thigh.

• Head of Femur: Proximal end; articulates with acetabulum of pelvis.

• Neck of Femur: Common fracture site.

• Greater Trochanter: Lateral projection; muscle attachment.

• Lesser Trochanter: Medial and posterior; muscle attachment.

• Intertrochanteric Fossa: Between condyles on posterior side.

• Linea Aspera: Ridge on posterior shaft.

• Medial & Lateral Condyles: Articulate with tibia.

• Medial & Lateral Epicondyles: Above condyles; ligament attachment.

• Patellar Surface: Anterior, articulates with patella.

Patella

• Apex of Patella: Pointed inferior tip.

• Base: Broad superior portion.

Tibia

• Tibial Tuberosity: Anterior; patellar ligament attachment.

• Medial & Lateral Condyles: Articulate with femur.

• Medial Malleolus: Inner ankle bump.

Fibula

• Head of Fibula: Proximal end; articulates with tibia.

• Lateral Malleolus: Outer ankle bump.

Foot

• Tarsals (7):

  • Calcaneus: Heel bone.

  • Talus: Articulates with tibia/fibula.

  • Navicular: In front of talus.

  • Cuboid: Lateral side.

  • Medial, Intermediate, Lateral Cuneiforms: Articulate with metatarsals.

• Metatarsals (5):

  • Numbered I–V from medial (big toe) to lateral.

• Phalanges (14):

  • Each toe: Proximal, Middle, Distal (except big toe – only proximal & distal).

Summary Table: Major Bones and Key Landmarks of the Lower Extremity

Bone	Key Landmarks	Function/Attachment
Ilium	Iliac crest, ASIS, PSIS, iliac fossa, greater sciatic notch	Muscle attachment, pelvic support
Ischium	Ischial tuberosity, lesser sciatic notch	Weight-bearing, muscle attachment
Pubis	Superior/inferior rami, obturator foramen	Pelvic structure, passage for nerves/vessels
Femur	Head, neck, greater/lesser trochanter, condyles, epicondyles, linea aspera	Thigh support, muscle/ligament attachment
Tibia	Tibial tuberosity, condyles, medial malleolus	Weight-bearing, knee/ankle joint
Fibula	Head, lateral malleolus	Stabilizes ankle
Foot	Calcaneus, talus, navicular, cuboid, cuneiforms, metatarsals, phalanges	Support, movement, balance

Additional info:

• The acetabulum is the socket in the pelvis that receives the head of the femur, forming the hip joint.

• The sacroiliac joint is a strong, weight-bearing synovial joint between the sacrum and ilium.

• The patella increases the leverage of the quadriceps muscle during knee extension.

• The medial and lateral malleoli form the prominent bumps on each side of the ankle.