Bones of the Lower Limb and Vertebral Anatomy – Study Notes

Common Vertebrae Anatomy

  • Vertebrae are divided into cervical, thoracic, lumbar, and sacral regions. While each region has distinguishing characteristics, all vertebrae share some common anatomy.
  • Identify the following landmarks:
    • Body
    • Neural arch
    • Articular Process
      • Superior
      • Inferior
    • Lamina
    • Pedicle
    • Spinous process
    • Transverse process
    • Vertebral notch
    • Superior
    • Inferior
    • Intervertebral foramen
    • composed of superior and inferior vertebral notches
    • Vertebral foramen
    • Vertebral canal
    • composed of several vertebral foramina
    • Intervertebral discs
  • Key concept: The vertebral column provides protection for the spinal cord, supports body weight, and allows flexibility through articulations at each vertebra.

Sacral Vertebrae Anatomy

  • The 55 vertebrae of the sacrum are fused together, creating a unique, shield-shaped structure with the alae forming the prominent wings on either side.
  • The posterolateral aspects of each alae form the auricular/articular surface, where the sacrum articulates with the ilium of the pelvis.
  • The sacrum acts as an attachment point for many ligaments of the pelvis, creating a sturdy girdle for weight bearing and stability.
  • The sacral promontory articulates with the 5th lumbar vertebra, marking the border of the pelvic inlet.
  • Nerve roots of the cauda equina enter the sacral canal, with the majority exiting through the foramina of the sacrum.
  • Upon observing the anterior aspect of the sacrum, you will see many sacral nerves exiting through the anterior sacral foramina and merging to form the large sciatic nerve. Various cutaneous nerves exit through the posterior sacral foramina. The handful of nerves that do not exit through the sacral foramina will exit at the distal end of the sacral canal called the sacral hiatus.
  • Identify the following landmarks on the sacrum:
    • Fused vertebrae (S11-S55)
    • Superior surface
    • Body of first sacral vertebra
    • Sacral promontory
    • Alae
    • Superior articular process
    • Anterior surface
    • Anterior sacral foramina
    • Lateral surface
    • Auricular/articular surface
    • Posterior surface
    • Posterior sacral foramina
    • Sacral canal
      • Sacral hiatus

Anterior, Posterior, Lateral Views of Sacrum

  • Visual landmarks include:
    • Anterior view: Body of first sacral vertebra, Sacral promontory, Alae, Superior articular process
    • Posterior view: Posterior sacral foramina, Sacral canal, Sacral hiatus
    • Superior view: Sacral promontory, Superior articular process
    • Lateral view: Auricular/articular surface

Bones of the Lower Limb

  • Identify the bones that compose the lower limb, then dive into specific bony landmarks in the sections below:
    • Hip Bone (pelvic bone) - os coxae
    • Ilium
    • Ischium
    • Pubis
    • Thigh
    • Femur
    • Leg
    • Tibia
    • Fibula
    • Ankle
    • Tarsals: Talus, Calcaneus, Navicular, Cuboid, Medial Cuneiform, Intermediate Cuneiform, Lateral Cuneiform
      • Notes: Calcaneus has groove for flexor hallucis longus tendon, sustentaculum tali, calcaneal tuberosity; Cuboid has groove for fibularis longus tendon.
    • Foot
    • Metatarsals (numbered 1-5 medial to lateral)
    • Digits (numbered 1-5 medial to lateral)
    • Phalanx (singular) || Phalanges (plural)
      • Digit 1 – divided into proximal and distal
      • Digits 2-5 – divided into proximal, middle, and distal

Hip Bone

  • The pelvis is comprised of three separate bones: the ilium (superiorly), the ischium (inferolaterally), and the pubis (inferomedially). All three bones articulate with each other forming the acetabulum, a socket on the lateral aspect of the pelvis for articulation with the head of the femur.
  • The pelvis acts as the weight-bearing girdle of the body, distributing weight from the spine equally to each femur as well as an attachment site for many strong abductors and lateral rotators of the femur.
  • Although containing the same structures, the female pelvis is wider to allow for a larger pelvic outlet to aid in childbirth.
  • Begin your examination of the pelvis with the largest and most superior of the three bones, the ilium.
    • Ilium
    • Anterior concave aspect forms the iliac fossa
    • Superior aspect forms the convex iliac crest
    • Iliac spines (anterior superior iliac spine [ASIS], anterior inferior iliac spine [AIIS], posterior superior iliac spine [PSIS], posterior inferior iliac spine [PIIS])
    • Greater Sciatic Notch
      • Forms the superior and lateral borders of the greater sciatic foramen, with borders being the sacrum medially and the sacrospinous ligament inferiorly
    • Auricular/articular surface (located between and slightly anterior to PSIS and PIIS)
    • Iliac tuberosity
    • Gluteal surface (attachment for gluteal muscles)
    • Pubis
    • Most anterior bone; U-shaped; composed of superior ramus and inferior ramus
    • Lateral aspect of the superior ramus forms the anterior portion of the acetabulum
    • Rami meet medially to form the body of the pubis
    • Superior border of the body is the pubic crest; apex bears the pubic tubercle
    • Left and right pubic bones meet at the pubic symphysis
    • Ischium
    • Most posterior bone; attachment site for most of the posterior thigh at the ischial tuberosity
    • Body
      • Lesser Sciatic Notch (slightly superomedially to the ischial tuberosity)
      • Ischial Spine
    • Ramus
      • Ischial Tuberosity
  • Identify the following structures on the hip bone:
    • Ilium
    • Iliac Crest
      • Anterior Superior Iliac Spine (ASIS)
      • Anterior Inferior Iliac Spine (AIIS)
      • Posterior Superior Iliac Spine (PSIS)
      • Posterior Inferior Iliac Spine (PIIS)
    • Greater Sciatic Notch
    • Iliac Fossa
      • Auricular/Articular Surface
      • Iliac Tuberosity
    • Gluteal Surface
    • Pubis
    • Body
      • Pubic Crest
      • Pubic Tubercle
    • Superior Ramus
    • Inferior Ramus
    • Ischium
    • Body
      • Lesser Sciatic Notch
      • Ischial Spine
    • Ramus
      • Ischial Tuberosity

Thigh (Between Hip and Knee)

  • The femur is the only bone in the thigh. A very strong, deep articulation is formed between the head of the femur and the acetabulum of the hip.
  • The femur is the strongest and heaviest bone in the human body, able to resist from 1800-25001800\text{-}2500 pounds of force.
  • Proximal landmarks:
    • Greater Trochanter (attachment point for several gluteal muscles)
    • Lesser Trochanter (posterior and medial, inferior to the neck)
    • Intertrochanteric Line (ridge on the anterior surface connecting the greater and lesser trochanters)
    • Pectineal Line (ridge on the posterior surface running inferior from the lesser trochanter)
    • Intertrochanteric Crest (ridge on the posterior surface connecting the trochanters)
    • Gluteal Tuberosity (on the posterior body)
    • Linea Aspera (sharp ridge on the posterior shaft; attachment for many thigh muscles)
    • Popliteal Surface (triangular area on the posterior distal shaft created by the two ridges of the linea aspera)
    • Patellar Articular Surface (anterior distal surface between the medial and lateral expansions)
  • Distal landmarks:
    • Lateral Condyle (smooth portion of the distal lateral expansion)
    • Lateral Epicondyle (rough, proximal lateral side of the condyle)
    • Medial Condyle (smooth portion of the distal medial expansion)
    • Medial Epicondyle (rough, proximal medial portion)
    • Adductor Tubercle (on the superior, medial border of the medial epicondyle)
  • Gluteal surface (as labeled on the femur)

Leg (Between Knee and Ankle)

  • The tibia is the main weight-bearing bone of the leg, articulating with the femur at the knee.
  • Proximal end features:
    • Medial Condyle
    • Lateral Condyle
    • Intercondylar Eminence (medial and lateral)
    • Tibial Tuberosity (on the anterior surface just below the condyles)
  • Body/Shaft:
    • Soleal Line (attachment site for muscles)
  • Distal end:
    • Medial Malleolus (medial projection of the tibia)
  • The fibula is a non-weight-bearing bone lateral to the tibia.
    • Head (proximal)
    • Neck
    • Lateral Malleolus (distal end; forms the lateral protrusion of the ankle; fracture of the lateral malleolus is the most common ankle fracture)
  • Identify the following landmarks:
    • On the tibia:
    • Proximal end: Medial Condyle, Intercondylar Eminence, Lateral Condyle, Tibial Tuberosity
    • Body/Shaft: Soleal Line
    • Distal end: Medial Malleolus
    • On the fibula:
    • Head
    • Neck
    • Lateral Malleolus

Ankle & Foot

  • The ankle is a complex joint where the tibia and fibula articulate with the talus; the talus articulates with the calcaneus (heel), which is the attachment site of the calcaneal tendon.
  • The calcaneus has important features:
    • Groove for flexor hallucis longus tendon
    • Sustentaculum tali
    • Calcaneal tuberosity
  • The tarsal bones (located proximal to the metatarsals) include:
    • Talus
    • Calcaneus
    • Navicular
    • Medial Cuneiform
    • Intermediate Cuneiform
    • Lateral Cuneiform
    • Cuboid
    • For the Cuboid, there is a groove for the fibularis longus tendon
  • Distal to the tarsal bones are the metatarsals and phalanges:
    • Metatarsals (numbered 1−51-5, medial to lateral)
    • Digits (numbered 1−51-5, medial to lateral)
    • Phalanx (singular) || Phalanges (plural)
    • Digit 1 – divided into proximal and distal
    • Digits 2-5 – divided into proximal, middle, and distal
  • Additional notes:
    • The foot contains 2828 bones in total, with a wide variety of joints and movements that adapt to biomechanical functions of different regions.
    • The Groove of Flexor Hallucis Longus Tendon and Groove of Fibularis Longus Tendon are key landmarks on the calcaneus and cuboid/navicular areas, respectively.
    • Plantar view and dorsal view are used to visualize the orientation of bones and grooves (as illustrated in the diagrams).
  • Practical implications:
    • Understanding these landmarks is essential for interpreting X-rays and planning orthopedic procedures.
    • Knowledge of the 28 bones in the foot and their articulations underpins the study of gait and weight distribution during movement.

Connections and Practical Relevance

  • Foundational principles: Axial vs. appendicular skeleton; articulations and joint types (e.g., ball-and-socket at hip, hinge at knee, synovial joints of the ankle and foot).
  • Real-world relevance: Injury risk in the lower limb (e.g., lateral malleolus fractures, hip dislocations, sacral injuries) and implications for mobility and rehabilitation.
  • Ethical/philosophical/practical implications: Accurate anatomy knowledge supports safe clinical practice, imaging interpretation, and respectful patient care during examinations and procedures.

Quick Reference: Key Numerical and Structural Points

  • Sacrum vertebrae: 55 fused vertebrae (S11-S55)
  • Digits in the foot: 1−51-5 (medial to lateral)
  • Metatarsals: 1−51-5 (medial to lateral)
  • Total foot bones: 2828
  • Femur weight-bearing capacity: 1800−25001800-2500 pounds of force
  • Intervertebral foramen formed by superior and inferior vertebral notches
  • Anterior sacral foramina; Posterior sacral foramina
  • Sacral hiatus at the distal end of the sacral canal
  • Ilium, Ischium, Pubis form the acetabulum
  • Lateral malleolus fracture: most common ankle fracture
  • Notation examples: $$ASIS, AIIS, PSIS, PIIS, greater sciatic notch, auricular surface, ilium tuberosity, gluteal surface, pubic tubercle, pubic crest, adductor tubercle, soleal line, tibial tuberosity, sustentaculum tali, groove for flexor hallucis longus tendon, groove for fibularis longus tendon