Lab 3: Lower Appendicular Skeleton

Structure of the Pelvis and Innominate Bones

• Pelvic Girdle Overview:
  • The full structure of the pelvis is formed by four primary skeletal components:     $\text{Pelvis} = \text{Right Innominate} + \text{Left Innominate} + \text{Sacrum} + \text{Coccyx}$

• Innominate Bone (Os Coxae):
  • Each innominate bone is formed by the fusion of three separate bones:     $\text{Innominate (Os Coxae)} = \text{Ilium} + \text{Ischium} + \text{Pubis}$

Detailed Landmarks of the Innominate Bone

Landmarks of the Ilium

• Iliac Crest: The superior border of the ilium.
• Iliac Fossa: The large, smooth, concave surface on the medial aspect of the ilium.
• Auricular Surface: Rough, ear-shaped surface located on the medial aspect, articulating with the sacrum.
• Anterior Superior Iliac Spine (ASIS): Anterior termination of the iliac crest.
• Anterior Inferior Iliac Spine (AIIS): Prominence located inferior to the ASIS.
• Posterior Superior Iliac Spine (PSIS): Posterior termination of the iliac crest.
• Posterior Inferior Iliac Spine (PIIS): Prominence located inferior to the PSIS.
• Greater Sciatic Notch: Large notch on the posterior aspect inferior to the PIIS, allowing passage for nerves and blood vessels.

Landmarks of the Ischium

• Ischial Spine: Pointed process extending posteriorly below the greater sciatic notch.
• Lesser Sciatic Notch: Indentation located directly inferior to the ischial spine.
• Ischial Tuberosity: Heavy, rough, inferior projection that supports body weight when sitting.

Landmarks of the Pubis

• Pubic Symphysis: Amphiarthrodial fibrocartilaginous joint joining the pubic bones anteriorly along the midline.
• Pubic Tubercle: Prominent forward-projecting tubercle lateral to the pubic symphysis on the superior pubic ramus.
• Pubic Angle / Arch: Inverted V-shaped arch formed inferior to the pubic symphysis by the convergence of the inferior rami of the ischium and pubis.

Additional Pelvic Structures and Joints

• Acetabulum: Deep, cup-shaped lateral socket formed by the junction of the ilium, ischium, and pubis that articulates with the head of the femur.
• Obturator Foramen: Large opening enclosed by the ischium and pubis rami.
• Sacroiliac Joint: Articular junction located posteriorly between the auricular surface of the ilium and the sacrum.

Landmarks of the Femur and Patella

Femur Structure and Features

• Head: Smooth spherical proximal articular surface that fits into the acetabulum.
• Neck: Constricted region connecting the head to the femoral shaft.
• Fovea Capitis: Small central pit on the femoral head for ligamentous attachment.
• Greater Trochanter: Large, blunt lateral elevation for muscle attachment.
• Lesser Trochanter: Conical projection on the posteromedial aspect, inferior to the neck.
• Intertrochanteric Crest: Prominent ridge on the posterior side connecting the greater and lesser trochanters.
• Gluteal Tuberosity: Rough vertical ridge on the proximal posterior shaft lateral to the midline.
• Linea Aspera: Prominent longitudinal ridge running down the posterior aspect of the femoral shaft.
• Adductor Tubercle: Small projection located superior to the medial epicondyle.
• Medial Epicondyle: Projection located proximal to the medial condyle.
• Medial Condyle: Smooth rounded articular process on the distal medial femur.
• Intercondylar Fossa: Deep depression between the medial and lateral condyles on the posterior aspect.
• Lateral Epicondyle: Projection located proximal to the lateral condyle.
• Lateral Condyle: Smooth rounded articular process on the distal lateral femur.
• Popliteal Surface: Smooth triangular space on the posterior distal femoral surface superior to the intercondylar fossa.
• Patellar Surface: Smooth anterior surface extending between condyles for articulation with the patella.

Patella Anatomy

• Base: Superior broad border of the patella.
• Apex: Pointed inferior tip of the patella.
• Articular Facets: Smooth posterior facets that articulate with the patellar surface of the femur.
• Quadriceps Tendon: Tendinous attachment extending from the quadriceps muscle group down to the base of the patella.
• Patellar Ligament (Tendon): Fibrous band extending from the apex of the patella to attach onto the tibial tuberosity.

Tibiofemoral Joint (Knee Joint)

• Cruciate Ligaments: Internal stabilizing ligaments within the capsule:
  • Anterior Cruciate Ligament (ACL): Prevents anterior displacement of the tibia.
  • Posterior Cruciate Ligament (PCL): Prevents posterior displacement of the tibia.
• Collateral Ligaments: Extracapsular stabilizing ligaments:
  • Medial Collateral Ligament (MCL): Provides medial stabilization.
  • Lateral Collateral Ligament (LCL): Provides lateral stabilization.
• Menisci: Fibrocartilaginous pads deepening the articular surfaces:
  • Medial Meniscus: C-shaped fibrocartilage pad on the medial tibial plateau.
  • Lateral Meniscus: Fibrocartilage pad on the lateral tibial plateau.

Anatomy of the Tibia and Fibula

Tibia Landmarks

• Head (Tibial Plateau): Broad expanded proximal end.
• Medial Condyle: Medial expansion on the proximal end.
• Intercondylar Eminence: Prominent ridge between the articular facets on the tibial plateau.
• Lateral Condyle: Lateral expansion on the proximal end.
• Tibial Tuberosity: Prominent anterior elevation for insertion of the patellar ligament.
• Anterior Tibial Crest: Sharp anterior border forming the shin ridge.
• Medial Malleolus: Distal medial process forming the inner ankle articulation.

Fibula Landmarks

• Proximal End (Head of Fibula): Rounded proximal expansion articulating with the lateral condyle of the tibia.
• Distal End: Distal extremity articulating with the talus and tibia.
• Lateral Malleolus: Prominent lateral process at the distal end forming the outer ankle projection.
• Malleolar Fossa: Posterior depression on the medial surface of the lateral malleolus.

Bones and Joints of the Foot

Tarsal Bones

• Talus: Superior tarsal bone articulating with the tibia and fibula ("ankle").
• Calcaneus: Heel bone ("calcan" ~ heel).
• Navicular: Boat-shaped tarsal bone anterior to the talus ("navicul" ~ little boat/ship).
• Medial Cuneiform: Medial wedge-shaped tarsal bone ("cune" ~ wedge).
• Intermediate Cuneiform: Middle wedge-shaped tarsal bone.
• Lateral Cuneiform: Lateral wedge-shaped tarsal bone.
• Cuboid: Cube-shaped tarsal bone on the lateral side ("cubo" ~ cube).

Mnemonic for Tarsal Bones

• "Cheap Tequila Causes Naughty Love In Mexico"
  • Cheap: Calcaneus
  • Tequila: Talus
  • Causes: Cuboid
  • Naughty: Navicular
  • Love: Lateral Cuneiform
  • In: Intermediate Cuneiform
  • Mexico: Medial Cuneiform

Metatarsals and Phalanges

• Metatarsals:
  • Five long bones numbered I to V from medial (great toe/hallux) to lateral (pinky toe).
• Phalanges:
  • Phalanx is the singular term.
  • Proximal Phalanx: Present in digits 1 through 5.
  • Middle Phalanx: Present in digits 2 through 5 (absent in the great toe / hallux).
  • Distal Phalanx: Present in digits 1 through 5.
• Mandatory Identification Rule: When labeling any metatarsal or phalanx, the associated numeric digit MUST be explicitly included (e.g., Metatarsal V/5, Distal phalanx of 3rd digit / Distal phalanx III/3).

Joints of the Foot

• Metatarsophalangeal Joint(s) [1-5]: Articulations between metatarsals and proximal phalanges for digits 1 through 5.
• Proximal Interphalangeal Joint(s) [2-5]: Articulations between proximal and middle phalanges for digits 2 through 5.
• Distal Interphalangeal Joint(s) [2-5]: Articulations between middle and distal phalanges for digits 2 through 5.