Anatomie Du Membre Inférieur - Chapitre 1 - Ostéologie du membre inférieur

Dibamus Cursoris: The First Known Biped

Overview of Dibamus Cursoris

• The Dibamus cursoris utilized its lower limbs for movement, achieving speeds of up to 24 km/h to escape predators.

• It is recognized as the first known bipedal reptile, existing approximately 290 million years ago.

Anatomy and Functionality

• The pelvis serves as a boundary between the abdominal cavity and pelvic cavity, similar to the role of the shoulder girdle in upper limb mobility.

• The pelvis transmits weight and mechanical stress from the spine to the lower limbs, contrasting with the shoulder girdle's focus on mobility.

Pelvic Structure

• The pelvic bones (os coxae) are connected at the front by the pubic symphysis and at the back by sacroiliac joints, which provide stability under mechanical loads.

• Key articulations include acetabulum where contact occurs between pelvis and femur, forming what is known as the pelvic ring.

Embryological Development

• The os coxae consists of three elements centered around a Y-shaped cartilage that forms the acetabulum: ilium, ischium, and pubis.

• Each element contributes differently; for instance, ilium forms a posterior wing while ischium participates in forming part of the pelvic floor.

Surface Features of Os Coxae

• The exopelvienne surface has three regions: gluteal face for muscle attachment, area around acetabulum for hip joint articulation, and perimeter surrounding obturator foramen.

• Notable features include iliac crest (upper border), anterior superior iliac spine (ventral termination), and various depressions indicating muscle attachment sites.

Anatomical Structures of the Hip and Pelvis

Overview of the Acetabulum and Gluteal Lines

• The depression above the acetabulum is defined by the inferior gluteal line, which is nearly horizontal.

• The anterior gluteal line is oblique, while the posterior gluteal line is vertical and near the posterosuperior angle of the os coxae.

Ligamentous Structures and Membranes

• The obturator membrane covers the obturator foramen but allows passage at its upper part, known as the obturator canal.

• The inguinal ligament extends from the anterior superior iliac spine to the pubic tubercle; a band called iliopectineal ligament connects it to the pubis.

Internal View of Os Coxae

• In an endopelvic view, key structures include:

• Iliac crest (convex upwards)

• Anterior superior iliac spine

• Pubic tubercle

• Obturator foramen

Ischial Tuberosity and Related Structures

• Notable features include:

• Ischial tuberosity

• Greater sciatic notch

• Lesser sciatic notch

• Iliac tuberosity where fibrous structures attach.

Muscular Insertions and Articulations

• The arcuate line limits what is known as iliac fossa, a smooth concave surface for muscle insertion.

• The auricular surface articulates with sacrum; it has an L-shape and concaves backward.

Fibrous Elements in Pelvic Anatomy

• The obturator membrane closes off the obturator foramen while allowing cranial structures through.

• Sacrotuberous ligament originates from posterior iliac spines converging towards ischial tuberosity with an arc-like extension called falciform process.

Ligaments Uniting Pelvic Ring

• Key ligaments include:

• Sacrotuberous ligament terminating at ischial tuberosity.

• Sacrospinous ligament located behind sacrotuberous ligament.

Anterior Sacroiliac Ligament Insights

• Anterior sacroiliac ligaments are weak but reinforce joint capsule anteriorly.

Fémur Structure Overview

• A diagram shows:

• Ventral face of femur on left,

• Dorsal face on right,

Anatomical Features of the Femur and Tibia

Overview of the Femur Structure

• The distal part of the femur corresponds to the distal epiphysis, while the proximal epiphysis features a femoral head covered in cartilage, resembling one-third of a sphere.

• Behind the femoral neck lies the greater trochanter, with a smaller relief on the medial side known as the lesser trochanter; both are connected by an intertrochanteric crest.

• The anterior face has an intertrochanteric line that is less pronounced than its posterior counterpart but distinctly separates the greater and lesser trochanters.

Key Lines and Reliefs on Femur

• On the dorsal side, there is an elongated bony relief called the linea aspera; its medial lip leads to a spiral line that wraps around to meet at the intertrochanteric line.

• The distal epiphysis shows two condyles: medial and lateral. Between them lies an intercondylar fossa, while on its ventral side is found the femoral trochlea.

Angles and Axes Related to Femur

• The cervical axis runs through both femoral head and neck centers, while another axis passes through diaphyseal center; these help define anatomical angles.

• The cervico-diaphyseal angle measures approximately 130°, with variations leading to either coxa vara (angle < 130°) or coxa valga (angle > 130°).

• A cranial view reveals anteversion of about 15°, while a vertical line drawn indicates a physiological valgus angle of approximately 7°.

Internal Structure of Proximal Epiphysis

• The internal structure is robust due to mechanical stress transmission; it features trabecular structures adapted for load-bearing.

• There are principal trabecular systems supporting body weight divided into cephalodiaphyseal (blue) and cephalo-cervical (red), alongside accessory systems represented in green and gray.

Fracture Vulnerability in Femur

• A notable area of weakness exists where fractures commonly occur—specifically at either femoral neck or pertrochanteric regions.

Anatomy of Tibia and Fibula

Structure of Proximal Tibia

• The tibia is located anteriorly and medially in relation to fibula; its proximal epiphysis consists of two condyles—medial and lateral—with articular surfaces separated by an interarticular space.

Features on Distal End of Tibia

• At this level, there’s a prominent tuberosity known as tibial tuberosity on its ventral surface along with an infracondylar tubercle laterally positioned.

Diaphyseal Characteristics

• The tibial diaphysis has multiple faces: medial, lateral, dorsal, with an anterior ridge termed anterior tibial crest being palpable under skin.

Distal Epiphysis Configuration

• This section appears flattened from front to back; it extends laterally into malleolus formation which is higher than lateral malleolus.

Fibula's Role

Anatomy of the Foot: Key Structures and Functions

Overview of the Foot Skeleton

• The fibula contributes to the formation of the lateral malleolus, which is positioned lower than the medial malleolus. Together, they create what is known as the bimalleolar clamp.

• The foot skeleton consists of 26 articulated bones divided into three groups: posterior tarsus, anterior tarsus, and metatarsals.

Tarsal Bones and Their Arrangement

• The posterior tarsus includes the calcaneus (heel bone), which is topped by the talus that articulates with the bimalleolar clamp formed by tibia and fibula.

• The anterior tarsus comprises several bones: cuboid (lateral), navicular (medial), and three cuneiform bones located anteriorly.

Articulations in the Foot

• Between metatarsals and phalanges lies the metatarsophalangeal joint; each toe has three phalanges except for the big toe, which has two.

• A significant structure called the support triangle forms at specific contact points on foot during weight-bearing activities.

Weight Distribution During Movement

• During walking, weight shifts onto what is termed as the propulsion triangle, contrasting with a support triangle used when standing still.

Medial View of Foot Structure

• The talus articulates with both tibia and fibula; it consists of a body and an anterior head that connects to navicular bone.

• Below talus lies calcaneus featuring a prominent tuberosity that contacts ground surfaces; this area supports various ligaments.

Arches of the Foot

• Two longitudinal arches exist: lateral arch from calcaneal tuberosity to fifth metatarsal head, and medial arch extending to first metatarsal head.

• A transverse arch also exists across different levels in foot structure providing additional support during movement.