Detailed Notes on Lower Limb Anatomy

Bones of the Lower Limb

Overview

The bones of the lower limb are divided into two groups:

  • Those that form the free part of the limb.

  • Those that attach it to the trunk, forming the pelvic girdle.

Pelvic Girdle

The bony pelvis consists of:

  • Sacrum and Coccyx

  • Left and right Os Coxae

The os coxae links the free part of the lower limb and the axial skeleton.

Os Coxae

  • Large, irregularly shaped bone.

  • Sometimes referred to as the "innominate," meaning "no name."

  • Composed of three bones that fuse in adulthood:

    • Ilium: Superior element.

    • Ischium: Posterior element.

    • Pubis: Anterior element.

  • These bones are separated by the Triradiate Cartilage in the Acetabulum (hip socket) prior to fusion.

  • The pubis and ischium are separated by cartilage below the large Obturator Foramen. In life, this foramen is covered by a tendinous membrane.

  • Posteriorly, each os coxae articulates with the ala of the sacrum via the Auricular Surface. This articulation is reinforced by strong Sacroiliac Ligaments.

  • Anteriorly, the os coxae articulate with each other at the Pubic Symphysis.

Key Features of the Os Coxae

  • Iliac Crest: Superior margin of the os coxae.

  • Anterior Superior Iliac Spine: Ventral projection of the iliac crest.

  • Ischial Spine: Projection of the ischium below the auricular surface.

  • Ischial Tuberosity: Lateral broadening of the ischium below the ischial spine.

  • Greater Sciatic Notch: Deep notch between the auricular surface and the ischial spine. Ligaments transform this into a foramen in life.

  • Lesser Sciatic Notch: Shallow notch between the ischial spine and the ischial tuberosity. Ligaments transform this into a foramen in life.

  • Pecten Pubis: Sharp crest formed by the superior ramus of the pubis.

  • Arcuate Line: Ridge on the inner surface of the ilium, continuing the line of the pecten pubis to the sacroiliac joint.

False vs. True Pelvis

  • The pecten pubis and arcuate line separate the pelvis into the False Pelvis (above) and the True Pelvis (Obstetrical Pelvis, below).

Bone Graft and Marrow Transplant

  • The iliac crest is a preferred site for removing bone or bone marrow for grafting or transplantation.

  • Bone Grafting: Surgical removal and placement of bone to aid in healing a broken bone.

  • Marrow Transplant: Removal of marrow from the iliac crest of a healthy individual and intravenous administration to restore hemopoietic function in a patient with marrow dysfunction (e.g., after chemotherapy or radiation therapy).

Thigh

The thigh contains a single bone, the femur, and the patella, which is suspended in a tendon.

Femur

  • Head: Hemispherical, articulates with the acetabulum of the os coxae.

  • Neck: Connects the head to the shaft.

  • Greater Trochanter: At the junction of the neck and shaft, with a deep fossa on its medial side.

  • Lesser Trochanter: Projects medially from the back of the shaft at the junction with the neck.

  • Intertrochanteric Crest: Ridge connecting the trochanters on the back of the shaft.

  • Gluteal Tuberosity: Roughened area lateral to the lesser trochanter.

  • Linea Aspera: Prominent ridge continuing down the back of the shaft from the gluteal tuberosity.

  • Popliteal Surface: Slightly concave area where the medial and lateral margins of the linea aspera diverge distally.

  • Lateral Condyle and Medial Condyle: Articular surfaces at the distal end that articulate with the tibia.

  • Patellar Surface: Spool-shaped surface anteriorly where the condyles merge, over which the patella glides.

  • Lateral Epicondyle and Medial Epicondyle: Expanded areas above the articular surface at the distal epiphysis.

Patella

  • Triangular sesamoid bone formed in the tendon of the Quadriceps femoris muscle.

  • Most of its posterior surface articulates with the patellar surface of the femur.

Leg

The leg comprises the tibia (medial) and the fibula (lateral).

Tibia

  • Tibial Plateau: Expanded proximal end that articulates with the femur via the Medial Condyle and Lateral Condyle.

  • Intercondylar Eminence: Separates the condyles in the center of the plateau.

  • Shaft: Rectangular in cross-section with an anterior edge (the "shin") just below the skin.

  • Tibial Tuberosity: Roughened tuberosity on the front of the shaft where the Quadriceps femoris tendon attaches.

  • Medial Malleolus: Projection of the medial side of the distal end that articulates with the talus.

Fibula

  • Head: Slightly expanded proximal end that articulates with a facet on the tibia just below its lateral condyle.

  • Shaft: Very slender because it bears little weight.

  • Lateral Malleolus: Slightly enlarged distal end held tightly against a notch in the tibia by ligaments. Its medial surface articulates with the talus.

Foot

The foot contains 26 individual bones divided into:

  • Tarsals (7 bones)

  • Metatarsals (5 bones)

  • Phalanges (14 bones)

Tarsal bones form the ankle, metatarsals form the sole, and phalanges form the five free digits. Each digit's phalanges and metatarsal form a Ray, numbered I-V from the big toe to the little toe.

Tarsal Bones

Seven irregularly shaped bones forming the ankle, heel, and back of the sole, arranged into proximal and distal groups.

Proximal Bones

  • Talus

  • Calcaneus

  • Navicular

The talus and calcaneus are the largest and most irregularly shaped.

  • Talus: Spool-shaped superior surface articulating with the distal end of the tibia and the medial and lateral malleoli of the tibia and fibula. Allows plantarflexion and dorsiflexion. Sits atop the calcaneus and articulates with the navicular.

  • Calcaneus: Articulates superiorly with the talus (Subtalar joint allows inversion and eversion). Articulates anteriorly with the cuboid bone. The posterior half is expanded into a tuberosity (the heel) for initial ground contact and attachment of the Achilles tendon.

  • Navicular: Elliptical bone with a concave proximal surface articulating with the talus and a convex distal surface articulating with the cuneiform bones.

Distal Bones

  • Cuboid

  • Three Cuneiforms (medial, intermediate, and lateral)

These form a row that articulates with the metatarsals.

Metatarsals

Five metatarsals form most of the sole. Each ray's first element (I-V) is its metatarsal.

  • Base: Expanded proximal end articulating with tarsal bones.

  • Head: Rounded distal end articulating with a proximal phalanx.

The first metatarsal (big toe) is very robust; the others are long and slender.

Phalanges

Fourteen phalanges constitute the toes.

  • Lateral Toes: Each has a Proximal Phalanx, Middle Phalanx, and Distal Phalanx.

  • Big Toe (Hallux): Only has a Proximal Phalanx and a Distal Phalanx.

The hallucial phalanges are the most robust due to the big toe's importance in weight-bearing.

Gout

A condition resulting from the deposition of urate crystals around a joint due to high blood levels of uric acid. A primary site is the first metatarsophalangeal joint.

The Arch of the Foot

A plantar arch is a characteristic feature of the human foot that resists deformation during walking and running.

Components and Maintenance

  • Longitudinal Arch: Runs along the medial side from the calcaneal tuberosity (heel) to the metatarsal-phalangeal joint (ball).

  • Transverse Arch: A result of the longitudinal arch being higher medially than laterally.

The arch is maintained by:

  1. Bones: Their shapes form an arch when viewed from the medial side. The talus acts as a keystone, wedged between the calcaneus and navicular. The back is formed by the calcaneus, and the front by the navicular, cuneiforms, and medial metatarsals.

  2. Ligaments: Bind the tarsals together, providing a rigid structure capable of movement. The Spring Ligament (Plantar Calcaneal-Navicular Ligament) is the most important, running from the sustentaculum tali of the calcaneus under the talus to insert onto the navicular.

  3. Plantar Aponeurosis: A thick fibrous layer just deep to the superficial fascia of the sole. It arises from the calcaneal tuberosity and fans out to insert onto the base of the proximal phalanx of each toe. Tightens as the toes dorsiflex, maintaining the arch.

The Abductor hallucis muscle also helps sustain the medial longitudinal arch during locomotion.

Plantar Fasciosis

Involves pain at the attachment site of the plantar fascia to the calcaneus due to tearing or degeneration. Symptoms include pain on the weight-bearing portion of the heel. Often referred to as plantar fasciitis, but plantar fasciosis is more accurate due to the frequent absence of inflammation.