1.3 Tibia and Fibula

Introduction

• The leg is supported by two bones:
  • Tibia
  • Fibula
• The tibia is the medial, larger, and weight-bearing bone of the leg.
• The tibia corresponds to the radius of the upper limb.
• The fibula is the lateral, slender, and non-weight-bearing bone of the leg.
• The fibula corresponds to the ulna of the upper limb.

Tibia

• Tibia is the medial and larger bone of leg (tibia = skin bone in Latin). Tibia is the second longest bone in the body (femur is the first).

Parts of tibia

Tibia has three parts:

• Upper end: It is expanded. It has medial and lateral condyles, and tibial tuberosity.
• Shaft: It is triangular in cross-section. It has
  • Three borders: Anterior, medial, and interosseous (lateral)
  • Three surfaces: Medial, lateral, and posterior
• Lower end: It has a bony projection as medial malleolus on the medial side.

Anatomical Position and Side Determination

• The broad upper end faces upward.
• The tibial tuberosity and sharp anterior border face forward.
• The medial malleolus projects from the medial side of the lower end.
• The side of the bone is identified by the direction of the medial malleolus.
  1. The right tibia has the medial malleolus on the right side.
  2. The left tibia has the medial malleolus on the left side.

Features of Tibia

• Tibia consists of an upper end, a shaft, and a lower end.

Upper End of Tibia

• The upper end is broad and expanded. Its transverse diameter is greater than its anteroposterior diameter. It consists of:
  • Medial condyle
  • Lateral condyle
  • Intercondylar area
  • Tibial tuberosity

Medial condyle

• The medial condyle is longer than the lateral condyle.
• The medial condyle has four surfaces:
  • Superior
  • Posterior
  • Anterior
  • Medial

Superior Surface

• The superior surface bears a smooth oval articular facet. Its long axis is directed anteroposteriorly. The articular facet articulates with the medial condyle of the femur.

Posterior Surface

• The posterior surface is grooved.
• Attachment: The groove provides insertion for the semimembranosus muscle.

Anterior and Medial Surfaces

• The anterior and medial surfaces are rough. Numerous vascular foramina are present on these surfaces.
• Attachment: The medial (tibial) collateral ligament attaches to the anterior and medial surfaces of the medial condyle.

Lateral condyle

• The lateral condyle is smaller than the medial condyle. The lateral condyle projects posteriorly and overhangs the shaft. The lateral condyle has four surfaces: Superior, posterior, anterior, and lateral

Superior Surface:

• The superior surface bears a circular articular facet. The articular facet articulates with the lateral condyle of the femur. The lateral meniscus covers the articular facet.

Posterior Surface

• Fibular Facet: The fibular facet is a circular articular facet on the posterior surface. The fibular facet articulates with the head of the fibula.
• Groove for Popliteus: A groove for the popliteus tendon lies just superior to the fibular facet.
• The tendon of the popliteus occupies this groove.

Anterior and Lateral Surfaces

• Gerdy’s Tubercle: Gerdy’s tubercle is a bony prominence on the anterior surface of the lateral condyle.
• Attachment: The iliotibial tract attaches to Gerdy’s tubercle.

Intercondylar area

• The intercondylar area is the rough region between the superior articular surfaces of the medial and lateral condyles of the tibia.
• It is narrow in the middle and broader at both the front and back.
• The central raised portion is called the intercondylar eminence.
• The intercondylar eminence has two small projections:
  • Medial intercondylar tubercle
  • Lateral intercondylar tubercle

Attachments (from anterior to posterior)

The intercondylar area provides attachment to the following six structures:

1. Anterior horn of the medial meniscus
2. Anterior cruciate ligament (ACL)
3. Anterior horn of the lateral meniscus
4. Posterior horn of the lateral meniscus
5. Posterior horn of the medial meniscus
6. Posterior cruciate ligament (PCL)

Mnemonic: Medical College Lucknow, Lucknow Medical College (MCL, LCL) helps recall the sequence of meniscal attachments from front to back.

Tibial tuberosity

• The tibial tuberosity is a prominent triangular projection on the front of the upper end of the tibia, with its base directed upward.
• It has two parts:
  • Upper smooth part
  • Lower rough part

Attachments and Relations

• The patellar ligament (ligamentum patellae) attaches to the upper smooth part of the tibial tuberosity.
• The lower rough part is separated from the skin by the subcutaneous infrapatellar bursa, which reduces friction during movement.

Shaft of Tibia

• The shaft of the tibia has:
  • Three borders: anterior, medial, and lateral (interosseous)
  • Three surfaces: lateral, medial, and posterior

Borders of tibial shaft

Anterior Border

• Also called the shin of the tibia. It is sharp, subcutaneous, and slightly S-shaped. It extends from the tibial tuberosity to the anterior border of the medial malleolus.

Medial Border

• It extends from the anterior end of the groove for the semimembranosus muscle on the medial condyle to the posterior border of the medial malleolus. It is well defined only in the middle part of the shaft.

Lateral (Interosseous) Border

• It extends from the fibular facet to the lower end of the tibia, where it divides into two limbs, enclosing a triangular area.
• Attachments:  The interosseous membrane attaches along the lateral border. The interosseous tibiofibular ligament attaches to the triangular area.

Surfaces of tibial shaft

• The shaft of tibia has three surfaces – medial, lateral, and posterior.

Medial Surface

• The medial surface lies between the anterior and medial borders. It is subcutaneous throughout its length.
• Attachments:
  • A rough area near the upper part of the medial border gives attachment to the tibial (medial) collateral ligament.
  • Just in front of the medial border, the upper part receives the insertion of the sartorius, gracilis, and semitendinosus muscles (from anterior to posterior).

Lateral Surface

• The lateral surface lies between the anterior and interosseous borders. It is slightly concave in the upper two-thirds and slightly convex in the lower one-third.
• Attachment:
  • The tibialis anterior muscle originates from the upper two-thirds of this surface.
• Relations (medial to lateral):
  • Tibialis anterior
  • Extensor hallucis longus
  • Anterior tibial artery
  • Deep peroneal nerve
  • Extensor digitorum longus
  • Peroneus tertius

Mnemonic: The Himalayas Are Never Dry Places

Posterior Surface

• The posterior surface lies between the medial and interosseous borders. It is broad above and narrow below.

Soleal Line

• The soleal line is an oblique rough ridge extending from the fibular facet to the junction of the upper and middle thirds of the medial border.
• Attachments:
  • Origin of the soleus muscle
  • Fascia covering the soleus and popliteus
  • Deep fascia of the leg

Areas Below the Soleal Line

• The soleal line divides the posterior surface into:
  • Upper triangular area: Forms the floor of the popliteal fossa and receives the insertion of the popliteus muscle.
  • Lower area: Divided by a vertical ridge into:
    • Medial area: Origin of flexor digitorum longus
    • Lateral area: Origin of tibialis posterior

Nutrient Foramen

• The nutrient foramen is located in the upper part of the posterior surface. It transmits the nutrient artery, a branch of the posterior tibial artery. This is the largest nutrient artery in the body.

Lower End of Tibia

• The lower of tibia has the following:
  • 5 surfaces: Anterior, posterior, medial, lateral, and inferior
  • 1 bony projection: Medial malleolus

Surfaces of lower end of tibia

• Anterior Surface: It has an upper smooth part and a lower grooved part.
• Posterior Surface: It contains a vertical groove on its medial side for the tendon of tibialis posterior.
• Medial Surface: It is convex and subcutaneous. It continues downward as the medial surface of the medial malleolus.
• Lateral Surface: It has a triangular fibular notch that articulates with the lower end of the fibula. The anterior and posterior margins of the notch provide attachment to the anterior and posterior tibiofibular ligaments.
• Inferior Surface: It is smooth and articular. It articulates with the superior surface of the talus, forming part of the ankle joint.

Medial malleolus

• The medial malleolus is a short, thick bony projection on the medial side of the lower end of the tibia. Its lateral surface has a comma-shaped articular facet that articulates with the medial surface of the talus.
• A groove on the anterior surface transmits the tendon of tibialis anterior. A groove on the posterior surface transmits the tendon of tibialis posterior. The tip of the medial malleolus lies higher than the tip of the lateral malleolus.
• Attachment: The deltoid ligament is attached to the tip of the medial malleolus.

Ossification of Tibia

• The tibia ossifies from three centers:
  • One primary center
  • Two secondary centers
• The primary ossification center appears in the middle of the shaft during the 7th week of intrauterine life.
• The secondary ossification center for the upper end appears at or shortly after birth and fuses with the shaft between 16 and 18 years.
• The secondary ossification center for the lower end appears during the first year of life and fuses with the shaft between 15 and 17 years.

Fibula

• The fibula is the lateral bone of the leg. It is a long, slender bone and is homologous to the ulna of the forearm.

Parts of fibula

• The fibula consists of: Upper end (head), shaft, and lower end.

Upper End (Head)

• It is rounded and expanded. It bears an articular facet for articulation with the tibia.

Shaft

• The shaft is long, thin, and slender.

Lower End

• It is flattened from side to side. Its lateral surface is non-articular and forms the lateral malleolus. The medial surface has:
  • A triangular articular facet anteriorly
  • A malleolar fossa located below and behind the articular facet

Anatomical Position and Side Determination

Hold the fibula vertically so that:

• The head is directed upward.
• The triangular articular facet at the lower end faces medially.
• The malleolar fossa lies below and behind the articular facet.
• The non-articular lateral surface of the lower end faces laterally, helping determine the side to which the bone belongs.

Features of Fibula

• Fibula has an upper end, a middle shaft, and a lower end.

Upper End of Fibula

• The upper end (head) is rounded and expanded.
• It consists of:
  • Articular facet
  • Styloid process
  • Neck

Articular Facet

• A circular or oval articular facet is present on the superior surface of the head. It articulates with the fibular facet on the lateral condyle of the tibia, forming the superior tibiofibular joint.

Styloid Process

• The styloid process is an upward projection from the posterolateral aspect of the head.
• Attachments:
  • The biceps femoris tendon inserts into the C-shaped area on the anterolateral slope, in front of the styloid process. The fibular (lateral) collateral ligament attaches within the C-shaped area.

Neck

• The neck is the narrow constricted part between the head and the shaft.
• Relation: The common peroneal (fibular) nerve winds around the posterolateral aspect of the neck, making it vulnerable to injury.

Shaft of Fibula

• The shaft of the fibula consists of the following:
  • 3 borders: Anterior, interosseous, and posterior
  • 3 surfaces: Medial, posterior, and lateral
  • 1 crest: Medial

Borders of shaft of fibula

The shaft of the fibula has three borders:

• Anterior border
• Posterior border
• Interosseous (medial) border

Anterior Border

• It begins from the lower part of the anterior aspect of the head and descends vertically. Near the lower end, it divides into two limbs, enclosing a triangular area on the lateral side of the fibula. This triangular area continues onto the lateral surface of the lateral malleolus.
• Attachments:
  • The anterior intermuscular septum attaches to the upper three-fourths of the border.
  • The superior extensor retinaculum attaches to the anterior margin of the triangular area.
  • The superior peroneal retinaculum attaches to the posterior margin of the triangular area.

Posterior Border

• The posterior border is rounded, thick, and less distinct. It extends from the posterior aspect of the head to the medial margin of the groove on the back of the lateral malleolus.
• Attachment: The posterior intermuscular septum attaches to the upper three-fourths of this border.

Interosseous (Medial) Border

• It lies close to the anterior border. It extends from the medial side of the head downward. Near the lower end, it divides into two limbs, enclosing a rough triangular area above the articular facet of the lateral malleolus.
• Attachments:
  • The interosseous membrane attaches along the entire border, except the lower bifurcated part.
  • The interosseous tibiofibular ligament attaches to the rough triangular area.
  • The anterior tibiofibular ligament attaches to the anterior margin of the triangular area.
  • The posterior tibiofibular ligament attaches to the posterior margin of the triangular area.

Surfaces of shaft of fibula

• The shaft of the fibula has three surfaces:
  • Medial (anteromedial/extensor) surface
  • Lateral (peroneal) surface
  • Posterior (flexor) surface

Medial (Anteromedial/Extensor) Surface

• This surface is more accurately called the anteromedial surface. It lies between the anterior and interosseous borders. It is very narrow in the upper part and may appear as a ridge.
• Attachments:
  • Extensor digitorum longus originates from the upper one-fourth and the anterior half of the middle half of the surface.
  • Extensor hallucis longus originates from the posterior half of the middle half.
  • Peroneus tertius originates from the lower one-fourth of the surface.

Lateral (Peroneal) Surface

• It lies between the anterior and posterior borders.
• Attachments:
  • Peroneus longus originates from the upper two-thirds of the surface.
  • Peroneus brevis originates from the lower two-thirds of the surface.

Posterior (Flexor) Surface

• It is the widest surface of the fibular shaft. It lies between the interosseous and posterior borders.

Medial Crest

• A vertical medial crest divides the posterior surface into two areas:
  • Medial (posteromedial) concave area
    • Gives origin to the tibialis posterior muscle.
  • Lateral (posterolateral) flat area
    • Upper one-fourth: Origin of the soleus muscle.
    • Lower three-fourths: Origin of the flexor hallucis longus muscle.

Nutrient Foramen

• The nutrient foramen is located in the upper part of the posterior surface and is directed downward. The nutrient artery of the fibula is a branch of the peroneal (fibular) artery.

Lower End of Fibula

• The lower end of the fibula extends downward to form the lateral malleolus.
  • The lateral malleolus has four surfaces: Lateral, medial , anterior, and posterior.

Lateral Surface

• It is smooth, triangular, non-articular, and subcutaneous.

Medial Surface

• It has:
  • An anterior triangular articular facet that articulates with the talus.
  • A posterior malleolar fossa (depression).
• Attachments: The posterior tibiofibular ligament attaches to the upper part of the malleolar fossa. The posterior talofibular ligament attaches to the lower part of the malleolar fossa.

Anterior Surface

• It is rough and rounded.
• Attachments: The anterior talofibular ligament attaches to the anterior surface. The calcaneofibular ligament also attaches to the anterior surface of the lateral malleolus.

Posterior Surface

• It has a vertical groove for the passage of the tendons of:
  • Peroneus brevis
  • Peroneus longus
• Attachment: The superior peroneal retinaculum attaches to the lateral margin of the groove.

Ossification of Fibula

• Fibula ossifies from
  • 1 primary center
  • 2 secondary centers [Reference: Gray’s Anatomy, 42nd edn.]
• Primary center for shaft appears in the 8th week of intrauterine life
• Secondary centers
  • 1 for upper end appears in the 3rd–4th year and fuses with shaft by 17–19th year of age
  • 1 for lower end appears in the 1st year and fuses with shaft by 15–17th year of age
• Thus, the upper end of fibula is the growing end.

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