TIBIA BONE

Learning objectives:

At the end of the lecture, the student should be able to describe:  The division of tibia bone in 3 parts  The surfaces and borders of tibia  The attachments of muscles on the tibia bone  The ossification of tibia and its primary and secondary ossification centers

Lecture outline:

Tibia:  Prismoid in form, expanded above, where it enters into the knee-joint, contracted in the lower third, and again enlarged but to a lesser extent below.  In the male, its direction is vertical, and parallel with the bone of the opposite side , in the female it has a slightly oblique direction downward and lateralwards, to compensate for the greater obliquity of the femur.  It has a body and two extremities/ ends (upper & lower).

The upper extremity:

 The upper extremity is large  Expanded into two eminences, the medial and lateral condyles.  The superior articular surface presents two smooth articular facets .

The medial facet :  oval in shape  slightly concave from side to side, and from before backward. The lateral facet :  nearly circular  is concave from side to side, but slightly convex from before backward, especially at its posterior part, where it is prolonged on to the posterior surface for a short distance.

The central portions of these facets articulate with the condyles of the femur, while their peripheral portions support the menisci of the knee-joint.

Intercondyloid eminence ( spine of tibia ):  Located between the articular facets  It is surmounted on either side by a prominent tubercle, on to the sides of which the articular facets are prolonged  In front of and behind are rough depressions for the attachment of the anterior and posterior cruciate ligaments and the menisci. Anterior surfaces of condyles:  Continuous with one another  Forms a large flattened triangular area which is broad above, and perforated by large vascular foramina; narrow below where it ends in tuberosity of the tibia

Tuberosity of the tibia :  A large oblong elevation.  Gives attachment to the ligamentum patellae  A bursa intervenes between the deep surface of the ligament and the part of the bone immediately above the tuberosity.

Posterior surfaces of condyles:

 Posteriorly , condyles are separated from each other by a shallow depression, the posterior intercondyloid fossa.  This fossa gives attachment to part of the posterior cruciate ligament of the knee-joint.  The medial condyle has a deep transverse groove posteriorly for the insertion of the tendon of the Semimembranosus.  Its medial surface is convex, rough, and prominent and gives attachment to the tibial collateral ligament.

The lateral condyle :  Posteriorly, it has a flat articular facet, circular in form which is directed downward, backward, and lateralward for articulation with the head of the fibula.

 Lateral surface is convex, rough, and prominent in front

 Has got an eminence, situated on a level with the upper border of the tuberosity and at the junction of its anterior and lateral surfaces, for the attachment of the iliotibial band.

 Just below this a part of the Extensor digitorum longus takes origin and a slip from the tendon of the Biceps femoris is inserted.

Body of tibia: Has three borders and three surfaces.

Borders : Anterior Medial Interosseous

The anterior crest or border :  The most prominent of the three  Commences above at the tuberosity  Ends below at the anterior margin of the medial malleolus.  Is sinuous and prominent in the upper two-thirds of its extent, but smooth and rounded below  Gives attachment to the deep fascia of the leg.

Surfaces: Lateral Medial Posterior

Lateral surface:  Narrower than the medial one  Upper two-thirds present a shallow groove for the origin of the Tibialis anterior  Lower third is smooth, convex, curves gradually forward to the anterior aspect of the bone  Is covered by the tendons of the Tibialis anterior, Extensor hallucis longus, and Extensor digitorum longus from medial to lateral side

Posterior surface:  Has a prominent ridge in its upper part, the popliteal line,  This line extends obliquely downward from the back part of the articular facet for the fibula to the medial border, at the junction of its upper and middle thirds

Attachments:  Marks the lower limit of the insertion of the Popliteus  Serves for the attachment of the fascia covering this muscle  Gives origin to part of the Soleus, Flexor digitorum longus, and Tibialis posterior.

 The triangular area, above this line, gives insertion to the Popliteus.

 The middle third of the posterior surface is divided by a vertical ridge into two parts; the ridge begins at the popliteal line and is well-marked above, but indistinct below; the medial and broader portion gives origin to the Flexor digitorum longus, the lateral and narrower to part of the Tibialis posterior.

 The remaining part of the posterior surface is smooth and covered by the Tibialis posterior, Flexor digitorum longus, and Flexor hallucis longus.

 Immediately below the popliteal line is the nutrient foramen, which is large and directed obliquely downward.

The lower extremity  The lower extremity, much smaller than the upper, presents five surfaces  It is prolonged downward on its medial side as a strong process, the medial malleolus.

Surfaces: The inferior articular surface  Is quadrilateral, and smooth for articulation with the talus.  It is concave from before backward, broader in front than behind, and traversed from before backward by a slight elevation, separating two depressions.  Is continuous with that on the medial malleolus.

The anterior articular surface  Is smooth and rounded above  Covered by the tendons of the Extensor muscles  Lower margin presents a rough transverse depression for the attachment of the articular capsule of the ankle-joint.

The posterior articular surface  Is traversed by a shallow groove directed obliquely downward and medialward,  It is continuous with a similar groove on the posterior surface of the talus and serving for the passage of the tendon of the Flexor hallucis longus.

The Lateral articular surface  Presents a triangular rough depression for the attachment of the inferior interosseous ligament connecting it with the fibula  The lower part of this depression is smooth, covered with cartilage in the fresh state, and articulates with the fibula.  The surface is bounded by two prominent borders, continuous above with the interosseous crest  They afford attachment to the anterior and posterior ligaments of the lateral malleolus.

The Medial articular surface  Is prolonged downward to form a strong pyramidal process, flattened from without inward—the medial malleolus.  The medial surface of this process is convex and subcutaneous  Its lateral or articular surface is smooth and slightly concave, and articulates with the talus  Its anterior border is rough, for the attachment of the anterior fibers of the deltoid ligament of the ankle-joint  Its posterior border presents a broad groove, the malleolar sulcus, directed obliquely downward and medialward, and occasionally double  This sulcus lodges the tendons of the Tibialis posterior and Flexor digitorum longus.  The summit of the medial malleolus is marked by a rough depression behind, for the attachment of the deltoid ligament. Ossification of tibia  The tibia is ossified from three centers one for the body and one for either extremity.  Ossification begins in the center of the body, about the seventh week of fetal life, and gradually extends toward the extremities.  The center for the upper epiphysis appears before or shortly after birth; it is flattened in form, and has a thin tongue-shaped process in front, which forms the tuberosity;  The center for the lower epiphysis appears in the second year.  The lower epiphysis joins the body at about the eighteenth, and the upper one joins about the twentieth year.  Two additional centers occasionally exist, one for the tongue-shaped process of the upper epiphysis, which forms the tuberosity, and one for the medial malleolus.