The tibia and the fibula are connected at their extremities by (1) the superior and (2) the inferior tibiofibular articulations, (3) In addition, the shafts of the bones are connected by the crural interosseous membrane.
1. THE SUPERIOR TIBIOFIBULAR JOINT
This articulation (fig. 563) is a plane joint between the lateral condyle of the tibia and the head of the fibula. The contiguous surfaces of the bones present flat, oval facets covered with cartilage, and the bones are connected by a capsular ligament and by anterior and posterior ligaments.
The capsular ligament is attached to the margins of the articular facets on the tibia and fibula; it is much thicker in front than behind. Not infrequently the synovial membrane of the joint is continuous with that of the knee-joint through the popliteus bursa.
The anterior ligament consists of two or three flat bands, which pass obliquely upwards from the front of the head of the fibula to the front of the lateral condole of the tibia.
The posterior ligament is a thick band, which passes obliquely upwards front the back of the head of the fibula to the back of the lateral condyle of tile tibia. It is covered by the tendon of the popliteus.
The crural interosseous membrane connects the interosseous borders of the tibia and fibula, and separates the muscles on the front from those on the back of the leg. It consists of oblique fibers, which for the most part run downwards and laterally; a few, however, pass downwards and medially. The anterior tibial artery passes to the front of the leg through a large oval opening in the uppermost part of the membrane, and the perforating branch of the peroneal artery pierces its lower part. It is continuous below with the interosseous ligament of the inferior tibiofibular joint. It is in relation, in front; with the tibialis anterior, extensor digitorum longus, extensor hallucis longus, peroneus tertius, and the anterior tibial vessels and anterior tibial (deep peroneal) nerve; behind, with the tibialis posterior and flexor hallucis longus.
3. THE INFERIOR TIBIOFIBULAR JOINT (TIBIOFIBULAR SYNDESMOSIS)
This syndesmosis is formed by the rough, convex surface on the medial side of the lower end of the fibula, and a rough, concave surface (the fibular notch) on the lateral side of the tibia. Below, to the extent of about 4 mm., these surfaces are smooth, and covered with cartilage continuous with that of the ankle-joint. The ligaments are: anterior, posterior, inferior transverse and interosseous.
The anterior inferior tibiofibular ligament (fig. 572) is a triangular band, broader below than above, which extends obliquely downwards and laterally between the adjacent margins of the tibia and fibula, on the front of the syndesmosis.
The posterior inferior tibiofibular ligament (fig. 369), smaller than the preceding, is disposed in a similar manner on the posterior surface of the syndesmosis. Its deep portion forms the inferior transverse ligament, a strong, thick band of yellowish fibers which passes transversely from the upper part of the malleolar fossa of the fibula to the posterior border of the articular surface of the tibia, almost as far as the medial malleolus. The inferior transverse ligament projects below the margins of the bones, and forms part of the articulating surface for the talus.
The interosseous ligament is continuous, above, with the crural interosseous membrane and consists of numerous, short, strong bands, which pass between the adjacent rough surfaces of the tibia and fibula, and constitute the chief bond of union between the lower ends of the bones.
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