TIBIO-FIBULAR ARTICULATION—THE HOCK JOINT 239 
flexion and extension. In the ordinary standing position the articular angle 
(behind) is about 140° to 150°. Flexion is limited only by contact of the leg with 
the thigh, if the hock is also flexed. Extension is incomplete, 7. e., the femur and 
tibia cannot be brought into the same straight line. Rotation is limited, and is 
freest during semiflexion. The patella glides on the femoral trochlea upward in 
extension, downward in flexion. 
Extension is checked mainly by tension of the cruciate and collateral ligaments. In extreme 
extension, which is accompanied by slight outward rotation of the leg, the patella can be pushed 
upward and inward so that its fibro-cartilage hooks over the upper-end of the medial ridge of the 
trochlea, but it will not remain there unless held in position. When pressure is removed, the base 
of the patella tips forward and the cartilage lies upon the most prominent part of the trochlear 
ridge. During flexion, which is accompanied by slight inward rotation of the leg, the condyles 
of the femur and the menisci glide backward on the tibia; the movement of the lateral condyle 
and meniscus is greater than that of the medial one. In extreme flexion the patellar and posterior 
cruciate ligaments are tense; the other ligaments are relaxed. The movement of the patella is 
gliding with coaptation, 7. e., different parts of the opposing articular surfaces come into contact 
successively. Only a narrow transverse strip (ca. 1.5-2 em. wide) of the patella is in contact 
with the trochlea at a time. 
TIBIO-FIBULAR ARTICULATION 
This joint (Articulatio tibiofibularis) is formed by the head of the fibula ar- 
ticulating with a crescentic facet Just below the outer margin of the lateral condyle 
of the tibia. The joint capsule is strong and close. The shaft of the fibula is at- 
tached to the lateral border of the tibia by the interosseous membrane of the leg 
(Membrana interossea cruris); this is perforated about an inch from its proximal 
end by an opening which transmits the anterior tibial vessels to the front of the tibia. 
A fibrous cord usually extends from the distal end of the shaft of the fibula to the 
lateral malleolus. The latter is the distal end of the fibula which has fused with the 
tibia. No appreciable movement occurs in this joint. 
THE HOCK JOINT 
This is a composite joint made up of a number of articulations (Articulationes 
tarsi). These are: (1) The tibio-tarsal articulation; (2) the intertarsal articula- 
tions; (3) the tarso-metatarsal articulation. 
The tibio-tarsal articulation (Articulatio talocruralis) is a typical ginglymus 
formed by the trochlea of the tibial tarsal bone and the corresponding surface of the 
distal end of the tibia. The ridges and grooves of these surfaces are directed ob- 
liquely forward and outward at an angle of about 12° to 15° with a sagittal plane. 
The trochlear surface is about twice as extensive as that on the tibia, and its ridges 
have a spiral curvature. The other articulations are arthrodia, which have joint 
surfaces and ligaments of such a nature as to allow only a minimal amount of glid- 
ing motion. 
As in the case of the carpal joints, it is convenient to describe first the common 
capsule and ligaments, which are the more important practically, and then to 
consider very briefly the special ligaments. 
The fibrous part of the joint capsule is attached around the margin of the 
tibial articular surface above and the metatarsal surfaces below; it is also attached 
in part to the surfaces of the bones which it covers, and blends with the collateral 
ligaments. Its dorsal part (anterior ligament) is rather thin; in distention of the 
capsule, as in “‘bog-spavin,” its antero-medial part, which is not bound down by 
the tendons passing over the joint, forms a fluctuating swelling over the medial 
ridge of the trochlea. The plantar part (posterior and tarso-metatarsal ligaments) 
is very thick below, and is intimately attached to the tarsal bones. It is in part 
cartilaginous, and forms a smooth surface for the deep flexor tendon. The proximal 
part pouches upward behind the distal end of the tibia for 4 distance of about two 
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