TIBIO-FIBULAR ARTICULATION — THE HOCK JOINT 239 



flexion and extension. In tlie ordinary standing position tiie 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, i. c, 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 tliat its fibro-cartilage hooks over the upper end of the medial ridge of the 

 trochlea, but it wiU 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 Hgaments are tense; the other ligaments are relaxed. The movement of the patella is 

 gliding with coaptation, i. e., different parts of the opposing articular surfaces come into contact 

 successively. Only a narrow transverse strip (ca. 1.5-2 cm. wide) of the patella is in contact 

 with the trochlea at a time. 



TIBIO-FIBULAR ARTICULATION 



This joint (Articulatio tibiofibularis) is formed bj^ the head of the fibula ar- 

 ticulating with a crescentic facet just below the outer margin of the lateral condj'le 

 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 ginglj-mus 

 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 johrt 

 surfaces and ligaments of such a nature as to allow only a minimal amount of ghd- 



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 margm 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 m 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 a distance of about two 



