Chap, xxiii.] THE ANKLE AND FOOT. 473 



The ankle-joint is a very powerful articulation, 

 its strength being derived not only from the shape of 

 its component bones, but also from the unyielding 

 ligaments and many tendons that are bound about it 

 like straps. Of the ligaments, the two lateral are 

 very strong, and have an extensive hold upon the 

 foot. The anterior and posterior are extremely thin 

 and insignificant, although the latter is supported 

 by the tendon of the flexor longus pollicis, which 

 crosses it. When effusion takes place into the joint, 

 it first shows itself in front, beneath the extensor 

 tendons, and just in front of the lateral ligaments. 

 This is due to the feebleness of the anterior liga- 

 ment and the extent and looseness of the synovial 

 sac in relation with that structure, More extensive 

 effusions cause a bulging behind through yielding 

 of the thin posterior part of the capsule, and fluctua- 

 tion can then be obtained on either side of the tendo 

 Achillis. In no ordinary case can fluctuation be 

 detected distinctly beneath the unyielding lateral 

 ligaments. Moreover, the loose synovial sac of the 

 ankle-joint extends both in front and behind beyond 

 the limits of the articulation, while, at the sides, it is 

 strictly limited to the joint surfaces. The ankle is a 

 perfect hinge-joint, and permits only of flexion and 

 extension. The very slightest amount of lateral 

 movement is allowed in extreme extension, when the 

 narrower, or hinder, part of the astragalus is brought 

 into contact with the widest, or anterior, part of the 

 tibio-fibular arch. When obvious lateral movement 

 exists at the ankle, the joint must be the seat of 

 either injury or disease, and it is important not to 

 mistake the lateral movements permitted between 

 certain of the tarsal bones for movements at the 

 ankle-joint. Flexion is limited by the posterior and 

 middle parts of the internal ligament, by the poste- 

 rior part of the external ligament, by the posterior 



