THE COFFIN JOINT 



189 



phalanx and its complementary fibro-cartilage. The lateral pair is attached above 

 to the middle of the borders of the first phalanx, the central pair lower down and 

 on the margin of the triangular rough area. 



These ligaments are very commonly thickened as a result of chronic inflammation, and then 

 are not well defined. The central ones blend below with the branches of the superficial fiexor 

 tendon and with the straight sesamoidean hgament. 



Movements. — These are very limited, and consist of flexion and extension. 

 The axis of motion passes transversely through the distal end of the first phalanx. 

 In the standing position the joint is extended. A small amount of volar flexion is 

 possible, and in this position slight lateral flexion and rotation can be produced by 

 manipulation. Dorsal flexion is prevented by the lateral, volar, and straight sesa- 

 moidean ligaments. 



Lateral cartilage 



THE COFFIN JOINT 



This joint, technically termed the distal interphalangeal articulation (Articu- 

 latio phalangis tertise), is a ginglymus formed by the junction of the second and 

 third phalanges and the third sesamoid bone. 



Articular Surfaces. — The surface on the distal end of the second phalanx is 

 convex from before backward, 

 concave transversely. The 

 articular surface of the third 

 phalanx slopes sharply up- 

 Avard and forward; its cen- 

 tral part is prominent, and is 

 flanked by two glenoid cavi- 

 ties. It is completed behind 

 by the articular surface of 

 the third sesmoid or navicular 

 bone. 



Joint Capsule. — This is 

 attached around the margins 

 of the articular surfaces. In 

 front and laterally it is tight, 

 and is blended with the exten- 

 sor tendon and the lateral liga- 

 ments respectively. Posteriorly, it forms a considerable pouch which extends 

 upward to about the middle of the second phalanx, where it is separated by a 

 fibrous membrane from tlie digital synovial sheath. Laterally small pouches pro- 

 ject outward (especially during volar flexion) against the lateral cartilages, just 

 behind the lateral ligaments.^ 



Ligaments. — The lateral ligaments, external and internal (Ligamentum coUa- 

 terale ulnare, radiale), are short strong bands which are attached above in the 

 depressions on either side of the lower part of the second phalanx, under cover of 

 the lateral cartilage. They widen below and end in the depressions on either side 

 of the extensor process and on the anterior end of the lateral cartilages. 



The suspensory navicular ligaments, external and internal (Ligamentum sesa- 

 moideum coUaterale ulnare, radiale)," are strong, somewhat elastic bands, which 

 form a sort of suspensory apparatus for the third sesamoid. They are attached 

 superiorly in and above the depressions on either side of the distal end of the first 



1 This should be noted in regard to resection of the lateral cartilage or other operations in 

 this vicinity. 



- These are termed the postero-lateral ligaments by M'Fadyean. They may well be called, 

 as by German authors, the suspensory ligaments of the navicular bone. 



ral lign7rients of 



intern joint 

 pensory liga- 

 ments of navicu- 

 lar bone 



Tendon surface 

 of navicular 

 bone 



Wi)igs of third 

 phalanx 



Volar foramina 



Fig. 152. — Lateral Ligamkni- h Ix-tebx Joint and Suspen- 

 sory LiG.vMENTS OF Na\i< Ti.AK BoNE. (After Schiiialtz, 

 Atlas d. Anat. d. Pferdes.) 



