The Articulation Of The First With The Second Phalanx, or The Pastern Joint. - Adhering to the limit we have set, this articulation should not receive our attention. As, however, we shall in a later page be concerned with fractures of the os coronae, which fractures may affect the articulation above mentioned, a brief note of its formation will not be out of place.

It is an imperfect hinge-joint, permitting of extension and flexion, allowing the first phalanx to pivot on the second, and admitting of the performance of slight lateral movements. It is formed by the opposing of the inferior surface of the os suffraginis with the superior surface of the os coronae. The articulating surface of the os coronae is supplemented by the addition behind of a thick piece of fibro-cartilage (the glenoid) attached inferiorly to the posterior edge of the upper articulatory surface of the os coronae, and superiorly by means of three fibrous slips on each side to the os suffraginis. The innermost of these three slips becomes attached to about the middle of the lateral edge of the suffraginis, and the remaining two, beneath the first, attach themselves to nearer the lower end of that bone. The posterior surface of the complementary cartilage forms a gliding surface for the passage of the perforans.

B The Ligaments 006

FIG. 6. - The Navicular Bone (Viewed From Below).
1, Inferior surface (smooth for the passage of the flexor perforans); 2, anterior edge of inferior surface; 3, posterior edge of inferior surface.

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FIG. 7. - The Navicular Bone (Viewed From Above, The Bone Tilted Posteriorly To Show Its Anterior Border).
1, Superior articulatory surface; 2, anterior border (grooved portion of); 3, anterior border (articulatory portion of).

Fig. 8.   Ligaments Of The First And Second Interphalangeal Articulations (Viewed From The Side)

Fig. 8. - Ligaments Of The First And Second Interphalangeal Articulations (Viewed From The Side). (After Dollar And Wheatley.)
1, Outermost Slip From The Glenoidal Fibro-Cartilage; 2, Lateral Ligament Of The First Interphalangeal Articulation; 3, Prolongations Of The Lateral Ligament Of The First Interphalangeal Articulation Attached To The End Of The Navicular Bone To Form The Postero-Lateral Ligament Of The Pedal Joint; 4, End Of The Navicular Bone; 5, Antero-Lateral Ligament Of The Pedal Joint.

The Lateral Ligaments. - These are large and thick, an outer and an inner, running obliquely from above downwards and backwards. Each is inserted superiorly into the lateral tubercle of the lower end of the first phalanx, and inferiorly to the side of the second phalanx, their most inferior fibres becoming finally fixed to the extremities of the navicular bone, where they form the postero-lateral ligaments of the pedal articulation. In front of the joint the extensor pedis plays the part of an additional ligament.

The Synovial Membrane. - This is limited in front by the tendon of the extensor pedis, on each side by the lateral ligaments of the joint, and behind by the glenoid fibro-cartilage. At this point it is prolonged upwards as a pouch behind the lower extremity of the first phalanx.

The Articulation Of The Second Phalanx With The Third, The Pedal, or The Coffin Joint. - This also is an imperfect hinge-joint, permitting only of flexion and extension, which movements are more restricted than in the previous articulation. Three bones enter into its formation: the second phalanx, the third phalanx, and the navicular bone. The lower articulatory surface is formed by the third phalanx and the navicular bone combined. To effect this the navicular is closely and firmly attached to the third phalanx by an interosseous ligament. The two bones, as one, are then connected to the second phalanx by four lateral ligaments, an anterior and a posterior on each side.

The Interosseous Ligament consists of extremely short fibres running from the extensively grooved portion of the anterior surface of the navicular bone to become attached to the os pedis immediately behind its articular surface.

The Antero-lateral Ligaments are attached by their superior extremities to the lateral surfaces of the second phalanx, and by their inferior extremities into the depressions on either side of the pyramidal process of the os pedis.

The Postero-lateral Ligaments. - As mentioned when describing the first interphalangeal articulation, these are in reality continuations of the lateral ligaments of that joint. Running obliquely downwards and backwards from their point of attachment to the first phalanx they curve round the lower part of the side of the second phalanx and end on the extremities and posterior surface of the navicular bone. Having reached that position, they send short attachments to the retrossal process of the os pedis and to the inner face of the lateral cartilage.

Fig. 9.   Ligaments Of The First And Second Interphalangeal Articulations (Viewed From Behind)

Fig. 9. - Ligaments Of The First And Second Interphalangeal Articulations (Viewed From Behind). (After Dollar And Wheatley.) 1, Suspensory Ligament; 2, Innermost Slip From Complementary Cartilage Of Pastern Joint; 3, Middle Slip From Complementary Cartilage Of Pastern Joint; 4, Outermost Slip From Complementary Cartilage Of Pastern Joint; 5, Glenoid Or Complementary Cartilage Of Pastern Joint; 6, Postero-Lateral Ligaments Of The Pedal Joint; 7, The Navicular Bone; 8, Interosseous Ligaments Of The Pedal Joint; 9, Semilunar Crest Of Os Pedis; 10, Plantar Surface Of Os Pedis.

Synovial Membrane. - This extends below the facets uniting the navicular to the pedal bone, and offers for consideration two sacs. A large one posteriorly running up behind the second phalanx to nearly adjoin the sesamoidean bursae, and a small one, a prolongation of the synovial membrane between the antero-lateral and postero-lateral ligaments of the same side. This latter is often distended, and on account of its close proximity to the seat of operation, is liable to be accidentally opened in excision of the lateral cartilage for quittor.