THE PATELLA. 



191 



Fractures of the upper third of the shaft are almost always the result of indirect violence, 

 whilst those of the lower third are the result, for the most part, of direct violence. In the 

 middle third fractures occur from both forms of injury in about equal proportions. Fractures 

 of the shaft are generally oblique, but they may be transverse, longitudinal, or spiral. The 

 transverse fracture occurs most frequently in children. The fractures of the lower end of the 

 femur include transverse fracture above the condyles, the most common ; and this may be com- 

 plicated by a vertical fracture between the condyles, constituting the T-shaped fracture. In 

 these cases the popliteal artery is in danger of being wounded. Oblique, fracture, separating 

 either the internal or external condyle, and a longitudinal incomplete fracture between the con- 

 dyles, may also take place. 



The femur as well as the other bones of the leg are frequently the seat of acute necrosis in 

 young children. This is no doubt due to their greater exposure to injury, which is often the 

 exciting cause of this disease. Tumors not unfrequently are found growing from the femur : 

 the most common forms being sarcoma, which may grow either from the periosteum or from the 

 medullary tissue within the interior of the bone ; and exostosis, which is commonly found 

 originating in the neighborhood of the epiphysial cartilage of the lower end. 



THE LEG. 



The skeleton of the Leg consists of three bones : the Patella, a large sesamoid 

 bone, placed in front of the knee : the Tibia ; and the Fibula. 



The Patella (Figs. 131, 132). 



The Patella (patella, a small pan) is a flat, triangular bone, situated at the 

 anterior part of the knee-joint. It is usually regarded as a sesamoid bone, 

 developed in the tendon of' the 

 Quadriceps extensor. It resem- 

 bles these bones (1) in its being 

 developed in a tendon ; (2) in 

 its centre of ossification pre- 

 senting a knotty or tuberculated 

 outline ; (3) in its structure 

 being composed mainly of dense 

 cancellous tissue, as in the other 

 sesamoid bones. It serves to 

 protect the front of the joint, 

 and increases the leverage of 

 the Quadriceps extensor by 

 making it act at a greater angle, 

 three borders, and an apex. 



The anterior surface is convex, perforated by small apertures, for the passage 

 of nutrient vessels, and marked by numerous rough, longitudinal striae. This 

 surface is covered, in the recent state, by an expansion from the tendon of the 

 Quadriceps extensor, which is continuous below with the superficial fibres of the 

 ligamentum patellae. It is separated from the integument by a bursa. The 

 posterior surface presents a smooth, oval-shaped, articular surface, covered with 

 cartilage in the recent state, and divided into two facets by a vertical ridge, which 

 descends from the superior border toward the inferior angle of the bone. The 

 ridge corresponds to the groove on the trochlear surface of the femur, and the two 

 facets to the articular surfaces of the tAvo condyles ; the outer facet, for articulation 

 with the outer condyle, being the broader and deeper. This character serves to 

 indicate the side to which the bone belongs. Below the articular surface is a 

 rough, convex, non-articular depression, the lower half of which gives attachment 

 to the ligamentum patellae, the upper half being separated from the head of the 

 tibia by adipose tissue. 



The superior border is thick, and sloped from behind, downward and forward : 

 it gives attachment to that portion of the Quadriceps extensor which is derived 

 from the Rectus and Crureus muscles. The lateral borders are thinner, converging 

 below. They give attachment to that portion of the Quadriceps extensor derived 

 from the external and internal Vasti muscles. 



The apex is pointed, and gives attachment to the ligamentum patellae. 



FIG. 131. Right patella, 

 terior surface. 



An- 



Fir,. 132. Right patella. 

 Posterior surface. 



It presents an anterior and a posterior surface, 



