230 



SPECIAL ANATOMY OF THE SKELETON 



Fracture of the shaft may occur at any part, but the most usual situation is at or near the 

 centre of the bone. They may be caused by direct or indirect violence or by muscular action. 

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

 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 frac- 

 ture 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 complicated 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 condyles, may also take 

 place. 



The femur and also the bones of the leg are frequently the seat of acute osteomyelitis 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 infrequently 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 epiphyseal cartilage of the lower end. 



Genu varum is a form of bow-leg in which the tibia and femur are curved outward, the knees 

 being widely separated. Both extremities are usually affected. In early life the disease is due 

 to rhachitis. In elderly people it may be due to arthritis deformans. Genu valgum (knock-knee) 

 is a condition in which the knees are close together, the feet are wide apart, and the internal 

 lateral ligament of the knee-joint is stretched. It is due to excessive growth of the inner con- 

 dyle of the femur, the shaft of the femur curving inward. It may be due to rhachitis, attitude of 

 an occupation, or flat-foot, and one or both knees may be affected. 



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, or Kneecap (Fig. 184). 



The patella 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 resembles such bones (1) in its being developed 



in a tendon; (2) in its centre of 

 ossification presenting a knotty 

 or tuberculated outline; (3) in 

 its structure being composed 

 mainly of dense cancellous tis- 

 sue, 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. It presents an 

 anterior and a posterior surface, 

 three borders, and an apex. 

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

 passage of nutrient vessels, and marked by numerous rough, longitudinal stria 1 . 

 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 (fades 

 articularis), covered with hyaline cartilage in the recent state, and divided into two 



FIG. 184. Right patella. 



A. Anterior surface, 

 surface. 



B. Posterior 



