388 



HUMAN ANATOMY. 



iii's 



vasti and semimembranosus and of their fascial expansions ; (5) the toughness of 

 the periosteum uniting it with the diaphysis ; and (6) the fact that while there is 

 no possibility of its displacement by muscular action, it does not project enough 

 to be exposed to the effects of direct violence. The possibility of disjunction of 

 this epiphysis complicating an injury to the knee continues up to the twentieth 

 year at least ; in injuries to the elbow epiphyseal separation may be excluded 

 after the eighteenth year. 



Three-fourths of the recorded cases have occurred in males, as might be 

 expected on account of their more frequent exposure to serious injury. The 

 epiphysis has been displaced forward, and outward and forward. It has never been 

 displaced backward, partly, at least, on account of the tongue-like process con- 

 necting it with the tibial tubercle. Its inward displacement would necessitate the 



separation of the head of the fibula or the laceration of the 

 Fig. 405. superior tibio-fibular ligaments. The attachment of the syno- 



vial membrane of the knee-joint does not descend to the level 



^^a^^^^^ffl of this epiphysis ; hence that articulation is often not involved 

 in these injuries. They should not, when severe, be mistaken 

 iit %^' *Wl,r ^*-*^ dislocation, or, when slight, for sprains of the knee. They 



may be distinguished from the former by the age of the patient 

 and the unimpaired mobility of the knee, and from the latter 

 by the situation of the pain or tenderness. Dislocation of the 

 knee is very rare in children. 



Good union has taken place in some cases ; arrest of growth 

 has followed in others, as might be expected from the fact that 

 the chief increase in length of the tibia takes place from this 

 epiphysis. 



The tubercle of the tibia has been detached in some 

 recorded instances, mostly males: nine from violent action of 

 the quadriceps in powerful young men, eight of whom were 

 between sixteen and eighteen years of age, the age of the 

 remaining male not having been mentioned (Poland). 



This separation should be carefully distinguished from frac- 

 ture of the patella. In disjunction the latter bone is drawn 

 upward, the patient is unable to extend the leg, and the swell- 

 ing following laceration of the subligamentous bursa may simu- 

 late swelling of the knee-joint. The latter may be involved 

 directly — as the synovial membrane is in close proximity to the 

 tubercle — or indirectly, through the occasional, though rare, 

 communication with the subligamentous bursa. Fracture of the 

 patella, however, does not occur in children and is very rare 

 in adolescence. In patella fracture the fragments of bone are 

 brought together, so that crepitus may be felt only by pushing 

 the two fragments towards each other; the groove between 

 them can almost always be recognized. In disjunction of the 

 Epiphyseal lines of tibia, tubercle crepitus Can be elicited only by pulling the fragment 



downward ; the outline of the patella is normal, and can usually 

 be made out. The X-rays would be conclusive. Bony union should be expected. 



The shaft of the tibia gradually decreases in size to about the junction of the 

 middle and lower thirds, and then expands again to the ankle. At its smallest 

 point — on an average about ten centimetres (four inches) above its lower end — it 

 has to bear a greater weight on a smaller area than any other bone (Humphry). At 

 this level meet the two independent vertical columns into which, according to 

 Fayel and Duret, the spongy tissue of the tibia is divided (one occupying the 

 upper two- thirds, the other the lower third of the bone), and hence these authorities 

 assert that this spot represents the minimum of resistance (Treves). In some 

 tibiae it is at or near the junction of an ill-defined long upper curve, in which the 

 crest terminates, and a short lower curve. On transverse section the tibia is seen 

 to be cylindrical in its lower third and three-sided above. As it has been demon- 

 strated that if two homogeneous solids present on section equal areas, the one 



