THE REGION OF THE KNEE 



467 



indirect violence. In the former case, the displacement is slight 

 because, although the bone may be comminuted, the expansions 

 of the vasti (lateralis and medialis) are not torn and they serve 

 to prevent excessive separation of the fragments. 



Fractures from indirect violence are brought about when the 

 patient, in the act of falling backwards, attempts to recover 

 his balance by powerful contraction of the quadriceps. At the 

 time of the accident the knee is semi-flexed and the patella is 

 snapped across the patellar surface of the femur. Rupture of 

 the quadriceps tendon or of the 

 ligamentum patellae are alterna- 

 tive possibilities to this fracture. 

 The two fragments are widely 

 separated, for, after the bone has 

 given way, the strain tears through 

 the expansions of the vasti ten- 

 dons (lateral patellar ligaments). 



When conservative treatment 

 is adopted, the limb is placed on 

 an inclined plane, with the knee 

 extended in order to relax the 

 quadriceps. The flexion of the 

 hip still further relaxes the rectus 

 femoris. Fibrous union, together 

 with varying degrees of separa- 

 tion of the fragments, may be the 

 outcome of this method of treat- 

 ment, but this condition does not 

 necessarily cause much disability. 



If the fragments are to be wired, 

 good exposure is obtained by a large U-shaped flap (p. 462). A 

 strong silver wire is passed transversely through each fragment 

 and the ends are twisted together at the margin of the patella. 

 In this way the wire does not invade either the articular or the 

 subcutaneous surface of the bone (Fig. 137). 



Dislocation of the Patella may be due to violence or to 

 exaggerated muscular action, occurring when the limb is extended 

 and the tendinous expansions of the vasti are relaxed. The 

 dislocation is usually over one or other condyle, but occasionally 

 the bone is twisted round through a right angle so that its 

 surfaces look medially and laterally. Reduction can only be 

 effected after complete relaxation of the quadriceps. 



FIG. 137. Diagram to illustrate 

 how a Fractured Patella may be 

 wired, without interfering with the 

 articular surface. 



A. Anterior view. 



B. Lateral view. 



