The Region of the Elbow. 71 



cation of both bones backward. Normally this displace- 

 ment is prevented by the curve, formed by the coronoid 

 and olecranon processes, grasping the rounded articular 

 end of the humerus in such a way that the coronoid 

 curves up in front and the olecranon behind, or, as 

 Deaver describes it "like a monkey-wrench fitted on to 

 a screw nut." This form of dislocation is generally the 

 result of force indirectly applied to the joint through the 

 radius, as, for instance, by falling on the palm when the 

 arm is extended so that the tip of the olecranon impinges 

 on the corresponding fossa of the humerus. This lifts 

 up or pries the coronoid from the front of the articular 

 surface of the humerus and thus removes the main 

 obstacle to dislocation, so that, the momentum of the body 

 continuing, while the hand remains stationary against the 

 ground, the lower end of the humerus is driven for- 

 ward, i.e., both bones are displaced backward. The 

 deformity in this displacement resembles that of fracture 

 above the condyles, for, though increased mobility is char- 

 acteristic of a fracture, and impaired mobility peculiar to 

 a dislocation, yet, in supracondyloid fracture, a few hours 

 may produce marked immobility, the result of muscular 

 contraction, hence, to diagnose the one from the other we 

 have to depend on features, other than the above, and, chief 

 among these, is, the relationship of the olecranon to the 

 internal condyle. When examining for any injury about 

 the elbow joint, the surgeon should sit facing the patient, 

 with the latter 's both arms flexed. He should then place 

 his thumb on one condyle, and the middle finger on the 

 other, and, with the index finger, should ascertain the 

 position of the olecranon with reference to the internal 

 condyle. Both arms should be examined at the one time 

 and it will be found, if both be normal, that the olecranon will 

 be on the same level as the condyles when the arm is 



