[Characteristics of articular caps of the elbow in relation to flex-extension movement]

Considering the factors limiting flexo-extension movements of the elbow, particular importance has been given to the possible existing contact between its articular ends in the final stage of the movement. However, this factor has different importance according to the angle formed by the ulnar and humeral diaphysis with their respective epiphysis. Some authors assert that humeral and ulnar articular ends do not come into any contact during the first stage of the sigmoid cavity movement on the trochlea, according to their opinion, in fact, an angle of 45 degrees should exist between the prolongation of the humeral diaphysis axis and the lower epiphysis and the great ulnar sigmoid cavity should be oriented forward and high forming an axis that is inclined of 45 degrees the horizontal plane. In order to verify this affirmation, we have measured the width of these angles in 50 soaked humeri and 50 ulnas. The same angle has been measured in 50 radiograms of partially flexed laterally projected elbows. The mean observed values have been of about 34 degrees for the distal epiphysis-diaphysis angle in humeri and of about 25 degrees for the inclination angle of the orientation axis of the great ulnar sigmoid cavity. The results show that - when humeral epiphysis-diaphysis angle is larger or eventually equal to the ulnar one - it is sufficient that the considered angles are less than 45 degrees to get a correct and complete flexo-extension movement.