The part of the ulna that forms a hinge with the humerus  is called the olecranon.  The smooth, round part of the  humerus the fits to the olecranon is known as the  trochlea. Olecranon fractures often occur as the result of a fall or  other direct trauma to the point of the elbow.  They may  also occur with a fall on an outstretched arm  accompanied by a strong contraction of the triceps  muscle. Olecranon fractures cause elbow pain, especially at the  back of the elbow.  The person may be unable to extend  (straighten out) the elbow.  There may be a divot just  below the tip of the elbow.  Elbow movement is painful.   Swelling and bruising are often present.  Pain/tenderness at the olecranon  Pain with elbow motion  Possible deformity Possible inability to actively straighten the elbow Diagnosis is based on:  History - fall or blow to the elbow resulting in elbow  pain. Physical exam - tenderness over the olecranon with  or without deformity or inability to extend the elbow. X-rays CT scan - a CT scan gives a more detailed, 3- dimensional view of the fracture.  A CT scan is not  always necessary, but can be helpful in evaluating  the fracture if surgery is being considered. A CT scan can provide a more detailed,  3-dimensional view. Treatment for olecranon fractures depends on whether  the olecranon is displaced and on whether the person  with the fracture is healthy and needs a well-functioning  elbow. A displaced olecranon fracture can result in damage to  the cartilage that pads the elbow joint.  It can also change  the mechanics of the elbow so it does not bend correctly.   Surgery involves making an incision over the olecranon to  expose the fracture.  The broken fragment is pushed back  into place (reduced) and fixed in place with hardware  such as a plate and screws.  This is known as open  reduction-internal fixation (ORIF). Nondisplaced fractures have the potential to heal without  surgery.    Long arm cast with elbow bent to about 45-90° Ice, elevation  Rest (no use of the arm) Protected range-of-motion exercises after 3 to 6  weeks X-rays are obtained every 1-2 weeks to ensure that the  fracture is healing well.  When there is evidence of solid  healing, activity can be gradually increased.