Stick Bones: Ulna

What if you were presented with the 4 stick bones? Would you be able to tell them apart?  The two bones of the lower arm, or the distal portion of the arm, have distinct shapes at their heads. These are their proximal ends.  The ulna has this characteristic U that students like to use to identify it.  The radiusLateral forearm bone (thumb side); rotates around ulna during pronation/supination. has this cup shaped end.   The tibiaShinbone; large, weight-bearing medial bone of the lower leg., like the ulna, is the larger of the lower leg bones.  The fibulaSlender lateral leg bone; stabilizes ankle but bears little weight., like the radius, is the smaller of the two bones leg bones.  For all of these bones, these are the heads.  We know that the head is usually found on the proximal end of the bones like the femurThigh bone; longest and strongest bone in the body; has a large round head and prominent trochanters. It is also found on the humerusLong bone of the upper arm; articulates with scapula at shoulder and radius/ulna at elbow.. The same applies here.  Just like the U on the ulna, there are other features that can help us tell apart these bones.  Understanding how the ulna fits into the radius is important. Knowing how the fibula fits into the tibia is also crucial. These insights can help us identify not only these bones but the landmarks on them.

Let’s shift now to the arm bones: the ulna and the radius.  I like to do the ulna first, which correlates with the tibia.  Let’s start with the distal end of this bone, which has a somewhat sharp point on it.  Bend the wrist of your left hand. Take your right index finger and thumb and feel the points on the lateralAway from the midline of the body. and medialToward the midline of the body parts of your wrist. These are the styloid processes.  A stylus is a pen or pencil.  These points use that reference in their names.  There are other styloid processes in your body, one being on the skull.  You will find that names are used to describe similar features on different bones.  The point on the medial or pinky side of your wrist is the styloid processThere are many styloid processes in the human body. All are pointed projections that serve as muscle of the ulna.  The wrist point on the thumb side of your wrist is the styloid process of the radius.  Look at a picture of an arm in the anatomical positionA standard reference position where the body stands upright, facing forward, with arms at the sides.  Notice how the ulna is medial in this view.  Yes, ulna, medial, pinky finger – don’t forget it.  This means that the radius is lateral to the ulna in the anatomical position.  This side-by-side orientation helps us understand where the radial notchSmall depression on ulna where head of radius fits. is.  It is on the lateral side of the ulna.  The radius articulates with the ulna at the radial notch.  

When we try to look at the head of the ulna, it’s useful to get the humerus involved.  If you have a disarticulated skeleton, be sure to have the ulna and the humerus out.  Move the elbow, watching the u of the ulna rotate around the trochleaSpool-shaped medial condyle that articulates with ulna at the elbow. of the humerus.  The U itself is called the trochlear notchDeep, U-shaped depression between coronoid and olecranon processes that grips the trochlea. and is where the trochlea of the humerus articulates with the ulna.  The top of the U fits into the back of the humerus or the olecranon fossaLarge posterior depression for olecranon process when elbow extends..  This point on the ulna is called the olecranon processLarge, curved posterior projection—forms the bony point of the elbow..  The other point of the U fits into the coronoid fossaSmall anterior depression above trochlea for coronoid process of ulna when elbow flexes..  This is the coronoid processTriangular projection on mandible’s upper front edge for muscle attachment; in front of the condyl.  The fossae on the humerus correspond in name to the processes on the ulna. This is why it might be important to study bones together and not necessarily separately.  

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