the body’s directions

Wednesday, March 1, 2017

Another evening in the world of sport and another round of players being helped off the court. Last night, it was Kevin Durant with a medial collateral ligament sprain and worry that because of mechanism of injury, his anterior cruciate, the ACL, might be torn. Anterior, posterior, medial, lateral, the directions of the body can be a mystery, even to those inside the medical community. North, south, east, west, up, down don’t exist in medicine.

The body’s road map has many different directions. and it all starts with the anatomic positon, best illustrated by Da Vinci’s Vitruvian Man and the basic coordinate   :

  • The heart is the center of the body. Move away from the heart and you’re going distal, move closer to the heart, you’re now more proximal. The wrist is distal to the elbow, but the elbow is proximal to the wrist.
  • The front of the body is anterior and the back is posterior. But it’s important to look at Da Vinci’s man because the hands are a special case that we’ll visit in a bit.
  • Draw a line from the nose to the belly button and that is the midline. Move away from the midline and you’re lateral; move closer to the midline and you’re now The ear is lateral to the cheek and the nose is medial to the eye.
  • Up and down don’t exist. You’re either moving cephalad towards the top of head or caudad towards the bottom or the tail.

The anatomy directions are standard stuff and don’t change regardless of whether the patient is standing, sitting or lying flat. But some parts of the body have special directions.

The hand is special perhaps because its function is so important to the way the body works. Look again at how Da Vinci lines up his man. The arms are at the side with the palms facing forward. That can be confusing because the little finger, what many people consider the outside of the hand is really medial and the thumb is lateral. To avoid any confusion, directions in the hand are different.

  • The anterior hand is called the palmar surface and the back of the hand is called the dorsum.
  • The radius and ulna are the two bones in the forearm that connect to the wrist. The thumb is on the radius side and the little finger on the ulna. The midline of the hand runs from the tip of the middle finger to the wrist and stuff is described as either radial or ulnar. The index finger is ulnar to the middle finger but medial to the thumb.
  • Each finger has three joints named by the bones that meet at each (the thumb only has two), metacarpophalageal joint (MCP), proximal interphalangeal joint (PIP)and distal interphalangeal joint (DIP). Describing the fingernail, it is located on the dorsum of the finger, distal to the DIP joint.

The abdomen is divided into quadrants, the neck has zones, the eye has chambers, the foot has a plantar surface (the sole). There are special terms for most body parts that become the foreign language that is medicine and anatomy.

It’s important to understand the body’s directions to help people understand, through words, the geography of the body, and to help explain to one another where stuff is happening. For Mr. Durant and his MCL injury, the medial collateral ligament runs from the femur to the tibia on the medial part of the knee. If you tried to explain it as the inside part, that might be confusing because the MCL is not located inside the knee joint, but instead it is outside the joint towards the midline of the body.

Direction terminology is especially important when health professionals talk to each other so that can help visualize the body and the description of an injury, rash, lump or bump. East and west is good for maps but not for arms and legs, while up and down works for elevators. But in the medical world, using the same language makes good things happen.


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