HUMAN KNEE ANATOMY

Standard Anatomical Position

The first thing to be aware of is the standard anatomical position. This is the position all movements are derived from of the human body. This position is important to remember; when we use terms of direction to explain limbs assuming that they're in the standard anatomical position.

In human anatomy 'left' and 'right' refer to the left and right of the topic of observation not the observer, for example if I were to refer to the left arm I would be referring to the arm on our (the observer's) right.

Planes

In human anatomy often hear planes used to describe modes of movement or the location of structures (in relation to other structures). A plane is essentially an imaginary line through the human body. Different planes divide the body into different sections. There are 3 basic planes:

Sagittal (median) Plane

This is any vertical plane which runs from the front of the body to the back. As a result it partitions the body into right (dexter) and left (sinister) sections.

It is important to remember this doesn't just apply to the human body as a whole; it can be applied to the orientation of any individual body part.

Coronal (frontal) Plane

The coronal plane is another vertical plane, but it runs at a right angle to the Sagittal plane. It runs from left to right dividing the body into front (ventral) and back (dorsal) sections.

As with the Sagittal plane, it can be applied to individual body parts as well as the whole body.

Transverse (axial, transaxial) Plane

The transverse plane is a horizontal plane that runs perpendicular to the Sagittal and Coronal planes. It separates the body into upper (superior) and lower (inferior) sections.

As always this plane can be applied to individual body parts.

Glossary of directional terms

Below are listed a number of commonly used directional terms relating to human anatomy. It is important to consider that whilst these terms are commonly used they can vary significantly between disciplines. It should be noted that these terms apply to human (medical) anatomy and physiology not veterinary (or zoological) anatomy.

Proximal and Distal: Proximal and distal are terms used primarily in the description of limbs. Distal means further away from the torso whilst Proximal refers to the point where an appendage or limb attaches to the torso. To connect the two points creates the Proximodistal Axis. It is important to remember that these terms are relative; for example, the elbow is distal to the shoulder but it is proximal to the hand.

Lateral (externo), Medial (interno) and Intermediate: These terms are used in reference to the mid-line of the human body (the line through which the sagittal plane runs). Medial refers to structures closer to the medial line (i.e. the centre) whilst lateral refers to structures further away. Intermediate describes a structure between a medial and lateral structure. It is important to remember these terms are relative. For example, the nose is medial to the eyes. The eyes are medial to the ears. The ears and eyes are both lateral to the nose, and the cheeks are intermediate between the nose and the ears.

Anterior and Posterior: The term anterior (or ventral) refers to the front of the body (as split by the coronal plane). Posterior (or dorsal refers to the back of the body. These terms are generally used in conjunction (i.e. anterior and posterior, not anterior and dorsal). Over the whole of the body these terms can be used interchangeably with the exception of the brain (where dorsal means toward the top of the head and ventral means toward the bottom).

Cephalic and Caudal: The term cephalic (also known as cranial, rostral or superior) means toward the upper section or head whilst Caudal (inferior) refers to the lower part of the structure or away from the head. These terms are used in conjunction (cephalic and caudal, superior and inferior, not cephalic and inferior). They are once again relative and can refer to individual body parts as well as the human body as a whole. For example the knee is inferior to the hip, but superior to the foot.

Superficial: This refers to structures close to the surface of the body. The opposing term is deep. For example the brain is deep to the skull whilst the skull is superficial to the brain.

Types of movement

Flexion and Extension: These terms are used to describe movements in the sagittal plane (i.e. movements forwards and backwards rather than side to side). Flexion decreases the angle between to bones at a joint, an example is when the knee is raised. Extension is the straightening of a limb (it increases the angle between two bones at a joint), for example bringing the hand down from the shoulder.

Additionally, flexion and extension in the ankle are know as Plantarflexion and Dorsiflection

Hyper-extension is the action of extending the joint beyond 180 degrees. Hyper-extension is most commonly associated with joint injury.

Protraction and Retraction: Protraction is the action of moving a part of the body forward along the transverse plane by movement of anterior muscles. Retraction is the exact opposite.

Abduction and Adduction: Abduction is the movement of a limb away from the coronal plane of the body. Raising the arms from the hips so a 'T' shaped is formed is an example of abduction, as is the spreading of the fingers. Adduction is movement of a limb back toward the coronal plane.

Rotation: This is movement around its axis without lateral or medial displacement, for the turning of the head to look left or right.

Circumduction: This term describes the actions of flexion, abduction, extension, adduction performed one after the other. The over all movement means that the proximal end of the limb remains stationary whilst the distal moves in a circel (the limb thus outlines a cone).

Pronation and Suppination: Pronation is the movement of the hand from upward facing palm (anterior position) to a downward facing (posterior) position. The rotation is in no way as a result of movement of the arm. Suppination is the exact opposite movement.

Elevation and Depression: Depression describes the movement at a joint which results in downward (inferior) movement. Elevation is the exact opposite of this and results in superior movement. The action of shrugging the shoulders is an example of elevation followed by depression.

Inversion and Eversion: These terms primarily refer to movements of the feet, often in relation to injury (e.g.sprains). Inversion is the movement in the sole inwards (toward the sagittal plane). Eversion is the movement of the sole to face outward (away from the sagittal plane).

Opposition, Aposition and Reposition: Opposition (a term used expressly to describe the thumb) occurs when the hand assumes a holding position. It is important to consider that this term is used with varying specificity (i.e. some anatomists may use this term only to describe the thumb in contact with the little finger, whilst others may be less specific). Aposition (again unique to the thumb) is a broader term used to describe numerous positions of the thumb whilst holding (some anatomists consider these positions to be covered by opposition). Reposition is the movement back to the standard position.

Testing yourself will speed up how quickly you're able to retain these terms and thus increase your understanding of anatomy.