Trapeziometacarpal Joint (Thumb)

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Wiki Revision Date - 14 Jun 2015 23:25

Trapeziometacarpal Joint (Thumb)

This section covers the first carpometacarpal joint (carpal to metacarpal) of the hand, this being the thumb however makes it a very unique joint (enabling us with a fully opposable digit) and therefore named after the carpal that it is connected to. The rest of the carpometacarpal joints are lumped in with the entire wrist.

Bones: The trapezium carpal bone and the first metacarpal of the hand (the thumb consisting of one metacarpal and two phalanx where as all the other fingers contain three phalanx).

Ligament: There are a number of ligaments holding the thumb bones in place, one of the most important being the anterior oblique ligament which connects from the trapezium to the metacarpal. This ligament takes place in abduction, extension, and pronation.

Tendon: There are a number of small tendons that connect at the thumb, the two most notable of which being the Extensor pollicus brevis and Extensor pollicus longus. These tendons run on the back of the thumb, if you place a a finger on the back of the thumb near the wrist and then expand your hand/fingers to the max you can feel the sharp rise of these tendons.

Muscles/Mechanics:

  • There is a bundle of muscles that form the meaty part of the thumb (which makes a portion of the striking surface for a palm heel strike) that include Abductor pollicus, Flexor pollicus brevis, and Abductor pollicus brevis all of which are the main force behind a strong grip closing the angle of the thumb.
  • Flexor pollicus longus: This is a deep forearm muscle that is unique in humans, it allows for the opposability of our thumb. It is on the inside of bottom of the forearm and flexes the thumb inwards towards the other fingers. You can feel the muscle's contraction with a finger placed middle inside of the bottom of the forearm and flex the thumb in, likewise with a finger at the wrist you can feel the tendon movement.
  • Adductor pollicis: This muscle is between the thumb and the index finger and brings the thumb into the same plane as the rest of the metacarpal bones. When done you can see and feel its tense contracted state on the back of the hand.
  • Extending and opening the thumb uses several muscles of the forearm being Extensor pollicis longus, Extensor pollicus brevis, and Abductor pollicis longus.

Range of motion: Flexing the thumb across the palm or extending it outwards has an overall angle of roughly 50 degrees. Adducting the thumb towards the hand or abducting it away yields roughly 40 degrees of motion. Between the different movements of the thumb there is roughly 17 degrees of rotation involved in the joint.

Opposability: Having a fully opposable thumb means that the thumb of that hand is able to touch every finger of that hand. This is what makes our thumb so useful in conjunction with our other fingers.

Usage:
Because of its full opposability the thumb's location is important in many hand strikes, here are a few examples.

  • The thumb is very important and is the main power behind a grab (opponent or weapon).
  • The thumb locks over the fingers in a punch or hammer fist strike, to avoid injury.
  • The thumb is pulled in line with the rest of metacarpals when executing a palm heel strike, to avoid injury.
  • The thumb can be clenched and braced against the first finger for a thumb knuckle strike.
  • The thumb knuckle strike can also be done open handed (thumb exercises recommended) and disguised as a slap.
  • The thumb can be clenched towards the base of pinky for a ridge hand strike, allowing the main striking surface to the be outside of the first Metacarpophalangeal Joint (Knuckle) and the Adductor pollicis.

Manipulation:

  • The thumb makes up the majority of a grasp, so if you have a weapon (with reach) the hand of the opponent can be struck.
  • Striking the back of the hand will do damage to the metacarpals and the shock damage to the top of the hand (where there are tendons for extension) will cause the hand to open some what. It will also make flexion of the fingers sore because the extensor tendon has to be stretched slightly to allow for flexion.
  • Striking to the inside of the hand will damage the small phalanxs of the fingers, as the fingers (especially the tips) have a high degree of sensitivity as the are our primary way of feeling things. That strike will also do damage to the thumb crippling the use of a grip.
  • Because of the many extrinsic muscles of the hand (muscles controlling the hand that are not in the hand) high impact to the muscles of the forearm will cause finger and thumb movement to be sore.
  • In disarming and opponent of a weapon such as a gun, quickly striking the tendons on the underside of the wrist causes the hand to flex and the fingers become loose momentarily.
  • Following the previous mechanic, say in the disarming of a knife (very useful) when close a large amount of pressure on the back of the hand will flex the wrist to its max. When this happens there is a great amount of strain on the extensor tendons of the hand which will no longer stretch (in respect to flexion) and they pull on the fingers opening the hand.
  • The thumb is built to flex and grab therefore opposite force is best to lock the thumb which will put immense force on the small tendons and ligaments which can literally bring and opponent to their knees.

Injury: Besides for random impact the main concern to this joint is arthritis where the main anterior oblique ligament may be elongated or missing entirely, and cause pain to the joint.

Strengthening: Using a small grip strengthening device, the fingers and thumbs will be come stronger. Training while gripping a jug with your fingers will strengthen the fingers and thumb as well as test the will and mindset of the student.

Stretching: Pushing the thumb backwards will help the thumb (slightly) to resist the initial pain, if their opponent knows how to manipulate the thumb. This sort of stretch designed to give you the extra half second you may need to try and get out of the hold (not to resist it entirely).

This joint because gripping works with the Metacarpophalangeal Joint (Knuckle), some of the mechanics of this joint was included as well.
For information on additional joints please refer back to the Joints page.



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