The trapezium bone is one of the carpal bones located in the hand. It forms the radial border of the carpal tunnel in the hand. The trapezium is an irregularly-shaped carpal bone.
The trapezium is found within the distal row of carpal bones, and is directly adjacent to the metacarpal bone of the thumb. The carpal bones function as a unit to provide a bony superstructure for the hand.
The trapezium is the most radial of the bones surrounding the carpal tunnel. It is important in primary movement of the thumb. Since this area is a helper in the primary movement of the thumb.
The trapezium is very susceptible to arthritis at the joint with the metacarpal bone of the thumb, due to overuse throughout time.
The first metacarpal bone is associated with the thumb. The joints between the carpals and the metacarpals are known as carpometacarpal joints.
The joints between the metacarpals and the proximal phalanges are known a metacarpophalangeal joints. In addition, the bases of the metacarpal bones articulate with each other.
The first carpometacarpal joint of the thumb is particularly important; the articulation between the first metacarpal and the trapezium bone forms a saddle joint and allows a wide range of movement, including flexion, extension, abduction, adduction, circumduction and opposition of the thumb.
The joint at the base of the thumb which allows flexion, extension, abduction, adduction, circumduction and opposition of the thumb is referred to as the basal joint or thumb CMC (carpometacarpal) joint.
Because the way this joint is designed, it tends to wear out and develop arthritis early in life. Basal joint arthritis is one injury that is common to the trapezium/first metacarpal joint.
It causes pain at the base of the thumb,particularly during pinching or gripping. It also results in weakness when pinching. This joint appears to be particularly prone to wear and tear from normal use of the hand.
Another injury that can happen to first metacarpal joint is a fracture. A common fracture to this area is called a Bennett's fracture. This fracture of the base of the first metacarpal is resultant dislocation of the first carpometacarpal joint.
The fracture is very unstable and inadequate treatment leads to osteoarthritis, weakness and loss of function of the first carpometacarpal joint. It is the most common fracture to affect the thumb and is a serious injury especially to this area.
Bennett's fracture usually occurs due to a blow to a partially-flexed first metacarpal, such a punch with a clenched fist.
A Bennett’s fracture can present as acute, severe pain and swelling at the base of the thumb, with grossly reduced movement at the first carpometacarpal joint. Instability at the carpometacarpal joint may be noted with gentle stressing of the thumb metacarpal bone.
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