Meaning: What is the Trapezoid Bone
The trapezoid bone, also known as the greater multangular bone, is one of the eight carpal bones in the human hand [1]. It belongs to the category of short bones, similar to all other wrist bones [2]. Its name is derived from its four-sided angular shape resembling a trapezoid [3].
Location of the Trapezoid Bone
Situated at the base of the thumb, the trapezoid bone is positioned as the first or most lateral bone in the distal carpal row [5]. It is located between the first metacarpal (the lowest bone in the thumb) and the scaphoid, with the trapezoid bone adjacent to it [6, 7].
Trapezoid Bone
Growth and Ossification
Similar to other carpal bones, the trapezoid bone is cartilaginous at birth and begins to ossify (becoming visible in an x-ray) around the age of 4 to 6 years, which is roughly the same time at which the scaphoid and the trapezoid bones start ossifying [8].
Trapezoid X-Ray Image
Anatomy and Structure of the Trapezoid Bone
Surfaces and Articulation
The trapezoid bone articulates with the scaphoid, the trapezium, and the first metacarpal bone [7].
The proximal surface of the trapezoid, together with the trapezium, forms a slightly concave facet that articulates with the distal surface of the scaphoid [11].
The medial surface contains a large concave facet that articulates with the trapezium [7].
The distal surface creates a concave articular surface for the first metacarpal, forming the carpometacarpal joint of the thumb or trapeziometacarpal joint [10]. Occasionally, the trapezoid bone may articulate with the second metacarpal (index finger) on the inferomedial side [20].
Trapezoid Bone Articular Surface Anatomy
The broad lateral surface of the bone is quite rough, primarily to accommodate ligament attachments, while the dorsal surface is smooth without any articulation or attachments [7].
The palmar or volar surface serves as the primary site for muscular attachments [7], featuring the trapezium’s groove [12] and the adjacent prominent bony ridge or tubercle [13].
Muscular Attachments
The tubercle mentioned above gives rise to the muscles flexor pollicis brevis, opponens pollicis, and the abductor pollicis brevis [4].
Ligament Attachment
The bone’s lateral surface serves as the attachment point for the radial collateral ligament, while the flexor retinaculum, the fibrous band forming the carpal tunnel’s roof, attaches to both sides of the groove on the palmar surface [14].
Blood Supply
The primary blood supply is provided by the distal branches of the radial artery, mainly through the bone’s non-articular dorsal surface [4]. Due to its rich and constant blood supply, the trapezoid bone seldom experiences avascular necrosis, a condition common in some other carpal bones due to inadequate blood circulation [15].
Functions: Role of the Trapezoid Bone
The trapezoid bone plays a critical role in shaping the wrist’s distal joint and maintaining its flexibility. The trapeziometacarpal or carpometacarpal joint of the thumb is especially crucial for hand function. As the only saddle joint in the human body [16], it allows the thumb to move more freely than any of the fingers or the wrist, enabling the grip of objects for various activities [10, 17].
Common Injuries and Related Conditions
Representing approximately 4% of all fractured carpal bones, trapezoid bone fractures are less common. These fractures usually occur concomitantly with injuries or fractures of other carpal and metacarpal bones, often resulting from a severe accident [18].
Basilar thumb arthritis, also known as arthritis of the base of the thumb, develops when the cartilage in the trapezium-first metacarpal joint wears out. In severe cases, treatment may involve the surgical removal of the trapezium bone [19].
References
- https://www.osmosis.org/learn/Trapezium_(bone)
- https://www.visiblebody.com/learn/skeleton/types-of-bones
- https://www.dummies.com/education/science/anatomy/bones-of-the-wrist-and-hand/
- https://radiopaedia.org/articles/trapezium
- https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0023132/
- https://www.orthopaedicsone.com/display/Main/Trapezium
- https://www.healthline.com/human-body-maps/trapezium-bone
- http://sketchymedicine.com/2016/01/carpal-bone-ossification/
- http://www.mananatomy.com/body-systems/skeletal-system/carpal-bones-wrist
- https://www.jospt.org/doi/pdf/10.2519/jospt.2003.33.7.386
- https://classes.kumc.edu/sah/resources/handkines/bone/trapezium.html
- https://www.bartleby.com/107/pages/page225.html
- https://books.google.co.in/books?id=QFz-YOM0GCoC&pg=PA127&lpg=PA127&dq=trapezium+ridge+groove+tubercle&source=bl&ots=pUck5NwEZN&sig=pq_LtOrDUDkUescFbXVqJjoOtxc&hl=en&sa=X&ved=0ahUKEwimvvyG1ILcAhUEro8KHYuHDeEQ6AEIpQEwFQ#v=onepage&q=trapezium%20ridge%20groove%20tubercle&f=false
- https://www.sciencedirect.com/topics/medicine-and-dentistry/carpal-tunnel
- http://www.wheelessonline.com/ortho/trapezium
- https://www.knowyourbody.net/saddle-joint.html
- https://www.joionline.net/trending/content/trapezium-and-first-metacarpal-joint
- https://www.uptodate.com/contents/trapezium-fractures
- https://medicine.umich.edu/dept/orthopaedic-surgery/patient-care-services-hand-upper-extremity/basilar-thumb-arthritis
- https://www.kenhub.com/en/library/anatomy/carpal-bones
