Purpose
To describe the shape of a biplanar thumb metacarpal (MC) head and identify how it
differs morphologically from previously described flat and round MC heads.
Methods
Lateral radiographs of the thumb were collected retrospectively from our patient database.
Patients were included in the study if they had an appropriate lateral radiograph,
met the age criteria (range; 18–75 years), and did not have severe metacarpophalangeal
(MCP) joint arthritis. Metacarpal heads were categorized as flat or round by dividing
the distance measured from the volar to the dorsal edge of the articular surface by
the radius of curvature of the articular surface. A ratio of 1.7 or greater indicated
a round MC head, whereas a ratio of less than 1.7 indicated a flat MC head.
Results
Among the 210 study participants, 110 were female and the average age was 47.3 years.
During the measurement and classification process, it was determined by a board-certified
hand surgeon that a subset of MCs did not meet the criteria for being categorized
as either flat or round because of the inability to appropriately measure the radius
of curvature of the MCP joint. Of the participants 113, 79, and 18, were classified
as having either round, flat, or biplanar MC head shapes, respectively.
Conclusions
We have identified a third, biplanar MC head shape. The biplanar head shape is more
triangular and has two distinct planes on the articular surface that converge into
an apex.
Clinical relevance
The shape of the MC head has been shown to influence the range of motion of the MCP
joint which may have an influence on the types of injuries that occur at the MCP joint.
Further studies are required to understand how shape classification of MC heads may
be useful and relevant to range of motion and risk of injury.
Key words
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References
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Article info
Publication history
Published online: December 19, 2021
Accepted:
September 22,
2021
Received:
September 14,
2020
Footnotes
G.M.P. and K.R.B. contributed equally to this manuscript.
No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
Identification
Copyright
© 2023 by the American Society for Surgery of the Hand. All rights reserved.
