Phalanges of the hands
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The phalanges (single: phalanx) of the hands are the tubular bones of the fingers and thumb. The second to fifth fingers each contain a proximal, middle and distal phalanx whereas the thumb only contains a proximal and distal phalanx.
The middle and proximal phalanges each have a base proximally, head distally, and body in between. The bases are concave in order to articulate with the convex head of the more proximal metacarpal or phalanx. The distal phalanges also have a concave base, taper distally, and then expand into a tuberosity that is roughened on the flexor surface for attachment of a digital fibrofatty pad 1.
- metacarpophalangeal joint: between the metacarpals and proximal phalanges
- proximal interphalangeal joint: between the proximal and middle phalanges
- distal interphalangeal joint: between the middle and distal phalanges
- the thumb only has a single interphalangeal joint
On the palmar aspect, the four tendons of flexor digitorum profundus attach to the proximal body of the distal phalanx. Flexor digitorum superficialis is inserted by two slips either side of the corresponding middle phalanx.
On the dorsal aspect, extensor digitorum spreads into the extensor expansion, which consist of three bands: lateral bands pass either side of the proximal phalanx to the distal phalanx, a median band passes to the base of the middle phalanx, and a retinacular ligament runs obliquely along the middle phalanx. The index finger expansions also receive the extensor indicis and the little finger expansions also receive the extensor digiti minimi. The interossei muscles (dorsal and palmar) also insert into the extensor expansions, with some fibers of both dorsal and palmar tendons also inserting into the base of the proximal phalanx.
The palmar ligaments (or volar plates) are thick bands of dense fibrous tissue that attach the metacarpophalangeal and interphalangeal joints. At the metacarpophalangeal joint, these are also united by the deep transverse ligament of the palm. Fibrous flexor sheaths bridge the palmar ligaments and attach along the proximal phalanges before surrounding the flexor digitorum profundus tendons on the distal phalanges. They form a series of annular (A1 to A5 from proximal to distal) and cruciform (C1 to C3) pulleys that surround the synovial sheath coverings of the flexor tendons. The A1, A3 and A5 pulleys arise from the volar plates; A2 and A4 arise from the periosteum on the proximal half of the proximal phalanx and the mid body of the middle phalanx respectively. C1 lies between A2 and A3, C2 between A3 and A4, and C3 between A4 and A5.
Collateral ligaments also attach on either side of the metacarpophalangeal and interphalangeal joints 1.
From the superficial palmar arch, a palmar digital artery supplies the ulnar aspect of the little finger. Three common palmar digital arteries then run distallly along the webspaces between the fingers, and bifurcate into proper palmar digital arteries that supply adjacent fingers on either side. From the deep palmar arch, the thumb is supplied by the princeps pollicis artery and the radial side of the index finger is supplied by the radialis indicis artery. The dorsal metacarpal arteries also provide anastomotic branches to the dorsal arch, superficial arch and common palmar digital arteries 1.
Sesamoid bones can sometimes be found at the metacarpal heads, especially the second and fifth, within the palmar capsule of the metacarpophalangeal joints. They can also occasionally be found at the interphalangeal joints 1.
The phalanges are ossified from the body and proximal extremity. Ossification of the body commences during the eighth week of fetal development. Ossification of the proximal extremity commences in the bones of the first row between the third and fourth years, and a year later in those of the second and third rows. The two centers become united in each row between the eighteenth and twentieth years 2.
The phalanges may be visualized on a number of series of the distal upper limb including:
- CT hand
- MRI finger
- MRI thumb
- phalanx fracture
- mallet finger
- jersey finger
- proximal phalanx fracture
- middle phalanx fracture
- distal phalanx fracture
- brachydactyly type A1 - Farabee type
- brachydactyly type A2 - Mohr Wreidt type
- brachydactyly type A3
- brachydactyly type A4 - Temtamy type
- Thiemann's disease
- volar plate avulsion injury
- tuberculous dactylitis
- psoriatic arthritis
- finger clubbing
- subperiosteal bone resorption