1 The Anatomy and Functional Importance of Finger Joints: A Short Atlas



Martin Franz Langer, David Warwick, Frank Unglaub, and Jörg Grünert


Abstract


The finger joints are incredible. They are effective and precise, mobile yet stable. This chapter presents an anatomical atlas to help the reader understand the detailed anatomy, kinematics, blood supply, and innervation of all the finger joints from the DIP to the CMC. Particular emphasis is placed on the precise structure and function of the collateral ligaments; the mechanics of the joints can be understood through the concept of two different centers of rotation of the joints: one osteocartilaginous and one ligamentous.




Key words

finger joint – anatomy – biomechanics – innervation – kinematics – collateral ligaments – blood supply – center of rotation

1 The Anatomy and Functional Importance of Finger Joints: A Short Atlas



1.1 Introduction


The wonderful diversity of hand function is achieved through the large freedom of movement of the fingers, which allows both stability and precise alignment of the finger joints. As Aristotle observes: “The hand is the ‘tool of tools’” (Aristotle, Parts of animals IV 10, 687a: 8–10).


The anatomy, biomechanics, and mode of action of the finger and thumb joints are illustrated throughout this chapter.

Fig. 1.1 (a) When the extended interphalangeal joints are flexed at the metacarpophalangeal joints so the finger tips are brought together, they enclose a sagittal axis that runs through the head of Metacarpal III. (b) If the fingers are bent at the interphalangeal and metacarpophalangeal joints, they enclose an axis that runs transversely in front of the metacarpal heads on the palmar side. The axes of the middle phalanges are centered on a point above the scaphoid or distal radius. (c) If the thumb and fingers are spread as far as possible, the fingers align in a circular plane. The axes of the metacarpal bones run toward a point in the radius shaft. The metacarpophalangeal joints of the fingers have the greatest lateral freedom of movement (about 40°) in this position, more toward the ulnar than the radial direction. © Martin F. Langer
Fig. 1.2 (a) Range of movement of the finger joints (metacarpophalangeal [MP or MCP], proximal interphalangeal [PIP], and distal interphalangeal [DIP]): Red: maximum range of movement. Green: functional range of movement. Blue: recommended angle for arthrodesis. The arthrodesis angles vary from digit to digit and according to the patient’s functional requirements. (b) Approximate distance of the flexor tendons and extensor tendons from the joint axes for simple rollover calculations. Tendon excursion with 10° joint flexion DIP 1 mm, PIP 1.5 mm, and MP 2 mm. © Martin F. Langer
Fig. 1.3 Which mechanisms are used to stabilize the joints? There are two important mechanisms that tension the collateral ligaments: the hypomochlion (lever-arm) mechanism and the cam mechanism (eccentric position of origin of the ligaments). In addition, the bony and ligamentous structures have different centers of rotation. This is the “double eccentric rule” of the finger joints. (a) The collateral ligaments are not stretched with a small radius. (b) With an increased radius, the collateral ligaments are tensioned. (c) In the horizontal course distally (without the hypomochlion or lever-arm), the collateral ligaments are relaxed. (d) When the joint is flexed, the collateral ligaments must run over the widened base (hypomochlion) and are tensioned. (e) The metacarpal heads are spherical dorsally and bicondylar palmar. (f) The heads of the proximal phalanges are dorsal and palmar bicondylar. (g) Metacarpophalangeal (MP) joint: The bone does not have a precise center of rotation for the joint but an area of centers of rotation on the bone (ACRb). (h) The collateral ligaments have another area of centers of rotation (ACRlig). This ACRlig is in the MP joints dorsal to the ACRb. (i) In flexion there is a double tensioning mechanism in the collateral ligament. First, due to the larger radius in flexion, and second, due to the wider base. (j) The widening of the base of the metacarpal head (hypomochlion) is blue. (k) In the MP joint both mechanisms of ligament tensioning act in the same direction. In extension both are loose and in flexion both are tensioned: “Metacarpophalangeal (MCP) additional tensioning.” (l) The ACRb of the proximal interphalangeal (PIP) joint. (m) In the PIP the ACRlig is proximal to the ACRb. The distance between ACRlig and the tubercles in extension is greater than in flexion. The collateral ligaments are tensioned. (n) In flexion the distance between ACRlig and the tubercle is short but the collateral ligament is tensioned by the hypomochlion of the palmar part of the head. (o) The widening of the palmar parts of the phalanx head (hypomochlion). (p) The cam mechanism (red) and the hypomochlion mechanism (blue) in the PIP are supplementary = “PIP supplementary-tensioning.” © Martin F. Langer
Fig. 1.4 Synovial fluid of the finger joints. (a) The incongruity of the joints is necessary. The greatest possible synovial flow is required to feed the cartilage. The contact areas of the adjacent cartilage are significantly smaller than the total cartilage area. When the finger is extended, the flexor tendon and the accessory collateral ligaments press the palmar plate against the joint and the synovial fluid from the palmar recess is pressed dorsally into the dorsal recess. (b) When the finger is flexed, the flexor tendon pulls on the palmar plate through the pulley. A suction develops that pulls the synovial fluid from the dorsal into the palmar recess. (c–e) The contact surfaces (red arrows) on the proximal interphalangeal (PIP) joint are on the inner sides of the condyles. The synovial cavity on the PIP joint is shown in (d) and (e). © Martin F. Langer
Fig. 1.5 (a) Blood supply of the metacarpophalangeal (MCP) joint. The synovial sac is amply supplied with blood at the edges of the recess. The collateral ligaments are supplied from the proximal and distal margins. (b) Blood supply of the proximal interphalangeal (PIP) joint. © Martin F. Langer
Fig. 1.6 (a) Nerve supply of the metacarpophalangeal (MP) joint. (b) Nerve supply of the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints. (c) Innervation of the first carpometacarpal (CMC1) joint—dorsal view. (d) Innervation of the CMC1 joint—palmar view. © Martin F. Langer
Fig. 1.7 CMC2 to CMC5 joints. (a) Dorsoulnar view of the hand skeleton. (b) Mobility of the CMC joints. Dorsopalmar mobility in metacarpal 3 (MC 3) is only 7°, in MC 4 20°, and in MC 5 28°. Together with MC 4, the MC 5 mobility is even 40°. (c) View of the distal articular surface of the distal carpal row. (d) There is very little mobility in the distal carpal row. © Martin F. Langer
Fig. 1.8 (a) Area of mobility of the thumb. (b) CMC 1 surface of the trapezium. (c) CMC 1 surface of the base of MC 1. © Martin F. Langer
Fig. 1.9 (a) Palmar view of the bony structures of the CMC 1. (b) Palmar ligaments of the CMC 1. (c)Thenar muscles acting on the CMC 1. ADD, adductor pollicis muscle; APB, abductor pollicis muscle; DAOL, deep anterior oblique ligament; DRL, dorsoradial ligament; FPB, flexor pollicis muscle; IML, intermetacarpal ligament; OPP, opponens pollicis muscle; SAOL, superficial anterior oblique ligament. © Martin F. Langer
Fig. 1.10 (a) Dorsal view of the bony structures of the CMC 1. (b) Dorsal ligaments of the CMC 1. (c) In abduction the radial ligaments are relaxed, the ulnar under tension. (d) In adduction the radial ligaments are tensioned the ulnar are relaxed. (e) The first carpometacarpal (CMC1) joint is a universal joint (Hooke or Cardan) with two axes. (f) Direction and position of the CMC1 joint. © Martin F. Langer
Fig. 1.11 (a) Perimetry of the index MP joint. The axis of the metacarpal is the green line. (b)Perimetry—areas of MP 2 to MP 5. (Modified from Shiino and Fick 1925.) © Martin F. Langer
Fig. 1.12 Anatomy of the metacarpophalangeal (MP) joint. (a) Metacarpal head, view from distal lateral. Dorsal part of the joint is spheric and narrow, palmar part is bicondylar and wide. (b) Origins and insertions of the collateral ligaments (red, orange, and yellow) and the accessory collateral ligaments (green, turquoise, and blue) in 0°. (c) MP ligaments in 0°. (d) Origins and insertions of the MP ligaments in 90° flexion. (e) MP ligaments in 90°. (f) Trabeculae of the metacarpal head and proximal phalanx base in sagittal section. Observe the thickness of the cartilage and of the dorsal and palmar plates. (g) Oblique view of the sagittal section of the metacarpal head. © Martin F. Langer
Fig. 1.13 Alignment of the metacarpal heads and the radial and ulnar collateral ligaments. (a) Normal position of the metacarpal heads in slightly arched position in the view from distal. The midline sagittal plane of the metacarpals is represented by black dotted lines; the main dorsal-palmar movement line represented in red is always ulnar. (b) Metacarpal head of index finger in 90° flexion shows a more prominent and more dorsal position of the radial collateral ligament. (c) Projection of the positions of the radial (blue) and ulnar (red) ligaments of the metacarpal heads. The radial ligaments are always more dorsal and more prominent. © Martin F. Langer
Fig. 1.14 Anatomy of the proximal interphalangeal (PIP) joint. (a) Lateral view on the PIP joint in 0° and 90°. The “most accurate” center of rotation of the proximal phalanx head is the red point. The centers of rotation of the radius of the proximal phalanx base are the two blue points. They differ between 0° and 90°. Notice the central contact area of the base in 0° and the more dorsal contact area in 90°. Distal-palmar to the area of centers of rotation is a flat area of the head. This flat area is important for stretching out of the collateral ligaments in flexion by the hypomochlion (lever-arm) effect. (b) The condyles of the proximal phalanx heads have an angle of divergence of 10° to 37°. (c) Dimensions of the proximal phalanx head. The summits of the condyles and the lows of the central groove are in curved lines. (d) Dimensions of the middle phalanx base. The troughs of the ulnar and radial grooves and the summit of the central ridge form curved lines. (e) Dorsal aspect of the PIP joint. (f) Palmar aspect of the PIP joint. © Martin F. Langer
Fig. 1.15 Asymmetries of the proximal interphalangeal (PIP) joints. (a) Radial and ulnar condyles of the PIP joint in the view from dorsal. Blue points: small contact area. Red points: centers of rotation of radial and ulnar condyles. Green points: centers of rotation of the radial and ulnar groove of the middle phalanx base. (b) The “PIP paradox.” Top row: axial view on the proximal phalanx heads: in most cases the radial condyles are greater than the ulnar condyles in second and third finger, and the ulnar is greater in ring and little finger. Lower row: dorsopalmar view of the proximal phalanx heads. Index and middle finger show in most cases a more prominent ulnar condyle; ring and little finger a more prominent radial condyle. So the radial condyle in index finger has the greater radius but is more proximal and the ulnar condyle is smaller but more distal. This is important for the confluence of the fingers in flexion. (c) Confluence of the fingertips in PIP flexion. Most radial and most ulnar fingers show a greater centralization. © Martin F. Langer
Fig. 1.16 Capsular structures of the proximal interphalangeal (PIP) joint. (a) Ligaments and capsular structures inserting at the base of the middle phalanx. (b) View inside the PIP joint with partially resected head and base. © Martin F. Langer
Fig. 1.17 Ligament structures of the proximal interphalangeal (PIP) joint. (a) Ligaments of the PIP joint. (b) Origins and insertions of the collateral ligaments (red, orange, and yellow) and the accessory collateral ligaments (green, turquoise, and blue) in 0°. (c) PIP ligaments in 0°. (d) Origins and insertions of the ligaments in 90°. (e) PIP ligaments in 90°. (f) The palmar parts of the condyles are most prominent laterally and form the hypomochlion parts together with the flat area. © Martin F. Langer
Fig. 1.18 Distal interphalangeal (DIP) joint anatomy. (a) Lateral view of the head of the middle phalanx. (b) Lateral view of the distal phalanx. (c) Dimensions of the head of the middle phalanx. (d) Dimensions of the base of the distal phalanx. (e) Dorsal aspect of the DIP joint. (f) Palmar aspect of the DIP joint. © Martin F. Langer
Fig. 1.19 View in the distal interphalangeal (DIP) joint after resection of the second phalanx. © Martin F. Langer


1.2 Suggested Readings










  • 8 BrandPW, HollisterAM. Clinical Mechanics of the Hand. 3rd ed. St. Louis: Mosby;1999


  • 9 BurfeindH. Zur Biomechanik des Fingers unter Berücksichtigung der Krümmungsinkongruenz der Gelenkflächen. Göttingen: Cuvillier;2003


  • 10 ChaoEYS, AnK-n, CooneyWP, LinscheidRL. Biomechanics of the Hand. World Scientific;1989











  • 20 Eaton RG. Joint Injuries of the Hand. Springfield: Charles C Thomas;1971


  • 21 Fick R. Handbuch der Anatomie und Mechanik der Gelenke Band 1–3. In: Bardeleben CV, ed. Handbuch der Anatomie des Menschen. Jena: Gustav Fischer; 1904–1911






  • 26 KaplanEB. Functional and Surgical Anatomy of the Hand. 2nd ed. Philadelphia: JB Lippincott Company;1965:39–45






  • 31 KoebkeJ. A Biomechanical and Morphological Analysis of Human Hand Joints. Berlin: Springer;1983























  • 53 SommerR. Die traumatischen Verrenkungen der Gelenke. Neue Deutsche Chirurgie Band 41. Stuttgart: Ferdinand Enke;1928







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May 4, 2022 | Posted by in ORTHOPEDIC | Comments Off on 1 The Anatomy and Functional Importance of Finger Joints: A Short Atlas

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