The scaphoid bone, as the largest carpal bone in the proximal carpal row, plays a crucial role in the wrist's mechanical integrity. This article offers an in-depth examination of the scaphoid bone's anatomy, mechanics, and significance.
Summary Card
Bone Anatomy The scaphoid has three regions: proximal pole, waist (corresponding to the anatomical snuffbox), and distal pole.
Ligament Anatomy Key ligaments include Scapholunate Interosseous and Radioscaphocapitate, with volar ligaments being stronger. Interaction with tendons like Flexor Carpi Ulnaris is notable.
Vascular Anatomy Radial artery provides 70-80% of blood supply. Dorsal blood enters via dorsal ridge foraminae; volar supply is 20-30% of internal vascularity, mainly in the distal pole.
Imaging Multiple angles needed, including PA view in ulnar deviation, 60° pronation, and 60° supination. Lateral view detects DISI or VISI deformities
The scaphoid was originally termed "Naviculare" based on the Latin "navis" (ship). It is now referred to as the "Scaphoid," derived from the Greek word "skaphe" meaning a skiff or boat.
Scaphoid Bone Anatomy
Key Point
The scaphoid has a proximal pole, waist, distal pole. Unique curvatures and angles allows articulation to radial, lunate, trapezoid, and trapezium bones.
Anatomical Regions
The scaphoid forms a mechanical linkage between the carpal rows. It serves as the lateral column in the proximal carpal row arch and can be divided into three basic regions:
- Proximal pole
- Waist
- Distal pole
It possesses both a palmar concave and medial (ulnar) concave curvature. The angle from the proximal to distal pole (ie the intrascaphoid angle) is 40°± 3° in the coronal plane and 32°± 5° in the sagittal plane (Berger, 2001)
Anatomical Surfaces
The scaphoid's surfaces are often described as proximal, lateral, distal, and medial surfaces. Each surface has a specific feature and articulation. This scaphoid anatomy is described in the image below.
- Proximal surface: hemispheric, articulates with scaphoid fossa of radius.
- Medial surface: flat and crescentic, articulates with the lateral lunate surface
- Distal surface: slightly convex, articulates with the trapezoid and trapezium.
Scaphoid Ligament Anatomy
Key Point
The scaphoid's ligaments, including the Scapholunate Interosseous, Radioscapholunate, Radioscaphocapitate, and Scaphotrapezium Ligaments, play a critical role in the stability of fractured fragments, with the carpal capsule being reinforced by stiffer volar ligaments.
The scaphoid's fracture serves to highlight the importance of its ligaments, which govern the stability of the fractured fragments. The carpal capsule receives reinforcement from both dorsal and volar ligaments, with the volar ligaments being notably stronger. Some ligaments to mention include:
- Scapholunate: C-shaped structure connecting the scaphoid and lunate bones, with a thicker dorsal fiber that provides the primary constraint to their translation, while its proximal fibers possess minimal mechanical strength.
- Radioscapholunate: "ligament of Testut and Kuentz" is not a true ligament, functioning only as a neurovascular conduit without adding mechanical strength.
- Radioscaphocapitate: ligament from the radial styloid to the capitate acts as a sling to support the waist of the scaphoid
The scaphoid is also acted on by flexor and extensor tendons. More specifically:
- Flexor Carpi Ulnaris Tendon: a fibro-osseous tunnel on its distal pole.
- Extensor Carpi Radialis Brevis and Longus: bolster the posterior wrist joint capsule covering the scaphoid.
The scaphoid serves as a focus of ligamentous attachment and represents one of two areas in the proximal carpal row, the other being the pisiform, that are dynamically influenced by extrinsic musculotendinous structures
Blood Supply to the Scaphoid
Key Point
The scaphoid primarily receives blood from the radial artery, accounting for 70-80% of its intraosseous supply, with vessels accessing both externally via dorsal and volar routes and internally, chiefly through dorsal ridge foraminae
The scaphoid's vascular supply is predominantly retrograde, intricately moving from distal to proximal. It primarily receives its blood supply from the radial artery (70-80%), which further bifurcates into the dorsal carpal branch and the superficial palmar/volar branch. These vessels enter the scaphoid through distal half of the bone.
Dorsal carpal branch
- Supplies ~70%, especially its distal two-thirds.
- Enters via the foramina on the dorsum oblique ridged between the articular surfaces for the radius and for the trapezium and trapezoid
Superficial palmar/volar branch
- Supplies ~30%, especially the distal tuberosity.
- Enters via the tubercle, which is concave volar aspected with a rounded elevation.
Gelberman's landmark paper in the 1980s showed:
- The ulnar artery doesn't contribute to the scaphoid's vascularity
- The anterior interosseous artery makes a significant contribution
- There are no significant intra-osseous anastomoses between the dorsal and volar branches of the scaphoid, a result of the scaphoid emerging from the fusion of two chondrification zones.
Imaging the Scaphoid Anatomy
Key Point
Multiple imaging angles, including PA view in ulnar deviation, 60° pronation, and 60° supination, are essential for the scaphoid's detailed assessment, while the lateral view helps detect DISI or VISI deformities
The scaphoid's complex anatomy demands multifaceted imaging for a comprehensive assessment. More than two views are required due to its intricate shape and alignment.
PA View in Ulnar Deviation:
- This extends the scaphoid to provide a clear image of all scaphoid regions.
- Minimal overlap of adjacent bones.
Oblique View
- 60° Pronation: focuses the distal pole and tubercle.
- 60° Supination: focuses the scaphoid's proximal pole
Lateral View:
- A difficult view to assess the scaphoid itself due to overlapping structures
- Useful for assess any DISI or VISI deformity.
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