Cast for schaphoid fracture

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Cast for Scaphoid Fracture

The Scaphoid (Thumb Spica) Cast

The standard cast for scaphoid fractures is the thumb spica cast (also called the "scaphoid cast"). The key positioning is:

Wrist: slight dorsiflexion (slight extension)
Thumb: abduction and slight flexion - as if holding a glass between the index finger and thumb
Extent: from just below the elbow to just proximal to the metacarpal necks; on the thumb, to just proximal to the interphalangeal joint

Scaphoid cast illustration - forearm cast with thumb immobilized

Figure: Standard scaphoid cast (Rockwood & Green's Fractures in Adults, 10th ed., p. 333)

A modification - the extended scaphoid cast - includes the entire thumb and is used for fractures distal to the MCP joint of the thumb.

Cast Type by Fracture Location

Fracture Location	Cast Type	Duration
Scaphoid tubercle (distal avulsion)	Short-arm thumb spica	4-6 weeks
Distal third	Short-arm thumb spica	4-6 weeks
Waist (middle third) - nondisplaced	Short-arm cast ± thumb spica	6-8 weeks (up to 10-12 weeks)
Proximal third	Long-arm thumb spica x 6 weeks, then short-arm thumb spica x 6+ weeks	Up to 6 months total

Above-Elbow vs. Below-Elbow Debate

This has been extensively studied. Multiple randomized trials have shown no advantage to above-elbow (long-arm) casts over below-elbow casts for waist fractures. A biomechanics study confirmed the key motions to prevent scaphoid stress are wrist extension and ulnar deviation - both controlled by a short-arm cast. Immobilization in slight extension is preferred, as immobilization in flexion reduces wrist extension at follow-up without improving union rates.

Current evidence therefore supports short-arm (below-elbow) cast as the preferred method for nondisplaced waist fractures, rather than the classic long-arm or scaphoid cast.

Management Protocol

Suspected fracture (radiograph negative, snuffbox tender):

Apply short-arm thumb spica cast immediately
Re-examine + repeat X-ray at 2-3 weeks
If still tender but no fracture visible: re-cast for 2-3 more weeks
If still no fracture on repeat imaging and tenderness resolves: no fracture was present

Confirmed nondisplaced fracture:

Short-arm cast for 6 weeks, then CT to assess healing
If <50% healed on CT: extend cast another 2-4 weeks
If >50% healed: begin active mobilization
CT confirmation of union at ~3 months; return to forceful activity only after clear radiographic union (typically 4-6 months)

Displaced fracture (gap >2 mm, scapholunate angle >60°, radiolunate angle >15°): Refer for surgical fixation (percutaneous screw).

Key Clinical Points

Always immobilize when snuffbox tenderness is present, even with negative initial X-rays - scaphoid fractures are notoriously occult on early plain films
Nondisplaced fractures achieve >90% union with cast alone
Proximal pole and displaced fractures carry higher risk of avascular necrosis and nonunion - these often need operative management or orthopedic consultation
Complications to counsel the patient about: AVN, delayed union, nonunion, and wrist arthritis

Sources: Rockwood & Green's Fractures in Adults, 10th ed. (2025), pp. 333, 1895-1900; Pfenninger & Fowler's Procedures for Primary Care, 3rd ed., p. 1322; Textbook of Family Medicine, 9th ed.

Anatomy of schaphoid bone

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Anatomy of the Scaphoid Bone

Overview

The scaphoid (from Greek skaphe = boat) is also called the navicular bone of the wrist. It is the largest bone of the proximal carpal row, located on the radial aspect of the wrist. It is a small, irregular, S-shaped tubular bone lying entirely within the wrist joint, oriented at a 45-degree angle to both the longitudinal and horizontal axes of the wrist.

Its long axis runs distally, laterally, and volarly - so it bridges the proximal and distal carpal rows simultaneously, which makes it unique.

Parts of the Scaphoid

The scaphoid is divided into three regions:

Region	Features
Proximal pole	Convex articular surface; articulates with the radius
Waist	Narrowest part; most common fracture site (~70% of fractures here)
Distal pole (tubercle)	Palpable volar prominence; has two facets for trapezium and trapezoid

The scaphoid tubercle is a palpable prominence on the volar (palmar) surface where the transverse carpal ligament (flexor retinaculum) attaches. It is a key surgical landmark and the site of entry for the volar blood supply.

The dorsal ridge (nonarticular dorsoradial surface) runs across the bone and carries the critical dorsal vessels and ligament attachments.

Articulations

The scaphoid articulates with 5 bones - more than any other carpal bone:

Surface	Articulates With
Proximal/lateral	Radius (radial fossa)
Distal (2 facets)	Trapezium and Trapezoid - forms the STT (scaphotrapezio-trapezoid) joint
Medial (ulnar side)	Lunate and Capitate (head of capitate fits into a sulcus on the scaphoid's ulnar surface)

Over 80% of the scaphoid's surface is covered with articular cartilage, leaving very little periosteal surface for bone healing - this is a major reason for the high rate of nonunion.

Blood Supply

The blood supply is precarious and largely retrograde - entering distally and flowing proximally - supplied by two pedicles from the radial artery:

Figure 44-17: The two vascular pedicles of the scaphoid (Rockwood & Green's, 10th ed.)

1. Dorsal branch of the radial artery (dominant supply)

Enters via small foramina along the dorsal ridge just distal to the waist
Flows retrograde (distally to proximally)
Supplies 70-80% of the scaphoid, including the entire proximal pole
This is the main reason why proximal fractures risk AVN

2. Volar (palmar) branch of the radial artery

Enters via the scaphoid tubercle
Supplies the remaining 20-30% - the distal portion only

Clinical consequence of this pattern:

Only 67% of scaphoids have arterial foramina throughout all three regions
20% have foramina mainly at the waist with virtually none in the proximal third
Proximal third fractures may have no residual blood supply to the proximal fragment
Risk of avascular necrosis (AVN) of the proximal pole: up to 35% for proximal pole fractures
Waist: the waist itself has minimal or no perforating vasculature - fractures here disrupt the retrograde flow

Ligamentous Attachments

The scaphoid has no tendon attachments. Its ligamentous attachments are mostly on the nonarticular dorsoradial surface:

Scapholunate interosseous ligament (SLIL): connects scaphoid to lunate; key stabilizer; rupture causes scapholunate dissociation
Radioscaphocapitate (RSC) ligament: does NOT attach to the bone itself - it crosses the waist, acting as a volar sling or fulcrum around which the scaphoid rotates
Short intrinsic ligaments: connect to adjacent carpal bones, especially the lunate
Dorsal intercarpal ligament: attaches on the dorsal ridge

The RSC ligament's sling-like relationship to the waist is important - it is why hyperextension of the wrist generates a bending moment at the waist, causing the classic waist fracture.

Biomechanical Role

The scaphoid acts as a "bridge" or intercalated segment linking and synchronizing motion between the proximal and distal carpal rows:

It rotates proximally and glides distally with wrist motion
It participates in nearly all carpal movements, especially volar flexion
Because it connects to so many bones (5 articulations), any disruption - fracture, nonunion, or ligament tear - causes progressive carpal collapse and wrist arthritis (SNAC wrist: Scaphoid Nonunion Advanced Collapse)

Why the Scaphoid Fractures So Easily

The combination of:

Bridging position spanning both carpal rows
45-degree oblique orientation
Large proportion of articular surface
Retrograde blood supply

...makes the scaphoid the most commonly fractured carpal bone (~60-70% of all carpal fractures), typically from a fall on an outstretched hand (FOOSH) with wrist hyperextension, where the RSC sling concentrates tensile forces at the waist.

Sources: Rockwood & Green's Fractures in Adults, 10th ed. (2025), pp. 1882-1884; Campbell's Operative Orthopaedics, 15th ed. (2026), p. 4192; Imaging Anatomy: Bones, Joints, Vessels & Nerves, pp. 550-551; Miller's Review of Orthopaedics, 9th ed., p. 733

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