Base of the Thumb Fractures
Thao Nguyen
Ngozi Mogekwu Akabudike
INTRODUCTION
Base of the thumb metacarpal fractures can be divided into:
Extra-articular fractures
Transverse
Oblique patterns
Intra-articular fractures (Figure 9.1)
Bennett—described by E. H. Bennett in 1881 to refer to an avulsion of the palmar-ulnar fragment of the metacarpal base.1 This fragment remains attached to the trapezium via the anterior oblique ligament (AOL).
Rolando—defined by S. Rolando in 1910 as a three-part Y- or T-fracture pattern that includes the shaft, the palmar-ulnar (Bennett) fragment, and the dorsal-radial fragment.2
Comminuted—reserved for less than three fragments; however, they are often classified with Rolando fractures.
Epidemiology
Fractures involving the thumb metacarpals are common, accounting for 25% of all metacarpal fractures in the hand, with 80% occurring at the base.3
Bennett fracture is the most common type of metacarpal base fracture of the thumb.3
Mechanism of injury
Bennett and Rolando fractures typically occur by an axial force on the thumb in flexion.
Anatomy
Muscles acting at the first trapeziometacarpal (TM) joint include (Figure 9.2):
Abductor pollicis longus (APL)—inserts at the radial base of the metacarpal
Adductor pollicis longus (AdPL)—inserts on the ulnar tubercle at the base of the proximal phalanx
Flexor pollicis longus (FPL)—inserts on the palmar base of the distal phalanx
Extensor pollicis longus (EPL)—inserts on the dorsal base of the distal phalanx
Extensor pollicis brevis—inserts on the dorsal base of the proximal phalanx
Joint stability is mainly derived from the:
Joint capsule
Bony anatomy
The TM joint is a double or biconcave saddle joint (Figure 9.3) that allows motion in several planes: flexion-extension,
abduction-adduction, and pronation-supination. Its biconcavity provides nearly 47% of the joint stability in opposition.4
The palmar beak of the thumb metacarpal interlocks into the recess of the trapezium.
Ligaments
The AOL, also known as the palmar beak ligament, originates from the trapezium and inserts at the palmar beak of the thumb metacarpal. The AOL provides 40% of the resistance to pronation.4 In addition, as the main capsular reinforcement, it resists dorsal radial subluxation during key pinch.
The anterior and posterior intermetacarpal ligaments, between the thumb and index metacarpals, provide resistance to supination.
The dorsal ligament complex, composed of the dorsal radial and the posterior oblique ligaments, originates from the trapezial tubercle and inserts at the radial base of the metacarpal and sometimes partly under the APL insertion.5 It is the main restraint in preventing dorsoradial subluxation and is the key in providing TM joint stability during power pinch/grasp.5,6,7
TM joint motion is coupled:
Flexion is combined with pronation
Hyperextension is combined with supination
Arc of motion is wide allowing for pinch, grip, and opposition.8
Flexion-extension on average is 53°
Abduction-adduction on average is 42°
Pathoanatomy
The direction of deforming forces is determined by the pull of the musculotendinous attachments.
Extra-articular fractures occur with apex dorsal angulation because the FPL flexes the distal fragment, whereas the APL extends the metacarpal base.
Intra-articular fractures
In Bennett fractures, the AdPL pulls the metacarpal shaft into adduction and supination, whereas the APL and thumb extensors displace it proximally.
In Rolando fractures, the palmar-ulnar (Bennett) fragment remains in place, attached to the trapezium via the AOL, whereas the APL displaces the dorsoradial fragment. The metacarpal shaft is adducted because of the pull of the AdPL and EPL.
 FIGURE 9.1 Classification of intra-articular thumb metacarpal fractures. |
 FIGURE 9.2 Forces acting at the first trapeziometacarpal joint. A, Illustration of the biconcave saddle joint of thumb trapeziometacarpal joint; B, Radiographs demonstrating the biconcave saddle joint of the thumb trapeziometacarpal joint. Courtesy of Thao Nguyen and Ngozi Mogekwu Akabudike. |
 FIGURE 9.3 Bony anatomy of the trapeziometacarpal joint. A, Illustration of the biconcave saddle joint of thumb trapeziometacarpal joint. B, Radiographs demonstrating the biconcave saddle joint of the thumb trapeziometacarpal joint. Courtesy of Thao Nguyen and Ngozi Mogekwu Akabudike. |
EVALUATION
History and physical examination
Patients will either report a fall on an outstretched hand or a direct axial load on the thumb from contact sports or high-energy trauma.
On examination, they will have swelling and ecchymosis at the base of the thumb along with tenderness. The thumb may be angulated with decreased range of motion.
Imaging
Standard radiographic imaging should be obtained for complete evaluation.
Anteroposterior (AP) view—to obtain a true AP or Robert’s view of the TM joint, the hand/forearm is hyperpronated so that the dorsum of the thumb lies flat on the radiographic plate (Figure 9.4A).
Lateral view—a true lateral or Bett’s view of the thumb requires the palm to be pronated 15° to 35° and the beam angled 20° distally9 (Figure 9.4B)
Oblique view
Traction radiographs may be helpful to assess the effect of ligamentotaxis on reduction.
Classification
Bennett fractures have been categorized into three types by Gedda10:
Type 1—a large single ulnar fragment and subluxation of the metacarpal base
Type 2—an impaction fracture without subluxation of the thumb metacarpal
Type 3—a small ulnar avulsion fracture fragment in association with metacarpal dislocationRelated posts:
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