Extensor Tendon Injuries

Mark Henry

INTRODUCTION

Pathoanatomy
- Extensor mechanism—multiple origins and multiple insertions
- Extensor digitorum communis (EDC) and proprius tendons—extrinsic origins
- Interossei and lumbricals—intrinsic origins
- Insertions—direct at the base of the distal phalanx (P3) and the middle phalanx (P2) via sagittal bands at the base of the proximal phalanx (P1)
- Juncturae tendinum transverse connections between EDCs at the metacarpal level.
Mechanism of injury
- Closed tensile failure rupture (base of P3, P2, sagittal bands)
- Open sharp laceration (anywhere)
- Segmental loss as part of industrial trauma involving adjacent structures
Epidemiology
- Active adults of all ages, both sexes, wide spectrum

EVALUATION

History
- Mechanism of injury—tensile overload versus sharp laceration versus complex trauma
- Closed versus open
- Specific object causing open injury
- Degree of contamination
- Patient demographics/risk factors (diabetes, vascular disease, smoking)
Physical examination
- Demonstration of tendon function/lack of function across injury zone (Figure 31.1)
- Appearance of early central slip avulsion is subtle (flexible boutonniere), but key is hyperextension of distal interphalangeal (DIP) with attempted proximal interphalangeal (PIP) extension (Figure 31.2).
- Active extension versus resistance from initially flexed PIP joint required to prove insertion at base of P2, simply maintaining extension not sufficient
- Check for coronal subluxation at metacarpophalangeal joints—ruptured sagittal band
- Proximal EDC laceration can be partially substituted by juncturae tendinum.
Imaging
- Distinguish tendon avulsion at base of P3 from shearing impaction fracture of DIP/PIP joint (Figure 31.3).
- Not all fracture fragments at the dorsal base of P2 represent loss of central slip continuity (Figure 31.4)—requires physical examination.
Classification (Table 31.1)

FIGURE 31.1 Terminal tendon avulsion leaves patient unable to actively extend distal interphalangeal joint.

FIGURE 31.2 Early evaluation of a central slip avulsion is subtle, but the hallmark feature is the hyperextension posture of the distal interphalangeal joint while the patient attempts to extend the proximal interphalangeal (further tested by resisted extension from a flexed posture).

ACUTE MANAGEMENT