Redefining Zone II: Anatomy of the Flexor Digitorum Superficialis Insertion

Abstract

The radial and ulnar FDS slips insert on average 3.22 mm distal to the PIP skin crease and vary by digit. Knowledge of the FDS insertion is clinically relevant when differentiating between flexor zone I and zone II injuries, planning surgical approaches to the finger, and in guiding patient expectations for surgery given the variability in outcome based on zone of injury.

Location of the Cut Flexor Tendons in the Palm Using Surface Anatomy: A Simple Guide for Minimal Incision Surgery

“…1 Nickle studied the junction of FDS tendon to the proximal interphalangeal crease in six pairs of hands-on cadavers. 16 He reported its location at about 3.22 mm more distal than the proximal interphalangeal crease, but this study only addressed the FDS junction with no description of the Zone 2 injuries and the position of flexor tendons in the palm. The present study examines the position of deep tendons in relation to the surface markers of the palm rather than the previously identified bone markers.…”

“…In this regard, Zone 2 is referred to as the "no man's land". 3 Some authors have proposed different methods to access the injury site. In 1944, Bunnell introduced the midaxial incision of flexor tendons; 4 the midlateral incision by Varden, 5 and in 1967, Bruner explained the zigzag volar-digital incision.…”

“…In general, the prognosis of Zone 2 injuries is poorer than the other hand zones. 3 Limited incisions prevent multiple skin flaps. However, these methods require knowledge of finger and hand surface markers to determine the exact location and anatomy of the tendons.…”

Outcomes of Primary Flexor Tendon Repairs in Zones 2 and 3: A Retrospective Cohort Study

“… 16 Tendons in zone 3 move in a more spacious environment without the confines of the fibro-osseous tunnel, allowing for surgery on both FDP and FDS tendons, even using a bulky repair. 10 , 14 , 17 In contrast, even a slight swelling of the tendon(s) in this tunnel can block zone 2 repair(s) and eventually lead to adhesions or even rupture. 14 , 18 …”

“…Zone 2 is located between the proximal border of the A1 pulley and the insertion of the flexor digitorum superficialis (FDS) tendon. 14 Zone 3 lies between the distal border of the transverse carpal ligament and the proximal edge of the fibro-osseous sheath. 15 Both zones include neurovascular structures and the flexor digitorum profundus (FDP) and FDS tendons.…”