Acute Flexor Tendon Laceration (FDS/FDP) in Zone II: A Detailed Clinical Case Study
Key Takeaway
Acute FDS and FDP lacerations in Zone II are diagnosed via patient history and detailed clinical examination. Key findings include inability to actively flex PIP/DIP joints, indicating tendon disruption. Neurological assessment is crucial for associated digital nerve injury. Plain radiographs rule out fractures, with advanced imaging reserved for complex cases.
A 32-year-old male presents 2 hours after a kitchen knife laceration to the volar aspect of his left middle finger. He is unable to actively flex his PIP or DIP joints. You are presented with the clinical examination and this radiograph.
Based on the history and clinical findings, what is your anatomical diagnosis, and why is the biomechanical detail regarding the finger's position at the time of injury critical for your surgical planning?
Candidate: The patient has a Zone II flexor tendon injury involving both the FDS and FDP. The history of the finger being flexed when the injury occurred is important because it tells us where the tendon ends are. Since the finger was flexed, the proximal ends of the tendons will have retracted significantly proximal to the wound, so I would need to perform a counter-incision in the palm to retrieve them.
Candidates often fail to mention the specific anatomical zones or neglect to explain the "why" behind the retraction. A poor answer ignores the clinical significance of the pulley system or fails to mention that the distal stump remains near the wound while the proximal stump retracts due to the muscle's resting tone and the flexion of the digit at the moment of injury.
The patient has a complete Zone II ("No Man's Land") laceration of both the FDS and FDP. The position of the digit at injury is a key prognostic and technical indicator: because the digit was flexed, the proximal tendon stumps will have retracted proximally away from the laceration site due to muscle-tendon unit elasticity. Recognizing this dictates that I must plan for a proximal counter-incision in the distal palmar crease to perform retrograde retrieval, thereby avoiding unnecessary digital trauma or 'fishing' that could damage the digital nerves or remaining pulley integrity.
You have decided to proceed with surgery. You are considering using the WALANT (Wide Awake Local Anesthesia No Tourniquet) technique. What are the major advantages of this approach in the context of a Zone II flexor tendon repair?
Candidate: WALANT allows the patient to be awake. The biggest advantage is that I can ask the patient to move their finger while I am still in the operating room. This lets me check that the repair is strong enough and that there is no catching or triggering as the tendon glides through the pulleys.
Focusing only on the lack of a tourniquet or avoiding general anesthesia costs. The crucial examiner-sought point is the "Active Intraoperative Testing," which allows for the objective assessment of the repair's gliding resistance and the prevention of post-operative triggering.
The primary advantage is the ability to perform active intraoperative assessment of the tendon repair. By having the patient actively flex the finger, I can confirm the structural integrity of the repair, ensure smooth gliding through the A2/A4 pulley system, and detect any "catching" or triggering due to bulky suture knots or sheath mismatch. This allows me to adjust the repair construct in real-time, effectively minimizing the risk of postoperative tendon rupture or adhesion-related stiffness.
During your repair, you mention the need to preserve the A2 and A4 pulleys. If these were inadvertently excised during the injury or your surgery, what would be the clinical consequence?
Candidate: If you lose the A2 or A4 pulleys, the tendon will move away from the bone when the patient tries to flex the finger. This is called bowstringing. It causes a loss of flexion power and range of motion because the moment arm is increased.
Forgetting to mention the mechanical disadvantage. Simply saying "the finger won't work" is insufficient. A high-scoring answer must link the loss of the pulley to the biomechanical "bowstringing" effect and the resulting decrease in digital flexion excursion and strength.
The critical consequence of A2 or A4 pulley loss is "bowstringing." Biomechanically, the pulleys act to hold the tendons close to the axis of rotation of the joints. Without them, the tendon loses its mechanical advantage; it displaces volarly during contraction, which significantly increases the work of flexion and results in a profound loss of active range of motion and grip strength. If these pulleys are damaged, they must be reconstructed to restore normal digital kinematics.
