A Closer Look at the Complications of Zone III Flexor Tendon Repairs of the Hand: An Analytical Cadaveric Study

Abstract

2. study of the sequential motion of the phalanges using videography fluoroscopy; and 3. a biomechanical vector analysis to examine the flexion-extension moment contributions applied by the following components at each stage of the reconstruction: a. Flexor tendon graft b. Extensor mechanism c. Lumbrical. Results: In the intact, normal digit, DIP motion is generated by the FDS (flexion) and lumbricals (extension), while PIP motion arises from activation of FDS, FDP and lumbricals (flexion) as well as EDC (extension). Following removal of FDS and FDP at Stage 1 of the reconstruction, the lumbricals relax and combine with EDC to produce PIP extension that is not counteracted by any flexor moment, thus leading to PIP hyperextension. At Stage 2 (FDP reconstructed), DIP flexion results from FDP activation. The lumbricals are simultaneously activated, but their excursion is limited by the DIP flexion. They act as a tension band, and continue to apply an extension moment at the PIP that is only partially counteracted by FDP. This tends to produce a swan neck deformity a combination of DIP flexion and PIP hyperextension. Conclusion: This analysis reveals that sacrifice of the flexor digitorum superficialis in 2 stage flexor tendon reconstruction causes the extensor force at the PIP joint to be imbalanced. Understanding of these altered vectors can aid in clinical decision making, therapy designs, and prevention of this deformity altogether.