Biomechanical analyses of the quadriga phenomenon of the fifth flexor digitorum profundus tendon

Abstract

Introduction: The quadriga phenomenon is a decrease in flexion of a normal finger after the proximal excursion of the flexor digitorum profundus (FDP) tendon of an adjacent injured finger has been limited. This phenomenon may reduce the normal physiological functions. The purpose of this study was to analyze changes in biomechanical parameters associated with normal and FDP tendon shortened fingers using a cadaver model to verify the quadriga phenomenon when the fifth FDP tendon was shortened incrementally, and to suggest the necessary surgical restoration of tendon length that will restore adequate function. especially in regards of fifth FDP tendon-injured patients. Methods: Ten fresh-frozen cadaveric hands were used for the experiments. After preparation of the FDP and extensor tendons, the cadaveric hands were fixed on a frame. The biomechanical parameters that were measured were the force to make the fifth finger flex fully, the excursion of the fourth FDP tendons, and the flexion angles of distal interphalangeal (DIP) joint, proximal interphalangeal (PIP) joint, and metacarpophalangeal (MCP) joint of the fourth and fifth fingers. The fifth FDP tendon was then incised and shortened by 5mm at a level in zone 3 and repaired with a modified Kessler method. The aforementioned biomechanical parameters were then re-measured. Subsequently, using similar methods, the fifth FDP tendon was shortened by a total 10 mm and 15 mm and the biomechanical parameters then re-measured. Results: The reduction in the total range of motion (ROM) of the fourth finger was dependent on the amount of shortening of the fifth FDP tendon. The flexion angles of the DIP, PIP and MCP joints of the fourth finger were increased when the fifth FDP tendon was shortened 5 mm, 10 mm, and 15 mm, respectively. The extension lag of the DIP, PIP and MCP joint angles of fourth finger varied linearly with shortening of fifth FDP tendon. The regression equation for extension lag of the DIP joint was Y = -2.17X + 60.0 (R2 = 0.616, p < 0.001), where Y is the amount of extension lag of the DIP joint and X is the amount of shortening (mm) of the fifth FDP tendon. Similarly, the regression equation for the PIP joint was Y = -1.67X + 81.68 (R2 = 0.392, p < 0.001), and Y = -1.25X + 79.65 for the MCP joint (R2 = 0.548, p < 0.001). The regression equation for the change of excursion of the fourth FDP tendon after shortening of the fifth FDP tendon was Y = - 0.926X + 32.52 (R2 = 0.505, p < 0.001), where Y is the change in excursion of the fourth FDP tendon and X is the same as described above. Conclusion: This study successfully demonstrated the quadriga phenomenon in a cadaveric model with fifth FDP tendon shortening model. Our results indicate that after fifth FDP tendon injury, it is important to restore the tendon to its original length accurately to ensure adequate function of adjacent fingers.