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Flexor Tendon Tensile Forces Following Zone 2 Repair: A Biomechanical Analysis in a Cadaveric Model
Eric R Taleghani, MD
1, Ryan Davenport, MD
1, Sean Bucherl, MS
2, Eric Nauman, PhD
2; Kagan Ozer, MD
1(1)University of Cincinnati College of Medicine, Cincinnati, OH, (2)University of Cincinnati School of Engineering and Applied Science, Cincinnati, OH
IntroductionThe effect of digital edema on tensile forces in zone 2 flexor tendon injuries has not been extensively investigated. In this study, we examined the effect of digital edema on the gliding forces following six-strand repair of a zone 2 deep flexor tendon (FDP) laceration. We also assessed how finger flexion forces change throughout the total arc of motion. We hypothesized that finger edema would increase the flexion forces, enough to exceed load to clinically significant gap formation.
MethodsEight cadaveric upper extremities were used in the study. All specimens were placed in a prefabricated dorsal blocking splint with the wrist in neutral and MPs at 45° of flexion. The tensile force to bring the four fingers into full flexion was continuously recorded. Next, via a standard volar approach, the superficial (FDS) and deep (FDP) flexor tendons of the ring finger were lacerated at the PIP joint. The FDP was repaired using 3-0 non-absorbable synthetic suture using the modified Tang six-strand technique, and the A2 and A4 pulleys were partially vented. A measurement was obtained following repair. Saline was injected sequentially throughout all four digits to simulate mild, moderate, and severe edema, with a measurement obtained for each level. In four specimens, coban was applied to the repaired digit, and another measurement was obtained. Last, the force required to produce two millimeters of tendon gap was measured as the load to failure in this model.
ResultsThe tensile force required to achieve a total arc of motion gradually increased following Zone 2 FDP repair with the A2 pulley vented, and again with each subsequent model of edema (Figure 2). The average peak forces for each experimental scenario were 10.4N, 16.1N, 21.4N, 28.1N, 34.3N, and 48.6N. The average load to failure was 44.6N. Digital flexion forces increased exponentially with progression through the arc of motion.
Conclusion Digits with severe edema approached load to failure at full flexion, while digits wrapped with coban exceeded this value. Flexion forces increase exponentially throughout the arc of motion. Early active motion between 45° to 180° appears to be safer than full active finger flexion.
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