A biomechanical comparison of multistrand flexor tendon repairs using an in situ testing model.

An in situ testing model was used to evaluate the performance of zone II flexor tendon repairs and to compare the biomechanical properties of 4-strand repairs with 2- and 6-strand repairs. Fifty digits from human cadaveric hands were mounted in a custom apparatus for in situ tensile testing. Intratendinous metallic markers were placed so that gap formation could be determined by fluoroscopy during tensile testing. Three 4-strand repairs (the 4-strand Kessler, the cruciate, and a locked modification of the cruciate repair) were compared with the 2-strand Kessler and the 6-strand Savage repairs. Ultimate tensile strength, load at 2-, 3-, and 4-mm gap formation, and work of flexion were determined. Work of flexion, while increased for the multistrand repairs, did not show a statistically significant correlation with the number of strands crossing the repair site. The tensile strength of the 6-strand repair was significantly greater than each of the 2- or 4-strand repairs. The tensile strength of all 4-strand repairs was significantly greater than the 2-strand repair. The 6-strand repair and the 2 cruciate repairs demonstrated a statistically increased resistance to gap formation compared with the 2-strand Kessler repair, but notably there was no statistically significant difference in gap resistance between the 2and 4-strand Kessler repairs. This in situ tensiletesting protocol demonstrated that 4- and 6-strand repairs have adequate initial strength to withstand the projected forces of early active motion protocols. Three of the 4 multistrand repairs demonstrated improved gap resistance compared with the 2-strand repair. The presence of the second suture in the Kessler configuration significantly increases its strength but not its gap resistance.