Reconstruction of the flexor pulley: The effect of the tension and source of the graft in an in vitro dog model

Flexor pulleys in the hindpaw digits of twenty-eight adult mixed-breed dogs were reconstructed in order to investigate the influence, on the reconstruction, of the source of the autogenous tissue (intrasynovial compared with extrasynovial tendon) and the tension applied during the repair. The ipsilateral peroneus longus tendon was used to reconstruct the A2 pulley with an around-the-bone technique in twenty-one digits; the graft was sutured at a tension of 0.49, 0.98, and 1.96 newtons in seven digits each. The flexor digitorum profundus tendon of an adjacent digit was used to reconstruct the A2 pulley, at a tension of 0.98 newton, in seven additional digits. The contralateral digits were used as controls for all twenty-eight treated digits. The digits were tested in a custom apparatus designed to measure the frictional force generated between the reconstructed pulley and the tendon beneath it. The frictional force did not differ significantly (p > 0.5) among the three groups repaired with peroneus longus tendon; however, the average value was more than five times that produced in the contralateral, control digits. The average frictional forces created by the flexor digitorum profundus grafts were similar to those in the contralateral, control digits. Reconstruction with the flexor digitorum profundus at a tension of 0.98 newton produced significantly less frictional force (p < 0.05) than that produced by the peroneus longus graft at the same tension. This in vitro model of reconstruction of the A2 pulley demonstrated that tendon from an intrasynovial source (the flexor digitorum profundus) produced less frictional resistance to gliding of the tendon than did tendon from an extrasynovial source (the peroneous longus). This result is consistent with previously published findings that intrasynovial tendons may make better grafts than extrasynovial tendons for the reconstruction of gliding flexor tendons because of decrease friction and better healing qualities. Intrasynovial tendons may also make better grafts for the reconstruction of flexor pulleys.