Gap Formation During Cyclic Testing of Flexor Tendon Repair

Purpose: Substantial gap formation of a repaired finger flexor tendon is assumed to be harmful for tendon healing. The purpose of this study was to investigate the relationship between gap formation and the failure of the repair during cyclic loading. Methods: Thirty-five porcine flexor tendons were repaired and tested cyclically using variable forces until failure or a maximum of 500 cycles. Depending on the biomechanical behavior during cyclic testing, specimens were divided into 3 groups: Sustained (no failure), Fatigued (failure after 50 cycles), and Disrupted (failure before 50 cycles). The relationships between the gap formations, time-extension curves, and group assignments of the samples were investigated. Results: The time-extension curves of the Fatigued specimens showed a sudden onset of repair elongation-a fatigue point-which preluded the subsequent failure of the repair. This point coincides with the start of plastic deformation and, thereafter, cumulative injury of the repair consistently led to failure of the repair during subsequent cycles. None of the sustained repairs showed a fatigue point or substantial gapping during loading. Conclusions: We conclude that the emergence of a fatigue point and subsequent gap formation during loading will lead to failure of the repair if loading is continued. Clinical relevance: The results of this experimental study imply that an inadequate flexor tendon repair that is susceptible to gap formation is under risk of failure.