Flexor Tendon Repair Using a New Looped Six- and Eight-Strand Technique-A Biomechanical Analysis

Background/Objectives: Tendon injuries are a common cause of emergency department presentation and impose a substantial socioeconomic burden. Despite advances in surgical techniques, rupture rates after primary repair remain at 3.1-11.7%. Contemporary repairs typically combine at least four core strands with epitenon sutures to achieve sufficient tensile strength while limiting bulk. Increasing the number of core strands improves strength but may impair gliding and healing. Looped core sutures increase the effective strand number without additional knots or passes, potentially allowing omission of the epitenon suture and thus limiting repair complexity and bulk. The objective was to determine whether six- or eight-strand looped core suture techniques provide sufficient tensile strength to allow omission of an epitenon suture without excessive repair bulk, compared with a conventional four-strand Adelaide repair. Methods: One hundred and twenty human flexor digitorum profundus tendons were harvested from fresh-frozen anatomical specimens and allocated to six groups: Adelaide (four-strand) ± epitenon suture, six-strand ± epitenon suture, and eight-strand ± epitenon suture. Repairs were performed in zone II. The cross-sectional area (CSA) was measured before and after repair to quantify bulkiness. Tendons were tested to failure using axial tensile loading, and the failure mode was recorded. Results: The Adelaide with epitenon suture, six-strand with epitenon suture, and eight-strand with epitenon suture demonstrated significantly higher load to failure than the Adelaide without epitenon suture. The eight-strand without epitenon suture achieved a load to failure comparable to the Adelaide with epitenon suture, while also resulting in a smaller increase in CSA. The Adelaide with epitenon suture showed the greatest increase in CSA, while the six-strand without epitenon suture showed the smallest increase in CSA. Suture breakage was the predominant failure mode. Conclusions: An eight-strand looped core suture without epitenon suture provides comparable tensile strength to the conventional Adelaide repair with epitenon suture while minimizing repair bulk. The six-strand with epitenon suture demonstrated similar tensile strength to higher-strand techniques and may represent a mechanically adequate alternative with less tissue manipulation. These findings support a more individualized approach to flexor tendon repair, in which the choice of repair construct can be tailored to biomechanical demands and clinical context rather than applying a single uniform technique.