Three-Anchor Knotless Compression Bridges Improve Contact Mechanics in a Biomechanical Model of Large, Single-Row Tendon Repairs.

PURPOSE: To investigate the influence of anchor density on tendon footprint contact mechanics in knotless all-suture anchor compression bridge constructs. METHODS: Unicortical polyurethane solid foam blocks with a cancellous density of 20 lb/ft3 and a cortical density of 40 lb/ft3 simulated bone. Tendons were replicated with 4.76-mm-thick 40A durometer polyurethane rubber sized to 27 × 12 mm. Test groups consisted of two 2.6-mm all-suture anchor single-row knotless compression bridge constructs evaluated at interanchor distances of 10, 15, 20, and 25 mm. A 3-anchor construct was also evaluated for the 25-mm (large tear) condition. The repair sutures of each construct were individually hooked onto a zeroed, handheld force gauge and manually tensioned to create a minor (<5 N) compressive preload through the tendon. Constructs were incrementally tensioned by +25 N on each suture until failure. Contact area (mm2), compressive force (N), and contact pressure (kPa) were recorded from the loaded sensing elements in the bridge region. RESULTS: The 25-mm, 3-anchor construct resulted in significantly greater compressive force than any of the 2-anchor groups (107 ± 9 N, P < .001). Adding a third anchor to the 25-mm bridge resulted in 37% more compressive force when compared with its 2-anchor equivalent. Contact area increased linearly with increasing bridge length. The largest contact area measured at 195 ± 11 mm2, observed in the 25-mm bridge distance with both the 2- and 3-anchor constructs. The largest contact pressure was achieved in the 10 mm group (1020 ± 58 kPa). Contact pressure significantly decreased with increasing bridge distance and was restored with the addition of a third anchor (683 ± 96 kPa) (P < .001). CONCLUSIONS: An inverse relation was identified wherein increasing knotless suture bridge length decreased tendon footprint contact pressure in single-row repairs. The addition of an in-line third anchor in a simulated large-tear model (25 mm) improved contact pressure and compressive force. CLINICAL RELEVANCE: The addition of a third knotless all-suture anchor to large single-row suture bridge repairs shows a noticeable improvement in tendon footprint restoration at time zero.