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

Abstract

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/ft 3 and a cortical density of 40 lb/ft 3 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 (mm 2 ), 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 mm 2 , 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.