Knotless Transosseous-Equivalent Rotator Cuff Repair Improves Biomechanical Self-reinforcement Without Diminishing Footprint Contact Compared With Medial Knotted Repair.

Purpose: To assess the effect of medial-row knots on self-reinforcement and footprint contact characteristics for transosseous-equivalent repair compared with the same construct without knots.

Methods: In 8 fresh-frozen human shoulders, transosseous-equivalent repairs with and without medial-row mattress knots were performed in each specimen. A pressure sensor was fixed at the tendon-footprint interface for all repairs. Parameters measured included footprint contact area, force, and pressure. The supraspinatus tendon was loaded sequentially from 0 to 60 N at 0° and 30° of abduction.

Results: Both repairs provided a linear progression (slope) of footprint force and pressure as increasing tendon loads were applied. However, the knotless repair had a significantly higher progression ("self-reinforcement" effect) than the knotted repair at both abduction angles (P = .006 at 0° and P = .021 at 30°). The addition of medial-row knots did not significantly change the footprint contact area (in square millimeters), contact force (in newtons), contact pressure (in kilopascals), or peak pressure (in kilopascals) at each load tested, as well as at both abduction angles. For a given repair, only the knotless repair had significant decreases in contact area, contact force, contact pressure, and peak pressure with increasing abduction angles from 0° to 30° (P = .004 and P = .048).

Conclusions: Knotless transosseous-equivalent repair shows an improved self-reinforcement effect, without diminishing footprint contact, compared with the same repair with medial knots. Although knotless repair itself can show diminished footprint contact with abduction, medial knots show an adverse biomechanical effect by inhibiting self-reinforcement, without improving contact characteristics compared with knotless repair at each abduction angle tested. Clinical outcomes with specific indications, on the basis of these findings, require further investigation.

Clinical Relevance: This study biomechanically helps to validate studies that have shown clinical success with knotless transosseous-equivalent repair. The inhibition of self-reinforcement may provide a quantified biomechanical rationale for medial tear patterns seen with knotted repairs.