Biomechanical effects of a 2 suture-pass medial inter-implant mattress on transosseous-equivalent rotator cuff repair and considerations for a "technical efficiency ratio"

Background: Rotator cuff repair involving fewer tendon suture passes without compromising biomechanical performance would represent a technical advancement. An inter-implant "medial pulley-mattress" transosseous-equivalent (MP-TOE) repair requiring fewer tendon suture-passes was hypothesized to provide equivalent biomechanical characteristics compared to the control. Methods: In 6 human cadaveric shoulders, a transosseous-equivalent (TOE) repair (control) was performed utilizing 2 separate medial mattresses resulting in 4 tendon-bridging sutures. In 6 matched-pairs, 2 single-loaded anchors were used to create a medial inter-implant mattress construct (all sutures shuttled in 1 tendon pass per anchor) dafter knot-tying, the same tendon-bridging pattern as the control was created. A materials testing machine cyclically loaded each repair from 10-180 N for 30 cycles; each repair subsequently underwent failure testing. Gap and strain were measured with a video digitizing system. A "technical efficiency ratio" (TER) was defined as: (#knots + #suture passes + #suture limbs)/#fixation points. Results: Cyclic and failure testing demonstrated no significant differences between constructs. Gap formation at cycle 30 was 5.3 +/- 0.8 mm (TOE) and 5.0 +/- 0.3 mm (MP-TOE) (P = .62). Cycle 30 anterior strain values were -16.0 +/- 7.3% (TOE) and -15.8 +/- 6.6% (MP-TOE) (P = .99). Yield loads were 208.7 +/- 2.7 N (TOE) and 204.0 +/- 1.3 N (MP-TOE) (P = .17). Mode of failure demonstrated less tendon cut-out with the MP-TOE repair. The MP-TOE repair has a TER of 2.0 vs 2.5 for the control. Conclusion: The MP-TOE repair requiring fewer tendon suture passes, yet creating an additional inter-implant mattress configuration, is biomechanically equivalent to the original TOE technique, and may limit failure with improved medial load-sharing capacity. A TER may help quantify technical ease and help standardize comparisons between repair techniques. (C) 2014 Journal of Shoulder and Elbow Surgery Board of Trustees.