Interlinked Knotless All-Suture Anchors Achieve Superior Footprint Optimization and Greater Fixation Strength over Intramedullary Cortical Button for Onlay Distal Biceps Tendon Repair: A Biomechanical Study

Objectives: Onlay distal biceps tendon repair (DBTR) is an advantageous fixation approach that reduces iatrogenic nerve injury risk, enhances bone preservation, and better recreates the tendon-bone interface anatomy. Although native footprint restoration is important to post-repair biceps function, and tendon-cortex contact area is essential to onlay healing, to date DBTR biomechanical studies have focused mainly on fixation strengths, not on post-repair footprints. Therefore, little is known about the potential interactions between onlay construct configurations, footprint optimization, and fixation security. The purpose of this biomechanical study was to evaluate and compare the footprint parameters and fixation strengths of two onlay DBTR constructs: 1) a novel construct with two interlinked, knotless all-suture anchors, and 2) a previously-studied intramedullary cortical button construct. We hypothesized the new interlinked construct will achieve a larger post-repair footprint, greater native footprint restoration, and higher fixation strength. Methods: Twenty fresh-frozen cadaveric elbows in 10 matched pairs were thawed, dissected, and side-randomized into 2 matched groups. All distal biceps tendons were sharply detached, secured distally with a tape-reinforced looping suture, then in one group repaired with 1) two unicortical, interlinked 2.6 mm knotless all-suture anchors with repair sutures passed through the looping suture reinforcement (Fig 1A), and in the other group repaired with 2) a 2.6 mm X 7.0 mm intramedullary cortical button with repair sutures in standard tension-slide configuration (Fig 1B). Native and post-repair tendon footprint areas and locations were captured with a 3D coordinate measurement machine (CMM). The tendon repairs underwent cyclic stressing under progressive loads (50/75/100 N loads, 100 cycles of 0-90° flexion at each load), then were loaded to failure with elbows fixed at 90° flexion. Data collected: post-cycling tendon-bone gap, ultimate failure load, native footprint, and post-repair footprint. Native/post-repair footprint overlap area as indicated by 3D CMM data was used to calculate the native footprint restoration percentage (overlap area divided by native footprint area)(Fig 2). Group means were compared with Two-Sample t Test. A sample size calculation based on a pre-study 1- vs 2-anchor pilot test showed n ≥ 8 per group would have sufficient power. Results: The twin interlinked knotless-anchor DBTR construct demonstrated significantly larger post-repair footprint area (55.1 ± 14.9 mm 2 vs 35.2 ± 19.8 mm 2 , p=0.032) with greater native footprint restoration percentage (42.7 ± 12.9% vs 20.2 ± 9.4%, p=0.003)(Table 1), lower post-cycling tendon-bone gap (3.2 ± 1.2 mm vs 12.4 ± 6.6 mm, p=0.003)(Fig 3A), and higher ultimate failure load (468.4 ± 124.2 N vs 313.2 ± 103.4 N, p=0.001)(Fig 3B), compared to the single intramedullary cortical button construct. Conclusions: In summary, the novel onlay DBTR construct with two interlinked knotless all-suture anchors exceled in footprint optimization and fixation security, achieving a significantly larger footprint with greater native footprint restoration, lower post-cycling tendon-bone gap, and higher ultimate failure load, over the single intramedullary cortical button construct. This is the first reported DBTR construct with suture interlinkage, a unique feature that directly compresses tendon to bone over a broad area, similar to the "suture bridge" effect in rotator cuff repair. With fixation strengths comparable to reported results for both inlay and onlay DBTRs, our findings suggest that an interlinked approach to distal biceps tendon repair can optimize post-repair footprint, without compromising fixation security. In conclusion, our study presents favorable biomechanical evidence that suggest the novel interlinked onlay DBTR construct can enhance repair healing, improve post-repair biceps function, and facilitate early rehabilitation, to improve overall clinical outcome.