Poster 164: Novel Distal Biceps Tendon Onlay Repair with Twin Interlinked Knotless All-Suture Anchors and Reinforced Looping Suture Demonstrates Favorable Failure Load, Footprint Restoration Accuracy, and Tendon-Suture Security: A Biomechanical Study
Authors: Hsu Jim , Fraipont Genevieve , McGarry Michelle , Adamson Gregory , Jewell Joshua , Kwak Daniel , Lee Thay 
Published: October 2024

Objectives: Accurate and sizeable footprint restoration, a secure tendon-suture interface, and high ultimate failure load (UFL) are keys to a successful distal biceps tendon repair (DBTR) that no current repair technique uniformly achieves. Inlay repair methods demonstrate satisfactory UFLs, but do not accurately restore the native footprint size or location. The smaller tunnels in onlay repairs help improve footprint location accuracy and bone preservation, but footprint area maximization has not been reported or studied, and concerns persist about their UFL and overall security. Tendon-suture interface remains a universal potential weak spot, as all current techniques rely on Krakow or whipstitch constructs. We developed a new onlay DBTR technique with novel reinforced tendon suturing, knotless anchors, and suture interlinkage, to specifically target the above concerns. The purposes of this study were: (1) to biomechanically characterize the new technique; (2) to evaluate the native and post-repair footprints for restoration size and accuracy; (3) to compare the tendon-suture interface integrity of the reinforced looping suture versus the standard whipstitch constructs; and (4) to establish the biomechanical benchmark for our new technique, with a comprehensive literature search for DBTR biomechanical studies and their highest reported UFLs. Methods: Twenty elbows from 10 donors were separated into in two matched, side-randomized groups, and their sharply excised distal biceps tendons were prepared with (1) whipstitch or (2) tape-reinforced looping suture. All elbows then underwent onlay DBTR, with two intramedullary 2.6 mm knotless all-suture anchors placed in the distal and proximal native footprint, and the repair sutures shuttled through the suture-tendon construct, over distal tendon tissue, and through the opposing anchor, creating a suture-bridge construct with broad tendon-bone compression upon maximal tensioning (Fig.1). Native and post-repair tendon footprints areas (mm2) and locations were digitized with a 3D coordinate-measuring machine (CMM), and native/post-repair location overlap (%) determined to quantify restoration accuracy. The repairs then underwent progressive cyclic loading (50/75/100N, 100 cycles/load). Bone-tendon gap, suture construct and total construct lengths were measured pre- and post-cycling. Repairs were then loaded to failure, and the UFLs and modes of failure recorded. Paired t-test and Fisher’s exact test were performed to compare continuous-variable and categorical results, respectively. We collaborated with a university library research consultation service to conduct a comprehensive multi-database search and review (PubMed, Embase, Scopus, Web of Science) of all peer-reviewed cadaveric DBTR biomechanical studies with reported UFL values over the past 20 years (October 2003 – September 2023), and documented the highest mean UFL achieved in each identified study, to define the historical and current biomechanical benchmark of our novel construct. Results: Mean UFL was 516±102 N in repairs with reinforced looping suture, and 471±134 N with whipstitch (N.S.). Nine (90%) whipstitch repair specimens failed at the tendon-suture interface, typically with sutures pulling through and splitting the tendons longitudinally, compared to three (30%) suture-tendon failures in the reinforced looping stitch repair group, typically at the proximal tendon-suture junction ( P = .02) (Fig.2). Mean native footprint area was 146±26 mm2, and mean post-repair footprint area was 91±7.4 mm2, with 89% of the post-repair footprint located within the native footprint (Fig.3). Compared to whipstitch repairs, reinforced looping suture repairs demonstrated 50% lower mean bone-tendon gap formation (0.8±0.1 mm vs 1.6±0.7 mm), 78% lower mean suture construct elongation (0.9±0.4 mm vs 4.0±1.8 mm), and 46% lower mean total construct elongation (3.0±0.5 mm vs 5.6±2.3 mm) after cyclic loading; the differences did not reach statistical significance. Our comprehensive literature search identified 27 peer-reviewed cadaveric biomechanical studies published between October 2003 and September 2023, describing a variety of onlay and inlay DBTR techniques. Compared to the range of mean UFL values reported in the 27 studies over the past 20 years (range 162-537 N, mean 308 N), our novel DBTR construct demonstrated the second-highest mean UFL (Fig.4). Conclusions: The use of knotless anchors in our construct, novel for DBTR, helped create a large and accurate footprint through a suture-bridge effect, without sacrificing satisfactory UFL. The reinforced looping suture, also novel, improved tendon-suture interface integrity, addressing a weak spot common to all current DBTR techniques. While a direct in-vitro comparison with all the reported methods was outside the scope of our study, the UFL range from all 27 identified DBTR biomechanical studies in the past 20 years provided an important biomechanical context, and suggests that our novel construct can achieve a satisfactory and likely high level of UFL. In summary, our novel DBTR technique demonstrated uniformly favorable performances in mean UFL, footprint restoration accuracy, and tendon-suture security, all the essential features we targeted, and may represent an advantageous new DBTR option. [Figure: see text][Figure: see text][Figure: see text][Figure: see text]