Effect of tendon-to-bone gap on adjustable- versus fixed-loop biceps tendon fixation.

backgroundDistal biceps tendon ruptures significantly impair forearm flexion and supination strength, particularly in active individuals. Suspensory fixation using cortical button devices is a widely accepted surgical approach. Adjustable-loop techniques allow maximal tendon-to-bone apposition, while fixed-loop methods are simpler but may leave a gap. Biomechanical differences between these techniques specific to the distal biceps tendon remain poorly investigated, especially given the unique loading patterns of the elbow compared to other joints.

methodsFinite element analysis was performed using ANSYS software. Three-dimensional models of the radius and distal biceps tendon were constructed from computed tomography data. Three configurations were compared: Model 1 (adjustable-loop with dense tendon-to-bone contact, 0 mm gap), Model 2 (fixed-loop with 1.0 mm gap), and Model 3 (fixed-loop with 5.0 mm gap). Cortical bone, tendon, suture, and titanium button properties were assigned based on literature values. A 500 N tensile load was applied at the proximal tendon boundary simulating 90° elbow flexion. Stress, strain, and displacement distributions were analyzed in the fixation system and tendon.

resultsMaximum tensile stresses in the fixation system were lowest in Model 1 (353 MPa) compared to Model 2 (407 MPa, + 15%) and Model 3 (423 MPa, + 20%). Tendon maximum stresses were similar across models (170-175 MPa), exceeding ultimate tendon strength only at isolated concentration nodes. Maximum strains in the fixation system followed the same pattern: 0.29 (Model 1), 0.33 (Model 2), 0.35 (Model 3). Maximum tendon displacements (d_t) were 5.4 mm (Model 1), 5.7 mm (Model 2), and 6.9 mm (Model 3), primarily due to suture elongation. The 90th percentile stresses (σ_P90) and strains (ε_P90) remained consistent across configurations. The superior biomechanical performance of the adjustable-loop technique primarily reflects its ability to achieve zero tendon-to-bone gap rather than the loop mechanism itself.

conclusionsSuspensory fixation with zero tendon-to-bone gap (achieved by adjustable-loop technique) demonstrated superior biomechanical performance, exhibiting lower peak stresses, strains, and displacements in the fixation system compared to fixed-loop techniques with gaps. These findings suggest improved construct stability with zero-gap apposition. Further in vitro cyclic loading studies and clinical validation are required.