# Construct strength of a drilling trajectory angled proximally avoiding the posterior interosseous nerve in single incision distal biceps repair; a comparative cadaveric study

## TL;DR

A modified drilling angle for biceps tendon repair reduces nerve injury risk without weakening the repair, according to a cadaveric study.

## Contribution

Demonstrates that a proximally angled drilling trajectory maintains biomechanical strength while potentially reducing nerve injury risk.

## Key findings

- Modified drilling trajectory showed comparable load-to-failure strength to traditional methods.
- No significant differences in stiffness or displacement between the two groups were observed.
- Failure modes were similar, with no significant differences between the groups.

## Abstract

Distal biceps tendon repair using a bicortical button is a biomechanically robust technique but carries a risk of posterior interosseous nerve (PIN) injury, particularly with traditional drilling trajectories. Cadaveric studies have suggested that angling the drill trajectory both ulnarly and proximally may increase the distance to the PIN and reduce this risk. However, the biomechanical construct strength of such modified trajectories remains unestablished.

Sixteen fresh-frozen human upper limbs were randomly assigned to either a control group (20° ulnar and perpendicular) or an intervention group (20° ulnar and 30° proximal). Standardized bicortical button repairs were performed following simulated distal biceps ruptures. All specimens underwent cyclic loading (1,000 cycles, 5-100 N, 2.5 Hz), followed by load-to-failure testing. Primary outcome was maximum load to failure. Secondary outcomes included construct stiffness, displacement, and mode of failure.

Two failures occurred during cyclic loading, both in the control group (P = .164). There were no significant differences in load to failure (control: median 247.2 N [range: 210.1-310.9]; intervention: 284.0 N [149.5-308.5]; P = .345), stiffness (control: 56.2 N/mm; intervention: 53.3 N/mm; P = .852), or displacement during cyclic loading or at failure (P > .3). Failure modes included suture rupture, tendon–suture interface failure, and bone fracture; all were classified as type 1 failures. No statistically significant differences in failure mode were observed between groups, although bone-related failure occurred only in the intervention group.

A proximally angled (30°) and ulnar (20°) drilling trajectory for distal biceps repair using a bicortical button yields construct strength comparable to the traditional perpendicular axial ulnar trajectory. This technique may reduce the risk of PIN injury without compromising mechanical integrity. Further clinical studies are warranted to confirm safety and efficacy in vivo.