Bare Area of the Proximal Radius and Its Relevance for Safe Repair of the Distal Tendon of the Biceps Brachii Muscle

Background: Distal biceps tendon ruptures often require surgical repair to restore elbow flexion and forearm supination. However, the reinsertion procedure may be complicated by postoperative posterior interosseous nerve palsy caused by iatrogenic injury to the deep branch of the radial nerve (DBRN). While safe drilling trajectories for distal biceps tendon repair have been extensively studied, the potential influence of a bony gap between the insertion sites of the supinator muscle layers, referred to as the bare area of the proximal radius, has not been adequately addressed. Purpose: To determine the frequency, morphometrics, and topography of the bare area and to propose a safe bicortical drilling trajectory for single-incision distal biceps tendon repair that minimizes the risk of injury to the DBRN in the context of the bare area. Study Design: Descriptive laboratory study. Methods: A cadaveric dissection of 100 formalin-fixed upper limbs was conducted. Additionally, 1000 dry radii were examined for an osseous groove corresponding to the bare area. Furthermore, 10 fresh-frozen elbows were used for assessment of safe bicortical drilling trajectories in the presence of the bare area. Results: The bare area was present in 56.0% of cases, with no significant side or sex predominance. The bare area was 13.7 ± 5.2 mm long and 5.1 ± 1.6 mm wide, and occupied an area of 58.7 ± 33.8 mm 2 . Direct contact between the DBRN and the periosteum of the radius was noted in 28.6% of specimens. The extent of an osseous groove corresponding to the bare area overlapped with the radial tuberosity in 28.5% of the cases. Experimentally, bicortical drilling directed 30° ulnarly and 45° proximally ensured a safe distance from both the DBRN and the bare area. Conclusion: The frequent occurrence of the bare area should be a critical consideration during bicortical drilling for distal biceps tendon repair. Drilling angles directed ulnarly and proximally are recommended to minimize the risk of neural injury. Clinical Relevance: This study highlights the increased risk of DBRN injury during distal biceps tendon repair in individuals with the bare area and provides safe drilling trajectories to guide surgeons in reducing the likelihood of this neural injury.