Influence of drill hole diameter for the long head of biceps tenodesis on the risk of pathological fractures of the proximal humerus

Background. Pathology of the long head of the biceps tendon (LHBT) includes dislocation/subluxation, tendinitis, and tendon rupture and is frequently associated with rotator cuff injuries. Surgical treatment options include tenotomy or tenodesis. Although the choice of the tenodesis level for the LHBT is largely subjective, the tenodesis site affects not only functional outcomes but also the risk of pathological fracture of the humerus. The aim of the study — to evaluate the influence of drill hole diameter for the suprapectoral tenodesis of the long head of the biceps on the risk of the pathological fractures of the proximal humerus using finite element analysis. Methods. A three-dimensional model of the humerus, including cortical and trabecular bone components, was constructed based on CT data of a 64-year-old patient. Finite element analysis (ANSYS; SOLID185 elements, average element size ~0.7 mm) included the following scenarios: (1) a fall with the arm abducted at 45°, (2) external and internal rotational loading of the humerus with kinematic rotation of 3°-6° in both directions, and (3) comparative stress distribution analysis in intact bone (no drill hole) and after creation of through holes. An intact humerus was compared with humeri containing suprapectoral through holes of d = 5.0/1.5 mm (anchor fixation) and d = 7.0/2.4 mm (screw fixation). Results. During a fall on an abducted arm, peak tensile stresses were localized in the region of the surgical neck on the medial surface of the humerus, while the bicipital groove and suprapectoral region remained outside the zone of critical stress. During rotational loading, the presence of a drill hole shifted the maximum shear stress toward the drilling zone. In intact bone, the critical external rotation angle decreased from 6° to 5° after drilling. In bone with reduced mineral density, it decreased from 6° to 3°. For internal rotation, the critical angle decreased from 5° to 4°. The influence of drill hole diameter was minimal, accounting for only a 1-2% increase in stress. Conclusions. This study identified critical patterns in how bone perforation affects the stress–strain state of the humerus. Bone strength was primarily dependent on the presence of perforation rather than on the drill hole diameter within the investigated range, and increasing the diameter from 5 to 7 mm resulted in only a minor increase in stress (1-2%). These findings suggest that the optimal strategy is to place the drill hole in the proximal humerus, where critical shear stress concentrations are not initially present.