Explanation
In a young adult patient, joint preservation through urgent anatomic reduction and stable internal fixation is the absolute gold standard. The key biomechanical challenge of a Pauwels type III (>50 degrees) fracture is that physiological loading translates into massive vertical shear forces across the fracture site. Parallel cannulated screws (Option A) rely on compression and offer poor resistance to vertical shear, leading to an unacceptably high risk of varus collapse, screw cut-out, and non-union in highly vertical fractures. A fixed-angle device, such as a Dynamic Hip Screw (Option B), provides a robust lateral cortical buttress. This fixed angle neutralizes vertical shear and converts it into controlled axial compression along the barrel. However, because the intracapsular femoral head fragment lacks muscular attachments, a supplementary derotation screw is mandatory to prevent rotational spinning of the head during lag screw insertion. Primary THA (Option D) is strictly a salvage operation in this demographic. Valgus osteotomy (Option C) is traditionally reserved for the management of established non-unions rather than acute fractures.

References:
1. Liporace F, et al. 'Femoral Neck Fractures: A Review of the Current Literature and Management in the Young Adult.' JAAOS (2008).
2. Court-Brown CM, et al. Rockwood and Green's Fractures in Adults, 9th Edition. Chapter: Intracapsular Hip Fractures.