Explanation:
The correct option is 'b'. Retrograde intramedullary nailing of the femur involves an intra-articular starting point in the intercondylar notch of the distal femur. Consequently, the most common complication unique to this approach (compared to antegrade nailing) is postoperative knee pain, which is reported in up to 36% of patients. Antegrade nailing is conversely associated with higher rates of hip/abductor pain.

Reference: Ostrum RF, Agarwal A, Lakatos R, Poka A. Prospective comparison of retrograde and antegrade femoral intramedullary nailing. J Orthop Trauma. 2000;14(7):496-501.