What occurs to displaced femoral neck fractures that are reduced and fixed with screws or pins?

When dealing with displaced femoral neck fractures that are reduced and fixed with screws or pins, a significant concern is the vascular supply to the femoral head. The femoral neck is highly dependent on blood flow for healing due to its unique anatomical positioning. Displacement of the fracture can compromise the vascular supply either directly through injury to the blood vessels or indirectly due to the malalignment of the fracture fragments.

If the vascular supply is severely compromised at the time of injury or remains interrupted post-reduction and fixation, the likelihood of healing diminishes markedly, potentially leading to avascular necrosis of the femoral head. This means that without adequate blood flow, bone healing is unlikely, and the bone can begin to undergo bone death due to a lack of necessary nutrients and blood supply.

In summary, the key factor affecting the healing potential of these fractures is the integrity of the vascular supply. If this supply is compromised, then correct healing cannot occur, making this the correct answer.