What type of flap requires the periosteum to remain intact?

The correct answer is the partial thickness flap. This type of flap, also known as a split-thickness flap, is characterized by the preservation of the periosteum, which is the dense layer of vascular connective tissue enveloping the bones. In a partial thickness flap procedure, the incision is made through the skin and mucosa, but the underlying periosteum is left intact. This approach helps maintain the blood supply to the tissue and reduces the risk of complications such as wound dehiscence or necrosis.

Maintaining the integrity of the periosteum is crucial because it plays a vital role in healing and regeneration after surgical procedures. The intact periosteum ensures that there is adequate vascularity, supporting a more favorable environment for tissue repair and healing.

In contrast, a full thickness flap involves removing all layers of soft tissue, including the periosteum, which can disrupt the blood supply and potentially lead to complications. Other options like the undisplaced flap and modified Widman flap have their specific indications and variations in technique but do not emphasize the necessity of preserving the periosteum as the partial thickness flap does.