What structure inflammation is the most likely cause of hip pain in a patient with localized tenderness over the lateral hip?

Localized tenderness over the lateral hip is a classic sign of trochanteric bursitis, which is the inflammation of the trochanteric bursa. This bursa is situated between the greater trochanter of the femur and the muscles and tendons that pass over it, serving as a cushion to reduce friction. Inflammation of the trochanteric bursa leads to pain that is often felt on the lateral aspect of the hip, particularly when the patient is lying on the affected side, getting up from sitting, or climbing stairs. The pain can also radiate down the thigh but is primarily localized to the area over the greater trochanter.

This makes the trochanteric bursa the most likely structure causing hip pain in this scenario, given the characteristic presentation of localized tenderness.