Piriformis Syndrome: This condition is characterized by pain in the posterior buttock that worsens with walking, due to the piriformis muscle compressing the sciatic nerve. The symptoms align closely with the presentation of pain in the posterior buttock exacerbated by walking.

Sciatica: Sciatica refers to pain that radiates along the path of the sciatic nerve, which runs from the lower back through the hips and buttocks and down each leg. Walking can exacerbate sciatica, causing pain in the posterior buttock.
Trochanteric Bursitis: This condition involves inflammation of the bursa over the trochanter (a bone on the outside of the hip), which can cause pain in the buttock area, especially when walking.
Gluteal Strain: A strain of the gluteal muscles can cause pain in the buttock, which may worsen with activities like walking.

Cauda Equina Syndrome: Although rare, this condition is a medical emergency. It involves compression of the nerves in the spinal canal, which can cause severe pain, numbness, and weakness in the legs, as well as bladder and bowel dysfunction. Missing this diagnosis could lead to permanent neurological damage.
Spinal Stenosis: Narrowing of the spinal canal can compress the spinal cord or nerves, leading to pain, numbness, or weakness in the buttocks, thighs, or legs, especially when walking. It's crucial not to miss this diagnosis due to its potential for significant morbidity.

Ischiogluteal Bursitis: Inflammation of the ischiogluteal bursa, located between the ischial tuberosity and the gluteus maximus muscle, can cause pain in the buttock that may worsen with walking or sitting.
Osteonecrosis of the Femoral Head: Although more commonly associated with hip pain, osteonecrosis (death of bone tissue due to lack of blood supply) of the femoral head can sometimes cause referred pain to the buttock area, especially with weight-bearing activities like walking.