Piriformis Syndrome: This condition is characterized by the piriformis muscle compressing the sciatic nerve, leading to pain in the posterior thigh and back. It's a common cause of sciatica and can be triggered by activities that involve sitting or running.

Lumbar Disc Herniation: Herniation of the lumbar discs can cause pressure on the nerves, leading to pain in the lower back and radiating down to the posterior thigh.
Lumbar Spondylosis: Degenerative changes in the lumbar spine can cause pain in the lower back and refer pain to the posterior thigh.
Hamstring Strain: Injury to the hamstring muscles can cause pain in the posterior thigh, which may also radiate to the lower back.
Trochanteric Bursitis: Inflammation of the bursa over the trochanter can cause pain in the lateral thigh but may also refer pain to the posterior thigh and lower back.

Cauda Equina Syndrome: A serious condition where the nerves in the spinal canal are compressed, leading to severe pain, numbness, and potentially permanent nerve damage if not promptly treated.
Spinal Stenosis: Narrowing of the spinal canal can cause compression of the spinal cord or nerves, leading to pain, numbness, and weakness in the legs.
Osteomyelitis or Discitis: Infections of the bone or disc can cause severe back pain and may radiate to the posterior thigh, requiring urgent medical attention.

Neurogenic Tumors: Tumors arising from the nerves, such as neurofibromas or schwannomas, can cause pain and neurological symptoms.
Vascular Claudication: Poor circulation can cause pain in the legs, including the posterior thigh, especially during exercise.
Inflammatory Arthropathies: Conditions like ankylosing spondylitis can cause back pain and stiffness, potentially radiating to the posterior thigh.