A patient complains of right buttock pain after slipping, with the right hip forced into internal rotation. Lumbar active motion testing is full and pain-free, and neurological findings are unremarkable. S1 provocation testing is unremarkable. Passive hip internal rotation is limited, with pain and pulling noted in the right buttock region. Resisted external rotation produces pain in the same region.

Based on these findings, the most likely diagnosis would be:

A. Piriformis strain
B. Quadratus lumborum strain
C. Lumbar disc herniation at L5/S1
D. Sacroiliac sprain/strain

A patient with right buttock pain after hip internal rotation and limited passive hip internal rotation with pain, as well as pain during resisted external rotation, is most likely experiencing a Piriformis strain. Option a) is the correct answer.

Based on the patient's symptoms of right buttock pain after an incident involving hip internal rotation, full and pain-free lumbar motion, unremarkable S1 provocation testing, and pain during both passive internal hip rotation and resisted external rotation, the most likely diagnosis is A. Piriformis strain.

Piriformis strain is supported by the specific location of pain in the buttock region and the mechanisms of onset, as the piriformis muscle assists in laterally rotating the femur at the hip.

The pain during resisted external rotation and limited passive internal rotation suggests that the involved muscles are those responsible for these actions, which include the piriformis muscle deeply located in the buttock area.