Hi there, Welcome to HCM, thank you for your question. Sacroilliatis is the inflammation for the joint between the spine and the pelvic bone know as the sacroiliac joint.Pain associated with sacroiliatis a chronic issue with acute exacerbations, with pain limited to lower back and not involving your leg.The treatment mainly includes non operative tratement with medicines and physiotherapy.Though surgery has been recently proposed, the long-term effectiveness of surgery for sacroiliac joint pain is yet to be proven. Since your pain also involves the left leg with narrowing seen on your lower spine corresponding to the side of pain,your symptoms are more likely to be due to the disc protrusion.Surgery for disc would be indictated if pain associated with weaknessential in your legs, new onset numbness,problems in passing urine or motions (all of which indicate severity of compression needing urgent intervention).Severe unrelenting pain or pain after 3 months of Conservative management would be a relative indication for surgery.Since your pain has been there for 3 months, It would be prudent to try physiotherapy, analgesics, core spinal exercises and spinal injection (based on assessment of your MRI)for another month before considering surgery.In the meantime avoid squatting, bending forwards, lifting weights and twisting movements of spine. Hope this answers your question. Thank you.All the best..with best regards. Dr.SBK