Historical Review of Studies on Sacroiliac Fatty Nodules (Recently Termed “Back Mice”) as a Potential Cause of Low Back Pain

Low back pain is a widespread and poorly understood condition that is frequently diagnosed as non-specific low back pain. We were intrigued by the presence of painful sacroiliac nodules in patients with this condition. We conducted a historical review to elucidate this relationship. This chronicled review summarizes the overlooked literature from different countries, especially from around the 1950s, regarding the diagnosis and management of these painful nodules. Biopsies have confirmed the adipose nature of these nodules and revealed distinct pathological signs, including oedema and fascial fatty herniation. Studies have suggested both intra-nodule local anaesthetic injection and surgery as successful treatments for managing pain on a short- or long-term basis. Recent ultrasound studies have confirmed these findings. The various terms used for these nodules over time are specifically described. We conclude that it may be necessary to reconsider the role of fatty tissue in the aetiology and treatment of low back pain in today’s mainstream medicine. This could lead to advances in understanding unexplained musculoskeletal pain disorders beyond low back pain. Meanwhile, despite the remaining questions, the treatments identified in these studies can help physicians manage patients’ unresolved pain. We recommend that future research use this review as a foundation for further study.