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

Abstract

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 longterm 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.

Episacroiliac Lipomas: A Possible Undetected Cause of Non-specific Low Back Pain

“…In a study performed by Bicket et al [6], among ambulatory patients with low back pain who seek treatment, estimates of back mice ranged from 33% to 58%, highlighting the incidence of this condition in the general population. A narrative review performed by Canis Parera et al in 2016 [5] reported the clinical signs commonly observed in the literature regarding episacroiliac lipomas. The clinical presentation described in the study matches that of the patients included in this case series, including nodule presence, chronology of symptoms, pain characteristics, palpation, referred pain patterns, as well as aggravating and relieving factors.…”

“…Episacroiliac lipomas, also known as "back mice", "sacroiliac fatty nodules", and "iliac crest pain syndrome" may be an undetected cause of non-specific LBP with a high incidence in the general population. These lipomas, as the name suggests, are deeply tethered masses of fatty tissue that seem to herniate from deep fat pads located at the lumbosacral spine [5]. They are usually located at the site of the sacroiliac joint but can also be found around the lumbar spine or the iliac crest [5].…”

“…These lipomas, as the name suggests, are deeply tethered masses of fatty tissue that seem to herniate from deep fat pads located at the lumbosacral spine [5]. They are usually located at the site of the sacroiliac joint but can also be found around the lumbar spine or the iliac crest [5]. Their consistency resembles one of trigger points, however they are usually oval shaped, elastic, and moveable in nature and can be found either unilaterally or bilaterally [6][7][8][9][10][11].…”

“…Available research suggests that diagnosis of this condition can be confirmed by ultrasonography, percutaneous radiofrequency with a needle, as well as anesthetic injections on the location of the painful nodule. Furthermore, through clinical examination, palpation, and differential diagnosis, this condition can also be identified in the absence of imaging studies [5]. The research on episacroiliac lipomas is limited and dated, however, the relationship between the herniation of these fat pads and LBP has been consistently reported through the available research.…”