Anatomical Basis of Episacroiliac Nodules (Copeman’s Nodules): Insights from Cadaveric Dissection and Three-Dimensional Reconstruction

Background Palpable lumbar nodules in the episacroiliac region—commonly referred to as Copeman’s nodules or “back mice”— are frequently encountered when specifically examined for, although often overlooked in routine practice. Historically, they have been associated with low back pain; however, their anatomical basis remains poorly defined and inconsistently interpreted. Objective To investigate the anatomical substrate and three-dimensional organisation of these nodular structures through cadaveric dissection. Methods Five embalmed cadavers underwent targeted lumbar dissections using a blunt dissection approach designed to preserve the fibro-fatty architecture of the episacroiliac region. Results Across all specimens, the episacroiliac DAT exhibited a recurrent multilobular arrangement composed of fibro-fatty lobules aligned in a craniocaudal gradient, with size and prominence varying according to overall adipose tissue volume. These structures showed a superficial encapsulated “tip” connected to the deeper adipose tissue through a narrower “neck”, occasionally traversing small fascial apertures. The lobules were consistently located immediately superior to the posterior superior iliac spine, with their deeper origins adjacent to the superior cluneal foramina. These observations were integrated into a three-dimensional model illustrating the spatial organisation of the episacroiliac DAT. Conclusion Palpable episacroiliac nodules appear to correspond to prominent fibro-fatty lobules within the deep adipose tissue rather than isolated pathological lesions. These findings may help explain the clinical and sonographic features previously described in the literature.