Twelfth Rib Length as a Predictor of Anatomic Variations in the Lumbosacral Plexus Associated With Atypical Radiculopathy in Lumbar Disc Herniation

Study Design. A combined clinical and cadaveric observational study. Objectives. To investigate whether anatomic variations in the lumbosacral plexus (LSP) are associated with diagnostic discrepancies in lumbar disc herniation (LDH) and to corroborate clinical findings with anatomic evidence. Summary of Background Data. LDH is typically diagnosed based on clinical neurological symptoms and the level of the compressed spinal nerve root (the responsible lesion) identified by magnetic resonance imaging. However, in some patients, radiculopathy symptoms do not always align with the responsible lesion, complicating the diagnosis. This discrepancy may be linked to anatomic variations in the LSP, although the exact cause remains unclear. LSP roots may exhibit cranio-caudal deviations, which tend to be associated with shorter or longer 12th ribs, providing a potential basis for investigation. Methods. We examined 12th rib length in 144 patients with LDH at Juntendo University Hospital and investigated the relationship between LSP branch deviations and 12th rib length in 29 Japanese cadavers, donated to Juntendo University School of Medicine. Results. Of the total, 102 cases showed matching radiculopathies and responsible lesions (matched group), whereas 42 cases exhibited discrepancies (mismatched group). The mismatched group was subdivided into: 19 cases with radiculopathy at a lower level than predicted by the responsible lesion (lower-level radiculopathy type) and 23 cases with radiculopathy at a higher level (higher-level radiculopathy). These types were significantly associated with shorter and longer 12th ribs, respectively, suggesting cranial and caudal deviations in LSP branches, confirmed by anatomic examination. Conclusion. These findings suggest that contradictory neurological symptoms in LDH may be largely due to cranio-caudal deviations in the LSP and its branches. Furthermore, the 12th rib length may help predict these anatomic variations, potentially improving diagnostic accuracy in LDH.