Extraforaminal entrapment of the fifth lumbar spinal nerve by nearthrosis in patients with lumbosacral transitional vert
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ORIGINAL ARTICLE
Extraforaminal entrapment of the fifth lumbar spinal nerve by nearthrosis in patients with lumbosacral transitional vertebrae Ryo Kanematsu1 · Junya Hanakita1 · Toshiyuki Takahashi1 · Manabu Minami1 · Yosuke Tomita1 · Fumiaki Honda1,2 Received: 5 January 2020 / Accepted: 10 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Purpose Lumbosacral transitional vertebrae (LSTV) often have nearthrosis between the L5 transverse processes and the sacral ala; this causes the formation of new bone and synovial-like tissue, which can entrap L5 nerve root. The present study aimed to examine the role of nearthrosis in L5 nerve root compression in patients with LSTV. Methods From 2008 to 2018, 65 patients were surgically treated for severe leg pain/numbness caused by L5 extraforaminal stenosis. The patients were assessed regarding the presence of LSTV, radiographic features of nearthrosis, operative/radiological findings, and clinical outcomes. CT/MRI were used to classify the patients into three groups: group A had L5 nerve root compression that was not related to nearthrosis, group B had L5 nerve root impingement due to nearthrosis with new bone formation, and group C had L5 nerve root impingement due to nearthrosis with synovial-like tissue. The relationships between the type of LSTV (based on the Castellvi’s classification) and these three groups were investigated. Results Although 26 of 65 patients had LSTV (40%), four were excluded because of less than 1-year follow-up. The 22 patients with LSTV were classified as type IA (n = 2), IIA (n = 13), and IIB (n = 7). In accordance with the radiological findings, there were eight patients in group A, six in group B, and eight in group C; the LSTV morphology did not significantly differ between groups. Conclusions L5 nerve root was compressed by nearthrosis in 64% of symptomatic patients with LSTV; this region should be carefully assessed in all symptomatic patients with LSTV. Keywords Extraforaminal entrapment · Extraforaminal stenosis · The fifth lumbar spinal nerve · Nearthrosis · Lumbosacral transitional vertebrae
Introduction The term “lumbosacral transitional vertebra” (LSTV) is used to describe congenital spinal anomalies comprising total or partial uni- or bilateral fusion of the transverse process of the lowest lumbar vertebra to the sacrum [1]. LSTV often involves nearthrosis between the L5 transverse process and the sacral ala at the LSTV, resulting in the formation of new bone and synovial-like tissue [2, 3]; this could cause entrapment of the fifth lumbar spinal nerve root. Bertolotti’s * Ryo Kanematsu [email protected] 1
Department of Spinal Disorders Center, Fujieda Heisei Memorial Hospital, Mizukami 123‑1, Fujieda, Shizuoka 426‑8662, Japan
Department of Neurosurgery, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
2
syndrome is the association of low back and sciatic pain with LSTV [4, 5]. Extraforaminal stenosis at the lumbosacral junction is not a single clinical entity and can
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