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; Lumbosacral transitional vertebrae; Nearthrosis; The fifth lumbar spinal nerve.