Introduction: There is a paucity of data regarding the condition of L5 isthmic spondylolisthesis (IS) concomitant with L4/5 disc herniation. This study aims to identify the incidence rate and to illustrate the possible risk factors for L4/5 disc herniation in L5 low-grade IS patients.
Methods: A total of 268 consecutive patients diagnosed as L5/S1 low-grade IS were retrospectively enrolled in this study. Depending on the presence of L4/5 disc herniation or not, patients were divided into L4/5 DH group and L4/5 Non-DH group. Radiographic parameters were measured and the ratios of L4-S1 segmental lordosis (SL) to lumbar lordosis (LDI), L4 IEP to L5 SEP (L4 IEP/L5 SEP) and L5 IEP to S1 SEP (L5 IEP/S1 SEP) were compared between groups. Besides, Pfirrmann’ grade of L4/5 disc, L5/S1 disc and Roussouly classifications of each patient were also recorded.
Results: There were 40 patients (14.9%) in L4/5 DH group. Regarding Roussouly classification, there was a slight significant difference between groups. In terms of Pfirrmann’ grade, L4/5 DH group showed more advanced disc degeneration at L4/5 than L4/5 Non-DH group. In contrast to L4/5 Non-DH group, L4/5 DH group had significantly larger L4 IEP, L4 IEP/L5 SEP, S1 SEP and LDI while smaller L4/5 Disc angle, L4/5 Disc height, slip percentage, LL and SS. Multivariate logistic regression analysis revealed that higher L4/5 disc Pfirrmann’ grade (P=0.004), decreased L4/5 disc height (P<0.001) and lower L5 slip percentage (P=0.022) were significantly associated with occurrence of L4/5 DH.
Discussion: This study observed an incidence rate of 14.9% of L4/5 disc herniation in patients concomitant with L5 low-grade IS. Advanced L4/5 disc degeneration, decreased L4/5 disc height and lower L5 slip percentage may be significantly associated with L4/5 disc herniation. As we all know, IS can be diagnosed just by the left and right oblique views of the lumbar spine, while diagnosis of disc herniation requires MRI and CT of lumbar spine. However, L5 IS and L4/5 DH will both compress the L5 nerve root, making it difficult for physicians to tell whether it is a nerve compression resulting from IS or DH. Thus, when facing an L5 IS patient with mild nerve root compression symptoms whose X-rays showed decreased L4/5 disc height and low L5 slip percentage, it is necessary to complete lumbar MRI and CT examinations to avoid misdiagnosis and missed diagnosis. This study emphasizes that: (1) it is not rare for L5 IS patients to present with supradjacent disc herniation; (2) complete MRI or CT of the lumbar spine is indispensable for physicians to determine treatment plans or even surgical plans when treating L5 IS patients, especially those with mild symptoms related to nerve root compression.