OBJECTIVETo summarize the clinical characteristics of severe lumbar dysplastic spondylolisthesis, and to investigate the effectiveness of the posterior surgery including decompression, partial reduction with instrumentations and interbody fusion.

METHODSTwelve patients of severe lumbar dysplastic spondylolisthesis treated between March 2007 and February 2012 were studied retrospectively. Twelve patients include 10 female and 2 male patients with an average age of 10.7 years (9-17 years). All of their spondylolisthetic level was L5 vertebrae. None of them were effective after regular conservative treatment. Eleven of 12 patients were treated surgically through a posterior decompression and instrumented reduction. One case was treated by L5 vertebrectomy and reduction of L4 onto sacrum. Their levels of instrumentations were L4-S1 in 8 patients and L5-S1 in 4 patients. All of 12 patients were fused via interbody fusion. The visual analog scale(VAS), Oswestry disability index (ODI), Japanese Orthopaedic Association(JOA) score, slip angle, percentage slip, lumbar lordosis, sagittal balance were used as outcome measures.

RESULTSAll of these patients were followed up regularly with an average follow-up of 32 months (6-64 months). Five of these 12 patients suffered postoperative nerve root impairment, including impairment of unilateral and bilateral L5 nerve roots. At the latest follow-up, only 1 case was still suffering from the weakness of unilateral peroneal long and short muscles, the other 4 patients recovered totally. The degree of their spondylolisthesis was reduced II degrees or more, and their slip angles decreased from 35.6 degree preoperatively to 9.8 degree postoperatively. The VAS, ODI , JOA, lumbar lordosis and sagittal balance were improved postoperatively. No instrumentation loosening or rupture was found.

CONCLUSIONSIn patients with severe lumbar dysplastic spondylolisthesis, isolated posterior decompression, reduction with internal fixation may lead to a satisfactory clinical outcomes. Surgical reduction is helpful to improve the interbody contact area, thus possibly improve the fusion rate. At the same time, reduction may reduce or correct the lumbar-sacral kyphosis, recover the normal lumbar lordosis and normal sagittal alignment with an excellent cosmetic result. The incidence of the postoperative nerve impairment is high because of the stretching of L5 nerve roots secondary to the reduction, but most of the patients with postoperative nerve impairment may recover gradually.