Mid-Term Results of 360-Degree Lumbar Spondylodesis with the Use of a Tantalum Implant for Disc Replacement

Abstract

PURPOSE OF THE STUDYThe study presents the mid-term results in patients treated with circumferential, i.e., 360-degreee, fusion of the lumbar spine carried out by posterolateral instrumented spondylodesis and anterior intersomatic fusion using a tantalum implant for replacement of an intervertebral disc. The aim of the study was to verify tantalum implant quality, to evaluate segment fusion and to assess the outcome of this method by patients' subjective findings. MATERIAL AND METHODSThe prospective non-randomised study included the implantation of 47 tantalum cages in 40 patients by the technique of anterior lumbar interbody fusion (ALIF) and posterolateral spondylodesis. Only patients followed up longer than for one year were included in this evaluation. The patient group comprised 16 men and 24 women, with an average age of 47.9 years. The patients indicated for this procedure had mono-or bisegmental lumbar disc degeneration with advanced changes of articular facets. The procedure involved posterior transpedicular screw fixation with decompression, if spinal stenosis existed, and reposition of the segment, if spondylolisthesis was present, and posterior spondylodesis by the open book method. No autogenous bone grafts were used because of the risk of donor-site pain and because one of the aims of the study was to test tantalum cage properties.Subsequently, ALIF and disc replacement with a tantalum cage were carried out after cage insertion, the anterior borders of the upper and lower adjacent vertebral bodies were adjusted so that the lamellar bone should overlap the cage and thus provide continual bridging for the segment, with an emphasis being on joining the lamellae with preserving their blood supply from the respective vertebral bodies. RESULTSImplant subsidence in a rotation/flexion fashion, i.e. ventrally into the upper endplate of the distal vertebra and dorsally into the lower endplate of the proximal vertebra, was observed in two cases; subsidence in a vertical fashion, i.e., symmetrically into the lower endplate of the upper vertebra was found in one patient. Neither vertical mode of subsidence into the upper endplate of the lower vertebra only, nor rotation/extension type of subsidence was recorded. No frontal/rotational mode of subsidence was found either. No osteolytic lesion between the implant and adjacent bone was diagnosed. No migration of an implant sideways or in a ventral/dorsal direction was detected. Anterior bridging fusion was observed in 32 cages. No fusion dorsal to or lateral to the cage was seen. Evaluation of bone ingrowth into the cage was not possible due to a high X-ray contrast effect of the material. High-quality bridging posterolateral spondylodesis was diagnosed in 33 cases.Subjective evaluation by the patients was based on a visual analogue scale (VAS) and an Oswestry Disability Index (ODI) questionnaire. For the whole group, the average VAS value for back pain dropped from 58.3 points before surgery to 18.1 points at one year post-operatively; there were no differences bet...