We reported the instrumentation failure rate of patients with instrumentation failure after TES with reconstruction using frozen autografts treated with liquid nitrogen. Revision surgery was performed using the posterior approach alone. Bone fusion was achieved, and there was no re-instrumentation failure in any patient at the follow-up period >2 years.
With continuing advances in cancer therapy, acceptable long-term prognosis can be expected even in patients with metastatic spinal tumors [21-24]. In TES, en bloc resection of a tumor-bearing vertebra can be curative, leading to longer-term survival, and achieving bone fusion of the reconstructed vertebral body is essential [25]. However, instrumentation failure caused by unsuccessful bone fusion is not a rare complication. Park et al. [10] reported that 12 (37.5%) of 32 patients experienced rod breakage at an average of 29.2 (range, 8−93) months after TES. Sciubba et al. [14] reported instrumentation failure in 9 (39.1%) of 23 patients who underwent lumbar-spine TES. Matsumoto et al. [12] reported instrumentation failure in 6 (40%) of 15 patients who underwent TES. In our study, instrumentation failure following the TES procedure was identified in 26 (42.6%) of 61 patients at an average of 32 (range, 11−92) months after TES, which was comparable to that of other studies.
The previously reported incidence rate of instrumentation failure after TES using the same reconstruction method as ours (except using fresh autologous bone for bone grafting) was 17.0% (8/47) [11]; in the present study, the instrumentation failure rate after TES using frozen bone was 42.6% (26/61). It was reported that bone formation tended to be delayed when frozen bone autografts were used compared with fresh bone autografts [25]; therefore, the instrumentation failure rate in the present study was higher than that previously reported [11]. Although bone fusion was delayed, complete bone fusion within the cage was obtained in the TES model canine using frozen bone [25]. The instrumentation failure rate following the first procedure was higher in the present study; however, stability was maintained for a long time in 35 (57.4%) of 61 patients. Considering the advantages of using liquid nitrogen-treated bone, we continue using frozen bone autografts in spinal reconstruction during TES. To decrease the incidence of instrumentation failure, we recently began using a more robust cage and cobalt chrome rods to create a stiffer construct of the operated spine and having additional bone graft around the cage to facilitate bone fusion.
In the present study, back pain and neurological deterioration caused by instrumentation failure developed in 19 (76.1%) and 8 (30.8%) patients, respectively. Matsumoto et al. [12] reported that all 6 (100%) patients experienced back pain and 1 (16.7%) experienced neurological deterioration at the time of instrumentation failure. Park et al. [10] reported that back pain developed in 7 (58.3%) patients, and no patients had neurological deterioration at the time of instrumentation failure. These findings suggest that most patients with instrumentation failure experienced significant clinical symptoms. Revision surgery is necessary to prevent decreased ADL performance among symptomatic patients with instrumentation failure.
Instrumentation failure is caused by delayed union between the cage and the vertebral body [11], and revision surgery is performed to achieve robust restabilization and bone fusion. In the present study, we performed robust restabilization in most patients by replacing titanium rods with cobalt chromium rods and by increasing the number of rods. We also performed bone grafting at the posterior aspect of the spine. During the primary surgery, bone grafting at the posterior element was difficult because there was no bed for bone grafting at the level of the resected vertebra. Moreover, because the space was covered with scar tissue, bone grafting was straightforward and secured during the revision surgery.
In the present study, 13 (72.2%) of 18 patients with >2 years of follow-up after revision surgery achieved bone fusion within the cage, but the remaining 5 (27.8%) did not achieve bone fusion; nevertheless, bone resorption within the cage improved. We believe that robust restabilization of the posterior instrumentation increased the stability of the spine, which facilitated bone fusion within the cage. In addition, bone fusion at the posterior aspect of the spine, which could not be applied in the primary surgery without the scar tissue of the resected vertebral area, was achieved earlier than that within the cage in cases where posterior bone grafting was performed. We believe that attaining bone fusion at the posterior aspect further increased the stability of the spine and favored bone fusion within the cage. This finding indicates that replacement of the cage using the anterior approach is unnecessary when the cage is restabilized using a stiffer construction by exchange and supplement of posterior instruments. Our recommended revision procedure is to perform posterior restabilization with three or four cobalt chromium rods and posterior bone grafting. In cases with a severely damaged cage (not observed in this study cohort), cage replacement using the anterior approach should be considered.
This study has some limitations. The small and heterogenous cohort with several tumor histologies and adjuvant therapies and the retrospective manner of data collection can introduce bias and errors. This retrospective study included various reconstruction procedures (e,g, the material and number of rods in revision surgery) differed depending on the time of surgery. The follow-up time was limited as well. Longer follow-up is required to determine the accurate incidence of instrumentation failure after revision surgery. Although all patients were diagnosed as having oligometastatic cancer in the present study, the indications for TES remain controversial because less invasive surgeries (e.g. separation surgery) have shown significant results recently. Despite these limitations, this study demonstrated the rate of instrumentation failure after TES with reconstruction using frozen autografts treated by liquid nitrogen and described a relatively simple and effective strategy for revision surgery and its favorable outcomes. The results obtained from this study will contribute to revision surgery for instrumentation failure after TES.