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 of > 2 years.
With continuing advances in cancer therapy, acceptable long-term prognosis can be expected even in patients with metastatic spinal tumours [21–24]. In TES, en bloc resection of a tumour-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. reported that 12 (37.5%) of 32 patients experienced rod breakage at an average of 29.2 (range, 8 − 93) months after TES [10]. Sciubba et al. reported instrumentation failure in nine (39.1%) of 23 patients who underwent lumbar-spine TES [14]. Matsumoto et al. reported instrumentation failure in 6 (40%) of 15 patients who underwent TES [12]. 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 of instrumentation failure after TES using the same reconstruction method as ours (except using fresh autologous bone for bone grafting) was 8/47 (17.0%) [11]; in the present study, instrumentation failure rate after TES using frozen bone occurred in 26/61 (42.6%). It was reported that bone formation tended to be delayed when frozen bone autografts were used compared to 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, it was previously demonstrated that 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.
In the present study, back pain and neurological deterioration caused by instrumentation failure developed in 19 (76.1%) and eight (30.8%) patients, respectively. Matsumoto et al. reported that all six (100%) patients experienced back pain, and one (16.7%) experienced neurological deterioration at the time of instrumentation failure. Park et al. reported that back pain developed in seven (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 performance of ADL 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 restabilisation and bone fusion. In the present study, in most patients, we performed robust restabilisation 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 follow-up after revision surgery achieved bone fusion within the cage, and the remaining five did not achieve bone fusion; nevertheless, bone resorption within the cage was improved. This finding indicates that replacement of the cage using the anterior approach is unnecessary when the cage is restabilised using a stiffer construction by exchange and supplement of posterior instruments. 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 tumour histologies and adjuvant therapies, and the retrospective manner of data collection, can introduce bias and errors. 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 favourable outcomes. The results obtained from this study will contribute to revision surgery for instrumentation failure after TES.