Because the anatomical structure of the spine is complex, radical spinal oncology resection for spinal neoplasms is nearly impossible [22, 23]. Although piecemeal or intralesional excisions may yield the complete resection of tumors, these procedures are associated with a high risk of local recurrence due to tumor contamination and residual tumors . It is, therefore, advantageous to use intralesional curettage in combination with adjuvant therapies, such as radiation therapy, to achieve local control in bone metastases . However, these adjuvants are not generally suitable for the spinal axis due to the risk of iatrogenic injury to neural elements and adverse effects on wound healing and bone fusion .
It has been confirmed that TES with wide/marginal surgical margins performed for solitary spinal metastasis and aggressive primary spinal neoplasms can yield excellent tumor control and prolong survival. Cloyd et al.  systematically reviewed the literature on TES, including 229 primary and 77 solitary metastatic tumors of the spine. The results showed that the 1-, 5-, and 10-year disease-free survival rates of the primary tumors were 92.6%, 63.2%, and 43.8%, respectively, and those of the metastatic tumors were 61.8%, 37.5%, and 0%, respectively. The 1-, 5-, and 10-year survival rates of the primary tumors were 96.3%, 82.2%, and 71%, respectively, and the 1- and 5-year survival rates of the metastatic tumors were 80.8% and 56.6%, respectively . Compared with piecemeal or intralesional excisions, TES is currently a more suitable surgical procedure yielding good long-term local control and longer survival rates for patients with spinal tumors and favorable circumstances, according to physicians, surgeons, and patients [5, 24, 26].
Considering that TES is indicated for patients with a longer life expectancy , solid spinal reconstruction is essential for the long-term quality of life of patients due to its longevity . A biomechanical study demonstrated that multi-segmental posterior fixation with anterior column reconstruction can provide better stability than short fixation and that fixation should be extended to 2~3 levels above and below the resected vertebrae . However, instrumentation failure, the incidence of which varies from 17.0 to 40%, is not a rare complication following a long-segment fixation procedure after TES [7, 13, 27, 28]. Among the types of IF, such as screw loosening, screw back-out, cage breakage, screw fracture, and rod breakage, rod fracture is the most common and often leads to a high reoperation rate due to aggravating back pain or neurologic deterioration [9, 27]. Cage subsidence, a history of radiotherapy, and a low spinal level of involvement have been confirmed to be risk factors related to rod fracture [7, 9, 27, 28]. The survival time of spinal tumor patients is longer when primary tumors and metastatic tumors are resolved, so reconstruction of the three columns of the spine with additional posterior column reconstruction is very important . The satellite rod technique, a multi-rod construct, has been proven to have the potential to reduce pseudarthrosis and fatigue fracture at the 3-column osteotomy site by enhancing the stability and stiffness of the construct for adult spinal deformity correction. Hyun et al.  used a multiple-rod construct, placing additional supportive rods across the 3-column osteotomy, to replace the standard 2-rod construct, resulting in a lower incidence of rod failure. Shen et al.  reviewed “dual construct” for 36 complex spinal reconstructions and found that the dual construct is a safe alternative to traditional 2-rod, which could avoid revision surgery after rod breakage. Some surgeons also attempted to connect additional rods to the broken rods in a reoperation for spinal tumors . This practice can serve as a reminder to add satellite rods during primary TES, and in this study, we routinely used satellite rods across the osteotomy area in patients with spinal tumors undergoing TES.
In our study, reconstruction with a posterior multi-rod construct combined with anterior TMC was performed in all patients, and instrumentation failure did not occur in the postoperative follow-up. We attributed this excellent result to the following factors: (1) Posterior instrumented fusion across the apex creates long lever arms and generates substantial stress on the apical osteotomy sites. Satellite rods can disperse the stress of each rod at the osteotomy site and create a gradual transitional zone from the osteotomy area to the non-instrumented region . (2) TMC subsidence prevents load sharing in the anterior column, which increases the load on the posterior fixation area and finally leads to the occurrence of a broken rod . The use of additional accessory rods increases the stiffness of the instrumentation, which results in improved load transfer to the posterior construct, thereby reducing the load acting on the anterior device . This factor may be the reason that TMC subsidence did not occur during the follow-up in our study. (3) Achieving solid bone fusion was vital to maintaining long-term stability for spinal reconstruction . In the presence of pseudarthrosis, rod breakage may be inevitable due to metal fatigue caused by repeated fretting . According to Wolff’s laws, mechanical forces influence bone formation and remodeling . The stability and stiffness of satellite rods allow early rehabilitation after TES, enabling enough strain to form at the fracture site to stimulate bone formation and prevent excessive strain, which results in instability followed by delayed healing or nonunion . In our cases, the overall solid fusion rate was 93.3% after a mean of 31.1 months after the surgery. Only one patient failed to obtain solid fusion because of tumor recurrence, and the patient died 6 months after the operation. (4) Radiotherapy, as a common preoperative and postoperative adjunctive therapy for spine tumors, has been proven to be a risk factor for IF after TES . In this research, we obtained a wide/marginal surgical margin to minimize tumor contamination and reduce the necessity for radiotherapy after surgery. Considering the patients’ long-term quality of life and the negative impact on bone quality and healing process of radiotherapy, in our study, only 2 patients and 1 patient underwent radiotherapy preoperatively and postoperatively, respectively, after careful treatment planning.
In the retrospective study, the postoperative VAS, ODI, and ASIA scores improved significantly compared to the preoperative values (P < 0.05). No loss of AVH or PVH or LKA progression was observed at the final follow-up. No reoperations were performed because of IF. These results show that TES combined with the satellite rod technique can improve the long-term quality of life of spinal tumor patients. All patients were routinely fixed with 2~3 vertebral levels above and below the diseased vertebrae. The average operation time was 316.7 min, and the average volume of blood loss was 2816.7 mL. In our study, there was only one superficial wound infection, and we postulate that the infection was not caused by the satellite rod. Therefore, this technique likely does not increase the infection rate, especially considering the short time required for positioning the satellite rod via a connector. Compared with the procedures in previous studies [6, 31, 32], the procedure did not significantly increase the number of fixed segments, operation time, volume of blood loss, or complications, although 2 additional rods were implanted. From the perspective of efficiency, procedure in which satellite rods are added is relatively safe, quick, and well controlled. Furthermore, satellite rods were cut from the long rod used in the operation, so this procedure did not increase the financial burden of patients. In addition, to prevent IF, several surgical techniques such as meticulous endplate preparation , TMC in the oblique position , and disk-to-disk cutting  are recommended.
Despite all its strengths, there may be some shortcomings about satellite rod technique. The multi-rod construct increases the metal bulk, which could result in additional metal artifact with postoperative imaging . The increased space occupation by the lateral and posterior multi-rod construct could also affect wound closure and osseous healing process [13, 33], due to proportionally less space available for placement of graft material . Furthermore, the subordinate rods are piggybacked off of the primary two longitudinal rods; as a consequence, the stress transfers distally or proximally, and eventually, the primary rod is prone to break above or below the satellite rod, although this did not occur in our research [29, 33, 34].
The present study has several limitations. First, the cases included in this study were single vertebral lesions, and the effect of the satellite rod technique in multiple TES remains to be further discussed. Second, TES at the lumbar spine had the highest risk of rod fracture compared with thoracolumbar and thoracic levels. In our study, the sample size for lumbar TES, especially lower lumbar TES, was small, which can limit the statistical power. Third, because of the limited sample size, we did not establish a control group, and a prospective randomized controlled trial with a large sample size is needed to verify the reliability of the results in our study.