This study compared the clinical effect of nonstructural autograft with titanium mesh filled up with autograft for bone graft and fusion in combination with posterior debridement and internal fixation for lumbar TB. The results demonstrated that the nonstructural autograft was equivalent to titanium mesh with autogenous bone for spinal reconstruction but had the advantages of diminished operation time and surgical trauma, except for delayed grafted bone fusion. Compared with implanting a titanium mesh cage, it is unnecessary to resect the pedicle for implanting bone granules into the lumbar vertebral space, therefor decreased the surgical trauma and maintained the spinal stability. Moreover, implanting bone granules into the intervertebral space is much easier than placing a titanium mesh cage during the posterior procedure, decreasing the risk of neurological elements injury. Furthermore, it will save health cost for patients when choosing nonstructural bone grafting as cutting down the expense of titanium mesh cage.
The objective of surgical treatment for STB is debridement, decompression, prevention or correction of deformity, reconstruction of stability with bone grafting and internal fixation. To date, however, the surgical approach hasn’t reached a consensus among the surgeons yet and has been evolving for decades. The anterior approach enables to direct removal of the TB lesions, but the risks of injuring great vessels are relatively large especially at lower lumbar spine . Combined anterior and posterior surgery improves the effects of debridement and spinal reconstruction, but the surgical trauma is enlarged . The single posterior surgery has become popular nowadays as the advantages of less surgical trauma, easier kyphosis correction, stable fixation and simple techniques [20–22].
The typical STB affects intervertebral disc and adjacent vertebral bodies, resulting in spinal instability and kyphosis. Based on the three-column theory of Denis  and load-sharing principles , anterior column reconstruction by a structural bone grafting was mandatory after removing the affected vertebral bones and intervertebral discs. Many types of bone grafts have been used, such as tricortical iliac bone, titanium mesh cage filled with bone granules, rib bone and so on [10, 25–26]. The autogenous strut harvested from iliac was frequently used to repair bone defects due to good osteogenesis, bone induction, bone conductibility and biocompatibility . However, harvesting a tricortical bone may increase the complications of donor site including chronic pain and infection . Harvesting spongy bone granules can be achieved by a tiny skin incision as 2 centimeters long in present study and fenestration of the posterior iliac crest, avoiding position change during the procedure and decreasing the donor site morbidity.
Titanium mesh cage used in the study was filled with resected cancellous bone from vertebral arch or harvested from the iliac crest. Although several studies reported that titanium mesh cage exhibited an important potential in reliable spinal reconstruction, high bone fusion, sufficient sagittal profile maintenance and lower implant-related problems, placing a titanium mesh cage from posterior approach in the lumbar spine would increase the operation duration and risk of injuring nerve roots. The operation time was longer, and the intraoperative blood loss was more in the structural bone grafting group in our study, as placing a titanium mesh cage required extensive bone removal during the operation, resulting in increased surgical time and intraoperative bleeding. However, thanks to application of the analgesic, VAS scores of back pains improved in both group although paravertebral muscle extensively stripped and posterior spinal structures sacrificed in the structural bone grafting group.
The most concern about nonstructural bone grafting is the failure of support and breakage of instrumentation as it seems to violate the rule of anterior column reconstruction. Nevertheless, several studies have reported the success of using nonstructural bone graft in lumbar STB [13–15]. Our previous study also demonstrated the nonstructural bone graft had comparable bony fusion rate and even shorter fusion time compared with titanium mesh cage in single segment thoracic tuberculosis. In the present study, however, the cancellous bone granules didn’t exhibit the similar bone graft fusion time compared with titanium mesh cage filled with autogenous bone. We think the reason is insufficient volume of bone graft and resorption of grafted cancellous bone granules in the early stage. Owing to the preservation of the posterior structure and reliable pedicle screws fixation, however, complications like internal fixation failure or TB recurrence were not present in nonstructural bone graft group except one case who didn’t regularly take the anti-TB drugs.
In the study, we found loss of Cobb angle was present in both groups. However, the Cobb angle loss in both groups is slight and the lumbar curvature are well maintained from post-operation to last follow-up, with no significant difference. However, the Cobb angle correction of nonstructural bone group was smaller than that of structural bone group, as the loose structure of granular bone could not bear the same supporting force as titanium mesh cage. To correct kyphosis through placement of contour rods and distracting intervertebral space, anterior support is necessary. In this case, structural bone grafts such as titanium mesh should be chosen instead of nonstructural bone grafts. Therefore, the essentials for success of nonstructural bone grafting are: 1) the posterior spinous process and ligamental complex should be retained during the operation to preserve the local stability. 2) during the procedure of debridement, the sclerotic bone and bone bridge between the anterior edge of vertebral bodies is preferred to be preserved. As more bony structure of vertebrae reserved, the volume of bone grafting needed is decreased and the demand for structural bone reconstruction could be avoided. 3) a rigid pedicle screw fixation should be guaranteed, without distraction of the vertebral interspace.
To the best of our knowledge, this is the first study comparing nonstructural bone with structural bone grafting in combination with posterior debridement and instrumentation for lumbar STB, and the results from follow-up time are good. However, the study still has some limitations. Firstly, this is a retrospective study of a small-scale of patients from a single center of institution. Second, the patients are not chosen randomly, so the selection bias is inevitable.