In the first place, primary thoracic spinal stenosis is rare [5]. The formation of T-OLF is strongly considered due to degenerative wear-and-tear, apart from external triggers such as biomechanical stress to the effect of posttraumatic ossification [15, 16]. There are reports on OLF manifestations in relation to DM, heavy manual labour in males, high-BMI values in females, increased bone density, and DISH [17], which is accordance with our present demographic data. Thus, T-OLF coincides with spinal osteoarthritis and spondylosis deformans, leading to a high incidence of tandem T-OLF and other stenosis lesions in the cervical or lumbar area, sometimes with ossification of ligaments. Cases with ossification of ligaments had a tendency to develop into tandem spinal stenosis (TSS) [10], therefore T-OLF seems no exception, which is frequently found in C-OPLL patients [3]. Whereas the spondylotic process was mainly confirmed in the lower lumbar spine of T-OLF patients, the incidence of lumbar ossified lesions (L-OLF or L-OPLL) was relatively low (5 cases, 8.2%). In the present study, up to 75.4% of thoracic myelopathic patients who underwent T-OLF surgeries had LCS, higher than that of cervical myelopathic patients (57.9%) [10], but well consistent with the previous study about thoracic myelopathy [18].
Patients with compressive myelopathy due to especially lower thoracic lesions often present with pain, numbness, or motor disturbance of lower limbs and neurologic claudication, which is similar to the symptoms with lumbar radiculopathy or cauda equine lesions. Spasticity of the lower limbs with hyperreflexia is often masked by cauda equine or lumbar nerve root disorders [6, 19]. These patients with complicated characteristics have the difficulty in diagnosing thoracic pathology. In spite of such a high rate of combined spinal stenosis, there have been few reports describing the clinical course of tandem thoracic and lumbar stenosis [5, 6, 19]. The present study includes a reasonable number of tandem T-OLF and LCS subjects and discusses several aspects of these peculiar cases.
Some reports mentioned that short preoperative symptom duration, single-level lesion, and the unilateral type were favorable prognostic factors, while bridged (fused) type, the beak type, intramedullary HIA on T2-weighted images, concomitant intervertebral degeneration (Modic change), and ventral compressive lesion were poor prognostic factors for the T-OLF surgery [11, 12, 20]. Contrary to expectations, we revealed that these were not statistically associated, but age, short statue, and coexistent LCS were related to the poor prognosis. Considering a smaller number of patients with cervical or upper thoracic lesions in the poor outcome group, the dynamic biomechanical factor based on their predilection in lower thoracic spine could be attributed to progressive thoracic myelopathy through the compression of the spinal cord.
The question is how to treat these elderly patients with tandem combined thoracic and lumbar stenosis, who have neurological deficits in the lower limbs. As a rule of the operative sequence for tandem T-OLF and LCS, the most clinically symptomatic area should be decompressed first. When both areas appeared equally symptomatic or hard to distinguish, the thoracic region should be decompressed first. Thoracic
decompression may provide some improvements in lumbar symptoms because the lumbar neural fibers may also be under compression by the processes of T-OLF formation. The patients with tandem T-OLF and LCS in this study exhibited elder age, lower preoperative MMT grade, greater SVA, and degenerative Modic change in thoracic lesion, resulting in lower postoperative T-JOA scores compared with non-LCS patients. Interestingly, the younger non-LCS group exhibited a higher coexistence rate of C-OPLL. The early formation of tandem ossifications, early detection, and younger age at T-OLF surgery could partially explain the good T-JOA scores found in the non-LCS cases. Advancing age was not only a determining factor in the tandem T-OLF/LCS occurrence (Fig. 2) [17], but might be also one of the most influential factors in neurological improvement in case of T-OLF. Eskander et al. reported that age increased the risk of major and minor complications regardless of the surgical algorithm chosen to manage tandem stenosis lesions [21]. Other reports concluded that the coexisting LCS in T-OLF had adverse effects on the surgical results in T-OLF, and vice versa [5, 6]. These seem to support our conclusion that the prognosis for T-OLF was paralleled that of isolated lumbar stenosis along age, rather than the preoperative symptom duration, the local T-OLF size, morphology, the number of affected OLF lesions, or radiographic cervical stenosis. Although the causal relationship between compressive lesions at levels below the operative site and the appearance of symptoms could be confirmed in the present cross-sectional study, the presence of LCS itself might partially augment the risk of thoracic cord compression, or even asymptomatic LCS might naturally progress, developing lumbar-related symptoms within a few years after thoracic surgery. Meanwhile, even surgical procedure with or without fusion did not affect the clinical outcome for T-OLF. The perioperative complication rate in this study was 13.1%, much lower than 21–35% of previous reports [22]. In some severe cases, the resection or floating of the involved OLFs could be successfully achieved, using one of the safe measures, O-arm imaging system (StealthStation; Medtronic, Inc., Minneapolis, MN, USA) [16].
We further investigated clinical outcomes after lumbar decompression in OLF patients to clarify the impact of concurrent LCS. 21.3% of the T-OLF patients required additional lumbar surgery. Although the recovery rate of the T-JOA score did not reach significance with or without lumbar decompression for LCS, we determined the effectiveness of additional lumbar decompression in cases of symptomatic tandem T-OLF and LCS after thoracic treatment.
It remains unknown which procedure, two-staged or single-stage surgery, is more effective for achieving postoperative neurologic improvement in T-OLF patients with symptomatic LCS. Neurological recovery of simultaneously single-stage surgery in tandem T-OLF and LCS was also equal to that of staged surgery. This result suggested that lumbar operations can be staged if the single stage surgery is considered to be too invasive for the patient.
This study has several other limitations, including the following: 1) the patient baseline was not controlled; 2) this was a retrospective investigation; 3) this was not population-based, and 4) an assessment of a correlation between the dynamic factor in OLF levels and clinical outcomes was inadequate. These limitations could be partially ascribed to the challenges of OLF-related surgery, and those of biomechanical evaluation in thoracic spinal system, which had a limited range of segmental motion. Prospective data collection is needed in the future to clarify more precise clinical outcomes in OLF cases. Apart from its great advantages for visualizing bony lesions, we must also take the potential risk of radiation by CT scanning into consideration. All patients in this study underwent CTM as a preoperative examination to determine the involved OLF level at which the surgical procedure should be performed, and to avoid missing other lesions affecting the spinal cord or cauda equine, which can lead to further neurological complications. The present study approached the cases in which thoracic decompressions are inevitable to disclose OLF epidemiology and pathology beyond these limitations.
Given these results, T-OLF could be related to age-, and life style-related disease, likely accompanied with other spinal stenosis lesions. The identification of the predominant lesion and the interpretation of clinical outcomes seems to be controversial and difficult in T-OLF cases. The prognosis for T-OLF with concurrent LCS was worse than for patients without LCS. The present study indicated that the severity of lumbar lesions could have a more critical impact on neurological improvement after thoracic surgery for OLF, and an additional surgery for another lumbar lesion could significantly improve neurological findings. Therefore, surgical management should be tailored to the patient’s age and general condition, whether it is by simultaneous or staged procedures.