Altogether, 238 abstracts were retrieved from the literature search (Fig. 1). Of these, 208 articles were excluded based on abstract or title. Most of the excluded studies were overlaps between the searched literature databases, animal studies, no original articles, or were articles investigating other pathologies or studies including cervical factures or thoracic or lumbar fractures only. Altogether, 30 articles were analyzed completely. Of these articles, 14 were excluded either because not comparing the thoracic spine with the lumbar spine, not focusing on osteoporotic fractures, or no radiological fracture evaluation was performed. Altogether, 222 articles were excluded (Fig. 1). All 16 remaining original articles, which covered the period from 1999 to 2018 are summarized in Tables 1–5. Levels of evidence were defined as described by Bassler and Antes  (Tables 1–5).
A total of two studies analyzed the frequency of fractures with respect to fracture location (Table 1). Both studies reported a peak of fractures at the TLJ and the mid-thoracic spine. Nevitt et al.  reported 7% of the fractures at Th12 and L1 and 5% at Th7 and Th8. Waterloo et al.  compared the fracture location between the genders and found a majority of fractures at Th7, Th9, Th12, and L1 in women with a similar distribution in men except of a higher frequency in Th8 instead of Th9. The highest vertebral deformities were seen in the mid-thoracic region and the TLJ.
Bone mineral density and regional blood flow
Three papers evaluated the differences of bone mineral density (BMD) and regional blood flow between the thoracic and lumbar spine (Table 2). With the intention to predict risk of vertebral fractures, previous investigations typically measured BMD in the lumbar spine, especially in L1. Anderson et al.  dealt with the question to what extent these BMD values can also be used to predict thoracic fractures. Therefore, the authors performed a community-based case–control study including 40 patients (46 vertebral fractures) with and 80 patients without vertebral fractures. BMD was measured by quantitative computed tomography-based bone measures. Low BMD measured in L3 was significantly associated with a higher fracture risk at the mid-thoracic spine and the TLJ. Similar, the observations in Th10—however, the expressiveness was lower compared to L3. The relationship between low BMD in Th10 and risk of fracture lost significance at the lumbar spine. In fact, strength and factor-of-risk measurement at L3 were more strongly associated with mid-thoracic fractures than measurements at T10. Beside this, the authors concluded that vertebral fracture etiology may vary by region, with vertebral fractures in the mid-thoracic spine more strongly relating to skeletal fragility.
Similar results were found by Watt and Crilly . They included 120 patients in their case–control study to determine if there is an association between vertebral fracture location and measured BMD T-score. They demonstrated that a lower lumbar BMD T-score was associated with a Th4–Th10 (p = 0.02) as well as the Th11–L4 vertebral fracture location (p < 0.001) in unadjusted analyses. After multivariable regression analyses, only the Th11–L4 fracture location remained significantly predictive of a lower lumbar BMD T-score (p = 0.005). The authors also examined the relationship between fracture and history of any traumatic injury depending on fracture location. They concluded that patients with vertebral fractures in the mid-thoracic spine (Th4–Th10) may be less likely to report about a traumatic cause of their vertebral fracture compared to lumbar one.
In contrast, Biffar et al.  examined plasma flow (PF), plasma volume (PV), and extraction flow (EF) in fractured and normal-appearing vertebrae by Dynamic Contrast-Enhanced MRI and their influence on manifestation of osteoporosis and vertebral fractures. Perfusion parameters were decreased significantly in normal-appearing vertebral bone marrow (vBM) of patients with osteoporosis compared to healthy subjects. Furthermore, significant perfusion alterations were observed in acute osteoporotic vertebral fractures compared to normal-appearing vertebrae. Interestingly, perfusion shows reproducible alterations in vBM, depending on the anatomic level. PF and PV values measured separately showed a gradual decline from Th8 to L5, indicating that lumbar vertebrae are less perfused. However, despite lower perfusion rates and lower BMD, the risk of osteoporotic fractures in the lower lumbar spine was not increased.
Five of the included studies examined biomechanical aspects (Table 3). Bruno et al.  analyzed spinal loading during daily activities to explain the fracture pattern and fracture distribution in a biomechanical model. The authors described the highest fracture risk at the TLJ due to a lower predicted strength compared to the lower lumbar spine. Interestingly, none of the 119 activities that were examined produced peaks in the factor-of-risk at the mid-thoracic region. Buckley et al.  tested the relative strength of isolated vertebral bodies under flexion and extension and reported an approximately 40% lower vertebral body strength under bending loads than pure compression. Bürklein et al.  studied the mechanical failure loads of thoracic and lumbar vertebrae and reported of significant lower failure loads at Th6 compared to Th10 and L3 without any significant differences of the failure loads between Th10 and L3. Okamoto et al.  analyzed the effect of a kyphotic deformity of 10° and 20° at Th12. This caused an increase in stress on adjacent vertebrae. Additionally, a bimodal peak of the stress was seen including the mid-thoracic region. Ignasiak et al.  evaluated the spinal loading effects between young and elderly individuals. Thereby, the maximum compressive loads in elderly were lower than those in young lumbar levels during flexion and for upper thoracic levels during stand-to-sit (Th1/Th2-Th8/Th9) and sit-to-stand (Th3/Th4-Th6/Th7). However, the maximum loads predicted for the lower thoracic levels (Th9/Th10–L1/L2) were similar compared to the young.
Four studies evaluated the risk of subsequent vertebral and/or extra-vertebral fractures after suffering an osteoporotic thoracolumbar fracture (Table 4). Generally, both can be considered as an indicator for impaired bone quality and a sign of frailty.
It could be shown that a severe thoracic vertebral fracture is a strong predictor for sustaining a subsequent hip fracture, whereas mild or moderate fractures and the number of compressed vertebrae were not found to be statistically significant risk factors . In a retrospective analysis on the relation of hip fractures and concomitant vertebral fractures, patients with a femoral neck fracture were observed to differ from patients with intertrochanteric fractures or only vertebral fractures in terms of both the number and distribution of their vertebral fractures—these being fewer, frequently single, and more often confined to the lower spine .
Data from the Registry of Pathological Osteoporotic Vertebral Fractures (REPAPORA) with 1005 patients and 2874 osteoporotic vertebral fractures indicated that patients with previous fractures of the thoracic spine between Th1 and Th9 are less likely to suffer subsequent fractures of the spine . Patients with a thoracic osteoporotic vertebral compression fracture will most likely sustain a subsequent fracture of the TLJ followed by the mid-thoracic spine while patients with an osteoporotic fracture of the lumbar spine will most likely have a subsequent fracture at the TLJ or the lumbar spine . The authors of this registry study named this phenomenon of a higher likelihood for subsequent fractures in the vertebral segments below the index fracture “lumbar drift” and conjectured that this may be due to kyphotic deformity and increased spinal load in the more caudal vertebral bodies.
This could also be the mechanics behind the clinical observation that elderly men with fractures in both the thoracic and lumbar regions are at an especially high risk of sustaining secondary fractures .
Two studies evaluated the clinical outcome of patients suffering of osteoporotic thoracolumbar fractures and analyzed the impact of fracture location (Table 5). Fechtenbaum et al.  included 629 post-menopausal women and reported no differences in the clinical outcome between thoracic and lumbar vertebral fractures location. In contrast, the authors found a significant association between both grades of vertebral deformity and number of fractures with inferior outcomes. In contrast, Suzuki et al.  evaluated 107 geriatric patients with thoracolumbar fractures and found that patients with lumbar fractures tended to improve steadily, whereas those with thoracic fractures tended to deteriorate after the improvement of the first three months. The authors postulated that the deterioration might be caused by the increased kyphosis at the thoracic spine leading to muscular overstrain.