The postoperative curative effect was satisfactory, and the paravertebral abscess was absorbed dramatically. Although the loss of segmental Cobb angle was 2.6° during the final follow-up, the VAS, ODI, and ASIA scores of all 21 patients were significantly improved compared with the scores preoperatively, and there was no recurrence of tuberculosis at the long-term follow-up. No serious complications such as intraspinal cement leakage, pulmonary cement embolism, or neurovascular injury occurred in all patients. There were no complications such as implant failure, proximal junctional kyphosis, or recurrence of tuberculosis at the minimum 5-year follow-up. These findings suggest that, for elderly patients with thoracolumbar spinal tuberculosis complicated with severe osteoporosis, after anterior or posterior debridement and bone grafting, PASF is effective and safe.
Spinal tuberculosis is a major cause of paraplegia in developing countries, and older people are at high risk of contracting the disease.11 Given that the elderly have many complications, such as poor physical tolerance and osteoporosis, it is particularly difficult to deal with senile spinal tuberculosis in clinical setting. Elderly patients with spinal tuberculosis usually have the following characteristics: owing to the existence of low back pain or neurological dysfunction, patients prefer to stay in bed, and reduced activity may aggravate the degree of osteoporosis, forming a vicious circle12; the nutritional status of elderly patients is sometimes poor, and most patients are complicated with hypoproteinemia and anemia, especially those with spinal tuberculosis. The accumulation of M. tuberculosis leads to poisoning symptoms affecting patients’ appetite and inducing fever. Insufficient protein intake and increased metabolism due to fever can reduce serum protein levels, leading to hypoproteinemia13; immunity function and compliance to systematic anti-tuberculosis treatment are really poor for elderly patients, most are complicated with huge abscess, sinus, and dead bone formation, and the value of conservative treatment is limited; tuberculosis recurrence is relatively high after the surgical intervention; in elderly patients with severe osteoporosis, multiple fractures of the thoracolumbar spine may coexist with tuberculosis. Most patients had severe kyphosis and/or neurological dysfunction when they sought medical care. The main purpose of the operation is to thoroughly remove the necrotic tissue and pus, relieve spinal cord compression, rebuild spinal stability, effectively control the disease, shorten treatment duration, and improve patients’ quality of life. 14 If reconstruction in such patients are performed using traditional implants, the loose cancellous bone of the vertebral body finds it difficult to provide sufficient holding force; further, the risk of implant failure is higher than that without osteoporosis, and the possibility of serious complications, such as bone nonunion and kyphosis aggravation, is increased.15–16 Burval et al. have found that the strength of pedicle screw fixation in patients with osteoporosis is only 40%-80% lower than that in people with normal bone mass.17 To overcome this problem, there are many ways to enhance the holding force of screws, such as increasing the length and diameter of screws, use of expansion screws or bone cement reinforced screws, and so on.18–19 However, some studies have pointed out that deeper screw placement may increase the risk of damage to anterior vital vessels and viscera, and the utilization of larger diameter screws may lead to burst fracture of the pedicle causing nerve root pinching.20 Expansion screw has been modified into expandable pedicle screw to prevent screw pullout. However, there is a certain loosening rate of the expandable pedicle screw in clinical practice, and the strength is lower than that of the bone cement reinforced screw.19 Two studies21–22 proved that bone cement reinforcement has a significant advantage in terms of biomechanics and can significantly improve the axial anti-pullout force of pedicle screws, especially for patients with osteoporosis. When 2.5 cm3 bone cement is injected into normal and osteoporotic vertebrae, the pullout force of screws can be increased by approximately 120% and 156%, respectively. Choma et al.23 considered that the holding force of pedicle screws strengthened with 2-ml bone cement can be increased 5 times. For elderly patients with both osteoporosis and degenerative spine diseases, application of bone cement reinforced screws provided satisfactory clinical results. Moon et al.5 have followed up 37 patients with thoracolumbar degenerative diseases accompanied with osteoporosis for 3 years, and found that the effect of bone cement reinforcement was satisfactory, and 34 of the 37 patients had satisfactory bone graft fusion. Liu et al.24 utilized PASF in elderly patients with fracture and found no complications, such as internal fixation loosening or increased Cobb angle at the 95-month follow-up. Hu et al.4 found that bone cement reinforcement can significantly improve the stiffness and strength of spinal internal fixation, which is conducive to the maintenance of spinal stability and promote bone graft fusion, which is among the key factors determining the long-term clinical outcome.
The emergence of new infection of tuberculosis or the spread of original infection after injecting bone cement into the fractured vertebral body has been reported in several case reports6–9, suggesting that injecting bone cement into the vertebral body of patients with infection or suspected infection is worrisome. However, there has been no study that has evaluated the safety and efficacy of PASF in treatment of elderly patients with thoracolumbar spinal tuberculosis accompanied with severe osteoporosis. Therefore, we mainly refer to the results of MRI in the selection of bone cement-reinforced vertebrae, but only in the vertebrae that are closest to the lesion and have no significant high signal intensity on T2 and fat compression sequences.
For elderly patients with severe osteoporosis, whether the injection of bone cement into the vertebral body will increase the risk of cement leakage and whether it will have an impact on tuberculosis treatment is another focus of this study. In the study of Martín25, Philippe26, and Guo27, bone cement leakage is mostly asymptomatic vascular leakage, which was similar to our study. We believe that the bone cement leakage is related to cement viscosity, injection volume, and distribution location. Low viscosity and over-injection of the cement will increase the symptomatic bone cement leakage risk. When the cement distribution was located at the back of vertebral body, the risk of leakage into the spinal canal increases, causing symptoms of spinal cord compression. Philippe et al.26 thought that an appropriate amount of bone cement (approximately 2.5 ml) could provide an ideal anti-pullout force of screws. However, Liu et al.18 thought that only the injection volume of bone cement controlled between 1.5 and 3.0 ml are safe and effective. In this study, we preferred to inject bone cement at the drawing period, and the injected amount was controlled within 1.5 ml. Therefore, there were no serious complications, such as intraspinal canal or pulmonary embolism, in this study.
It should be taken into account that surgery can only accelerate patients’ recovery, and drug treatment is the fundamental and key to cure spinal tuberculosis. We recommend at least 1 year of anti-tuberculosis treatment until the indications of drug withdrawal are fulfilled. Despite bone cement injection into the vertebral body, no spread or recurrence of tuberculosis infection was found at > 5-year follow-up. Toyone et al.28 reported that there is a high incidence of adjacent segment fractures within 2 years after spinal internal fixation. Besides osteoporosis, it was associated with the increase of mechanical stress to the adjacent level. No proximal junctional kyphosis occurred in our cases. We speculated that, in addition to full-course anti-tuberculosis treatment, systematic anti-osteoporosis treatment during each follow-up visit should be ensured.