In surgical correction of ASD, high load bearing requirements for the pedicular screw/bone interface is essential for rigid posterior internal fixation system, which is important for spinal fusion. Bone quality is crucial to pedicle screw performance17. However, elderly patients with ASD are commonly accompanied with low BMD or osteoprosis in clinical practice. It has been proven that osteoporotic bone can increase the risk of implants failure 17. Patients with low BMD or osteoporosis are more likely to suffer from PJK/PJF6,18,19. A propensity score matching study showed that low BMD was a significant risk factor for PJF with a odds ratio of 6.46, which was consistent with our present study. After propensity score matching, the result showed that patients in group B with low BMD or osteoporosis were more inclined to develop into PJF or pedicle screws loosening compared to the patients in group A with “normal bone quality” (whose vertebrae was reinforced with PMMA cement).
In the last two decades, pedicle screw cement augmentation has been used to increase fatigue strength and kyphoplasty or verterbraplasty is commonly used to treat osteoporotic vertebrae fracture 12,20. In management of ASD with low BMD or osteoporosis, prophylactic verterbraplasty (PV) at UIV + 1 and (or) UIV was proposed to prevent PJK/PJF. Robert A Hart, et al20 firstly reported that 15 patients with osteoporosis (underwent PV at UIV + 1) did not suffer from proximal junctional acute collapse after long posterior lumbar fusion and PV was considered as a cost-effective intervention. Later, Aydogan, M, et al11 reported that 36 patients, who underwent pedicle screw fixation with vertebroplasty and PV at UIV + 1 and LIV, with bone T-score lower than − 2.5 had no proximal and distal junctional fractures. Furthermore, the reports of Ghobrial GM, et al 7 and Martin CT, et al10 supported that prophylactic vertebroplasty (PMMA at the UIV and UIV + 1) could prevent PJK and PJF. However, the efficacy of prophylactic cement augmentation in the treatment of ASD was not supported by recent studies8,13. These results showed that bone cement reinforcement at UIV and UIV + 1 cannot prevent PJK/PJF. In our current study, the result of both pre- and post-propensity scoring matching showed that combination of CAFPS and PV at UIV + 1 could prevent PJF, but could not reduce the incidence of PJK. It suggested that cement augmenttation could not reduce the risk of disc failure, disruption of the posterior osseo-ligamentous complex and fragile paraspinal muscle, which might cause PJK.
The reasons for the controversy about whether prophylactic cement augmentation could minimize the risk for PJK and PJF were as follows. Firstly, multiple risk factors could be correlated with PJK and PJF, previous studies did not eliminate the heterogeneity of ASD population between groups, such as age, BMD or spino-pelvic parameters. In this study, we carried out the propensity score matching analysis aiming to minimize the heterogeneity of multiple risk factors causing the PJK and PJF and also to avoid selection bias. Our results showed that both two groups were comparable after propensity score matching (Table 2). Secondly, there was still no consensus on the definition of PJK or PJF, which might be another factor that influence the evaluation of prophylactic cement augmentation. The previous definition of PJF is a progressive form of the PJK or the symptomatic PJK that requires surgery1,2. However, according to our experience, some cases with acute proximal junctional frature did no present the progressive form of the PJK. Therefore, in our study we adjusted definition of PJK and PJF based on previous articles1–3.
In surgical treatment of patients with osteoporosis, cement‑augmented fenestrated pedicle screw (CAFPS) had been safely used15,21. CAFPS could provide comparable screw stability to solid pedicle screws augmented with high-viscosity cement22. In our study, the CAFPS did not develop into screw pull-out from the vertebrae, but one case in group A had pedicle screw loosening at LIV. Our result indicated that CAFPS might not prevent the pedicle screw loosening of ASD patients with osteoporosis treated by long posterior instrumented fusion.
The complication of cement leakage had received high concern. The high risks for cement leakage after vertebroplasty or kyphoplasty included intravertebral cleft, cortical disruption, low cement viscosity and high volume of injected cement23. Previous report indicated that the risk for CAFPS relevant symptomatic pulmonary cement embolism included CAFPS used in more than 7 vertebrae or more than 14 fenestrated screws, severe osteoporosis and the total cement volume more than 20 to 25 ml. In this study, no cases used more than 20 ml cement volume in total and PMMA cement volume for per vertebrae was less than the critical value reported previously15,23. Besides, the vertebroplasty was prophylactic treatment without the risk of intravertebral cleft or cortical disruption. Therefore, no cases in group A have complications correlated with cement leakage, though peri-vertebral cement leakage in 5 cases was detected. Thus, it could be safe to use CAFPS and PV in the management of ASD with osteoporosis.
There are some limitations in this study. Firstly, the potential weakness of this study was its relatively small sample size (n = 58). Future studies with a larger sample size could yield more accurate results. Secondly, though this propensity score matched cohort analysis minimized the heterogeneity of ASD, some potential risk factors for PJK or PJF were not commonly assessed, such as prevalence of sarcopenia in middle-aged and elderly women 24 and disruption of the posterior osseo-ligamentous complex.