PKP has been proved to be one of the most useful methods to treat OVCF (1–4). In the previous studies, many reports show that the vertebral body height restoration and kyphotic changes are very significant. As a result, PKP could not only stable the fractured vertebra body and reveal the severe pain immediately, but also restore the vertebral body height and correct the local kyphosis by inflating of the balloon(6, 9, 10). However, there is no study investigate the influence of PKP on the spinopelvic alignment or sagittal balance of the entire spine. Sagittal imbalance of spine is becoming one of the most important factors in assessing degree of spinal deformity. If PKP could improve sagittal imbalance of spine, and if the clinical outcome is associated with the sagittal imbalance improvement are still unknown.
Previous studies have proved that sagittal balance of entire spine plays important roles in the spinal function and outcomes of many spinal operations(11). Healthy adults tend to stand in negative sagittal balance as determined by the SVA, as human grow older, adults tend to stand in positive sagittal balance. What’s more, lumbodorsal muscles tend to atrophy and center of gravity move forward with ages, these may result in increased pressure of the anterior column and tension of the posterior column, all of these points may lead to backache and compression fractures of vertebral body(12–14). In patients with severe sagittal imbalance of entire spine, posterior rotation of the pelvis around the hip joint takes place to compensate for sagittal imbalance even to a small extent and that this compensatory mechanism leads to a decrease in sacral slope and an increase in pelvic tilt. And then, flexion of the knee joints and hyperextension of the hip joints are involved in the compensatory mechanism. These compensatory mechanisms serve as factors responsible for dysfunction of the lower limbs and low quality of life(15). Recovery of the sagittal balance will dramatically improve the health-related quality of life (16). Therefore, it is desirable that spinal operation associated with any pathologic condition be designed to correct sagittal imbalance.
As we all know, SVA is one of the most important index in evaluation of sagittal balance. In healthy adults, SVA usually is minus or smaller than 4 centimeters, sagittal imbalance of spine happens the when SVA is more than 4 centimeters(17). On the other hand, VCF patients show significant decrease of sacral slope and increase of pelvic tilt and SVA compared to healthy adults. This kind of sagittal imbalance may related to Age-related spinal degeneration and the aggravation of kyphosis caused by vertebral collapse and the pain avoiding posture caused by patients' pain(15). When PKP was performed in OVCF patients, SVA decreased, thus resulting in partial correction of the sagittal imbalance. After PKP treatment, SVA of patients decreased, which may be due to the relief of back pain, the recovery of back activity unit function, and the ability to maintain a relatively natural posture. But more importantly, the height of pathological vertebral body recovered to a certain extent, and the local kyphosis angle decreased, which is also a reason for SVA reduction. On the other hand, the changes of ll and SSA mean that the overall sagittal balance of the spine is improved significantly. This shows that PKP can not only relieve the patients' back pain, but also improve the patients' sagittal imbalance in the treatment of OVCF, so as to improve the patients' quality of life.
In this study, within 2 days after PKP, SVA decreased, ll and SSA increased, but after long-term follow-up, we found that with the increase of patients' age, SVA increased gradually, but there was no significant change in VAS score and ODI score, which indicated that sagittal kyphosis can be a natural trend of human degeneration(13). Nevertheless, with the SVA increases and the body leans forward, the pressure on the anterior column of the spine increases, and then the possibility of secondary vertebral fractures may increases significantly (18). Therefore, in the process of PKP, it is necessary to restore the height of vertebral body and local kyphosis angle as much as possible to further improve SVA, thus to reduce the risk of vertebral fracture, and end the vicious circle of fracture.