PKP has become increasingly popular in the treatment of OVCFs since the first case of PKP was successfully treated. PKP not only quickly eliminates the severe pain that is difficult to relieve with bed rest, but also effectively reduces cement leakage due to the presence of the expandable balloon [1, 14]. After surgery, patients can recover vertebral height, improve the kyphosis and maintain the normal sequence of the spine in a short time. As an enhanced recovery after surgery (ERAS) technique, PKP allows patients to get out of bed early for functional exercises after surgery, reducing multiple complications caused by long-term bed rest and improving patients' quality of life. However, any new clinical technique is often accompanied by a series of complications. Common complications after PKP surgery include bone cement leakage, pulmonary embolism, refracture and increased postoperative back pain. Refracture have received a significant amount of attention in previous studies due to the increased pain of reoperation as well as the financial cost to the patient. Lee [1] found that PKP did not increase the risk of refracture in patients with OVCFs compared to conventional conservative treatment. PKP is not a major risk factor for vertebral fracture, but only a progressive process of osteoporosis. A total of 392 patients were included in our study, 19 of whom developed refracture after PKP, with an incidence of approximately 4.8%. There are no uniform criteria for the factors affecting refracture after PKP. Therefore, adequate assessment to predict the risk of refracture after PKP. Early identification of high-risk patients and intervention can reduce the incidence of refracture and improve patient prognosis.
PKP can be injected into vertebrae by unilateral or bilateral injection. A cement-free section exists between the bone cement and the upper and lower endplate. The cancellous bone in this area is susceptible to collapse under prolonged stress. Therefore, the strength of the vertebrae is positively correlated with the rate of contact between the bone cement and the upper and lower endplate[11]. When the bone cement was injected into the vertebrae with adequate dispersion, the risk of postoperative refracture would reduced. The ideal distribution is when the postoperative bone cement is uniformly diffused over the anterior two-thirds of the vertebrae [15]. Previous meta-analyses have shown no difference in clinical efficacy between unilateral and bilateral injection. By creating a vertebral compression fracture model, Chen [16] concluded that both unilateral and bilateral punctures can significantly increase vertebral stiffness. Unilateral puncture creates a biomechanical imbalance secondary to the uneven diffusion of the bone cement within the vertebrae [17, 18]. The imbalance of spinal biomechanics is an essential influence on vertebral fractures. When vertebrae ware under prolonged high load, the side with poorer biomechanics is more at risk for refracture. He [19] evaluated the effect of different bone cement distribution on the clinical efficacy by a retrospective analysis. After more than 1 year of follow-up, patients with bilateral punctures are mostly “H” distributed on both sides of vertebrae, and they can achieve better outcomes in the short term. Currently, many surgeons commonly treat patients using unilateral puncture in their clinical practice [9, 20–22]. They concluded that unilateral puncture could achieve acceptable biomechanical stability with cement filling beyond the midline of vertebrae [16]. However, the unilateral puncture approach inevitably fails to effectively diffuse the bone cement into vertebrae due to its limited puncture angle [23]. Therefore, we recommend that bilateral puncture remains the preferred approach when bone cement filling is less effective or when the patient suffers from severe osteoporosis.
Lower BMD reflects the severity of osteoporosis. With decreasing T-values, the incidence of refracture
Increases [6, 8–10, 12]. Meanwhile lower BMD means that bone cement is more likely to leak from cancellous bone. The value of BMD was closely related to the course of OVDFs. Qi [24] concluded from examining bone biopsy specimens and blood samples from 206 patients with OVCFs that low BMD is often associated with reduced bone formation capacity, severe loss of vertebral height and large amounts of necrotic bone. Lower BMI often means that patients have a lower long-term protein intake. Protein and amino acids are the raw materials for bone production. When protein is chronically deficient, bone production is reduced, further aggravating the process of osteoporosis.
The more vertebrae fractured in the initial surgery, the greater disruption of the normal spinal biologic force line [25]. Bone cement infusion in multiple segments has a significant impact on the biomechanics and load transfer of the entire spine. Among the bone cement leaks that lead to refractures, intervertebral disc leakage is the most common [6, 13]. Sun [26] showed that if there is no leakage, the refracture is 7%. However, when disc leakage occurs, this rate increases to 14%. Leakage of bone cement in the intervertebral disc accelerates the degeneration of the disc and other structures. The bone cement weakens the mechanical cushioning effect of the disc, resulting in uneven mechanical conduction. In addition, the bone cement can produce mechanical damage to the endplate. Leakage of the bone cement triggers multiple destructive mechanisms that combine to cause refracture.
However, this study has several limitations. First, refracture occurred mostly within 6 months after surgery. However, the long-term follow-up results show that vertebral fractures were inevitable with the progressive course of osteoporosis. In contrast, the mean follow-up time of the study was 12 months, which limits our investigation of the change in the probability of postoperative vertebral refracture over time. Second, our study is a single-center retrospective study. Although internal validation using enhanced Bootsrap can be effective in evaluating model performance, additional large-scale clinical cohorts are still needed for external validation.