For older patients suffering from vertebral body fractures with posterior wall disruption, called OVBFs, treatments are aimed to reduce back pain and promote healing of vertebral fractures, thus further avoiding fractured fragment displacement leading to nerve compression [2–4, 10]. The mechanical stability of the fractured vertebral body is one of the most critical factors affecting the union of fracture [21, 22]. Therefore, in this study, we attempted to inject bone cement as close as possible to the endplate using a lateral opening injecting tool; this procedure helped provide mechanical stability of the fractured vertebral body [20, 23, 24]. The bone cement was symmetrically and evenly distributed in the anterior-middle part of the vertebral body, which increased the stability of the vertebra while reducing the risk of bone cement leakage into the spinal canal . All patients achieved obvious back pain relief after treatment, most patients achieved early movement out of bed, and the bone fragments healed in all patients.
Some studies have attempted to use PVP or PKP to treat OVBFs and have obtained satisfactory results [2–6, 10, 17, 18]. For example, Nakano et al. first performed PVP by using calcium phosphate cement to treat patients with thoracolumbar burst fractures without neurological deficits . Then, Hiwatashi A and Westesson PL found OVBF patients with spinal canal compromise could be safely treated with PVP, and this treatment could reduce pain, decrease the wedge angle and increase the vertebral body height . Furthermore, other authors reported that PKP was an effective and safe method for treating OVBF patients with spinal canal compromise, achieving obvious kyphotic angle reduction and vertebral height restoration and further leading to good pain relief and functional improvement [3, 4]. However, all these reports did not specifically mention how to deal with the posterior wall of the fractured vertebral bodies and healing of the fractured posterior wall, which was a fundamental reason for the controversy on PVP or PKP to treat OVBFs. In this study, by adjusting the injecting direction through the lateral opening hole, the bone cement was kept away from the fractured posterior wall of the vertebral body and reduced the influence of blood supply of fractured areas as much as possible. We suggested that the union of the posterior vertebral wall in OVBFs could increase the stability of the fractured vertebral body, further reducing the risk of bone cement protrusion into the spinal canal and nerve compression due to bone cement loosening . In addition, reoperations after PVP or PKP for removing bone cement displacement into the spinal canal are usually due to the incomplete union of the posterior wall of the vertebral body [26, 27]. Therefore, in this study, we specifically observed the bone healing of the posterior wall of the fractured vertebral body. The distribution of bone cement in our patients was kept a certain distance from the fractured posterior fragments, which avoided the influence of bone cement on the blood supply of the bone fragments and provided the possibility of observing bone healing during imaging follow-up . One month after the operation, the CT images showed callus formation at the posterior wall of the fractured vertebral body, which was an obvious sign of bone healing. Three months after the operation, the CT images showed that the bone fragments of the posterior fractured vertebral body had healed in all cases. In addition, the vertebral height of the fractured vertebral body was not obvious lost at 6 months postoperatively compared with 1 day, 1 month and 3 months postoperatively, and no patients complained of nerve dysfunction symptoms caused by bone cement loosening in the long-term follow-up. The above results proved that the posterior stability of the fractured vertebral body in OVBFs was important for long-term prognosis, and our surgical procedures might be helpful for the union of fractures in the posterior vertebral wall.
The distance between the PMMA bone cement and endplate is a crucial risk factor for the stability of the treated vertebrae after PVP or PKP, and the closer the distance of the bone cement is to the upper and lower endplates, the better the stability of the longitudinal support of the vertebral body [20, 23, 24]. In addition, even the cement distribution in the fractured vertebral body might be the optimal pattern for providing better stability than bulky bone cement, and the symmetrical bilateral injection of bone cement may promote even cement distribution [25, 29]. Because the posterior wall of the vertebral body was damaged in OVBF patients, many surgeons controlled bone cement only injection into the front 3/4 of the vertebra to reduce the risk of bone cement leakage into the spinal canal [4, 6]. Therefore, when the patients got out of bed early, the vertical support provided by the bone cement in the anterior 3/4 of the vertebral body was essential for loading the vertical pressure instead of the posterior wall of the fractured vertebral body to avoid the nonunion or displacement of bone fragments [8, 30]. Using the lateral opening bone cement injection tool, the direction of the lateral opening can be adjusted to artificially control the distribution of the bone cement as close as possible near the upper and lower endplates while reducing the appearance of bulky bone cement, making the bone cement distribution more even. In our study, 60/66 cases demonstrated a “contacted” bone cement distribution on at least one side, and the bone cement distribution was symmetrical and even between the anterior 1/4 and posterior 2/3 of the vertebrae, which provides adequate mechanical support for the fractured vertebral body and is helpful for the healing of posterior bone fragments.
According to Denis’ three-column system, the completed middle column structure, including the posterior wall of the vertebral body, the posterior longitudinal ligament and the posterior annulus fibrosus, is very important for maintaining the stability of the spine [7, 8]. Although the bone cement could increase the stability of the anterior part of the vertebral body, we cannot confirm whether the whole vertebral body could fully bear the longitudinal pressure for the stability defect of the posterior 1/4 of the vertebral body with a burst fracture. Some previous reports regarding PVP or PKP treatment for OVBFs did not pay special attention to the need for bed rest and did not propose related recommendations [4, 6, 17]. Once elderly patients suffer from poor healing of vertebral body fractures, such as refracture and Kummell disease, they usually need to undergo reoperations that require additional financial burden [29, 31]. Therefore, in this study, we recommended that patients perform some simple activities with lumbar brace protection for 1 month after the operation. In addition, previous studies have suggested that the distance between the bone cement and endplate could affect the stability of fractured vertebral bodies. Therefore, for the purpose of clinical safety, we recommend that 6 patients with “uncontacted” bone cement distribution stay in bed for 3 weeks to increase the stability of fractured vertebral bodies in the early stage. At the 3-month follow-up, the CT images showed that the fractures healed in all patients, and no patients experienced new burst fractures of the posterior wall in the treated vertebral body. Because the amount of time for bed rest was short, and moderate activities in bed were encouraged, complications due to bed rest were rare in our patients, except for one patient who suffered an infection of the urinary system.
There were some limitations in our study. First, the sample size was still small, which should be expanded in further studies. Second, for clinical safety, patients with “uncontacted” bone cement distribution were recommended to under absolute bed rest for 3 weeks in our study. However, there was no suggestion on whether bed rest protection was necessary and the length of bedtime for the patients with “uncontacted” cement distribution. Third, the patients with a different spinal canal occupational ratio who can be treated with our PVP method are not confirmed.