The incidence of Kummell's disease is relatively low and nonsurgical treatments have usually been less effective. Hence, many surgeons have advised that Kummell's disease should be treated by operative intervention [8]. For the posterior vertebral wall rupture, combined with severe kyphotic deformity and neurological symptoms at stage III of Kummell's disease, open surgery is recommended [9]. Patients with stage I and II Kummell's disease have no neurological symptoms, and the main goal of surgery is to eliminate fractured vertebral micromotion and reconstruct spinal stability, therefore, PVP or PKP is recommended [10]. Both PVP or PKP can achieve satisfactory clinical efficacy. Compared with PVP, PKP has advantage in terms of correcting kyphosis [4]. In this study, the clinical symptoms of patients in the two groups were improved significantly with satisfactory efficacy.
Controversy remains regarding whether a unipedicular or bipedicularis PKP is superior [5–7]. Researchers who supported unipedicular PKP considered that unipedicular PKP is comparable to bipedicular approach in clinical efficacy, while given the advantages of short operative time, low radiation exposure and incidence of complications, unipedicular approach should be recommended [11]. In this study, two surgeons simultaneously established the working channel through bilateral pedicle puncture in bipedicular group. The scan times of X-Ray in bipedicular group and surgery duration were comparable to that in unipedicular group. Bone cement leakage is a common complication of PKP. In order to decrease the leakage rate, intraoperative lateral C-arm fluoroscopy was used to observe the diffusion of bone cement discontinusously. We stopped injection when bone cement diffused to the posterior wall of the vertebral body. There were 4 cases of cement leakage in both groups, with leakage rates of 21.1% and 19.0%, respectively. There was no spinal canal involved by the bone cement leakage, all the leaky cement were along lateral vertebral body and the difference between the two groups was not significant.
The optimal bone cement injection volume for vertebroplasty remains controversial. Molly et al. reported that restoration of stiffness in the thoracic region required fill volumes of 2 mL cement, 4 mL in the thoracolumbar region, 8 mL in the lumbar region, while restoration of strength in vertebral body required 4 mL of cement [12]. Kim et al. revealed that stiffness was restored when bone cement filling volume reached 30% of the volume of a vertebral body [13]. Liebschner et al. found that bone cement fill with unipedicular injection resulted in asymmetric distribution of the cement and further led to unstable conditions and deformation of vertebral body due to the single-sided load [14]. Chevalier et al. proved that compliant cement distribution touching the inferior and the superior endplate in vertebroplasty was helpful to prevent future recollapse or fracture [15]. Hence, proper bone cement fill volume and uniform distribution are essential for vertebral reconstruction. Unilateral puncture achieves the expected amount of cement perfusion and satisfactory distribution required the cement distribution across the midline [16], so that during puncture, the needle insertion point should be outward, or directly from the transverse-pedicle junction, while the abduction angle needs to be increased with the risk of intraoperative rupture of the medial wall of the pedicle, cement leakage, and nerve injury.
Kummell's disease is a rare type of osteoporotic vertebral compression fracture with obvious cleft and cavity in the fractured vertebral body in which cavity was filled by gas or liquid, or mixed gas and liquid, and changed with body position [17]. Elimaination of mechanical instability plays a key role in reducing pain, however, volume of cement injected as well as the correction of the kyphosis are also important for Kummel’s disease. The efficacy of vertebral augmentation techniques on height restoration and kyphotic deformity correction were more remarkable in vertebrae with intravertebral cleft than in those without intravertebral cleft. Unrelieved or recurrent pain was reported to be related to incomplete filling of the cleft or interface failure between bone and cement [18–20]. For pain relief and functional recovery, the spongy group was superior to the blocky group. Therefore, the spongy distribution pattern should be formed during the injection of bone cement to obtain better therapeutic effect [21]. Yu et al. concluded that due to the presence of fibroperichondrium on the inner wall of the cleft and sclerosis of the surrounding bone, bone cement is difficult to diffuse into the surrounding cancellous bone and form effective adhesion, only form solid lump in the cleft [22]. The limited bone cement mass cannot be connected with the upper and lower adjacent endplates and cannot strengthen cancellous bone of vertebrae, which is more prone to stress shielding leading to recollapse, and cannot support the normal physiological stress from the body resulting in the continued existence of pain symptoms caused by osteoporosis [23].Hence, bone cement injection should fill both the cleft in the vertebral body and the bone tissue around the cleft to increase the stability and prevent later loss of average vertebral height.
In this study, to ensure better homogeneity of baseline characteristics, we included patients with Kummell's disease of a single vertebra in the thoracolumbar region. The bone cement injection volume in unipedicular group was less than 4 ml and bone cement failed to diffuse to the midline in some patients. In our patients, individualized techniques of PKP were performed to make the cement sufficiently fill the cleft and anchor the peri-cleft bones, especially in the bipedicluar group, which could avoid two percutaneous working canals enter the cleft simultaneously. The bone cement volume and direction in bipedicular group could flexibly adjusted as needed with asymmetric distribution of the cement and easy to form spongy distribution pattern. The bone cement volume was higher in bipedicular group than that in unipedicular group. For postoperative pain relief and imaging results, VAS, local kyphotic angle and average vertebral height at 1 day after operation and the last follow-up improved more obviously in bipedicular group than in unipedicular group, which suggested that bipedicular group achieved better efficacy.
This study also has limitations. Some patients did not take X-ray examination at 2 years follow up, we could not collecte all patients’ imaging data, the comparative study could not be carried out. This study is a single-center retrospective study with limited cases and short follow-up time, so the long-term randomized controlled study with large sample are needed to further verify the clinical efficacy of bipedicular PKP in the treatment of Kummell's disease.