PKP and PVP are widely used for the treatment of symptomatic OVCF and symptomatic vertebral fracture caused by malignant spinal lesions. The rate of significant back pain relief has been reported to be 78%-95.3% among patients with OVCFs and 73%-100% for patients with malignant spinal lesions [10, 11]. Significant back pain relief was 90.39% (771/853) in the current study, which was consistent with the previously published literature. Although the majority of patients achieved satisfactory results, some patients still had residual back pain. Residual back pain was defined as a VAS > 3, which can affect sleep. Significant differences in VAS scores were observed in the early stage post-operatively, including post-operative day 1 and month 1. The OVCF patients were placed at bed rest, wore a brace when walking, underwent regular anti-osteoporosis treatment, and were prescribed analgesics when necessary. Patients with malignant spinal lesions underwent radiofrequency ablation, radiotherapy, or interstitial radiotherapy. After these methods, most patients with residual back pain recovered at 3 months post-operatively and significant differences were not observed at 3 months post-operatively. In the current study, the results showed that unsatisfactory cement distribution, a smoking history, osteogenic vertebral tumors, osteolytic vertebral tumors, and thoracic fractures were independently associated with residual back pain after PVP or PKP at an early post-operative stage.
The best choice for the treatment of VCF between PKP and PVP is controversial. Cloft et al. [12] demonstrated that PKP has no significant advantages compared to PVP with respect to back pain relief and the cost of PKP is greater than PVP [12]. In contrast, Dohm et al. [13] reported that the PKP group had more complete back pain relief and a lower incidence of post-operative cement leakage compared with the PVP group. A meta-analysis published by Kaloostian et al. [11] showed that the percentage of back pain improvement was 91% (range, 73%-100%) in the PVP group and 93% (range, 80%-100%) in the PVP group. Whether a PVP or PKP with the unilateral or bilateral approach provides similar efficacy is controversial. In a recent systematic review, no difference was found between the unilateral and bilateral approaches [14]. In the current study, there was no statistically significant difference in surgical approach and surgical type between the two groups. We think that the most important factor causing residual back pain is unsatisfactory cement distribution (OR, 5.84); unsatisfactory cement distribution did not induce a better effect to stabilize micromovements and fill the gap between microfractures. Yang et al. [10] showed that unsatisfactory cement distribution was a strong risk factor associated with residual back pain after PVP or PKP, which is in agreement with the current study. Accurate cement filling can completely occupy the fracture area and fractured vertebrae can be stabilized, and exert a good analgesic effect. The direction of the trocar cannot be uniformly specified from the back of the vertebra to the front, but should be based on the fracture location. As for different parts, individual selection of puncture points and the trocar make the cement pusher point to the fracture area. This is particularly important for fractures located at the anterior superior vertebra. Surgeons should not only attempt a unilateral puncture if the distribution of cement is unsatisfactory, and a bilateral puncture and filling should be added in time. The surgeon should not blindly pursue the amount of cement filling. As long as the cement is well-distributed, the excessive filling amount is not proportional to the back pain relief and will only increase the risk of leakage. Surgeons should reasonably use various techniques for cement filling, such as secondary filling, and the purpose is to achieve a satisfactory distribution.
Shi et al. [15] demonstrated that epidemiologic evidence shows that smoking is a risk factor for chronic pain. Ditre et al. [16] observed modest evidence to support the notions that smoking may be a risk factor in the multifactorial etiology of some chronically painful conditions. In the current study, the smoking history was a risk factor for residual back pain; the underlying mechanism may be as follows [15]. First, nicotine may produce central anti-nociceptive effects by agonizing nicotinic acetylcholine receptors in the brainstem, particularly the α4β2 subtype, resulting in activation of the spinal cord descending pain inhibitory pathways. Second, nicotine increases attentional resources and leads to attentional narrowing. Attentional narrowing is believed to restrict attention to a smaller number of the most salient environmental cues. Thus, smoking may result in greater awareness of painful stimuli when there is no alternative distractor to focus on.
Deramond et al. [17] and Chiras et al. [18] concluded that the complication rates of PKP and PVP were higher in patients with metastatic lesions (5%-10%) than in patients with osteoporotic fractures (1%-3%). The current study showed that compared with OVCF, residual back pain occurs more frequently in osteogenic vertebral tumors (OR, 4.62) and osteolytic vertebral tumors (OR, 2.71), which is in agreement with the existing literature. The higher incidence of residual back pain in malignant vertebral compression fractures compared to OVCFs is due not only to the fracture, but also the tumor. Compared to osteogenic vertebral tumors and osteolytic vertebral tumors, the vertebrae of osteogenic vertebral tumors are much harder, so the puncture is more difficult and the cement could not distribute satisfactorily.
Some patients who have vertebral fractures in the thoracic spine complained of midline and non-midline back pain areas, such as the rib, chest, hip, groin, and buttocks. Among the non-midline back pain, the ribs were the most common site, most of which are considered to be the result of stimulation of the intercostal nerve at the affected vertebral segment [19]. The specific mechanism underlying the pain is not clear at present, and the possible reasons may be stimulation of the displaced fracture block, decreased vertebral height, and local inflammatory stimulation [19, 20]. Such patients after PKP or PVP achieve more rapid relief, but intercostal nerve pain of some patients still exist to different degrees and the residual time also varies. The residual back pain was also worsened by a change in posture and will lead to the treatment unsatisfaction; the protection still lacks effective measures in addition to the symptomatic treatment. By multifactor logistic regression analysis of the current study, when comparing lumbar with thoracic vertebral compression fractures, the OR was 0.28. Therefore, it is necessary to know the location of the vertebral compression fracture before the operation and inform the patient of the possible outcome to obtain their understanding and face the issue correctly, cooperate with the follow-up auxiliary treatment, and improve the overall satisfaction rate.
There were several limitations to this study. Residual back pain in vertebral compression fractures is associated with multiple factors. Only the common factors associated with back pain were included in this analysis. This study included patients with residual back pain during the first month post-operatively; the long-term complications, such as non-union or secondary vertebral fractures were not included. A further prospective controlled study is needed to explore the risk factors associated with residual back pain.