Approximately 85% of patients with the three most commonly malignant tumor (lung, breast, and prostate) suffered from skeletal metastatic lesions, of which spine is the most vulnerable site.[10] Spinal metastases, of which 70% are located in the thoracic spine, 20% in the lumbar spine and 10% in the cervical spine.[3] Based on CT findings of lesions, spinal metastases may be classified as purely osteolytic (78.3%) lesions, mixed osteolytic and osteoblastic lesions (20.1%), and purely osteoblastic (1.6%) lesions.[11] Nowadays, PKP has been safely employed in the management of vertebral collapse caused by lytic metastasis.[12-14] However, there have been few reports on the role of PKP in the management of spinal osteoblastic metastases.
Because spinal osteoblastic metastasis hardened the diseased vertebral body, it was difficult to penetrate diseased vertebra with kyphoplasty puncture needles and to inflate balloons, resulting in a possibility of smaller cavity created inside the diseased vertebral body and a relatively smaller quantity of bone cement compared with patients with osteolytic spinal metastasis. In our present study, mean mount of PMMA is 2.6 mL in per veterbra, which is less than that in PVP for osteoblastic lesion (3.3mL).[15] However, the analgesic effect of PKP in patients with spinal metastasis is not related to the quantity of bone cement injected, which supports the management of pure osteoblastic lesions as well as mixed and purely osteolytic lesions.[16,17]
The predominant symptom for the patients suffering from spinal metastatic lesions is intractable pain, including persistent localized, radicular and axial pain.[18,19] The mechanism of pain causing by spinal metastasis is currently unclear yet. Generally, the reasons include segmental instability, stimulation of neural endings and pathological fractures have been proposed. Some reports hold the opinion that the asymmetry of compressibility of the vertebral body might result in stress fractures, causing intractable pain for osteoblastic bone lesions.[8,20] Despite the technical challenge of the treatment of osteoblastic spinal metastasis, pain of relief was acheived immediately after PKP in all erolled patients, which is consistent with previous study.[21] Some studies demonstrated that the mechanism of PKP treating spinal osteolytic and osteoblastic lesions is similar, though it still remains unclear.[3] And many studies have speculated that the relief of pain by PKP in patients with spinal metastasis was not only associated with enhancement of the vertebral body, but also related to chemical and exothermic reaction of the cement, which may have the capacity to destroy the sensory nerve endings and kill the tumor cells.[20,22,23]
Pain relief is vital to achieving a better KPS and QOL for patients with spinal metastasis in palliative treatment. In a result, KPS and QOL of enrolled patients also acheived substantial improvement in our present study. Generally speaking, patients with spinal metastasis always developed new painful metastasis, resulting in KPS and QOL deteriorated along with time. Nevertheless, in our present study, the significantly differences were observed at all study time points after PKP compared with preoperation, and there was improvement of KPS and QOL. The successful long-term pain relief in patients with spinal metastasis might be connected with the fact that the patients were treated regular treatments after PKP, such as chemotherapy or radiotherapy, which might have helped control the development of the cancer, although it may also be a study confounder.
The most commonly reported complication associated with PKP is extravasation of the bone cement.[24] Kyphoplasty has not been proven to be superior to vertebroplasty in treating painful spinal metastsis.[25] However, kyphoplasty has a significant advantage over vertebroplasty when comparing the incidence of cement leakage.[26] In our present study, the incidence rate of cement leakage is 6.7%, which is consistent with previous study.[27] Bone cement leakage was found by intraoperative fluoroscopy, and bone cement injection was stopped immediately. No obvious symptoms were observed after surgery. The dominant reason for cement leakage can be attributed to cortical damage.
Several limitations should not be ignored in our study. First of all, it was a single-center retrospective rather than a prospective study, leading the nature of data collection subjects the study to selection bias. Secondly, our study included a relatively small number of patients, and the follow-up time for evaluating patient outcome was relatively short. In addition, most patients had terminal-stage disease, resulting in precluded the follow-up time for evaluating patient outcome. A randomized controlled trial by different surgical approaches with a larger population and longer follow-up time is warranted to further confirm our findings.
In conclusion, PKP could serve as an effective and safe treatment in the management of spinal osteoblastic metastases. It may not only effectively alleviated the pain, but also safely improved the QOL of spinal osteoblastic metastatic patients.