Over the last few decades, PVP has emerged as one of the fastest-evolving techniques in spine surgery[17]. Characterized by minimally invasive and immediate pain relief, PVP is the most widely used treatment for osteoporotic vertebral compression fractures[18, 19]. In spite of this, there are still some procedural complications such as cemented vertebral recollapse, adjacent vertebral fractures, cement leakage as well as facet joint violation[20–25]. Furthermore, some studied reported that unsatisfied bone cement distribution, low bone cement volume and individual factors such as fascia oedema, paraspinal muscle degeneration and intervertebral cleft could also cause residual back pain and adversely affected the patient's quality of life[8].
FJVs have a reported incidence of 15.9% and cause significant residual pain after PVP surgery. However, how to avoid or decrease the occurrence of FJV has not been mentioned[25]. In this study, we proposed and employed an extra-facet trajectory to protect the facet joint from violating. The trajectory between the lateral margin of facet joints and the lateral wall of pedicle was designed preoperatively according to CT scan. Moreover, the distance from the entry point to the lateral facet border was measured according to preoperative CT scan.
As a result, extra-facet puncture significantly decreased the incidence of FJV as shown in Table 3. Furthermore, it was demonstrated that VAS and ODI scores in the non-FJV group were significantly lower than those in the FJV group. However, we noted that though differences in VAS and ODI scores were observed between traditional puncture group and extra-facet puncture group, the improvements in extra-facet puncture group were not impressive and significant. Major, but not exclusive, the small proportion of FJV should be responsible for this. Hence, we introduced the MCID to assess the clinal outcomes in the two groups. Under the definition of great pain relief is achieving MCID in VAS scores, the proportion of patients with great pain relief in extra-facet puncture group was obvious higher than that in traditional puncture group (p = 0.003) at the first postoperative day (Table 6).
Although the results of extra-facet puncture were promising, generalization of the outcomes must be considered carefully. Moreover, the shortcomings of extra-facet puncture merits serious discussion. After reviewing the data of patients who did not get obvious pain relief after surgery in extra-facet puncture group, we found one patient suffered transverse process facture. Also, there are some risks of damage to lateral structures during extra-facet puncture.
Bone cement distribution is considered as an independent predictor for residual back pain in patients underwent PVP surgery. Li et.al reported that the blocky distribution of bone cement may increase the incidence of residual back pain after PVP surgery[8]. Moreover, Wang et.al showed that separated cement distribution was a strong risk factor in predicting residual back pain[25]. We divided the bone cement distribution into three types: symmetrical distribution, eccentric distribution and unilateral distribution. Unilateral distribution may cause subsequent residual pain. Extra-facet puncture can significantly increase the probability of cement symmetric distribution.
Apart from that, we studied the orientation of facet joints at thoracolumbar segments aiming to unmask the connection between FJV and the morphology of the thoracolumbar facet joints. As a result of the change in direction of facet joints at the thoracolumbar junction, the orientation of the facet joints changes from the sagittal plane to the coronal plane abruptly (Fig. 4). This also leads to a sudden increase of the facet joint angle (FJA) in thoracic vertebrae (Fig. 5). A high-FJA is an independent risk factor of FJV [26]. Taking this into account, the conclusion can be drawn that traditional puncture in thoracic vertebrae is more prone to violate the facet joint. At the same time, our findings were consistent with this speculation shown in Table 3.
Limitations
There is no patient with upper thoracic spine fracture and whether the extra-facet puncture PVP is suitable for the treatment of upper thoracic spine fracture remains unknown. Moreover, the incidence rates of FJV were not high so the sample size in the FJV group was small.