Unilateral PVP is attracting increasing attention because of its advantages, including a shorter surgery time, less trauma, less bone cement leakage, and less radiation exposure compared with bilateral PVP. PVP via the unilateral pedicular approach reportedly achieves an ideal clinical effect in the treatment of osteoporotic fractures [10, 13, 16–19].
However, there have been reports that the use of the bilateral approach during PVP might have better long-term outcomes and result in less cement leakage than unilateral puncture for patients with acute osteoporotic vertebral fracture. The puncture angle has been intentionally increased to improve the probability of puncture success; this might increase the risk of spinal cord and nerve root injury and bone cement leakage. It is difficult for surgeons to evaluate the pros and cons of each PVP approach [11, 12, 15]. Because of the anatomical distinctions among different lumbar levels and between the two sexes, the degree of difficulty in unilateral puncture is variable. Analysis of the differences in the unilateral puncture success rates among different lumbar segments, between the sexes, and between the left and right sides is relevant because it might guide spinal neurosurgeons to select the optimal PVP approach. In this study, we explored the anatomical differences among different lumbar levels through puncture simulation using MRI and provided reference points for the surgeons in selecting a unilateral or bilateral pedicular PVP approach.
In our study, the puncture success value, which was more objective and specific than the puncture success rate, was defined to assess the difficulty of unilateral puncture. The puncture success values for L1 and L2 were lower than those for the other levels. Particularly for L1, the mean puncture success value was <34, and it successful puncture appeared to be difficult at this level. However, the puncture success values for L3 and L4 were >34, and we consider that unilateral PVP is feasible and reliable for these segments. Although the pedicle diameter of L5 was the largest of the five vertebrae tested, the puncture success value was slightly lower than that for L3 or L4 because of the iliac crest block. Compared with that of L1 and L2, it was easier to succeed with a unilateral puncture. The puncture success rate and puncture success value were higher in men than in women except at L5. A higher incidence of iliac crest block in men led to a reduction of the puncture success rate. The data analysis revealed obvious differences in the puncture success rate and puncture success value between the left and right sides except at L5. For L1 to L4, the puncture success rate and puncture success value were higher on the left than on the right, which may have occurred because of anatomical differences between the left and right sides of the lumbar spine. The underlying cause remains to be further studied.
Studies by Steinmann et al. [11, 12, 14] on vertebral stiffness under different conditions of bone cement distribution suggested that with unipedicular PVP, biomechanical balance predominantly depends on the distribution of bone cement. If the bone cement is augmented exclusively on one side, the stiffness of the nonaugmented side might be significantly lower than that of the augmented side, which might lead to an imbalance of stress on the vertebrae. However, when the cement augmentation crossed the midline, the stiffness of both sides increased comparatively, and biomechanical balance was thus achieved.
In our study, the anterior trisection point was set as the target for successful puncture as in previous studies. Generally, bone cement can diffuse to the contralateral side, and biomechanical balance can be achieved if the puncture reaches the target. According to our study, a unilateral puncture cannot consistently reach the ideal target. The success rate of lumbar unilateral PVP via the pedicular approach is closely associated with the vertebral segment, patient sex, and left or right location. Given these findings, we present the following suggestions: For L1 and L2, particularly in women, it is reasonable and safe to select bilateral PVP. For L3 to L5, unilateral puncture is feasible and reliable, particularly for men. Success appears to be more likely with a puncture through the left pedicle for L1 to L4. Even for L4, for which unilateral puncture has a high probability of success, unilateral puncture failure remained a possibility in a few patients. It is necessary and beneficial to carefully analyze the imaging data before determining the optimal approach for each individual [13, 16].
These statistics are theoretical and should be used exclusively to illustrate the trends in puncture difficulty among different segments. Consistent performance of the puncture at the maximum angle cannot be ensured; therefore, the actual unilateral puncture success rate might be lower, which is one of the limitations of our study. The puncture success and safety are closely related to the operator’s experience and to the ancillary equipment. Extensive experience with the puncture procedure and effective assistance from the O-arm or C-arm could improve the puncture success rate.
This study had the following limitations. The anteroposterior and left–right diameters of the vertebral body and the pedicular width affected the success of unilateral puncture. Additionally, an iliac crest block should be considered for L5. These factors were considered to the maximum extent in our study design. However, the MRI scans were obtained parallel to the upper endplate. In practice, punctures parallel to the upper endplate might not be necessary in every case. The anatomical conformation of the pedicle in the coronal and sagittal planes also influenced the puncture.
Another limitation is that we defined Point T as the demarcation point of puncture success based on prior research. However, there is some controversy about the definition, and some researchers hypothesize that vertebrae can be strengthened bilaterally only if the puncture reaches or passes the midline of the vertebral body and the bone cement is distributed to the other side of the vertebral body [6, 7]. In previous studies, the bone cement diffused to the other side only if the puncture reached or approached the midline; thus, biomechanical balance was achieved.