This study found that the operation time, bleeding volume, postoperative bedtime, and hospitalization period in PKP group were lower than those in PPSF group, which indicated that PKP had less surgical trauma than PPSF. Despite this, our study did not find any significant difference in the VAS score immediately after operation between PKP group and PPSF group. The possible reasons are as follows: (1) PKP can quickly relieve clinical symptoms by stabilizing small fractures in injured vertebrae and restoring biomechanical properties, the exothermic reaction of bone cement solidification destroys pain nerve endings, toxic destruction of bone cement destroys sensory nerve endings and partial decompression of spinal nerve roots. (2) due to the enhanced recovery after surgery (ERAS) and reasonable analgesia program carried out in our hospital, the pain feedback after PPSF is reduced to the minimum. However, VAS scores in PKP group was lower than PPSF group 3 days after operation, which may be related to the discontinuation of painkillers after operation. There was no difference in VAS scores between two groups at the last follow-up, which also showed that both PKP and PPSF were effective in relieving pain in patients with osteopenic VCFs. At the same time, we found that the postoperative ODI scores in PKP group was lower than PPSF group, which may be due to some damage to the soft tissue during the placement of nails and rods during PPSF operation. However, there was no obvious difference in the last follow-up, which may be related to the recovery of muscle and soft tissue injury at the end of follow-up. Undeniably, compared with other surgical methods, PKP has a strong efficacy in rapidly relieving clinical symptoms. This is crucial for elderly patients with underlying diseases, which means it can improve the quality of life of them and reduce the risk of bedridden complications.
In this study, it was found that the AH of injured vertebrae in both groups recovered significantly after the operation, and lost to some extent during the follow-up period, but there was no difference in AH between two groups at the last follow-up. This result is different from the previous research view that PPSF has stronger kyphosis correction ability[15, 16]. By analyzing the characteristics of the cases included in our study, we found that more patients with lumbar fractures were included into PKP group, especially male patients. Considering the differences in vertebral height of different genders and different segments of the spine, we introduced the concept of Anterior Height Ratio (AHR), that is, the anterior height of the injured vertebra / the average anterior height of the upper and lower vertebrae adjacent to the injured vertebra. The results also showed that the AHR in PPSF group was higher than PKP group after operation and in the last follow-up, indicating that PPSF could better restore the height of injured vertebrae. The KA in PPSF group was lower than that in PKP group after operation and in the last follow-up, which confirmed that PPSF had higher kyphosis correction ability than PKP.
Previous studies have suggested that the holding force of pedicle screws may be weakened due to bone loss. Through a series of biomechanical studies, Lukas et al. considered that the stability of pedicle screws may be obviously insufficient when the bone mineral content of thoracolumbar vertebrae is less than 80 mg/cm3, so it is necessary to apply additional measures to enhance the stability of screws. At the same time, the study found that longer bed rest time will accelerate bone mass loss, and eventually lead to disused osteoporosis. Although the patients included in our study had osteopenia, no implant-related complications such as screw loosening were found, which may be due to: (1) The age of patients is not old enough (average age: 59.56 ± 3.04, which indicated that the loss of bone mass may not severe. (2) PPSF is beneficial to the bony healing of injured vertebrae. Once bony healing is achieved, the incidence of screw loosening is low. (3) All patients with PPSF wore lumbar brace after the operation. Bone mineral density is an important factor in the correction of vertebral kyphosis after PKP, and lower bone mineral density often means better correction of wedge angle and kyphosis angle after operation. Heini et al[21, 22]. found in vitro experiments that lower bone mineral density is more conducive to the penetration and dispersion of bone cement in the trabecula. A series of clinical and basic studies have shown that there is a good positive correlation between bone mineral density and fracture compression force and vertebral stiffness. Therefore, we believe that the lower the bone mineral density, the more definite the surgical indications of PKP. During the follow-up, we found that there was a case of vertebral re-fracture in PKP group. We analysed that the patient was a postmenopausal woman with a T value of-2.4 before the first operation, which was close to the diagnosis of osteoporosis, and the patient was not given continuous BMD-monitoring and regular anti-osteoporosis treatment after discharge, so there was a high risk of bone mass loss. This result also reminds us that the effective detection of bone mineral density and timely and regular anti-osteoporosis treatment are of great significance for patients with osteopenic vertebral compression fractures. There was no significant difference in the overall incidence of complications between two groups during the follow-up period, and all complications were cured after active treatment, which confirmed the safety of both PPSF and PKP in the treatment of osteopenic compression fractures.