Over the past few decades, Pedicle screw (PS) fixation has become the most classic and commonly used internal fixation method in spinal surgery [15]. Nonetheless, traditional pedicle screws are subject to some defects, such as the exposure of the lateral facet joint, longer surgical incision and extensive muscle peeling, which tend to cause postoperative anemia [16]. To overcome the above limitations, a new pedicle screw implantation technique with better biomechanical strength and performance, cortical bone trajectory (CBT), which was proposed by Santoni et al [8].As stated by Karataglis et al., the entry point of CBT is more inward, requires no exposure of facet joints and transverse process, and reduces soft tissue peeling [17]. In addition, by placing nails from the bottom up in the sagittal plane, the surgical incision can be shortened by the traditional pedicle technique, thus greatly reducing intraoperative bleeding [8]. Despite the advantages of CBT technique such as short incision, less trauma and less intraoperative bleeding, the present research obtained the average perioperative total blood loss of CBT-TLIF patients at 603 ± 232 ml and the Hb loss of 18.3 ± 7.2 g ml, higher than the expectation of spinal surgeons. Specifically, the HBL was 280 ± 227 ml, occupying 46.4% of the total blood loss, and the recessive blood loss was almost half of it after CBT-TLIF. Hence, recessive blood loss is concluded as a potentially major cause of the higher-than-expected blood loss for CBT-TLIF patients.
Concerning the specific factors of HBL caused by perioperative CBT-TLIF, the analysis is as follows: (1) Age: at present, advanced age is widely accepted by domestic and foreign scholars as an important factor affecting the amount of HBL. In this research, patients aged over 60 displayed significantly higher recessive blood loss than patients aged no more than 60, showing a statistical significance. CBT technology is often applied to elderly patients with osteoporosis because of its good biomechanical properties, which may lead to more HBL. (2) The time of operation: it is generally believed that longer operation time leads to longer tissue exposure time, which means more hidden blood loss during the operation. Here, it was found that the patients with operation time more than 3 h had more HBL than those with less than 2 h, showing a statistical difference; therefore, the operation time was considered a factor influencing HBL in the CBT group. (3) The bleeding surface of the cancellous bone: the CBT nail placement point is the intersection of the vertical line of the center of the superior articular process and the 1mm horizontal line below the inferior edge of the transverse process. It is located on the outside of the isthmus, where the bone is relatively hard. Most of the patients with lumbar degeneration suffer from serious osteophyte hyperplasia, and a grinding drill is often needed to remove part of the cortical bone and part of the upper and lower lamina during the operation, and to thoroughly scrape the cartilage endplate for promoting interbody fusion. This will expose a large area of the cancellous bone surface, resulting in slow postoperative bleeding. (4) Venous plexus injury: it is easy to injure the intraspinal venous plexus during intraspinal decompression, which may impede the process of stopping bleeding. (5) Rehydration: after blood loss, thrombocytopenia occurs in the body. Rehydration after coagulation factors is diluted and the blood coagulation function is decreased, making it easier to ooze blood after the operation.
In conclusion, for the patients with CBT screw for lumbar fusion, the small incision, less muscle peeling and relatively less dominant blood loss lead to the speculation of the small blood loss of patients after CBT-TLIF. However, it was found that the recessive blood loss of patients after CBT-TLIF was not less than that of traditional pedicle screw fixation, accounting for almost 1 / 2 of the total blood loss. Therefore, the postoperative blood loss of patients is more likely to be ignored, resulting in postoperative anemia and covering up the causes of anemia. This will reduce the opportunity of postoperative rehabilitation, prolong the length of stay of patients, and even endanger the life of patients. Therefore, for the patients with CBT screw internal fixation, we should actively evaluate the factors affecting postoperative occult blood loss before the operation. Other strategies are also needed, such as taking further preventive measures for high-risk patients, stopping bleeding during the operation, shortening the time of operation, paying close attention to recessive blood loss after the operation, and reexamining blood routine in time to supplement blood volume.
Still, some limitations exist in the present study. First of all, all patients were from one institution, bringing a potential risk of bias. Second, the sample size was insufficient. Therefore, more samples are needed for further study. Third, the results of this retrospective study are not convincing enough and the level of evidence is insufficient. Therefore, a prospective randomized controlled study on the application of CBT in lumbar surgery is needed.