To Explore the Risk Factors of Postoperative Shoulder Imbalance After Selective Thoracolumbar Fusion (STLF) Surgery in Adolescent Idiopathic Scoliosis(AIS)

PSI as a postoperative complication of Selective Thoracic-Lumbar Fusion (STLF) in AIS patients has been proven by numerous scholars to be an important factor affecting patients' satisfaction with the surgery and the mental health of adolescents, with an incidence rate of 25%-57%. Currently, most scholars' research on shoulder imbalance risk factors is mainly focused on coronal plane parameters and still remains highly controversial.In their study, Lee found that the preoperative Risser sign level of the PSI group was significantly higher than that of the non-PSI group during postoperative follow-up. Some domestic experts believe that the preoperative upper thoracic Cobb angle (PTC Cobb) and the ratio of preoperative upper thoracic to main thoracic curves (Pre PTC/MTC) have a certain predictive value for the occurrence of PSI after surgery. It has also been shown that the preoperative shoulder imbalance in the PSI group was significantly more severe than in the non-PSI group during the last follow-up. The preoperative presence of shoulder imbalance is of great significance in guiding the surgeon's choice of upper instrumented vertebra (UIV). Rose, Lenke, Qiu Yong, and others believe that different preoperative shoulder heights should lead to different choices of UIV. When the right shoulder is higher, it is recommended to fix the UIV at T4/T5, and when the preoperative shoulder height is already balanced, the UIV should be selected at T3 or T4. However, when the left shoulder is higher preoperatively, it should be fixed at the T2 level. Brooks, through a study of 648 AIS patients, found that the probability of PSI occurring after surgery in patients with UIV=T4 is the lowest compared to UIV=T2, T3, T5. Furthermore, incorrect correction of PTC and MTC by the surgeon can also lead to PSI in patients. Different researchers have given different answers on how to choose the appropriate PTC/MTC correction rate. Zhang and others believe that to prevent PSI in Lenke 1 patients after surgery, it is important to fully correct the upper thoracic curve and appropriately correct the main thoracic curve. In a study by John et al. on the risk factors for postoperative PSI in Lenke 1 and 2 patients, it was found that when the correction rate of the main thoracic curve was greater than 54% and the correction rate of the upper thoracic curve was less than 52%, 59% of the patients experienced PSI during the last follow-up. In a study by Ke et al., it was found that when the correction rate of the upper thoracic curve exceeded 55.3%, 88.4% of the individuals could maintain shoulder balance during the last follow-up, while when the correction rate of the main thoracic curve was greater than 56% and the correction rate of the upper thoracic curve was less than 55.3%, 66.3% of AIS patients would develop PSI at the last follow-up after surgery. Some experts believe that not only the position of the upper fixed vertebra affects the postoperative shoulder balance but also the choice of the lowest fixed vertebra affects the postoperative shoulder balance in AIS patients. To avoid the occurrence of PSI in AIS patients after surgery, Tatsuya Sate suggests that the lowest fixed vertebra should be selected at the lowest touchable vertebra (LTV) or the vertebra above LTV.

Although STLF can effectively improve the spinal deformity of AIS patients and has been used in clinical practice for many years, some scholars have found that while correcting the coronal imbalance of patients with this procedure, it often sacrifices the sagittal balance. The size of coronal and sagittal parameters in patients with spinal scoliosis can effectively assess the severity of spinal deformity. AIS, as a three-dimensional spinal deformity, has a correlation between sagittal and coronal deformities. Wu et al.'s study indicated that the main curve Cobb angle in AIS patients is related to sagittal parameters such as thoracic kyphosis (TK), lumbar lordosis (LL), and sacral slope (SS). Studies have shown that with the correction of the main curve, it may simultaneously lead to a decrease in sacral slope (SS) and an increase or decrease in thoracic kyphosis (TK). The sagittal structure of the spine is considered a chain-like structure, and when there is a change in any segment of the cervical, thoracic, lumbar spine, and pelvic segments, the remaining segments compensate to restore the sagittal alignment of the spine. Through the study of the shoulder joint and surrounding anatomy, it is known that the shoulder joint, spine, and clavicle are not directly connected but rely on soft tissues such as muscles and ligaments in between, and the support of the shoulder strap mainly relies on the rhomboid and trapezius muscles. The presence of the trapezius muscle allows the scapula to adhere closely to the chest wall, avoiding excessive elevation. When the strength of these muscles changes, the body may not be able to maintain shoulder balance. In recent years, it has been found that sagittal parameters of the spine, such as thoracic kyphosis and pelvic incidence angle, are related to the strength of the back muscles, such as the trapezius and rhomboid muscles. In addition, the magnitude of thoracic kyphosis (TK) may affect the rotation of the upper curve. Since the rotation axis of the spine is in front of the thoracic spine, when the thoracic kyphosis decreases, the distance between the thoracic vertebra and the spinal rotation axis is reduced, resulting in a simpler rotation of the thoracic vertebra in this segment. The final result may lead to an increase in the rotation degree of the upper curve. In recent years, Mitsuru Yagi proposed a new radiographic parameter, the Clavicle-Chest Cage Angle Difference (CCAD). Mitsuru Yagi found that the CCAD in patients with postoperative PSI group was significantly greater than that in the non-PSI group during preoperative, postoperative, and postoperative follow-up. Subsequent studies by Xiao et al. indicated that the preoperative CCAD can effectively predict whether AIS patients will develop PSI after surgery. Currently, the reasons for the occurrence of CCAD and how it affects postoperative shoulder balance in AIS remain inconclusive. Some scholars have proposed several possible reasons for CCAD leading to postoperative PSI in AIS patients: 1. The existence of residual CCAD after surgery may mean that there is residual rotational deformity in the upper curve of AIS patients after surgery. The residual rotational deformity of the upper curve may cause the elevation of the left shoulder, affecting the postoperative shoulder balance of the patients. 2. The residual rotation of the upper curve after surgery may lead to atrophy of the soft tissues connecting the shoulder joint, spine, causing atrophy of the shoulder joint, and eventually resulting in shoulder imbalance. The relationship between sagittal parameters of the spine and the strength of the soft tissues connecting the scapula, clavicle, and spine has been reported in previous studies. In conclusion, we hypothesize that the occurrence of postoperative PSI in AIS patients may be correlated with the preoperative and postoperative sagittal parameters of the patients Subject population

The subjects of this study sought medical treatment in the Department of Spinal Orthopedics, Southern Hospital, Southern Medical University, and referred to the "Clinical Practice

Diagnosis of adolescent idiopathic scoliosis using textbooks such as Orthopedics and Surgery, as well as imaging evidence

Adolescent idiopathic spine with protruding patients who require posterior selective thoracolumbar fusion surgery as determined by clinical physicians