The upper thoracic spine is a special anatomical region where lateral kyphosis due to hemivertebrae can lead to significant changes in the patient’s appearance at an early stage; worsening of the deformity can also lead to impairment of spinal cord and neurological function. These characteristics determine the significance of early surgery for deformities of the upper thoracic segment. Because the upper thoracic segment is obstructed by the sternum, clavicle and sternoclavicular joint anteriorly, and the vertebral body is adjacent to the vascular nerve anteriorly, anterior surgery is risky; moreover, when the deformity is heavy, anterior surgery is limited to correct the posterior convexity deformity. Therefore, posterior one-stage hemivertebral resection and internal fixation with bone graft fusion is the commonly used procedure in this region.
1. Clinical data.
There were 8 cases of congenital lateral kyphosis of the upper thoracic segment of the spine, 4 males and 4 females; ages ranged from 11 to 15 years, with a mean age of 13 years. Preoperatively, three patients showed neurological symptoms such as hypesthesia, decreased muscle strength, and difficulty in urination (see Table 1). All patients had preoperative standing spine X-ray, right and left Bending position X-ray, CT three-dimensional reconstruction, myelography or MRI to clarify the diagnosis, determine the position of the hemivertebral body and its relationship with adjacent vertebrae, and exclude concomitant spinal cord abnormalities. Left and right Bending x-ray is mainly used to evaluate compensatory bending flexibility to determine the extent of fusion.
2.Treatment methods.
(a) Surgical method: general anesthesia with tracheal intubation, patient in prone position. A posterior median cervicothoracic incision is made, and the posterior structures are exposed according to the preoperative determination of the extent of fusion. After positioning the hemivertebral body with a “C” arm X-ray machine, pedicle screws were placed in the upper and lower hemivertebral bodies. A rod was temporarily fixed on the concave side to prevent spinal cord shear injury after hemivertebral body resection. The spinous process, lamina, transverse process, and pedicle of the hemivertebral body are removed, and the ribs are bitten off at the transverse rib junction with an occlusal forceps up to the small head of the rib. The anterior vertebral body, its upper and lower discs, and cartilage plates are then removed through the pedicle. The laminae of the upper and lower vertebral bodies are subconsciously removed to prevent compression of the dura and spinal cord during compression. Intervertebral bone grafting was performed with the occluded vertebral cancellous bone. In a patient with severe kyphosis, a Mesh cage was added for anterior support fusion. A rod of appropriate length was pre-bent and attached to the convex side screw and pressurized until the lamina space was largely closed. The dura should be observed at any time during the compression process for obvious folds, and the compression should be stopped when folds occur, and the lamina should be continued to be occluded to prevent spinal cord injury. Perform an arousal test or monitor the spinal cord during compression to monitor the spinal cord somatosensory evoked potential (SSEP), and lock the internal fixation device after determining normal spinal cord function. The rod is then repositioned on the concave side and locked after moderate spreading. A nerve stripper is used to detect any posterior displacement of the anterior dural fragments, and if so, it is punched forward to avoid anterior dural compression. Close the incision after fusion with the resected cancellous bone for the vertebral plate and articular eminence, and if the cancellous bone is not enough, add homogeneous dry bone.
(B) postoperative treatment: the second to fifth postoperative day can be out of bed activities. Strictly wear a cervicothoracic brace for 3 months.
3.Efficacy evaluation.
During the follow-up period, all patients had standing spinal X-ray taken to record the Cobb angle of lateral and posterior convexity of the upper thoracic segment; patients were asked about the recovery of symptoms; and the recovery of the nervous system was assessed by the JOA scale.
4. Results.
All cases were followed up for 6 to 50 months, with a mean of 22.8 months. The operative time ranged from 150 to 420 min, with a mean of 278 min. intraoperative bleeding ranged from 500 to 3500 ml, with a mean of 1787 ml. fixed fused segments ranged from 4 to 11 segments, with a mean of 8.5 segments. The average correction rate was 68.4%, with no significant loss at follow-up; the average correction rate was 54.9%, with no significant loss at follow-up; the average correction rate was 54.9%, with no significant loss at follow-up; the three patients with combined neurological injury had different degrees of improvement at follow-up, with chest pain and urinary The relief of chest pain and difficulty in urination was the most obvious. The average preoperative JOA score was 5 and the average follow-up score was 8, with an improvement rate of 37.5%.
Complications:In one patient, after hemivertebrectomy, the fusion was fixed from C5 to T7. 3.5 mm titanium rods were used for the cervical segment and 5.5 mm titanium rods were used for the thoracic segment, which were fixed by DOMINO connectors. At the follow-up visit in October after the operation, a fracture of the thin rod at the upper end of the right side was found, and the fractured internal fixation rod was revised and replaced, and a brace was worn for protection for 6 months after the revision operation, with no loss of orthosis at the follow-up of 24 months.
5. Discussion.
Hemivertebral deformity is a defect in vertebral body formation, and its cause of scoliosis accounts for approximately 46% of congenital scoliosis. Except for bilaterally symmetrical hemivertebrae, most hemivertebral deformities are characterized by progressive worsening of the deformity, with an average annual worsening of about 4° (1°-33°). Therefore, surgery is the only effective treatment for this type of deformity. The upper thoracic segment of the spine is located between the most mobile cervical vertebrae and the least mobile thoracic vertebrae. Lateral kyphosis in this region can lead to significant changes in the patient’s appearance at an early stage; the aggravation of the deformity can also lead to impairment of spinal cord and neurological function and the appearance of corresponding symptoms. Therefore, early surgical treatment is even more important. The upper thoracic segment of the spine is also an important structural confluence area with complex anatomy, with the sternum, clavicle, and sternoclavicular joint blocking it anteriorly, and with the vertebral body adjacent to large vessels such as the aortic arch, the recurrent laryngeal nerve, the thoracic duct, and the sympathetic chain, all of which increase the risk of surgery.
Combined with the anatomical features of the region, the anterior approach reveals a good field of view and allows complete removal of the hemivertebral body under direct vision. However, the upper thoracic segment is obstructed by the sternum, clavicle and sternoclavicular joint anteriorly, and the vertebral body is adjacent to the vascular nerve anteriorly, which makes the surgery risky; moreover, when the deformity is heavy, the correction of the posterior convexity deformity is limited. The combined anterior and posterior approach can achieve complete removal of the hemivertebral body and adequate orthosis. However, the surgery requires two incisions, is prolonged and traumatic, and carries the risk of intraoperative contamination; from the literature, the incidence of neurological complications is high. Posterior surgery is anatomically simple, less traumatic, and avoids interference with the mediastinum and thoracic cavity; it is not restricted by segmentation, easy to operate, and can well correct the posterior convexity deformity after hemivertebrae resection. Therefore, in this group of 8 patients, we chose to perform posterior hemivertebral body resection and internal fixation and bone graft fusion in one stage. The postoperative orthopedic results were satisfactory, and the patients had significant symptom relief.
The upper thoracic segment is located between the most mobile cervical vertebra and the least mobile thoracic vertebra, which is a stress concentration area and requires high internal fixation. Short segment fixation should not be used, and the fusion range should be extended to fuse all vertebrae in the lateral and posterior convex arc. All eight patients in this group were fused according to this principle, and no significant loss of orthosis was observed at the time of follow-up.
Currently, cervical screw placement techniques commonly used in the cervicothoracic segment include the lateral block screw technique and the cervical pedicle screw technique. In the literature, it has been reported that lateral block screws are less strong than pedicle screws in terms of flexion, rotation, and extraction resistance; the stability of internal fixation is significantly lower than that of pedicle screws, and extension of the fixation segment is required to increase stability during cervicothoracic spinal fixation. The cervicothoracic pedicle screw has good biomechanical strength, can shorten the fixation segment and preserve the motion function, which has certain clinical superiority. In order to obtain a balance between preservation of motion and strong internal fixation, it is recommended that the cervicothoracic segment be fixed with pedicle screws whenever possible. In all cases in this group, cervicothoracic segment pedicle screw fixation was performed, and no improper screw placement was found on postoperative x-ray, and no complications such as pedicle cut were found on follow-up. Our experience is that: C3-C6 nail entry point is the intersection of the middle and upper lateral block with the middle and outer 1/4; C7 is the intersection of the middle drape of the articular eminence with the upper edge of the lateral block 2-3 mm below; T1 and T2 are the intersection of the outer edge of the articular eminence with the midline of the transverse eminence; T3-T10 are the intersection of the outer edge of the articular eminence with the upper edge of the transverse eminence. The direction of the nail entry was referred to the angle of the lateral arch root tilt shown in the preoperative CT and the head tilt angle of the upper endplate of the vertebral body shown in the intraoperative X-ray.
Complications and their prevention.
Common complications in the perioperative period of hemivertebrectomy include nerve root, spinal cord, and vertebral artery injuries, mainly caused by improper placement of pedicle screws. The local anatomy and adjoining relationships of the upper thoracic segment are complex, the pedicle diameter is thin, the angle is special, and the operation of transpedicular pedicle screw fixation is risky, so it is necessary to be familiar with the local anatomy when performing pedicle screw fixation in the spine. Rao et al. suggested that the diameter of the pedicle is highly dependent on gender and segment and should be individualized. It is recommended that the projection of the cervicothoracic segmental pedicle axis on the posterior attachment, the camber of the pedicle screw, and the cephalad angle be carefully measured using CT reconstructed images routinely before surgery, which is significant for individualized cervicothoracic segmental pedicle screw placement.Lee et al. concluded that 3D computer-assisted navigation can improve the accuracy of screw placement, and the accuracy of cervicothoracic segmental pedicle screw placement was 61/86 ( 70.9%) and 40/45 (89%) for cervicothoracic segment screw placement with freehand and navigation, respectively. It was also pointed out that there was a significant difference in the penetration rate of the pedicle in different segments during computerized navigation, with the highest rate in C7 (28.6%), which may be related to the absence of transverse processes in C7 and the high intraoperative mobility that affects the accuracy of navigation.
The cervicothoracic segment has concentrated stress and is subjected to higher shear forces. A common complication in the distant future is internal fixation fracture. A biomechanical study of the movement patterns of the cervicothoracic segment and the stresses on the internal fixation showed that, among the three fixation methods of shifting rods, coarse and fine rods connected by DOMINO connectors and fine rods, the shifting rods and coarse and fine rods connected by DOMINO connectors were significantly better than the simple fine rod fixation in terms of resistance to flexion and rotation. In our group of 8 patients, 5 cases were fixed with coarse rods, 2 cases were fixed with DOMINO connectors, and 1 case was fixed with shifting rods. One of the patients with DOMINO connector connected to coarse and fine rod fixation. During the revision surgery, it was found that a pseudo-joint was formed at the bone grafting site of the right cervicothoracic segment, and the bone graft was re-grafted after chiseling the original bone graft to the cancellous bone surface, and attention was paid to increasing the amount of bone graft. The brace was strictly worn for 6 months after surgery, and there was no loss of orthopedic shape for 24 months after the revision surgery. Therefore, we believe that in the prevention of internal fixation fracture, firstly, we should try to avoid the use of simple thin rod fixation, secondly, we should pay attention to adequate bone grafting, and patients need to wear the brace strictly after surgery, and for patients with poor cooperation, we can consider extending the brace wearing time to 6 months.
Summary.
The deformity of the upper thoracic segment due to hemivertebrae develops rapidly and can lead to significant changes in shape at an early stage, and the aggravation of the deformity can lead to damage to the spinal cord and neurological function. Therefore, early hemivertebral resection should be performed. The anatomy of this region is special. When choosing surgical treatment, we should combine the characteristics of the specific deformity, select the correct surgical approach, reasonable internal fixation methods and instruments, and actively prevent various complications in order to achieve the best clinical outcome.