In the present study, we evaluated the mid-long term (average 4.5 years follow-up) clinical outcome after posterior only instrumented fusion surgery for NF–1 patients with dystrophic EOS. The mean preoperative major curve was corrected from 66.1±16.22 degrees (range: 43 to 90.3 degrees) to 31.1±14.6 degrees (range: 13.4 to 51.2 degrees) (P = 0.00). However, the average major curve at the final follow-up fell back to 40.95±16.01 degrees (range:17 to 70.3 degrees). The T1-S1 length increased by 2.77±1.0 cm on average after surgery and increased at a speed of 0.6±0.30 cm per year. However, the incidence of the alignment complication was relatively high during the follow-up.
About 10% of children with NF–1 develop scoliosis that predominantly involves the cervical and thoracic spine.13 Dystrophic scoliosis with NF–1 has a high risk of rapid progression.(5) The progression of the dystrophic curve can be neither stopped nor relieved by corset therapy.(10) Therefore, the aggressive surgical treatment of dystrophic scoliosis in NF–1 patients was widely recommended.3,15
Traditionally, the combined anterior and posterior fusion was supported by most authors and was recognized as the most reliable method.16–18 The clinical outcome of dystrophic scoliosis patients treated with posterior-only fusion by using hooks and rods demonstrated that the pseudarthrosis rate was high and curve progression was common.(11) Recently, some good results of posterior only fusion surgeries in NF–1 patients with dystrophic scoliosis have been reported.9,10, 19 In this study, we reported our results about the posterior only fusion procedure in NF–1 patients with EOS.
In addition to our study, there are currently only two articles specifically described the effect of fusion procedure to treat EOS in NF–1 patients Greggi et al. (12)reported that NF–1 EOS patients underwent posterior fusion if the thoracic kyphosis was less than 50°, or underwent anterior-posterior spinal fusion surgery if the thoracic kyphosis was 50° or more. In their study, the correction rate on average was 60%, slightly higher than our results. And the follow-up results were good as well, showing no significant progress. Ryoji Tauchi and his colleagues applied the anterior-posterior fusion surgery techniques to all EOS patients before their age reached 10 and the orthopedic effect was more noticeable. The main curve was corrected from 71.2° to 24.1° (66.15%). After a follow-up averaged on 14 years, the result showed that there was no significant progress in scoliosis. Their correction rate was superior to our study in both groups, which might be related to better anterior release due to the combination of the anterior and posterior spinal surgery. Ryoji Tauchi also performed tumor resection at the anterior concave side in combination with the anterior and posterior approach, rib support and bone graft, accounting for the possible reason for the fact that his surgery maintained good correction rates at follow-up(13).
In contrast to Greggi’s criteria for grouping patients with kyphotic angles, we used posterior orthopedic fusion procedures for all patients and did not separate the patients by degree of kyphosis or deformity disposal. In our patients with a kyphotic angle greater than 50°, the initial postoperative correction rate was 44.5%, the last follow-up correction rate was 31.1%, and the loss rate was 13.4%. In patients with a kyphotic angle of less than 50°, the initial postoperative correction rate was 67.5%, the last follow-up correction rate was 43.8%, and the loss rate was 23.7%. Patients with a more than 50° kyphotic angle had both a lower initial correction rate and a lower final follow-up correction rate than those patients who had a lower kyphotic angle of 50° or less. But the two groups were similar in terms of subsequent orthopedic maintenance. Compared with the anterior and posterior fusion, simple posterior only orthopedic surgery may not be able to satisfy orthopedic maintenance in NF–1 patients with EOS, while simple posterior orthopedic fusion in patients with larger kyphosis may not even meet the needs of initial orthopedic surgery.
Five years of clinical follow-up showed that crankshaft occurred in 6 of 10 patients and the Cobb’s angle of fusion segments increased by 10°. By group comparison, we also found that the incidence of the crankshaft was significantly higher for children who were under seven years of age than that of patients who were 7 to 10 years old. Using a single posterior approach to orthopedic fusion surgery was at very high risk of the crankshaft, which was consistent with the previous non-surgical observation of such patients(2).
In addition, some scholars have found that higher density of pedicle screw placement can help to improve the postoperative correction rate of EOS in NF–1patients(9, 14). The lack of O-arm at the early stage of our study, at that time, we can only apply ordinary fluoroscopy. Which made it difficult to place the pedicle screws. The average ratio of fixed/surgical segments was 0.69. However, we found that there were three patients whose fixed/surgical segment ratio was above the average, reaching 63.91% on average. The correction rate at the last follow-up was 48.47%, and the rate of loss was 15.44% for these three patients. For the other patients, the average postoperative correction rate was 49.4 %, the final follow-up correction rate was 34.78%, and the correction loss rate was 14.62%. Perhaps the insufficiency of screws placed on the spine resulted in the insufficiency of the correction force, which led to the poor initial orthopedic effect on the patients included in the current study. However, lacking enough screws did not significantly affect the result of the surgery in terms of the prevention of scoliosis progress.
It is generally accepted that scoliosis caused by NF–1 is relatively stiff and the preoperative traction may contribute to the improvement of orthopedic effect. However, no specific study on this problem has been published yet. Tauchi et al. had given HALO traction to scoliosis patients with a Cobb degree of 80° or more, while Greggi did not use preoperative traction(12). For most patients with severe scoliosis, preoperative traction can improve the orthopedic effect, but it also increases the medical costs and the distress of patients. And poor compliance was found in patients with EOS due to their young age. Therefore, further evidence is needed to conclude the effect of preoperative traction for EOS in NF–1patients.
In Tauchi and coworkers’ study, augmentation and bone graft surgery could maintain good orthopedic effect if dura mater or tumor growth were developed20. Follow-up data demonstrated that patients received an average number of 1.5 intensive procedures. This may also be a reasonable and applicable way to maintain the good orthopedic effect. In our study, patients did not undergo an MRI assessment during follow-up duration, so it is not clear if the progress of scoliosis, was related to an intraspinal deformity. Based on the published knowledge, it may be necessary to be examined in long-term follow-up for NF–1 patients with EOS.
The average fusion segments we performed was 8.1 while it was 13.1 in Tauchi’s study20. It suggested that fewer fusion segments in our study led to the poor orthopedic maintenance. In our study, the majority of spine fusion ranges were from upper end vertebrae to lower stable vertebrae, which was adequate for patients with AIS and NF–1 patients with non-dystrophic scoliosis, but insufficient for NF–1 patients with dystrophic EOS. For EOS patients, height retention is one of the factors we must take into account, because maintaining spinal length is critical factor in allowing adequate lung development, which is a major goal of EOS treatment.The average length of T1-S1 in our patients was 34.5 cm and 39.8 cm preoperatively and at the last follow-up, respectively. There was a 5.3 cm growth. The length of T1-T12 was 21.4cm preoperatively and 24.5 cm at the final follow-up, resulting in a 3.1 cm growth. In Tauchi’s study, the average preoperative and final follow-up of T1-S1 were 30.7 cm and 36.2 cm respectively, resulting in a 5.5 cm growth. The preoperative and final follow-up of T1-T12 length was 18.8 cm and 21.9 cm, respectively, resulting in a growth of 3.1cm. Compared to Tauchi’s study, our surgery was not superior in preserving trunk length. This might be due to the shorter follow-up time, 4.5 years in our study and 14 years in Tauchi’s study, and the fact that patients in our study have the potential to continue their torso growth.
In this study, there was no significant improvement in lung function relative to preoperative lung function at the patient’s last follow-up, probably because the patient’s preoperative lung function impairment was not significantly associated. On the other hand, the early fusion of the spine did not cause damage to the patient’s lung function, which may be due to the shorter fusion segment we chose.
In this study, higher complication rates were associated with posterior-only fusion surgery during the perioperative period and the follow-up, such as crankshaft phenomenon, scoliosis progress, and adding-on phenomenon. A possible reason for these complications may be the overload of the posterior fixation system. Internal fixation complication that occurred at the interface between the implant and the bone was associated with the presence of osteoporosis in neurofibromatosis. There was no neurological complication (transient or permanent neurological deficiency) observed. Considering the facts that the complication rate of anterior-posterior approach is as high as 64%, the probability of perioperative pulmonary dysplasia is as high as 45.4% and lung injury and dural tear are also seen 20, we suggest that posterior fusion surgery may be a good alternative way to get a better postoperative outcome and reduce the postoperative complications.
Until now, none of the current approaches to treat EOS in NF–1 patients has found a balance between maintaining good orthopedic outcomes and reducing complications and patient distress. Will non-fusion technology be the new direction for the treatment of NF–1patients with EOS. Jain et al. (15)used the growth-bar technique on 14 NF–1 patients with EOS in 5 centers and performed an average follow-up of 54 months. It was shown that the correction rate at the final follow-up was 51% and the annual spine length increase was 1.1 cm. Considering the correction rate and retaining of the space to grow, it is undoubtedly worth the wait. Of course, there are disadvantages of growth rod technology as well such as the high incidence of complications associated with internal fixation. Although further observation on non-fusion technology to treat NF–1 patients with EOS is needed, it is undoubtedly that this is another promising new choice to treat the disease.