Cervical abnormalities associated with NF-1 include enlarged neural foramina, cervical kyphosis, and gross cervical kyphosis with subluxation or dislocation. Kyphosis is the most common deformity and surgical management of this deformity has received little attention in literature reviews. For cervical kyphosis in NF-1, successful managements requires early recognition , a more aggressive and reliable intervention to prevent disastrous worsening of the deformity. Several factors complicate the treatment and they are: i) a potential high risk of spinal cord injury during the correction. ii) difficulties in placing stable anchors in dystrophic vertebrae. iii) difficulty in obtaining solid bone fusion and iv) manipulation of the extreme degree of deformity in the presence of compromised cord may lead to severe cord damages and ischemia.
Three approaches were recommended to manage cervical kyphosis; Anterior-only(AO) approach, Posterior-only(PO) approach and combined anterior and posterior(AP) approach[10, 12]. Most previous studies have recommended AP approach , while a few studies have suggested anterior fusion or posterior fusion alone for cervical kyphosis associated with NF-1 because of some reasons, such as fusion failure, pseudoarthrosis and correction loss in follow-up[7, 11]. A successful spinal fusion via single approach is fraught with difficulties in NF-1. Winter and workmates[13, 14] and Sirois and Drennan reported a 64% and 72% incidence of fusion failure. In a study from Parisini et al, fusion failures affected 53% of patients who received posterior instrumented fusion alone in comparison with 23% who underwent sequential anterior and posterior fusion. Hsu et al reported a 7.5% incidence of failure in dystrophic curves managed by AP. Therefore, how to manage the fusion failure is a challenge for kyphosis correction in NF-1. It is well known that NF-1 affects bone quality (osteoporosis) and quantity (vertebral body dysplasia). It is extremely difficult to place stable anchors where there are severe dystrophic changes in the cervical spine [19, 20]. Without stable anchors, the correction will eventually be suboptimal. Moreover, the other surgical challenge seen in NF-1 is lower bone mineral density (BMD). It has been reported that decreased bone BMD in both sexes at an early age is up to 50% of individuals with NF-1. Therefore, dystrophic and osteoporotic vertebral bodies may be insufficient to hold screws. Furthermore, preoperative HGT can also have an impact on the BMD. Long traction duration may bring more bone mineral loss. In this study, CIH-HT combined PO approach was used for the treatment of cervical kyphosis in patients with NF-1. In order to achieve stable fixation and successful bone fusion via PO approach, two points, more anchor points and abundant bone graft, in the operation are particularly important. More lateral mass and/or pedicle screws, hooks, even short screws, could provide more anchor points, which could disperse correction force and stabilize the correction result. Additionally, Abundant bone graft(allograft bone and / or autogenous iliac bone) was adopted to provide enough solid support for a successful bone fusion. As a result, the correction result was stable and bone fusion was successful in follow-up. After the operation, all the patients wore a cervicothoracic orthosis for three months, postoperative external fixation is mandatory to maintain the correction and to obtain solid bone union. Our study showed that with support of more anchors, abundant bone graft and postoperative external fixation, a stable fixation and successful bone fusion can be achieved via PO approach for cervical kyphosis correction in patients with NF-1.
The application of HGT for treatment of cervical kyphosis in NF-1 is still controversial despite the use of halo spinal traction being widely used for treating severe spinal deformity[22-26]. Ward et al reviewed 2 adult patients with cervical kyphosis in NF-1 and argued that traction can have a positive effective or lead to a disastrous consequence. Steinmetz et al believed that the time limit for traction is 3-5 days. There is no improvement of kyphosis if traction was more than 5 days. However, some authors believed that traction was very important adjuvant treatment for cervical kyphosis. Recent studies have further shown the safety and efficacy of HGT as an operative adjunct procedure for cervical kyphosis correction. Kawabata et al described preoperative HGT as a safe means to straighten cervical kyphosis before surgery in 3 patients with NF-1. HGT could provide a slow and gradual correction while the patients were awake , which typically decreased the amount of corrective force that needed to be applied to the cervical spine. With the help of preoperative HGT, partial correction of the deformity can be achieved to make the surgical procedure easier with less operative risk. In this study, each patient underwent CIH-HT prior to the correction surgery. 44% traction correction rate was achieved eventually and the cervical kyphosis was corrected to safe preoperative levels. Our study further proved that CIH-HT was safe and an effective adjuvant management for cervical kyphosis correction in NF-1.
Compared with several previous studies[7, 8, 10, 11, 29, 30](table 4), CIH-HT combined PO approach had a better correction. CIH-HT provided the first level correction (44%), and surgery provided the second level correction (48%). CIH-HT provided safe partial correction, and typically decreased the amount of corrective force that needed during the surgery. Some factors contribute to the high traction correction rate. In this group, most of patients were presented with flexible kyphosis without a rigid facet joint and they underwent prolonged traction (an average of 20.9 days, the maximum of 61 days). The soft tissue and facet joint can be released to the maximum as a result of long time and heavy traction. Additionally, there is no strong muscles and ligaments around cervical vertebrae and long time hyperextension traction, which provided a continuous forward force in the cervical spine, and contributed to partial correction. Subsequently, intraoperative traction and PCO(posterior column osteotomy) was performed to provide a safe surgical correction rate and surgical correction rate eventually reached up to 48% via PO approach.
The complication rate for the management of cervical kyphosis associated with NF-1 has not been well defined. It was considered that surgical correction of cervical kyphosis in patients with NF-1 has one of the highest rates of complications in cervical spine surgery . Postsurgical complications included cutaneous infection, junctional kyphosis, kyphosis progression, fusion failure and pseudarthrosis at final follow-up. However, a previous study from Helenius stated that the risk of complications did not differ significantly according to the surgical approach. Additionally, Preoperative halo traction was not associated with a lower risk of complications (44% compared with 69%; p = 0.24). In this study, the incidence of complications was 36.8% (7/19). Although this complication rate is high, most of the complications ( 6/7) were traction-related as a result of being in bed for a long time and only 1 case underwent surgery-related complication. Our study indicates that CIH-HT combined PO approach for the treatment of cervical kyphosis in patients with NF-1 did not increase postsurgical complications.
Improvement of neurological deficits via PO approach is a challenge in cervical kyphosis correction. NF-1 may present multiple levels of involvement and is likely to form complicated paraspinal and/or intraspinal tumors. A intraspinal tumors or tumors with nerve root invasion should be resected to achieve nerve decompression, and this procedure should be performed before a manipulation for deformity correction is done. In addition, a progressive deformity can also lead to severe neurological impairment. When a neurological deficit is present in a young patient with NF-1, it is usually caused by increased kyphosis. In this study, neurological deficits were improved to some degree via CIH-HT combined with PO approach. We inferred the following reasons to project the improvement of neurological deficits. Firstly, the neurological deficits caused by cervical kyphosis in NF-1 are mainly compression in front of the spine. It could be improved simultaneously with cervical kyphosis through a long time standard traction. Secondly, the anterior column of the cervical spine is prolonged and the posterior column is relatively shortened via long time hyperextension traction. As a result, the compression in the front of spine can be improved. Thirdly, compression in cervical kyposis is caused by apical vertebra and adjacent intervertebral disc. Traction can expand the intervertebral space and make intervertebral disc recovery to mean decompression. Also, the tolerance of spinal cord to ischemia and hypoxia was increased via a CIH-HT to reduce the risks of intra-operative neurological injury. Lastly, Posterior Column Osteotomy (Ponte osteotomy and SPOs) in apical region under intra-operative traction further released facet joint and shortened the posterior column, which decreased traction in the rear of spinal cord. Moreover, postoperative neurological deficit is another issue for cervical kyphosis correction in patients with NF-1. In a systematic literature review, Guzman et al reported that the prevalence of C5 nerve root palsy was 7.7% after anterior cervical procedures and 7.8% after posterior procedures ; however, most of the deficits were resolved spontaneously during the 2-year follow-up period. In this study, postoperative neurological deficits occurred only in 1 patient (5.3%, 1/19) who recovered after a revision surgery. We found that CIH-HT combined PO approach can also reduce the risk of postoperative neurological deficits.