Craniocervical instability in children with Down’s syndrome

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Introduction. Pathology of the craniovertebral zone in children with Down’s syndrome is a very important topic, because of the high risk for developing neurological complications in these patients, after even a minor trauma.

Material and methods. We performed a review of the literature highlighting the disorders of the cervical spine in children with Down’s syndrome.

Results. We gathered data on the etiology, pathogenesis, and clinical presentation of craniocervical instability in children with Down’s syndrome. We reviewed the existing surgical treatment options, and presented our own clinical cases. We also developed a protocol for the management of these patients.

Discussions. Understanding the several forms of craniocervical instability in children with Down’s syndrome is very important. As it is a very dangerous condition that can lead to devastating neurological deficits, all medical specialties working with these patients should be aware of them. There are clinical and radiological criteria for this condition that can help in the management of such patients. Surgical treatment is an effective option, but it has a high complication rate and rarely results in neurological improvement.

Down syndrome is the most common genetic disease, with an incidence of 1 in 660 newborn infants [1]. Apart from characteristic phenotypic signs, a range of problems occur in diverse organs and systems, such as the cardiovascular, nervous, gastrointestinal, endocrine, and musculoskeletal systems [2]. The pathology of the craniovertebral area, represented by atlanto-occipital and/or atlantoaxial instability (AAI) and (less often) by different variants of craniovertebral area dysplasia (hypoplasia/aplasia of the odontoid process, the presence of odontoid bone, or assimilation of the atlas) is complicated by the development of craniocervical instability [3, 4]. Depending on the criteria determining the concept of “instability,” according to various authors, the occurrence rate of the pathology varies between 10% and 60% [5, 6]. The first description in the literature dates back to 1961 [7]. According to authors, it is widely accepted that the condition is more frequently observed in female patients [8–10]. In contrast, other authors have reported a higher frequency in male patients [11], while some experts do not distinguish sex differences [12].

The significance of the problem is determined by the relatively high risk of the development of neurological disorders related to the compression of the spinal cord during contact sports exercises and medical procedures (e.g., tracheal intubation) [13]. In the literature, a case of sudden development of tetraparesis with the impairment of pelvic organ function in a 13-year-old child with Down syndrome after the instillation of eye drops was described [14]. A symptomatic variant of instability is observed in 1%–2% of patients with the syndrome [5].

The importance of the pathology is attested by the fact that in 1984, the American Academy of Pediatrics developed recommendations for the examination of children with Down syndrome who were willing to engage in contact sports [15]. A year earlier, the Specialty Committee of Olympic Games had introduced an examination protocol for athletes with Down syndrome for participation in competitions, including functional radiographs of the neck in the lateral projection [16]. However, existing data show that sports restrictions have no positive effect on the radiologic indicators of patients [17]. Besides, there are no reports on cases of AAI against a background of Down syndrome causing sudden death of a sportsperson. This and also the fact that in some cases AAI develops during adolescence in patients who previously had no radiologic signs of the pathology were probably used as a reason for not performing routine functional radiographs in 3- to 12-year-old children with Down syndrome in a number of countries, such as the United Kingdom [18].

The clinical manifestations of symptomatic AAI are the following: sensation of discomfort and pain in the cervical spine, suddenly developed torticollis, gate and pelvic organ disorders, decrease in motion activities of the lower limbs, spasticity of the muscles of the lower limbs, and hyperreflexia.

Assessment of the clinical symptomatology necessitates an instrumental examination of the patient. The radiographic signs correlated with the presence of the pathology are as follows: increase in the atlantodental interval by more than 5 mm, increase in the basilar–dental distance by more than 12 mm, and a Power index value more than 1.0 (anterior atlanto-occipital instability) or less than 0.55 (posterior atlanto-occipital instability) [19–21] (Fig. 1). In addition, for the evaluation of atlanto-occipital instability, increased anteroposterior skull translation, assessed by the method by Weisel et al. (more than 2 mm), is characteristic. The present technique is considered to be more accurate than the Power method [22, 23] (see Fig. 1).

The following signs constitute evidence for the possible presence of compression of the spinal cord: increase in the atlantodental interval by more than 10 mm, decrease in the size of the reserve space around the spinal cord (SAC) less than 13 mm, and infringement of the “Still’s three principles;” in such cases, magnetic resonance tomography (MRT) is indicated for determining the true value of stenosis and the condition of the spinal cord [24–26]. Some authors recommend performing MRT in the extreme flexion and extension positions for the evaluation of instability and spinal cord compression intensity [27]. Nakamura et al. proposed a new AAI diagnostic criteria: the inclination angle of the C1 vertebra and the coefficient С1/SAC-С4 [28] (Fig. 2). The possibility of performing the evaluation in the neutral position is a distinguishing feature of the technique as, according to some authors, performing functional radiographs can lead to the aggravation of neurologic symptomatology [29–34]. Performing computed tomography allows verifying diverse types of dysplasia of the craniocervical zone, different variants of atlas assimilation; odontoid bone; and hypoplasia and aplasia of the odontoid process, and differentiating congenital conditions from consequences of a trauma in areas that are sometimes quite problematic [11].

The increased elasticity of the transverse ligament of atlas (lig. transversum), related to dysplasia of connective tissue caused by the abnormal collagen structure due to the presence of three copies of the genesCOL6A1 and COL6A2, is considered to be one of the reasons of instability development [35]. In some cases of rupture/acute decompensation of the ligament, the remaining odontoid ligaments (lig. alaria) continue to be the main holding structures and restrict forward atlas translation; in this case clinical manifestations are limited by discomfort or pain and moderate myelopathy manifestations. Rupture of the odontoid ligaments leads to the complete destabilization of the С1–С2 segment and consequently increases the risk of the development of spinal cord compression accompanied by severe neurological disorders [36]. However, some investigators do not support this theory [17]. After comparing the radiographic data of patients with Down syndrome categorized by the presence or absence of the clinical signs of hypermobility according to Wynne-Davies and Gormley, the authors did not reveal significant differences [37]. However, it was proved that even a minor trauma or an infection of the nasopharyngeal region and middle ear can lead to the development of AAI [10, 38].

The abnormal development of bone structures, observed somewhat more often in patients with Down syndrome than in other patient groups, leads to hypoplasia of the occipital bone condyles, assimilation of the atlas, odontoid bone, and hypoplasia and aplasia of the odontoid process, which may also cause instability development [5, 39]. The study comparing computed tomography data showed that the size of the reserve space around the spinal cord in patients with Down syndrome was smaller than that in the general population (505 mm2 versus 602 mm2); therefore, even minimal pseudo-luxation can lead to the development of symptoms. The presence of hypoplasia of C1 in patients in this group can cause spinal stenosis development even after insignificant increases in the atlantodental interval (approximately 6 mm) [40, 41]. It is known that such congenital anomalies are found in newborns with a confirmed diagnosis of Down syndrome [42]. In such cases, a key feature is the possible development of not only anteroposterior instability but also lateral instability. This is associated with a comparatively increased severity and frequency of neurological manifestations and, as a consequence, a more aggressive surgical treatment approach for this group of patients.

Currently, the necessity to perform preventive stabilizing surgeries in the presence of a symptom-free form of craniocervical instability is not recognized [43]. Most long-term follow-up studies indicate that spontaneous stabilization of the С1–С2 segment occurs as patients grow older (Alvarez, 2004, unpublished data). In a number of cases, worsening of the existent situation and development of a symptomatic form of instability in people without previous clinical and radiographic signs were noted [44]. There are no criteria for the transition of the symptomatic form to the symptom-free form and vice versa.

Indications for performing different types of surgical interventions, including stabilizations of different lengths and both anterior and posterior spinal cord decompression, are the following: presence of neurological manifestations caused by spinal cord compression; presence of radiographic signs of obvious AAI (increase in the atlantodental interval of more than 10 mm) [15], decrease in the reserve space around the spinal cord of less than 13 mm, and infringement of the “three Still rule;” and some unstable forms of craniocervical zone instability (the odontoid bone), atlanto-occipital instability, and basilar impression [5]. In the absence of clinical manifestations and in the presence solely of a radiographic sign of AAI showing an increase of 5 to 10 mm in the atlantodental interval, the exclusion of a child’s participation in contact sports, carefully implemented medical procedures, and regular (annual) radiologic examinations are indicated.

There are different kinds of surgical treatments for this group of patients. The goal of the treatment is the stabilization of damaged spinal motion segments using metal hardware (wire, hook, screw, and hybrid) with the subsequent formation of a bone block and, if needed, the elimination of spinal stenosis. Posterior decompression—resection of the posterior arch of the atlas and part of the occipital bone concluded by occipitospondylodesis—is the most frequently used type of surgical intervention [45]. In cases of the absence of fusion after dorsal approach intervention, transoral/transmandibular resection of the odontoid process of C2 and anterior fusion allow obtaining the desired outcome [46, 47]. The latter option is technically more complicated and is rarely performed. Today, when choosing metal hardware, preference is given to more rigid frame structures with screw or hook support elements because such stabilization mechanisms do not increase the frequency of complications while allowing successful fusion outcomes in a larger proportion of cases compared with wire fixation [48–53]. The use of the HALO apparatus is restricted due to the low intelligence level in the vast majority of patients. This also explains difficulties in postsurgical care and the necessity for close patient monitoring. Many authors report quite high frequencies (70%–100%) [54, 55] of complications, including absence of the bone block formation (up to 50 %) [56], destabilization of metal hardware, neurological disorders [57], and fatal cases [54, 58, 59]. Besides, in only small number of patients (approximately 20%), neurological impairment is observed [54].

The problem of craniovertebral area pathology involving craniocervical instability in children with Down syndrome is extremely important because it entails a high risk of the development of severe neurological disorders and thus requires strict medical vigilance. As many of these children wish to participate in sporting events or engage in contact sports, the early recognition of the problem allows identifying children in the risk group and implementing safeguard measures. Although effective, the surgical treatment of patients with neurological impairment or radiographic signs of pronounced craniocervical instability is associated with a large number of complications and rarely leads to the amelioration of neurological manifestations. Criteria for clinical/instrumental diagnoses of the condition have been developed and determine patient surveillance. We consider it expedient to design a protocol scheme based on such criteria for further development and clinical use (Fig. 3).

Information on funding and conflict of interests

This work was supported by The Turner Scientific and Research Institute for Children’s Orthopedics, Saint Petersburg, Russian Federation. The authors declare no evident or potential conflicts of interests related to the publication of the present paper.

Nikita O Khusainov

The Turner Scientific and Research Institute for Childrens Orthopedics

Author for correspondence.
MD, PhD student of the Turner Scientific and Research Institute for Children’s Orthopedics

Sergei V Vissarionov

The Turner Scientific and Research Institute for Childrens Orthopedics

MD, PhD, professor, Deputy Director for Research and Academic Affairs, head of the department of spinal pathology and neurosurgery. The Turner Scientific and Research Institute for Children’s Orthopedics. Professor of the chair pediatric traumatology and orthopedics. North-Western State Medical University n. a. I.I. Mechnikov.

Dmitriy N Kokushin

The Turner Scientific and Research Institute for Childrens Orthopedics

MD, research associate of the department of spinal pathology and neurosurgery. The Turner Scientific and Research Institute for Children’s Orthopedics.

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Copyright (c) 2016 Khusainov N.O., Vissarionov S.V., Kokushin D.N.

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