High cervical myelopathy due to bony craniovertebral junction anomalies (atlantoaxial dislocation) in pediatric population- clinical scoring system

The craniovertebral junction (CVJ) is a complex transition zone between the cranial cavity and the rostral spinal column. Various conditions affect and destabilize this region; of these conditions, congenital atlantoaxial dislocation (AAD) is the most common anomaly (1, 2). The management of congenital CVJ anomalies is complex due to the relative difficulty in accessing the region, the critical relationship of neurovascular structures, and the intricate biomechanical issues involved, which revolve primarily around the attainment of neural decompression and stabilization (3). The difficulty accessing the CVJ relates primarily to ventrally compressing pathologies in which the transoral procedure is required to take out the offending bony element. In comparison, posterior access to the CVJ does not pose much of a problem but has threat of neural injury.

The most common age group affected by congenital AAD is the second and third decade; however, the incidence in the paediatric population is not uncommon. A wide variety of congenital anomalies of the CVJ occur due to an insult of bony and soft tissue elements, between the fourth and seventh week of intrauterine life (4). The clinical manifestations are most often delayed into the second and third decade because they are usually subtle and easily missed in children unless looked for specifically (1, 5). Moreover, this disease process is slowly progressive and manifests due to chronic compression of the cervicomedullary junction; it is usually brought about by triggering events such as trauma (1, 5, 6). The criteria for diagnosis of AAD differ between children and adults. The normal atlas to dens interval is greater in children compared with adults; thus, AAD is diagnosed on the basis of atlantodental distance greater than 4 mm in patients younger than 9 years of age and greater than 3 mm for those 9 years of age or older (6). The management of these patients becomes even more difficult as a result of the general issues of managing children, which add to the typical issues of managing the complicated anomaly itself. There has been a progressive change in the approaches and techniques used for management (7). The outcome analysis performed to assess the surgical result has relied on Di Lorenzo's grading (DLG) system, which is a four-grade system based on functional dependence (Table 1) (3, 5, 8). This has been the most widely used and accepted grading system to assess AAD patients undergoing treatment. The grading system has stood the test of time and has excellent reproducibility and inter observer reliability (7). However, although the DLG grading system is universally acceptable in adults, it may not be as readily applicable and useful in children. Children are unable to quantify their functional status and are otherwise dependent for their daily activities. Hence, it is difficult to access their functional disabilities caused by the disease process. Categorization according to disabilities as is done in the DLG may not be precise in this age group and lacks interobserver reliability and reproducibility.

Moreover, grading the patients into just four groups does not allow for the observation of subtle changes in neurological status. There is a large subset of patients who remain in the same grade even though they have subjective improvement or deterioration in their neurological status. It may be opined that a comprehensive and precise neurological examination may be more valuable in accessing the response to treatment. If a scoring system is developed that relies on these factors, it may be better reflective of progression of the disease course. Such a score should be detailed enough to recognize subtle neurological status changes but simple enough to be performed routinely. The purpose of the present study was to formulate a new scoring system based on comprehensive neurological examination and to assess its applicability in children compared with the DLG.

A study was done at SGPGIMS, Lucknow to introduce new scoring system; this was based on clinico- radiological evaluation of 177 cases operated over period of 14 years by single surgeon (RK). Statistical analysis was performed on children with age less than 14 years (n=67). The diagnosis was based on a minimum atlantodental interval of 4 mm. The patients who had associated Chiari- I malformation, AAD and associated genetic syndromes , or follow up of Less than 12 months were excluded. The assessment of patients was done preoperatively and postoperatively & follow up. The following points affecting the outcome were taken into consideration to fetch a new and precise scoring system for better evaluation of children suffering from congenital AAD (Table 2). There were 36 males and 31 females, with a mean age 9.36±3.51 years (range 2-14 years). The results were compared with Di Lorenzo grading system.