Craniocervical junction disorders often require reconstruction of stability through strong internal fixation. At present, screw-rod fixation is most commonly used in posterior atlantoaxial fixation [9, 10], and plate-screw-rod fixation in posterior occipitocervical fixation [11, 12].
The range of motion in the craniocervical junction is large, thus methods to improve the stability of internal fixation structures are continually explored. Stability of the internal fixation a crucial factor for bony fusion and consequently for a good clinical outcome. According to the results of many biomechanical research studies, C1 and C2 pedicle screws are applied preferentially in clinics to obtain better stability [6, 13, 14]. However, in the presence of anatomic variation, C1 lateral mass screws, C2 pars screws, and C2 translaminar screws were used as substitutes, thereby reducing the stability of the internal fixation [13, 15, 16, 17]. Currently, the use of a transverse link in posterior screw-rod and plate-screw-rod fixation is a common method to increase the stability [3, 4, 5]. Nevertheless, the large bending and limited space of the rod make the placement of a transverse link difficult, increasing the operative time and risk of infection and spinal cord injury. It is therefore worthwhile to seek a simpler, practicable process to improve the stability.
Both the posterior atlantoaxial screw-rod and occipitocervical plate-screw-rod fixations in current clinical use utilize a parallel rod configuration with a “II” shape. In 2011, Gabriel et al. [6] first studied the novel crossed rod configuration by comparing its biomechanical stability to that of the traditional parallel rod configuration in an occipitocervical fixation using a C2 translaminar screw. The crossed rod configuration showed 29%, 15% and 16% decrease in range of motion of flexion-extension, lateral bending and axial rotation in comparison to the parallel rod configuration. In 2017, Shen et al. [7] compared the crossed and parallel rod configurations in atlantoaxial fixation using a unilateral C1 posterior arch screw and C2 laminar screw combined with an ipsilateral C1-C2 pedicle screw, obtaining similar results to Gabriel et al. Recently, Qiu et al. [8] investigated the biomechanics of the crossed and parallel rod constructs in the posterior atlantoaxial screw-rod fixation using a C1 bilateral pedicle and C2 pedicle screw, or C2 lamina screws, which revealed that the crossed rod configuration could provide superior stability in axial rotation, lateral bending and extension. The crossed rod technique’s “X” shape forms a multi-triangle construction that has better structural stability, and is a simpler way to increase the stability of both posterior atlantoaxial screw-rod and occipitocervical plate-screw-rod fixation. Until now, however, the clinical application of this technique has not been studied.
The aim of this study was to investigate the primary clinical outcomes of the crossed rod configuration used in posterior occipitocervical and atlantoaxial fixation. As expected, this technique can provide reliable internal fixation for craniocervical junction in clinical use. All 21 patients in this study had improved neurological function after operation and obtained bone fusion without internal fixation failure, signs of instability, or any other complications during the follow-up period.
There are several limitations in the current study. First, the sample size is small, and research with a larger number of cases is needed in the future. Second, the present study is retrospective in nature; future prospective studies may better control for follow-up timing intervals and may have the potential to include more standardized outcome measures. In addition, the evidence level of this study is relatively low due to lack of a control group. A randomized controlled trial will be needed in the future to further evaluate the technique comprehensively.