The atlas, the ring-shaped first cervical vertebra, does not have a vertebral body or spinous process. It is formed by the anterior and posterior arches and the two lateral masses. The weakest points of the atlas are the regions of the anterior and posterior arches that connect with the lateral masses, which are most likely to be injured with two or more fractures in the ring structure [12]. The stability of atlas fractures has historically been based primarily on the integrity of the TAL [2]. But, it is now believed that combined fractures of the anterior and posterior atlantal arches are the unstable fractures, whether or not they are associated with rupture of the TAL [3, 4, 8].
Symptoms of neurological dysfunction are rare in patients with atlas fracture because fractures of the atlas ring increase the space that is available for the dural sac, thereby inhibiting compression [13]. So that, stabilization of fractures is the most important factor for the treatment of atlas fractures. Although there is an agreement regarding treatment of stable atlas fractures, the optimal management of unstable atlas fractures remains controversial. Previously, nonsurgical treatments with skull traction, followed by external halo-vest immobilization, has been commonly suggested [14]. Most patients are can be treated by external immobilization with satisfactory outcomes. However, a follow-up study of 22 patients with atlas burst fractures by Dvorak et al. [15] showed that patients that underwent conservative treatments failed to regain functional preoperative levels, and hinted that nonsurgical treatments were not optimal management options. The strongest Halo-vest has only 75% restriction on cervical flexion and extension activity, so that, preservative treatment with a Halo-vest has a high risk of nonunion [5]. Immobilization of the cervical spine for several months may result in significant discomfort and other complications especially in elderly patients [16]. Moreover, mechanical instability and incongruence of the atlanto-occipital and the atlanto-axial joints may lead to arthrosis, persistent neck pain, and even neurologic injury.
Posterior C1–C2 or C0–C2 fixation and fusion techniques are widely used in unstable atlas fractures, including C1–C2 transarticular screw fixation, C1–C2 screw-rod fixation, and C0–C2 plate-screw-rod fixation [17, 18]. These fixation techniques promote biomechanical stability and guarantee a high bone fusion rate [19, 20, 21, 22]. However, these treatments sacrifice the normal motion of the C1–C2 joints and possible increase the incidence of subaxial cervical spine degeneration [2].
In 2004, Ruf et al. [7] firstly reported a motion-preserving technique, C1-ring osteosynthesis, using a lateral mass screw-rod construct by transoral approach for unstable atlas fractures, with favorable clinical outcomes. Dickman hypothesizes that permanent anterior instability of C1–C2 results from TAL rupture [23]. However, biomechanical studies showed that within the physiological loading range, the longitudinal ligaments had sufficient capacity to maintain the stability of the atlantoaxial joint even with concomitant TAL injuries in atlas fractures [24, 25]. C1-ring osteosynthesis may therefore be a valid alternative to C1–C2 fusion in the treatment of unstable atlas fractures even with TAL rupture [7, 8, 26, 27]. But, a lateral mass screw-rod construct used by Ruf et al. [7] was not suitable for anterior anatomy of the atlas. Ma et al. [8] and Hu et al. [9] used a reconstruction plate in transoral anterior C1-ring osteosynthesis for unstable atlas fractures, but this plate did not have reduction mechanism. Thus, we performed transoral anterior C1-ring osteosynthesis for unstable atlas fractures using a laminoplasty plate which has a reduction function, that can restore fractures and preserve normal C1–C2 motion.
In our study, 13 patients with an unstable atlas fracture were treated with a laminoplasty plate C1-ring osteosynthesis by transoral anterior approach and were followed-up to assess the preliminary efficacy of this technique. All cases achieved well-preserved range of motion and satisfactory bone union without signs of instability or complications. Wound infection can be a serious problem for the transoral anterior approach. But with proper preoperative preparation and postoperative care, the infection can be reduced and even prevented [8, 28]. In this study, no signs and symptoms of infection were found after surgery and during the follow-up.
There are several limitations in the current study. First, the small sample size is the primary limitation. The safety and efficacy of this technique need to be evaluated with more cases. In addition, 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.