Most of stable atlas fractures can be treated conservatively . However, as to unstable C1 fracture, surgical strategies have become the standard of care. Unstable atlas fracture usually accompanies TAL injury, behaving as separation of the lateral masses, and subluxation or dislocation of atlantoaxial joint .There is also a point that atlas fractures, not C1 posterior arch fractures, destroyed the stability of the upper cervical spine. The spinal cord is under danger since the displacement of bone fragments or atlantoaxial dislocation, which resulting in severe complications like paraplegia even death [8, 9]. Treatment aspires to reduce the fracture, correct dislocated fracture, stabilize the atlantoaxial joint, and preserve the maximum ROM of the upper cervical spine [10, 11]. However, the surgical strategies of unstable C1 fractures is still controversial.
Value of C1-ring osteosynthesis in unstable atlas fracture
Conservative therapy in unstable atlas fracture for several months may lead to severe discomfort and high incidence of bony nonunion.Simultaneously,the inconsistency and mechanical instability of occipitocervical junction may restricted motion and cause continuous neck pain.To date,the posterior atlantoaxial or occipitocervical fusion is supposed to be the main surgical method,but the motion of upper cervical spine was sacrificed.The ideal treatment method is limited fixation without restricting the ROM of upper cervical spine. For this, many spine surgeons gave up the posterior fusion and recommend C1-ring osteosynthesis[15, 16]. The question regarding of relationship between C1-ring osteosynthesis and integrity of the TAL is still controversial.Traditionally, the integrity of TAL is key in determining the stability of C1 fractures. Rule of Spence  showed that total LMD over 6.9 mm on open-mouth radiographs correlated with rupture to TAL has important clinical value in determining whether surgical intervention is needed and is currently being questioned.What’s more,there are other tissues that help maintain C1-C2 stability and restrict motion notwithstanding rupture of TAL.Some scholars’ founding shown that the significance of axial ligamentous tension of craniocervical junction has been underrated .Because of its unique anatomical structure and biomechanical environment, occipitocervical junction mainly stabilized by the ligamentous complex of C0-C1-C2. Previous literature had showed that C1 burst fractures are axial load entities and better to maintain the integrity of secondary stabilizers comprised the alar ligaments, facet capsule and neck musculature. C1-ring osteosynthesis techniques is able to restore the axial tension of ligamentous complex of C0-C1-C2 through reduction of fracture. Studies have shown that even with the rupture of TAL,C1-ring osteosynthesis can provide sufficient stability under physiological load. Thus, incompetence of TAL may not be a contraindication to C1-ring osteosynthesis.The conventional definition of C1 instability based on the integrity of TAL underestimates the number of fractures requiring surgical intervention and overestimates the number requiring C1-C2 fusion.
Advantage of anterior C1-ring osteosynthesis using JeRP system
C1-ring osteosynthesis using both posterior approach and transoral approach has been published.With posterior C1-ring osteosynthesis techniques,posterior arch fracture and the lateral mass displacement could be satisfactorily reduced by the compression force on the end of bilateral mass screws.However,it makes the front of the lateral mass screw swing laterally, leading to insufficient reduction of anterior arch fracture of C1.
Anterior direct reduction of the atlas fractures promotes the rate of bony union of fractures by improving the integrity of C0-C1-C2 complex structure.This approach has a good safety profile,avoiding fusion of important motion segments, and restoring the C0-C2 height. Over last decade, results of transoral C1-ring osteosynthesis for unstable atlas fracture have been verified. However, many surgeons are hesitant about this technique,because of unfamiliarity with the transoral approach,the theoretical increased risk of infection.The universal shortcoming of transoral C1 osteosynthesis published previously is that reduction of C1 fracture is only an acceptable repair rather than anatomical reconstruction.The transoral C1-ring osteosynthesis is technically challenging, and there is no specific instrumentation devices or spinal implants designed for treating unstable atlas fracture.The main problem with current techniques is that the posterior pharyngeal soft tissue which is not thick enough to cover the plate or rod,thus increasing the risk of wound complications.Additionally,it is difficult to implement satisfactory reduction of atlas fracture in the deep and narrow space. Simultaneously,the end of the lateral mass screw via transoral approach is too high,which may easily cause the wound of the posterior pharyngeal wall to crack or postoperative dysphagia.In this study,the use of JeRP-system is introduced for anterior C1-ring osteosynthesis.The advantage of it lies in the use of a dedicated reduction instrument, which not only satisfies the reduction of the fracture end,but also can place the fixation screws in the fracture reduction state and the reduction instrument will not affect the screw placement. Generally,it is acceptable to follow the principle that the screws don’t penetrate the edge of the lateral mass into the atlanto-occipital joint, and don’t enter atlantoaxial joint.The lateral mass is wedge-shaped, with higher outside and lower inside.The insertion point of the screw is deviation inward, which easily leads to the screw entering joint. In our paper,1 lateral mass screws were observed to enter atlanto-occipital joint.In the series, 22 patients had bone fusion, and wound infection and dehiscence had not been observed.The main advantage of JeRP-system is not only ideally reduction of C1 fracture performed via anterior approach, but also inserted plate and screws could not interfere with midline wound closure.The incongruency of the C0-C1 and C1-C2 joints is rectified, and the ligamentous tension band of craniocervical junction is regained as well.As far as we know,this new technology can minimize lateral mass displacement.JeRP-system appears to be an effective and safe method to deal with unstable C1 fractures, which achieve ideal bone fusion and motion-preserving of craniocerivcal junction.
The original intention of the JeRP-system designed is to be used for unstable C1 fractures with TAL intact,and its indication is very narrow. In the actual process, we also applied the JeRP-system to C1 fractures with TAL rupture,and achieved satisfactory results. Among them,3 patients with Dickman type I TAL injury occurred atlantoaxial dislocation postoperatively,while the patients with Dickman type II TAL injury had good effect. Hence, the primary indication for JeRP system is an unstable C1 fracture (Gehweiler type I/III) with or without TAL injury (Dickman type II).