Pearls And Pitfall Of The Free-hand Axis Pedicle Screw Placement Technique

BackgroundThe diseases of craniocervical junction (CVJ) mostly cause the atlantoaxial instability which will result in compression of the spinal cord and medulla oblongata, and consequently may cause the neurological symptoms, thus the atlantoaxial joint is the key point for surgical decompression and hard fixation. The instability can be divided into two kinds:reducible and irreducible. For reducible patients, single internal fixation is enough, but for irreducible patients, anterior release surgery should be performed before the posterior fixation. Occipitocervical fusion and atlantoaxail fusion are the most common surgery in the treatment of CVJ diseases。 Axis as an important anatomical structure of the craniocervical junction, plays an important part in biomechanical stabilization of CVJ, and plays a rigid anchor in the reconstruction of stability of CVJ. Axis pedicle screw placement as a basic technique of the CVJ fusion surgery, is also a demanding technique. Clinical application and biomechanical studies show that axis pedicle screws can achieve three-point fixation, the biomechanical strength of which is more powerful than other fixations, thus it has obvious advantages especially in terms of axial rotation and extension stability. The fixation systems composed of axis pedicle screws have ideal biomechanical strength, which meet the requirements of mechanical stability of bone graft fusion, this technique is safe and feasible, and has achieved satisfactory clinical effects.There are two main methods of the axis pedicle screw placement:free-hand technique and intraoperative imaging navigation system. Free-hand axis pedicle screw placement means that the screws are being placed without imaging navigation systems.,so surgeons should have much surgical experience and rich knowledge of anatomy about CVJ. Through careful study of preoperative imaging, and sufficient exposure of the axis pedicle in the surgery, screws are placed under direct vision in ideal position. In recent years, with the development of imaging technique, the intraoperative imaging navigation system which can improve the accuracy of the axis pedicle screw placement is used in the surgery, but at the meantime, patient and doctor may suffer from exposure to radiation, and it prolongs the operation time and increases the cost, and the improved accuracy of the screw placement and its decrease of the rate of related complications has not been confirmed yet. Free-hand axis pedicle screw placement technique means through the exposure of anatomic structures and landmarks, then placing the screws under direct vision. This technique can be easily controlled, and convenient for individuals, which has been more and more widely recognized and used.ObjectiveThrough the analysis of complications and postoperative imaging of patients with CVJ diseases, to discuss the safety and feasibility of the free-hand axis pedicle screw placement.MethodsA retrospective analysis of50patients suffered CVJ diseases who were treated in the First Affiliated Hospital of Zhengzhou University from2009August to2012December was done. There were21men and29women, the average age of all the patients was48.6years(ranging from4to66years). All patients underwent MRI and CT preoperative in order to determine whether they were suitable for axis pedicle screw placement. All patients underwent X-ray at one week、3month、6month and12month after surgery, and CT should be done at6months after surgery to record the fusion rate and accuracy of screw placement. Postoperative CT scans were evaluated to observe the presence and extent of cortical breach, and all the complications were recorded. A grading system based on CT scans was created to characterize such breaches objectively by location (lateral, superior, or medial) and magnitude by percentage of screw diameter beyond cortical edge (0=<no; Ⅰ=25%; Ⅱ=26-50%; Ⅲ=51-75%; Ⅳ=>76%). The screws of grade0as group A, the screw breaches that are located laterally which were magnituded in the grade Ⅰ, Ⅱ, Ⅲ, Ⅳ as group B, the screw breaches that are located superiorly which were magnituded in the grade Ⅰ, Ⅱ, Ⅲ, Ⅳ as group C. The axis pedicle width (the width of pedicle that next to the transverse foramen), pedicle height (the height of the pedicle inside the transverse foramen), cephalad angle and medial angle were measured in A、B、C group. The data were recorded as X±S, SPSS15.0statistical analysis software was used in this syudy,t test was used to analyze the quantitative data, and χ2test was used to analyze qualitative data, P<0.05was considered to be significant.Results5patients underwent atlantoaxial fixation, and45patients underwent occipitocervical fixation. All patients underwent autogenous bone graft from iliac crest for bone fusion。 a total of95axis pedicle screws were placed.In5cases, the screw was placed unilaterally because of the preexisting vertebral artery or pedicle deformity. The average operation time was160min, and the average amount of bleeding in surgery was200ml. There were no severe complication occurred intraoperatively. There was no vertebral artery or neurological complications occurred in all of the50patients postoperatively. Postoperative complications occurred in3patients, one is infection of the incision, another is fat liquefaction of the incision, this2patients recovered after treatment; CT scan of the last patient showed that the axis pedicle screws loosening bilaterally3months after the surgery, but this patient has already got bony fusion, and there was no neurological symptoms, so we do nothing about it.6months after surgery, all of the50patients got bony fusion.There are16cortical breaches in all of the95axis pedicle screws, and2patients were found with bilateral cortical breaches.13cortical breaches appeared in the lateral side of the pedicle, and3breaches appeared in the superior side of the pedicle. No cortical breach was found in the medial side of the pedicle. The magnitude of the 16cortical breaches was classified as follows:grade Ⅰ10cases, grade Ⅱ4cases, grade Ⅲ1case, grade Ⅳ1case. Pedicle width and medial angle of group B were (6.1±2.0)mm、(15.8±6.2)°, and compare to the data (6.9±1.8)mm、(19.0±6.9)°of group A, the differences were significant between the two groups(P<0.05), and the difference between the two group about the height of the pedicle and cephalad angle were insignificant (P>0.05). The cephalad angle of pedicle screw was (29.1±7.1)°of the group A, and it was (30.2±7.0)°of the group C, the difference was statistically significant between the two groups (P<0.05), and the medial angle of pedicle screw、the width and height of the pedicle showed no significant difference between the two groups (P>0.05). There are13cortical breaches in the all47screws which are placed at the left side of pedicle, and3cortical breaches in the all48screws which are placed at the right side, through the χ2test,the value of the χ2is7.77, so the difference was significant (P<0.05)Conclusions1. The accuracy of the free-hand technique in this study is83.2%, and it suggests that this technique is feasibility and safe. The fixation systems which included the axis pedicle screws can provide satisfying biomechanics strength, and the bony fusion rate achieved100%6months after surgery. Excellent clinical effects are achieved in the treatment of craniocervical junction diseases.2. When breaches do occur, they are overwhelmingly appeared in the lateral side of the pedicle in location, and most of the breaches were not more than50%of the screw diameter, and no vertebral artery or neurological complications occurred because of the cortical breaches.