Clinical and radiological outcome after minimally invasive surgical approach for type II unstable odontoid fractures.

INTRODUCTION: Anterior odontoid screw fixation is a valid surgical option for unstable odontoid fractures, as type II Anderson D'Alonzo fractures. Grauer further divided type II fractures in subtypes according to the fracture line, providing recommendations for implementation of screw fixation techniques. OBJECTIVE: Primary endpoint of our study is to evaluate the postoperative results of minimally invasive odontoid screw insertion in terms of outcome, fusion rate and stability of cranio-cervical junction. Secondary endpoint was to investigate the influence of age or fractures' features on outcome and fusion rate. MATERIALS AND METHODS: We report the clinical and radiological features of 32 patients harbouring unstable type II fractures operated by a minimally invasive odontoid screw insertion technique. All patients underwent a high resolution multiplanar CT in order to assess fracture features according to Grauer's classification; the integrity of ligaments was investigated by MRI. In addition, a preoperative neurological performance (modified Rankin Scale, mRS) was evaluated for patients either directly or interviewing their families. Follow-up at one, three and six months and 1 year have been performed (averaging 13.5 months) by cervical CT (fusion rate and stability) and mRS update. In order to investigate the influence of age on postoperative neurological performance, two groups (≤50 yrs, 9 pts/>50 yrs, 23 pts) were separately considered and analysed. Overall, we observed no surgery related complications. We also analysed the fusion rate and its correlation with patient age and Grauer's subtype of fracture. RESULTS: At last available clinical follow-up, the preoperative performance was preserved (mRS 0/1: 24, 75%; mRS 2-4: 9, 15%) although with slight reduction of intact patients (mRS 0: 22 vs. 19; 71.8 vs. 59.3%). Younger patients (≤50 yrs) fared significantly better than older ones, achieving a good clinical outcome (mRS 0/1) in 100% vs. 69.5% (9/9 vs. 16/23 pts). Statistical analysis showed a fair correlation between age and outcome. Other factors such as sex and Grauer's type did not influence significantly the clinical outcome. Nine patients did not complete a full radiological follow-up and were therefore excluded from analysis of radiological outcome. Among the remaining 23 patients, only 25% of those who were followed three months or less showed fusion; conversely, all patients who have been examined from 6 to 48 months fused. Among the non-union patients, two underwent a second surgery by posterior approach. CONCLUSIONS: In our recent experience, the minimally invasive AOSF proved safe and effective in treating odontoid peg fractures. Selection based on Grauer's type is mandatory to achieve best results. While in the elderly, an anterior approach is well accepted as the first choice treatment, we recommend that this option should be offered as a suitable alternative to Halo or orthosis also in younger patients since it provides prompt, excellent clinical outcome and high fusion rate especially in this age group.