Preservation of mobility and physiological range of motion combined with stable fixation is one of the major goals in orthopedic trauma surgery. The complex area of the occiput, atlas, and axis achieves the greatest mobility of any segment within the spine . The major part of the spine’s flexion, extension, and rotation occurs in the upper cervical spine (C0 to C2) [2, 3, 16, 17]. The primary motion of the occipitoatlantal segment is the flexion and extension, and additionally, the atlantoaxial joint is very mobile in axial rotation. As a result, the upper cervical spine is of utmost importance for mobility of the head. Therefore, it presents unique challenges to stable internal fixation in case of injuries. The complex anatomy of the cervical spine as well as the great range of motion in this area influences the surgeons regarding decision-making and execution of internal fixation. More stable procedures tend to reduce the range of motion significantly and, therefore, often result in greater impairment of the patients.
In most western countries, demographics show a graying trend over the last 30 years. The percentage of elderly patients with cervical spine injuries, secondary to falls, has been on the rise and will continue to increase in the future related to increased life expectancy. Geriatric patients have a higher risk of low-energy injuries secondary to osteopenia, osteoporosis, and decreased total mobility due to degenerative changes . Improvements in health contributed to the growth of the older population over the past century and result in greater activity of the elderly population. Upper cervical spine disorders are severe injuries due to the risk of myelopathy and death from proximal spinal cord compression.
Management of cervical spine injury in the elderly remains controversial because of many influencing factors such as the quality of the bone, osteoarthritis, classification, and type of the fracture [6, 7, 10, 19, 20]. Treatment might be complicated by numerous comorbidities and reduced bone quality. Therefore, injuries to the C1/C2 region are often treated posteriorly by fusion procedures which might be advantageous in a current meta-analysis . It can be difficult to achieve a balance between optimizing the stabilization and minimizing the impairment of motion.
Atlantoaxial fixation for C1/C2 injuries provides immediate biomechanical stability to the atlantoaxial complex and results in high arthrodesis rates (> 90%) [12, 22,23,24,25,26]. The advantage of this surgical technique is the greater range of motion by preserving the C0/C1 motion segment compared to occipitocervical fusion. Postoperatively, flexion and extension of the upper cervical spine are preserved. But atlantoaxial fixation is not always feasible in the elderly.
There are multiple OCF techniques currently available, and they have all proved high fusion rate and reduced pain levels [27, 28]. Currently, rod-wire systems, rigid rod-screw fixation, and occipital hooks and cervical claws are being used, and all shown to have high fusion rates (89–100%) [28,29,30,31]. Therefore, occipitocervical fusion allows a valid and reliable surgical technique in upper cervical spine disorders [11, 32,33,34,35] but is accompanied by severe limitation of range of motion of the neck [2, 36]. As a consequence, flexion and extension are reduced by 23–24.5°. Additionally, lateral bending and axial rotation are limited by 3.4–5.5° and 2.4–7.2°, respectively . Normally, the complex C0/C1 joint allows for > 50% of all head and neck movements .
Despite distinct impairment of range of motion, OCF often is the first choice for craniocervical instability in the elderly [38, 39]. Several studies [40,41,42,43] have shown that as age increases cervical spine mobility decreases. In the geriatric population, there is a frequent presence of osteoarthrosis of the upper cervical spine with subsequent primary limitation of extension and flexion of the neck. Kuhlmann  worked out that the elderly had significantly less range of motion at the upper cervical spine than the younger control group. This motion loss was greater for cervical extension and least for cervical flexion or rotation. This leads to the conclusion that geriatric patients with age-related restrictions, especially with reduced extension, do not feel strongly impaired after OCF.
Cappuccio et al.  recommended OCF in case of post-traumatic cervical instability because the C0/C1 joint sacrifice in an elderly ankylotic spine does not make a relevant clinical difference in the final functional outcome. In case of C2 fractures, Shousha et al.  compared anterior odontoid screw fixation with AAF and also concluded that the posterior motion preservation techniques should be limited to younger patients.
In this study, comparisons were made between demographic data, clinical outcomes, and complications after OCF and AAF based on the data of patients with at least 6-month follow-up. Regarding clinical outcomes, no statistically significant differences, such as NPRS or NDI score, were found between OCF and AAF. Moreover, additional fusion of the C0/C1 segment, with lack of flexion, extension, and rotation of the neck (OCF group), did not lead to an increase in pain or disability in daily life. Postoperatively, both study groups presented with nearly the same pain level (OCF, mean NPRS score 2.9; AAF, mean NPRS score 2.0). There were no statistical differences of NDI scores between both groups, but patients who underwent OCF had a slightly higher NDI score (moderate pain level) compared to patients after AAF (mild pain level). Hu et al.  compared the clinical outcome parameters between OCF and AAF in treatment of the unstable atlas fracture and reported that all patients had a significant improvement of neck pain after fixation of the upper cervical spine. But there was a statistically significant difference in the satisfaction of these both groups (p = 0.0085). All OCF patients (n = 20) complained of severe restriction of cervical spine flexion, extension, and rotation, and only 14 patients were satisfied with their outcome. Both groups had a restricted rotation of the neck, yet the additional OCFs’ restriction of the extension and flexion led to significant self-reported disability. The average age of the OCF group was 53 years (35–78) , and therefore, these patients were relatively young and might have had higher expectations of their postoperatively function.
A significant improvement in neck pain was also documented by Hu et al. . The average NPRS score of the AAF group was 1.0 ± 0.4 and 1.3 ± 0.9 of OCF patients postoperatively (p < 0.01). They used the Japanese Orthopaedic Association (JOA) score to assess the severity of clinical symptoms in their patients. According to our results, both groups presented with mild symptoms after fixation of their upper cervical spine. In summary, and according to other studies [28, 39, 47, 48], OCF and AAF enable a sufficient improvement of pain with a reasonable level of activities in daily life.
Our study shows a negative correlation between follow-up time and NDI score. The longer the follow-up time, the better the NDI score. Similar results were found by Yuan et al. . This implies a kind of patients’ adaptation to their disability and health state. Additionally, a positive correlation between the patients’ age and NDI score was found in our actual study. Advanced age was related to increased postoperative disability, thus an increased NDI score. The slightly higher NDI score of our OCF group can be explained by the fact that this patient collective has significantly more comorbidities than the AAF patients and displays a shorter follow-up period (OCF group 6.3 months versus AAF group 14.3 months). It is therefore to be expected that the NDI score of the OCF group will be even better with an extended follow-up time. It can be assumed that the current, relatively slight difference between both groups will even more decline. With the reduction of disabilities during follow-up, further approximation of the NDI score of AAF and OCF patients might be expected.
Regarding postoperative adverse events, no statistically significant differences, such as infection or revision rate, were found between our study groups. The postoperative revision rate was 13.6–17.3%, and the hematoma and/or infection rate was 4.5–7.7%. In a systematic review, Winegar et al.  reported about 68 documented cases of postoperative adverse events such as wound complications. Of these 68 cases, 21 cases exhibited wound infection and dehiscence. Therefore, their postoperative infection rate (30.9%) was much higher than in our study groups. Additionally, a higher wound infection rate (13.3%) was reported by another study .
We acknowledge the limitations of our study. The major limitation of this study was its retrospective design and relatively small sample sizes. Due to the advanced age of the collective, many patients were deceased at time of follow-up. The lack of long-term follow-up data is another limitation of this study. Additionally, we did not have data on preoperative scores (NDI and NRPS) or range of motion. Therefore, further data and studies are warranted.