The goal of this clinical trial is to compare two treatment options-surgery or rigid collar bracing-for unstable neck fractures (odontoid fractures) in adults aged 70 years and older. These fractures are common in older adults and can significantly impact mobility, independence, and quality of life. There is currently no clear evidence to determine which treatment is better for this population. The main questions it aims to answer are:

• Does surgery or conservative collar treatment lead to better improvement in daily living, measured by the Barthel Index, after 12 weeks?
• What are the differences in pain, disability, and quality of life between the two treatments?

The study team will compare patients who receive surgical stabilization with those who are treated with a rigid cervical collar to see which approach supports better functional outcomes and healing.

Participants will:

• be randomly assigned to either surgery (posterior C1-C2 screw-rod fixation) or conservative collar treatment
• attend study visits at 12 weeks and 6 months
• complete questionnaires on daily functioning, pain, and quality of life
• undergo CT scans and other medical assessments
• record collar use (for conservative group) in a diary
• be monitored for any complications or changes in treatment (including crossover to surgery if needed)

The study aims to include 322 participants to provide evidence on which treatment helps older adults recover better from odontoid fractures with fewer complications and improved quality of life.

The SCORE study is a multicenter, randomized, controlled, open-label, parallel-group non-inferiority trial designed to provide evidence on whether conservative treatment is non-inferior to surgical stabilization regarding recovery of daily functioning.

Study Objectives A) Primary Objective: To compare the effectiveness of surgical versus conservative treatment for unstable OFs in patients aged 70 or older in terms of recovery in activities of daily living, measured by the change in Barthel Index (BI) from baseline to 12 weeks.

B) Secondary Objectives: To compare the effects of treatment on:

• Quality of life (EQ-5D)
• Neck pain (Visual Analog Scale)
• Neck-specific disability (Neck Disability Index)
• Radiographic fracture healing
• Treatment compliance
• Rate of crossover from conservative to surgical treatment
• Incidence of adverse and serious adverse events

This is a prospective, two-arm, multicenter, randomized controlled non-inferiority trial with parallel-group design. Patients will be randomized 1:1 to receive either surgical stabilization (posterior C1-C2 screw-rod fixation) or conservative treatment with a rigid cervical collar. Randomization will be stratified by center using permuted blocks via the secure online platform randomizer.at. Participants are followed up at 12 weeks and 6 months post-injury. An additional visit ~2 weeks after surgery is conducted for those undergoing surgical treatment. Patients in the conservative arm may cross over to surgery up to week 12, based on clinical indication or patient preference.

Intervention Descriptions A) Surgical Group: Posterior stabilization using a screw-rod system without additional external bracing. The surgery lasts ~100 minutes and requires ~6 days of hospital stay. This approach is tailored for geriatric patients and excludes anterior fixation due to biomechanical concerns in the elderly.

B) Conservative Group: External immobilization using a rigid cervical collar for 12 weeks. Compliance is monitored via patient diaries, acknowledging real-world challenges in consistent brace use. Lack of adherence is considered reflective of routine clinical practice.

Statistical Analyses The primary analysis will assess non-inferiority of conservative treatment versus surgery using a mixed model for repeated measures (MMRM) of the BI at 12 weeks. Covariates include treatment, time, interaction terms, baseline BI, age, and CCI; study center is treated as a random effect (excluded if convergence fails). Non-inferiority is defined by a margin of 5 BI points, which is more conservative than the minimal clinically important difference (MCID) of 9.8 and closer to the smallest detectable change (SDC) of 3.0, based on prior studies. The study has 90% power to detect non-inferiority (one-sided α = 0.025). A total of 137 patients per arm (274 total) are needed, inflated to 322 to account for 15% attrition.

Secondary analyses will use similar mixed models for continuous variables and generalized estimating equations for binary outcomes. Sensitivity analyses include "as-treated" models accounting for crossover. No adjustment for multiple comparisons will be made.

Randomization Procedure Randomization is conducted after informed consent via randomizer.at. Lists are stratified by center and use permuted blocks. Access is password-protected and managed by study personnel.

An independent Data and Safety Monitoring Board (DSMB) will oversee the study. All adverse events and serious adverse events are recorded at each visit and coded per MedDRA prior to analysis.

Inclusion Criteria:

• At least 70 years old
• Acute unstable OFs (types II, III as classified by Anderson and d'Alonzo, and atypical)
• Less than two weeks post injury
• Written informed consent

Exclusion Criteria:

• Previous treatment for odontoid fracture
• Concomitant fractures of the subaxial cervical spine necessitating surgery
• Significant comorbidity resulting in inoperability of the patient: i.e. ASA score > 4
• Neurological compromise due to displaced fracture