Early Fracture Migration After Internal Fixation of Femoral Neck Fractures in Young Adults

The goal of the clinical trial is to assess a novel implant (Dynaloc, Swemac) for internal fixation of femoral neck fractures and compare it to standard treatment with cannulated cancellous screws using AutoRSA (Radiostereometric analysis).

The main question it aims to answer is:

Is internal fixation with the novel implant consisting of three angle stable screws locked together by a plate equal to internal fixation with cancellous screws in young adults under 65 years of age in terms of fracture migration?

Researchers will assess postoperative complications and functional outcomes as well as fracture migration using AutoRSA.

The participants will be treated with either Dynaloc or cannulated cancellous screws and followed up at 6 weeks, 12 weeks, 6 months and 12 months.

Objective The overall purpose is to assess a novel implant (Dynaloc, Swemac) for internal fixation of femoral neck fractures and compare it to treatment with cannulated cancellous screws (CCS) using fracture migration as the primary outcome.

Both Dynaloc and CCS are CE-marked medical devices used as intended by the manufacturer.

Trial design The study is designed as a single blinded randomised controlled trial (RCT) with Radiostereometric Analysis (RSA).

Interventions Patients will be randomised to internal fixation with three CCS or a novel implant designed to minimise fracture migration (Dynaloc, Swemac). The operation procedures will be according to the manufacturer's surgical technique/instructions for use.

Sample size calculation Primary outcome is shortening of the femoral neck at 12 weeks. A clinical relevance can be expected at \>5mm shortening of the femoral neck. Femoral neck shortening in the group randomised to internal fixation with CCS is expected to be 5.3mm (SD 4.5mm) at 6 weeks according to Van Embden et. al. and we do not expect further shortening of the femoral neck between 6 and 12 weeks.

Using power 0.9, significance level 0.05, and expecting femoral neck shortening of maximum 1 mm for the angle stable implant (Dynaloc) compared with 5.3mm (SD 4.5mm) using three CCS a total sample size of N=50 can be calculated, N=25/group in this equality study design.

We expect approximately 10% loss to follow-up and will therefore include a total of 54 patients.

Randomization/allocation If informed consent is provided, eligible patients can be enrolled in the study.

Patients will be entered into an electronic database and randomised to either CCS or Dynaloc using blocks of n=4 and n=6 and will be stratified based on the Garden classification (Garden 1-2 or 3-4) to account for fracture displacement and stratified based on hospital of admission. The patients will be stratified according to the Garden classification as studies show significantly higher failure rates in Garden type 3 and 4. The operating surgeon will contact a central coordinator, who performs the randomisation, prior to the surgery. Therefore, the surgeon knows which implant to use before entering the operating theatre.

Blinding The implant and outcome will be blinded to participants and care providers. A standard phrase for the surgery will be used.

Data Collection Project staff will collect data, CT scans and radiostereometric x-rays and will analyse using AutoRSA. Screening will be performed by the admitting doctor. Baseline data will be collected during admission and will be entered directly into REDcap by project personnel. Questionnaires will be sent directly to the patients using REDcap, and the answers will be automatically uploaded into REDcap. At follow ups, project personnel will see the patients in the outpatient clinic, and enter data directly into REDcap.

Statistical methods Randomisation groups will be kept blinded during statical analyses. The data distribution will be assessed and data presented accordingly. Continuous data will be analysed using Linear Mixed Model statistics and categorical data will be compared using the χ2 test or the Fisher exact test.

A p-value of \<0.05 will be considered statistically significant. The postoperative complication rates will be defined as the sum of the individual rates of complications and reoperations. Mortality will be analysed using Cox-regression. Computerised statistical software packages (STATA 18, StataCorp) will be used for analyses and graphical presentation.

Eligibility Criteria:
Inclusion Criteria:

* Femoral neck fracture (DS720)
* Age 18-64 years
* Ability to speak and read Danish
* Willingness to participate

Exclusion Criteria:

* Pathological, basicervical or transcervical fracture
* Clinical Frailty Scale ≥5, indicating mild to severe frailty prior to the fracture
* Cognitive impairment that hinders informed consent
* Previous fracture in the ipsilateral femur
* Patients who are unwilling or incapable of following post-operative care instructions.
* Comorbidities making the participant ineligible for internal fixation such as:

  * Material sensitivity, documented or suspected
  * Active or suspected latent infection, sepsis or marked local inflammation in or around the surgical area
  * Compromised vascularity, inadequate skin or neurovascular status
  * Compromised bone stock that cannot provide adequate support and/or fixation of the device due to disease, infection or prior implantation
  * Other physical, mental, medical or surgical conditions that would preclude the potential benefit of surgery.