Evaluation of Fracture Migration After Internal Fixation of Femoral Neck Fractures in Younger Adults: A Clinical RCT Using RSA

Objective The overall purpose of the study is to assess internal fixation methods for femoral neck fractures in adults under 65 years of age. The primary objective is to compare fracture migration following internal fixation with a novel angle-stable implant (Dynaloc, Swemac) and cannulated cancellous screws (CCS), using fracture migration as the primary outcome.

In addition, a cohort of patients treated with a sliding hip screw (SHS) as part of standard care will be included to provide an additional basis for comparison.

Dynaloc, CCS, and SHS are all CE-marked medical devices used in accordance with the manufacturers' intended use.

Trial design The study is designed as a multicentre, single-blinded randomised controlled trial with radiostereometric analysis (RSA), including an additional prospective cohort.

Patients undergoing internal fixation with Dynaloc or CCS will be randomised, while patients treated with a sliding hip screw will be followed as a separate cohort using the same imaging and follow-up protocol.

Interventions Eligible patients will be randomised to internal fixation with either three CCS or the Dynaloc implant.

Patients who do not undergo randomisation and are treated with SHS as standard care may be included in a prospective cohort and followed according to the study protocol.

All surgical procedures will be performed according to the manufacturers' surgical techniques and instructions for use.

Sample size calculation The primary outcome is shortening of the femoral neck at 12 weeks. A clinically relevant difference is defined as femoral neck shortening greater than 5 mm. Femoral neck shortening in patients treated with CCS is expected to be 5.3 mm (SD 4.5 mm) at 6 weeks, and no further clinically relevant shortening is expected between 6 and 12 weeks.

Using a power of 0.9, a significance level of 0.05, and assuming a maximum femoral neck shortening of 1 mm in the Dynaloc group compared with 5.3 mm (SD 4.5 mm) in the CCS group, a total sample size of 50 randomised patients (25 per group) is required.

In addition, a cohort of 25 patients treated with a sliding hip screw will be included for comparative purposes.

Inclusion will continue until all 50 randomised patients and all 25 cohort patients have completed the 12-week follow-up for the primary outcome. Due to the rarity of femoral neck fractures in this age group, up to approximately 20% additional patients may be included to ensure complete 12-week follow-up.

Randomization/allocation After informed consent is obtained, eligible patients will be enrolled and entered into an electronic database. Patients will be randomised to either CCS or Dynaloc using block randomisation with block sizes of 4 and 6. Randomisation will be stratified by Garden classification (Garden 1-2 vs. 3-4) to account for fracture displacement and by hospital of admission.

The operating surgeon will contact a central coordinator to perform the randomisation prior to surgery and will therefore know the allocated implant before entering the operating theatre.

Blinding Participants and care providers will be blinded to the allocated implant. A standardised description of the surgical procedure will be used. Treatment allocation will remain blinded during statistical analyses.

Data Collection Project staff will collect clinical data, CT scans, and radiostereometric X-rays and perform image analyses using AutoRSA. Screening will be conducted by the admitting physician. Baseline data will be collected during admission and entered directly into REDCap by project personnel.

Patient-reported outcome questionnaires will be distributed electronically via REDCap, with responses automatically uploaded to the database. Follow-up visits will take place in the outpatient clinic, where project personnel will complete and verify data entry.

Statistical methods Treatment groups will remain blinded during statistical analyses. Data distribution will be assessed and results presented accordingly. Continuous outcomes will be analysed using linear mixed-effects models, and categorical variables will be compared using χ² or Fisher's exact tests, as appropriate.

A p-value of <0.05 will be considered statistically significant. Postoperative complication rates will be defined as the combined incidence of complications and reoperations. Mortality will be analysed using Cox regression. Statistical analyses and graphical presentation will be performed using STATA 18 (StataCorp).