RHEVOLUTION Clinical Trial: Radial Head Arthroplasty for the Treatment of Acute Traumatic Elbow Instability, a Randomized Trial Comparing Two Implant Designs

Study Title: RHEVOLUTION Clinical Trial: Radial Head Arthroplasty for the Treatment of Acute Traumatic Elbow Instability, a Randomized Trial Comparing Two Implant Desings

Principal Investigator: Dr. Blanca Diez Sánchez, MD, PhD. Orthopaedic Department blanca.diez@salud.madrid.org Collaborators: Dr. Raúl Barco, Dr. Juan Ameztoy Gallego, Dr. Luis Palacios, Dr. Alfonso Vaquero-Picado and Dr. Samuel Antuña Institution: Hospital Universitario La Paz

1. Abstract:

Study design: A randomized, parallel-group, single-blind clinical trial that will use two radial head arthroplasty designs (an anatomic design from Skeletal Dynamics and a smooth-stemmed spacer from Stryker) for the treatment of elbow fracture-dislocations. These two arthoplasty designs are already used in routine clinical practice at our center. However, patients are currently assigned one or the other based on availability and surgeon preference, not randomized. In the RHEVOLUTION clinical trial, patients will be randomly assigned to one radial head arthroplasty or the other, so that the patient (single-blind) will not know which implant they have received. There will be no active patient recruitment; instead, patients will be enrolled in the study if they meet the inclusion criteria and are referred consecutively to the department.

Inclusion criteria: Age over 18 years, acute, non-reconstructable radial head fracture, able to understand the informed consent and provide written consent and compliant with the planned clinical follow-up: at 6 weeks, 3 months, 6 months, 12 months, and 24 months. Only patients who underwent acute surgery using either of the two designs will be included.

Randomization will be performed using permuted blocks, with stratification by age group (18 to <50 years and ≥50 to 90 years) and fracture pattern (simple patterns include fractures with medial or posterolateral instability and complex patterns include the terrible triad and transulnar fracture-dislocations and Monteggia variants).

Primary objective: To compare the patient-reported Mayo Elbow Performance Score (MEPS) at 24 months. Secondary objectives include evaluating flexion-extension range of motion, pronation-supination, pain, patient satisfaction, Oxford Elbow Scale, Disabilities of the Arm, Shoulder and Hand Scale (Quick-DASH), radiological findings, and complications. Patients will be reviewed clinically and radiographically at 6 weeks, 3 months, 6 months, 12 months, and 24 months. 2. Background and rationale:

Radial head arthoplasty is a recognized treatment for comminuted radial head fractures or those associated with olecranon fractures or ligamentous injuries that lead to complex instability patterns of the elbow. There are two main philosophies in implant design: anatomic models and simpler prostheses that act as a spacer. Anatomic designs aim to replicate the native anatomy, with an elliptical head and a press-fit stem that must osseointegrate to function in its intended position. Spacer models, on the other hand, have a spherical head and a smooth, polished stem that does not integrate with the bone but has some mobility within the radial canal. Companies like Skeletal Dynamics have designed anatomic arthroplasties like the Align design, while others like Stryker Corporation has design a smooth stem spacer called Evolve.

Anatomic press-fit designs have demonstrated good clinical results in retrospective studies, but also radiological findings such as loosening and proximal bone loss in the radial neck, associated with elbow stiffness. Spacer-type models, while showing good clinical results, are inherently loose, making it difficult to assess the clinical significance of the radiolucent lines observed in radiographic follow-up, which some authors have linked to forearm pain.

These two designs are used in routine clinical practice at our center, but the literature lacks prospective data comparing the outcomes between these two implant philosophies or randomized controlled trials. Currently, no randomized clinical trial has demonstrated differences in outcomes between the two prosthesis designs, highlighting a critical gap in the available evidence.

Complications of radial head arthroplasty include: Oversizing of the prosthesis, with persistent pain and the need for removal; loosening, with the appearance of radiolucent lines around the stem; stress shielding, due to changes in load transfer in designs with proximal bone integration; subluxation or misalignment of implants; residual instability.

Implants used in RHEVOLUTION clinical trial: both the Align Anatomic radial head replacement (Skeletal dynamics) and the Evolve system (Stryker corporation) will be used in this study. 3. Hypothesis and objetives:

Our hypothesis is that different radial head arthoplasty designs will present distinct clinical efficacy and safety in the treatment of comminuted radial head fractures associated with elbow instability. The investigators propose that there is no single prosthesis universally valid for all patients and injury patterns, but rather implants with specific advantages and limitations whose suitability depends on the clinical, anatomical, and functional characteristics of each case. This allows for a more personalized implant selection in routine clinical practice. Both prosthesis designs can provide satisfactory clinical and functional results for radial head fractures, but there will be specific conditions and complications for each design that could justify the use of one prosthesis or the other depending on the characteristics of each patient.

Primary objetive: To compare functional outcomes at 24 months postoperatively between groups using the Mayo Elbow Performance Score (MEPS) in a superiority clinical trial.

Secondary objectives: compare clinical outcomes (Range of motion, satisfaction, strength, Oxford elbow score, and Quick-DASH), complications (infection, stiffness, neurological injury, revision surgery) and radiologic results (implant malposition, oversizing, loosening, stress shielding, and ectopic bone deposits). 4. Study design:

Prospective, single-center, randomized clinical trial comparing:

Align anatomic radial head replacement and Evolve smooth-stem spacer for comminuted fractures. Allocation ratio: 1:1 Randomization: permuted blocks, with stratification by age group (18 to <50 years and ≥50 to 90 years) and fracture pattern (simple patterns include fractures with medial or posterolateral instability and complex patterns include the terrible triad and transulnar fracture-dislocations and Monteggia variants). Surgeons and investigators cannot be blinded due to prosthesis design.

Minimum follow-up: 24 months. Recruitment: Consecutive until target sample size reached. 5. Study population:

All consecutive patients diagnosed with a radial head fracture non amendable to fixation who meet eligibility criteria and provide informed consent.

Inclusion criteria: Age over 18 years, acute, non-reconstructable radial head fracture, able to understand the informed consent and provide written consent, able to and compliant with the planned clinical follow-up: at 6 weeks, 3 months, 6 months, 12 months, and 24 months. Patients who underwent acute surgery using either of the two designs, excluding treatment for sequelae. 6. Study variables:

Demographic Variables, including age, sex, affected side, dominance, fracture type, energy of the traumatism, occupational activity.

Clinical variables: Mayo Elbow Performance Score (MEPS), range of motion, satisfaction, strength, Oxford elbow score, and Quick-DASH. Complications (infection, stiffness, neurological injury, revision surgery) Radiological variables: implant malposition, oversizing, loosening, stress shielding, and heterotopic ossifications. 7. Data source:

Data will be collected from the electronic medical record system (HCIS) of La Paz University Hospital.

Patients will be pseudonymized using a study identification number. Data will be stored in Excel databases on secure hospital servers. Retention period: During the study and up to 10 years after completion. 8. Statistical analysis plan:

Sample size calculation: The sample sizes for groups of 40 and 40 (80 participants) achieve 87% power to detect a 6-point difference between the null hypothesis that the means of MEPS for both groups are 94 and the alternative hypothesis that the mean of group 2 is 88, with estimated standard deviations for the groups of 7 and 10 and a significance level (alpha) of 5% using a two-tailed t-test. Taking into account loss to follow-up, approximately 10% is added to the total estimated sample size, resulting in sample sizes for groups of 45 and 45 (90 participants in total). 9. Ethical considerations:

Conducted in accordance with:

Good Clinical Practice (GCP) Declaration of Helsinki (75th WMA General Assembly, 2024) Spanish Law 14/2007 on Biomedical Research GDPR (EU 2016/679) Spanish Organic Law 3/2018 Approved by the Research Ethics Committee (CEIm) of La Paz University Hospital. 10. Data management and privacy:

Data will be pseudonymized. Only investigators will access identifiable information.

Re-identification permitted only if necessary for patient safety. Access restricted to investigators, ethics committee, health authorities, and inspectors. 11. Biological Samples /adverse drug reactions:

Not applicable. 12. Publication and transparency:

Results will be published in a peer-reviewed scientific journal. Data retained for up to 10 years. 13. Funding: No external funding. 14. Conflict of interest:

Investigators declare no conflicts of interest.