The CARBO CARBON Study

Healthcare contributes substantially to global greenhouse gas emissions, with orthopedic surgery representing a resource- and carbon-intensive part of the healthcare system. For metacarpal shaft fractures, surgical treatment is widely used despite limited evidence of superiority to non-operative management. The difference in environmental impact of the two treatment options remains unexplored.

This prospective multicenter observational comparative cohort study is conducted alongside a randomized controlled trial called the MetaCARpalBOne trial (The CARBO trial). Environmental impact will be estimated using LCA according to four standard phases: (1) goal and scope definition, (2) Life Cycle Inventory (LCI), (3) Life Cycle Impact Assessment (LCIA) and (4) interpretation including sensitivity and uncertainty analysis. All this will be based on detailed activity data for materials, energy use, pharmaceuticals and waste across the treatment pathway from inclusion in the study to 12 months post-treatment. Climate change impact will be calculated within defined system boundaries and expressed as kilograms of carbon dioxide equivalent (CO₂e) per treatment pathway. The primary outcome is the difference in mean CO₂e between treatment groups. Secondary outcomes include fine particulate matter formation, water consumption, weight of combustible waste and direct cost differences. Explorative outcomes will include all other environmental impact categories covered by the selected LCIA method and identification of major emission hotspots.

Appropriate parametric or non-parametric statistical tests will be applied to estimate the difference between treatment pathways. Normal distribution will be tested by Kolmogorov-Smirnov and Shapiro Wilk's test. If data is not normally distributed, we will present a median with a corresponding interquartile range and compare groups by Mann-Whitney U-test. To account for uncertainty both in the life cycle assessment (LCA) estimates and in the intervention effect, Monte Carlo-generated datasets will be analyzed using a linear mixed-effects modelling approach. The robustness of the results for the primary and secondary outcomes will be assessed using sensitivity analyses changing key assumptions regarding: energy mix, lifespan of products, allocations, and anesthesiology methods.

The study evaluates environmental impact and costs only and does not involve analysis of personal data. Ethical approval has been obtained from the Swedish Ethical Review Authority (DNR 2025-04413-01; amendment DNR 2025-07659-02). Results will be disseminated through peer-reviewed publications.

Inclusion criteria

for the CARBO trial:

Age ≥18 years.

Access to a valid e-mail.

Injury within 10 days prior to inclusion.

Normal bilateral hand function prior to injury.

Ability and willingness to provide written informed consent

Single, displaced spiral or oblique diaphyseal fracture of the second to fifth metacarpals with definition of diaphysis as described by AO 2018 (AO/OTA as 77.2-5.2A) (Meinberg et al., 2018).

Fracture line length at least twice the diameter of the bone at the level of the fracture.

Fractures with at least 2 mm of radiological displacement and/or malrotation of injured finger compared to uninjured side regardless of fracture displacement.

Exclusion criteria

The patient is not expected to have difficulty adhering to the study protocol (e.g., due to insufficient language proficiency, dementia, substance abuse, or other reasons).

The patient does not have an open fracture (Gustilo-Anderson grade > I) or a pathological fracture.

The patient does not have an ipsilateral fracture of the upper extremity, polytrauma, or generalized joint dysfunction (e.g., rheumatoid arthritis).