The CARBO CARBON Study (CARBO CARBON)

The CARBO CARBON Study: a Prospective Observational Comparative Cohort Study on Environmental Impact From Two Metacarpal Shaft Fracture Treatment Pathways

This study examines the environmental impact of two common treatment pathways for hand fractures (metacarpal shaft fractures): surgical and non-surgical management. Healthcare contributes significantly to climate change, and orthopedic surgery in particular generates substantial greenhouse gas emissions. Although surgical treatment is frequently favored for these fractures, it is not always superior to non-surgical treatment, and the difference in environmental impact between these options is not well understood.

In this study, researchers will measure and compare the environmental impact of each treatment pathway, from inclusion to twelve months follow-up. This includes environmental impact related to single-use material, medical equipment, energy use, medications, and waste. A Life Cycle Assessment (LCA) will be performed and a mean difference in environmental impact between treatments pathways will be calculates. A Hotspot analysis will also be performed to highlight key sources of environmental impacts. The findings may help guide more sustainable healthcare practices without compromising patient care.

Study Overview

• Status: Recruiting
• Conditions: Metacarpal Shaft Fractures; Greenhouse Gas Emissions
• Intervention / Treatment: Procedure: Non-operative treatment; Procedure: Surgical fixation

Detailed Description

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.

• Study Type: Observational
• Enrollment (Estimated): 30
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Cecilia Mellstrand Navarro, MD, PhD; Phone Number: +46709280114; Email: cecilia.mellstrand.navarro@ki.se
• Study Contact Backup: Name: Elsa Pihl, MD, PhD; Phone Number: +46 8 123 550 00; Email: elsa.pihl@ki.se

Study Locations

• Sweden
  • Stockholm County
    • Stockholm, Stockholm County, Sweden, 18288
      • Recruiting
      • Karolinska Institutet, Danderyd's hospital
      • Contact: Cecilia Mellstrand Navarro, MD, Ass Professor; Phone Number: +46 709 280114; Email: cecilia.mellstrand.navarro@ki.se
      • Contact: Elsa Pihl, MD, PhD; Phone Number: +46739705669; Email: elsa.pihl@ki.se

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

The observational cohorts will include all patients enrolled in the CARBO trial, where participants are randomized to either surgical or non-surgical management. The intervention cohort will consist of patients allocated to non-surgical management, whereas the control cohort will comprise patients allocated to surgical management.

Description

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).

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Non operative treatment, early mobilisation; Non-operative treatment by immediate unrestricted mobilization with optional buddy taping or removable splinting for comfort	Procedure: Non-operative treatment; Non-operative treatment through immediate unrestricted mobilization with optional buddy taping or removable splinting for comfort.
Operative treatment, open reduction and surgical fixation; Operative treatment, open reduction and surgical fixation with plate and screws or screws only, post operative plaster immobilisation followed by rehabilitation	Procedure: Surgical fixation; Open reduction and internal fixation with plate and screws or screws only, followed by postoperative imobilisation and rehabilitation.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Global warming potential	The primary outccome is global warming potential expressed as the mean carbon dioxide equivalent (CO₂e) emissions between the treatment pathways early rehabilitation without surgery and surgical treatment followed by rehabilitation of metacarpal shaft fractures. Our functional unit is defined as the full treatment pathway from inclusion in the study to 12 months post-treatment	12 months

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Waste	Include the total weight of combustible waste generated at each healthcare visit, measured in kilograms using a calibrated hanging scale	12 months
Direct costs	Difference in direct costs within our study boundary between the treatment methods.	12 months
Ambient air pollution	The mean emission of ambient air pollution expressed as fine particle matter formation (PM2.5) for the two treatment pathways.	12 months
Water comsumption	The mean water comsumption in cubic meters for the two treatment pathways.	12 months

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Emission hotspots	Identification of major emission hotspots (e.g., operating room energy use, single-use materials, pharmaceuticals, transport).	12 months
Environmental impact categories	All other environmental impact categories covered by the selected LCIA method	12 months

Collaborators and Investigators

• Sponsor: Karolinska Institutet
• Investigators: Principal Investigator: Cecilia Mellstrand Navarro, MD, PhD, ass professor, Karolinska Institutet

Study record dates

Study Major Dates

• Study Start (Actual): March 23, 2026
• Primary Completion (Estimated): March 1, 2028
• Study Completion (Estimated): March 1, 2028

Study Registration Dates

• First Submitted: April 2, 2026
• First Submitted That Met QC Criteria: April 2, 2026
• First Posted (Actual): April 13, 2026

Study Record Updates

• Last Update Posted (Actual): June 4, 2026
• Last Update Submitted That Met QC Criteria: June 2, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: metacarpal fractures; carbon dioxide emissions; LCA analysis; greenhouse gas emissions; carbon dioxide equivalent
• Additional Relevant MeSH Terms: Surgical Equipment; Equipment and Supplies; Surgical Fixation Devices
• Other Study ID Numbers: 2025-07659-02

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No