metaCARpal Bone Osteosynthesis Trail (CARBO)

The CARBO Study (metaCARpal Bone Osteosynthesis)

Background Metacarpal shaft fractures account for 30-50% of hand fractures (Karl et al., 2015; Kollitz et al., 2014; van Onselen et al., 2003), with diaphyseal spiral and oblique fractures of the second to fifth ray posing unique challenges due to the risks of shortening and rotational deformities. Current standard care of displaced fractures involves operative fixation.

However, retrospective studies have indicated that nonoperative treatment, involving early mobilization or buddy taping, can achieve outcomes comparable to operative treatment (Daher et al., 2023). There is only one published, with a small sample size, randomized controlled trial (RCT) investigating this issue (Peyronson et al., 2023). This highlights the need for a robust multicenter RCT to address these gaps in evidence.

Aim The aim of this study is to compare the one-year outcomes of non-operative treatment involving immediate unrestricted mobilization versus operative treatment of displaced oblique or spiral diaphyseal metacarpal fractures in adults.

Materials and Methods This is a multicenter, pragmatic, prospective, noninferiority RCT involving 552 adult patients with displaced oblique and/or spiral diaphyseal metacarpal fractures of the second to fifth ray. Participants will be randomized 1:1 to receive either nonoperative treatment with unrestricted mobilization and rehabilitation) or operative treatment (with screw or plate fixation) followed by rehabilitation.

The primary outcome is grip-strength in the injured hand presented in kilograms at one year.

Secondary outcomes include questionnaires, complications, range of motion, patient reported outcome measures, health related quality of life, patient satisfaction, and radiographic healing.

A power calculation proposes a study size of 552 participants to detect a noninferiority margin of 10% in grip strength.

Study Overview

• Status: Recruiting
• Conditions: Metacarpal Shaft Fractures
• Intervention / Treatment: Procedure: Non-operative treatment with early mobilization; Procedure: Operative treatment

• Study Type: Interventional
• Enrollment (Estimated): 552
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Cecilia Mellstrand Navarro, Associate professor; Phone Number: +46709280114; Email: cecilia.mellstrand.navarro@ki.se
• Study Contact Backup: Name: Elsa Pihl, PhD; Phone Number: +46739705669; Email: elsa.pihl@ki.se

Study Locations

• Sweden
  • Stockholm County
    • Stockholm, Stockholm County, Sweden, 18288
      • Recruiting
      • Karolinska Institutet, Danderyd's hospital
      • Principal Investigator: Cecilia Mellstrand Navarro, MD, PhD
      • 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
      • Sub-Investigator: Elsa Pihl, MD, PhD

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• 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?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Non-operative with early mobilization; Participants randomized to the nonoperative group will receive immediate unrestricted mobilization, with optional buddy taping or removable splinting for comfort. Closed reduction will not be attempted. Rehabilitation protocol with early mobilization will be standardized across study centers with printed standardized information to patients and rehabilitation staff.	Procedure: Non-operative treatment with early mobilization; Participants randomized to the nonoperative group will receive immediate unrestricted mobilization, with optional buddy taping or removable splinting for comfort. Closed reduction will not be attempted. Rehabilitation protocol with early mobilization will be standardized across study centers with printed standardized information to patients and rehabilitation staff.
Active Comparator: Operative; Participants randomized to the operative group will undergo open reduction and internal fixation (ORIF) of the MSF. Peri-operative antibiotic prophylaxis will be administered according to local guidelines. The surgical approach and fixation method (e.g. compression screws and/or plate, not K-wires) will be at the discretion of the treating surgeon, following standard surgical principles. Postoperative immobilisation will adhere to surgeons' preference but not exceed two weeks fixation.	Procedure: Operative treatment; Participants randomized to the operative group will undergo open reduction and internal fixation (ORIF) of the MSF. Peri-operative antibiotic prophylaxis will be administered according to local guidelines. The surgical approach and fixation method (e.g. compression screws and/or plate, not K-wires) will be at the discretion of the treating surgeon, following standard surgical principles. Postoperative immobilisation will adhere to surgeons' preference but not exceed two weeks fixation.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Grip strength	The primary outcome is grip-strength measured in the injured hand using a JAMAR dynamometer at 12 months and presented in kilograms. Measurement method will follow the technical description presented in the HAKIR manual (HAKIR, 2023).	From enrollment to the end of follow-up at 12 months

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Complications	infection, malunion, nerve injury, reoperation	From enrollment to the end of follow-up at 12 months
Pain in injured hand NRS	NRS (Numerical Rating Scale) at rest and when it is at its worst	From enrollment to the end of follow-up at 12 months
Rotational deformity	0 - no deformity, 1 - minimal deformity, 2 - clearly visible deformity but acceptable functional limitation, 3 - great deformity and functional limitation	12 months
PROM - patient rated outcome measure	Quick-DASH-9 score (Gabel et al., 2009)	6, 12 weeks, 12 months
Range of motion	total active motion and extension lag	6, 12 weeks, 12 months
Pinch grip strength		12 weeks, 12 months
Radiographic shortening	according to Sletten (Sletten et al., 2013)	12 months
Radiographic healing	defined as bridging callus formation over the fracture line on a plain x-ray anterio-posterior and/or lateral projection. (Hayes et al., 2023)	12 weeks, 12 months
Sick leave duration	in days	12 months
Patient satisfaction	Patient Acceptable Symptom State, PASS (Daryoush et al., 2025)	From enrollment to the end of follow-up at 12 months
Quality of life measured by PROM	EQ-5D EuroQol Group, 1990; Taft et al., 2004)	From enrollment to the end of follow-up at 12 months
Quality of life measured by SF-12	SF-12 (EuroQol Group, 1990; Taft et al., 2004)	From enrollment to the end of follow-up at 12 months

Collaborators and Investigators

• Sponsor: Karolinska Institutet
• Collaborators: University of Oslo; Uppsala University; Göteborg University; Umeå University; Linkoeping University; Tampere University; Region Stockholm; Östersund Hospital; Københavns Universitet

Study record dates

Study Major Dates

• Study Start (Actual): March 23, 2026
• Primary Completion (Estimated): March 15, 2030
• Study Completion (Estimated): March 15, 2031

Study Registration Dates

• First Submitted: December 15, 2025
• First Submitted That Met QC Criteria: January 21, 2026
• First Posted (Actual): January 22, 2026

Study Record Updates

• Last Update Posted (Actual): March 24, 2026
• Last Update Submitted That Met QC Criteria: March 23, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: mobilization; operative; Non-operative; shaft; displaced; metacarpal
• Additional Relevant MeSH Terms: Therapeutics; Patient Care; Rehabilitation; Aftercare; Continuity of Patient Care; Early Ambulation
• Other Study ID Numbers: 2025-04413-01; FoUI-1022484 (Other Grant/Funding Number: ALF Region Stockholm)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Data on group level will be made available upon reasonable request.

Drug and device information, study documents

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