Thumb carpometacarpal osteoarthritis is common and may cause severe pain and functional limitation. Trapeziectomy is widely used, whereas prosthetic arthroplasty may offer faster early recovery. However, detailed information on early postoperative and long-term radiological outcomes remains limited.

This is a single-centre, blinded randomised controlled trial at Sahlgrenska University Hospital, Gothenburg, Sweden. Adults aged 18-69 years with symptomatic thumb carpometacarpal osteoarthritis (Eaton grade 2-3) refractory to at least 3 months of non-operative treatment will be randomised 1:1 to trapeziometacarpal prosthetic arthroplasty or trapeziectomy. The primary outcome is day-by-day pain (registration on a numeric rating scale NRS, 0-10). Secondary outcomes include day-by-day analgesic consumption for 90 days, orthosis use after cast removal, patient-reported function (HQ-8, QuickDASH, and Nelson score) at 30, 45, 60, 75 and 90 days, assessor-measured range of motion and strength at 45 and 90 days, and long-term clinical follow-up at 6 months and 1, 2, 5 and 10 years. Cone beam computed tomography will be obtained in the arthroplasty group at 1 week postoperatively as reference and at 6 months and 1, 2, 5 and 10 years to assess implant position, migration and loosening. The target sample size is 64 participants (32 per group), providing 95% power to detect a 1-point between-group difference on the pain scale. Analyses will follow the intention-to-treat principle.

Aim and objectives The primary aim is to compare early postoperative pain trajectories after CMC-1 arthroplasty versus trapeziectomy for symptomatic thumb carpometacarpal osteoarthritis, using day-by-day patient-reported pain measurements during the first 90 postoperative days.

Secondary aims are to compare:

(i) Daily analgesic consumption during the first 90 postoperative days (ii) Orthosis use after cast removal (iii) Patient-reported hand/upper limb function using HQ-8, QuickDASH and Nelson score (iv) Blinded clinical measures of thumb range of motion, grip strength and pinch strength (v) Long-term clinical outcomes up to 10 years. Additionally, in the arthroplasty group, a long-term aim is to evaluate migration and radiological signs of implant loosening using cone beam computed tomography (CBCT). Similarly, in the trapeziectomy group, CBCT will be used to monitor and quantify metacarpal 1 proximal migration.

This protocol has been prepared in accordance with SPIRIT 2025 guidance [18], and includes a PRO EDI participant characteristics (Table 1).

Trial design This is a single-centre, assessor-blinded randomised controlled trial (RCT) with 1:1 allocation to prosthetic CMC-1 arthroplasty or trapeziectomy.

Study setting The study will be conducted at the Hand Surgery Clinic, Sahlgrenska University Hospital, Gothenburg, Sweden. All operations will be performed by surgeons experienced in both techniques at least level 3 according to Giddins-Tang classification [19] and have at minimum overcome the previously described learning curve thresholds [20,21].

Eligibility criteria

Inclusion criteria:

• Pain at the base of the thumb affecting activities of daily living and insufficient response to at least 3 months of non-operative treatment (orthosis, non-steroidal anti-inflammatory drugs, and/or corticosteroid injections).
• Radiographic thumb carpometacarpal osteoarthritis, Eaton grade 2-4.
• For Eaton grade 2, age ≥50 years.
• Age 18-69 years.
• Provision of written informed consent.

Exclusion criteria:

• Symptomatic osteoarthritis of adjacent joints (e.g., scaphotrapeziotrapezoid joint, STT-joint).
• Need for concurrent surgery in the metacarpophalangeal joint (e.g. arthrodesis or capsulodesis).
• Post-traumatic thumb carpometacarpal osteoarthritis.
• Previous surgery for thumb carpometacarpal osteoarthritis in the contralateral hand.
• Inflammatory arthritis (e.g., rheumatoid arthritis or systemic lupus erythematosus).
• Osteoporosis/osteopenia of such severity that secure cup placement in the trapezium is not possible (for arthroplasty).
• Ongoing systemic corticosteroid treatment.
• Other hand surgical condition in the same hand that could confound outcomes (e.g., carpal tunnel syndrome or de Quervain tenosynovitis).
• Cognitive impairment preventing reliable participation.
• Ongoing, or suspected ongoing, alcohol or drug misuse.
• Insufficient Swedish language proficiency to complete the questionnaires.

Participant identification, recruitment and consent Potential participants will be identified among patients referred for surgical evaluation of symptomatic thumb carpometacarpal osteoarthritis at the study site. Eligible patients will receive verbal and written information about the study. Written informed consent will be obtained before any study-specific data collection.

At baseline, participants will complete the HQ-8, QuickDASH and Nelson score questionnaires. Baseline demographic characteristics will be recorded in line with the PRO

Inclusion Criteria:

• Pain at the base of the thumb affecting activities of daily living and insufficient response to at least 3 months of non-operative treatment (orthosis, non-steroidal anti-inflammatory drugs, and/or corticosteroid injections).
• Radiographic thumb carpometacarpal osteoarthritis, Eaton grade 2-3.
• For Eaton grade 2, age ≥50 years.
• Age 18-69 years.
• Provision of written informed consent.

Exclusion Criteria:

• Symptomatic osteoarthritis of adjacent joints (e.g., scaphotrapeziotrapezoid joint, STT-joint).
• Need for concurrent surgery in the metacarpophalangeal joint (e.g. arthrodesis or capsulodesis).
• Post-traumatic thumb carpometacarpal osteoarthritis.
• Previous surgery for thumb carpometacarpal osteoarthritis in the contralateral hand.
• Inflammatory arthritis (e.g., rheumatoid arthritis or systemic lupus erythematosus).
• Osteoporosis/osteopenia of such severity that secure cup placement in the trapezium is not possible (for arthroplasty).
• Ongoing systemic corticosteroid treatment.
• Other hand surgical condition in the same hand that could confound outcomes (e.g., carpal tunnel syndrome or de Quervain tenosynovitis).
• Cognitive impairment preventing reliable participation.
• Ongoing, or suspected ongoing, alcohol or drug misuse.
• Insufficient Swedish language proficiency to complete the questionnaires.

After either intervention, patients will be masked to the hand therapist