Thumb carpometacarpal (CMC-1) osteoarthritis is a common condition causing pain and disability, particularly among middle-aged and older women. When non-operative treatment fails, surgery is indicated. In Sweden, trapeziectomy (TE), with or without tendon-based adjuncts, is the standard procedure and recommended in the National Care Program introduced in 2022. However, total joint arthroplasty (TJA) has gained popularity because of reports of faster recovery and improved early function, although concerns remain regarding complications, durability, and cost. Comparative studies are therefore needed.

The aim of this study is to compare patient-reported outcomes after dual-mobility TJA versus TE, with or without tendon-based adjuncts, for CMC-1 osteoarthritis using data from the Swedish Hand Surgery Quality Register (HAKIR). To reduce bias in observational data, the study will emulate a hypothetical randomized target trial.

This registry-based cohort study will include adults aged 45 years or older undergoing primary surgery for CMC-1 osteoarthritis. Patients with previous CMC-1 surgery, bilateral procedures, inflammatory joint disease, or extensive missing baseline data will be excluded. Baseline is defined as the date of surgery, and patients will be followed using patient-reported outcome measures collected preoperatively and at 3 and 12 months.

The primary outcome is change in pain on load measured with the HQ-8 questionnaire at 12 months. Secondary outcomes include pain at 3 months, low pain levels at 12 months, other HQ-8 domains, QuickDASH score, patient satisfaction, grip and pinch strength, thumb range of motion, time to reoperation, and postoperative complications.

Potential confounders will be identified using a directed acyclic graph (DAG). Measured confounders include age, sex, surgical centre, calendar year, baseline pain, baseline function, and smoking. Unmeasured factors such as surgeon preference, patient preference, and disease severity not captured in the registry may still cause residual confounding.

Primary analyses will use linear mixed-effects regression to compare adjusted mean pain outcomes between groups at 12 months while accounting for clustering by patient and centre. Secondary outcomes will be analysed using ordinal logistic regression, Cox proportional hazards regression, and logistic regression. Missing data will be handled using multiple imputation, and sensitivity analyses using inverse probability weighting will assess the impact of reoperations and selection bias

Inclusion Criteria:

adults aged ≥45 years with a diagnosis of CMC-1 osteoarthritis (ICD-10 code M18) who have failed non-operative treatment and are scheduled for primary CMC-1 surgery.

Exclusion Criteria:

• Bilateral CMC-1 surgery or other simultaneous hand interventions
• Previous CMC-1 surgery on the affected hand
• Inflammatory joint disease affecting the hands (e.g., rheumatoid arthritis, systemic lupus erythematosus)
• 30% missing baseline (preoperative) variables

Eligible patients are adults aged ≥45 years with a diagnosis of CMC-1 osteoarthritis (ICD-10 code M18) who have failed non-operative treatment and are scheduled for primary CMC-1 surgery.

Data generated and analyzed during this study are stored within HAKIR and are subject to Swedish data protection legislation and the GDPR. Due to legal and ethical restrictions, individual-level participant data cannot be made publicly available. Access to de-identified study data may be granted to qualified researchers upon reasonable request and subject to approval by the Swedish Ethical Review Authority and the HAKIR steering committee. Access to the statistical code will be granted after reasonable request.