Carpal tunnel syndrome is a common compression neuropathy of upper extremities. Its usual symptoms are pain, numbness and tingling of fingers, which tend to be worse at night. Splinting the wrist with an external orthosis is usually a first-line treatment provided to most people with mild to moderate disease.

The FINCROSS trial (randomized cross-over trial) aims to assess the effect of night-time and full-time splinting in comparison with no-treatment. It also aims to identify possible subgroups of people who would benefit from splinting, as well as assess if positive response to splinting is associated with subsequent lower need of surgery.

The trial will recruit 110 people with carpal tunnel syndrome in Finland. Each participant will undergo all three treatment periods in a randomised order: 1) splinting at night-time for six weeks, 2) splinting both day and night for six weeks; and 3) be assessed under a six weeks long control period of no-treatment.

Each treatment period will be separated with a three-week washout period. Therefore, the whole treatment sequence for each participant lasts 24 weeks after randomization. The participant will be followed-up to 1 year after the randomisation.

Additionally, the participants will get instructions for self-administered stretching exercises to perform throughout the study. All participants will be asked to avoid any intervention administered or supervised by medical personnel (such as structured supervised exercises, manual therapy, steroid injections, surgery, etc.).

Inclusion Criteria:

1. Clinically confirmed carpal tunnel syndrome (CTS) of any severity level (diagnostic criteria: numbness, pain or paraesthesia in the median nerve distribution area of wrist and fingers),
2. Symptom duration of CTS for at least 3 weeks,
3. No previous corticosteroid injection for CTS during last 6 months,
4. No previous surgery for CTS,
5. Aged 18 years or older,
6. Able to complete self-report questionnaires electronically,
7. Able to understand Finnish,
8. Willing to join the study and follow the study protocol instructions,
9. Sign informed consent.

Exclusion Criteria:

1. Nerve root or plexus disorders that might be causing CTS mimicking symptoms (e.g., cervical radiculopathy, thoracic outlet syndrome, or whiplash associated disorders),
2. Other neurological condition affecting the function of the hand such as Multiple Sclerosis, previous nerve injury,
3. Active Rheumatoid arthritis or any other active inflammatory joint disease affecting the hand,
4. Thenar muscle atrophy,
5. Untreated hypothyroidism,
6. Known allergy to any of the splint materials (self-reported by patient),
7. Long term treatment (over 4 months) for CTS with no response,
8. Any other known reason that could prevent from participation for the study time.