What is the rationale for using carpal tunnel wrist splints (CTS) in patients with mild to moderate carpal tunnel syndrome (CTS), particularly those with underlying medical conditions such as diabetes or thyroid disease?

Rationale for Wrist Splinting in Carpal Tunnel Syndrome

Wrist splinting works by maintaining the wrist in a neutral position during sleep and daily activities, which reduces pressure on the median nerve within the carpal tunnel and prevents symptom-provoking wrist flexion or extension postures. 1

Mechanism of Action

The therapeutic rationale for splinting is based on biomechanical principles:

• Neutral wrist positioning minimizes carpal tunnel pressure. When the wrist is held in 0-5 degrees of extension (neutral), intracarpal pressure is lowest, reducing compression on the median nerve 2, 3

• Prevention of nocturnal wrist flexion is critical. Most patients unconsciously flex their wrists during sleep, which dramatically increases carpal tunnel pressure and causes the characteristic nighttime numbness and tingling 4

• Immobilization reduces repetitive trauma. By limiting wrist motion during activities, splinting decreases cumulative microtrauma to the already compressed median nerve 1

Evidence for Clinical Effectiveness

The evidence base shows modest but real benefits, particularly in specific patient populations:

• Splinting provides symptom relief in mild-to-moderate CTS, though effects are small. A Cochrane review found that splinting improved symptoms by 0.37 points on the BCTQ Symptom Severity Scale (1-5 scale) compared to no treatment, which may not reach the minimal clinically important difference of 1 point 2

• Night-time splinting increases the likelihood of overall improvement. Patients using night splints were 3.86 times more likely to report overall improvement compared to no treatment (NNTB = 2) 2

• Only 10% of patients achieve long-term symptom resolution with splinting alone. However, this conservative approach successfully identifies the subset of patients who can avoid surgery 5

• Predictors of splinting success include symptom duration less than 3 months and absence of sensory impairment at presentation. These patients are most likely to respond to conservative splinting 5

Role in Treatment Algorithm

The American College of Physicians recommends nighttime wrist splinting as first-line conservative treatment before considering surgical decompression. 1

The treatment sequence should be:

• Initial conservative management with splinting for 6-12 weeks in patients with mild-to-moderate CTS without thenar atrophy 1, 2

• Longer splinting duration (6 months) may provide superior benefits compared to shorter courses (6 weeks), though evidence is limited 2

• Surgical referral is appropriate after failed conservative management, particularly since 48-63% of patients with mild electrodiagnostic findings respond to conservative measures 1

Special Populations

In pregnancy, nighttime wrist splinting is the recommended first-line treatment given the high rate of spontaneous postpartum resolution and the need to avoid surgery and minimize medication exposure 4

For patients with underlying conditions:

• Diabetes and thyroid disease do not contraindicate splinting, though these conditions should be optimized as they may contribute to neuropathy 1

• Laboratory testing (HbA1c, TSH) should be considered to identify reversible causes in patients with atypical presentations, but routine testing is not recommended for typical CTS 1

Critical Pitfalls to Avoid

Excessive or prolonged immobilization can be counterproductive:

• Splinting may increase attention and focus to the affected area, potentially exacerbating symptoms 6

• Immobilization can lead to muscle deconditioning, increased accessory muscle use, and learned non-use 6

• In functional neurological disorders presenting with CTS-like symptoms, splinting may worsen outcomes and strategies encouraging normal movement patterns should be tried first 6

NSAIDs and acetaminophen should not be relied upon as adequate conservative treatment, as they do not address the underlying median nerve compression and have limited efficacy for nerve compression syndromes 1

Practical Implementation

The optimal splinting approach includes:

• Neutral position wrist splints (0-5 degrees extension) are standard, though splints incorporating metacarpophalangeal joint support may provide additional benefits for pain reduction and function 7, 8

• Night-time wear is the minimum recommendation, though some evidence suggests full-time wear may be beneficial in the initial weeks 2

• Duration of 6-12 weeks is reasonable for initial trial, with consideration of longer duration (up to 6 months) if partial response occurs 2

• Regular monitoring is essential to assess response and identify the minority of patients who achieve lasting benefit, allowing them to avoid surgery 5