Efficacy of splinting the wrist and metacarpophalangeal joints for the treatment of Carpal tunnel syndrome: an assessor-blinded randomised controlled trial

Introduction

Carpal tunnel syndrome (CTS) is among the most frequently diagnosed peripheral nerve entrapment disorders of the upper extremity,¹ and the most expensive upper extremity musculoskeletal disorder in the USA, with an estimated cost of medical care of more than $2 billion annually.² CTS has a prevalence rate of 3% in the general population and 8% in the working population,¹ resulting in significant days away from work that exceed 28 days.³ The overall incidence rate of CTS in a general population ranges from 3.3 to 3.5 per 1000 person/year, with women being more likely to be affected than men, and an incidence peak between 40 and 60 years of age.⁴ CTS results from median nerve compression in the carpal tunnel (CT) area and is typically characterised by sensory symptoms in the median nerve distribution of the hand, such as paresthesia and pain, as well as sensorimotor control deficits. More severe cases of CTS have significant sensory loss and motor involvement, such as weakness and muscle atrophy. If left untreated, CTS can cause permanent damage to the median nerve and may consequently result in significant work disability.

Mild-to-moderate CTS cases are most typically treated conservatively by splinting the wrist in a neutral position.^4–7 Anti-inflammatory medications and corticosteroid injections into the CT space are also prevalent interventions for CTS.^{4 5} Surgery is considered for those who do not respond to conservative interventions or for those with severe symptoms indicative of thenar motor denervation, constant paresthesia, muscle atrophy or proven nerve conduction studies and electromyography changes.^{4 8} Both surgical and non-surgical intervention approaches are beneficial for patients with CTS. When compared together, surgery is reportedly superior to conservative interventions, although it is associated with a greater risk of complications.^{4 8 9}

The justification for splinting the wrist to reduce the symptoms of CTS is that splinting maintains the wrist in an anatomical position (neutral) where the CT is at its widest, which maintains the CT pressure at its minimum.⁴ This justification is supported by anatomical^{5 10} and clinical studies.^{5 11} Although wrist splinting is shown to reduce CTS symptoms and improve functional status,^5–7 the extent of the effectiveness of splinting is limited, and patients with CTS commonly resolve to surgery as the final means of treating their CTS.⁶ More effective conservative interventions for the treatment of mild-to-moderate CTS are therefore needed. Several studies have shown that more efficient medical care regimens and return-to-work strategies offer clinical and financial benefits.^12–14

One reason for the limited effectiveness of wrist splinting may be the lack of consideration for the lumbrical muscles. During active finger flexion, the lumbrical muscles migrate into the limited CT space. This increase in the content of the CT causes an increase in CT pressure, which ultimately adds to the compression of the most delicate structure in the CT, namely the median nerve. The evidence supporting the consequences of active finger flexion on lumbrical muscle incursion into the CT and its effects on increased CT pressure^{15 16} and on the anatomical properties of the median nerve^15–19 is abundant. Thus, when splinting for CTS, preventing the lumbrical muscle incursion into the CT (through restricting metacarpophalangeal (MCP) active flexion) may increase the effectiveness of splinting in managing the symptoms of CTS. This concept has been suggested and debated widely in literature and conferences, yet empirical studies that have researched this topic are scarce.

There are limited clinical splinting studies that assessed the efficacy of restricting the fingers’ MCP joint positioning in relation to the symptoms and function of patients with CTS.^20–23 One study reported that participants who wore a hand brace that supported the third and fourth digits in the extension had significant reductions in CTS symptoms and improved functional status.²⁰ A limitation of this study is that they compared the splint intervention group with a control group that did not receive any treatment. Three other studies found that splints that restricted the wrist and MCP had better outcomes than splinting the wrist only.^21–23 A limitation of these studies is that their patients were instructed to wear splints only at night and were permitted to use their hands freely during the day. This may have limited the results, as daytime use may have contributed to CTS.

Clinical studies that have investigated the effectiveness of restricting finger flexion lack definitive evidence that would support or refute their advantage over traditional splints in the treatment of CTS. The purpose of this assessor-blinded randomised controlled trial (RCT) is to compare the effectiveness of traditional cock-up splints (which restrict the wrist in neutral) with customised splints (which restrict the wrist and the MCP joints of the medial four digits in neutral) in the treatment of mild-to-moderate CTS. Our hypotheses are that (1) the splinting interventions would reduce CTS symptoms and improve functional status in patients with mild-to-moderate CTS in both groups and (2) the group that receives the splint that supports the wrist and MCP joints would show better outcomes (ie, a greater reduction in symptom severity and an improvement in functional status) than the group that receives the traditional wrist cock-up splint.

Materials and methods

Results

A total of 66 adults with CTS were enrolled in the study and randomised according to a 1:1 allocation ratio to the wrist and MCP splint intervention groups. Three participants withdrew from the study and opted for alternative intervention instead (ie, steroid injection), and four participants were lost to follow-up. Fifty-nine participants completed the study and were included in the analysis. The mean age of participants was 54.8 years (SD=10.8), of whom 86.4% were female. In terms of occupational distribution, 40.7% were housewives, 13.6% were retired, while the others included teachers (8.5%), healthcare professionals (5.1%) and secretaries (6.8%), among others (eg, civil servants, business clerks and engineers). The demographic characteristics of the participants are shown in table 1, and clinical features are shown in table 2. The demographic characteristics and clinical features of both groups were statistically similar at baseline.

Overall, the participants adhered to the splint-wearing schedule, with an average wearing time of 12.8 (SD=3.4) hours for the wrist splint group and 14.7 (SD=3.9) hours for the MCP group (p=0.054). Compared with the baseline at the end of the sixth week of splint use intervention, both groups improved significantly from splint use in some clinical features. The wrist splint group and the MCP splint group had significant improvements in lateral pinch strength (p=0.032 and p=0.002, respectively), two-point discrimination sensation of the thumb (p=0.003 and p=0.041, respectively), two-point discrimination sensation of the index (p=0.035 and p=0.023, respectively) and the Phalen’s manoeuvre symptoms (p=0.025 and p=0.002, respectively). The MCP splint group had additional improvements over the wrist splint group in tip pinch strength (p=0.012) and Palmar pinch strength (p=0.011).

At the 24-week follow-up, the wrist splint group maintained the significant improvements gained from baseline in lateral pinch strength (p=0.008), two-point discrimination sensation of the thumb (p=0.044) and Phalen’s manoeuvre symptoms (p=0.041), but regressed to a baseline condition in two-point discrimination sensation of the index (p=0.350). The MCP splint group maintained the improvements gained from the splint in tip pinch (p<0.001), Palmar pinch (p<0.001), lateral pinch strength (p<0.001), two-point discrimination of the thumb (p=0.020) and two-point discrimination of the index (p=0.039). Further improvements were evident in grip strength (p≤0.001) and Tinel sign (p=0.002) for the MCP group. More detailed statistics of the clinical differences within the three follow-up periods for both groups are presented in table 3.

When comparing between groups (type of splint), both groups performed similarly from baseline to 6 weeks postintervention in all measures, except for pinch strength (p=0.046), two-point discrimination of the thumb (p=0.044) and two-point discrimination of the index (p=0.045), where the MCP splint group was significantly better.

Nonetheless, at 24-week follow-up, the MCP splint group showed significant advantages over the splint group in grip strength (p=0.002), tip pinch strength (p=0.026), two-point discrimination sensation of the thumb (p=0.037), two-point discrimination sensation of the index (p=0.030), Phalen’s manoeuvre (p=0.020) and Tinel sign (p=0.021). Further details for the clinical differences between groups for the three follow-up periods are presented in table 4.

Discussion

Several splint types have been used as conservative interventions to improve the symptoms of CTS. The traditional wrist cock-up splint, which immobilises the wrist in 0–5° of extension, is the most prevalent splint design used in hand therapy clinics, although the evidence of its effectiveness in comparison to other splint types is lacking.^{22 23} In this RCT, we used multiple standardised outcome measures to compare the effectiveness of the traditional wrist cock-up splint in comparison to a splint that incorporates the wrist and MCP joints to treat mild-to-moderate CTS.

The mean age (54.8 (SD=10.8)) and sex distribution (86.4% female and 13.6% male) of the participants were consistent with previous CTS studies.^{21 23} The main finding of this study is that, when compared with baseline at the end of the sixth week of splint use, both splint groups improved in multiple clinical features (ie, lateral pinch strength, two-point discrimination sensation, Phalen’s manoeuvre and BCTQ Symptom Severity Scale as well as Functional Status Scale). However, the MCP splint group yielded further improvements over the traditional wrist splint in tip pinch strength as well as palmar pinch strength. This main finding is consistent with other studies in the field that have demonstrated clinical gains from using splints.^{9 23 30} This finding asserts the effectiveness of splints as a viable intervention to improve the symptoms of mild-to-moderate CTS cases.

When comparing the long-term outcomes between the two splint designs, the MCP splint was superior to the traditional wrist splint. At 6-month follow-up postsplint interventions, the wrist splint group maintained the improvements in lateral pinch strength, two-point discrimination sensation to the thumb, Phalen’s manoeuvre and BCTQ Functional Status Scale but lost two-point discrimination sensation to the index and BCTQ Symptom Severity Scale. However, the MCP splint group not only maintained all the previously gained improvements (ie, tip, palmar and lateral pinch strength, two-point discrimination to the thumb and index, Phalen’s manoeuvre and both BCTQ scales), but additionally improved in grip strength and Tinel sign.

The superiority of the MCP splint over the traditional wrist splint is possibly caused by the lumbrical factor. Previous studies have demonstrated that making a fist with full finger flexion caused the lumbrical muscles to migrate inside the CT space, which led to an increase in pressure within the tunnel that potentially exerts more force on the median nerve.²³ This evidence was supported by cadaver studies^{17 31} as well as in vivo studies using ultrasonography^32–34 and MRI.¹⁹ This migration of lumbricals into the CT space is restricted by splints that incorporate the MCP joints but not the traditional splint, which allowed full finger flexion. The improvements demonstrated by the MCP splint over the traditional wrist splint in this study consolidate the findings from previous research.^20–23

The grip strength did not improve from baseline to 6 weeks postsplint use. However, at the 6-month follow-up, the grip strength of the MCP splint group was significantly stronger when compared with 6 weeks postintervention. This may be explained by the restrictions imposed by the splints when performing hard labour or activities that would have promoted grip strength. When the splint was discharged and the hand became free to perform all types of activities, in combination with the benefits gained from 6 weeks of intervention, the patients were likely to have engaged in grip activities that facilitated grip strength. This was predicted by Golriz, who suggested that an increase in grip strength after using an MCP splint may show in long-term follow-up assessments.²³ Moreover, Gellman et al noted that grip strength requires up to 3 months after intervention before returning to normal values.³⁵ A recent clinical practice guideline for CTS adds further support to our findings of delayed improvements in grip strength, which reported grip strength not being sensitive to change over time and may not begin to increase until the third month postintervention.⁶ Overall, our results are consistent with previous studies that showed better improvements in grip strength for the MCP splint group over the traditional wrist group.^21–23 Although the gain in grip strength found in previous studies was evident after only 6 weeks of splint use, our findings were evident after a more extended period of time.

Although the protocol for this study included wearing the splint all day and night for 6 weeks, the wrist splint group wore the splint 1.9 hours more than the MCP splint group, which indicates that the wrist splint was more comfortable and functional than the MCP splint. Nonetheless, the average wearing time of 12.8 hours for the MCP splint was sufficient to yield significant clinical and functional improvements that lasted for 6 months. The hand therapy community would therefore benefit from future research that sheds more light on the ideal splint-wearing time for patients with CTS. Such research would prevent patients from needlessly wearing splints.

Clinically, the results of this study demonstrate the effectiveness of using splinting as a treatment modality for mild-to-moderate CTS. Additionally, incorporating the MCP joints into the splint to restrict the digits from performing full finger flexion yielded additional clinical benefits. Hand therapists are therefore recommended to fabricate their CTS splints by factoring in the role of lumbricals by restricting MCP flexion.

Supplementary Material

Data availability statement

Data are available upon reasonable request. The data generated during the current study (including entire blinded datasets, study protocol and statistical analysis) are available from the corresponding author after study publication, upon reasonable request.

Ethics statements