What’s new in carpal tunnel syndrome? Commentary and personal opinions

Carpal tunnel syndrome (CTS) is the most common nerve compression encountered in clinical practice. Surgical treatment is overwhelmingly effective in alleviating symptoms and improving function for carefully selected patients, but the debate continues as to whether diagnostic tests are useful or not in the management of the condition. Another area of discussion is outcome measurements, which arguably should be standardized in order to compare studies. In this month’s issue of the Journal, we have several scientific articles centred around CTS. I would like to share some of my thoughts on four of these articles (Asserson et al., 2021; Matsuki et al., 2021; Postma and Kemler, 2021; Ratasvuori et al., 2021).

In their article on the use of the extensor indicis proprius (EIP) tendon for opponensplasty in patients with severe CTS and thenar atrophy, Matsuki et al. (2021) report a large series of 40 patients who have undergone this procedure with simultaneous carpal tunnel decompression. This study is interesting for two reasons: first, the use of the EIP tendon, although well described, is not widely used in carpal tunnel decompression, largely because of the success and convenience of the Camitz transfer using the palmaris longus tendon. This study establishes that the EIP technique is as effective and can be a useful tool in patients without a palmaris longus tendon. Second, the authors included the documentation of postoperative neurophysiological measurements, which suggests significant recovery of abductor pollicis brevis (APB) function at a mean follow-up of 16 months, raising the question of whether this motor recovery can be relied upon, and indeed whether the motor recovery accounts for part of the improvement in DASH score seen, rather than just from the EIP opponenplasty alone. These findings help debunk the myth that carpal tunnel release in the presence of severe motor loss is ineffective. However, the question of whether an opponenplasty procedure should be performed concurrently in every patient with severe CTS remains debatable, although this article makes a convincing argument.

The article by Asserson et al. (2021) reports on return to work following carpal tunnel decompression performed using the thread carpal tunnel release method and comparing the results following traditional open carpal tunnel release. This is a relatively novel technique, having been first described 2015. The technique itself has the same principles as endoscopic release, with theoretical preservation of the skin, specialized fat and superficial fascia overlying the flexor retinaculum. Although the study has relatively small numbers, patients who underwent thread carpal tunnel release returned to work significantly earlier than with open carpal tunnel release. This finding is unsurprising since endoscopic carpal tunnel release has been shown to reduce return to work time in many previous studies, although very few have a difference of the magnitude seen in this article. There is a lack of evidence that such minimally invasive techniques improve overall patient-reported outcome measures (PROMs) at 1 year, and traditionally, societal costs are not considered when approving funding for specialist equipment or resources. There is perhaps a need for more published series of minimally invasive surgery of this nature demonstrating similar costs with an earlier return to work, which would make it more likely for these techniques to reach a tipping point and change practice.

Ratasvuori et al. (2021) report on the use of ultrasound scanning (USS) in the diagnosis of CTS. Using USS as an alternative to nerve conduction studies has long been proven to be effective (El Meidany et al., 2004), with ongoing debate as to which is the better method. Both have similar sensitivities and specificities with variable cut-off rates for diagnosing CTS: nerve conduction studies give information about nerve function that may be useful from a prognostic perspective, but USS is more useful at picking up local pathologies, such as tenosynovitis or underlying structural abnormalities, within the carpal tunnel. The hardware for both USS and nerve conduction studies have a similar cost, and both require specialist training in order to use them effectively. Finally, although nerve conduction studies are routine in many centres around the world, there remains a general consensus that the diagnosis and treatment of CTS on clinical grounds alone is usually reliable, and therefore further investigation is not routinely required (Graham et al., 2016).

In terms of referrals in hand surgery from primary to secondary care, CTS accounts for the largest numbers per annum and as such, streamlining pathways for diagnosis to treatment always has the potential to reduce cost. Where patients are routinely assessed in a consultant clinic, any investigation has additional cost. If pathways can be developed that bypass the consultant clinic by using a clinical score, supplemented with either neurophysiology tests or USS, then costs could be reduced. We have demonstrated that the local pathway in our department, which is reliant on readily available neurophysiology with a technician-led service, allows us to significantly reduce the number of new patient appointments required. Our pathway developed in this way because of the availability of local resources rather than any proven superiority of neurophysiology over USS (Stirling et al., 2020).

Measuring the cost-effectiveness of any surgery is important when planning services. In terms of hand surgery, establishing a cost per quality-adjusted life year (QALY) for hand operations can be a useful way of measuring this, calculated by multiplying the postoperative change in EuroQol 5 Dimensions Score (EQ-5D) score for each individual in the cohort by the expected number of remaining life years for the individual patient. This gives a cost per QALY for each patient, for which the median for the cohort can then be identified.

In the United Kingdom, the National Institute for Health and Care Excellence (NICE), the national governing body for budgeting healthcare, recommends an upper limit of cost per QALY of £20,000 (McCabe et al., 2008). However, there remain variable factors in calculating this cost that remain unresolved; in particular, whether an immediate postoperative score can be reliably maintained in the long term, or whether this score deteriorates with time as patients age and develop co-morbidity (Stirling et al., 2021).

In the final article, Postma and Kemler (2021) reported on the effect of carpal tunnel release on health-related quality of life of 2346 patients over a 5-year period. The improvement in EQ-5D was 0.12 at around 6 weeks postoperatively, with similar postoperative scores reported by Marti et al. (2016), although their reported improvement overall was 0.07. Interestingly, Marti et al. (2016) used the 5-level rather than the 3-level version of the EQ-5D, and the potential increased ceiling effect of the 3-level version may account for the increased change in EQ-5D. Alternatively, this could reflect the differences in national datasets for the score. Although there is evidence that the upper-limb-specific PROM scores are maintained between 6 weeks and 1 year, this is less likely to be the case for elderly patients or those with co-morbidity. This has led some to argue whether the value should be discounted with time, with 3% or 5% suggested as possible constant discounting values (Severens and Milne, 2004). Previously published cost utility analyses in this journal have incorporated the discounting principle to the calculation of cost per QALY (Stirling et al., 2020).

The methodology used by Postma and Kemler (2021) assumes that the 6-week EQ-5D score is maintained at 1 year, and subsequently maintained for the remaining life years. As such, the reported cost per QALY outlined may be the best possible using this approach. Their reported cost per QALY for the population of the Netherlands remains low, confirming the long-established opinion of both patients and surgeons, that carpal tunnel decompression remains a procedure of high clinical value. The debate for calculating cost effectiveness is likely to continue, but it may be time to set the criteria and methods for calculating cost per QALY in hand surgery procedures in order to allow comparison between datasets.

These articles have highlighted several ongoing debates in the diagnosis and management of CTS. We continue to encourage high-quality research in this area in the hope that they will be resolved in time.