In this large register study of patients who underwent OCTR between 2010–2016, women rated their preoperative functional disability higher than men, irrespective of age and prevalence of diabetes. Women also rated their preoperative symptoms in terms of pain, weakness, stiffness and numbness/tingling higher than men.
Electrophysical data was not available for the study population and thus we do not know whether there were any gender differences in preoperative nerve conduction. However, in previous reports women reported more discomfort and symptoms related to CTS than men, although men had greater changes on preoperative neurography (7, 9, 23).
That women with CTS rate their disability and symptoms higher than men have previously been described, but not explained (8–11). Padua et al argued for a greater tolerance to carpal tunnel discomfort among men, whereas Greenslade et al pointed out that several questions in the patient-reported outcome measures commonly used concern household chores, such as making beds and gardening, which more often are performed by women (9, 10). Another explanation could be that women wait longer to seek healthcare and thus have more discomfort at the time of seeking medical care.
In the present report, women above 45 years still rated their functional disability higher than men up to 12 months after surgery, whereas there was no gender-related difference in functional outcome among the younger patients. Hobby et al evaluated symptoms and functional disability with the Boston Carpal Tunnel Questionnaire (BCTQ) before and 6 months after surgery in 97 patients and found that women reported significantly worse preoperative symptoms and disability then men, but there was no difference in postoperative scores (8). Greenslade et al prospectively evaluated 57 patients and found higher preoperative DASH scores in women than in men, but no difference in functional disability 3 months after surgery (10). Age was not adjusted for in these reports.
Others have found that older age correspond to worse outcome after OCTR (6, 10). However, the possible effect of gender was not taken into consideration in these reports, and considering the gender distribution among the elderly with CTS, where women outnumber men, a confounding effect of age should be taken into account (3). Compared to previous studies, our large data material allowed for subgroup analyses according to age and gender and we found that there was a relationship between age and worse postoperative functional disability among women, but not among men.
The largest improvement in postoperative QuickDASH score occurred within 3 months after surgery, although there was a tendency for continued improvement up to 12 months after OCTR in our material. The significant difference in change in QuickDASH scores from baseline to 12 months between men and women adjusted for age and diabetes, disappeared after adjusting for preoperative QuickDASH score in the multivariate linear regression analyses, indicating that the overall relative improvement after OCTR was not dependent on gender or diabetes, but could be subject to a ceiling effect. However, when analyzing the subgroups, changes in QuickDASH score from baseline to 12 months were similar between men and women aged 18–44 and 65 and above, whereas the relative improvement in women aged 45–64 was significantly higher than in men. Changes in female sex hormones around menopause have been proposed to influence the high incidence of CTS among women (23). Kim et al observed an up-regulation of estrogen receptor alfa and beta (ERα and ERβ) in the tenosynovial tissue of postmenopausal women with idiopathic CTS (24). In addition, Al-Rousan et al observed a protective effect of menopausal hormone therapy on the incidence of CTS among postmenopausal women (20). Mitake et al speculated that hormone-induced edema in the tenosynovium could increase the intra-carpal tunnel pressure in female patients, resulting in a less neurodegenerative pathogenesis compared to neuropathy seen for example in CTS patients with diabetes (23). If this is the case, an OCTR could be expected to be an efficient intervention in patients with edema-induced CTS and could partly explain the larger improvement in women around menopause, that we observed.
Women consequently scored their symptoms in terms of weakness and pain on load higher than men. It is possible that these variables are influenced by carpometacarpal I joint osteoarthritis, which is more common in women than in men, particularly in the elderly (25). Hand osteoarthritis is also associated with prevalence of CTS (26). Concomitant hand conditions might affect the QuickDASH scores, since it is not a disease specific instrument. However, the study by Hobby et al (n = 97, 75 women) used the disease specific BCTQ and found no gender differences in postoperative score, although women scored their symptoms higher preoperatively (8). Greenslade et al assessed the responsiveness of the DASH questionnaire compared to BCTQ in patients with CTS and found DASH to be a reliable, responsive and practical outcome measure in patients with CTS (10). The normative QuickDASH values in the general population also differs according to age and gender, as pointed out by Aasheim et al (27). The normative values are higher among the elderly and among women (27). It is also debatable whether the seen differences between genders are clinically significant. Recently, the minimal clinically important difference (MCID) in QuickDASH for CTS was reported to be 10.4 points, hence our results are just slightly higher than the MCID (28). There is not yet an established MCID for HQ-8.
The main strength of this study is the large study population. The main limitation is the response rate. However, the response rate is similar to response rates of other large registries (29, 30), and the non-responders did not differ substantially from the responders in our material.
HAKIR contains no clinical information, and hence the only variable on concomitant disease that we could include, was diabetes. We did not have data on smoking status, obesity, thyroid disease, rheumatoid arthritis or other possible confounders.