Previous epidemiological studies of upper extremity nerve injuries are mainly composed from patient samples of a single hospital or region. Our study evaluated nerve injuries of the upper extremity in the whole population of Finland (1998–2016). Our nationwide study included 13,458 upper extremity nerve injury cases, and the most common injured area in the upper extremity was the wrist and hand.
A Swedish study also found that most PNIs occur in the wrist and hand region 12. In our study, the most commonly damaged nerve was the digital nerve in the fingers and thumb, consisting of 5,532 cases. The mean standardised annual incidence rate of digital nerve injuries was 0.4 among men and 0.14 among women, and for the thumb 0.12 among men and 0.05 among women per 100,000 person-years.
The incidence rate of PNIs in upper extremities varies between countries and studies. Comparisons of the studies are difficult since these studies have not standardised their results. In Sweden, the incidence rate of digital nerve injuries treated with surgery (S64.3, S64.4 and S64.7) was 6.2 per 100,000 inhabitants yearly, and the cases consisted mostly of men 15.
The incidence rate of any upper extremity nerve injury in our study was highest among young working-aged men. This is similar to earlier studies 121516. In our study, there was an incidence peak in the 20–29-year-old age group. Overall, our study revealed that young working-age men have higher a two-fold risk of getting an upper extremity nerve injury compared to women.
In comparison to men, women over 80 years of age had significantly more nerve injuries. This might be due to osteoporotic fractures, which are more common among women of this age group compared to men of the same age 17. A higher number of severe fractures might lead to a higher likelihood of combined nerve injuries.
Our study also included rare upper extremity nerve injuries such as musculocutaneous and axillary nerves. In our study population, of 13,458 patients, 62 had musculocutaneous and 298 axillary nerve injuries. To the authors’ knowledge, there are no previous population-based studies of incidence of musculocutaneous or axillary PNIs. An insurance-based study of PNIs in US emergency departments estimated an annual crude incidence for axillary nerve injury at 0.2 per 100,000 and musculocutaneous nerve injury at 0.06 per 100,000 10. A previous single-hospital study reported 6 (4.9%) iatrogenic musculocutaneous nerve injuries of 122 surgically treated patients 18. According to the literature, axillary nerve injuries may be caused in surgeries for shoulders or humeral fractures, or glenohumeral dislocation 1819. In our study, the standardised incidence of axillary nerve injury in men was 0.024, and women 0.012.
According to previous studies, acute care for median or ulnar PNIs may cost up to 169,408 USD 13. In Sweden, total costs per patient involved in working-life was 51,233 euros for a median nerve injury and 31,186 euros for ulnar nerve injury; 87% of total costs resulted from loss of productivity due to sick leaves 20. Focusing on factors that cause nerve injuries of the upper extremity might help to prevent them. Attention should be paid to occupational safety in particular.
The strengths of our study include nationwide data obtained from a very reliable register: the Care register for Health care has proven to be reliable, including both inpatient- and outpatient-based services of both public and private hospitals nationwide 21. In Finland, the healthcare system is based on publicly funded universal healthcare. Usually, PNIs are treated in specialist care, so we assume that the vast majority of them are included in our register. On the other hand, using registry data has the risk of coding error and missing diagnoses, and the data only included patients seeking medical advice for their injury. Additionally, based on ICD-10 codes, the site, exact finger, or cause of the PNI remains unknown.