Trigger Finger From Ocean Rowing: An Observational Study

Abstract

Background: Trigger finger has a prevalence of 2% to 3% in the general population. Although anecdotal evidence exists, there is a lack of conclusive data that prove a relationship between repetitive power grip and flexion with triggering. Ocean rowing is becoming a popular sport, with the race across the Atlantic alone attracting more than 100 participants annually. Anecdotal reports suggest ocean rowing may be a significant cause of trigger finger. We aimed to identify whether the sport causes an increased prevalence of triggering, whether there were any alleviating or compounding factors, and, finally, whether there was any effect on performance. Methods: A prospective observational study was carried out. A questionnaire was sent to all participants of the Talisker Whisky Atlantic Challenge 2018, which included a trigger finger self-scoring system and the Oslo Sports Trauma Center Overuse Injury Questionnaire. Results: Responses were received from 67 rowers (83% response rate). Age ranged from 21 to 62 years, with a mean of 40 years. In all, 49.3% had clinical triggering, with 79.3% reporting bilateral symptoms. The length of continuous rest time had a significant impact on the incidence of finger triggering and disease stage (P = .0275 and .0353, respectively; multivariate logistic regression). High-grade triggering had a more negative effect on rowing performance than low grade or no triggering (not significant). Conclusion: Ocean rowers suffered a 15-fold increase in trigger finger prevalence compared with the general population. This was increased in those who took shorter, more frequent rest periods. This study provides new conclusive evidence that the repetitive power grip and flexion involved in rowing increase the prevalence of trigger finger.

Introduction

Trigger finger is a common hand condition characterized by symptoms including clicking, locking, or pain in the affected digit. ¹ It has a prevalence of 2% to 3% of the general population and therefore makes up a significant proportion of the hand surgeon’s elective workload.^2-4 Trigger finger is more common in women and patients with diabetes, with symptom onset most commonly occurring in the fifth or sixth decade of life.^4,5 This condition is typically chronic, with symptoms as a result of inflammation, swelling, and nodule formation in the flexor tendon sheath. ⁶ There are a variety of opinions as to the exact etiology of trigger finger, including anecdotal links made to occupations that require repetitive power grip and flexion, although studies to date have failed to demonstrate a conclusive relationship.^1,7 It is likely to be multifactorial, with other potential contributors including trauma, degenerative change, and genetic predisposition. ⁵ Theoretically, repetitive activities could cause swelling of the tendon within the first annular pulley (A1), resulting in tendon locking. ⁶ Tendons are load-bearing tissues that respond to mechanical loads by altering their structural properties. ⁸ Previous studies have demonstrated that excessive mechanical work causes an increase in proinflammatory gene expression and factors that lead to swelling and ultimately degradation. ⁸ It has therefore been postulated that ongoing activity results in enduring irritation, but the pressure involved from power grip reduces edema, resulting in temporary symptom relief; it is during rest periods that the tendon swells and triggering redevelops or worsens. ⁶

Ocean rowing is the sport of traversing oceans by human rowing power alone. It is becoming ever more popular, with several thousand people having completed a crossing to date and up to 200 new attempts annually. Ocean rowing expeditions typically involve shift style rowing, with teams rotating in 2- to 4-hour shifts, 24 hours per day. Ocean crossings typically take anywhere from 28 to several hundred days, depending on team size, ability, and weather conditions, to name a few. Taking a rowing stroke requires powerful grip and flexion on the oar handles to convert power from the body into boat propulsion (Figure 1). Carrying out a fitness expedition of this magnitude results in an array of repetitive strain injuries, although the effect on trigger finger is less well understood. The pressure induced on the volar surface of the hands over such a prolonged period is likely to cause injury and even trigger finger, if the anecdotal reports on ocean rowers are true. We aimed to identify whether ocean rowing can indeed cause trigger finger and whether there were any significant compounding or alleviating variables. In doing so, we hoped to delineate whether prolonged flexion and power grip do in fact cause trigger finger.

Figure 1.

Illustration of the area of the hand involved in rowing oar grip. It is throughout this region that power is transmitted from the body to the oar handles to produce boat propulsion.

Materials and Methods

Study Participants

This was a prospective observational study. All 88 participants enrolled in the 2018 Talisker Whisky Atlantic Challenge (TWAC) were consented and recruited prior to the race start. Participants were excluded if they did not successfully complete the race. An online questionnaire was sent to all contenders on completion of the 2800-mile rowing crossing.

Patient and Public Involvement

Previous ocean rowers helped set the research question and were intimately involved in the design and implementation of the study. Individuals involved in ocean rowing preparation and training, in addition to the race organizers, have been central to the dissemination of information both during and after the study.

Questionnaire

The questionnaire collected demographic and rowing race data, which included age, sex, handedness, comorbidities, training, crew size, length of crossing, shift pattern, and hand protection used. A validated scoring system from Shultz et al ¹ was used to collect data on the incidence and severity of trigger finger. This was modified into descriptive lay language to allow self-scoring. Participants were asked to score any trigger-related symptom against this defined scale (Table 1). Clinical triggering was defined as stages 1 to 4, with stage 0 considered “preclinical,” stages 1 to 2 considered “low grade,” and stages 3 to 4 considered “high grade.” Those who had trigger-related symptoms were also asked to report what treatment (if any) they sought and whether they had ongoing symptoms.

Table 1.

Trigger Finger Scoring System.

Stage	Symptoms/Signs	Grade
0	Tenderness over the A1 pulley; no clicking, popping, or locking	Preclinical
1	Clicking, popping, and palpable nodule, but without locking	Low grade
2	Locking overcome with affected hand
3	Locking overcome with opposite hand	High grade
4	Inability to flex or extend affected digit

Note. Data taken from Shultz et al. ¹

The Modified Oslo Sports Trauma Research Center Overuse Questionnaire (Figure 2) was incorporated to record any effect of finger triggering on rowing performance. ⁹ This was completed at the same time as the remainder of the questionnaire.

Figure 2.

The Oslo Sports Trauma Center Overuse Injury Questionnaire modified for use with hand injuries. Data taken from Clarsen et al. ⁹

Statistical Analysis

Data were analyzed using the R project for statistical computing. Statistical significance was taken at the 95% confidence interval. Univariate and multivariate logistic regression analyses were used to identify statistical significance.

Results

Eighty-eight race entrants met the inclusion criteria. Three individuals were excluded as they did not finish the race. Complete survey responses were received from 67 participants, a response rate of 79%. Age ranged from 21 to 62 years, with a mean of 40 years; 67.7% were men (n = 44) and 32.3% women (n = 23); and 72.8% of participants had never rowed competitively prior to registering for the TWAC race, 16.8% had rowed to school or university level, and 10.6% to national or international level.

Very few comorbidities were reported by the study participants. Three percent had rheumatoid arthritis (n = 2), and 1.5% had gout (n = 1). Other conditions included asthma, high cholesterol, and acid reflux. None of the study participants were diabetic, and 13.4% (n = 9) documented a previous history of trigger finger.

Of the total respondents, 64.2% had trigger-related symptoms (stages 0-4) during the row (n = 43). In concordance with published literature, stages 1 to 4 on the trigger finger scoring system were deemed as “clinical triggering,” with stages 1 to 2 considered “low grade” and 3 to 4 “high grade.” In addition, 49.3% reported having experienced clinical triggering during the row (n = 33), of which 54.5% were low grade (n = 18) and 45.5% high grade (n = 15) (Table 2). Seventy-nine percent had bilateral symptoms (n = 26). The middle and ring fingers were the most commonly affected (33.5% and 31.6%, respectively). Participants also documented symptoms in the index (21%) and little fingers (14%), but none had symptoms in the thumb. Fifty-seven percent reported symptoms commencing during their rest periods, and 82% documented symptoms temporarily resolving during their rowing shift. Ninety-five percent had complete symptom resolution at 6 months, with only 1 individual seeking any form of medical help (physiotherapy).

Table 2.

Prevalence of Trigger Finger in Ocean Rowers by Grade of Disease.

Trigger grade	Frequency	Percentage	Mean age, y	Sex (M:F)
Asymptomatic	24	35.8	42	3:2
Preclinical (0)	10	14.9	38	3:2
Low grade (1-2)	18	26.9	41	3:2
High grade (3-4)	15	22.4	39	3:1

Includes mean age and sex (expressed as a ratio) for each grade.

Participants were asked to record whether they used any self-imposed protective measures to prevent hand injury during the challenge. Fifty-five percent (n = 37) wore gloves while rowing, and 34% (n = 23) reported performing self-directed hand exercises (nonstandardized, no professional advice sought). None of the participants documented use of nonsteroidal anti-inflammatory medications. Univariate logistic regression analysis was used to identify whether either gloves or exercises had any effect on either the development of clinical trigger finger or stage of disease. Neither measure was found to have any effect on the development of trigger finger or stage of disease (exercises: P = .391 and .442; gloves: P = .703 and .837).

Previous history of trigger finger had no significant effect on the development of triggering or the stage of disease (P = .271 and .146, respectively). Rowers who had no previous history of triggering were just as likely to develop symptoms as those who had previously had trigger finger. Similarly, age, sex, and hand dominance all demonstrated no significant effect on the incidence of triggering or stage of disease (age: P = .58 and .219; sex: P = .601 and .318; hand dominance: P = .525 and .249). Length of the rowing crossing (measured in days) and the type of rowing training carried out prior to the event also had no significant effect on the development of clinical triggering or stage of disease.

Rowers were asked to document their rowing shift patterns. These were hugely varied and included 2 hours of rowing, 2 hours of rest (24 hours per day) and 3 hours of rowing, 3 hours of rest (24 hours per day). Others rowed for longer continuous periods during the day but with a 4-hour or longer break overnight. For analysis, rowers were grouped into those who took a minimum of one 4-hour or more break per 24 hours and those who did not (ie, rest periods were always shorter than 4 hours) (Figure 3). These groups were then analyzed using univariate logistic regression. Those who took longer rest periods were found to be significantly less likely to develop clinical trigger finger (P = .0257), and those who did develop symptoms tended to be of lower grade, although this was not significant (P = .0539).

Figure 3.

Effect of rest period length on incidence of trigger finger. A 4-hour or longer break per 24 hours was found to be significantly protective against developing symptoms (P = .0257, multivariate logistic regression).

A multivariate logistic regression model was used to identify whether there was any association between the length of rest period and trigger finger, when adjusted for other variables (age, sex, hand dominance, exercises, gloves, length of crossing, training type). This confirmed the finding that longer rest periods were indeed significantly protective against developing clinical trigger finger (P = .0275; adjusted odds ratio, 0.132; 95% confidence interval, 0.016-0.683) and significantly protective against suffering a higher stage of disease (P = .0353; adjusted odds ratio, 0.258; 95% confidence interval, 0.0732-0.907).

Performance Data

Effect on performance was assessed using the Oslo Sports Trauma Center Overuse Injury Questionnaire, where increasing scores indicate increasing severity of condition negatively affecting sport performance. Univariate logistic regression modeling was used to identify statistical significance. High-grade triggering was noted to have an adverse effect on performance (Figure 4), but this was not significant (P = .14). A multivariate logistic regression model was used to identify any association between performance and stage of triggering while accounting for other variables (age, sex, hand dominance, previous trigger, rest period, length of crossing, training type). Triggering stage had no significant effect on performance in multivariate analysis. Both increasing age and length of crossing were found to significantly negatively affect performance (P = .00372 and .0329, respectively).

Figure 4.

Box plot diagram showing the effect of triggering grade on symptom severity and therefore performance.

Note. High-grade trigger resulted in a subjective increased symptom severity and negative effect on performance (nonsignificant, P > .05, multivariate logistic regression). Key: box = interquartile range (IQR), red line = mean, whiskers = 1.5× the IQR.

Discussion

Trigger finger is a debilitating condition caused by an imbalance in the relative sizes of the flexor tendon and A1 pulley, resulting in pain, clicking, and locking of the affected digit. The exact etiology is poorly understood, although significant links have been made with metabolic disorders, chronic use, and advancing age. ¹⁰ Mechanical stress, including repetitive movements, local trauma, and compression, has been postulated as a further etiology for the condition, ¹⁰ although limited definitive proof exists in the current medical literature. ¹ Trigger finger has previously been linked to sport, with anecdotal reports from professional golfers and climbers documented in previous studies. ¹¹ Rowing is a sport that involves prolonged finger flexion and pressure over the volar surface of the hand and is therefore likely to be a risk factor for developing trigger finger when performed for prolonged periods.

Our results have identified a high incidence of trigger finger in ocean rowers, with nearly 50% of participants suffering from the condition and an almost equal split between high- and low-grade diseases. This represents a 15-fold increase compared with the prevalence found in the general population and therefore provides significant evidence for the conclusion that ocean rowing is a cause of trigger finger. ¹ Although a minority of patients reported a previous history of trigger finger, this was not linked to the likelihood of developing the disease during the row. It is likely that symptoms were caused by prolonged flexion and repetitive stress over the volar surface of the hand during rowing shifts. The majority developed symptoms in their rest period and reported some relief when active during the rowing shift. This corroborates the idea from Golas et al ⁶ that repetitive actions and pressure irritate and can also reduce excess edema within the tendon, temporarily improving glide. At rest, swelling increases and triggering reappears. ⁶ Ultrasound studies of patients with trigger finger have previously found differing mechanisms of tendon locking, with 30% as a result of tendon swelling with no associated pulley abnormality. ¹² Perhaps the cyclical nature of symptoms within our cohort is as a result of this underlying pathophysiology where only the tendon is affected and pulley spared.

In concordance with the literature, symptoms of trigger finger in rowers did not demonstrate a predilection for the dominant hand, with the vast majority having bilateral symptoms. ¹³ This is relatively unsurprising given the equal stress placed on both hands, regardless of hand dominance. The increased propensity for triggering in the middle and ring fingers partially corroborates previous finger exclusion studies on grip strength that have identified the importance of the ring and little fingers to maintaining a strong power grip. ¹⁴ The observed effect on the middle over the little finger could be as a result of the specific grip position required in ocean rowing and therefore the location of the maximum force transmitted to the hands. Interestingly, age and sex had no bearing on the likelihood of the study participants developing trigger finger. In the general population, triggering is more common in women and in the fifth or sixth decade of life. ¹⁰ This could be because of differing pathophysiologies: disease in the general population is normally not as a result of mechanical trauma or repetitive insult but due to chronic inflammation and degenerative change.

No defined intervention was carried out to either prevent or alleviate symptoms in the study cohort. Rowers did, however, use self-directed measures to try to limit the stress on their hands, including gloves and hand exercises. These were not standardized and were found to not offer any protective effect on the development or stage of trigger finger. There is no evidence in the literature to suggest that the use of gloves may be beneficial in preventing triggering, but patients who have been treated with physiotherapy alone do appear to receive some symptom alleviation and functional improvement. ¹⁵ It is likely that rowers did not use standardized, regular, evidence-based hand exercises, and so these negative findings should not be considered significant.

We investigated whether rowing shift pattern affected the likelihood of study participants developing symptoms. Our study found that a 4-hour break or longer every 24 hours was significantly protective against developing trigger finger compared with those who took shorter, more frequent rest periods. Those who did develop trigger finger in the longer rest group had significantly less severe symptoms. These findings are important for not only future ocean rowers but also individuals partaking in high-risk occupational or other sporting activities: no matter how intense the stressor, longer rest periods are indeed protective. Further work is required to delineate the ideal period of rest across different occupational stressors to reduce the incidence of trigger finger in the general population.

Perhaps surprisingly, no association was found between the development of trigger finger and performance. Our study did show that those with high-grade triggering were unable to perform as well as their low-grade counterparts, but this was not significant. These findings need to be taken with slight caution: the performance score was taken at a snapshot in time during the first month after completion of the row. The score was not completed during the row itself and referred purely to symptoms in the post-row period. Equally, all rowers did not fill out the questionnaire at the same time point after completion. Even if triggering did in fact have no direct effect on performance, the negative impact of continuous pain and discomfort on morale is likely to indirectly effect the participants’ ability to row effectively. This could become dangerous if symptoms reach a degree where rowing is impossible, due to the remote and inhospitable environment of an ocean with limited rescue options. Age and duration of row were, however, found to have a significant effect on performance. If we interpret this based on the limitations of the performance measuring methodology, increasing age and a long row adversely affected participants’ ability to row in the post-row period.

Study Limitations

This study was an observational study of ocean rowers. Assessment relied on the subjective assessment of symptoms by the rowers themselves as clinical examination by a medical professional was not feasible based on the location and format of the race. The performance data were not collected at a set time point and purely reported effect on ability to row in the period immediately following the row.

Conclusion

Ocean rowing is a significant cause of trigger finger, likely as a result of the prolonged flexion and pressure on the volar surface of the hand. This study therefore provides strong evidence that repetitive, mechanical stressors can indeed cause trigger finger. These findings may also indicate that river rowing, and other sports with similar stressors, may also cause symptoms of trigger finger. Longer rest periods were found to be protective, but the self-imposed measures introduced by the rowers themselves offered no beneficial effect. Further work is required to identify whether standardized, evidence-based protective measures such as splinting and exercise can reduce the incidence in at-risk individuals. If successful, these interventions may have an advantageous effect in preventing trigger finger in professional rowers, climbers, cyclists, and other sports involving prolonged flexion and excess pressure on the volar surface of the hand.