Ulnar nerve compression at the elbow is encountered frequently but until recently its exact incidence was unknown [1, 2]. Mondelli performed a retrospective study based on electromyography and estimated the standardised yearly incidence of ulnar nerve compression at the elbow at 20.9 per 100,000 [7]. This figure motivated the authors to design a case control study exploring the aetiology of ulnar nerve compression at the elbow. To our knowledge, this is the first hospital based case control study investigating this issue.
Several risk factors have been identified in this study. A number of these have been described in retrospective cohort studies, but in the absence of a control arm, questions arise as to the strength of the correlation between risk factors and ulnar nerve compression put forth in these publications. The following serve to highlight this point [1–3, 8]. Many reports state that male gender predisposes to the development of ulnar nerve compression at the elbow. In our study, gender and BMI (even if we divide the score in quartiles) do not meet the threshold for risk factors. A possible explanation for this discrepancy may lie in the fact that men previously performed heavier labour than women. However, even if gender and total working experience are combined, the odds ratio does not change (odds ratio for total working experience remains 1.25) and as such gender cannot be considered a risk factor.
Some authors have found that women with a lower BMI had a greater likelihood of developing ulnar nerve compression [3, 11], whereas others have reported that this occurred irrespective of the BMI [4]. Our study supports the concept that BMI, gender and nerve compression are independent variables.
In accordance with other studies [12] smoking was found to be a risk factor for the development of ulnar nerve compression. This is. The biological substrate is unclear and there was no evidence of a dose — response relationship. Nevertheless, it is possible that the effects of smoking on the microvasculature may reduce the likelihood of recovery in a damaged nerve. Alternatively, it may be postulated that the repetitive movement involved with smoking (flexing and extending the elbow) may predispose to nerve compression. However, smoking hand dominance is not correlated with the side on which surgery is performed, nor the amount of cigarettes smoked daily. Regular alcoholic consumption is not a risk factor as has previously been reported [12].
Heavy work is also a risk factor. If occupation is corrected for total duration of work, it is clear that jobs requiring heavier labour (higher score on the classification of work (Table 1) are associated with a greater risk of developing ulnar nerve compression at the elbow. This holds true even when work is subdivided into light and heavy labour. If work experience is adjusted for highest level of education, then the level of education is most relevant. This analysis reveals that a lower level of education predisposes to an increased risk of ulnar nerve compression at the elbow; it seems reasonable that occupation and highest level of education are closely related. In the future, we propose to investigate level of education and work experience in relation to ulnar nerve compression at the elbow.
We found that a fracture of the elbow does not predispose to an ulnar nerve compression at the elbow. Although the odds ratio does suggest an influence, the 95% confidence limit clearly contradicts this conclusion. The number of patients in the clinical and control group does not explain this contradiction. Therefore, in the current study no evidence was found that an elbow fracture and development of ulnar nerve compression at the elbow are related. This is also of historical interest, since the alternative term “tardy ulnar palsy” was given to this condition based on the belief that it occurred after a fracture of the elbow [5]. Admittedly, the descriptions of selected cases without a control group does support this correlation [6].
Repetitive movement of the arm during work is not a risk factor. The data required to answer this specific issue is difficult to acquire. The problem is the precise de- finition of repetitive arm movements and the frequency of such movements. All patients were asked if they made repetitive movements and to provide a description of these movements. The variation is enormous and ranges from typing to operating an industrial machine. Several patients could not recall how many times the movements were performed daily. The data is therefore weak and drawing conclusions from them is difficult. Recently, it has been reported that holding a tool in the same position is a predictive factor [4].
This study could be criticised for its bias. We do not believe that selection bias holds true for our study. Indeed, our clinical and control patients were all selected from those referred to a hospital setting. It is admitted that patients with minimal symptoms relating to ulnar nerve compression have been excluded from the study. However, the exact numbers are not known and therefore the effect on calculations and conclusions cannot be determined. Furthermore, in our practice, the referral pattern for patients with an ulnar nerve compression at the elbow is the same as for those with a herniated cervical or lumbar disc. Conclusions regarding risk could not be formulated for those patients with hypothyroidism and a history of luxation of the elbow because of the small numbers with these conditions. However, we do not think this is influenced by selection. The possible selection bias in the exclusion of ulnar nerve compression that does not cause severe symptoms or is of only very short duration not warranting surgical intervention is noted. Since exact numbers are not known, we do not speculate about the influence this group has on our calculations and conclusions. Confounding bias is also a common criticism. Prior to this investigation we defined gender as a possible confounder but multiple multivariate regressions did not confirm this assumption.
In our opinion, information bias is not a problem since the patients were questioned regarding actual and very recent habits. The determination of repetitive arm movements whilst working is difficult to assess both in terms of type and frequency. For studies involving the general population, this bias will remain a problem. However, selecting a defined group of industrial workers with a known working history may be helpful in overcoming this problem and may indeed establish whether repetitive movement is a risk factor for ulnar compression.
Finally, the incomplete survey response is a limitation of the study. We cannot know what effect the nonresponders may have had on the conclusions drawn from this study.