Abstract
Background:
A biphalangeal fifth toe is a common variant in the European population. The frequency is higher in the Japanese population. It is considered an anatomical variant of the normal triphalangeal fifth toe.
Methods:
Patients divided into three study groups were retrospectively reviewed to determine the effect of a biphalangeal fifth toe on the occurrence of clinically symptomatic pathology of the fifth ray.
Results:
The prevalence of a biphalangeal fifth toe in patients with hammer or claw toes was 65%, bunionettes 47%, and overriding fifth toe 37%. Only for the group with hammer or claw toes was prevalence significantly higher than that in the control group (39%).
Conclusion:
The stiffness and rigidity of the biphalangeal fifth toe may predispose it for symptomatic hammer or claw toe.
INTRODUCTION
Although the biphalangeal fifth toe was first described by Leonardo da Vinci in 1492, 6 later anatomists such as Vesalius 9 depicted the three-phalanged form. The biphalangeal fifth toe was thought to be caused by a pathologic fusion of the middle and terminal phalanges during postnatal life, attributable to trauma or disuse of this joint. 5 The terminal phalanx of the biphalangeal form is described frequently as fused, as seen in nomenclature such as synostosis, symphalangism, and interphalangeal coalition. However, the frequency of biphalangism of the fifth toe in fetuses does not differ from that in adults (Table 1). 2 Biphalangism may be the result of incomplete segmentation, with failure of development of the distal interphalangeal joint. Since biphalangism is an exclusively human phenomenon, it is possibly a response to bipedalism. 5 Most authors consider this anomaly as a normal anatomical variant and not the product of pathologic processes. The reported overall prevalence of biphalangeal fifth toe in Europe is between 35% to 45%, which is lower than that in the Japanese population (70% to 80%). 9 Biphalangeal toe does not occur only in the fifth toe but is observed in the other toes with less frequency (Table 1). Biphalangism of a more medial toe (except the hallux) seems to occur only if a more lateral toe also is biphalangeal. 10
The objective of this study was to determine whether this common anatomical variant plays a role in creating a clinical problem of the fifth ray, because it may be stiffer and less able to accommodate pressure.
MATERIALS AND METHODS
Radiographs of patients who had fifth toe surgery from 1996 through 2000, were retrospectively reviewed. This population was divided into three study groups, depending on fifth ray pathology: hammer or claw toe, bunionette, or overriding (curly) toe.
If radiographs were not available, patients were excluded (32 patients). A total of 51 feet were reviewed in the group that had surgery to correct a painful fifth hammer or claw toe: 36 women and 11 men (four women had bilateral surgery). The mean age was 52 years. A total of 91 feet were included in the bunionette group: 67 women and 18 men (three men and three women had bilateral surgery); the mean age was 46.9 years. The group with a curly fifth toe included 49 feet: 30 women and six men (11 women and two men had bilateral surgery); the mean age was 44 years. The comparative control group was collected in September and October of 2001, during outpatient clinics and included 296 feet from 148 patients (113 women and 35 men). They complained about symptoms elsewhere in their feet. Patients presenting with fifth ray deformity or fifth ray surgery in the past were excluded. The mean age of all patients was 48 years. All patients were Caucasian. All feet were reviewed by anteroposterior weightbearing radiographs and nonweightbearing oblique radiographs to see if there was a biphalangeal fifth toe.
Review of previous studies.
A chi square analysis was performed on the frequencies of biphalangism in each study-group compared with the control-group to see if fifth ray deformity was related to this variant. P-values smaller than 0.01 were considered significant.
RESULTS
Among the study group with hammer or claw toes, 33 feet had a biphalangeal fifth toe (65%) in 26 women and seven men. There were two patients who had a biphalangeal fifth toe only in their right foot. One of them showed the opposite; she had a symptomatic triphalangeal claw toe surgically treated and an asymptomatic biphalangeal fifth toe on the right. Another patient also had a biphalangeal fourth toe (Figure 1).
The bunionette group included 43 feet with biphalangeal fifth toe (47%) in 34 women and nine men. Five patients had biphalangeal fifth toes unilaterally, in four on the left (three women, one man) and in one woman on the right.
Among the patients with an overriding fifth toe 18 of 49 feet had biphalangeal fifth toes (37%):15 women and three men. One patient also had bilateral biphalangeal fourth toes.
The control group consisted of 296 feet. There were 114 biphalangeal fifth toes (39%) (96 women and 18 men) (Figure 2). In six women, this variant occurred unilaterally (four left, two right). One man and one woman also had biphalangeal fourth toes. One female patient had a biphalangeal third toe (Table 2).
The difference in frequency of biphalangeal fifth toe between hammertoe or clawtoe and controls was significant. Patients with symptomatic hammertoe or clawtoe deformities had a significantly higher frequency of biphalangeal fifth toe than asymptomatic controls (Table 2). In the other two study groups, there was no clear evidence for such a correlation between biphalangeality and symptomatic deformity.
Study results: frequency of biphalangeal fifth toe in hammertoe and clawtoe; bunonette, and overriding fifth toe.
Study results
Biphalangeal third, fourth, and fifth toes bilaterally.
DISCUSSION
A correlation between a biphalangeal fifth toe and a predisposition to symptomatic deformity has not been well documented. It had been suggested that there is a greater possibility of developing hard and painful corns in a biphalangeal toe. 1 In a previous study, 60% of patients who had surgery to correct a painful fifth hammer or claw toe had a biphalangeal fifth toe, compared with only 45% in the control group (p < 0.05). 9 The results of our study confirm the correlation between biphalangeal fifth toe and hammer or clawtoes. A biphalangeal fifth toe is stiffer and less able to accommodate the pressure of conventional shoe wear. However, a biphalangeal fifth toe was not correlated with entire fifth ray problems, such as a bunionette, which is a metatarsal problem, 2 or an overriding fifth toe, which is a soft tissue and rotating abnormality in the metatarsophalangeal joint. Perhaps biphalangeal fifth toe is only correlated with phalangeal problems, such as hammertoes or clawtoes. Although the aim of this study was not to estimate the prevalence of biphalangeal fifth toe in the European population, we can compare our results with the studies that did. The current control-group excluded patients with symptomatic problems of the fifth ray. The frequency of biphalangeal fifth toe does not differ much from the results of studies a century ago (Table 1). In a recent study, 46% of patients younger than 25 years had biphalangeal fifth toes, and 31% of patients older than 75 years had this variant. 4 This difference might be due to the variation of ethnic origin between the two age groups. In our study, we could not compare the prevalence of biphalangeal fifth toe between two generations because of the small populations; only 51 patients were younger than 25 years and 15 patients were older than 75 years.
In one study, no difference in the incidence between men and women was found, 5 but others concluded that this variant is found more often in women. 10 Our results indicate that the frequencies are comparable between men and women. However, in the control group there were significantly more women with biphalangeal fifth toes. Symptomatic problems of the forefoot predominate in women. 3 In the literature, unilateral biphalangeal fifth toe is rare (6%). 8 This percentage is comparable to the frequencies found in our study: 7% (Table 2).