Plantar aspect of the talus (no. 43). Four distinct articular surfaces can be observed anterior to the sulcus tali. 1, posterior calcaneal articular facet; 2, middle facet for calcaneus; 3, facet for plantar calcaneonavicular ligament; 4, anterior facet for calcaneus; 5, navicular articular surface. 

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... human tarsal anatomy includes the follow- ing four joints: talocalcaneal, talocalcaneonavicular, calcaneocuboid, and, rarely, cuboideonavicular. Tarsal coalitions (TC) and joint variants occur in these joints. TC are defined as fibrous, cartilaginous, or osseous unions of at least two tarsal bones (Mosier and Asher, 1984; Kulik and Clanton, 1996; Sakellariou and Claridge, 1999); however, their prevalence has not been convincingly determined. Clinical studies report a prevalence of TC of Ͻ 1% (Harris and Beath, 1948; Vaughan and Segal, 1953); but, because between 34% (Varner and Michelson, 2000) and 76% (Leonard, 1974) show no symptoms, the prevalence, including non-symptomatic cases, could be as high as 4%. TC are often associated with secondary degenerative changes (Sakellariou and Claridge, 1999) that direct the therapy modality (e.g., resection versus fu- sion). Furthermore, TC have been associated with altered motion in the subtalar joint complex, flat foot, and peroneal spasm (Harris and Beath, 1948; Leonard, 1974; Sakellariou and Claridge, 1999; Varner and Michelson, 2000). Clearly, a knowledge of the prevalence, distribution, and pathologic significance of TC has clinical importance. Secular trends have been shown for anatomical variants (Henneberg and George, 1995) and for pathologies (Henneberg and Henneberg, 1999); therefore, evidence of an altered prevalence of TC would be of interest. The aim of our study was to investigate the prevalence of TC and tarsal joint variants as well as the association between TC and tarsal arthritis and accessory tarsal bones. One hundred fourteen feet from 62 cadavers (32 female; 30 male) with an average age of 77.7 years were dissected at the Department of Anatomical Sciences, The University of Adelaide (the remaining 10 unpaired feet were used in another project). No feet showed obvious signs of local pathology. Medical records of the cadavers were not available. All individuals lived before their death in the area of Adelaide and were of European ancestry. This study is part of a larger still ongoing research project examining the diagnostic value of computed tomography (CT) for TC. Location, size, and constitution (non-osseous versus osseous) of TC or tarsal joint variants as well as aspects of articular surfaces (e.g., degenerative changes) were described with arthritis being reported for joints showing partial or full thickness chondral defects grade III or IV according to Miller (1998). The overall prevalence of primary non-osseous (fi- brocartilaginous) TC was 8.8% (10/114): 7% were calcaneonavicular coalitions (CNC, 8/114, Fig. 1) and 1.8% talocalcaneal coalitions (TCC, 2/114). Because a total of eight individuals were affected, the overall prevalence was 12.9% (8/62). From our gross morpho- logic examination of the whole feet and dissected bones, supported by CT imaging, we found no primary osseous coalitions or any signs of secondary coalitions that may have been due to trauma, infections, or neoplasm. One of the two TCC was in an extra- articular location (anterolateral to the posterior talocalcaneal joint (10 mm in length and 10 mm in width); the other (also 10 ϫ 10 mm) was at the middle articular facet. The sizes of the CNC varied from 5 ϫ 15 mm to 15 ϫ 35 mm. Severe tarsal arthritis was present in 32.5% of all feet (37/114). Both cases of TCC but none of the CNC exhibited arthritis. TC occurred more often in females (70%; 7/10) than males (30%; 3/10). One third of all affected individuals showed bilateral CNC (2/6). There was no obvious lateral asymmetry in the occurrence of TC (Table 1). Concerning joint variants, a fully developed synovial calcaneonavicular joint was present in 7.9% (9/ 114) of feet and a cuboideonavicular joint was present in 30.7% (35/114). Two, instead of three, talar articular surfaces were present on the calcaneus in 9.7% (11/ 114) of feet; two instead of three facets for the calcaneus were present on the talus in 29% (33/114). Four distinct articular surfaces of the talus for the talocalcaneonavicular joint were observed in one foot (Fig. 2). The frequency of sesamoid bones in the tibialis posterior and fibularis (peroneus) longus tendons was 27.2% (31/114) and 14.9% (17/114), respectively. An accessory bone, a so-called os trigonum, located pos- terior to the posterolateral tubercle of the talus, was found in 7% of feet (8/114). All joint variants found in individuals with TC are listed in Table 1. The biological significance and the etiology of TC are still debated. Explanations include failure of dif- ferentiation and segmentation of fetal mesenchyme (Harris, 1955; Leonard, 1974; Mosier and Asher, 1984), or as an incorporation of accessory bones into nearby tarsals (Pfitzner, 1896; Badgley, 1927; Leonard, 1974). We found no correlation between the occurrence of TC and of accessory tarsal bones and, therefore, we cannot support the latter theory of coalition development. The prevalence of TC and the question of normal variation still remains unknown because most studies are of symptomatic samples (Table 2). Clinical samples based on radiologic assessment of symptomatic patients usually fail to record asymptomatic cases. Additionally, in such studies the various imaging tech- niques show equivocal results; CT and MR imaging have been shown to be of the highest diagnostic value for TC (Pachuda et al., 1990; Wechsler et al., 1994; Sakellariou and Claridge, 1999). It is unclear if TC represent pathological conditions or anatomic variations. These uncertainties are important because TC have clinical significance when symptomatic. Some of the non-osseous coalitions may ossify in early adoles- cence (Badgley, 1927; Drennan, 1996; Sakellariou and Claridge, 1999) and then become symptomatic. Non- osseous TC that persist into adulthood, it has been suggested, could cause pain and arthritic changes due to “microfractures and remodelling on the boundaries between bone and coalitions” (Kumai et al., 1998). Difficulties in estimating the prevalence of TC are numerous. Prevalence per foot or per individual must be stated: for example, in our sample, prevalence would be 8.8% (10/114) and 12.9% (8/62), respectively. The questionable accuracy of the prevalence is revealed in a study by Harris and Beath (1948). They state that “in nearly all cases [of peroneal spastic flat foot] the lateral radiograph showed lipping of the superior margin of the head of the talus;” such lipping “strongly suggest[ing] the existence of one or other [the calcaneonavicular bar and the talocalcaneal bridge] of the congenital anomalies.” Thus, undetec- ted coalitions could well have been present in studies dealing with asymptomatic samples. In the only other reported cadaver study, an overall prevalence of TC of 2.5%, which is much lower than our data, was found (Pfitzner, 1896). The secular trend in the prevalence of TC in our study in comparison to other adult samples (Table 2) could represent a short-term response to changes in life-style (restrictive footwear, occupation) or high- light an ongoing microevolutionary trend. In our sample, two out of six individuals with CNC showed this condition bilaterally, which is similar to earlier reports (Drennan, 1996; Kulik and Clanton, 1996; Sakellariou and Claridge, 1999). Similar to Pfitzner (1896) our right/left ratio did not indicate lateral asymmetry. We found the prevalence of CNC versus TCC to be 4:1. This is in contrast to previous studies showing an equal distribution (Kulik and Clanton, 1996; Sakellariou and Claridge, 1999) or a ratio of 7.5:1 (Pfitzner, 1896). Additionally, we detected no link between non-osseous CNC and tarsal arthritis, even with se- vere tarsal arthritis recorded in one third of all feet. The male/female ratio of the incidence of TC was 3:7 in our sample; again, this is unlike earlier findings showing either an 80% male dominance (Stormont and Peterson, 1983) or sex equality for TC (Pfitzner, 1896; Leonard, 1974). Microevolutionary changes in occurrence or expression of body structures within a short time are well known for anatomical variations, such as the median artery of the forearm (Henneberg and George, 1995; Aziz et al., 1996) or human pathologies, such as spina bifida occulta (Henneberg and Henneberg, 1999). Re- laxed natural selection was earlier mentioned as a possible factor favoring such microevolutionary trends (Stephan and Henneberg, 2001). Major etiologies of microevolutionary trends seem to be either environmental (even intrauterine) or genetically based. Ac- cording to a study by Harris (1955), 20% of a sample of apparently normal embryos (4/20; 9 –13th week of gestation, age estimated according to Benson and Doubilet, 1998) showed TC. Even for Harris (1955) the permanent character of this high number of TC was not convincing: because joints usually develop after the 7th week of gestation, these frequent conditions could at this stage of development be of tempo- rary nature only. If so, they should not be regarded as “coalitions.” Genetic influence on the occurrence of TC is ...