Subluxation of the talocalcaneal joint in adults who have symptomatic flatfoot

Background: When flatfoot is acquired during adulthood, the shape of the fo ot changes. In addition to a decreased arch, there may be valgus angulation of the hindfoot or abduction of the forefoot, or both. However, there is l ittle objective information to provide a better understanding of the anatom ical or morphological changes that occur in acquired adult flatfoot, We won dered if such an understanding of the three-dimensional anatomy might shed light on the pathway by which these changes occur. We designed this study t o measure the three-dimensional position of the talocalcaneal joint in pati ents who have painful flatfoot. Methods: Computed tomography scans of the feet of eight patients who had sy mptomatic flatfoot were used to construct a model of the talocalcaneal arti culation. The scans were performed on a custom loading frame developed to s imulate weight-bearing with the foot in a neutral position while a seventy- five-newton axial compressive load was applied. The digital data from the s cans were used to make three-dimensional computer models of the articular s urfaces of the talus and calcaneus of each foot. These models then were use d to calculate the percentage of the articular surface that was in contact and, conversely, the percentage that was subluxated. Two surfaces were mode led for each bone; the posterior facet formed one surface, and the anterior and middle facets were combined to form the second surface. The data were compared, with use of Mann-Whitney nonparametric U analysis, with those der ived from scans of the feet of four patients without a deformity of the hin dfoot who served as controls. Results: A mean (and standard deviation) of 68 +/- 9 percent of the posteri or facet of the calcaneus was in contact with the talus in the patients who had flatfoot compared with 92 +/- 2 percent in the controls, and a mean of 51 +/- 23 percent of the anterior and middle facets of the calcaneus was i n contact with the talus in the patients who had flatfoot compared with 95 +/- 6 percent in the controls. These differences were significant (p = 0.00 66 for both). Conclusions: Marked subluxation of the talocalcaneal joint occurs in some p atients who have symptomatic planoabductovalgus deformity.