The unreliability of the intermetatarsal angle in choosing a hallux abducto valgus surgical procedure.

Conventional thinking holds that high intermetatarsal and hallux abductus angles (>15° and >25°, respectively) are associated with a hypermobile first ray and require a Lapidus procedure to achieve satisfactory correction for the treatment of hallux valgus. However, normal first ray motion may be misinterpreted as hypermobility, and it is possible to take advantage of this motion to correct some portion of a large hallux abductovalgus deformity with distal procedures, such as the Austin or first metatarsophalangeal joint fusion. We retrospectively examined radiographs of 61 patients with first intermetatarsal and hallux abductus angles greater than 15° and greater than 25°, respectively, who had undergone hallux abductovalgus correction via Lapidus, Austin, or first metatarsophalangeal joint fusion. Preoperative and postoperative radiographic measurements of the intermetatarsal and hallux abductus angles were made. The results revealed no statistically significant differences in the amount of correction achieved by any of the 3 procedures in comparison with the others. We concluded that, given appropriate patient selection, an Austin or first MTPJ fusion could reliably correct large intermetatarsal and hallux abductus angles that, in the hands of many surgeons, are often treated by means of Lapidus arthrodesis.

Discrimination Between Equations of State.

Eight isothermal equations of state are analyzed to yield quantitative measures of the degrees to which equation pairs can he discriminated for real data, data of limited span and precision. Calculated curves allow one to assess the span and precision necessary in P-V data to allow unambiguous discrimination of various pairs. Some discussion is presented of bias and systematic error which may arise in least squares fitting. Using exact synthetic data, we also illustrate for seven equation pairs the very large relative systematic errors in parameter and standard deviation estimates which arise from such fitting of data of limited span with an incorrect but "close" equation model. General conclusions following from these results are discussed. Although the present work is principally concerned with discrimination between equations of state, its results are pertinent to the more general problem of choosing a "best" analytical model (linear or nonlinear) to represent experimental results.