Measurement of the Forefoot with Roentgen Stereophotogrammetry in Hallux Valgus Surgery

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Abstract
Eight hallux valgus patients were marked with tantalum markers in conjunction with hallux valgus surgery (seven proximal osteotomies and one chevron osteotomy). Changes on weightbearing before surgery as well as corrective changes after surgery were analyzed with roentgen stereophotogrammetry (RSA) and with standard x-rays. RSA is accurate to 0.6° in rotational changes and 0.3 mm in translation. Weightbearing changes were inconsistent, and minimal with both standard x-rays and RSA. It was possible to analyze the correction at the osteotomy site with RSA. In half the cases, the correction measured by RSA corresponded with that measured with standard x-rays, within measurement error; in the other cases, RSA showed that the correction was of a different size or direction than that measured on standard x-rays. Corrective changes in hallux valgus surgery are complex, including angular and translational changes at several levels and in several joints in order to produce a clinical resultant. Rotational changes can be evaluated with RSA. Although RSA in an optimal situation is very accurate, it is still limited to a laboratory setting.