Der Talometatarsalindex („TMT-Index“): Ein wertvoller Röntgenparameter zur Differenzierung zwischen Normalfuß und Planovalgusdeformität beim Kind und Jugendlichen

INTRODUCTION The development of the shape of the shape from childhood to adulthood is a complex continuum. Deviations from this process occur frequently and, especially in asymptomatic patients, do not always include the need for therapeutic intervention. In the current S2-guideline on the juvenile flexible flatfoot, established x‑ray parameters for assessing the flatfoot deformity were judged to be sensitive, whereby no statement was made regarding the value of the parameters among themselves. The aim of the present work is to assess the talometatarsal Index (TMTInd) in comparison to established angle measurements. METHODS Twenty-two feet with and 22 feet without planovalgus deformity (age: 10-14 years) were investigated. Established radiological parameters (lateral view: talocalcaneal angle (TC-lat), calcaneal pitch angle (Calc-B), Costa-Bartani angle (Costa-B), talometatarsal‑I angle (TMTI-lat); dorsoplantar view: talometatarsal-I-basis angle (TMTIB), talonavicular coverage (TNG), calcaneal metatarsal- V angle (Calc-MTV), talocalcaneal angle (TC-dp), and talometatarsal‑I angle (TMTI-dp)) were measured on standardized X‑ray images and compared with the values of the TMTInd. RESULTS All parameters other than Calc-MTV, TC-dp, TC-lat and Calc‑B, showed a statistically significant difference between normal and planovalgus feet, although for almost all values measured (apart from TMTI-lat and TMTInd) there was a large overlap area (>10°) between the two groups. The comparison of TMTInd to all other parameters showed the highest discrimination factor (area-under-the-curve) for the TMTInd in the distinction between the groups. CONCLUSION Compared to conventional radiological parameters, the TMTInd shows the highest validity in the distinction between normal and planovalgus feet and can provide valuable information in clinical decision-making with regard to therapy specification.