# Reliability and Validity of the Orthotic Deformation Test
## 4 Discussion
Similarly, 10% arch deformation took place below and above of 40 N of vertical force for the positive and negative test, respectively (Figure 6C). An excessive deformation of the orthoses is interpreted by clinicians as a failure of the orthosis to prevent foot collapse and establish the efficient windlass mechanism. These results suggest that failures in orthoses mainly manifest while the first 50 N of force is applied. Therefore, clinicians should identify this failure in orthoses early during the evaluation of the ODT. Failure in the custom foot orthoses occurs as a consequence of repeated cycles of applied forces with each step that the patient takes. Those forces are correlated with use time and the patient's weight, foot deformities, and type of activity. Evaluation of foot orthoses stiffness is widespread in clinical practice and is used to make decisions about the modifications required by custom foot orthoses. [PERSON], who evaluated patients as they stood on orthoses, proposed that 5 mm of longitudinal medial arch deformation was excessive for relieving symptoms related to medial arch collapse [29]. Results of this study reveal that a vertical force of 150 N applied by the compression device to orthoses with a positive ODT deformed the orthoses by a median of 5.62 mm; orthoses with a negative ODT deformed by a median of 4.56 mm. A clinician's thumb could not collapse the arch by more than 5 mm in the majority of orthoses with a negative test. According to our results, the hypothesis proposed by [PERSON] is supported; 5 mm of deformation should be considered the threshold for custom foot orthoses used to treat biomechanical pathologies. Different custom foot orthoses intended to treat a variety of foot types were used in this study; different foot types generate different stresses, strains, and forces on dorsal arch support. Plantar pressures are increased in the midfoot in patients with flatfoot [13]. Therefore, clinicians tend to prescribe more rigid longitudinal medial arches for bearing midfoot plantar forces. New pes planus orthoses with added rearfoot and forefoot posts are expected to offer more resistance; pes cavus orthoses and used orthoses are expected to offer less resistance. However, this heterogeneity was not reflected in the ODT results (\(p\) = 0.003). Finally, our results revealed that the opinions of the researcher with the fewest years of experience were incongruent with those of the more experienced researchers (\(p\) = 0.493 [\(-\)0.378-0.181]; \(p\) = 0.452 [\(-\)0.332-0.150]). These findings suggest that clinical experience is a factor that influences the interpretation of the ODT and highlight the need to establish teaching strategies that shorten the time necessary to identify the failure in custom foot orthose by the ODT. It is necessary to carefully follow the test steps and conduct training to ensure consistent interpretation of the ODT results. Common errors that can improve reproducibility include not exerting a maximal force with the thumb over the orthosis, not applying enough resistance with the non-dominant hand to the lateral arch to prevent rotation of the orthosis, and not applying vertical force at the appropriate point (i.e., the apex of the medial longitudinal arch near the edge of the orthosis). Applying force to other areas of the medial longitudinal arch should be avoided because the applied lever arm of the thumb can vary and decrease the applied force. Furthermore, we propose a combination of applying a vertical force with the thumb and interpreting the deformation of the longitudinal arch with the patient standing on the orthoses to reduce resulting variability when working with novice clinicians. Furthermore, this study included a small number of researchers evaluating ODT. Three researchers with different levels of experience were included in this study because the objective was to evaluate the impact of researcher expertise on the interpretation of this subjective test.