Subtalar dislocation is a rare injury caused by high-energy trauma. Current treatment strategies include leg casts, internal fixation and external fixation. Among these, external fixators are the most commonly used as this method is believed to provide better stabilization. However, the biomechanical stability provided by these fixators has not been demonstrated. This biomechanical study compares two commonly used external fixators, i.e. Mitkovic and Delta. CT imaging data were used to reconstruct three-dimensional models of the tibia, fibula, talus, calcaneus, navicular, cuboid, three cuneiforms and five metatarsal bones. The 3D models of the bones and cartilages were then converted into four-noded linear tetrahedral elements, whilst the ligaments were modelled with linear spring elements. Bones and cartilage were idealized as homogeneous, isotropic and linear. To simulate loading during walking, axial loading (70 N during the swing and 350 N during the stance phase) was applied at the end of diaphyseal tibia. The results demonstrate that the Mitkovic fixator produced greater displacement (peak 3.0mm and 15.6mm) compared to the Delta fixator (peak 0.8mm and 3.9 mm), in both the swing and stance phase, respectively. This study demonstrates that the Delta external fixator provides superior stability over the Mitkovic fixator. The Delta fixator may be more effective in treating subtalar dislocation.
Charcot neuroarthropathy (CN) is a rare, progressive, deforming disease of bone and joints, especially affecting the foot and ankle and leading to considerable morbidity. It can also affect other joints such as the wrist, knee, spine and shoulder. This disease, described originally in reference to syphilis, is now one of the most common associates of diabetes mellitus. As the number of diabetics increase, the incidence of CN is bound to rise. Faster initial diagnosis and prompt institution of treatment may help to reduce its sequelae. There should be a low threshold for ordering investigations to assist coming to this diagnosis. No single investigation is the gold standard. Recent studies on pathogenesis and development of newer investigation modalities have helped to clarify the mystery of its pathogenesis and of its diagnosis in the acute phase. Various complementary investigations together allow the correct diagnosis to be made. Osteomyelitis continues to be confused with acute CN. Hybrid positron emission tomography has shown some promise in differentiating these conditions. A multispecialty approach involving diabetologists, orthopaedists and podiatrists should be used to tackle this difficult problem. The aim of this article is to describe current knowledge about CN with particular reference to the status of diagnostic indicators and management options.
BACKGROUND: Flexible flat foot is described as a reduction in the height of the medial longitudinal arch and may occur from abnormal foot pronation. A foot orthosis is thought to modify and control excessive pronation and improve arch height.
OBJECTIVE: To compare the immediate effect of three types of orthoses on foot mobility and the arch height index in subjects with flexible flat feet.
STUDY DESIGN: A quasi-experimental study.
METHOD: The dorsal arch height, midfoot width, foot mobility and arch height index were assessed in 20 participants with flexible flat feet (mean age = 23.2 ± 3 years) for three different foot orthosis conditions: soft, semi-rigid and rigid University of California Biomechanics Laboratory (UCBL).
RESULTS: Maximum midfoot width at 90% with arch mobility in the coronal plane was shown in the semi-rigid orthosis condition. The semi-rigid orthosis resulted in the highest mean foot mobility in 90% of weight bearing, and the rigid orthosis (UCBL) had the lowest mean foot mobility. The soft orthosis resulted in foot mobility between that of the rigid and the semi-rigid orthosis. UCBL orthosis showed the highest arch height index, and the semi-rigid orthosis showed the lowest mean arch height index.
CONCLUSION: Due to its rigid structure and long medial-lateral walls, the UCBL orthosis appears to limit foot mobility. Therefore, it is necessary to make an orthosis that facilitates foot mobility in the normal range of the foot arch. Future studies should address the dynamic mobility of the foot with using various types of foot orthoses.
CLINICAL RELEVANCE: Although there are many studies focussed on flat foot and the use of foot orthoses, the mechanism of action is still unclear. This study explored foot mobility and the influence of foot orthoses and showed that a more rigid foot orthosis should be selected based on foot mobility.
KEYWORDS: Foot orthosis; arch height index; foot mobility magnitude