Flatfoot deformity is characterized by loss of the medial longitudinal arch, forefoot abduction, hindfoot eversion, and often Achilles tendon contracture. Our objectives were to validate a cadaveric flatfoot model that involves selective ligament attenuation and to determine if Achilles tendon overpull is associated with increased pes planus severity. We measured the three-dimensional (3D) orientation of the bones of interest in the unloaded, loaded, and Achilles tendon overpull conditions. A flatfoot model was created by attenuating ligaments involved in the pes planus deformity followed by cyclic axial loading, and bone orientations were acquired in the three conditions. Significant differences seen between normal feet and flat feet were consistent with those seen with the pes planus deformity. The first metatarsal dorsiflexed and abducted relative to the talus. The navicular abducted relative to the talus. The calcaneus everted relative to the tibia. The talus plantar flexed and adducted. Achilles overpull resulted in first metatarsal-to-talus dorsiflexion and navicular-to-talus abduction. Thus, selective ligament attenuation followed by cyclic axial loading can create a cadaveric flatfoot model consistent with the in vivo deformity. Longitudinal arch depression, hindfoot eversion, talonavicular joint abduction, forefoot abduction, and talar plantar flexion were seen. Simulated Achilles tendon contracture increased the severity of the deformity, particularly in arch depression and forefoot abduction.
"Although technically feasible, only a limited number of in vitro studies explicitly explored the effect of individual muscle activity on bone motion    . Kim et al. described the unique role of the individual extrinsic foot muscles on center of pressure but did not report individual bone kinematics. "
[Show abstract][Hide abstract] ABSTRACT: Activity of the extrinsic ankle-foot muscles is typically described for the whole foot. This study determines if this muscle activity is also confirmed for individual foot segments defined in multi-segment foot models used for clinical gait analysis. Analysis of the individual bone motion can identify functional complexes within the foot and evaluates the influence of an altered foot position on muscle activity. A custom designed and built gait simulator incorporating pneumatic actuators is used to control the muscle force of six muscle groups in cadaveric feet. Measurements were performed in three static postures in which individual muscle force was incrementally changed. The motion of four bone embedded LED-clusters was measured using a Krypton motion capture system and resulting motion of calcaneus, talus, navicular and cuboid was calculated. Results indicate that primary muscle activity at bone level corresponds with that described for the whole foot. Secondary activity is not always coherent for bones within one segment: decoupling of the movement of medial and lateral foot bones is documented. Furthermore, secondary muscle activity can alter according to foot position. The observed medio-lateral decoupling of the foot bones dictates the need to extend some of the multi-segment foot models currently used in clinical gait analysis.
[Show abstract][Hide abstract] ABSTRACT: Accessory tarsal navicular is a common anomaly in the human foot. It should be in the differential of medial foot pain. A proper history and physical, along with imaging modalities, can lead to the diagnosis. Often, classification of the ossicle and amount of morbidity guide treatment. Nonsurgical measures can provide relief. A variety of surgical procedures have been used with good results. Our preferred method is excision for small ossicles and segmental fusion after removal of the synchondrosis for large ossicles. In addition, pes planovalgus deformities need to be addressed concomitantly.
[Show abstract][Hide abstract] ABSTRACT: The symptomatic flatfoot deformity (pes planus with peri-talar subluxation) can be a debilitating condition. Cadaveric flatfoot models have been employed to study the etiology of the deformity, as well as invasive and noninvasive surgical treatment strategies, by evaluating bone positions. Prior cadaveric flatfoot simulators, however, have not leveraged industrial robotic technologies, which provide several advantages as compared with the previously developed custom fabricated devices. Utilizing a robotic device allows the researcher to experimentally evaluate the flatfoot model at many static instants in the gait cycle, compared with most studies, which model only one to a maximum of three instances. Furthermore, the cadaveric tibia can be statically positioned with more degrees of freedom and with a greater accuracy, and then a custom device typically allows. We created a six degree of freedom robotic cadaveric simulator and used it with a flatfoot model to quantify static bone positions at ten discrete instants over the stance phase of gait. In vivo tibial gait kinematics and ground reaction forces were averaged from ten flatfoot subjects. A fresh frozen cadaveric lower limb was dissected and mounted in the robotic gait simulator (RGS). Biomechanically realistic extrinsic tendon forces, tibial kinematics, and vertical ground reaction forces were applied to the limb. In vitro bone angular position of the tibia, calcaneus, talus, navicular, medial cuneiform, and first metatarsal were recorded between 0% and 90% of stance phase at discrete 10% increments using a retroreflective six-camera motion analysis system. The foot was conditioned flat through ligament attenuation and axial cyclic loading. Post-flat testing was repeated to study the pes planus deformity. Comparison was then made between the pre-flat and post-flat conditions. The RGS was able to recreate ten gait positions of the in vivo pes planus subjects in static increments. The in vitro vertical ground reaction force was within ± 1 standard deviation (SD) of the in vivo data. The in vitro sagittal, coronal, and transverse plane tibial kinematics were almost entirely within ± 1 SD of the in vivo data. The model showed changes consistent with the flexible flatfoot pathology including the collapse of the medial arch and abduction of the forefoot, despite unexpected hindfoot inversion. Unlike previous static flatfoot models that use simplified tibial degrees of freedom to characterize only the midpoint of the stance phase or at most three gait positions, our simulator represented the stance phase of gait with ten discrete positions and with six tibial degrees of freedom. This system has the potential to replicate foot function to permit both noninvasive and surgical treatment evaluations throughout the stance phase of gait, perhaps eliciting unknown advantages or disadvantages of these treatments at other points in the gait cycle.
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