Influence of tibialis posterior muscle activation on foot anatomy under axial loading: A biomechanical CT human cadaveric study
Introduction
Generally, it is believed that flatfoot deformity results from failure of the tibialis posterior (TP) tendon [1], [2], [3]. Therefore, posterior tibial tendon dysfunction is frequently used as a synonym for an adult-acquired flatfoot deformity, although there are some discussions in the literature about the role of the TP tendon as first and/or essential lesion [4].
The resting position of the foot can vary greatly with the weight bearing fashion which is dependent on bone morphology [5], [6] and pathology [7], [8], [9]. This variation can be quite outspoken, especially in flatfoot deformity, and has been demonstrated numerous times in plane radiographies. Most diagnostic methods, such as computer tomography (CT) and magnetic resonance imaging (MRI), are generally not applied under weight bearing of the examined lower limb. Comparison of a non-weight bearing to a weight bearing CT scan would help to make the dynamic nature of the anatomy easier to assess.
The objective of this study was to perform ex-vivo CT investigation on human feet in preloaded foot-flat condition and under defined axial loading simulating single-leg stance weight bearing, to determine the impact of weight bearing on the hallmarks of flatfoot deformity and investigate the effect of TP muscle activation on the behavior of the medial column of a foot without pre-existing pathology.
Section snippets
Methods
An air pressure-controlled radiolucent frame was specifically designed for positioning and axial loading of human cadaveric lower legs during CT scanning (Fig. 1).
Eight pairs of fresh-frozen (−20 °C) human cadaveric lower legs from Caucasian donors (5 males and 3 females, 79.4 years average age, standard deviation (SD) 10.9 years, range 59–91 years) were used in the current study. All specimens were checked for pathologies or any previous surgeries, as well as for integrity of the joints. The
Results
The intra-observer measurements correlated significantly with each other for all outcomes, p < 0.01. Pearson correlation coefficient was 0.99 for subtalar (ST) subluxation and forefoot arch angle (FAA), 0.93 for talo-first metatarsal (Meary’s) angle and 0.97 for talo-navicular coverage (TNC) angle.
The increase of axial loading from 75 N (foot-flat) to 700 N (single-leg stance) resulted in significant changes for all outcomes (Table 1). Subtalar subluxation increased from 4.49 mm to 5.22 mm on average
Discussion
Utilizing a cadaveric lower leg model which simulates forces existing in foot-flat and single-leg stance states, by application of standard CT methods we were able to register changes seen in the medial column and hindfoot configurations after weight bearing. Our model demonstrated such changes, classically described for a ‘flattening’ foot, as talar subluxation, uncovering of the talar head, increase in the Meary’s angle and decrease in the forefoot arch angle [16], [17], [18]. Tensioning the
Conclusions
This study demonstrates in an ex-vivo study model the significant effect weight bearing has on the medial longitudinal arch behavior and the subtalar joint configuration. However, in absence of other medial column derangement, actuation of the TP tendon alone does not seem to reconstitute the integrity of the medial longitudinal arch or correct hindfoot subluxation under weight bearing. While further clinical investigations are still needed, the present study corroborates the growing evidence
Conflicts of interest
The authors declare no conflicts of interest.
Acknowledgements
The authors are not compensated and there are no other institutional subsidies, corporate affiliations or funding sources supporting this work unless clearly documented and disclosed. This investigation was performed with the assistance of the AO Foundation via the AOTRAUMA Network (Grant No.: AR2014_02).
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