Elsevier

Foot and Ankle Surgery

Volume 23, Issue 4, December 2017, Pages 250-254
Foot and Ankle Surgery

Influence of tibialis posterior muscle activation on foot anatomy under axial loading: A biomechanical CT human cadaveric study

https://doi.org/10.1016/j.fas.2016.07.003Get rights and content

Highlights

  • Effect weight bearing has on foot configuration investigated.

  • Actuation of TP tendon does not reconstitute medial longitudinal arch integrity under weight bearing.

  • Actuation of TP tendon does not correct hindfoot subluxation under weight bearing.

Abstract

Background

Collapse of the medial longitudinal arch and subluxation of the subtalar joint are common occurrences in adult flatfoot deformity. Controversy exists about the role of the tibialis posterior (TP) tendon as first and/or essential lesion. Subtle changes in the foot configuration can occur under weight bearing.

Purpose

This human cadaveric study is designed to investigate the effect that isolated actuation of the TP tendon has on the medial longitudinal arch and the hindfoot configuration under simulated weight bearing.

Methods

A radiolucent frame was developed to apply axial loading on cadaveric lower legs during computer tomography (CT) examinations. Eight pairs of fresh-frozen specimens were imaged in neutral position under foot-flat loading (75 N) and under single-leg stance weight bearing (700 N) without and with addition of 150 N pulling force on the TP tendon. Measurements of subtalar joint subluxation, forefoot arch angle and talo-first metatarsal angle were conducted on each set of CT scans.

Results

Subtalar subluxation, talo-first metatarsal angle and talo-navicular coverage angle significantly increased under single-leg stance weight bearing, whereas forefoot arch angle significantly decreased. Actuation of the TP tendon under weight bearing did not restore the forefoot arch angle or correct subtalar subluxation and talo-metatarsal angle.

Conclusion

Significant effect that weight bearing has on the medial longitudinal arch and the subtalar joint configuration is demonstrated in an ex-vivo model. 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 the hindfoot subluxation under weight bearing.

Clinical relevance

The findings of this study together with the developed model for ex-vivo investigation provide a further insight in foot anatomy.

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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