Involvement of the Medial Column Ligaments in Biomechanically Simulated Adult Acquired Flatfoot Deformity

Author: Arjun Sivakumar

Sivakumar, Arjun, 2018 Involvement of the Medial Column Ligaments in Biomechanically Simulated Adult Acquired Flatfoot Deformity, Flinders University, College of Science and Engineering

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Background: Adult acquired flatfoot deformity (AAFD) is one of the most common

etiologies, estimated to affect approximately 8% of adults (aged 21 and over) in the U.S. (NPD

Group for the Institute for Preventive Foot Health, National Foot Health Assessment 2012).

This corresponds to approximately 19 million people (U.S. Census Bureau, 2017).

Classification systems describing the symptoms of AAFD are widely used in the clinical

assessment and treatment of the condition (‘Stage I – IV Flatfoot’) and recognize the spring

ligament as the most contributing stabilizing structure of the medial ankle during all stages of

the condition, with the deltoid ligament described to only experience substantial deterioration

at the end stage of the condition (Stage IV flatfoot). In spite of this, the biomechanical

involvement of these ligaments as the physical deformity progresses has not been established.

Objectives: The aim of this study was to better understand the biomechanical contribution of

the primary static stabilizing ligaments of the medial column (spring ligament, deltoid

ligament, talocalcaneal interosseous, cuneonavicular ligaments) during the physical

progression of AAFD.

Methods: 9 unmatched Fresh-frozen cadaveric feet specimens were used. The age of the

specimens ranged from 44 to 84 years and the cause of death was not related to the foot.

Except for the posterior tibial tendon (dynamic stabilizer), all other structures were kept intact.

Small tantalum beads were carefully implanted at the attachment sites of the deltoid,

talocalcaneal, navicular cuneiform and spring ligaments (superomedial calcaneonavicular and

inferior calcaneonavicular).

A characteristic physical deformity anatomically similar to AAFD was progressively produced

in the cadaveric feet using a novel six degree of freedom (6DOF) Hexapod Robot. This was

produced under load control through applying 10 degrees of dorsiflexion, followed by a series

of 5 incremental loads (100N, 230N, 460N, 690N, 920N) with the foot fully unconstrained.

Left and right stereo-radiographs were taken of the foot in its unloaded state, as well as at each

of the loadsteps. Radiostereometric Analysis (RSA) was then used to, digitize and track the

displacement of the tantalum markers in 3D space and calculate the strain within each of the

ligaments at each progressive loadstep.

Results: The strains for each of the 11 ligaments at 5 progressive loads were calculated, from

which the sequence of recruitment of the ligaments could be observed at each stage through

the interacting elongations and subsequent contractions of the stabilizing ligaments at

progressive loads. The tibiocalcaneal portion of the deltoid ligament exhibited the highest

strain at each loading condition.

Conclusion: Under the tested conditions, the biomechanical contribution of the static

stabilizing of the medial column as the physical deformity progresses was evaluated. The

deltoid ligament was found to experience higher strains than the other ligaments at each stage

of the condition. An understanding of the contribution of the ligaments during the onset of

AAFD is essential for optimizing the management of symptomatic AAFD. From this study, it

is suggested that more attention be given to the deltoid ligament at all stages of AAFD.

Keywords: Adult Acquired Flatfoot Deformity, Medial Column Ligaments, Biomechanics, Contribution, Strain, Radiostereometric Analysis

Subject: Engineering thesis

Thesis type: Masters
Completed: 2018
School: College of Science and Engineering
Supervisor: Associate Professor John Costi