FIFTY-SIX MARKERS TO THE FOOT - a new study in understanding foot and ankle movement

by Dr Christopher Nester Senior Research Fellow, Centre for Rehabilitation and Human Performance Research,

Brian Blatchford Building, University of Salford, Salford, M6 6PU England.

Email: c.j.nester@salford.ac.uk

Researchers from the University of Salford (UK) and Iowa State University (USA) are collaborating on a novel project to improve our understanding of the human foot and ankle. Dr Chris Nester, Dr David Howard and Mr Anmin Liu from Salford's Centre for Rehabilitation and Human Performance Research Centre are sponsored by the UK Engineering and Physical Sciences Research Council for an 18 month project which aims to provide a detailed description of the kinematics of tibia plus 14 bones of the foot. Using this information a scientific rationale for the best way to segment the foot will be derived.

The project is based on the Iowa State “walking simulator”. Dr Erin Ward, Dr Jay Cocheba, both US Podiatrists, and Professor Pat Patterson worked from 1996-2002 to build one of only a few machines to enable researchers to manipulate cadaver feet in a manner close to in vivo walking. Others are at Penn State University1, Mayo Clinic Rochester2 and University of Tubingen3. For this project the Iowa based team is strengthened by Dr Tim Derrick, Associate Professor at Iowa State University (Figure 1).

The Iowa State simulator4 consists of a rigid metal frame supported by four wheels, which is pulled along a track by a motor and cable (Figure 2). Attached to the frame is a pneumatic cylinder which applies vertical load to a passive hinged “knee” joint, attached to which is the cadaver tibia. Nine artificial muscle forces are applied through attachments to nine individual tendons (tibialis posterior, tibialis anterior, flexor hallucis longus, extensor digitorum longus, flexor digitorum longus, Achilles, peroneus brevis, peroneus longus, and extensor hallucis longus) using nine motors connected to the tendons by cables and braided lines, each with an in-line load cell. The tendon actuation has been adjusted to achieve a match with the temporal characteristics described by Perry5 and the theoretical muscle forces calculated by Dul et al6. In terms of achieving a realistic walking speed the ISU simulator is the most advanced, with a stance duration of between two and three seconds (see website for video). Another critical improvement over other simulators is the independent control of all nine artificial muscle forces. Also, ground reaction forces reach in vivo levels (600-800 N vertically). The angular motion of the heel, relative to the tibia, closely matches the well-established pattern of heel eversion after heel strike followed by gradual inversion after midstance. Likewise, plantar pressure data are close to the accepted patterns for in vivo walking, with the heel loading first, followed by lateral forefoot loading, gradual medial forefoot and hallux loading, and the lateral forefoot unloading towards the end of stance.

The project is using 15 clusters of four 4mm markers to identify the kinematics of the foot (Figures 3, 4 and 5). These data are then being used to rationalize which bone segments to combine in rigid body model. Current rigid segment models are based on the practicalities of marker attachment and camera line of sight. The project will provide some of the first descriptions of inter metatarsal and mid foot motion during walking-like activities, and be able to reflect on some of the clinical models of foot structure. “We are already seeing that there is far more motion within the foot than we anticipated”, says Dr Nester; “the fourth and fifth metatarsals are capable of a very large range of motion relative to each other and the cuboid, and their motion is complex, with significant frontal plane rotation”.

A Vicon 460 system is being used to capture this novel kinematic data, with BodyBuilder for computation of joint angular rotations. Early results were presented at the Podiatry Foot Orthoses Association meeting in Las Vegas at the end of November 2003. Dr Nester also attended the Foot and Ankle Retreat II April 30th - May 1st 2004 in Los Angeles, and will be at the Western Podiatry meeting at the end of June (Anaheim, USA). Abstracts have been submitted to ISPO 2004 (Hong Kong). Journal publication is expected in late 2004/early 2005.

Future work is in the planning stages. There has already been a further research funding proposal submitted, and there is progress on plans for expansion of the work to in vivo kinematic data collection.

Dr Chris Nester and Dr David Howard are leading members of the Centre for Rehabilitation and Human Performance Research (CRHPR) at Salford University. CRHPR is rapidly building on Salford's well-established track record in the development and evaluation of assistive devices, such as prosthetics, orthotics, footwear and functional electrical stimulation, studies of human movement disorders (eg in cerebral palsy and stroke), and investigations into the fundamental characteristics of human movement, particularly walking. Since 2001, and following strategic investment in the Centre, including the appointment of four full-time permanent Research Fellows, the group's activities have expanded rapidly. Grant income since 2001 is over £1.4 million from the EPSRC, EU 5th and 6th Frameworks, Department of Health, European Social Fund, the NHS, the Ministry of Defence, UK charities and the commercial sector. In September 2001, the Centre launched its now established biennial series of international conferences, “Biomechanics of the Lower Limb in Health, Disease and Rehabilitation”, the 3rd conference is in September 2005. The University has recently awarded the Centre £400,000 from its Science Research Investment Fund (SRIF) allocation to support the establishment of a new human movement laboratory within the new £18 million Health Faculty building, due for completion in 2005. This new laboratory will complement the existing gait laboratory which houses three motion analysis systems (including a Vicon 460), two pairs of force plates, two EMG systems, and other associated instrumentation (eg: gas analysis, isokinetics).

See web site for further information:

http://www.healthcare.salford.ac.uk/crhpr/

References

1. Sharkey NA,.Hamel AJ. A dynamic cadaver model of the stance phase of gait: performance characteristics and kinetic validation. Clin.Biomech.) 1998;13 :420-33.

2. Kim K, Kitaoka H, Luo Z, et al. In vitro simulation of the stance phase of human gait. J. Musculoskeletal Research. 2001 5:113-121.

3. Hurschler C, Emmerich J, Wulker N. In vitro simulation of stance phase gait part I: Model verification. Foot Ankle Int. 2003 Aug;24(8):614-22.

4. Ward ED, Smith K, Cocheba JR, Patterson P, Phillips RD. In Vivo Forces in the Plantar Fascia During the Stance Phase of Gait: Sequential Release of the Plantar Fascia J Am Podiatr Med Assoc 2003 93: 429-442.

5. Perry J. Gait analysis: Normal and pathological function. Thorofare, NJ: SLACK Incorporated. 1992.

6. Dul J, Shiavi R, Green NE. Simulation of tendon transfer surgery. Eng Med. 1985;14:31-8.