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Effect on motion Movement is created from the result of forces generated by influences such as gravity, body weight, ground reaction force and muscles acting around joints and causing leverage.

Root in 1977 postulated that a functional foot orthotic should be able to change the position about which the subtalar, mid- tarsal and first metatarso-phalangeal joints work (2). The effect being to realign the reaction force of the ground on the foot.

Also in 1977, Veres determined that an arch support may move the ground reac- tion forces forward from the hindfoot reducing the loading on the talo-navicular joint (3). By reducing this loading it is possible to prevent the talo-navicular joint from subluxing. As a result the com- ponents of the foot are better able to resist the ground reaction forces imposed on them. It is worth noting that distal hypermobility often follows on from prox- imal instability.

Foot orthoses work on the principle that they control the subtalar joint - as this is an excellent torque converter through the talus, it will compensate for changes either in the terrain or body position.

Functional foot orthoses (FFO) encourage the subtalar joint to function around its individual neutral position during the stance phase of gait. Therefore, when the foot enters the propulsive phase, the sub- talar joint moves from its neutral position into a supinated position while the mid- tarsal joint is held fully pronated. The pronating force applied by the FFO to the forefoot during midstance phase ensures that the midtarsal joint is locked allowing adequate forefoot stability for the resupination of the subtalar joint. FFO also ensure that all normal joint motions remain unrestricted.

Research limitations Research methodologies have varied wide- ly largely due to the differences in orthot- ic material, orthotic manufacturing tech- niques, test surfaces, exercise protocols and types of footwear used in the studies. The major limitation of these studies has been the difficulty in assessing the move- ment of the foot inside the shoe. With technological advances, quantitative gait

FOOT ORTHOSES MAY BE PRESCRIBED TO ACHIEVE: (1) Support of the abnormal structural position of the forefoot e.g forefoot invertus, forefoot evertus, plantarflexed first ray. Without this support the rear- foot may function abnormally, abnormal compensation (2) Support of the rearfoot abnormal structural position eg. rearfoot varus, rear- foot valgus. Without this support subtalar joint may excessively pronated and thus affect the gait cycle (3) Resistance to the abnormal forces from the leg that cause abnormal prona- tion or supination of the foot due to the abnormal medial or lateral distribution of extrinsic forces across the subtalar joint eg. genu valgum/varum, external and internal tibial torsion (4) Repositioning of the calcaneum to a more correct position at heel strike (5) An improved contact phase thus reduce shock absorption

analysis and the effect of foot orthoses on gait, using computer aided motion sys- tems in combination with force measure- ment and dynamic electromyography, are becoming recognised as valuable tools.

Foot orthoses and pain relief There is a substantial amount of research documenting the objective efficacy of foot orthoses in controlling excessive prona- tion and the symptomatic relief of pain (2,4). Unfortunately most of the pain relief studies have been subjective and while the research frequently reports improvements, resolution of injuries and ‘return to sport’ rates of between 70-83%, they should be viewed with caution.

It is important to note that in a review of literature there is an absence of reported complications resulting from use of foot orthoses. While the incidence of ‘no improvement’ ranged from 4-12%, no direct injury has been documented as a specific result of foot orthoses.

Although, in 1998, Padhiar and King investigated intra-compartment pressures in legs of subjects with chronic compart- ment syndrome (CCS) and found that foot orthoses could increase this intra-com- partment pressure in legs (5). They also found that orthoses had no significant reduction in pain and therefore concluded that they should be used with caution in subjects with CCS.

Summary Functional foot orthoses are corrective devices designed to promote structural integrity of the joints of the foot and lower limb (6). They achieve this by resisting ground reaction forces that cause abnormal skeletal motion during the stance phase of gait and by reducing

abnormal biomechanical compensation. The end result is to reinstate the timing mechanism of the gait cycle while allowing normal joint motion to occur unrestricted.

References and further reading 1. Padhiar N, Bader DL and King JB. A pilot study to identify pathomechanical factors in exercise induced leg pain. J.Br.Pod.Med. 1997;52(1):3-5 2. Root ML, Orien WP and Weed JH. Normal and abnormal function of the foot. Clinical Biomechanics Corporation, Los Angeles. Vol.II, 1977 3. Veres G. Graphic analysis of forces acting upon a simplified model of the foot. J.Prosth.Orthotics Int. 1977;1:161-172 4. Smith LS, Clarke TE and Hamill CL. The effects of soft and semi-rigid orthoses upon rearfoot movement. J.Am.Pod.Med.Assoc. 1986;76:227-233 5. Padhiar N and King JB. Foot orthoses can change compartmental pressure in the legs. Br.J.Sports Med. 1998;32(1):89 6. Anthony RJ. The manufacture and use of functional foot orthoses. S.Karger. A.G (first ed.), Switzerland, 1991 7. Blake RL and Denton JA. Functional foot orthoses for athletic injuries. J.Am.Pod.Med.Assoc. 1985;75:359 8. Mann RA and Hagy J. Biomechanics of walk- ing, running and sprinting. Am.J.Sports Med. 1980;8:345-350

Nat Padhiar is an honorary consultant and research podiatrist within the Surgical and Musculoskeletal Directorate at the Royal London Hospital. He is also a member of the medical team support- ing the Daily Telegraph marathon squad.

Resources ● Talar Made Orthotics Ltd. offer a

range of sports insoles and prescrip- tion orthotics. Tel. 01246 268456 ● Ecobrands has recently opened a

biomechanics suite in London offer- ing a full range of foot analysis and prescription orthoses. Tel. 020 7460 8101

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