Original paperFoot morphology and foot/ankle injury in indoor football
Introduction
The relationship between foot morphology and lower extremity injury is unclear, with both high and low arches reported as making the foot more prone to injury.1, 2, 3 Excessive foot pronation has been implicated as a risk factor for injuries in football,4 netball5 and in the development of medial tibial stress syndrome.6, 7 Interestingly, supinated foot types have also been found to be associated with increased risk of sustaining overuse injuries.8, 9 Other prospective studies have even suggested that a pronated foot type is a protective factor against injury.10, 11, 12 Reasons for these divergent views remain unresolved; however, they may be due to problems related to sports-specific requirements, the different methodologies employed, varying semantics and foot type measurement methods.
It is likely that the functional requirements of participants’ feet vary between sporting disciplines such that the optimal foot type for footballers is different from that for marathon runners. Indeed, sport-specific foot morphology of athletes engaged in various sporting disciplines has recently been demonstrated.13 An association was determined between sporting disciplines and a footprint measure used to indicate arch height for young, adult, elite and non-athletic males. This cross sectional study found that footprints of gymnasts and wrestlers significantly differed from those of soccer players, weightlifters and handball players, while gymnasts and handball players differed from non-athletic controls. While footprint measures provide only a single-plane assessment of a multi-planar entity, the results support the notion that there is a degree of sport-specific athletic selection which occurs according to an athlete's longitudinal arch height, such that athletes in a particular discipline may display similar foot morphology. A natural selection process would suggest that athletes with a less than optimal foot type for their chosen sport would either sustain an injury that limits participation or simply fail to attain their desired level of performance.
Foot type is not readily characterised with a single measure such as arch height or footprint indices.14, 15 In spite of this, single measures are commonly employed in practice. Traditional measures of foot type have problems in the areas of validity, reliability, definition and clinical applicability.
The absence of clinically useful, valid and reliable measures of foot posture gave rise to the development of the 8-point Foot Posture Index (FPI-8).16 The FPI is a criterion based rating system for weightbearing foot alignment, quantifying the degree to which a weight bearing foot can be considered to be in a pronated, supinated or neutral position, providing an indication of the overall foot posture.16, 17 The FPI assessment is quick and easy to perform and allows a multiple segment, multiple plane evaluation that offers some advantages over existing clinical measures of foot posture.17, 18 The FPI attaches a score on a 5-point scale between −2 and +2 to each of the measures that constitute it. The resulting aggregate score for the original eight-item version of the FPI (FPI-8) ranges from −16 (supinated characteristics) to +16 (pronated characteristics) on a 33-point scale.16 More recently, a final version has been proposed comprising six-items (FPI-6) and has an aggregate score ranging from −12 to +12 on a 25-point scale.17 This final version contains only those items that passed through a thorough validation process against three-dimensional and dynamic motion tracking of the lower limb using the Fasttrak™ electromagnetic system.17 Furthermore, the FPI-6 has been significantly correlated to radiographic arch height (r = 0.36–0.59), and concluded that it provides valid information regarding the structure of the medial longitudinal arch.19, 20, 21 The reported inter-tester reliability of the FPI-8 has been reported as moderate to excellent in a variety of populations (Intraclass correlation coefficients (ICC) = 0.58–0.91).22, 23 The FPI-8 has also demonstrated acceptable intra-tester reliability in the literature (ICC = 0.61–0.92).6, 20, 22, 23, 24 To date, reliability of the final FPI-6 version has not been reported in the literature
Despite the commonly held belief that a “neutral” foot type (neither pronated nor supinated) is the ideal or “normal”, research utilising both the FPI-6 and FPI-8 has revealed paradoxically that the “normal” or average foot (found most commonly in the population) is not a “neutral” foot (neither pronated nor supinated). Rather the average foot type in the sampled populations is a mildly to moderately pronated foot.8, 17, 19, 21
It could be expected that foot posture would have more of an influence on ability and injury in fast sports where the focus of the game is on agility and rapid changes of direction. Indoor football or Futsal is one such sport. Futsal requires frequent accelerating and stopping, jumping, tackling and irregular and feigned movements.25 Periods of play are spent in single-leg stance on the non-dominant foot while the dominant foot manipulates the ball and the player simultaneously fends off incoming opponents (Fig. 1). These techniques place stresses through the ankles and feet, potentially increasing the risk for injury and highlighting the importance of foot function. Because the playing level of a footballer is not wholly determined by ability, and since other factors influence a player's selection, rating of ability may be best determined by experienced coaches. Therefore, the aim of this study was to determine whether foot posture, as measured by the FPI-6, was associated with coach-rated ability levels and reports of ankle/foot overuse injury in adolescent male Futsal players.
Section snippets
Methods and procedures
Reliability pre-testing was performed on 10 participants by 3 examiners using the FPI-6 with the methodology described below. One examiner was a practising podiatrist with 9 years of clinical experience (6 years of using the FPI-8); another was a manipulative physiotherapist with 18 years of clinical experience, (no experience with the FPI-6) and the other a third year physiotherapy student with some supervised clinical experience. Two 2-hour training sessions were held for the examiners to
Demographics
When considering the FPI-6 as a 25 point scale whereby negative scores imply a supinated foot type and positive scores a pronated foot type,17 71 (93%) of the participants scored more than 0 and can therefore be defined as “pronated”. Two participants (3%) scored 0 and are defined as having a “neutral” foot type and only 3 participants (4%) could be described as having a “supinated” foot type.
For the sample of 76 male Futsal players, the FPI-6 scores obtained ranged from −4 to +10 (mean = 5.36,
Discussion
For adolescent male Futsal players, having an under-pronated to supinated foot type with a FPI-6 score of +2 or less, is associated with a significant increase in the risk of incurring an overuse ankle/foot injury. This is in accordance with previous findings that suggest that supinated and under-pronated feet may be more vulnerable to overuse injuries in a rapidly-paced, hard floor sport.8, 9 However, adolescents with such foot types are also rated by coaches as having higher levels of ability.
Conclusion
The FPI-6 measure of foot morphology was found to have good inter-rater reliability, and when employed with a group of adolescent male Futsal players, showed that an under-pronated to supinated foot type was associated with higher coach-rated ability. At the same time, an under-pronated to supinated foot type was found to be at significantly higher risk of overuse ankle/foot injuries in adolescent Futsal players. These findings suggest that early screening of foot posture may identify athletes
Practical implications
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The Foot Posture Index is a quick, easy to perform, reliable, valid and clinically applicable measure of foot posture.
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Screening of adolescent male Futsal players to identify those players who may be at risk of ankle/foot overuse injury.
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Possibility of improving Futsal performance of pronated feet through orthoses, footwear, taping and motor control.
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Possibility of reducing injury in supinated Futsal players by footwear, socks, orthoses, floor surface and addressing range of motion.
Acknowledgements
The researchers gratefully acknowledge the New South Wales Futsal Association and the staff and players of Dural Sport and Leisure Centre, Sydney for their generous assistance in data collection.
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