Some (Redmond et al 2006, McPoil and Hunt 1995, Perry 1992, Dananberg 2000, Kirby 1989) have proposed new and alternative descriptions or models of the biomechanical function and assessment of the foot to the Root et al (1971, 1977) description. However, these new models (Redmond et al 2006, McPoil and Hunt 1995, Perry 1992, Dananberg 2000, Kirby 1989) lack the in-depth and structured information that the Root et al (1971, 1977) description provides, and have failed to be full adopted into clinical practice.
The Foot Posture Index (Redmond et al 2006)
The “Foot Posture Index” (Redmond et al 2003, Redmond et al 2006) has capitalised on the need for a static examination protocol that aims to accurately define overall foot posture. The Foot Posture Index a simple method for classifying how pronated, neutral or supinated the foot is during static, weight bearing double limb stance (Redmond et al 2006). The Foot Posture Index classifies six sections of the foot. These are: talar head palpation, superior and inferior lateral mallelous curvature, calcaneal frontal plane position, bulge in the talo-navicular joint, congruence of the medial longitudinal arch, and the degree of adduction or abduction within the forefoot compared to the rearfoot. Redmond et al (2006) stated that each stage is graded on a scale from -2 for supinated, to +2 for pronated. Overall, it will produce a score of between -12 (supinated), and +12 (pronated).
104 This categorisation is then divided into:
- Supinated (-1 to -4) and Highly Supinated (-5 to -12)
- Neutral (0 to +5)
- Pronated (+6 to +10) and Highly pronated (+10 to +12)
(Redmond et al 2006).
Redmond et al (2008) proposed from a series of separate investigations which in total includes 619 asymptomatic participants what scores from the Foot Posture Index represent the normal foot. Overall, Redmond et al (2008) stated that a Foot Posture Index score of +4 represents the ideal normal foot. Although, the range of Foot Posture Index scores for a normal foot can be between +7 to +1, and is therefore a neutral to mildly pronated foot. Redmond et al (2008) stated that a Foot Posture Index score range of between -3 to +10 could infer a potential predisposition to pathology or development of injury. A score of between <-3 to >+10 indicates a more severely pronated or supinated foot, which is commonly associated with pathology or the development of injury. The use of a range of values to represent the normal, pre-disposed to injury or pathological foot is a definite step forward from the preciseness of the Root et al (1977) based measurements. The intra- and inter- assessor reliability of the Foot Posture Index has been reported as good for both asymptomatic and symptomatic populations. Cornwall et al (2008) reported ICC values of up to ICC = 0.937 for intra, and up to ICC = 0.655 for inter-assessor reliability. Cornwall et al (2008) suggested that an individual becomes significantly more reliable and proficient at conducting the Foot Posture Index examination with more practice. However, the Foot Posture Index scores in Cornwall et al (2008)
105 changed by only 0.1 across all assessors between assessment 1 and 2. This is not enough to change the Foot Posture Index classification of the foot. Using the 8 stage criteria of the Foot Posture Index, Evans et al (2003) reported high ICC values for intra-assessor reliability with ICC = 0.809, although comparatively lower ICC values for inter-assessor reliability with 0.58.
Redmond et al (2006) proposed that the aim of the Foot Posture Index (Redmond et al 2006) is to provide a valid and reliable classification tool,that can be used to predict how a foot will function during walking. However, the ability of the Foot Posture Index to predict the movement and function of the foot during walking remains inconclusive. For example, Chuter (2010) reported r values of up to 0.92 (p = <0.05) for the correlation between the Foot Posture Index score and the peak angle of the calcaneal eversion relative to the tibia during the stance phase of walking. In contrast, Barton et al (2011) reported low to moderate r values of only r = 0.230 (p=0.370) for the same correlation. r values in Barton et al (2011) dramatically improved when correlations were made between the Foot Posture Index and any foot parameter that was measured relative to the laboratory rather than the tibia. For example, for the correlation between the Foot Posture Index for the range of eversion of the calcaneus relative to the tibia was r = -0.022 (p=0.640). When compared relative to the tibia r = 0.614 (p=0.009). Barton et al (2011) suggested that this may because using foot parameters relative to the laboratory focuses on just the movement of that segment, which will be more sensitive to foot motion.
The relationship between the Foot Posture Index and the movement of the midfoot during walking is similarly inconclusive. Nielson et al (2008) reported r² = 0.132 (p <0.0001) between the Foot Posture Index and the minimal height of the navicular, and r² = 0.450 (p <0.0001) for the measurement of the navicular drop. Although, the
106 advantage of Nielson et al (2008) is that they measured 280 feet, there are several limitations of the investigation. Such as the use of 2D video analysis, and the measurement of the navicular is not disclosed. There is similar poor correlation between the Foot Posture Index classification and plantar pressure data (Teyhan et al 2011, Sanchez-Rodriguez et al 2012). For example, Teyhan et al (2011) reported r values between the Foot Posture Index classification and the peak pressure under the hallux of r = <0.26, first metatarsal r = < -0.23 and lateral hindfoot r = - 0.22.
The tissue stress model (McPoil and Hunt 1995)
The tissue stress model developed by McPoil and Hunt (1995), aimed to instruct clinicians how to identify the cause of tissue stress that has resulted in the development of the presenting injury. Through various methods of conservative treatment the aim is to reduce this stress to a tolerable level, and therefore reduce the symptoms a patient presents with to a tolerable level. The tissue stress model (McPoil and Hunt 1995) differs from the Root et al (1977) description because it aims to assess and treat the presenting injury, rather than just identify a structural deformity of the foot. However, the protocol for the assessment of the foot in the tissue stress model as described by McPoil and Hunt (1995) lacks the in-depth structure, and design of the Root et al (1971, 1977) protocol. It primarily offers a brief critique of some aspects of the Root et al (1971, 1977) protocol for the examination of the subtalar joint, and it offers no new methods. There have also not been any conclusive developments of the tissue stress model since its initial publication in 1995. Some elements of it are discussed in some text books (Brukner and Khan 2009), but it is not a widely used model in clinical practice.
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The sagittal plane theory (Perry 1992, Dananberg 2000)
Perry (1992) stated that the facilitation of sagittal plane motion within the foot, leg and lower limb is maintained by three anatomical rockers. These are situated within the foot and help to maintain a pendulum type movement of the foot, leg and lower limb in the sagittal plane during walking. Perry (1992) stated that at initial contact, the “heel rocker” will maintain forward progression of the foot and leg. The round posterior surface of the calcaneus will aid the movement of the centre of pressure, and ground reaction vector forwards from the heel through the foot. The second rocker is the “ankle rocker,” Perry (1992) proposed that this will aid the forward facilitation of the tibia and lower limb above the foot, which can remain fixed to the floor during single limb stance. The third rocker is the “forefoot rocker” which Perry (1992) described how with heel lift, body weight can pivot over the first metatarsophalangeal joint as it dorsiflexes.
However, the sagittal plane theory is predominantly theoretical ideas with largely un- validated use clinically. Lundgren et al (2007) and others (Manter 1941, Nester et al 2003, Nester et al 2006, Leardini et al 2007, Hunt et al 2001a, Cornwall and McPoil 1999a, Lundberg et al 1989a, Lundberg et al 1989b, Lundberg et al 1989b) have all demonstrated that the joints of the foot move in the sagittal, frontal and transverse planes, and that movement in the frontal and transverse planes should not be ignored. Neither Perry (1992), nor Dananberg (2000) provide a protocol for the static or dynamic biomechanical assessment of the foot. The static assessment of the range of dorsiflexion at the ankle joint and first metatarsophalangeal joint as Root et al (1971, 1977) described have been criticised for questionable validity and little relation to dynamic function of the foot (Rome 1996, Halstead and Redmond 2006, Cornwall and McPoil 1999b, Munteanu and Bassed 2006, Hopson et al 1995).
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The Kirby skive technique (Kirby 1989)
The “Kirby skive technique” (Kirby 1989) is an orthotic manufacturing technique for creating a unique design of an inverted varus heel cup. Kirby (1989) proposed that rotational equilibrium across the subtalar joint axis is where there is a balance in pronation and supination moments around the axis of the subtalar joint. This is hypothesised to be the optimum position of the foot to function normally. The identification of the subtalar joint axis in a non-weight bearing assessment as described by Kirby (1989) involves application of force onto the plantar surface of the foot in the proposed location of the subtalar joint axis. When no motion of the foot is evident, it represents the position of the axis of the subtalar joint and small pen marker crosses are drawn onto the foot. Kirby (1989) stated that application of pressure medial to the axis of the subtalar joint, would create a supination moment, and lateral to the axis of the subtalar joint, would create a pronation moment. However, this procedure is inherently unreliable due to patient pro-prioception and muscular contraction response. Therefore it would make it very difficult to conduct accurately. The proposed importance and use of identifying the subtalar joint axis is predominantly based on Kirby (1989) own clinical experience, and theoretical ideas of which the validity and reliability of this procedure is yet to be properly critiqued. The Kirby skive technique (Kirby 1989) is very limited, and its use sporadic among clinicians. It is also not supported by evidence based reliable and peer reviewed research, and it is used almost exclusively within podiatry.
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2.4.9 A summary of the key points derived from a critical review of the Root et