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Root et al (1977) stated that propulsion is defined from when the heel begins to lift from the ground to toe off. During propulsion, Root et al (1977) proposed that the normal foot will remain as a rigid and propulsive lever. This according to Root et al (1977) will ensure the foot remains stable as the heel lifts from the ground, and body weight is transferred onto the forefoot. Stability of the foot during this phase is described by Root et al (1977) as essential. This is so that the first

52 metatarsophalangeal joint can dorsiflex sufficiently during the final stages of propulsion.

Agreeably, some (Hunt et al 2001, Sarrafian 1987, Bojsen-Moller 1979) have described the importance of stability during propulsion, particularly highlighting the role of the plantar fascia. However, they do not propose that the foot is rigid, and many (Lundgren et al 2007, Jenkyn and Nicoll 2007, MacWilliams et al 2003, Leardini et al 2007, Nester et al 2006) have reported a greater range of motion within the joints of the midfoot and forefoot during propulsion than the other phases of the gait cycle.

The subtalar joint

Root et al (1977) stated that during propulsion in the normal foot, the subtalar joint will supinate through its neutral position just prior to heel lift to be in a supinated position. It will continue to supinate until the final stages of propulsion where it will then pronate. Root et al (1977) stated that supination of the subtalar joint throughout propulsion is the integral mechanism for ensuring the foot remains a rigid and propulsive lever.

Wright et al (1964) described how the subtalar joint will supinate 4° around its axis of rotation during propulsion. However, Wright et al (1964) stated that this includes plantarflexion, inversion and adduction. This is again indicative of Root et al (977) description of open chain supination, not closed chain supination as Root et al (1977) is pertaining too.

53 In agreement with Root et al (1977), Lundgren et al (2007) and others (Kitaoka et al 2006, Hunt et al 2001a, Cornwall and McPoil 1999a, Jenkyn and Nicol 2007, Moseley et al 1996, Rattanaprasert et al 1999) reported that the calcaneus inverted relative to the tibia and talus during propulsion. However, the range of inversion measured appears to be dependent on the method of measurement, but it is still larger than that described by Wright et al (1964). Lundgren et al (2007), Nester et al (2006) and Arndt et al (2004) reported 5° of inversion, while Cornwall and McPoil (1999a), Moseley et al (1996), Hunt et al (2001a) and Leardini et al (2007) measured between 6°-10° inversion. Although, results from Lundgren et al (2007), Nester et al (2006) and Arndt et al (2004) indicate that the talus is also inverting relative to the tibia, and this movement would be included when measuring the calcaneus relative to the tibia.

All investigations (Cornwall and McPoil 1999a, Moseley et al 1996, Hunt et al 2001a, and Leardini et al 2007, Lundgren et al 2007, Nester et al 2006 and Arndt et al 2004) reported in agreement with Root et al (1977) that the calcaneus everted relative to the tibia during the final stages of propulsion. This is hypothesised by Huson (1991) and Root et al (1977) to help maintain the contact of the medial aspect of the foot with the supporting surface, and aid the dorsiflexion of the first metatarsophalangeal joint.

In the transverse plane, Moseley et al (1996), Leardini et al (2007) and Nester et al (2006) reported that the calcaneus adducted relative to the tibia or talus. In contrast Cornwall and McPoil (1999a) and Hunt et al (2001a) stated that the calcaneus abducted relative to the tibia during propulsion. There is also a considerable difference in the range of adduction, or abduction measured by these investigations. For example, Moseley et al (1996) reported 10°, while Leardini et al (2007)

54 measured less than 4° adduction of the calcaneus relative to the tibia. However, a possible reason for the difference between these investigations maybe caused by inter-participant variation, which the mean values cannot convey. This is supported by Lundgren et al (2007), who reported no consistent trend between participants in the direction, or the range of transverse plane motion of the calcaneus relative to the talus and/or tibia. This variation between participants which are all asymptomatic suggests that contrary to Root et al (1977), feet that are symptom free, do not demonstrate precise movement patterns at some joints in the foot.

The ankle joint

Root et al (1977) proposed that the ankle joint will reach a peak angle of dorsiflexion at heel lift, and will then rapidly plantarflex. This is in agreement with Nester et al (2006), Arndt et al (2004), and Lundgren et al (2007) who reported that the talus and calcaneus began to plantarflex relative to the tibia from heel lift, and the range of plantarflexion during this phase is between 5°-10°.

However, the results from Moseley et al (1996), Cornwall and McPoil (1999a), Leardini et al (2007) and Hunt et al (2001a) indicate that the calcaneus continued to dorsiflex relative to the tibia during the initial stages of propulsion. There are also considerable differences between these investigations in the range of sagittal plane motion measured with Moseley et al (1996) reporting only 9° of plantarflexion while Hunt et al (2001a) reported a mean of 24° plantarflexion during propulsion.

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The midtarsal joint

Root et al (1977) proposed that during propulsion in the normal foot, the midtarsal joint will supinate around the oblique axis, and remain in a pronated position around its longitudinal axis. This Root et al (1977) stated will maintain the stability within the foot, and allow for the transfer of weight across the forefoot from lateral, to medial. Agreeably, Nester et al (2006), Lundgren et al (2007), Leardini et al (2007) and DeMits et al (2012) reported that the midfoot (or navicular and cuboid) inverted relative to the calcaneus (or talus) during propulsion. Although, the midfoot plantarflexed and adducted to indicate overall supination of the midtarsal joint during this phase. With exception of Nester et al (2006), all investigations reported a definite trend in the movement of the midfoot during propulsion, which Root et al (1977) does not describe. During the first half of propulsion, there was minimal movement of the midfoot (or navicular and cuboid) across all planes of motion relative to the calcaneus (or talus). The mean value indicates less than 1° of motion. During the second half of propulsion, the midfoot rapidly plantarflexed, inverted and adducted relative to the calcaneus. All investigations (Lundgren et al 2007, Leardini et al 2007 and DeMits et al 2012) reported that there is considerable inter-participant variation in the range, and direction of motion; particularly in the sagittal and transverse planes. This suggests that it would not be correct to describe specific movement patterns of the midfoot, or of the bones within in it. Overall this emphasises that movement of this region of the foot is much more complex than Root et al (1977) hypothesised.

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Forefoot

Root et al (1977) stated that the first metatarsophalangeal joint must dorsiflex to at least 65° during propulsion, and that this is dependent on the movement of the subtalar and midtarsal joints. If the movement of these joints is what they determine to be normal, then the movement of the forefoot will also be normal.

Supination of the subtalar joint during propulsion is described by Root et al (1977) as essential for aiding the function of the forefoot during this phase. This is because it will pronate the midtarsal joint around its longitudinal axis to maintain the rigidity within the forefoot. Simultaneously it will supinate the midtarsal joint around its oblique axis, and with plantarflexion and eversion of the first ray, it will allow for the transference of weight from lateral, to medial across the forefoot. This will help to maintain the first metatarsal head in contact with the supporting surface. However, results from Nester et al (2006), Lundgren et al (2007), DeMits et al (2012) and Leardini et al (2007) indicate that there is not skeletal rigidity within the forefoot during propulsion. They reported that there is a greater range of motion within and between the forefoot relative to midfoot during propulsion than the midstance or contact phases.

Schwartz et al (1964) stated that during propulsion the main weight bearing capacity of the forefoot is centralised onto the third metatarsal head. However, Huson (1991) suggested that this role is more likely to be provided by the second metatarsal. The second metatarsal is tightly connected to the tarsus, and this will allow it to hypothetically function similar to a spoke of a wheel, allowing the medial and lateral regions of the forefoot to rotate either side of it. Therefore, with inversion of the tarsus, Huson (1991) described how the second metatarsal will allow the third to

57 fifth metatarsals to invert and dorsiflex relative to it. This is supported by kinematic data from Nester et al (2006), DeMits et al (2012) and MacWilliams et al (2003). In contrast, with inversion of the tarsus, Huson (1991) stated that the first metatarsal will plantarflex so to remain in contact with ground. This is also in agreement with the kinematic data reported by Nester et al (2006), Lundgren et al (2007) and Leardini et al (2007). To aid the contact of the first metatarsal with the supporting surface, Root et al (1977) described how the shape of the forefoot is important, again emphasising the structural shape of the foot rather than its function. The first metatarsal head is shorter than the second metatarsal head, and sesamoids which are commonly situated under the first metatarsal head help facilitate the movement of the underlying tendons in and around the joint which is in agreement with Shereff et al (1986).

The first metatarsophalangeal joint

Root et al (1977) proposed that the first metatarsophalangeal joint must be dorsiflexed to 65° at the end of propulsion. The tibia will be tilted forward from vertical by 45° and the ankle joint will be plantarflexed 20°, so the first metatarsophalangeal joint can and must dorsiflex to 65°. Root et al (1977) described how the movement of the first metatarsophalangeal joint during propulsion involves the fixation of the hallux to the supporting surface, and the proximal phalanx of the hallux will move to the dorsal and anterior aspect of the head of the first metatarsal. As the heel continues to lift from the ground, Root et al (1977) described how the first metatarsal must plantarflex against the base of proximal phalanx of the hallux.

58 This will continue until the maximum range of dorsiflexion at the first metatarsophalangeal joint is reached.

The key reference used by Root et al (1977) to describe the range of motion available at the first metatarsophalangeal joint was Joseph (1954). Joseph (1954) measured the range of dorsiflexion at the first metatarsophalangeal joint in fifty men using different non-weight bearing, and weight bearing static based examinations captured by radiographic imaging. Joseph (1954) reported that the first metatarsophalangeal joint dorsiflexed to 70° in a non-weight bearing static examination. As Root et al (1977) proposed that the results of a static examination can predict the dynamic function of the foot, this value is proposed by them to represent the angle of dorsiflexion of the first metatarsophalangeal joint during propulsion.

The majority of more recent literature report that the first metatarsophalangeal joint will dorsiflex to much less than 65° during propulsion. For example, Halstead and Redmond (2006) 36.9°, Nawoczenski et al (1999) 42°, Turner et al (2007) 29.2° (SD = 6.9°), Simon et al (2006) 48.0° and Carson et al (2001) 38°-40°. Simon et al (2006), Halstead and Redmond (2006), Nawoczenski et al (1999), and Turner et al (2007) also all reported that the first metatarsophalangeal joint plantarflexed towards the end of propulsion, and the peak angle of dorsiflexion was during propulsion and not at toe off. In contrast, Van Gheluwe et al (2006) measured 80°, and Hopson et al (1995) measured 64.5° angle of dorsiflexion at toe off. However, Hopson et al (1995) used two dimensional video analysis which lacks the accuracy of three dimensional analysis used by most of the other investigations afore-mentioned. . There are also no details provided by Van Gheluwe et al (2006) to explain the position of the foot used to represent the zero reference position. The position used

59 may explain the considerably larger angle of dorsiflexion measured compared to the other investigations.

A key feature from the results of Joseph (1954) is the considerable inter-participant variation. This strongly indicates that stipulating a single angle to represent the normal range of dorsiflexion at the first metatarsophalangeal joint as Root et al (1977) proposed is not suitable. Joseph (1954) measured 100 feet (50 right) and reported standard error of the mean (SEM) values of = 3.4 for that examination. The standard deviation, and standard error of the mean results from Halstead and Redmond (2006) SD =7.9° (15 feet), Nawoczenski et al (1999) SEM=2.3 (33 feet), and Hopson et al (1995) SD=8.5° (20 feet) are similar to Joseph (1954), even though they have tested fewer numbers of feet and measured the movement of that joint during walking. Collectively these studies demonstrate the large variation in the kinematics of asymptomatic feet.