Static foot posture has been discussed in previous research as possibly contributing to the onset and progression of a number of lower limb musculoskeletal conditions (Donatelli, 1987, Tiberio, 1987, Reilly et al., 2009, Levinger et al., 2010, Gross et al., 2011, Levinger et al., 2012, Abourazzak et al., 2014, Buldt et al., 2015) as it may alter the mechanical alignment and dynamic function of the lower limbs (Guichet et al., 2003, Levinger et al., 2010). Little is known about the consequences of abnormal foot morphology (pes planus and pes cavus) and the risk of knee and lower limb tissue damage and symptoms despite the central role foot posture plays in lower extremity biomechanics (Gross et al., 2011, Buldt et al., 2015).
A study by Gross et al., (2011) investigated the relation between foot posture, knee pain and compartment specific knee cartilage damage in 1903 older adults using the Staheli Arch Index (SAI) and concluded that a pes planus foot posture is associated with knee pain, medial tibiofemoral, and patellofemoral cartilage damage in older adults. Findings indicated a
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biomechanical link between an excessively pes planus foot posture and mechanical stress on the tibiofemoral and patellofemoral compartments of the knee (Gross et al, 2011).
However, there has been little investigation into foot posture and function as an outcome measure for predicting the EKAM. The precise underlying mechanism articulating foot posture and function to the aetiology of knee injury has not been identified within the literature, and therefore it remains unclear (Gross et al., 2011, Buldt et al., 2015). Reilly et al., (2009) advocates that foot posture and function possibly play a role in the pathogenesis of medial knee OA as previous investigations have identified differences in the foot postures of healthy individuals and individuals with medial compartment knee OA. The effectiveness of certain orthotic interventions such as lateral wedge insoles (LWI) when used in the treatment of a number of musculoskeletal conditions may be influenced by foot posture (Reilly et al., 2009). Previous research has recommended an in depth knowledge of foot posture and also investigator competency in the assessment of foot posture in order for a full understanding of the effect of interventions used to treat musculoskeletal conditions and their effects on the knee and lower limb joints to be attained when conducting future research into the lower limbs and orthotic interventions (Levinger et al., 2010, Levinger et al., 2012). A comprehensive understanding of orthotic interventions would enable investigators of future research projects to identify participants who are most likely to benefit from these types of interventions (Levinger et al., 2010, Levinger et al., 2012). Accurate and reliable assessment of foot posture can provide an appreciation into how foot postures may influence or be influenced by certain musculoskeletal conditions, for example reducing the loading on the medial compartment of the knee in patients with knee osteoarthritis (OA) and an understanding of the effects of foot posture on the efficacy of certain interventions can be gained (Redmond et al., 2006, Reilly et al., 2009), for example the biomechanical response and non-response (the increase or decrease in the magnitude of the EKAM) to LWI, which may vary according to specific foot types. In healthy limbs, foot pronation in the coronal plane of motion (eversion) relates to low arched (planus) feet and a more medial centre of pressure (COP) (Chiu et al., 2013) with the level of low arch depending on an individual’s subtalar joint/ankle complex motion. If excessive subtalar joint/ankle complex motion is present, the foot is more planus and has more contact with the supporting surface on the medial/plantar aspect of the foot. However, in patients with medial compartment Knee OA, rearfoot pronation (eversion) has been suggested to potentially reduce the adduction moment by shifting the centre of pressure laterally, indicating an
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adaptation by the foot in the presence of certain musculoskeletal conditions (such as medial compartment knee OA) to reduce the load on the medial compartment of the knee (Levinger et al., 2010, Buldt et al., 2015).
In medial compartment knee OA patients, evidence of altered foot kinematics have been identified during gait that are symptomatic of a more everted foot type, including a reduction in the rearfoot frontal plane range of motion (Reilly et al., 2009, Levinger et al., 2010, Gross et al., 2011, Abourazzak et al., 2014). A proportion of the load is shifted away from the medial compartment of the knee during foot pronation (eversion) by shifting the centre of pressure laterally, providing some symptom relief (Desal et al., 2007, Levinger et al., 2010, Levinger et al., 2012, Levinger et al., 2013).
Lateral wedge insoles have been reported to alter foot motion within the literature; leading to an increase in rearfoot pronation (the subtalar joint valgus moment) (Nester et al., 2003, Kakihana et al., 2005, Levinger et al., 2013). Tibial malalignment (valgus and varus) and the extent of rearfoot range of motion (ROM) may affect individual responses to load altering interventions, such as LWI (Levinger et al., 2012). Using a LWI to increase rearfoot pronation on an already pronated foot could potentially lead to unfavourable alterations to lower limb kinematics and therefore the development of musculoskeletal disorders in other areas of the body and at proximal joints (Levinger et al., 2010, Levinger et al., 2012, Resende et al., 2015). Currently, the literature investigating foot posture and its effects on the EKAM and efficacy of LWI in shod concurrently is limited. Understanding the effects of LWI on the subtalar ankle joint complex is paramount in identifying why individuals respond differently to LWI. A study by Chapman et al., (2015) investigated the relationship between response to LWI, and evaluated whether dynamic ankle joint complex coronal plane biomechanical measures could identify participants that were classified as biomechanical non-responders (showing an increase in the EKAM), and participants that were classified as biomechanical responders (showing a decrease in the EKAM) with the use of LWI compared to a control shoe, and explain why such results were attained. Chapman et al., (2015) concluded that coronal plane ankle joint complex biomechanics play an essential role in reducing the EKAM when using LWI, which may assist in the identification of those individuals who benefit from LWI intervention. However, no clinical data was obtained during the Chapman et al., (2015) trial, and therefore further investigation using clinical assessment techniques is required in order to identify if any
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relationship exists between clinical static foot posture and dynamic foot motion, and their effects on the magnitude of the EKAM.
The Foot Posture Index (FPI) is a valid, efficient and reliable clinical method of assessing static foot posture (Redmond et al., 2008, Abourazzak et al., 2014) and allows the assessor to quantify the degree to which a foot is pronated, supinated or neutral (Abourazzak et al., 2014). Certain musculoskeletal disorders (for example; knee OA) cause an elevated average FPI score when compared to healthy subjects, indicating a more pronated foot posture in the knee OA population, as identified in a study by Reilly et al., (2009) which aimed to identify if the FPI can effectively describe the foot posture of individuals with medial compartment knee OA compared to healthy age-matched controls. The study by Reilly et al., (2009) only assessed static foot posture however, and did not investigate dynamic rearfoot or the magnitude of the EKAM. The rearfoot was therefore investigated, as rearfoot motion may influence the effectiveness of LWI intervention due to the rearfoot contacting the ground first and the first peak in EKAM relating to this time period.
Therefore, the first section in this chapter will assess static foot posture in subjects using the FPI in order to identify any relationship between rearfoot motion (dynamic) and foot posture (static), relative to the magnitude of the EKAM. This will provide an understanding of foot posture in barefoot and whether there is a relationship between the static and dynamic rearfoot and the magnitude of the EKAM.