The Effectiveness of Felt in Reducing Peak Plantar Pressures at the 1st Metatarsophalangeal Joint: In a Healthy Population

Semi-compressed felt is frequently used in clinical podiatric practice to ooad areas of high pressure, particularly in patients with chronic ulceration. The study aimed to assess the effectiveness of semi-compressed felt, on plantar pressures, in ooading the 1 st metatarsophalangeal joint, whilst assessing pressure encountered at the peripheries. Elevated plantar pressures are a strong predictor of ulceration in patients with diabetic foot disease, where undetected mechanical trauma can rapidly become ulcerative. In this study, plantar pressure was assessed using the Foot Work Pro plate (AM CUBE, Inc., France, www.amcube.net), in three conditions: barefoot; 5mm thickness and 10mm thickness conditions. This study was of a cross sectional design, where participants were conveniently sampled within the Podiatric Medicine student population within the National University of Ireland, Galway. 33 participants (28 females; 5 males) with a mean age of 23 years (Interquartile Range, 18-44). Plantar pressures at the 1 st metatarsophalangeal joint decreased (P<0.01; P<0.01), when semi-compressed felt was applied to ooad the 1 st metatarsophalangeal joint. Whereas, plantar pressures were found to be increased at both the 3 rd metatarsophalangeal joint (P= 0.04; P= 0.01) and the 5 th metatarsophalangeal joint (P=0.82; P=0.40), as a result of applying felt to the 1st metatarsophalangeal joint. Evidently, ooading one joint subjected other joints to greater mechanical load allowing insight into the mechanical redistribution associated with the use of felt in ooading, which must be accounted for in the high risk diabetic foot.

the 1 st metatarsophalangeal joint. Whereas, plantar pressures were found to be increased at both the 3 rd metatarsophalangeal joint (P= 0.04; P= 0.01) and the 5 th metatarsophalangeal joint (P=0.82; P=0.40), as a result of applying felt to the 1st metatarsophalangeal joint. Evidently, o oading one joint subjected other joints to greater mechanical load allowing insight into the mechanical redistribution associated with the use of felt in o oading, which must be accounted for in the high risk diabetic foot.

Background
Hyperkeratotic lesions are a result of thickening of the stratum corneum of the epidermis caused by cellular hypertrophy (1), predominately due to abnormal mechanical stresses, often resulting in elevated plantar pressures (2,3). Such mechanical stresses are resultant of a combination of intrinsic and extrinsic factors: for example biomechanical factors; footwear and activity levels (4). As the epidermis thickens, both stress and pressure increase at vulnerable sites of the foot (5).
Within podiatric practice, advancing age can contribute to an increased risk of both hyperkeratosis and ulceration. Changes associated with ageing include: thinning of the epidermis and dermis; decreased subcutaneous fat; atrophy of microvasculature; reduced sebum production and secretion; and reduced sensation (6). Therefore, it must be noted that o oading is essential to help reduce and redistribute pathological pressures, especially in patients living with chronic conditions such as diabetes (7,8). O oading sites exposed to high pressure is essential in the healing of active ulceration and in reducing the risk of amputation in those at risk (9).
Plantar pressure assessment actively demonstrates the effect that kinematic changes, within joint complexes, has on surrounding tissues as a vertical force (10). Clinically, studies have found an a correlation between plantar pressure patterns and various pathological conditions such as posterior tibial tendon dysfunction (11), medial midfoot arthritis (12), rheumatoid arthritis (13) and diabetes (14).Generally, normative dynamic values fall in the region of 200-500 kPa, which is comparitive to those with diabetic neuropathy, where values from 1000-3000 kilopascals (kPa) have been recorded (15). Although the relationship between ulceration and plantar pressures remains ambiguous, excess pressure caused by lesions or deformity can inhibit tissue regeneration, and the cumulative effect can eventually lead to tissue breakdown and ulceration (16). Similarly, foot deformity, such as prominent metatarsal heads and lesser toe deformities, has been found to have a signi cant relationship with ulceration (17). In a diabetic neuropathic population, peak pressures were 1.7 times higher in studied subjects with lesser toe deformities when compared to those without deformity (18).
For individuals living with chronic disease, o oading with semi-compressed felt (SCF) is a vital in the reduction and redistribution of pathological pressures. O oading sites of high pressure is essential in the healing of active ulceration and in reducing the risk of amputation in those at risk (9). Advantages include affordability, accessibility, and ease of use. It is recognised as an easily customised 'chairside' modality of o oading in clinical practice (19). While anecdotally, SCF is regularly used as an off-loading modality; it is important that its e cacy is investigated; and the effect that thickness of SCF application has on plantar pressure measurements.
The primary aim of this study was to investigate: 1. the effectiveness of a SCF cut-out in reducing peak plantar pressures at the 1st metatarsophalangeal joint (MTPJ) under two conditions: 1)5mm thickness 2)10mm thickness.
The secondary aim of this study was to investigate: 1. the effect of a SCF felt cut-out, o oading the 1st MTPJ, on the peak plantar pressures at the 3rd MTPJ and the 5th MTPJ.

Patients/materials And Methods
This study utilised a cross-sectional and same-subject design involving a healthy population of NUIG Podiatric Medicine students. The primary aim of this study was: to investigate the effectiveness of a 5mm SCF plantar metatarsal pad (PMP); and a 10mm SCF PMP in reducing peak plantar pressures at the 1 st MTPJ. The secondary aim of this study was to investigate: the effect on peak plantar pressures at the 3 rd

Inclusion & Exclusion Criteria
Data collection was conducted on a 'healthy' student population. 'Healthy' was de ned as having an ability to ambulate without aid whilst having no signi cant vascular, neurological or orthopedic impairment. Participants were included if they were: 18 years of age and older; and had the ability to ambulate independently of assistance. A total of 33 participants were included in the study. Informed written consent was obtained prior to entry into the study, and each participant was required to attend for one single data collection appointment.
The following anthropometric and demographical data were recorded; age, gender, height, weight, body mass index (BMI). Foot posture was classi ed according to the Foot Posture Index (FPI) (20). Bony landmarks were identi ed on the plantar aspect of both feet to facilitate standardised application of SCF padding ( Figure 1). A two-step protocol to collect plantar pressures was utilised (18, 22). Participants were instructed to start walking in a particular sequence: by stepping initially with one foot on the ground; taking the next step on the pressure plate; and walking a further 3 steps. This was to ensure a standardised procedure and to avoid direct targeting of the pressure plate. Participants were instructed to walk across the walkway with their head up and looking straight ahead to further avoid targeting (Richards, 2018). Participants were allowed a period of acclimatisation with the equipment prior to data collection. Five measurements were taken per foot per condition, whereby the 1 st and the 5 th reading were discarded (Lavery et al., 1997; Gatt et al., 2016).
An average was calculated from the 2 nd , 3 rd and 4 th reading for each condition ( Table 1).
The three conditions analysed are described in Table 1 Table 3

Discussion
Results indicated that a SCF PMP o oads the 1st MTPJ by 4.2% when 5mm is applied to o oad, whereas SCF o oads the 1st by 19.76% when 10mm was used. Although both were statistically signi cant, it was evident that 10mm was more effective in reducing PPs at the 1st (P < .001) when applied to o oad the 1st MTPJ. This contrasts with other studies that observed a signi cant decrease in plantar pressure when 5mm was applied to o oad the 1st MTPJ, ranging from 23.9% -31.48% (23); and similarly when 7mm was applied to o oad the 2nd MTPJ, 25% (24). Although it must be acknowledged that different measurement systems were used. Interestingly, it was shown in this current study that the peripheries experienced excess pressure applied upon increase of o oading material to the joint of interest. This phenomenon relates to the 'edge effect' introduced previously whereby an increase in pressure was observed at the immediate peripheries of the padding (25). However, in this current study the surrounding joints were studied. Therefore, demonstrating the potentially detrimental effect padding can have in a high-risk pathological foot.
The current study was subject to limitations. The chosen 'healthy' cohort was based on the exclusion of vascular, neurological or orthopaedic impairment to allow for a homogenous sample. The sample consisted of a female majority (28 female; 5 male) and it is possible that this may have introduced a form of gender bias which is often the case in a healthcare educational setting (27). Gender imbalance can also be a common consequence of convenience sampling in a healthcare cohort, as recruitment is based on accessibility, availability, and ease of access (28).
Although limb dominance was not recorded in this study, it has been demonstrated that the dominant leg takes an increased load (29), which must be considered when considering o oading interventions. Only unshod conditions were investigated, which may considerably alter pressure distribution, material compression and overall o oading effectiveness.
The PTI or the shear stress was not investigated. It was decided to focus this current study and examine three joints of interest ( 1st, 3rd and 5th MTPJs), due to the in uence of a study where it was determined there is possibly no signi cance in reporting both PTI and peak pressures (30).

Conclusion
Traditionally, in the clinical setting it is hypothesised that the thicker the o oading material the better the effect. Indeed, this is the case however, one must consider the shifting of force to other areas of vulnerability on the plantar aspect of the foot. Results from this study should allow a better insight into the mechanical redistribution associated with the use of plantar padding in o oading, and the possible implications associated with this redistribution, especially if the patient wears unsuitable footwear. This is integral if the aim of the clinician is to reduce plantar stresses in a 'high risk' compromised foot. All data generated or analysed during this study are included in this published article (and its supplementary information les).

Competing interests
The authors declare that they have no competing interests.  Plantar Pressure Data Trend Plot