This is the first study to investigate the frequency of application for a range of forefoot orthotic modifications amongst NZ podiatrists. These findings highlight the regular use of FLW within this cohort of NZ based podiatrists, with FLWs reportedly included in almost half of all orthotic prescriptions. This makes them the second most widely applied orthotic modification. This survey identified the majority of respondents prescribed between 0 and 10 orthotics or modified insoles per week. A similar frequency of prescription as that reported by Chapman et al. (20) who found that NZ podiatrists on average prescribed 12 orthoses, per week.
Peroneal tendinopathy and CAI were the diagnoses which most frequently lead to FLW prescription. Both diagnoses have been linked to patients whose COP is laterally deviated (22, 23). Therefore, if the widely held assumption revealed in this survey is true, and FLWs do shift the COP medially, this is likely to have a positive impact on these clinical presentations. However, this assumption contrasts current research which suggests that lateral wedges shift the COP laterally (5). There is currently limited evidence investigating this function of FLWs, or any positive outcome effect when managing peroneal tendinopathy. It has been postulated that orthoses have a positive impact on CAI, due to heightened input to mechanoreceptors, although limited work has been completed exploring the role of FLWs in this scenario (24). Kakihana et al. (2) compared full length lateral wedges in people with and without ankle instability and concluded that in those with unstable ankles, the change in sub-talar joint moments is the same as age matched controls. Plantar heel pain was the third most likely diagnosis to be managed with FLW. The in vitro study by Kogler et al. (12) provides the only evidence regarding lateral wedging configurations and their impact on the plantar fascia with data indicating that FLW reduced plantar fascial strain. The limitation of this work was the use of cadaveric limbs.
The Tissue Stress theory was found to be the most influential paradigm that guided orthotic modification and prescription. The Tissue Stress theory works on the premise that orthoses are used to reduce stress being placed on a tissue, to a tolerable level (16). Therefore, based on the study data, the assumption made when using FLWs under the guidance of the tissue stress model is that FLW will positively impact tissue stresses.
This survey has revealed incongruity between the surmised function of FLW and the inferred explanations of podiatric theories of foot function. This is highlighted in two examples related to the application of the Root theory and Sagittal Plane Facilitation theory. Regarding the Root theory, almost a quarter of respondents primarily use FLW to ‘balance the foot’, and most respondents identified the patient’s forefoot position and rearfoot pronation/supination as ‘important’ when prescribing FLWs. These concepts are key pillars of the Root theory (13, 25), despite the Root theory being rated as the least influential paradigm by respondents. Regarding the Sagittal Plane Facilitation theory, almost all respondents believed that FLW increased the ROM in the first MPJ, and this was reported as the most common reason for FLW use in both walking and running gait. However, there is very limited evidence exploring the impact of FLWs on first MPJ kinematics. The Sagittal Plane Facilitation theory, ranked by participants as the second most influential paradigm, places a great deal of importance on first MPJ ROM (14). This theory suggests that first MPJ movement to engage the windlass mechanism is essential for efficient forwards transfer of weight. The Windlass mechanism was first discussed by Hicks (17) and relates to the association between MPJ position and the plantar fascia, said to cause the medial arch to rise and the forefoot to supinate. The contradiction in this case is that Hicks (17) described the irresistible supination of the forefoot as the windlass mechanics is engaged, yet over half of our respondents believe that FLWs both shift the COP medially and increase first MPJ ROM. Extrapolation of the original windlass mechanism description would suggest that first MPJ range of motion cannot increase at the same time as the COP shifts medially. However, recent data has shown the plantar fascia to be extensible (18), something that was not considered in the original explanations of the Windlass mechanism. What was previously thought to be a direct link between first MPJ kinematics and medial arch height, appears to be an oversimplification of a complex interaction between the plantar fascia and intrinsic muscles of the foot (18, 26). If extensibility of the plantar fascia also impacts the associated forefoot supination, then this could create the possibility of a concurrent medial shift in COP alongside an increase in first MPJ ROM, as participants in the current survey believe is true. However, there is limited evidence to support this supposition and further investigation is required.
Data indicated respondents believed FLW functioned differently in walking gait versus running gait. Respondents also indicated that the biomechanical objectives for FLW prescription were entirely different when managing runners and that running gait enhances the effect of a FLW. Whilst research has indicated biomechanical outcomes derived from orthoses differ between walking and running gait (27), there is limited data supporting functional differences from FLW use between walking and running gait. Given the differing use and the beliefs of clinicians that there are functional differences when using FLW in running versus walking gait, further investigation is warranted.
Full-length lateral wedges have frequently been examined in research, notably for their biomechanical effect in the management of medial knee osteoarthritis (3). However as indicated by survey data, full length wedges made up a small percentage of lateral wedges prescribed by respondents. Evidence contrasting the effect of varying wedge length (full length vs FLW) is limited. Van Gheluwe et al. (7) compared the impact of lateral wedge length on plantar pressure and found FLW increased peak plantar pressure in the lateral forefoot, whereas rearfoot lateral wedges had no effect on forefoot plantar pressure. Further supporting the biomechanical impact of FLW, Kogler et al. (12) demonstrated that wedging under the lateral aspect of the forefoot provided the most significant reduction in strain in the plantar fascia.
The most common material thickness used to manufacture FLWs was 3mm. However, it is important that the difference between inclination angle and material thickness (in the case of wedges, referring to the thickest part) is clearly understood. Three-millimetre (3mm) material does not produce a consistent angle as this depends on the width of the modification. Figure 4 displays the relationship between thickness and width, in which the width of a wedge entirely changes the inclination angle if the thickness remains constant. For example, 3mm material bevelled to 0mm over a width of 60mm (a relatively small FLW) produces an inclination angle of 2.9o, whereas that same material bevelled over 100mm (a large FLW) produces an angle of 1.7o. This difference means if the same material thickness is used regardless of modification width, patients with larger feet receive wedges with lower inclination angles. This is an important distinction as research has previously indicated that for a range of biomechanical outcomes, a larger inclination angle elicits a larger response (11).
The survey data must be considered in the context of its limitations. Firstly, despite efforts to maximise recruitment, the sample size was lower than anticipated, which may limit the generalisability of the data. Whilst the response rate was low, recent NZ podiatry workforce data indicated only 19% of NZ podiatrists worked in the area of sports medicine (28). Consequently, the survey may have only been of interest to a relatively small percentage of the NZ podiatry workforce. However, the study was the first to examine practice habits related to FLW. The responses allowed participants to select a range of common presentations, modifications and beliefs that underpin the prescription of FLW. This allowed space for reflection on their practice habits and established a benchmark for current clinical practice in NZ.