Patterns of mediolateral asymmetry in worn footwear

Background: Debate over footwear design and prescription is currently shaped by two opposing paradigms to which the clinician or researcher subscribes. Human structure is considered either ‘poor’ requiring intervention or ‘well-adapted’. The interventionist paradigm directs research on the effect of changing mediolateral footwear bias either within the shoe design or using inserts. However, the mediolateral condition of shoes worn by individuals has seldom been considered or measured. Objective: To describe a clinical assessment tool to measure outer-, mid- and innersole footwear components and report on patterns of mediolateral heel asymmetry in a sample of commonly used footwear. Main Outcome Measure: Total mediolateral asymmetry that includes the difference between medial and lateral outersole (mm), innersoles (mm) and mid- and innersole stiffness (Asker C). Results: A total of 212 shoes provided by 106 participants were assessed, with average shoe age 11.9 months (SD 11.4) and mean use 4.6 hrs.d−1 (SD 3.9). Shoe drop between 1.0 and 3.0 cm was measured in 87.8% of shoes. Zero or symmetrical wear was observed for 41.5% of shoes while 57.6% of shoes had 1 to 5 mm lateral heel degradation. The most frequent was 1 mm (30.2%) followed by 2 mm (12.3%) and 15.1% had 3 to 5 mm. Only 0.9% (2/212) had 1 mm of medial degradation. Asymmetry of wear was influenced by the reported age of the shoe, and females were likely to have greater lateral wear than men.Conclusions: Lateral heel degradation was the most frequently measured mediolateral asymmetry. Mediolateral asymmetry by design and/or degradation was measured in the outer-, mid- and innersoles. These results may be important for related footwear research on aberrant ankle and knee joint function.