Lateral wedge insoles worn by people with medial knee osteoarthritis (OA) provide a limited amount of immediate biomechanical improvement during walking and may be best suited to people who have biomechanical phenotypes that would benefit the most, according to findings from a systematic review and meta-analysis of studies examining the intraindividual effects of the insoles.
“This review is ... the most definitive, up-to-date and comprehensive analysis on this issue to clarify the effects of lateral wedge insoles on biomechanical risk factors for knee OA progression,” wrote lead investigator John Arnold, Ph.D., of the University of South Australia, Adelaide, and his colleagues (Arthritis Care Res. 2015 Nov 25. doi: 10.1002/acr.22797).
Courtesy National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
The investigators reviewed 18 studies with a total of 534 participants and found small, but statistically significant reductions in estimates of knee joint loading based on the surrogate measures of external knee adduction moment (EKAM) and the knee adduction angular impulse (KAAI).
Most studies (14) tested full-length insoles, and the remaining four allowed a customized amount based on comfort and/or pain level. Another two used heel wedges, and two others tested both. The inclination angle of the insoles was most commonly 5 degrees, but ranged from 4 to 11 degrees. Some studies used a concomitant medial arch support; these were of a generic design in four studies and were made to order in another three. The lateral wedge insoles were compared against flat insoles, the patients’ own footwear, or standardized footwear.
The pooled effect sizes of both the first and second peak EKAM reductions were small, with standard mean differences of –0.20 to –0.25. For the first EKAM, the effect sizes did not vary according to whether studies used flat insoles or shoes only as comparators, whereas for the eight studies that reported second EKAM outcomes, there was a larger pooled effect size for comparisons against shoe-only than for one study that made flat insole comparisons. The pooled estimate for the standard mean difference in nine studies that reported KAAI was –0.14.
There was only weak evidence for publication bias in all the comparisons for the surrogate measures, and most had a low level of statistical heterogeneity between the outcomes of the studies.
The investigators noted that this meta-analysis of surrogate measures for knee joint loading does not take cumulative loading into account, so that even though the reduction in peak EKAM and KAAI was small, it may amount “to a large cumulative effect imparted on the knee over the course of the day. This should be considered when interpreting the findings of this review and future research on load modifying interventions in knee osteoarthritis.” They said that while EKAM has been associated with OA progression, KAAI has been thought to be a better measure of the duration and magnitude of loading in knee OA and has been associated with medial tibiofemoral cartilage loss over 1-2 years.
“Prescription [for lateral wedge insoles] based on biomechanical response and use of insoles only in individuals who show reductions in knee joint loading (biomechanical phenotypes) appears more appropriate to increase the likelihood of a favorable long-term response regarding the attenuation of structural changes. This would limit their application and benefit to a smaller number of individuals, but is still likely to be significant considering the overall prevalence of knee OA and projected rise due to population aging and rising obesity levels,” the authors concluded.
The investigators had no outside funding source for their systematic review. One of the authors may receive royalties from Salford Insole, a manufacturer of lateral wedge insoles.