ReviewEffect of footwear on the external knee adduction moment — A systematic review☆
Introduction
Osteoarthritis (OA) of the knee is one of the most common rheumatic diseases with an estimated 12% of the American population over the age of 60 years being affected [1]. It is commonly associated with substantial pain and immobility [1]. More recently, the lifetime risk of symptomatic knee OA has been found to be nearly 1 in 2 overall, more than 1 in 2 for those with a history of a knee injury, and nearly 2 in 3 for obese people [2].
It is widely accepted that biomechanical forces are associated with the pathogenesis of OA [3], [4], [5]. In healthy subjects, the peak medial knee compartment load during early stance of walking is 2.3–2.6 times the bodyweight (BW) [6], [7], [8], [9], while the lateral compartment is subjected to a peak load of 1.7 times BW [9]. The higher bone mineral density of the subchondral bone of the proximal medial tibia compared to the lateral side supports the difference in mechanical stress between both knee compartments [10]. These findings may explain the higher prevalence of medial knee OA, which is estimated to be 10 times more frequent than lateral knee OA [11].
Since direct measurement of knee joint load is invasive, gait analysis has been used as an indirect method to quantify forces acting upon the lower extremity. The external knee adduction moment (EKAM) is a valid and reliable representative of the medial-to-lateral knee load distribution [7], [12]. This varus torque shows a typical pattern of a higher first peak and a lower and less distinct second peak during early and late stance, respectively, in both healthy and symptomatic subjects [13], [14]. There is evidence showing that patients with medial knee OA have a significantly higher first peak EKAM compared to a healthy population [14], [15], [16], [17], [18], [19], [20], [21], [22].
The EKAM during walking has been linked to the symptoms, initiation and progression of knee OA [23], [24], [25], [26]. Consequently, the first peak EKAM has become an important variable in research to determine the risk and progression of medial knee OA, and to evaluate the effects of interventions, such as surgery, in the management of patients with this disorder. Further, other lesions of the lower limb, such as an anterior cruciate ligament (ACL) or meniscal injury have also been associated with increased peak EKAM during walking [27], [28]. As these injuries form a high risk for the development of future knee OA, [5], [29], [30] it may be important that rehabilitative strategies are implemented with the goal of decreasing EKAM during activity.
Over the past two decades, modified footwear has been investigated as potential conservative management of knee OA. More specifically, lateral wedging has been used with the goal of reducing symptoms associated with medial knee OA, hypothetically by reducing the peak EKAM in these patients [4]. If specific footwear interventions are associated with decreased EKAM during walking and other physical activity, these may be useful toward the management of symptoms of patients with medial knee OA, and potentially to reduce the risk of future OA in people who are at increased risk, such as those with knee injuries. This review aims to evaluate the current knowledge on various footwear interventions in relation to the peak EKAM in healthy and subjects with disorders of the knee.
Section snippets
Search strategy
An electronic search was undertaken without language restriction of Medline, PubMed, AMED, CINAHL, EMBASE and Scopus databases from their original available dates to January 2011. The search strategy included a combination of keywords for inclusion and exclusion factors (Appendix A). These were followed by hand searches relevant journals. Finally, the citation lists of included studies were screened for additional relevant articles via the database Web of Science.
Inclusion criteria
- i.
Peer-reviewed and published
Database search
The full search yielded 348 articles (Fig. 1). After exclusion of duplicates, irrelevant titles and screening of abstracts 39 remained. Six articles were excluded after full assessment as they did not use knee joint moments as an outcome measurement, used a biomechanical model instead of common footwear or were not published in peer-reviewed journals. Thus, 33 articles qualified for this review.
Risk of bias
The mean quality score ± SD of the included studies was 73.1 ± 10.6% (Appendix B). Fifteen of the studies
Discussion
This review investigated the effect of various footwear types on the EKAM in healthy and symptomatic subjects. Main subgroups were found for studies comparing wedges to a non-wedged or no insole, and studies comparing shod to barefoot walking. With the exception of two studies, all those that included subjects with medial knee OA using lateral wedges in a shoe reported significant reductions in the first peak EKAM, with a mean reduction ranging between 2.1 and 11.9%. A 5° lateral wedge was the
Conclusion
This systematic review provides evidence for immediate effects of footwear on the EKAM. There is evidence that: (i) the lateral wedge decreases the first peak EKAM during walking and (ii) shod conditions increase the first peak EKAM compared to barefoot walking and running. The orthotic is effective as a load-reducing intervention for patients with medial knee OA, while normal walking shoes were shown to be unfavorable compared to barefoot. In healthy subjects modern footwear increased EKAM
Conflict of interest
There is no conflict of interest.
Funding
No funding has been received for this study.
Acknowledgment
We wish to thank Professor Peter Herbison (Department of Preventive and Social Medicine, University of Otago) for his assistance with the analysis of this review.
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Conflict of interest: The authors state that there are no conflicts of interest, which might have influenced the preparation of this manuscript.