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Rehabilitation medicine in rheumatic diseases: Edited by Kent Kwoh

Advances in insoles and shoes for knee osteoarthritis

Hinman, Rana S; Bennell, Kim L

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Current Opinion in Rheumatology: March 2009 - Volume 21 - Issue 2 - p 164-170
doi: 10.1097/BOR.0b013e32832496c2
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Knee osteoarthritis is a chronic joint disorder predominantly affecting older individuals. As there is no cure, traditional management aims to reduce pain, improve function and enhance quality-of-life while minimizing adverse effects of therapy. Nonpharmacological conservative interventions, such as insoles and shoes, are considered the first-line approach to disease management. However, given that a significant proportion of knee osteoarthritis cases demonstrate disease progression, contemporary management also aims to reduce the risk of structural deterioration. Research over the past decade demonstrates that increased knee joint loading is an important risk factor for progression. The knee adduction moment (Fig. 1) is widely accepted as an indicator of medial compartment load and, as such, offers a potential target for treatment strategies to slow disease course over time. This review aims to highlight recent research findings, including their clinical application, for insoles and footwear in knee osteoarthritis. In particular, it will examine their effect on knee load, osteoarthritis symptoms and disease progression.

Figure 1
Figure 1:
Representation of the knee adduction moment

Effect of insoles on knee load, osteoarthritis symptoms and disease progression

Wedged insoles have received the most attention and will be the major focus of this review. Other types that could potentially play a role in knee osteoarthritis, such as shock-absorbing insoles or textured insoles, will not be discussed given their lack of research in this patient population.

Lateral-wedged insoles

Wedged insoles were first proposed for knee osteoarthritis in the 1980s [1,2]. By virtue of the lower limb's closed kinetic chain during weightbearing, wedged insoles inserted into shoes can modify knee-joint moments. Lateral wedges have been advocated for medial compartment osteoarthritis and medial wedges for lateral-compartment disease. Due to the predominance of medial tibiofemoral osteoarthritis [3], lateral wedges have been the most widely researched.

Biomechanical studies show that lateral wedges reduce the adduction moment during walking by 4–12% compared with barefeet or shoes alone in medial knee osteoarthritis [4•–6•,7,8,9•,10]. Lateral wedges cause a small lateral shift in the centre of pressure location of the ground reaction force [7,8]. This likely decreases the knee joint moment arm, thereby reducing the adduction moment. Recent mechanical modelling has shown that as little as 1 mm lateral displacement of the centre of pressure decreases the adduction moment by 2%, resulting in a 1% reduction in medial compartment load [11•]. Promising research demonstrates that long-term use of lateral wedges can induce gait adaptations, leading to reduced adduction moments when walking [12].

It is important to note that individual biomechanical responses to lateral wedges vary and in some cases wedges may actually increase the adduction moment [4•–6•,7,8,13]. This suggests that patient or shoe characteristics may mediate biomechanical-wedge effects, and that certain patient subgroups are more likely to respond. There is little research evaluating the role of individual characteristics. Disease severity may be important, with wedge-related decreases in the adduction moment observed in participants with mild but not moderate or severe osteoarthritis [10]. Other characteristics that could mediate biomechanical responsiveness include forefoot and rearfoot alignment and motion, frontal plane alignment and baseline knee adduction moment. Of these, only rearfoot motion has been evaluated, with an abstract describing greater reductions in the adduction moment in participants with more frontal plane rearfoot motion [14]. Further studies in this area would help target lateral wedges to the most appropriate patient subgroups.

Biomechanical effects are also influenced by wedge design features. Reductions in the adduction moment are related to wedge inclination; however, greater inclination (10°) is likely to cause discomfort [8]. Recently, biomechanical benefits were shown using a customized wedge inclination, defined as the minimal amount needed for maximal pain reduction during a lateral step-down [4•]. As no study has directly compared customized and standardized wedges, it is unclear if customization offers superior biomechanical benefits. We have shown that insoles wedged laterally along the full length of the foot significantly reduced the knee adduction moment whereas a rearfoot lateral wedge did not [5•]. This supports prescription of full-length rather than rearfoot wedges. A combined treatment approach, using elastic subtalar strapping with lateral wedges, reduces the adduction moment more than wedged insoles alone, particularly in mild and moderate medial osteoarthritis [9•]. This may be because strapping causes valgus angulation of the talus leading to correction of the femorotibial angle, further reducing medial joint load [15].

The use of lateral wedges for symptomatic benefit is recommended by 13 out of 14 guidelines for knee osteoarthritis [16], including those recently published by Osteoarthritis Research Society International (OARSI) [16]. However, nonexperimental and quasiexperimental studies demonstrating pain-relieving effects of lateral wedges in many patients with knee osteoarthritis [1,6•,17–20] have not been confirmed by the limited number of randomized controlled trials [21••,22,23]. One found that customized lateral wedges worn for 2 years reduced intake of nonsteroidal anti-inflammatory drugs but did not alter pain, stiffness or function [22,23]. More recently, a well designed double-blind crossover trial [21••] found no statistical or clinical effect of a 5° lateral wedge worn for 6 weeks. In nonrandomized studies [24–26] of women with medial osteoarthritis, wedges combined with subtalar strapping provided better clinical benefit than conventional wedges. However, several disadvantages of the combined intervention include more adverse effects [27] and the need for shoes larger than normal [26].

Given individual variations in biomechanical response, it is probable that not all patients with medial knee osteoarthritis will benefit clinically. Of the few studies investigating predictors of clinical outcome with insoles, results are inconsistent. Better outcomes are observed with less severe disease [1,6•,18,19,21••], with increased lower limb lean mass [28] and in younger [28] and less obese [21••] patients. We also found that individuals who experienced the greatest immediate reductions in pain and knee adduction moment with insoles demonstrated the greatest improvement in function after 3 months' use [6•]. Another factor that may account for variability in clinical response is the type of shoes the insoles are inserted in. Results of a recent large trial suggest that optimal usage of a lateral-wedged insole may entail insertion in socks (for indoors) or flat footwear without heels [29•]. Variation in daily usage of wedged insoles may also influence clinical outcome with a nonrandomized trial [30] finding greatest clinical benefits from 5–10 h of daily use compared with less than 5 h or more than 10 h.

Given their effectiveness at reducing the adduction moment, lateral wedges have potential for slowing osteoarthritis progression. However, in a randomized trial [23], rearfoot lateral wedges had no effect on joint space narrowing rate over 2 years. In a nonrandomized comparison [26] of lateral wedges with subtalar strapping versus conventional wedges, no differences in progression rates were noted, although no control group was included. These null findings may in part be due to the relative insensitivity of X-rays to the wedge designs or to the heterogenous patient samples. We are currently evaluating structural effects of lateral wedges over 12 months using the more sensitive technique of magnetic resonance imaging [31].

Medial-wedged insoles

Little research has evaluated medial-wedged insoles for lateral compartment knee osteoarthritis. A case series involving 10 patients with lateral knee osteoarthritis showed that medial wedges reduced lateral thrust and pain in walking [19], whereas a more recent study in 10 healthy people found that medial wedges attached to the sole of the shoe alone or combined with ankle orthoses altered frontal knee loading favourably for the lateral-knee compartment [32]. In the only randomized controlled trial [33••] conducted, improved pain and function, together with improved femorotibial angle, was observed with a rearfoot medial wedge worn with an ankle support for 8 weeks, compared with a neutral insole in women with valgus lateral compartment osteoarthritis. This supports the use of medial wedges for predominant lateral compartment osteoarthritis but further research into medial wedges is needed to validate these findings.

Medial arch supports

Medial arch supports are widely available and commonly used but could be detrimental in medial compartment osteoarthritis, as they may shift the centre of pressure medially, thereby increasing the adduction moment and potentially hastening disease progression. A recent study [34••] showed that flexible medial arch supports resulted in a 6% increase in the second peak knee adduction moment during walking in young healthy people. Although the effects of medial arch supports need to be clarified in people with medial osteoarthritis, at this stage they should be used cautiously in this patient population. This includes footwear with in-built medial arch supports.

Effect of footwear on knee loading and osteoarthritis symptoms

Wearing appropriate footwear is a management strategy recommended in recent knee osteoarthritis clinical guidelines [16]. This recommendation is based solely on expert opinion. With the exception of the work commenced by Kerrigan et al.[35–38] 10 years ago, most research into the potential role of shoes for knee osteoarthritis has been conducted in the past 2 years only. A proportion of this work is available only in abstract form. Other limitations of the current research include the use of younger healthy individuals without osteoarthritis and primarily biomechanical evaluations addressing effects of shoes on loading rather than symptoms.

Effect of shoes on knee joint loading compared with that of bare feet

Evidence from two studies in knee osteoarthritis has shown that wearing shoes significantly increases medial knee load compared with walking in barefeet. A recent study [39•] evaluated the effects of wearing the participant's own everyday shoes on the knee adduction moment in 40 people with medial compartment osteoarthritis. Compared with walking barefoot, wearing shoes resulted in a 7.4% increase in the adduction moment. These findings confirmed those of an earlier study [40]. Changes in joint loading when wearing shoes are not explained by alterations in gait pattern [40], suggesting that the design of everyday off-the-shelf shoes may predispose knee osteoarthritis patients to excessive joint loading. This hypothesis is supported by data demonstrating that the effect of shoes on knee loads is not systematic. Although most participants in the study by Kemp et al.[39•] demonstrated an increased adduction moment with shoes, considerable individual variation was observed, with 15% of individuals showing reduced knee loading with shoes and some showing increased loading by 20–30% (compared with barefoot), far in excess of the average 7.4% increase demonstrated by the entire cohort. As participants wore their own shoes in this study, it seems likely that individual shoe characteristics may mediate effects of footwear on knee loading. On the basis of research showing that a one-unit increase in the adduction moment increases the risk of osteoarthritis progression 6.5 times [41], the more conservative findings of Kemp et al.[39•] suggest that wearing shoes may increase the risk of disease progression by a factor of 2.8 on average. As walking barefoot is impractical and potentially dangerous, research is focused on determining the optimal off-the-shelf shoe type for knee osteoarthritis, as well as exploring whether shoe modifications or custom-designed shoes have a role to play in knee osteoarthritis.

Off-the-shelf shoes and their effects on knee load

Some off-the-shelf shoes increase knee loads more than others. Studies in healthy women without knee osteoarthritis revealed that walking in high-heeled shoes (2.5–2.8 inches) resulted in greater loads across the medial knee compartment and the patellofemoral joint compared with bare-foot walking [38], irrespective of the heel width [37]. Although these early studies did not include a flat-heeled comparison shoe, a later study [35] demonstrated that moderate-heeled (1.5 inches) shoes resulted in 9–14% increases in late stance varus knee torque (adduction moment) in younger and older healthy women compared with flat-heeled control shoes. In contrast, men's dress shoes and sneakers, with an average 0.5-inch heel, did not significantly affect joint torques (other than that explained by changes in walking speed) compared with barefoot walking in healthy men [36]. These studies clearly show that shoes with a heel of more than 1.5 inch detrimentally influence medial knee loads and should be avoided or worn minimally by patients with medial knee osteoarthritis. Long-term effects of wearing high-heeled shoes on disease incidence and progression remains unknown, as is their effect on knee symptoms.

A recent abstract compared the effects of four common shoe types (clogs, stability athletic shoes, flexible walking shoes and flip-flops) to barefoot walking in a small cohort with knee osteoarthritis [42••]. Both clogs and stability athletic shoes significantly increased the adduction moment compared with barefoot walking, whereas the flexible walking shoes and flip-flops had no effect. It appears that flexible footwear better approximates barefoot walking and minimizes knee loading whereas supportive stability footwear may have detrimental biomechanical effects. Further research is required to determine which off-the-shelf shoes are optimal for knee osteoarthritis and to evaluate their long-term effects on symptoms and disease progression.

Footwear modifications and their potential applications in knee osteoarthritis

Recent research has focused on the development and evaluation of shoes modified to reduce the knee adduction moment. The ‘mobility’ shoe is a flexible light-weight shoe designed to mimic essential features of natural foot motion via specialized grooves placed at the major foot flexion points [43••]. Data from participants with knee osteoarthritis show that the adduction moment recorded with the mobility shoe approximates that of barefoot walking. Research demonstrates it can significantly reduce the adduction moment by 12% compared with a control shoe and by 8% compared with conventional self-selected walking shoes. Although immediate benefits are evident, it is unknown whether reductions in knee load can be maintained with prolonged use of the mobility shoe.

‘Unstable’ shoes have been designed to strengthen lower extremity muscles that contribute to static and dynamic stability [44,45]. The shoe has a multilayered sole that changes flat hard surfaces into uneven ground, demanding increased muscle activity to maintain stability. A small study [45] in young healthy people showed that ‘unstable’ shoes produced changes and trends in kinematic, kinetic and electromyographic characteristics deemed by the authors to be advantageous. A 12-week randomized controlled trial [44] conducted in 123 people with knee osteoarthritis compared unstable shoes to off-the-shelf walking shoes. Both groups demonstrated reductions in knee pain with generally no differences between the two shoe types tested. Although there were trends towards improved balance performance in the group wearing unstable shoes, differences were not significant between groups. No differences between groups regarding joint motion or strength were observed. At this stage, a specially designed unstable shoe appears to offer little clinical benefit to patients with knee osteoarthritis.

On the basis of the promising results of studies evaluating inserted lateral wedge insoles, some studies have evaluated the effects of shoes modified to include a laterally angled sole. In young healthy adults, Fisher et al.[46••] demonstrated that shoes with either a 4 or 8° valgus shoe sole angle significantly reduced the knee adduction moment compared with a control shoe. Participants with higher knee adduction moments in the control shoe prior to intervention demonstrated greater reductions in moments with the wedged sole shoes. In contrast, another study that attached a 14° wedge to the shoe did not reduce the varus knee moment unless combined with a rigid ankle-stabilizing orthosis [32]. It is not clear why results of these studies differ, but differences in the type of shoe used or the length of the sole wedging may be responsible.

Modifications to shoe sole stiffness have also been tested for their potential application to knee osteoarthritis. A variable-stiffness sole that is denser (rigid) laterally than medially can significantly reduce the adduction moment in healthy young adults compared with control shoes of uniform sole stiffness [46••]. Similarly to the wedged sole shoe, participants with higher knee adduction moments in the control shoe prior to intervention demonstrated greater reductions in moments with the variable-stiffness sole shoes. Data from older individuals with medial knee osteoarthritis show similar results. Erhart et al.[47••] tested a variable-stiffness shoe in 79 people with medial osteoarthritis and found average reductions in the knee adduction moment ranging from 2.4 to 6.2%, depending on walking speed and compared with a constant-stiffness control shoe. Importantly, reductions in the knee adduction moment did not occur at the expense of overloading other lower joints. Furthermore, an abstract [48••] reporting findings from a small randomized controlled trial showed improvements in pain and function at 12 months with variable-stiffness shoes compared with control shoes. Variable-stiffness sole shoes offer great potential for medial knee osteoarthritis and should be subjected to further larger clinical trials that include measures of structural disease progression.


Increased joint loading significantly increases the risk of osteoarthritis progression, but is amenable to change using insoles or footwear. Accordingly, insoles and footwear offer great potential as simple, inexpensive treatment strategies for knee osteoarthritis. On the basis of current research, clinical recommendations for the use of lateral wedge insoles in people with medial knee osteoarthritis include:

  1. Wedge full length of foot not just heel.
  2. Wedge tilt of around 5° as greater tilt (10°) is more likely to be associated with discomfort.
  3. Addition of elastic subtalar strapping or ankle support may improve wedge effectiveness (but may also increase the likelihood of adverse effects and a larger shoe may be required to allow fitting).
  4. Daily usage of 5–10 h may be optimal.
  5. Wedges should be worn in shoes with flat heel and without medial arch supports.
  6. Wedges should immediately reduce pain, if longer term clinical benefits are to be achieved.
  7. Patients who achieve greatest benefits may include those who are younger, are less obese, have less severe disease and have greater lower limb lean muscle mass.

Recent research also allows some recommendations for guiding the clinical use of footwear (Table 1); however, further research is needed to evaluate the efficacy of shoes and shoe modifications in relieving osteoarthritis-associated symptoms and whether biomechanical benefits translate into a reduced risk of disease progression. Research is also required to determine which patient subgroups are most likely to respond to treatment.

Table 1
Table 1:
Recommendations for footwear for people with medial compartment knee osteoarthritis based on current research


This work was supported by funding from the National Health & Medical Research Council of Australia (Project Grant #61788).

References and recommended reading

Papers of particular interest, published within the annual period of review, have been highlighted as:

• of special interest

•• of outstanding interest

Additional references related to this topic can also be found in the Current World Literature section in this issue (pp. 195–196).

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29• Toda Y, Tsukimura N. Influence of concomitant heeled footwear when wearing a lateral wedged insole for medial compartment osteoarthritis of the knee. Osteoarthritis Cartilage 2008; 16:244–253. This study highlights the influence of different types of footwear in mediating the clinical benefits of laterally wedged insoles. On the basis of its findings, insertion in socks (for indoors) or flat footwear without heels would be recommended to use with wedges.
30 Toda Y, Tsukimura N, Segal N. An optimal duration of daily wear for an insole with subtalar strapping in patients with varus deformity osteoarthritis of the knee. Osteoarthritis Cartilage 2005; 13:353–360.
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32 Schmalz T, Blumentritt S, Drewitz H, Freslier M. The influence of sole wedges on frontal plane kinetics, in isolation and in combination with representative rigid and semi-rigid ankle-foot-orthoses. Clin Biomech 2006; 21:631–639.
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39• Kemp G, Crossley KM, Wrigley TV, et al. Reducing joint loading in medial knee osteoarthritis: shoes and canes. Arthritis Rheum (Arthritis Care Res) 2008; 59:609–614. This paper highlights the fact that wearing shoes increases knee loading compared with barefoot walking, and that increases in loading are not systematic but may be mediated by patient or shoe characteristics.
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42•• Sengupta M, Mikolaitis RA, Trombley RM, et al. The effects of common footwear on dynamic joint loading in osteoarthritis of the knee. Arthritis Rheum 2007; 56:S119. This abstract reports the first study to compare the effects of different common types of off-the-shelf shoes on knee loading in people with knee osteoarthritis. This study highlights that some shoe types significantly increase joint loading whereas others do not.
43•• Shakoor N, Lidtke R, Sengupta M, et al. Effects of specialized footwear on joint loads in osteoarthritis of the knee. Arthritis Rheum (Arthritis Care Res) 2008; 59:1214–1220. This is the first full paper to report the evaluation of a novel custom-designed ‘mobility’ shoe in people with knee osteoarthritis. Results showed that it can immediately reduce knee load compared with both control shoes and self-chosen walking shoes.
44 Nigg BM, Emery C, Hiemstra LA. Unstable shoe construction and reduction of pain in osteoarthritis patients. Med Sci Sports Ex 2006; 38:1701–1708.
45 Nigg BM, Hintzen S, Ferber R. Effect of an unstable shoe construction on lower extremity gait characteristics. Clin Biomech 2006; 21:82–88.
46•• Fisher DS, Dyrby CO, Mundermann A, et al. In healthy subjects without knee osteoarthritis, the peak knee adduction moment influences the acute effect of shoe interventions designed to reduce medial compartment knee load. J Orthop Res 2007; 25:540–546. This study describes a range of shoe modifications that can significantly reduce medial knee load in healthy people, and thus offers potential interventions for future testing in patients with medial knee osteoarthritis.
47•• Erhart J, Mundermann A, Elspas B, et al. A variable-stiffness shoe lowers the knee adduction moment in subjects with symptoms of medial compartment knee osteoarthritis. J Biomech 2008; 41:2720–2725. This study reports the biomechanical benefits of a variable-stiffness shoe on knee loading observed in a large cohort with medial knee osteoarthritis. This study showed that benefits did not occur at the expense of overloading other lower limb joints.
48•• Erhart JC, Giori NJ, Andriacchi TP. Variable-stiffness walking shoe lowers knee adduction moment, reduces pain, and improves function in patients with osteoarthritis after one year. 54th Annual Meeting of the Orthopaedic Research Society; 2008, San Francisco, USA. This abstract reports the first clinical trial to evaluate the effects of a modified shoe on joint loading and symptoms in patients with knee osteoarthritis. Findings showed that a shoe with a variable-stiffness sole could reduce loading and improve symptoms.

footwear; insoles; knee osteoarthritis; orthotics; shoes

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