More than 20 million people worldwide suffer from knee osteoarthritis and the prospect of non-surgical relief fuels significant interest in easy, inexpensive treatments. Lateral shoe wedging for knee osteoarthritis is one of these approaches – you place a small wedge under the sole of the foot that would tip the foot outward and theoretically relieve loading from the most commonly affected region of the joint. It seems simple, almost too simple.
But the truth is, it’s more complex. Here’s everything you need to know about lateral wedge insoles, the evidence, safe usage, and how they compare to other treatments.
Lateral Shoe Wedging for Knee Osteoarthritis Basics
Lateral wedge insoles are shoe insoles that are thicker on the outer edge of your foot than on the inside, and decrease in thickness as they cross over to the inside of the foot. The insoles are inserted into normal shoes, causing the foot to tilt into a slight everted position – where the sole of the foot tilts outward. The insole is intended for use by people with the most common type of knee osteoarthritis, which affects the inside of the knee joint (called medial compartment knee osteoarthritis).
The theory is that tilting the foot out slightly changes the forces that travel up the leg when you walk.
How Lateral Wedges Affect Knee Mechanics
To cut a long story short, the primary mechanical aim is to decrease the force called the knee adduction moment, that is measured in the lab as an indication of the extent to which the weight of your body goes through the inside of your knee with each step. As you would expect, it turns out that lateral wedges have been shown in the lab to slightly decrease this force, generally by about 5-10%. That sounds good.
Who May Be a Candidate?
Perhaps the most popular targets for this treatment are those who have been diagnosed with medial compartment OA, especially those earlier on in their disease progression. However, we know from previous research and the knowledge base that each person’s anatomy, walking style, and limb alignment all play a role on whether this technology will actually be helpful. If a person has a large bowing (beyond 3 degrees), they will probably not have the same response as someone who has a mild bow.
Research on Lateral Shoe Wedging for Osteoarthritis
The clinical data on lateral wedge insoles has grown substantially over the last 20 years. The reality that has emerged is both disappointing and has changed as the quality of trial data has become more rigorous. Lateral wedges have proven to be no more effective than flat insoles or shoe inserts for significant clinical outcomes in the general population of patients.
Effects on Pain and Function
Most more modern high quality evidence has shown almost no statistically significant improvement in pain scores or physical function compared with control insoles. A Cochrane review of the use of wedged insoles for medial knee OA found no convincing evidence of benefit for pain, stiffness or disability outcomes. There are individual patients who do subjectively experience a small improvement and a few subgroups, perhaps those with specific alignment profiles, may respond better.
But on average in study populations the effect is modest and variable. And that, is not a reason to throw these things out altogether.
Biomechanical Effects Versus Clinical Outcomes
The disconnect between biomechanics and clinical outcomes has always been a problem in musculoskeletal research. (And reducing an adduction moment in a research setting is, in fact, easy to measure and repeat). But how much reduction will be enough, and for how long and in what way, to actually protect cartilage and offer pain relief in everyday life — these are tougher questions. Long-term structural data (imaging of joint space or cartilage volume over time) is still sparse, and assertions that the intervention slows disease are not yet supported by the evidence.
Potential Benefits, Limitations, and Risks
Lateral wedges, in spite of the small clinical evidence, are relatively low risk and virtually costless in comparison to many other interventions. For some people, even a small decrease in pain while walking can be extremely important. And, as non-invasive methods, they do not rule out the use of others.
Nonetheless, limitations and potential disadvantages should be fairly acknowledged.
Comfort, Foot Symptoms, and Adaptation
Fit counts a lot. A large, ill-fitting, or otherwise inappropriate insole can generate pressure spots, force undesirable gait patterns, and can be so uncomfortable that the wearer abandons it. Several anecdotal reports from initial-week users have experienced greater outer ankle, outer knee, or foot arch discomfort – again, often due to altered load distribution across the lower limb.
Persistent discomfort beyond two to four weeks of gradual adaptation is definitely a red flag to be raised with a clinician.
Why Results Differ Between Individuals
Wedge angle, shoe type, initial gait mechanics, as well as where and how much joint damage exists can all impact effectiveness. The same 5-degree wedge shoe worn in a soft flat shoe differs from that same wedge in a better heel-to-toe walking shoe. And if the patient is pronated or flattened foot already, the wedge device may work in concert with altered lower-limb mechanics in ways that are impossible to predict without testing.
This, plus individual variations in data that averages out in groups, explains why testing under supervision and tracking every step (pun intended) can be very smart.
How to Use Lateral Wedges Safely
Beginning with an assessment by a healthcare professional is always the most prudent approach. The clinician can verify if the suspected osteoarthritis compa rtment is involved, as well as determine the degree of the misalignment, gait, the suggested degree of wedge (generally 5-10 degrees), and an appropriate shoe that will not interfere with the wedge. Over the counter generic shoe insoles purchased at a pharmacy may help, but they’re not designed for the individual shape of the foot or gait.
Choosing and Fitting an Insole
If the device is well-matched to the shoe it is in, with proper depth and a solid sole, it will work better than if same device is stuffed into a narrow or a soft shoe. The shoe influences the way forces are transmitted. The rocker bottom shoe, for example, interfaces with wedge insoles in a way that either magnifies or diminishes their benefit.
Proper fitting (preferably by a podiatrist or orthopedist) minimizes trial and error.
Monitoring Response and Warning Signs
Six to eight weeks of tracking symptoms is enough time to assess benefit. Use a pain diary to chart activity level, shoes worn, and comfort. Discontinue use and consult your health professional if your balance is affected, if you develop a new knee, ankle, or hip pain, or if your symptoms become worse rather than better.
Alternatives and Shared Treatment Planning
Lateral wedge insoles are most effective when part of a multi-modal treatment plan and not a complete solution. Knee osteoarthritis can be managed with a multi-modal approach and there is substantial evidence for a number of non-operative options.
Evidence-Based Non-Surgical Options
In terms of evidence strongest evidence for conservative management of knee OA is on exercise therapy (specifically strengthening quadriceps and hip abductors). Weight loss (if indicated) is arguably more effective at decreasing load on the joint than any insole design. Education, activity modification, and analgesia are beneficial to help manage symptoms.
Knee bracing, and particularly a valgus unloading brace is likely to provide more consistent biomechanical corrections than a wedge insole.
Questions to Ask a Healthcare Professional
Before you try a wedging device, it’s worth asking your doctor or therapist a few questions, such as: What is the worst-affected compartment?
How likely is a wedge to suit me given my alignment?
What wedge angle and footwear combination would work with my gait?
How long should I be tested for and what change would be considered a success?
Are there other options, such as an exercise program or a brace, that might be preferable?
These discussions can help guide more realistic expectations and avoid fruitless efforts.