PT Classroom - Effects of Wedged Insoles on Knee Osteoarthritis ׀ by Jessica Johnson, MPT

Effects of Wedged Insoles on Knee Osteoarthritis

Osteoarthritis is one of the most incapacitating diseases affecting older populations. Greater than ten percent of people age 65 and over suffer from pain, functional limitations, and reduced quality of life because of knee osteoarthritis. The medial compartment of the knee is affected ten times more often than the lateral (1). Though knee osteoarthritis is very significant in the elderly, it is not inevitable with age.

Osteoarthritis is believed to be caused by knee mechanics during gait. Throughout normal gait knees exhibit medial and lateral thrust patterns. These thrust patterns of the knee are limited by the LCL and MCL respectively but produce increased loading at the opposite joint compartment. The lateral structures of the knee oppose lateral thrust of the knee, causing a varus moment and loading the medial joint surface damaging articular cartilage (17). The varus moment during normal gait is nearly 2.5 times that of the valgus force. In knees with varus deformity the same ratio is increased to 3.3 (11). Surgical procedures such as high tibial osteotomy and total knee arthroplasty have been effectively employed to treat medial knee OA, though these procedures are costly and incur significant risk for complications. Early investigators hypothesized that fitting patients with laterally-wedged insoles would create significant differences in static and dynamic torques at the knee both through a change in tibiofemoral angle (19) as well as a change in whole limb angle with respect to gravity (15).

Analysis of normal gait cycle shows knee varus torque peaks twice. The greatest varus torque occurs at the transition through terminal stance and pre-swing. The second peak occurs during weight acceptance. Crenshaw (2) was one of the first researchers to demonstrate significant reduction in peak varus torques with the use of laterally-wedged insoles in symptomatic patients with osteoarthritis. The magnitude of literature available demonstrates not only biomechanical significance but also reduction in symptoms and improvement of function with the use of wedged insoles. This research touts that fitting patients with wedged insoles is a cost-effective and minimally invasive procedure, which consumes very little time for a physical therapist to administer.

The Osteoarthritis Research Society International (OARSI), a multidisciplinary team of sixteen experts from two continents and six countries, devised 54 treatment recommendations for knee OA based on sound scientific judgment including a thorough review of the literature. The first 11 recommendations fall under the scope of practice of a physical therapist with recommendation number 4 specifically describing a referral to physical therapy for evaluation and treatment. While experts carefully worded all other recommendations to include suggestions where patients “…might benefit from…” or “…may reduce symptoms with…” A strongly worded recommendation number 9 states “Every patient with hip or knee OA should receive advice concerning appropriate footwear.” Experts go on to concur with the literature that laterally-wedged insoles may be of benefit to many patients with knee osteoarthritis (22).

Researchers agree that the use of wedged insoles is most beneficial to patients with mild OA of the knee. All found some benefit to patients with Kellgren & Lawrence grades of II or less (18, 21) and one study showed improvement in patients with moderate (K-L level III) disease severity (11). When patients with symptomatic OA were compared to healthy controls significant differences in the amount of varus reduction was found. Healthier knees were consistently found to have more dramatic biomechanical responses to wedged insoles (5).

Researchers have found positive outcomes for patients with the use of orthotics wedged anywhere from 4 degrees (which corresponds to <5mm) all the way to 16mm inclinations to determine which were most beneficial. Kerrigan et al first described the correlation between increased angulation of insoles and relief, but Fang and colleagues found that within 4 weeks of use of simple 4 degrees shoe inserts without subtalar strapping 10% of participants reported a 70% reduction of symptoms on the WOMAC subscales of pain, stiffness, and function (7, 8, 9). Angulation of lateral wedges produces a correlative reduction in knee varus torque, however subjects randomized to 12mm and 16mm groups had subsequent complaints of foot discomfort (20). Kakihana et al found that the center of pressure of the foot which is always parallel to the subtalar joint axis shifts laterally with lateral wedge placement in most patients (5). Almost exclusively researchers utilized a full length foot orthotic.

Investigators have recently capitalized on the previous research for medial knee OA and produced data supporting the use of medial-wedged insoles for the treatment of lateral knee OA (14).

The current research is not without limitations. The most proximal joints to the wedge are the subtalar joint at the rearfoot and the 1st MTP at the forefoot. Several attempts to construct a stabilizer for the subtalar joint have been successful in further reducing the knee varus torque as compared to simple wedging. In earlier studies, Toda et al constructed a subtalar strapping technique then had to revise it because of secondary complaints of pain or discomfort from the strap (19). Through 6-month follow up, Toda et al found that the participants did not continuously use the insoles citing that the insoles required them to wear shoes one size larger than they commonly wore (21). Toda’s paper also represents the only long-term research to date. At the same 6-month follow up nearly 1/4 of patients elected to discontinue the study and forego the 2-year study participation most complaining of inconvenience of the inserts, very few reported no benefit of the treatment. Of the 48 women who agreed to continuously use the insoles for 2 years, only those with strapped subtalar joints demonstrated reduction of static tibiofemoral angle over time as compared to those who wore simple inserted wedges. Similarly, Toda’s research eludes to potiential prevention of osteoarthritis progression via use of laterally-wedged insoles with subtalar stabilization based on the Kellgren & Lawerence grading scale (21). It should be noted that Toda holds a patent for the design of the subtalar strapping method. Rodriques and her team utilized an over the counter sock-type ankle support to secure the orthotic to the foot as well as stabilize the talus and found similarly beneficial results in reduction of torques at the knee (14).

No research to date has addressed potential effects or control for the 1st MTP, which is undeniably an important generator in foot pain.

The research also lacks predictive variables to identify which patients are most likely to benefit from wedged insoles. A vast majority of patients in the research studies benefited from laterally-wedged insoles for medial knee OA, but a small portion of the patients in multiple research studies had worsening of knee varus moments during gait with use of these insoles (5).

A note of caution has been introduced by researchers Franz et al in 2008 (4). It is becoming common to treat patients symptomatically with medial-wedged or cushioned inserts for common overuse injuries. In this study healthy recreational runners were recruited to investigate changes in knee varus torques with insoles. Not surprisingly, medial-wedged insoles produced a 4% increase during running and 6% increase during running. The authors caution that symptomatic reduction for acute injuries may not outweigh the damage caused by increased medial knee compression forces with medial wedge inserts. The same authors cited previous research demonstrating 23-26% increases varus torque during wear of high-heeled shoes. Men and women have no significant differences in knee torques during barefoot walking, which suggests that extrinsic biomechanical differences like footwear are to blame for the doubled incidence of knee OA among women (9).

Future studies should examine possible predictive variables to reduce the frequency of prescribing this intervention to patients who’s condition may be worsened with wedged insoles, investigate potential effects relative to 1st MTP biomechanics, preventative use of insoles, and more long term studies on footwear patterns as predictors in the development of knee OA. As the tensile forces of ligaments are directly implicated in providing opposite side joint compression, researchers will also benefit to control for varying degrees of ligamentous laxity or musculotendinous flexibility. These soft tissue structures may restrict joint motions even when the bony architecture is corrected.

 

In summary, laterally wedged insoles are an excellent inexpensive treatment option for the treatment of knee arthritis in conjunction with other therapeutic procedures and appropriate patient education. Patients with mild to moderate knee arthritis will likely benefit from wedged insoles. Utilization of subtalar stabilization and inclination of wedges as high as the patient can tolerate without secondary foot pain is most beneficial. Clinical or telephone follow up within 4-8 weeks of issue is essential to determining the effectiveness of wedged insoles and as a safety procedure to direct patients to stop the use of insoles if they do not notice a reduction of symptoms at that time. All therapeutic procedures carry side effects and risk including administration of orthotics, exercise, and education. Wedged orthotics for any condition should be carefully supervised and re-evaluated so as to minimize negative effects of their use. Imagine, nearly a year after your clinic opening, one of your patients develops a superficial burn from a hot pack!