Jennifer C. Erhart

Changes in in vivo knee loading with a variable-stiffness intervention shoe correlate with changes in the knee adduction moment.

External knee adduction moment can be reduced using footwear interventions, but the exact changes in in vivo medial joint loading remain unknown. An instrumented knee replacement was used to assess changes in in vivo medial joint loading in a single patient walking with a variable‐stiffness intervention shoe. We hypothesized that during walking with a load modifying variable‐stiffness shoe intervention: (1) the first peak knee adduction moment will be reduced compared to a subjects personal shoes; (2) the first peak in vivo medial contact force will be reduced compared to personal shoes; and (3) the reduction in knee adduction moment will be correlated with the reduction in medial contact force. The instrumentation included a motion capture system, force plate, and the instrumented knee prosthesis. The intervention shoe reduced the first peak knee adduction moment (13.3%, p = 0.011) and medial compartment joint contact force (12.3%; p = 0.008) compared to the personal shoe. The change in first peak knee adduction moment was significantly correlated with the change in first peak medial contact force (R2 = 0.67, p = 0.007). Thus, for a single subject with a total knee prosthesis the variable‐stiffness shoe reduces loading on the affected compartment of the joint. The reductions in the external knee adduction moment are indicative of reductions in in vivo medial compressive force with this intervention.

A variable-stiffness shoe lowers the knee adduction moment in subjects with symptoms of medial compartment knee osteoarthritis

The purpose of this study was to evaluate the effectiveness of variable-stiffness shoes in lowering the peak external knee adduction moment during walking in subjects with symptomatic medial compartment knee osteoarthritis. The influence on other lower extremity joints was also investigated. The following hypotheses were tested: (1) variable-stiffness shoes will lower the knee adduction moment in the symptomatic knee compared to control shoes; (2) reductions in knee adduction moment will be greater at faster speeds; (3) subjects with higher initial knee adduction moments in control shoes will have greater reductions in knee adduction moment with the intervention shoes; and (4) variable-stiffness shoes will cause secondary changes in the hip and ankle frontal plane moments. Seventy-nine individuals were tested at self-selected slow, normal, and fast speeds with a constant-stiffness control shoe and a variable-stiffness intervention shoe. Peak moments for each condition were assessed using a motion capture system and force plate. The intervention shoes reduced the peak knee adduction moment compared to control at all walking speeds, and reductions increased with increasing walking speed. The magnitude of the knee adduction moment prior to intervention explained only 11.9% of the variance in the absolute change in maximum knee adduction moment. Secondary changes in frontal plane moments showed primarily reductions in other lower extremity joints. This study showed that the variable-stiffness shoe reduced the knee adduction moment in subjects with medial compartment knee osteoarthritis without the discomfort of a fixed wedge or overloading other joints, and thus can potentially slow the progression of knee osteoarthritis.

Changes in knee adduction moment, pain, and functionality with a variable-stiffness walking shoe after 6 months

This study tested the effects of variable‐stiffness shoes on knee adduction moment, pain, and function in subjects with symptoms of medial compartment knee osteoarthritis over 6 months. Patients were randomly and blindly assigned to a variable‐stiffness intervention or constant‐stiffness control shoe. The Western Ontario and McMaster Universities (WOMAC) score served as the primary outcome measure. Joint loading, the secondary outcome measure, was assessed using the external knee adduction moment. Peak external knee adduction moment, total WOMAC, and WOMAC pain scores were assessed at baseline and after 6 months. The total WOMAC and WOMAC pain scores for the intervention group were reduced from baseline to 6 months (p = 0.017 and p = 0.002, respectively), with no significant reductions for the control group. There was no difference between groups in magnitude of the reduction in total WOMAC (p = 0.50) or WOMAC pain scores (p = 0.31). The proportion of patients achieving a clinically important improvement in pain was greater in the intervention group than in the control group (p = 0.012). The variable‐stiffness shoes reduced the peak knee adduction moment (−6.6% vs. control, p < 0.001) in the 34 intervention subjects at 6 months. The adduction moment reduction significantly improved (p = 0.03) from the baseline reduction. The constant‐stiffness control shoe increased the peak knee adduction moment (+6.3% vs. personal, p = 0.004) in the 26 control subjects at 6 months. The results of this study showed that wearing the variable‐stiffness shoe lowered the adduction moment, reduced pain, and improved functionality after 6 months of wear. The lower adduction moment associated with wearing this shoe may slow the rate of progression of osteoarthritis after long‐term use.

Predicting changes in knee adduction moment due to load-altering interventions from pressure distribution at the foot in healthy subjects

The purpose of this pilot study of healthy subjects was to determine if changes in foot pressure patterns associated with a lateral wedge can predict the changes in the knee adduction moment. We tested two hypotheses: (1) increases or decreases in the knee adduction moment and ankle eversion moment due to load-altering footwear interventions can be predicted from foot pressure distribution and (2) changes in magnitude of the knee adduction moment and ankle eversion moment due to lateral wedges can be predicted from pressure distribution at the foot during walking. Fifteen healthy adults performed walking trials in three shoes: 0 degrees , 4 degrees , and 8 degrees laterally wedged. Maximum heel pressure ratio, first peak knee adduction moment, and peak ankle eversion moment were assessed using a pressure mat, motion capture system, and force plate. Increases or decreases in the knee adduction moment and ankle eversion moment were predicted well from foot pressure distribution. However, the magnitude of the pressure change did not predict the magnitude of the peak knee adduction moment change or peak ankle eversion moment change. Factors such as limb alignment or trunk motion may affect the knee adduction moment and override a direct relationship between the pressure distribution at the shoe-ground interface and the load distribution at the knee. However, changes (increases or decreases) in the peak knee adduction moment due to load-altering footwear interventions predicted from pressure distribution during walking can be important when evaluating these types of interventions from a clinical perspective.

An analysis of the mechanisms for reducing the knee adduction moment during walking using a variable stiffness shoe in subjects with knee osteoarthritis

Variable stiffness shoes that have a stiffer lateral than medial sole may reduce the external knee adduction moment (EKAM) and pain during walking in patients with medial compartment knee osteoarthritis (OA). However, the mechanism by which EKAM may be reduced in the OA knee with this intervention remains unclear. Three hypotheses were tested in this study: (1) The reduction in EKAM during walking with the variable stiffness shoe is associated with a reduction in GRF magnitude and/or (2) frontal plane lever arm. (3) A reduction in frontal plane lever arm occurs either by moving the center of pressure laterally under the shoe and/or by dynamically reducing the medial component of GRF. Thirty-two subjects (20 male, 12 female; age: 58.7 ± 9.3 years; height: 1.62 ± 0.08 m; mass: 81.3 ± 14.6 kg) with medial compartment knee osteoarthritis were studied walking in a gait laboratory. The frontal plane lever arm was significantly reduced (1.62%, 0.07%ht, p=0.02) on the affected side while the magnitude of the GRF was not significantly changed. The reduction in the lever arm was weakly correlated with a medial shift in the COP. However, the combined medial shift in the COP and reduction in the medial GRF explained 50% of the change of the frontal plane lever arm. These results suggest that the medial shift in the COP at the foot produced by the intervention shoe stimulates an adaptive dynamic response during gait that reduces the frontal plane lever arm.

Response to 'Plasma proteins present in osteoarthritic synovial fluid can stimulate cytokine production via Toll-like receptor 4' - authors' reply

We thank Oliviero and colleagues for their interest in our recent publication [1] and for reporting their very interesting related experiments [2]. Th eir results strongly support the concept that extravascular plasma proteins may act as damage-associated molecular patterns, and specifi cally as Toll-like receptor 4 agonists. In addition, we note that the NALP-3 infl ammasome exhibits dependence on Toll-like receptor 4 or other mechanisms of priming of IL-1β transcription, thereby generating pro-IL-1β that can be converted to IL-1β by the activated infl ammasome [3]. Although biochemical measurement of plasma and serum were not performed, we suspect the enhanced eff ect of serum compared with plasma could be related to mediators generated in the clotting process or released by platelets during the clotting process (but not released in the generation of plasma) and not related to the removal of fi brinogen. Th e observation that fi brinogen is itself able to prime the response to calcium crystalinduced infl ammation further supports the role of fi brino gen as a Toll-like receptor 4 agonist [4,5], as demon strated by its ability to prime the infl ammasome for response to activation by calcium crystals. We thank Oliviero and colleagues for sharing their results and look forward to future studies elucidating the potentially critical role of plasma proteins as extravascular damage-associated molecular patterns.

Regional Cartilage Thinning Occurs First in the Walking Weight Bearing Regions of the Femur in Medial Compartment Knee Osteoarthritis

Osteoarthritis (OA) of the knee affects an estimated 20–40% of individuals over the age of 65 [1], and is nearly 10 times more common in the medial compartment than the lateral compartment [2]. Plain radiography measurements using the Kellgren and Lawrence (KL) scale have been the gold standard for diagnosis of knee osteoarthritis [3]. However, for new treatment interventions for medial compartment knee OA such as load modifying footwear, it would be important to know if the disease-related cartilage loss in the medial compartment occurs initially and predominantly in regions that are weight bearing during walking. Because walking results in highest weight bearing occurring in the anterior and middle regions of the femoral condyle and the anterior region of the tibial plateau, seeing a pattern of thinning in these areas would suggest that walking is an important activity for understanding both the cause and treatment of osteoarthritis.Copyright

Relationship of Knee Articular Cartilage Thickness to Body Mass Index and Gait Mechanics

In longitudinal studies, obesity has been shown to be a major risk factor for knee osteoarthritis (OA) (Felson, 1988), but the cause of this increased prevalence is not yet clear. A common hypothesis is that obesity increases joint loads due to increased body mass, causing the articular cartilage to experience higher load and degenerate more quickly (Griffin, 2005). However, it has been shown that in healthy, normal-weight subjects, knee cartilage thickness increases in proportion to the loads applied during ambulation (Andriacchi, 2004). It is not known whether this same relationship also holds true for obese people who do not have OA. Because it is difficult to measure joint loads directly in vivo, the external adduction moment can be used as a surrogate measure of the relative load distribution between the medial and lateral compartments of the knee (Andriacchi 2004). If cartilage responds positively to load, a higher adduction moment will be correlated with thicker cartilage on the medial side and thinner cartilage in the lateral compartment. Similarly, average cartilage thickness should be proportional to body mass index. Therefore the purpose of this study was to examine the following hypotheses in a group of healthy-weight, overweight, and obese individuals: 1. Average cartilage thickness in both compartments is proportional to body mass index (BMI). 2. Average cartilage thickness in the lateral compartment is inversely proportional to the knee adduction moment. 3. Average cartilage thickness in the medial compartment is proportional to the knee adduction moment. 4. The ratio of medial to lateral cartilage thickness is proportional to the adduction moment.Copyright

Reduction in the Knee Adduction Moment During Walking Using Laterally-Wedged Shoes With and Without Ankle Support

A high maximum adduction moment at the knee during walking has been associated with an increased rate of progression [1] and worse treatment outcome [2] of medial compartment osteoarthritis (OA) of the knee. Laterally-wedged insoles and shoes have been shown to reduce the knee adduction moment in healthy and osteoarthritic populations [3,4]. However, the mechanism of the effectiveness of such interventions is not well understood. Toda et al. showed that subtalar strapping with laterally wedged insoles in osteoarthritic subjects can improve valgus correction, but the authors did not look at the dynamic effects of walking [5]. A second study looked at the effects of lateral wedges with both semi-rigid ankle support and a rigid ankle-foot-orthosis and found a reduction in the adduction moment only with ankle support and a 10° lateral wedge. The wedge alone did not produce a reduction in the adduction moment [6]. Thus, it seems that the mechanism of action of the lateral wedge may be influenced by ankle motion.Copyright

Reduction in the Medial Compartment Force Correlates With the Reduction in Knee Adduction Moment Using a Variable-Stiffness Shoe With an Instrumented Knee

Osteoarthritis (OA) of the knee affects an estimated 20–40% of individuals over the age of 65 [1], and is nearly 10 times more common in the medial compartment than the lateral compartment [2]. Many studies have reported the effectiveness of footwear modifications using laterally-wedged insoles [3,4] and more recently, variable-stiffness soles [5] in reducing the adduction moment at the knee in patients with medial compartment knee OA. The adduction moment is known to be associated with the progression [6] and treatment outcome [7] of medial compartment knee OA, and has been shown to be correlated with medial compartment joint loading [8]. However, the exact changes in medial compartment joint loading in vivo with the variable-stiffness shoe remain unknown. The development of an instrumented total knee implant which has the ability to directly measure tibial forces, and can differentiate between medial and lateral joint loads in vivo during walking [9], allows the testing of changes in the medial compartment loading with an intervention shoe.Copyright