Jennifer C. Erhart-Hledik

Effect of variable-stiffness walking shoes on knee adduction moment, pain, and function in subjects with medial compartment knee osteoarthritis after 1 year.

This study investigated the load‐modifying and clinical efficacy of variable‐stiffness shoes after 12 months in subjects with medial compartment knee osteoarthritis. Subjects who completed a prior 6‐month study were asked to wear their assigned constant‐stiffness control or variable‐stiffness intervention shoes during the remainder of the study. Changes in peak knee adduction moment, total Western Ontario and McMaster Universities (WOMAC), and WOMAC pain scores were assessed. Seventy‐nine subjects were enrolled, and 55 completed the trial. Using an intention‐to‐treat analysis, the variable‐stiffness shoes reduced the within‐day peak knee adduction moment (−5.5%, p < 0.001) in the intervention subjects, while the constant‐stiffness shoes increased the peak knee adduction moment in the control subjects (+3.1%, p = 0.015) at the 12‐month visit. WOMAC pain and total scores for the intervention group were significantly reduced from baseline to 12 months (−32%, p = 0.002 and −35%, p = 0.007, respectively). The control group had a reduction of 27% in WOMAC pain score (p = 0.04) and no significant reduction in total WOMAC score. Reductions in WOMAC pain and total scores were similar between groups (p = 0.8 and p = 0.47, respectively). In the intervention group, reductions in adduction moment were related to improvements in pain and function (R2 = 0.11, p = 0.04). Analysis by disease severity revealed greater efficacy in adduction moment reduction in the less severe intervention group. While the long‐term effects of the intervention shoes on pain and function did not differ from control, the data suggest wearing the intervention shoe reduces the within‐day adduction moment after long‐term wear, and thus should reduce loading on the affected medial compartment of the knee.

Age-related differences in sagittal-plane knee function at heel-strike of walking are increased in osteoarthritic patients.

OBJECTIVE To compare age-related patterns of gait with patterns associated with knee osteoarthritis (OA), the following hypotheses were tested: (H1) The sagittal-plane knee function during walking is different between younger and older asymptomatic subjects; (H2) The age-related differences in H1 are increased in patients with knee OA. DESIGN Walking trials were collected for 110 participants (1.70 ± 0.09 m, 80 ± 14 kg). There were 29 younger asymptomatic subjects (29 ± 4 years) and 81 older participants (59 ± 9 years), that included 27 asymptomatic subjects and 28 and 26 patients with moderate and severe medial knee OA. Discrete variables characterizing sagittal-plane knee function were compared among the four groups using ANOVAs. RESULTS During the heel-strike portion of the gait cycle at preferred walking speed, the knee was less extended and the shank less inclined in the three older groups compared to the younger asymptomatic group. There were similar differences between the severe OA group and the older asymptomatic and moderate OA groups. Both OA groups also had the femur less posterior relative to the tibia and smaller extension moment than the younger group. During terminal stance, the severe OA group had the knee less extended and smaller knee extension moment than the younger asymptomatic and older moderate OA groups. CONCLUSIONS The differences in knee function, particularly those during heel-strike which were associated with both age and disease severity, could form a basis for looking at mechanical risk factors for initiation and progression of knee OA on a prospective basis.

Age and obesity alter the relationship between femoral articular cartilage thickness and ambulatory loads in individuals without osteoarthritis

Articular cartilage is sensitive to mechanical loading, so increased risk of osteoarthritis in older or obese individuals may be linked to changes in the relationship between cartilage properties and extrinsic joint loads. A positive relationship has been reported between ambulatory loads and cartilage thickness in young individuals, but whether this relationship exists in individuals who are older or obese is unknown. This study examined the relationship between femoral cartilage thickness and load, measured by weight × height and the peak adduction moment, in young normal‐weight (28 subjects, age: 28.0 ± 3.8 years, BMI: 21.9 ± 1.9 kg/m2), middle‐aged normal‐weight (27 subjects, 47.0 ± 6.5 years, 22.7 ± 1.7 kg/m2), young overweight/obese (27 subjects, 28.4 ± 3.6 years, 33.3 ± 4.6 kg/m2), and middle‐aged overweight/obese (27 subjects, 45.8 ± 7.2 years, 31.9 ± 4.4 kg/m2) individuals. On the lateral condyle, cartilage thickness was positively correlated with weight × height for all groups (R2 = 0.26–0.20) except the middle‐aged overweight/obese. On the medial condyle, weight × height was significantly correlated only in young normal‐weight subjects (R2 = 0.19), as was the case for the correlation between adduction moment and medial–lateral thickness ratio (R2 = 0.20). These results suggest that aging and obesity are both associated with a loss of the positive relationship between cartilage thickness and ambulatory loads, and that the relationship is dependent on the compartment and whether the load is generated by body size or subject‐specific gait mechanics.

A relationship between mechanically-induced changes in serum cartilage oligomeric matrix protein (COMP) and changes in cartilage thickness after 5 years.

OBJECTIVE To evaluate the hypothesis that a mechanical stimulus (30-min walk) will produce a change in serum concentrations of cartilage oligomeric matrix protein (COMP) that is associated with cartilage thickness changes on magnetic resonance imaging (MRI). METHODS Serum COMP concentrations were measured by enzyme-linked immunosorbent assay in 17 patients (11 females, age: 59.0±9.2 years) with medial compartment knee osteoarthritis (OA) at study entry immediately before, immediately after, 3.5 h, and 5.5 h after a 30-min walking activity. Cartilage thickness changes in the medial femur and medial tibia were determined from MR images taken at study entry and at 5-year follow-up. Relationships between changes in cartilage thickness and COMP levels, with post-activity concentrations expressed as a percentage of pre-activity levels, were assessed by the calculation of Pearson correlation coefficients and by multiple linear regression analysis, with adjustments for age, sex, and body mass index (BMI). RESULTS Changes in COMP levels 3.5 h and 5.5 h post-activity were correlated with changes in cartilage thickness in the medial femur and tibia at the 5-year follow-up. The results were strengthened after analyses were adjusted for age, sex, and BMI. Neither baseline pre-activity COMP levels nor changes in COMP levels immediately post-activity were correlated with cartilage thickness changes. CONCLUSIONS The results of this study support the hypothesis that a change in COMP concentration induced by a mechanical stimulus is associated with cartilage thinning at 5 years. Mechanically-induced changes in mechano-sensitive biomarkers should be further explored in the context of stimulus-response models to improve the ability to assess OA progression.

General scheme to reduce the knee adduction moment by modifying a combination of gait variables

Reducing the knee adduction moment (KAM) is a promising treatment for medial compartment knee osteoarthritis (OA). Although several gait modifications to lower the KAM have been identified, the potential to combine modifications and individual dose‐responses remain unknown. This study hypothesized that: (i) there is a general scheme consisting of modifications in trunk sway, step width, walking speed, and foot progression angle that reduces the KAM; (ii) gait modifications can be combined; and (iii) dose‐responses differ among individuals. Walking trials with simultaneous modifications in step width, walking speed, progression angle, and trunk sway were analyzed for 10 healthy subjects. Wider step width, slower speed, toeing‐in, and increased trunk sway resulted in reduced first KAM peak, whereas wider step width, faster speed, and increased trunk sway reduced the KAM angular impulse. Individual regressions accurately modeled the amplitude of the KAM variables relative to the amplitude of the gait modification variables, while the dose‐responses varied strongly among participants. In conclusion, increasing trunk sway, increasing step width, and toeing‐in are three gait modifications that could be combined to reduce KAM variables related to knee OA. Results also indicated that some gait modifications reducing the KAM induced changes in the knee flexion moment possibly indicative of an increase in knee loading. Taken together with the different dose‐responses among subjects, this study suggested that gait retraining programs should consider this general scheme of modifications with individualization of the modification amplitudes.

A neural network model to predict knee adduction moment during walking based on ground reaction force and anthropometric measurements

The external knee adduction moment (KAM) is a major variable for the evaluation of knee loading during walking, specifically in patients with knee osteoarthritis. However, assessment of the KAM is limited to locations where full motion laboratories are available. The purpose of this study was to develop and test a simple method to predict the KAM using only force plate and anthropometric measurements. Three groups of 28 knees (asymptomatic, mild osteoarthritis, and severe osteoarthritis) were studied. Walking trials were collected at different speeds using a motion capture system and a force plate. The reference KAM was calculated by inverse dynamics. For the prediction, inter-subject artificial neural networks were designed using 11 inputs coming from the ground reaction force and the mechanical axis alignment. The predicted KAM curves were similar to the reference curves with median mean absolute deviation (MAD) of 0.36%BW*Ht and median correlation coefficient of 0.966 over 756 individual trials. When comparing mean group curves, the median MAD was 0.09%BW*Ht and the median correlation coefficient 0.998. The peak values and the angular impulses extracted from the predicted and reference curves were significantly correlated, and the same significant differences were obtained among the three groups when the predicted or when the reference curves were used for 95% of the comparisons. In conclusion, this study demonstrated that a simple method using a generic artificial neural network can predict the KAM curve during walking with a high level of significance and provides a practical option for a broader evaluation of the KAM.

New insight in the relationship between regional patterns of knee cartilage thickness, osteoarthritis disease severity, and gait mechanics.

To test if the relationship between knee kinetics during walking and regional patterns of cartilage thickness is influenced by disease severity we tested the following hypotheses in a cross-sectional study of medial compartment osteoarthritis (OA) subjects: (1) the peak knee flexion (KFM) and adduction moments (KAM) during walking are associated with regional cartilage thickness and medial-to-lateral cartilage thickness ratios, and (2) the associations between knee moments and cartilage thickness data are dependent on disease severity. Seventy individuals with medial compartment knee OA were studied. Gait analysis was used to determine the knee moments and cartilage thickness was measured from magnetic resonance imaging. Multiple linear regression analyses tested for associations between cartilage thickness and knee kinetics. Medial cartilage thickness and medial-to-lateral cartilage thickness ratios were lower in subjects with greater KAM for specific regions of the femoral condyle and tibial plateau with no associations for KFM in patients of all disease severities. When separated by severity, the association between KAM and cartilage thickness was found only in patients with more severe OA, and KFM was significantly associated with cartilage thickness only for the less severe OA subjects for specific tibial plateau regions. The results support the idea that the KAM is larger in patients with more severe disease and the KFM has greater influence early in the disease process, which may lessen as pain increases with disease severity. Each component influences different regions of cartilage. Thus the relative contributions of both KAM and KFM should be considered when evaluating gait mechanics and the influence of any intervention for knee OA.

Adduction moment increases with age in healthy obese individuals

There is a need to understand how obesity and aging interact to cause an increased risk of medial knee osteoarthritis (OA). This study tested whether the knee adduction and flexion moments increase with age in healthy normal‐weight and obese adults, as well as the mechanism of this increase. We analyzed whether ground reaction force magnitude, knee alignment, step width, toe‐out angle, body volume distribution, and limb position (knee position relative to the pelvis center) are associated with the adduction moment and whether these variables also change with age. Ninety‐six healthy volunteers (60 normal‐weight and 36 obese) were tested using marker‐based gait analysis; knee alignment was based on marker positions during quiet standing. Adduction moment increased with age in obese (R2 = 0.19), but not in normal‐weight individuals (R2 = 0.01); knee flexion moment did not change with age in either group. In the obese, only knee alignment and limb position were related to the adduction moment (R2 = 0.19 and 0.51), but only limb position changed with age (R2 = 0.26). The resulting increase in adduction moment suggests greater medial compartment loads, which may combine with elevated levels of inflammation to contribute to the increased risk of medial OA in this population.

Baseline ambulatory knee kinematics are associated with changes in cartilage thickness in osteoarthritic patients over 5 years

Although kinematic alterations during walking have been reported with knee osteoarthritis (OA), there is a paucity of longitudinal data, therefore limiting our understanding of the role of kinematics in OA development. This study tested the hypothesis that less knee extension angle and less posterior displacement of the femur relative to the tibia during the heel-strike portion of the gait cycle are associated with greater loss of medial cartilage thickness during a follow-up period of five years. This study also tested for associations between flexion-extension angle and anterior-posterior displacement during other periods of the gait cycle and 5-year cartilage thinning. 16 subjects with moderate medial knee OA were tested with gait analysis and MRI at baseline and had a follow-up MRI after 5 years. Linear regressions were used to assess the relationship between changes in cartilage thickness and baseline kinematics using Pearson correlation coefficients. Multivariate regressions were also performed to adjust for gender, baseline age, BMI, walking speed, Kellgren/Lawrence grade, and baseline knee pain score. As hypothesized, baseline knee flexion angle and femoral displacement during heel-strike and other gait cycle periods were significantly associated with medial femoral and tibial cartilage thinning at the 5 year follow-up; these associations were strengthened after adjustment for covariates. This study provided new insight into the pathogenesis of knee OA where baseline knee kinematics were associated with longitudinal disease progression. These results could serve as a basis for developing newer gait modification interventions to reduce the risk for developing knee OA.

Gait mechanics 2 years after anterior cruciate ligament reconstruction are associated with longer-term changes in patient-reported outcomes.

This study tested the hypothesis that side‐to‐side differences in knee gait mechanics 2 years after anterior cruciate ligament (ACL) reconstruction are associated with long‐term (∼8 years post‐reconstruction) changes in patient‐reported outcome scores. Sixteen subjects (5 males; age: 29.1 ± 7.1 years) with primary unilateral ACL reconstruction were gait tested at baseline (2.2 ± 0.3 years post‐ACL reconstruction) and filled out KOOS and Lysholm surveys. At long‐term follow‐up (7.7 ± 0.7 years post‐ACL reconstruction), the same subjects completed KOOS and Lysholm surveys. Pearson correlation coefficients assessed relationships between side‐to‐side differences in kinematics and kinetics at baseline and changes in Lysholm and KOOS Pain/QOL scores from 2 to 8 years post‐ACL reconstruction. Significant associations were seen between greater average varus rotation (Lysholm: R = −0.654, p = 0.006) and less anterior femoral displacement (Lysholm: R = 0.578, p = 0.019) during stance of the ACL reconstructed knee versus the contralateral knee at baseline and worse follow‐up outcome scores. Significant associations were seen between greater peak knee flexion moment (KOOS Pain: R = −0.572, p = 0.026; KOOS QOL: R = −0.636, p = 0.011), peak knee adduction moment (Lysholm: R = −0.582, p = 0.018; KOOS Pain: R = −0.742, p = 0.002; KOOS QOL: R = −0.551, p = 0.033), and peak internal rotation moment (Lysholm: R = 0.525, p = 0.037; KOOS Pain: R = 0.815, p < 0.001; KOOS QOL: R = 0.777, p = 0.001) in the ACL reconstructed knee at baseline with worse follow‐up outcomes. The results of this study support the hypotheses that early changes in gait mechanics following ACL reconstruction are associated with longer‐term clinical changes in patient‐reported outcomes, suggesting that biomechanical markers obtained as early as 2 years after ACL reconstruction may be useful to understand clinical outcomes in this population.