Julien Favre

Ambulatory measurement of 3D knee joint angle

Three-dimensional measurement of joint motion is a promising tool for clinical evaluation and therapeutic treatment comparisons. Although many devices exist for joints kinematics assessment, there is a need for a system that could be used in routine practice. Such a system should be accurate, ambulatory, and easy to use. The combination of gyroscopes and accelerometers (i.e., inertial measurement unit) has proven to be suitable for unrestrained measurement of orientation during a short period of time (i.e., few minutes). However, due to their inability to detect horizontal reference, inertial-based systems generally fail to measure differential orientation, a prerequisite for computing the three-dimentional knee joint angle recommended by the Internal Society of Biomechanics (ISB). A simple method based on a leg movement is proposed here to align two inertial measurement units fixed on the thigh and shank segments. Based on the combination of the former alignment and a fusion algorithm, the three-dimensional knee joint angle is measured and compared with a magnetic motion capture system during walking. The proposed system is suitable to measure the absolute knee flexion/extension and abduction/adduction angles with mean (SD) offset errors of -1 degree (1 degree ) and 0 degrees (0.6 degrees ) and mean (SD) root mean square (RMS) errors of 1.5 degrees (0.4 degrees ) and 1.7 degrees (0.5 degrees ). The system is also suitable for the relative measurement of knee internal/external rotation (mean (SD) offset error of 3.4 degrees (2.7 degrees )) with a mean (SD) RMS error of 1.6 degrees (0.5 degrees ). The method described in this paper can be easily adapted in order to measure other joint angular displacements such as elbow or ankle.

Functional calibration procedure for 3D knee joint angle description using inertial sensors

Measurement of three-dimensional (3D) knee joint angle outside a laboratory is of benefit in clinical examination and therapeutic treatment comparison. Although several motion capture devices exist, there is a need for an ambulatory system that could be used in routine practice. Up-to-date, inertial measurement units (IMUs) have proven to be suitable for unconstrained measurement of knee joint differential orientation. Nevertheless, this differential orientation should be converted into three reliable and clinically interpretable angles. Thus, the aim of this study was to propose a new calibration procedure adapted for the joint coordinate system (JCS), which required only IMUs data. The repeatability of the calibration procedure, as well as the errors in the measurement of 3D knee angle during gait in comparison to a reference system were assessed on eight healthy subjects. The new procedure relying on active and passive movements reported a high repeatability of the mean values (offset<1 degrees) and angular patterns (SD<0.3 degrees and CMC>0.9). In comparison to the reference system, this functional procedure showed high precision (SD<2 degrees and CC>0.75) and moderate accuracy (between 4.0 degrees and 8.1 degrees) for the three knee angle. The combination of the inertial-based system with the functional calibration procedure proposed here resulted in a promising tool for the measurement of 3D knee joint angle. Moreover, this method could be adapted to measure other complex joint, such as ankle or elbow.

Three-dimensional knee moments of ACL reconstructed and control subjects during gait, stair ascent, and stair descent

Changes in knee mechanics following anterior cruciate ligament reconstruction (ACLR) have been implicated as a contributor to the development of premature osteoarthritis (OA). However, changes in ambulatory loading in this population have not been well documented. While the magnitude of the external knee moment vector is a major factor in loading at the knee, there is not a comprehensive understanding of the changes in the individual components of the vector following ACL reconstruction. The purpose of this study was to test for differences in the three components of the external knee moment during walking and stair locomotion between ACLR, contralateral and healthy control knees. Forty-five ACLR and 45 healthy control subjects were tested during walking, stair ascent and descent. ACLR knees had a lower first peak adduction moment than contralateral knees during all three activities. Similarly, additional cases of significant differences between ACLR and contralateral knees consisted of lower peak moments for the ACLR than the contralateral knees. These differences were due to both ACLR and contralateral knees as the ACLR knees indicated lower and the contralateral knees greater peak moments compared to healthy control knees. The results suggest a compensatory change involving greater loading in the contralateral knee, perhaps due to lower loading of the ACLR knee. Further, lower knee moments of the ACLR knee suggest that increased joint loading may not be the initiating factor in the development of OA following ACL reconstruction; but rather previous described kinematic or biological changes might initiate the pathway to knee OA.

Functional testing provides unique insights into the pathomechanics of femoroacetabular impingement and an objective basis for evaluating treatment outcome

Femoroacetabular impingement (FAI) has been recognized as a significant clinical problem. While hip reshaping surgery for treating FAI has had positive clinical outcomes, there remains a need for objective functional outcomes of FAI treatment. We tested the hypothesis that during walking and stair climbing significant changes in hip kinematics would occur following hip reshaping surgery that indicate restoration of normal function post‐operatively. Hip and pelvic kinematics were collected for 17 FAI patients pre‐ and 1 year post‐operatively and compared to 17 healthy matched controls. Prior to surgery, FAI patients had significantly reduced hip internal rotation and hip sagittal plane range of motion during walking (p = 0.01, p < 0.001, respectively) and stair climbing (p = 0.01, p < 0.001, respectively) as compared with controls. Post‐operatively, these motions were restored to normal during walking (p = 0.70, p = 0.46, respectively), but remained significantly reduced in the FAI patients during stair climbing (p = 0.03, p < 0.001, respectively). These results have important implications for understanding the functional pathomechanics of FAI and providing an objective basis for evaluating treatment outcome. The stair climbing results indicate that problems still exist in the hip joint for activities requiring higher ranges of hip motion and suggest a basis for exploring future improvements for the treatment of FAI.

The relationship between peak knee extension at heel-strike of walking and the location of thickest femoral cartilage in ACL reconstructed and healthy contralateral knees

Reports that knee cartilage health is sensitive to kinematic changes, combined with reports of extension loss following ACL reconstruction, underscores the importance of restoring ambulatory knee extension in the context of preventing premature osteoarthritis. The purpose of this study was to test the relationship between individual variations in peak knee extension at heel-strike of walking and the anterior-posterior location of thickest cartilage in the medial and lateral femoral condyles of healthy contralateral and ACL reconstructed knees. In vivo gait analysis and knee MR images were collected from 29 subjects approximately 2 years after unilateral ACL reconstruction. Knee extension was measured at heel-strike of walking and 3-D femoral cartilage thickness models were reconstructed from MR images. The ACL reconstructed knees had significantly reduced knee extension (-1.5±4.2°) relative to the contralateral knees (-4.6±3.4°) at heel-strike of walking but did not have side-to-side differences in the anterior-posterior location or magnitude of thickest medial and lateral femoral cartilage. The anterior-posterior location of the thickest medial femoral cartilage was correlated with knee extension at heel-strike in both the healthy contralateral (R(2)=0.356, p<0.001) and reconstructed (R(2)=0.234, p=0.008) knees. These results suggest that ACL reconstruction can impair terminal extension at periods of ambulatory loading known to be related to cartilage morphology in healthy joints. The fact that the femoral cartilage thickness distribution had not changed at 2 years post-op, even in the subset of subjects with extension loss, suggests that loads may be shifted to thinner cartilage regions, which could have important implications on long-term joint health.

Inertial Sensor-Based Feedback Can Reduce Key Risk Metrics for Anterior Cruciate Ligament Injury During Jump Landings

Background: The incidence of anterior cruciate ligament (ACL) injury can be decreased through the use of intervention programs. However, the success of these programs is dependent on access to a skilled trainer who provides feedback; as such, these programs would benefit from a simple device with the capacity to provide high-quality feedback. Hypothesis: Feedback based on kinematic measurements from a simple inertial sensor-based system can be used to modify key ACL injury risk metrics (knee flexion angle, trunk lean, knee abduction moment) during jump landing. Study Design: Controlled laboratory study. Methods: Seventeen subjects (7 male) were tested during drop jump tasks. Their movements were measured simultaneously with inertial, optoelectronic, and force platform systems. Feedback provided to the subjects was based only on measurements from the inertial sensor-based system (knee flexion angle, trunk lean, and thigh coronal velocity). The subjects conducted a baseline session (without landing instructions), then a training session (with immediate feedback), and finally an evaluation session (without feedback). The baseline and evaluation sessions were then tested for changes in the key risk metrics. Results: The subjects increased their knee flexion angle (16.2°) and trunk lean (17.4°) after the training. They also altered their thigh coronal angular velocity by 29.4 deg/s and reduced their knee abduction moment by 0.5 %BW·Ht. There was a significant correlation (R2 = 0.55) between the change in thigh coronal angular velocity and the change in knee abduction moment. Conclusion: Subjects reduced key risk metrics for ACL injury after training with the system, suggesting the potential benefit of instrumented feedback for interventional training. Clinical Relevance: Interventional training for reducing the risk of ACL injury could be improved with a simple device that provides immediate feedback.

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.

Ambulatory assessment of 3D ground reaction force using plantar pressure distribution.

This study aimed to use the plantar pressure insole for estimating the three-dimensional ground reaction force (GRF) as well as the frictional torque (T(F)) during walking. Eleven subjects, six healthy and five patients with ankle disease participated in the study while wearing pressure insoles during several walking trials on a force-plate. The plantar pressure distribution was analyzed and 10 principal components of 24 regional pressure values with the stance time percentage (STP) were considered for GRF and T(F) estimation. Both linear and non-linear approximators were used for estimating the GRF and T(F) based on two learning strategies using intra-subject and inter-subjects data. The RMS error and the correlation coefficient between the approximators and the actual patterns obtained from force-plate were calculated. Our results showed better performance for non-linear approximation especially when the STP was considered as input. The least errors were observed for vertical force (4%) and anterior-posterior force (7.3%), while the medial-lateral force (11.3%) and frictional torque (14.7%) had higher errors. The result obtained for the patients showed higher error; nevertheless, when the data of the same patient were used for learning, the results were improved and in general slight differences with healthy subjects were observed. In conclusion, this study showed that ambulatory pressure insole with data normalization, an optimal choice of inputs and a well-trained nonlinear mapping function can estimate efficiently the three-dimensional ground reaction force and frictional torque in consecutive gait cycle without requiring a force-plate.