Comparison of strain-gage and fiber-optic goniometry for measuring knee kinematics during activities of daily living and exercise

There is increasing interest in wearable sensor technology as a tool for rehabilitation applications in community or home environments. Recent studies have focused on evaluating inertial based sensing (accelerometers, gyroscopes, etc.) that provide only indirect measures of joint motion. Measurement of joint kinematics using flexible goniometry is more direct, and still popular in laboratory environments, but has received little attention as a potential tool for wearable systems. The aim of this study was to compare two goniometric devices: a traditional strain-gauge flexible goniometer, and a fiberoptic flexible goniometer, for measuring dynamic knee flexion/extension angles during activity of daily living: chair rise, and gait; and exercise: deep knee bends, against joint angles computed from a "gold standard" Vicon motion tracking system. Six young adults were recruited to perform the above activities in the lab while wearing a goniometer on each knee, and reflective markers for motion tracking. Kinematic data were collected simultaneously from the goniometers (one on each leg) and the motion tracking system (both legs). The results indicate that both goniometers were within 2-5 degrees of the Vicon angles for gait and chair rise. For some deep knee bend trials, disagreement with Vicon angles exceeded ten degrees for both devices. We conclude that both goniometers can record ADL knee movement faithfully and accurately, but should be carefully considered when high (>120?deg) knee flexion angles are required.     

Gait characteristics of patients with knee osteoarthritis.

The knee kinematics and kinetics of 139 patients (47 males and 92 females) with Grade II knee osteoarthritis (OA) were measured during level walking, stair ascent and stair descent. There was no significant difference in knee motion between the patients and normal subjects. The patients with knee OA had a significantly reduced internal knee extensor moment compared to normal subjects. This difference reflects the patient's compensation to reduce the knee joint loading. Further, subjects with OA and a higher body mass index have a lower knee extensor moment. The female subjects had significantly greater knee flexion and a greater knee extensor moment. This gender difference may partially explain the increased prevalence of OA in females. Most tests of OA treatments are assessed by criteria that do not reflect functional activities. This study demonstrates that objective gait analysis can be used to document gait adaptations used by patients with knee OA.     

1998 Basmajian Student Award Paper: Movement patterns after anterior cruciate ligament injury: a comparison of patients who compensate well for the injury and those who require operative stabilization

The purpose of this study was to describe kinematic and kinetic differences between a group of ACL deficient subjects who were grouped according to functional ability. Sixteen patients with complete ACL rupture were studied; eight subjects had instability with activities of daily living (non-copers) and eight subjects had returned to all pre-injury activity without limitation (copers). Three-dimensional joint kinematics and kinetics were collected from the knee and ankle during walking, jogging and going up and over a step. Results showed that both groups mitigated the force with which they contacted the floor but non-copers consistently demonstrated less knee flexion in the involved limb. The copers used joint kinematics similar to those of their uninvolved knees and similar to knee motions reported in uninjured subjects. The reduced knee motion in the involved knee of the non-copers did not correlate directly with quadriceps femoris muscle weakness.

The data suggest that the non-copers utilize a stabilization strategy which stiffens the knee joint which not only is unsuccessful but may lead to excessive joint contact forces which have the potential to damage articular structures. The copers use a strategy which permits normal knee kinematics and bodes well for joint integrity.     

Effects of soft tissue artifacts on the calculated kinematics and kinetics of the knee during stair-ascent

Biomechanics of the knee during stair-ascent has mostly been studied using skin-marker-based motion analysis techniques, but no study has reported a complete assessment of the soft tissue artifacts (STA) and their effects on the calculated joint center translation, angles and moments at the knee in normal subjects during this activity. This study aimed to bridge the gap. Twelve young adults walked up a three-step stair while data were acquired simultaneously from a three-dimensional motion capture system, a force plate and a dynamic fluoroscopy system. The "gold standards" of poses of the knee were obtained using a 3D fluoroscopy method. The STA of the markers on the thigh and shank were then calculated, together with their effects on the calculated joint center translations, angles and moments at the knee. The STA of the thigh markers were greater than those on the shank, leading to significantly underestimated flexion and extensor moments, but overestimated joint center translations during the first half of the stance phase. The results will be useful for a better understanding of the normal biomechanics of the knee during stair-ascent, as a baseline for future clinical applications and for developing a compensation method to correct for the effects of STA.     

The effects of femoral graft placement on cartilage thickness after anterior cruciate ligament reconstruction

Altered joint motion has been thought to be a contributing factor in the long-term development of osteoarthritis after ACL reconstruction. While many studies have quantified knee kinematics after ACL injury and reconstruction, there is limited in vivo data characterizing the effects of altered knee motion on cartilage thickness distributions. Thus, the objective of this study was to compare cartilage thickness distributions in two groups of patients with ACL reconstruction: one group in which subjects received a non-anatomic reconstruction that resulted in abnormal joint motion and another group in which subjects received an anatomically placed graft that more closely restored normal knee motion. Ten patients with anatomic graft placement (mean follow-up: 20 months) and 12 patients with non-anatomic graft placement (mean follow-up: 18 months) were scanned using high-resolution MR imaging. These images were used to generate 3D mesh models of both knees of each patient. The operative and contralateral knee models were registered to each other and a grid sampling system was used to make site-specific comparisons of cartilage thickness. Patients in the non-anatomic graft placement group demonstrated a significant decrease in cartilage thickness along the medial intercondylar notch in the operative knee relative to the intact knee (8%). In the anatomic graft placement group, no significant changes were observed. These findings suggest that restoring normal knee motion after ACL injury may help to slow the progression of degeneration. Therefore, graft placement may have important implications on the development of osteoarthritis after ACL reconstruction.     

Measuring clinically relevant knee motion with a self-calibrated wearable sensor

Low-cost sensors provide a unique opportunity to continuously monitor patient progress during rehabilitation; however, these sensors have yet to demonstrate the fidelity and lack the calibration paradigms necessary to be viable tools for clinical research. The purpose of this study was to validate a low-cost wearable sensor that accurately measured peak knee extension during clinical exercises and needed no additional equipment for calibration. Sagittal plane knee motion was quantified using a 9-axis motion sensor and directly compared to motion capture data. The motion sensor measured the field strength of a strong earth magnet secured to the distal femur, which was correlated with knee angle during a simple calibration process. Peak knee motions and kinematic patterns were compared with motion capture data using paired t-tests and cross correlation, respectively. Peak extension values during seated knee extensions were accurate within 5 degrees across all subjects (root mean square error: 2.6 degrees, P = 0.29). Knee flexion during gait strongly correlated (0.84 ≤ r_xy ≤ 0.99) with motion capture measurements but demonstrated peak flexion errors of 10 degrees. In this study, we present a low-cost sensor (≈$ 35 US) that accurately determines knee extension angle following a calibration procedure that did not require any other equipment. Our findings demonstrate that this sensor paradigm is a feasible tool to monitor patient progress throughout physical therapy. However, dynamic motions that are associated with soft-tissue artifact may limit the accuracy of this type of wearable sensor.     

Dynamic Frequency Analyses of Lower Extremity Muscles during Sit-To-Stand Motion for the Patients with Knee Osteoarthritis

Objective

Muscle activities during the sit-to-stand motion (STS) are characterized by coordinated movements between hip extensors and knee extensors. However, previous reports regarding the STS and lower extremity muscle activities have focused on some quantitative assessment, but little qualitative research. This study aimed to examine the muscle activities of the lower extremity both quantitatively and qualitatively.

Methods

Study participants included 13 patients with knee osteoarthritis (knee OA) and 11 age-matched asymptomatic controls. The task was STS from a chair with a height-adjustable seat. EMG activities were acquired using surface electromyogram. The root mean square signals normalized as a percentage of maximum voluntary isometric contraction values (RMS%MVC) and the mean power frequency (MPF) were calculated.

Results

During STS, knee OA patients had increased RMS%MVC of the vastus medialis and raised MPF of the rectus femoris before buttocks-off.

Conclusion

These findings suggest that STS of knee OA patients not only increased relative muscle activity of the vastus medialis, but also enlisted the rectus femoris in knee extension to improve muscle contraction force by activating more type II fibers to accomplish buttocks-off.     

Correlation of compartment pressure data from an intraoperative sensing device with postoperative fluoroscopic kinematic results in TKA patients

Fluoroscopy has recently been used to analyze postoperative kinematics in total knee arthroplasty (TKA). These analyses have reported varying results even in patients with similar implant design. In addition, patterns of wear in retrieved tibial polyethylene inserts of similar design have been found to vary substantially. These findings suggest that surgical technique, especially soft tissue balancing, may play a role in postoperative kinematics and implant failure. Accurate soft-tissue balancing is hypothesized to result in similar pressures within the medial and lateral compartments of the knee. However, a method of easily measuring these pressures at TKA has not been developed. In the present study, 32 patients were implanted with a mobile-bearing LCS TKA utilizing the balanced gap technique. An electronic pressure sensor, developed specifically to record pressure magnitude and distribution in the medial and lateral compartments, was incorporated into the implant trials. The knee was then passively taken through a range of motion while pressure data was recorded via computer. Postoperatively, 16 patients underwent active fluoroscopic kinematic analysis to assess for condylar liftoff and femorotibial translation. We found that abnormal compartment pressures and distributions as recorded by the intraoperative pressure sensor were correlated with inappropriate or paradoxical postoperative kinematics. In addition, subjects having similar pressures in both compartments throughout a range of motion did not experience condylar liftoff values greater than 1.0 mm. These data suggest that surgical technique influences the magnitude and distribution of forces at the articulation, postoperative kinematics, and likely, implant longevity.     

Lower extremity coupling parameters during locomotion and landings

During ballistic locomotion and landing activities, the lower extremity joints must function synchronously to dissipate the impact. The coupling of subtalar motion to tibial and knee rotation has been hypothesized to depend on the dynamic requirements of the task. This study was undertaken to look for differences in the coupling of 3-D foot and knee motions during walking, jogging, and landing from a jump. Twenty recreationally active young women with normal foot alignment (as assessed by a licensed physical therapist) were videotaped with high-speed cameras (250 Hz) during walking, jogging, hopping, and jumping trials. Coupling coefficients were compared among the four activities. The ratio of eversion to tibial rotation increased from the locomotion to the landing trials, indicating that with the increased loading demands of the activity, the requirements of foot motion increased. However, this increased motion was not proportionately translated into rotation of the tibia through the subtalar joint. Furthermore, the ratio of knee flexion to knee internal rotation increased significantly from the walking to landing trials. Together these findings suggest that femoral rotation may compensate for the increase in tibial rotation as the force-dissipating demands of the task increase. The relative unbalance among the magnitude of foot, tibial, and knee rotations observed with increasing task demands may have direct implications on clinical treatments aimed at reducing knee motion via controlling motion at the foot during landing tasks.     

Kinematic evaluation of cruciate-retaining total knee replacement patients during level walking: A comparison with the displacement-controlled ISO standard

Differences between wear-scar features of simulator-tested and retrieved tibial total knee replacement (TKR) liners have been reported. This disagreement may result from differences between in vivo kinematic profiles and those defined by the International Organization for Standardization (ISO). The purpose of this study was to determine the knee kinematics of a TKR subject group during level walking and compare them with the motion profiles defined by the ISO standard for a displacement-controlled knee wear testing simulator. Twenty-nine patients with a posterior cruciate ligament-retaining TKR design were gait tested using the point cluster technique to obtain flexion–extension (FE) rotation, anterior–posterior (AP) translation and internal–external (IE) rotation knee motions during a complete cycle of level walking. Relative ranges of motion and timing of key points within the in vivo motion data were compared against the same ranges and same key points from the input profiles of the displacement-controlled wear testing standard ISO14243-3. The subjects exhibited a FE pattern similar to ISO, with an insignificant difference in range of FE rotation from midstance to terminal stance. However, the subjects had a significantly higher range of knee flexion from terminal stance into swing. The subjects also exhibited a phase delay for the entire gait cycle. For AP translation, the standard profile had statistically significant lower magnitudes than seen in vivo. Opposite pattern of AP motion was also apparent from midstance and swing. Similarly, ISO specified a smaller IE total range of rotation with a motion pattern in complete opposition to that seen in vivo. In conclusion, significant differences were found in both the magnitudes and pattern of in vivo motion compared with ISO.     

Standardized Loads Acting in Knee Implants

The loads acting in knee joints must be known for improving joint replacement, surgical procedures, physiotherapy, biomechanical computer simulations, and to advise patients with osteoarthritis or fractures about what activities to avoid. Such data would also allow verification of test standards for knee implants. This work analyzes data from 8 subjects with instrumented knee implants, which allowed measuring the contact forces and moments acting in the joint. The implants were powered inductively and the loads transmitted at radio frequency. The time courses of forces and moments during walking, stair climbing, and 6 more activities were averaged for subjects with I) average body weight and average load levels and II) high body weight and high load levels. During all investigated activities except jogging, the high force levels reached 3,372–4,218N. During slow jogging, they were up to 5,165N. The peak torque around the implant stem during walking was 10.5 Nm, which was higher than during all other activities including jogging. The transverse forces and the moments varied greatly between the subjects, especially during non-cyclic activities. The high load levels measured were mostly above those defined in the wear test ISO 14243. The loads defined in the ISO test standard should be adapted to the levels reported here. The new data will allow realistic investigations and improvements of joint replacement, surgical procedures for tendon repair, treatment of fractures, and others. Computer models of the load conditions in the lower extremities will become more realistic if the new data is used as a gold standard. However, due to the extreme individual variations of some load components, even the reported average load profiles can most likely not explain every failure of an implant or a surgical procedure.     

Image based weighted center of proximity versus directly measured knee contact location during simulated gait

To understand the mechanical consequences of knee injury requires a detailed analysis of the effect of that injury on joint contact mechanics during activities of daily living. Three-dimensional (3D) knee joint geometric models have been combined with knee joint kinematics to dynamically estimate the location of joint contact during physiological activities—using a weighted center of proximity (WCoP) method. However, the relationship between the estimated WCoP and the actual location of contact has not been defined. The objective of this study was to assess the relationship between knee joint contact location as estimated using the image-based WCoP method, and a directly measured weighted center of contact (WCoC) method during simulated walking. To achieve this goal, we created knee specific models of six human cadaveric knees from magnetic resonance imaging. All knees were then subjected to physiological loads on a knee simulator intended to mimic gait. Knee joint motion was captured using a motion capture system. Knee joint contact stresses were synchronously recorded using a thin electronic sensor throughout gait, and used to compute WCoC for the medial and lateral plateaus of each knee. WCoP was calculated by combining knee kinematics with the MRI-based knee specific model. Both metrics were compared throughout gait using linear regression. The anteroposterior (AP) location of WCoP was significantly correlated with that of WCoC on both tibial plateaus in all specimens (p<0.01, 95% confidence interval of Pearson?s coefficient r>0), but the correlation was not significant in the mediolateral (ML) direction for 4/6 knees (p>0.05). Our study demonstrates that while the location of joint contact obtained from 3D knee joint contact model, using the WCoP method, is significantly correlated with the location of actual contact stresses in the AP direction, that relationship is less certain in the ML direction.     

Kinematic motion of the anterior cruciate ligament deficient knee during functionally high and low demanding tasks

The purpose of this study was to determine whether mechanical adaptations were present in patients with anterior cruciate ligament (ACL)-deficient knees during high-demand activities. Twenty-two subjects with unilateral ACL deficiency (11 males and 11 females, 19.6 months after injury) performed five different activities at a comfortable speed (level walking, ascending and descending steps, jogging, jogging to a 90-degree side cutting toward the opposite direction of the tested side). Three-dimensional knee kinematics for the ACL-deficient knees and uninjured contralateral knees were evaluated using the Point Cluster Technique. There was no significant difference in knee flexion angle, but an offset toward the knee in less valgus and more external tibial rotation was observed in the ACL-deficient knee. The tendency was more obvious in high demand motions, and a significant difference was clearly observed in the side cutting motions. These motion patterns, with the knee in less valgus and more external tibial rotation, are proposed to be an adaptive movement to avoid pivot shift dynamically, and reveal evidence in support of a dynamic adaptive motion occurring in ACL-deficient knees.     

The chronopathology of breast pre-cancer

Breast temperatures have been measured by the automated instrumentation called the 'Chronobra' for 16 progesterone cycles in women at normal risk for breast cancer and for 15 cycles in women at high risk for breast cancer. Circatrigintan and circaseptan rhythm parameters have been examined by the single and population mean cosinor technique. In the first analysis there was strong evidence for a loss of the 28-day rhythm and its replacement by a 7-day rhythm (? frequency multiplication). In the more rigorous population mean cosinor method the presence of a phase and frequency synchronized rhythm with a period at or close to 28 days was sustained in the normal-risk subjects and it was confirmed that this rhythm is absent in the high-risk subjects. At tau = 7 days there was no rhythm detected in the normal-risk subjects and only a weak effect (p = 0.07) in the high-risk subjects. In other words, the circaseptan expression was detected in the high-risk breasts but then not in every case. The MESOR of the high-risk cases was highly significantly warmer than in the controls.     

Knee mechanics: a review of past and present techniques to determine in vivo loads

This review article evaluates various techniques that have been used to determine in vivo loads in the human knee. Two main techniques that have been used are telemetry, which is an experimental approach, and mathematical modeling, which is a theoretical approach. Telemetric analyses have previously been used to determine the in vivo loading of the human hip and more recently evaluated in the determination of in vivo knee loads. Mathematical modeling approaches can be categorized two ways; those that use optimization techniques to solve an indeterminate system and those that utilize a reduction method that minimizes the number of unknowns, keeping the system solvable as the number of equations of motion are equal to the number of unknown quantities. More recently, we have developed an approach that relies fully on the use of in vivo data from fluoroscopy, CT scanning, magnetic resonant imaging and a revised motion analysis technique that involves only two markers on each rigid body. A review of all techniques revealed a wide range of forces at the human knee, ranging from 1.9 to 7.2 times body weight during level walking.     

Can a finite set of knee extension in supine position be used for a knee functional examination?

The kinematic magnetic resonance imaging technique has been developed to provide a functional examination of the knee. Technical limitations require this examination to be performed in supine position, and the knee motion is represented by an assembly of static positions at different knee angles. However, the main knee function is to support the body weight and perform continuous motion, e.g. parallel squat. Our study quantified the knee kinematics of 20 healthy subjects in different motion conditions (finite and continuous) and in different mechanical conditions (continuous unloaded and continuous loaded). We evaluated the angular and localisation difference of a finite helical axis of the knee motion for parallel squat, continuous knee extension in supine position and the finite set of knee extension in supine position. We found large inter-individual dispersion. The majority of subjects had equivalent knee kinematics between continuous knee extension and the finite set of knee extension in supine position, but not between continuous knee extension in supine position and the parallel squat. Therefore, results from a functional examination of a finite set of knee extensions in supine position do not represent the knee motion in a parallel squat. Our results suggest that functional examination of the knee from magnetic resonance imaging do not necessarily reflect the physiological kinematics of the knee. Further investigation should focus on a new magnetic resonance imaging acquisition protocol that allows image acquisition during weight bearing or includes a special device which reproduces the loaded condition.     

Estimation of muscle response using three-dimensional musculoskeletal models before impact situation: a simulation study

When car crash experiments are performed using cadavers or dummies, the active muscles' reaction on crash situations cannot be observed. The aim of this study is to estimate muscles' response of the major muscle groups using three-dimensional musculoskeletal model by dynamic simulations of low-speed sled-impact. The three-dimensional musculoskeletal models of eight subjects were developed, including 241 degrees of freedom and 86 muscles. The muscle parameters considering limb lengths and the force-generating properties of the muscles were redefined by optimization to fit for each subject. Kinematic data and external forces measured by motion tracking system and dynamometer were then input as boundary conditions. Through a least-squares optimization algorithm, active muscles' responses were calculated during inverse dynamic analysis tracking the motion of each subject. Electromyography for major muscles at elbow, knee, and ankle joints was measured to validate each model. For low-speed sled-impact crash, experiment and simulation with optimized and unoptimized muscle parameters were performed at 9.4 m/h and 10 m/h and muscle activities were compared among them. The muscle activities with optimized parameters were closer to experimental measurements than the results without optimization. In addition, the extensor muscle activities at knee, ankle, and elbow joint were found considerably at impact time, unlike previous studies using cadaver or dummies. This study demonstrated the need to optimize the muscle parameters to predict impact situation correctly in computational studies using musculoskeletal models. And to improve accuracy of analysis for car crash injury using humanlike dummies, muscle reflex function, major extensor muscles' response at elbow, knee, and ankle joints, should be considered.     

Identification of ankle sprain motion from common sporting activities by dorsal foot kinematics data

This study presented a method to identify ankle sprain motion from common sporting activities by dorsal foot kinematics data. Six male subjects performed 300 simulated supination sprain trials and 300 non-sprain trials in a laboratory. Eight motion sensors were attached to the right dorsal foot to collect three-dimensional linear acceleration and angular velocity kinematics data, which were used to train up a support vector machine (SVM) model for the identification purpose. Results suggested that the best identification method required only one motion sensor located at the medial calcaneus, and the method was verified on another group of six subjects performing 300 simulated supination sprain trials and 300 non-sprain trials. The accuracy of this method was 91.3%, and the method could help developing a mobile motion sensor system for ankle sprain detection.     

A standard operating procedure for assessing liquid handler performance in high-throughput screening

The thrust of early drug discovery in recent years has been toward the configuration of homogeneous miniaturized assays. This has allowed organizations to contain costs in the face of exponential increases in the number of screening assays that need to be run to remain competitive. Miniaturization brings with it an increasing dependence on instrumentation, which over the past several years has seen the development of nanodispensing capability and sophisticated detection strategies. To maintain confidence in the data generated from miniaturized assays, it is critical to ensure that both compounds and reagents have been delivered as expected to the target wells. The authors have developed a standard operating procedure for liquid-handling quality control that has enabled them to evaluate performance on 2 levels. The first level provides for routine daily testing on existing instrumentation, and the second allows for more rigorous testing of new dispensing technologies. The procedure has shown itself to be useful in identifying both method programming and instrumentation performance shortcomings and has provided a means to harmonizing instrumentation usage by assay development and screening groups. The goal is that this type of procedure be used for facilitating the exchange of liquid handler performance data across the industry.