Forces in the knee joint whilst rising from a seated position

Transition from sitting to standing after trans-femoral amputation

Standing up is an important and common daily activity. It is essential for independence and a prerequisite for walking. Many elderly and many subjects with impairments have problems with transition from sitting to standing. The aim of the present study was to determine whether there was any difference between the characteristics of standing up in trans-femoral amputees and healthy subjects. Five young trans-femoral amputees and five healthy subjects were included in the study. They were asked to stand up. The body motion was recorded using an Optotrak contactless optical system. The force and moment vectors exerted on the seat were recorded by a JR3 six-axis robot wrist sensor. The force under the feet was recorded by two AMTI force plates. The trans-femoral amputees were found to stand up more slowly than the healthy subjects. The angles of the hip, knee, and ankle joints on the amputated side were different from the angles on the healthy side or in the healthy subjects. There was also a great difference in loading between the healthy and the prosthetic foot. It can be concluded that there are differences in standing up between the trans-femoral amputees and the healthy subjects. These differences may indicate a reason for problems many elderly trans-femoral amputees face when standing up.

An implantable telemetry device to measure intra-articular tibial forces

Tibial forces are important because they determine polyethylene wear, stress distribution in the implant, and stress transfer to underlying bone. Theoretic estimates of tibiofemoral forces have varied between three and six times the body weight depending on the mathematical models used and the type of activity analyzed. An implantable telemetry system was therefore developed to directly measure tibiofemoral compressive forces. This system was tested in a cadaver knee in a dynamic knee rig. A total knee tibial arthroplasty prosthesis was instrumented with four force transducers located at the four corners of the tibial tray. These transducers measured the total compressive forces on the tibial tray and the location of the center of pressure. A microprocessor performed analog-to-digital signal conversion and performed pulse code modulation of a surface acoustic wave radio frequency oscillator. This signal was then transmitted through a single pin hermetic feed-through tantalum wire antenna located at the tip of the stem. The radio frequency signal was received by an external antenna connected to a receiver and to a computer for data acquisition. The prosthesis was powered by external coil induction. The tibial transducer accurately measured both the magnitude and the location of precisely applied external loads. Successful transmission of the radio frequency signal up to a range of 3m was achieved through cadaveric bone, bone cement, and soft tissue. Reasonable accuracy was obtained in measuring loads applied through a polyethylene insert. The implant was also able to detect unicondylar loading with liftoff.

Influence of the relative difference in chair seat height according to different lower thigh length on floor reaction force and lower-limb strength during sit-to-stand movement

Chair-seat height affects the burden on the lower-limbs during sit-to-stand (STS) movement. Previous studies used the same height chair, attaching importance to practicability, but the difference in each subject's lower thigh length may relate to the burden on the lower-limbs. This study aimed to examine the influence of different lower thigh lengths on floor reaction force and lower-limb strength during an STS movement. Thirty young-adult male subjects participated in this study (age: 22.7+/-2.6 yr, height: 172.8+/-4.8 cm, body-mass: 66.3+/-5.2 kg). The subjects were divided into three groups (G1>42 cm, 42 cm > or =G2 > or =38 cm, 38 cm >G3) based on lower thigh length (G1: 44.1+/-2.5 cm, G2: 39.8+/-1.3 cm, G3: 34.3+/-2.1 cm). Namely, G1 was characterized by lower thigh length longer than 105% of 40 cm, G2 by 95-105% of lower thigh length and G3 by lower thigh length less than 95% of 40 cm, respectively. Subjects performed an STS movement twice from chairs at 40 cm-height and height adjusted by the lower thigh length of each subject. Vertical floor reaction force and electromyogram (EMG) on the rectus femoris and tibialis anterior muscles during an STS movement were measured to evaluate the force of knocking over and the burden on the lower-limbs. Fifteen parameters regarding floor reaction force (10) and EMG (5) were selected for analyses. Significant differences were found in floor reaction force at hip-syneresis (F1) and the impulse between hip-syneresis and appearance of the peak floor reaction force (F2). G1 was greater than G2 for the former, and G3 for the latter. Significant differences were found in active muscle mass of the tibialis anterior from the beginning of an STS movement to hip-syneresis (TE1) and peak active muscle level of the tibialis anterior (TE6). G1 was greater than G2 for the former, and G2 and G3 for the latter. It was suggested that when an STS movement is performed using a chair with the same height for each subject, the load imposed on the subject's leg at the time of an STS movement and the STS movement achievement strategy differed since chair seat height changes relatively by the difference in lower thigh length. Moreover, it is thought that the difference in these load conditions and movement strategies occurs when the chair seat height of a subject's lower thigh length is longer than 110%. When conducting the ability to achieve STS movement rating test, chair seat height considering each subject's lower thigh length may be needed.

The effect of tibial insert design on rising from a chair; motion analysis after total knee replacement

BACKGROUND

There are few previous studies of sit-to-stand movement following total knee arthroplasty. Aim of the study was to test the hypotheses that total knee replacement alters the maximum trunk, hip, knee and ankle flexion-extension movements during chair rising, and that the design of the tibial plateau has small influence on the kinematics.

METHODS

A motion analysis system was used to evaluate kinematics of the trunk, hip, knee and ankle when rising from one chair and sitting down on another. Patients with 5 degrees varus/valgus alignment or less received either a flat or a concave tibial insert with retention of the posterior cruciate ligament. Patients who had more malalignment and /or extension defect of 10 degrees or more were randomized to receive the concave or a posterior-stabilized tibial component with resection of the posterior cruciate ligament. The two groups of patients operated with and without resection of the posterior cruciate ligament were analysed separately and compared with a control group. 28 patients (29 knees) and 16 controls were in the final analysis.

FINDINGS

Decreased hip and knee extension compared to the controls was seen, but there were no statistically significant differences in kinematics between the designs.

INTERPRETATION

Choice of implant design in total knee arthroplasty had no detectable effects on kinematics of hip and knee joints during sit-to-stand movement.

A method for measuring vertical forces applied to the upper limb during sit-to-stand

The aim of this study was to develop a basic measurement system to estimate the vertical loading of the upper limb during the sit-to-stand activity, with a view to increasing the understanding of the loading of the wrist in daily living activities. A chair was adapted and instrumented with strain gauges and position sensors so that the force applied through the upper limbs to the arms of the chair could be calculated. Four aspects of the chair's geometry could be varied. A force plate was positioned on the floor between the legs of the chair to record the corresponding foot loading. Twenty normal subjects (22-56 years, mean 32.7 years) participated in a pilot study in which loading through the upper and lower limbs was recorded for a range of chair geometries. The vertical force transmitted through each upper limb was typically 20-30 per cent of bodyweight. The vertical upper limb load averaged across all subjects showed a small reduction when either the seat height or the height of the chair arms was increased.

Femoral loads during passive, active, and active-resistive stance after spinal cord injury: a mathematical model

OBJECTIVE

The purpose of this study was to estimate the loading environment for the distal femur during a novel standing exercise paradigm for people with spinal cord injury.

DESIGN

A mathematical model based on experimentally derived parameters.

BACKGROUND

Musculoskeletal deterioration is common after spinal cord injury, often resulting in osteoporotic bone and increased risk of lower extremity fracture. Potential mechanical treatments have yet to be shown to be efficacious; however, no previous attempts have been made to quantify the lower extremity loading during passive, active, and active-resistive stance.

METHODS

A static, 2-D model was developed to estimate the external forces; the activated quadriceps forces; and the overall bone compression and shear forces in the distal femur during passive (total support of frame), active (quadriceps activated minimally), and active-resistive (quadriceps activated against a resistance) stance.

RESULTS

Passive, active, and active-resistive stance resulted in maximal distal femur compression estimates of approximately 45%, approximately 75%, and approximately 240% of body weight, respectively. Quadriceps force estimates peaked at 190% of body weight with active-resistive stance. The distal femur shear force estimates never exceeded 24% of body weight with any form of stance.

CONCLUSIONS

These results support our hypothesis that active-resistive stance induces the highest lower extremity loads of the three stance paradigms, while keeping shear to a minimum.

RELEVANCE

This model allows clinicians to better understand the lower extremity forces resulting from passive, active, and active-resistive stance in individuals with spinal cord injury.

Trunk movement in Parkinson's disease during rising from seated position

Parkinson's disease (PD) is associated with particular difficulties rising from a seated position. Little is known about the mechanisms of sit-to-stand in this condition. We sought to define trunk movement during sit-to-stand in a group of patients with PD. Six patients and seven normal volunteers were studied using a six camera ELITE motion analysis system (BTS, Milan, Italy), which permitted data collection in the coronal, sagittal, and transverse planes. Retroreflective markers were positioned along the spine at C7, T3, T6, T9, T12, L3, and the sacrum. Whole-trunk kinematics and the movement at the six different trunk markers were recorded during rising. PD patients have a significantly greater degree of trunk flexion than controls, showing a significant increase in angular velocity of the trunk in the sagittal plane. The total range of movement of trunk rotation was significantly smaller in the PD group, but lateral movement in the trunk was greater than normal. These data suggest that patients with early PD compensate for their difficulties rising from a chair by generating greater trunk flexion at higher angular velocity, thus developing greater forward momentum. This process results in a decrease in the duration of the unstable transitional phase of sit-to-stand, allowing PD patients to reach the upright position as easily and safely as possible. Small rotational movements are an effective way to maintain the centre of mass within the base of support during sit-to-stand. This mechanism appears to be denied to the PD patients who may use increased movements in the coronal plane as an alternative strategy.

Relationship between knee extension force and stand-up performance in community-dwelling elderly women

OBJECTIVE

To describe the relationship between knee extension force and stand-up performance.

DESIGN

Prospective, cross-sectional, descriptive, and correlational.

SETTING

Community.

PARTICIPANTS

Fifty-five community-dwelling women 60 or more years old.

INTERVENTIONS

Information pertaining to stand-up performance was gathered via structured questions. The time to complete 1 sit-to-stand from a bench of known height (16in) was obtained in conjunction with subjects' ratings of perceived exertion (RPEs) relative to the task. Bilateral lower extremity knee extension strength was measured with a hand-held dynamometer and normalized against body weight.

MAIN OUTCOME MEASURES

Total knee extension forces (raw and body-weight normalized values) generated by each subject were correlated with 3 measures of stand-up performance.

RESULTS

Low to moderate correlations (r = -.323 to -.526) were found between knee extension forces and the stand-up performance measures of bench stand time and stand-up difficulties. Normalized knee extension force had a higher correlation than raw knee extension force with stand-up difficulties and RPE. Correlations were higher when the curvilinear nature of the relationship was taken into account. The highest correlation was between normalized knee extension force and the RPE associated with the bench stand task (r = -.767).

CONCLUSION

Knee extension force offers an important but incomplete explanation of stand-up performance from low surfaces by elderly women. Interventions leading to increased knee extension force may improve stand-up performance.

Quadriceps moment arm and quadriceps forces after total knee arthroplasty

Knee prosthetic designs that increase quadriceps moment arm can reduce quadriceps tension and patellofemoral compressive forces. Six knees from cadavers were tested on the Oxford knee rig, which simulates closed chain knee extension under load. Three conditions were tested sequentially for each knee: Normal, Control (implanted with the Osteonics 7000 knee design), and Scorpio (implanted with the Osteonics Scorpio design). The center of flexion-extension of the Scorpio design was 10 mm posterior to that of Control that served to lengthen the quadriceps moment arm. An electromagnetic tracking system measured dynamic knee kinematics, and a uniaxial load cell measured quadriceps tension. The Scorpio design reduced quadriceps tension when compared with the Normal or Control knee ranging from 5% to 20%. This was statistically significant at flexion angles greater than 50 degrees. In three knees, the patellar component was instrumented with a triaxial load cell that measured patellofemoral forces. Patellofemoral forces were lower with the Scorpio design compared with the Control. Increasing quadriceps lever arm reduces quadriceps forces and can facilitate activities of daily living and enhance patient rehabilitation. Reduced quadriceps forces may result in reduced patellofemoral forces that can have a beneficial effect on anterior knee pain, patellar component wear, and loosening.

Sit-to-stand at different periods of pregnancy

OBJECTIVE

This study was performed to determine the biomechanics of chair rising by pregnant women.

DESIGN

Relative body joint position and ground reaction forces were measured by a motion analysis system and one force plate.

BACKGROUND

Physiological and psychological changes during pregnancy impose postural demands and limit the performance of daily living activities such as rising from sitting to standing position.

METHODS

Twenty-four pregnant women, divided into three groups, were studied performing sit-to-stand transition from an armless and adjustable chair. By kinematic and kinetic analysis, the angles and moments of hip, knee and ankle joints were investigated.

RESULTS

The chair height has great influence on knee joint and hip joint moments, but less on ankle joints. In the third trimester for all chair heights, because of a marked increase in abdominal depth, the maximum hip moment is significantly less than that in first trimester, while the maximum knee moment is significantly larger. Pregnant women in third trimester produced larger knee moment during sit-to-stand transition from lower chair height.

CONCLUSIONS

The mechanism of sit-to-stand is affected by the physical changes of pregnant women at different periods of pregnancy, e.g. increased loading of knee joint and decreased hip joint moment, especially in the last trimester period of pregnancy.

Biomechanical analysis of effects of foot placement with varying chair height on the motion of standing up

Individual experience reveals that posterior foot placement enables one to stand up easily from a chair. However, the way in which foot placement affects this motion has not been investigated in detail. This study was performed to examine the effects of foot placement in the initial stage of the dynamics of standing up from a chair. Subjects wearing light-emitting diode markers and surface electrodes stood up from a chair over force plates, and ground reaction force, joint angle, and muscle activity were measured. The motions required to stand up from chairs 30, 40, or 50 cm in height were analyzed with anterior, vertical, and posterior foot placement. With anterior foot placement, the forward-acceleration components of the ground reaction force were recorded with simultaneous and long-sustained activity of the muscles in order to shift the center of gravity of the body forward even more after lift-off. Our findings indicate that the distance between the center of gravity and the point of application of ground reaction force at lift-off are critical factors in the standing-up motion, and that chairs should be of adequate height as well as having sufficient space under the seat to permit the backward movement of the lower legs.

Sit-to-stand movement analysis in obese subjects

OBJECTIVES

The aim of this study was to evaluate the typical strategies of obese subjects during a sit-to-stand task (a typical daily living activity) and to assess the load conditions of hip, knee and ankle joints.

DESIGN

Cross-sectional, controlled (obese patients vs controls) study on sit-to-stand movement analysis

SUBJECTS

Ten adult young volunteers (five men and five women, mean age 28, s.d. 3 y; mean BMI 22, s.d. 2.3 kg/m2) and 30 obese subjects 25 women and five men, mean age 39.4, s.d. 13.7 y, mean BMI 40, s.d. 5.9 kg/m2) suffering from chronic lower back pain were analyzed in a sit-to-stand task (10 trials for each subject).

MEASUREMENTS

Angle parameters carried out from a quantitative three-dimensional analysis of sit-to-stand (STS) movement, using an optoelectronic system.

RESULTS

STS task in controls was characterized by a fully forward bending strategy of the trunk, while in obese patients at the beginning (first trial) of the STS task they limited the forward bending in order to protect the vertebral column. When fatigue increased during the execution of multiple STS tasks, the protection of the vertebral column was secondary to the execution of the task. In order to limit the muscle fatigue they increased the forward bending in order to decrease knee joint torque.

DISCUSSION

The analysis of the strategy used by obese patients in STS task can be used in the design of future trials to assess the efficacy of rehabilitative treatment.

Activation of human quadriceps femoris muscle during dynamic contractions: effects of load on fatigue

Muscle fatigue is both multifactorial and task dependent. Electrical stimulation may assist individuals with paralysis to perform functional activities [functional electrical stimulation (FES), e.g., standing or walking], but muscle fatigue is a limiting factor. One method of optimizing force is to use stimulation patterns that exploit the catchlike property of skeletal muscle [catchlike-inducing trains (CITs)]. Although nonisometric (dynamic) contractions are important parts of both normal physiological activation of skeletal muscles and FES, no previous studies have attempted to identify the effect that the load being lifted by a muscle has on the fatigue produced. This study examined the effects of load on fatigue during dynamic contractions and the augmentation produced by CITs as a function of load. Knee extension in healthy subjects was electrically elicited against three different loads. The highest load produced the least excursion, work, and average power, but it produced the greatest fatigue. CIT augmentation was greatest at the highest load and increased with fatigue. Because CITs were effective during shortening contractions for a variety of loads, they may be of benefit during FES applications.

Knee joint loading in forward versus backward pedaling: implications for rehabilitation strategies

OBJECTIVE

To use forward dynamic simulations of forward and backward pedaling in order to determine whether backward pedaling offers theoretical advantages over forward pedaling to rehabilitate common knee disorders.DESIGN. A comparison of knee joint loads was performed during forward and backward pedaling.BACKGROUND. Pedaling has been shown to be an effective rehabilitation exercise for a variety of knee disorders. Recently, backward gait has been shown to produce greater knee extensor moments and reduced patellofemoral joint loads compared to forward gait. But to date, no study has examined the efficacy of backward pedaling as a safe alternative to forward pedaling in rehabilitation programs.METHODS. A musculoskeletal model and optimization framework was used to generate simulations of forward and backward pedaling. Tibiofemoral and patellofemoral joint reaction forces were quantified.RESULTS. Lower tibiofemoral compressive loads, but higher patellofemoral compressive loads, were observed in backward pedaling. Lower protective anterior-posterior shear force was observed in backward pedaling near peak extension.CONCLUSIONS. Backward pedaling offers reduced tibiofemoral compressive loads for those patients with knee disorders such as menisci damage and osteoarthritis, but higher patellofemoral compressive loads. Therefore, backward pedaling is not recommended for patients experiencing patellofemoral pain. Further, backward pedaling should not be recommended after anterior cruciate ligament injury or reconstruction.RelevanceThe results of this study indicate that the design of rehabilitation programs including pedaling exercises should be injury specific with particular attention paid to the mechanics of the task.

Arm motion and load analysis of sit-to-stand, stand-to-sit, cane walking and lifting

OBJECTIVE

To conduct a pilot study to characterize the hand loads, arm joint angles and external moments corresponding to five activities of daily living demanding of the shoulder, for healthy subjects over 50 years of age.

DESIGN

The tasks were sit-to-stand, stand-to-sit, cane walking, lifting a 5 kg box with both hands, and lifting a 10 kg suitcase.

BACKGROUND

Arm motion and loading have not been previously studied for functional daily-living tasks involving substantial external loads.Methods. Motion was tracked using an optoelectronic system. Loads were measured using an instrumented chair arm, a force plate, and gravitational and acceleration loads. Six healthy volunteers (3 male, 3 female), mean age 55, with no history of shoulder problems participated in the study.

RESULTS

Average peak external moments ranged from 12.3 N m for sitting down into a chair to 27.9 N m for lifting a suitcase. Except for lifting the box, which had much lower loads, average peak hand loads varied from 16% to 19% of body weight (114-134 N). The arcs of motion were larger than for seated activities of daily-living studied previously.

CONCLUSIONS

The five tasks studied are commonly performed, yet involve large external moments. Lifting represents the greatest potential loading at the shoulder as it resulted in the highest external moments; furthermore, loads larger than those used in this study might be commonly lifted.

RELEVANCE

External moments at the shoulder should not be underestimated, even for activities of daily living.

Strength requirements for internal and external prostheses

Throughout the history of development of joint replacement implants and external prostheses there have been mechanical failures due to a discrepancy between material strength, cross-sectional characteristics and the loads developed in normal or abnormal function by the patient utilising the device. Particularly for internal prostheses attention is being paid at the present time to wear characteristics and the requirements for the articulating surfaces and the volume of wear particles produced during tests simulating the use of the device within the patient. The particular importance of the wear particles is that they seem to be associated with accelerated resorption of bone at areas essential for successful fixation of the implant within it. This article will consider joint replacements at the knee and hip and external prostheses for the leg. If failure due to external trauma is ignored the loads to be considered in testing standards correspond in implants to the muscular and ligamentous forces related to the forces developed between ground and foot and to the bending moments in the structure of leg prostheses. Generally it can be assumed that the treatment of the patient following trauma is more easily accomplished and more likely to be successful if the prosthesis has failed and not the bony structure of the patient. However, the author is unaware that these devices have ever been designed to have lower intrinsic strength than the anatomical structures to which they are connected; indeed in many cases particularly for implants they are much stronger than the bone to which they are connected. The major difficulty in rational design of prosthetic devices has been uncertainty about the importance of occasionally applied loads of a high value relative to those on a frequent basis and also to the frequency of application of these overloads. In this paper consideration is given to methods of determination of load systems relevant to the mechanical performance of implanted joint replacements at the hip and the knee and external prostheses for leg amputees. New data are presented relating to walking, other daily activities and the corresponding frequency of occurrence of these. Loading data on implants obtained by various biomechanical models is compared and related to the loads actually measured by implanted transducers. The philosophy of the standardised test load systems and the performance requirements is reviewed.

In vitro forces in the normal and cruciate-deficient knee during simulated squatting motion

Three orthogonal components of the tibiofemoral and patellofemoral forces were measured simultaneously for knees with intact cruciate ligaments (nine knees), following anterior cruciate ligament resection (six knees), and subsequent posterior cruciate ligament resection (six knees). The knees were loaded using an experimental protocol that modeled static double-leg squat. The mean compressive tibial force increased with flexion angle. The mean anteroposterior tibial shear force acted posteriorly on the tibia below 50 deg flexion and anteriorly above 55 deg. Mediolateral shear forces were low compared to the other force components and tended to be directed medially on both the patella and tibia. The mean value of the ratio of the resultant tibial force divided by the quadriceps force decreased with increasing flexion angle and was between 0.6 and 0.7 above 70 deg flexion. The mean value of the ratio of the resultant tibiofemoral contact force divided by the resultant patellofemoral contact force decreased with increasing flexion and was between 0.8 and 1.0 above 55 deg flexion. Cruciate ligament resection resulted in no significant changes in the patellar contact forces. Following resection of the anterior cruciate ligament, the tibial anteroposterior shear force was directed anteriorly over all flexion angles tested. Subsequent resection of the posterior cruciate ligament resulted in an approximately 10 percent increase in the quadriceps tendon and tibial compressive force.

Rising from chair after total knee arthroplasty

OBJECTIVE: This study was performed to determine the biomechanics of chair rising by patients after successful total knee arthroplasty (TKA). DESIGN: Relative full body joint positions and ground reaction forces were measured by a motion analysis system and two force plates. BACKGROUND: Chair-rise produces increased joint forces and moments compared with level walking, and it is difficult to rise from a chair for most patients with neurological or musculoskeletal abnormalities. Previous motion studies of patients after TKA had focused on gait analysis and stair climbing. METHODS: Twelve patients after successful TKA were studied while performing sit-to-stand transfer from a chair at four chair heights without the use of arm rests. The results of this group were compared with those of 12 healthy elderly subjects and 14 osteoarthritic patients before TKA. RESULTS: Compared with the healthy elderly group during chair rising, the patients after TKA had increased horizontal mass center velocity, increased vertical hip joint forces, the maximum sound-side hip extension moment, but decreased vertical mass center velocity. CONCLUSIONS: Compensatory mechanisms of chair rising were adopted by the arthritic patients before and after TKA. The mechanisms include increased forward body bending and more weight shift on the sound side.

A kinematic and kinetic analysis of the sit-to-stand transfer using an ejector chair: implications for elderly rheumatoid arthritic patients

Twelve elderly female rheumatoid arthritis patients (mean age = 65.5 +/- 8.6 yr) were assessed rising from an instrumented Eser Ejector chair under four conditions: high seat (540 mm), low seat (450 mm), with and without the ejector mechanism operating. Sagittal plane motion, ground reaction forces, and vertical chair arm rest forces were recorded during each trial with the signals synchronised at initial subject head movement. When rising from a high seat, subjects displayed significantly (p < 0.05) greater time to seat off; greater trunk, knee and ankle angles at seat off; increased ankle angular displacement; decreased knee angular displacement; and decreased total net and normalised arm rest forces compared to rising from a low seat. When rising using the ejector mechanism, time to seat off and trunk and knee angle at seat off significantly increased, whereas trunk and knee angular displacement, and total net and normalised arm rest forces significantly decreased compared to rising unassisted. Regardless of seat height or ejector mechanism use, there were no significant differences in the peak, or time to peak horizontal velocity of the subjects' total body centre of mass, or net knee and ankle moments. It was concluded that increased seat height and use of the ejector mechanism facilitated sit-to-stand transfers performed by elderly female rheumatoid arthritic patients. However, using the ejector chair may be preferred by these patients compared to merely raising seat height because it does not necessitate the use of a footstool, a possible obstacle contributing to falls.

Instrumented implant for measuring tibiofemoral forces

Experimental measurement of loads occurring in the human knee joint will allow validation of analytical models and provide data for the design of total knee implants. A customized transducer was developed to measure the dynamic tibiofemoral force and center of pressure after total knee arthroplasty. The transducer consists of a standard tibial component to which four uniaxial load cells and an additional tibial tray have been added. The transducer was calibrated using a loading device traceable to the National Institute of Standards and Technology (NIST). The transducer was accurate to within 1% in magnitude, 0.07 mm in medial/lateral location and 0.24 m in anterior/posterior location.

Trunk movements in older subjects during sit-to-stand

Sitting to standing (STS) is an activity that is performed many times during the course of a day and is an important prerequisite to the achievement of many functional goals. This article presents the results from a pilot study, the purpose of which was to develop a method for investigating the activity of sit-to-stand. The study describes STS timing and patterns of trunk movement during standing up in a population of 30 normal older adult subjects (mean age, 61.6 years; SD, 7.7 years). Data were gathered using a three-dimensional movement analysis system, CODA-3. Time taken to stand up was recorded, as were the trunk movements of pelvic and shoulder rotation, trunk lateral flexion, pelvic and shoulder lateral shift, and backward shoulder movement to achieve stance. Results show that normal subjects stood up quickly (mean, 1.67 sec; SD, .27 sec; range, 1.26 to 2.13 sec), and despite large amounts of trunk forward flexion and upward motion necessary to achieve the task of standing up, only small amounts of trunk rotation, trunk lateral flexion, and trunk lateral shift were measured during the activity. The identification of these movements characteristics may be beneficial in assisting with analysis of the STS movement pattern.

Direct in vitro determination of the patellofemoral contact force for normal knees

Results of the direct in vitro measurement of the full three-dimensional representation of the patellofemoral contact force and the point of application on the patella of the resultant contact force for eleven normal knees are presented. The applied knee moment versus flexion angle pattern was similar to that experienced when rising from a chair. There was a wide variability of the details of the patellofemoral force interaction among the specimens tested. The magnitude of the resultant contact force increased approximately linearly with flexion angle for some knees while in others the force leveled off or decreased at higher flexion angles. The change in direction of the resultant contact force with respect to the patella was relatively small compared to the angular rotation of the patella. The medial-lateral component of the contact force exhibited substantial variability among knees. The direction of this force (medially or laterally directed) varied among knees and, in some knees, changed direction as a function of flexion angle. The point of application on the patella of the resultant contact force migrated superiorly from 20 to 90 deg flexion. About 90 deg flexion this point tended to migrate inferiorly. The only significant and consistent effect of varying the direction of the quadriceps extension force was a change in the medial-lateral component of the contact force. In all cases, the tendency to sublux laterally increased when the extensor force was rotated 10 deg laterally and decreased when the extensor force was rotated 10 deg medially.

Two strategies of transferring from sit-to-stand; the activation of monoarticular and biarticular muscles

In this study, two different strategies of rising from a chair were compared, using integrated biomechanical and electromyographic analyses. Nine healthy subjects were instructed to rise using two different strategies: natural sit-to-stand transfer (NSTS) and a sit-to-stand transfer with full flexion of the trunk (FSTS). Sagittal kinematics and ground reaction forces were registered. Muscle activity of nine muscles of the right leg were recorded by means of surface EMG. All signals were synchronized at seat-off. The results show that no differences occur between the kinematics of knee and ankle, whereas the hip flexion is, as expected, higher during FSTS. The higher moment about the knee during NSTS is shifted to proportionally higher moments about the hip and ankle during FSTS. It is mainly the differences in the EMG-levels of the biarticular hip and knee muscles which might explain the differences in net moment. These results are in accordance with a theory about a particular role of biarticular muscles. On the other hand, the shift from knee to ankle cannot be associated with a particular increase in activity of the biarticular m.gastrocnemius. It is hypothesized that about the ankle, control of stability is preferred over movement control. An important conclusion for rehabilitation medicine is that a lower net moment about the knee in FSTS does not automatically imply that this reduces the load on the knee extensors.

A three-dimensional representation of an athletic female knee joint using magnetic resonance imaging

Intense interest in knee joint mechanics has resulted in the development of numerous models to predict forces acting at the knee. However, few models have accounted for the unique geometric characteristics of the knee joint's articular surfaces when predicting the mechanical response of the joint. The purpose of this study was to stimulate accurately the complex geometric characteristics of the tibiofemoral joint for input into a finite element model representing the knee joint of athletic females. The right knee of an athletic female with no history of knee joint trauma was imaged using a 0.5 T magnetic resonance imaging (MRI) unit. Twelve cross-sectional slices of the knee were scanned in each of three orthogonal planes (coronal, sagittal and axial) at slice intervals of 6 mm, 7 m, and 8 mm respectively. A scan plan (two coronal images and an axial image) was also generated to enable calculation of the orthogonal scans with respect to one another. Select anatomical reference points representing cancellous and compact bone, major ligament attachment areas, and articular cartilage of the distal femur and proximal tibia were digitized from the processed shadowgraphs. The processed digitized data were input into a computer graphics program which was the pre- and post-processing software for the finite element analysis package. Contours of the cancellous and compact bone of the tibial and femoral condyles were generated using beta and cubic spline curves. Bezier quadratic and cubic polynomials were used to reconstruct the tibial and femoral shafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Elbow kinematics during sit-to-stand-to-sit of subjects with rheumatoid arthritis

Independence in mobility is dependent on the ability to rise from a chair. Elbow kinematics of subjects with rheumatoid arthritis were compared to those of subjects with no known elbow pathology. Through a case study approach, four subjects with varying elbow pathology and symptoms, were compared with a control group of 10 subjects on four kinematic variables. Results indicated that whereas the overall movement pattern was similar between the two groups, a trend toward increased deviation occurred with increased elbow involvement (as measured using the Morrey Elbow Evaluation). The total time taken to complete the task increased and the maximum velocity decreased as scores on the Morrey Evaluation decreased. When the minimum flexion angle (maximum extension) used during the activity was compared with the minimum flexion angle available, the angle used was consistently 15 degrees to 20 degrees less than that available. This possible need for a residual range raises questions about the generally accepted belief that activities require between 30 degrees to 130 degrees of flexion and 100 degrees of rotation.

Biomechanics and muscular activity during sit-to-stand transfer

In the present study 10 healthy subjects were measured, performing sit-to-stand transfers in a natural way. Starting position and speed of movement were standardized. Sagittal kinematics, the ground reaction force, and muscle activity of nine leg muscles were recorded. During sit-to-stand transfer the mass centre of the body was moved forward and upward. Based on the velocity of the mass centre of the body three phases were distinguished. In horizontal direction forward rotation of the upper body contributed to the velocity of the mass centre of the body, whereas extension of the legs contributed considerably in vertical direction. After seat-off most muscles were concentrically active, whereas the shortening velocity of the rectus femoris was very low. Thus hip and knee joints were extended and a relatively high knee moment was delivered to control the ground reaction force in a slightly backward direction. Co-contraction of hamstrings and rectus femoris in sit-to-stand transfer was judged to be efficient.

Transfer strategies used to rise from a chair in normal and low back pain subjects

The mechanics of rising from a chair are analysed in two groups of male subjects including five normal subjects and five chronic non-specific, low back pain subjects. Chair height, foot placement and arm position were controlled while force plate, video and electromyographic data were collected. The task was broken into three phases: initiation, chair unloading, and ascending. Moment and power analyses of the ascending phase showed two different strategies were used among the normal subjects. A 'knee strategy', comprising higher knee muscle moments, propelled the body into the standing posture while keeping the trunk relatively vertical; a 'hip-trunk strategy' flexed the trunk farther forward, decreasing the knee moments, but at the same time increasing the moments at the hip and low back. The low back pain subjects used a modified strategy that distributed the moments and power more evenly throughout the lower limb and low back.

A six-degree-of-freedom transducer for in vitro measurement of patellofemoral contact forces

A satisfactory design of the patellar component used in total knee arthroplasty and a general understanding of the effects of orthopedic procedures require, in part, an accurate description of patellofemoral contact forces. Experimental determination of the contact stress distribution requires integration to estimate the contact forces. Due to complex patellar geometry, the determination of the components of the resultant load is difficult. Current techniques for the direct measurement of contact loads either report a single load component or require sequential experiments to fully describe the contact force. The present study describes the development of a six-degree-of-freedom patellofemoral force transducer. This transducer allows the simultaneous determination of the three components of the contact force with an increase in accuracy over available devices. The contact forces components are accurate to 1% of full scale (900 N anterior-posterior, +/- 200 N medial-lateral and inferior-superior). The location on the patella where the resultant force acts is determined to within 1 mm. Relative movement of this point as a function of either normal change in knee flexion angle or as a result of a typical orthopedic procedure is determined to within 0.1 mm. A protocol is presented that allows the contact forces to be determined for either the anatomically normal patella or a patella following total knee arthroplasty.

Elbow kinematics during sit-to-stand and stand-to-sit movements

The sit-to-stand and stand-to-sit movements of 10 healthy women (mean age 52.4 years) were subjected to a descriptive analysis that yielded a definition of phases, determination of the peak angles reached, maximum angular velocity during each movement, and the sequencing of key events. While subjects showed little intrasubject variability, intersubject variability was evident. Subjects differed in the joint angles and angular velocity recorded, but the sequence of flexion/extension and rotation events were unchanged. Changes in direction of flexion/extension and rotation tended to occur very close in time, if not at the same time.

Validity of cadaveric data for muscle physiological cross-sectional area ratios: a comparative study of cadaveric and in-vivo data in human thigh muscles

Muscle physiological cross-sectional area (PCSA) is calculated from muscle volume, fibre length and fibre pennation angle, and is a measure of force/stress. Muscle force analyses in the human body usually yield combined forces of groups of synergistic muscles rather than individual muscle forces, because of the constraints of statically determinate models. As stresses acting in a group of muscles are uniform, the ratio of the physiological cross-sectional areas of a group of muscles can be used to divide the combined force into its component parts. This paper investigates the validity of the common practice of using cadaveric physiological cross-sectional area to divide in-vivo group muscle forces into component parts. Muscle volumes were determined in vivo using a combination of radiographic techniques for a small number of active young males, and 'in-vivo' physiological cross-sectional areas were calculated using cadaveric data for fibre length and pennation angle. As would be expected, in absolute terms, the 'in-vivo' values were much larger than those of cadavers. Comparison of the percentage contribution of each muscle to the total value of its group showed little difference between the cadaveric and 'in-vivo' data. We conclude that it is reasonable to use cadaveric data when only relative physiological cross-sectional areas are required, more so in the quadriceps than in the hamstrings. Considering data from active young subjects and cadavers, we have shown the ratios of the physiological cross-sectional area of the individual muscles of the quadriceps (and to a lesser extent the hamstrings) to be comparable. This validates the practice of using cadaveric data for relative physiological cross-sectional area in statically determinate force analysis in the human body. 9n-vivo' ratios are also presented for future use.

Bioengineering aspects of rehabilitation

This paper discusses the development of bioengineering in the field of human joints and its particular relevance to rehabilitation.

Dynamic joint forces during knee isokinetic exercise

This study analyzed forces in the tibiofemoral and patellofemoral joints during isokinetic exercise using an analytical biomechanical model. The results show that isokinetic exercise can produce large loads on these joints, especially during extension exercises. The tibiofemoral compressive force (4.0 body weight) is approximately equal to that obtained during walking but it occurs at 55 degrees of knee flexion. Anterior shear forces (resisting force to anterior drawer) exist during extension exercise at less than 40 degrees of knee flexion, with a maximum of 0.3 body weight. Posterior shear forces (resisting force to posterior drawer) exist during extension exercise at knee joint angles greater than 40 degrees and during the flexion portion of isokinetic exercise. The maximum posterior shear force is 1.7 body weight. The patellofemoral joint can encounter loads as high as 5.1 body weight which are 10 times higher than during straight leg raises. These results suggest that isokinetic exercise should be used cautiously in patients with knee lesions.

Analysis of standing up and sitting down in humans: definitions and normative data presentation

A formal definition of human standing up and sitting down movements based on sagittal plane goniometric and force plate data from 20 normal subjects is presented. This definition is comparable to the established gait cycle diagram, and consists of defined characteristic events and relative time intervals between them. The characteristic events are selected primarily on changes in ground reaction forces. The terminology proposed may be valuable for introducing more formalized and standardized reporting of both qualitative and quantitative studies in both normals and in patients. This presentation is directed toward the process of defining generally acceptable standards for human standing up and sitting down movements.

The influence of chair height on lower limb mechanics during rising

The mechanics of the lower limb were analyzed in young, adult normal subjects when rising from a seated position. Limb mechanics were described in terms of flexion-extension motion and moments at the hip, knee and ankle while rising from four seat heights corresponding to 65, 80, 100, and 115% of the subject's knee joint height. The results indicate that the maximum moment tending to flex the hip joint was higher than that occurring at the knee or ankle. The magnitude of the maximum flexion moment at the hip was not substantially influenced by chair height, changing by less than 12% between the highest and lowest chair heights. Conversely, the maximum knee flexion moments were found to be highly dependent on chair height and nearly doubled from the highest to the lowest position. The magnitude of the moments at the ankle did not change with chair height and were significantly lower than the magnitude of the moments found during normal walking. The magnitude of motion and moments at the hip were greater during chair-rising than during stair-climbing or walking. The range of motion required at the knee for the lower chair heights was also greater than was reported during stair-climbing studies. Thus, the combination of moments in joint angles during chair-rising are unique among common activities of daily living and should be considered in chair selection as well as in the guidelines for prosthetic devices.

Effect of limited knee-flexion range on peak hip moments of force while transferring from sitting to standing

The hypothesis that limiting the knee-flexion range increases the peak hip-extension moment while transferring from sitting to standing was tested by filming (100 fps) ten normal human volunteers. With the knees flexed 105 degrees from full extension (0 degrees) the mean (+/- 1 S.D.) peak hip-extension moment was 142 (+/- 37) Nm. With the knees flexed only 75 degrees subjects threw their arms and trunks forward to a greater extent, with a peak moment of 253 (+/- 65) Nm (p less than 0.0001). If the peak moments rise to a similar degree in patients with arthritis and limited knee-flexion range, they may accelerate hip joint damage or the loosening of hip endoprostheses.

State variable approach to the function of the muscular system supporting the hip joint during normal walking

In Figures 6 and 7, the results of the forces Fk and Fm are analytically represented. The signs of these forces show the direction of the corresponding moment which emanates from this force, since this sign is stable throughout the entire duration of the interval. The resultant moment, included in the equation 7 or 8, is expressed as Fkdk or Fmdm respectively. The direction of this moment is positive if F1 or F3 is operational, and negative if F2 or F4 is operational, therefore the sign attached to this force must follow the sign of the corresponding moment. The results show that this is satisfied for all values, except for those at the 65 and 75% point of the period. This is probably because the value of the corresponding moment is very small, about 0.1, and the resultant force is primarily due to the effect of the moment Mx. In this work, the flexion-extension and abduction-adduction forces, Fk, Fm respectively, were found to take their maximum and minimum values at times which are proximal to those found by Paul and other authors. On the other side there is a difference in values which fluctuates between 15 and 35% at various points; this divergence should be generally acceptable, given that it concerns models describing biological systems. These results seem to lend encouraging support to our method and suggest that the model should be reliable and effective and could be further enhanced if the time intervals were shorter but more numerous.

Tibiofemoral joint forces during ergometer cycling

Six healthy subjects pedaled on a weight-braked bicycle ergometer at different workloads, pedaling rates, saddle heights, and pedal foot positions. The subjects were filmed with a cine-film camera and pedal reaction forces were recorded from a force transducer mounted on the left pedal. Net knee moments were calculated using a dynamic model, and the tibiofemoral shear and compressive force magnitudes were calculated using a biomechanical model of the knee. During cycling at 120 W, 60 rpm, midsaddle height, and anterior pedal foot position, the mean peak tibiofemoral compressive force was 812 N [1.2 times body weight (BW)]. The maximum anteriorly directed tibiofemoral shear force was found to be low (37 N). The compressive and shear forces were significantly increased by an increased ergometer workload. The pedaling rate had no influence on the tibiofemoral force magnitudes. The stress on the ACL was low and could be further decreased by use of the anterior foot position instead of the posterior.

Joint forces in extension of the knee. Analysis of a mechanical model

A two-dimensional model of the tibio-femoral joint was constructed by using the results of cadaver knee dissections together with radiographic landmarks on healthy knees loaded at various angles of flexion. The tibio-femoral compressive force during isometric knee extension had the same magnitude as the patellar tendon force. The tibio-femoral shear force changed direction from posterior at full flexion to anterior when the knee was extended, indicating that high forces may arise in the anterior cruciate was extended, indicating that high forces may arise in the anterior cruciate ligament in the straight knee. Women developed some 20 per cent higher knee joint forces than men for the same extending muscular moment higher knee joint forces than men for the same extending muscular moment, since women's patellar tendon moment arms were found to be shorter. The model presented may be used for quantifying tibio-femoral forces during knee extending activities.

Needs and opportunities in rehabilitation. Aids and the environment

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