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

In vivo changes in the human patellar tendon moment arm length with different modes and intensities of muscle contraction

The purpose of this study was to examine the effect of different muscle contraction modes and intensities on patellar tendon moment arm length (d(PT)). Five men performed isokinetic concentric, eccentric and passive knee extensions at an angular velocity of 60 deg/s and six men performed gradually increasing to maximum effort isometric muscle contractions at 90( composite function) and 20( composite function) of knee flexion. During the tests, lateral X-ray fluoroscopy imaging was used to scan the knee joint. The d(PT) differences between the passive state and the isokinetic concentric and extension were quantified at 15( composite function) intervals of knee joint flexion angle. Furthermore, the changes of the d(PT) as a function of the isometric muscle contraction intensities were determined during the isometric knee extension at 90( composite function) and 20( composite function) of knee joint flexion. Muscle contraction-induced changes in knee joint flexion angle during the isometric muscle contraction were also taken into account for the d(PT) measurements. During the two isometric knee extensions, d(PT) increased from rest to maximum voluntary muscle contraction (MVC) by 14-15%. However, when changes in knee joint flexion angle induced by the muscle contraction were taken into account, d(PT) during MVC increased by 6-26% compared with rest. Moreover, d(PT) increased during concentric and eccentric knee extension by 3-15%, depending on knee flexion angle, compared with passive knee extension. These findings have important implications for estimating musculoskeletal loads using modelling under static and dynamic conditions.

Time-of-day effect on patella tendon stiffness alters vastus lateralis fascicle length but not the quadriceps force–angle relationship

AIM

To examine the time-of-day (TOD) effect on torque-force/angle, fibre length (FL), tendon stiffness (K), stress, and strain using the quadriceps muscle-tendon complex as a model.

METHODS

Twelve healthy young men (aged 27+/-2.0 years) were studied at AM (7h45) and PM (5h45). Maximal isometric contractions were carried out on an isokinetic dynamometer, with real-time recordings of vastus lateralis (VL) FL and patella tendon K using B-mode ultrasonography. Percutaneous electrical twitch doublets superimposed on maximal torque were used to test for muscle activation capacity (AC).

RESULTS

At PM, torque and force increased by 16+/-3.0% (P<0.01) over 30-90 degrees knee angles. Where the load was standardised (at 250N) in order to discriminate between torque generation capacity and tendon K changes, PM relative to AM, there were 8% and 13% (P<0.01) reductions in relaxed and contracted FL, respectively. Average K decreased by 21% (P<0.001) and the maximal stress and strain were increased at PM by 11% and 16%, respectively (P<0.01). No TOD effect on AC was seen.

CONCLUSION

The quadriceps torque or force-angle relationships shift upwards at PM vs. AM, with no shift in the position of the optimal knee angle. This torque or force increase appears not to be centrally modulated. Although K decreases with TOD thereby potentially shortening the working length of the sarcomeres, these changes overall do not affect the ability of the muscle to produce greater torque in the evening.

Human patellar tendon moment arm length: measurement considerations and clinical implications for joint loading assessment

Detailed understanding of the knee joint loading requires the calculation of muscle and joint forces in different conditions. In these applications the patellar tendon moment arm length is essential for the accurate estimation of the tibiofemoral joint loading. In this article, different methods that have been used to determine the patellar tendon moment arm length under in vivo and in vitro conditions are reviewed. The limitations and advantages associated with each of the methods are evaluated together with their applications in the different loading conditions that the musculoskeletal system is subjected to. The three main measurement methods that this review considers are the geometric method, the tendon excursion method and the direct load method. A comparison of relevant quantitative results is presented to asses the impact of the errors of each method on the quantification of the patellar tendon moment arm and the implications for joint loading assessment in clinical applications.

Can the patellar tendon moment arm be predicted from anthropometric measurements?

The purpose of this study was to examine the relations between patellar tendon moment arm length and several relevant anthropometric characteristics of 22 healthy men. The patellar tendon moment arm length was measured using magnetic resonance imaging with two different methods: (1) measurement of patellar tendon moment arm length (d(PT)) with respect to the tibiofemoral contact point (d(PTCP)) and (2) measurement of d(PT) with respect to the intersection point of the anterior and posterior cruciate ligament (d(PTIP)). Pearson correlation coefficients and a stepwise linear regression analysis were used to examine the relationships between the d(PT) and anthropometric measurements taken. Furthermore, a Student's t-test was used to determine differences between the d(PTCP) and d(PTIP) values. Only knee circumference was a significant d(PTCP) predictor (P < 0.05) but with a very low R2 (0.139). None of the anthropometric parameters examined was found to be a significant d(PTIP) predictor. The correlation coefficients ranged from -0.04 to 0.42. The d(PTIP) values were significantly higher (by 0.84-1.89 cm) than the d(PTCP) values (P < 0.05). These results are in disagreement with previous in vitro findings that d(PT) variance may be explained by knee joint size differences. Hence, existing imaging-based methodologies remain necessary for accurate quantification of the patellar tendon moment arm.

Estimation of bone-on-bone contact forces in the tibiofemoral joint during walking

In this study, the tibiofemoral contact forces were estimated from standard gait analysis data of adult walking. Knee angles, ground reaction forces, and external flexion-extension knee moments together with lines of action and moment arms of the force bearing structures in the knee previously determined were used to obtain bone-on-bone contact forces. The heel strike, the onset of single limb stance and terminal extension before toe-off each corresponded to a significant turning point on the force versus gait cycle curve. The tibiofemoral bone-on-bone peak forces calculated reached an estimated three times bodyweight. The estimated joint loads are clinically relevant and can either be used directly for evaluation of subjects in a gait analysis, or indirectly in studies of the knee joint where models simulating loading conditions are used to investigate various pathologies.

Orientation of tendons in vivo with active and passive knee muscles

Tendon orientations in knee models are often taken from cadaver studies. The aim of this study was to investigate the effect of muscle activation on tendon orientation in vivo. Magnetic resonance imaging (MRI) images of the knee were made during relaxation and isometric knee extensions and flexions with 0 degrees , 15 degrees and 30 degrees of knee joint flexion. For six tendons, the orientation angles in sagittal and frontal plane were calculated. In the sagittal plane, muscle activation pulled the patellar tendon to a more vertical orientation and the semitendinosus and sartorius tendons to a more posterior orientation. In the frontal plane, the semitendinosus had a less lateral orientation, the biceps femoris a more medial orientation and the patellar tendon less medial orientation in loaded compared to unloaded conditions. The knee joint angle also influenced the tendon orientations. In the sagittal plane, the patellar tendon had a more anterior orientation near full extension and the biceps femoris had an anterior orientation with 0 degrees and 15 degrees flexions and neutral with 30 degrees flexions. Within 0 degrees to 30 degrees of flexion, the biceps femoris cannot produce a posterior shear force and the anterior angle of the patellar tendon is always larger than the hamstring tendons. Therefore, co-contraction of the hamstring and quadriceps is unlikely to reduce anterior shear forces in knee angles up to 30 degrees . Finally, inter-individual variation in tendon angles was large. This suggests that the amount of shear force produced and the potential to counteract shear forces by co-contraction is subject-specific.

Real in vivo kinematic differences between mobile-bearing and fixed-bearing total knee arthroplasties

We did an in vivo fluoroscopic study comparing the sagittal plane kinematics of mobile-bearing and fixed-bearing total knee arthroplasties in a unique group of patients. These patients were part of a larger bilateral randomized controlled outcome trial with each patient having received both types of total knee arthroplasties. Invited patients did three exercises with each of their different knee replacements; extension against gravity, flexion against gravity, and a step-up. These exercises were recorded using video fluoroscopy, and a series of still digital images over the flexion range were retrieved. The relationship of patella tendon angle to knee flexion angle for each patient was derived. The patella tendon angle to knee flexion angle of the mobile-bearing knee behaved in a linear manner more closely replicating the normal knee, whereas the fixed-bearing knee behaved in a nonlinear, more variable manner. This pattern of results was similar for all three exercises with each patient having one knee replacement that behaved differently in the sagittal plane when compared with their other knee replacement. These kinematic differences may explain the clinical differences observed in the randomized controlled trials that compared these two total knee arthroplasties.

Sagittal plane kinematics of a mobile-bearing unicompartmental knee arthroplasty at 10 years: a comparative in vivo fluoroscopic analysis

This study compares in vivo sagittal plane kinematics of the Oxford mobile-bearing unicompartmental knee arthroplasty (UKA) at 1 and 10 years' postsurgery (10 knees) with a fixed-bearing total knee arthroplasty (TKA) (5 knees) and the normal knee (5 knees), using dynamic fluoroscopic measurement of the patellar tendon angle. The Oxford UKA preserved normal changes in patellar tendon angle with flexion, and this was maintained at 10 years. In contrast, an abnormal pattern was seen with the TKA. The results suggest that a normal pattern of sagittal plane knee kinematics exists following Oxford medial UKA and imply that anterior cruciate ligament function is maintained in the long term.

Simultaneous In Vitro Measurement of Patellofemoral Kinematics and Forces

This study involved the development and testing of a system for the simultaneous in vitro measurement of tibiofemoral kinematics and patellofemoral kinematics and forces. Knee motion was tracked using a Vicon 370, and patellofemoral force was measured using a six degree-of-freedom transducer based on the design of Singerman et al. Using this system, twelve knee specimens were tested in supine leg extension under a simulated quadriceps force. The comprehensive set of results corresponds well to the individual results of previous studies. The measurement system will be of value in assessing the effects of total knee arthroplasty on patellar function.

Femoro-tibial and menisco-tibial translation patterns in patients with unilateral anterior cruciate ligament deficiency--a potential cause of secondary meniscal tears

OBJECTIVE

To analyze menisco-tibial and femoro-tibial translation patterns in healthy and ACL-deficient knees in different knee flexion angles under muscle activity.

METHODS

The ACL-deficient and contralateral healthy knees of 10 patients were examined with an open MRI system at 30 degrees and 90 degrees of knee flexion, under isometric contraction of the extensors or flexor muscle groups. Translations between the tibia, the femoral condyles and the menisci were analyzed by three-dimensional image postprocessing.

RESULTS

Posterior translation of the femur and menisci relative to the tibia occurred during knee flexion (30-90 degrees) in all knees. In ACL-deficient knees, posterior translation of the medial femoral condyle (+1.3 +/- 3.8 mm) was significantly larger than in healthy knee (-0.9 +/- 2.9 mm; p<0.05), while the translation pattern of the menisci was similar (med. meniscus 0.6 +/- 2.3 mm vs. 0.6 +/- 2.7 mm). Under isometric contraction of the extensors (relative to the flexor muscle group), an increased posterior position of the femur and menisci was observed at 30 degrees knee flexion, but not at 90 degrees. This applied to ACL-deficient and healthy knees.

CONCLUSIONS

This study shows a significant increase of translation of the medial femoral condyle in ACL-deficient knees, whereas menisco-tibial translation remains almost unchanged. This difference in translation patterns indicates that the posterior horn of the medial meniscus might encounter shear, potentially explaining the high rate of secondary medial meniscal tears in patients with ACL-deficiency.

Gender differences in patellofemoral joint biomechanics

Patellofemoral pain is associated with patellar malalignment and quadriceps weakness which are seen more commonly in women. The objective of the current study was to determine the effects of gender, vastus medialis strength, and tibial rotation on patellofemoral joint biomechanics. Twelve fresh-frozen knees from cadavers were tested using a custom knee jig. Anatomic multiplane loading of the extensor mechanism was used with varying vastus medialis loads. Patellofemoral contact area and pressure were measured using pressure sensitive film at knee flexion angles of 0 degrees, 30 degrees, 60 degrees, and 90 degrees with the tibia in neutral and 15 degrees internal and external tibial rotation. Patellofemoral joint contact areas in specimens from men were larger at knee flexion angles greater than 30 degrees. A significant increase in mean patellofemoral contact pressures was seen for specimens from women when compared with specimens from men at 0 degrees and 30 degrees knee flexion. The knees from women also showed a greater change in contact pressures to varying vastus medialis load at knee flexion angles of 0 degrees, 30 degrees, and 60 degrees. The results of the current study indicate that there are gender differences in patellofemoral contact areas and pressures. These differences may help explain the increased incidence of patellofemoral disorders in women.

Tibiofemoral contact points relative to flexion angle measured with MRI

OBJECTIVE

To determine whether knee flexion influenced bony contact movements during flexion.

DESIGN

Accurate three-dimensional (3D) measurements of tibiofemoral bony contact points in vivo was performed using magnetic resonance imaging technology at 0 degrees, 30 degrees and 60 degrees of flexion.

BACKGROUND

Magnetic resonance imaging is an accurate non-invasive tool for visualizing muscles, tendons, and bone, and provides precise 3D co-ordinates.

METHODS

Magnetic resonance imaging recordings were made from the right knee of 16 subjects with no history of knee dysfunction at 0 degrees, 30 degrees and 60 degrees of flexion. Joint contact movements were reported as changes of the contact point's position on the medial and lateral tibial condyle with respect to a fixed reference point for each flexion angle.

RESULTS

The dominant motion of the centroid of the contact area was posterior with a concomitant inferior and lateral displacement when flexing from 0-30 degrees. Increased flexion to 60 degrees the contact points moved slightly anterior, superior and continued laterally. Comparing movements between the medial and lateral compartments, larger displacement magnitudes were observed laterally. Additionally, tibial rotations of 3-5 degrees were noted relative to the femur.

CONCLUSION

Based on magnetic resonance imaging co-ordinates and the rotated anatomical reference frame, the geometric equations to derive the contact point between the tibiofemoral articulating surfaces is a viable means to investigate tibiofemoral bony contact movement.

RELEVANCE

Contact areas and pressure distributions have been reported using cadaveric specimens but interpretation of the results is limited. Other investigations have been restricted to sagittal plane movement. Using kinematic magnetic resonance imaging, accurate non-invasive 3D recordings of the normal knee at increments of flexion are possible. The normative baseline date can be compared against that of the pathological knee, such as cruciate ligament injury or the status of post-operative meniscectomy in order to examine skeletal joint motion and stability.

A modeling study of partial ACL injury: simulated KT-2000 arthrometer tests

A partial ACL injury may involve different levels of fiber disruption, orfibers may sustain microscopic changes in their structure without gross disruption, resulting in a change in ligament function. The effect of partial ACL tears on the mechanical and functional stability of the knee has not been well documented, in part because of diagnostic difficulties. A computer model of the knee in the sagittal plane was used in this study to simulate tests using the KT-2000 Knee Arthrometer, which quantifies Lachman's test for ACL injury. A variety of partial ACL anterior and posterior bundle injuries were simulated. Anterior and posterior bundle injuries were subdivided into four different simulated injury levels: mild (one-half tear of the bundle), moderate (complete tear of the bundle), severe (complete tear of the bundle and tear of one-half of the other bundle), and more severe (severe injury plus an additional elongation of the other bundle represented by 5% increases of its initial strain). Force-displacement results obtained from simulated KT-2000 knee arthrometer tests depended on the level of injury. Mild and moderate injuries produced only small change in the anterior tibial translation--at different force levels. Severe injury produced increased anterior tibial translation depending on which bundle was completely ruptured. The compliance index defined as the ratio of the displacement and the force within 68 N and 90 N anterior drawer forces, the stiffness, and the rate of change of stiffness of the anterior force-displacement were found to be better at predicting partial ACL ruptures than simple differences in anterior tibial translation. It was possible in the model results to discriminate knees with various levels of partial ACL injuries using the first and second derivatives of the force-displacement curve.

A radiographic analysis of anterior-posterior translation in total knee arthroplasty

We performed radiological analyses to examine the relationship between the knee flexion angle and the anteroposterior translation movement relative to the prosthetic components (NexGen type) after total knee arthroplasty (TKA). Cruciate-retaining (CR) type TKA was performed in 12 knees with osteoarthritis (OA) and 9 knees with rheumatoid arthritis (RA) in which no posterior cruciate ligament (PCL) tear was present. Posterior-stabilized (PS) type TKA was performed in 7 OA knees and 7 RA knees in which the PCL was defective or resected. The measurements were performed according to the methods of Watanabe. The contact point ratio (percentage) was calculated by dividing the distance to the contact point (CP; the closest point of contact between the femoral and tibial components) by the antero-posterior length of the tibial component. After TKA, the CP at full extension was positioned more posteriorly than in the normal knee both under weight-bearing and non-weight-bearing conditions. Except for the RA knees in the PS group, the CP translated anteriorly in the early phase of flexion and then posteriorly. Under weight-bearing conditions, the posterior translation occurred earlier and was smaller in magnitude. For RA knees in the PS group, the CP moved gently posteriorly right from the beginning.

Defining the femoral axis on lateral knee fluoroscopy

The methodological detail about determining the femoral axis on lateral fluoroscopic images of the knee is lacking. This paper reports on the use of the posterior border of the lower femoral diaphysis to represent the axis. This method is accurate, simple, reliable and can be used by researchers studying knee joint kinematics using dynamic video fluoroscopy. It is also useful in the outpatient clinic to assess the flexion/extension position of femoral components after knee arthroplasty.

Rotational moment arms of the medial hamstrings and adductors vary with femoral geometry and limb position: implications for the treatment of internally rotated gait

Persons with cerebral palsy frequently walk with a crouched, internally rotated gait. Spastic medial hamstrings or adductors are presumed to contribute to excessive hip internal rotation in some patients; however, the capacity of these muscles to produce internal rotation has not been adequately investigated. The purpose of this study was to determine the hip rotation moment arms of the medial hamstrings and adductors in persons with femoral anteversion deformities who walk with a crouched, internally rotated gait. A musculoskeletal model with a "deformable" femur was developed. This model was used, in conjunction with kinematic data obtained from gait analysis, to calculate the muscle moment arms for combinations of joint angles and anteversion deformities exhibited by 21 subjects with cerebral palsy and excessive hip internal rotation. We found that the semimembranosus, semitendinosus, and gracilis muscles in our model had negligible or external rotation moment arms when the hip was internally rotated or the knee was flexed -- the body positions assumed by the subjects during walking. When the femur was excessively anteverted, the rotational moment arms of the adductor brevis, adductor longus, pectineus, and proximal compartments of the adductor magnus in our model shifted toward external rotation. These results suggest that neither the medial hamstrings nor the adductors are likely to contribute substantially to excessive internal rotation of the hip and that other causes of internal rotation should be considered when planning treatments for these patients.

The effect of hamstring muscle compensation for anterior laxity in the ACL-deficient knee during gait

The hamstring muscles have been recognized as an important element in compensating for the loss of stability in the ACL-deficient knee, but it is still not clear whether the hamstring muscle force can completely compensate for the loss of ACL, and the consequences of increased hamstring muscle force. A two-dimensional anatomical knee model in the sagittal plane was developed to examine the effect of various levels of hamstring muscle activation on restraining anterior tibial translation in the ACL-deficient knee during level walking. The model included the tibiofemoral and patellofemoral joints, four major ligaments, the medial capsule, and five muscle units surrounding the knee. Simulations were conducted to determine anterior tibial translation and internal joint loading at a single selected position when the knee was under a peak external flexion moment during early stance phase of gait. Incremental hamstring muscle forces were applied to the modeled normal and the ACL-deficient knees. Results of simulations showed that the ACL injury increased the anterior tibial translation by 11.8mm, while 56% of the maximal hamstring muscle force could reduce the anterior translation of the tibia to a normal level during the stance phase of gait. The consequences of increased hamstring muscle force included increased quadriceps muscle force and joint contact force.

Do the hamstrings and adductors contribute to excessive internal rotation of the hip in persons with cerebral palsy?

Children with cerebral palsy frequently walk with excessive internal rotation of the hip. Spastic medial hamstrings or adductors are presumed to contribute to the excessive internal rotation in some patients; however, the capacity of these muscles to produce internal rotation during walking in individuals with cerebral palsy has not been adequately investigated. The purpose of this study was to determine the hip rotation moment arms of the medial hamstrings and adductors in persons who walk with a crouched, internally-rotated gait. Highly accurate computer models of three subjects with cerebral palsy were created from magnetic resonance images. These subject-specific models were used in conjunction with joint kinematics obtained from gait analysis to calculate the rotational moment arms of the muscles at body positions corresponding to each subject's internally-rotated gait. Analysis of the models revealed that the medial hamstrings, adductor brevis, and gracilis had negligible or external rotation moment arms throughout the gait cycle in all three subjects. The adductor longus had an internal rotation moment arm in two of the subjects, but the moment arm was small (<4 mm) in each case. These findings indicate that neither the medial hamstrings nor the adductor brevis, adductor longus, or gracilis are likely to be important contributors to excessive internal rotation of the hip. This suggests that these muscles should not be lengthened to treat excessive internal rotation of the hip and that other factors are more likely to cause internally-rotated gait in these patients.

Cruciate ligament forces in the human knee during rehabilitation exercises

OBJECTIVE

To determine the cruciate ligament forces occurring during typical rehabilitation exercises.Design. A combination of non-invasive measurements with mathematical modelling of the lower limb.Background. Direct measurement of ligament forces has not yet been successful in vivo in humans. A promising alternative is to calculate the forces mathematically.

METHODS

Sixteen subjects performed isometric and isokinetic or squat exercises while the external forces and limb kinematics were measured. Internal forces were calculated using a geometrical model of the lower limb and the "dynamically determinate one-sided constraint" analysis procedure.

RESULTS

During isokinetic/isometric extension, peak anterior cruciate ligament forces, occurring at knee angles of 35-40 degrees, may reach 0.55x body-weight. Peak posterior cruciate ligament forces are lower and occur around 90 degrees. During isokinetic/isometric flexion, peak posterior cruciate forces, which occur around 90 degrees, may exceed 4x body-weight; the anterior cruciate is not loaded. During squats, the anterior cruciate is lightly loaded at knee angles up to 50 degrees, after which the posterior cruciate is loaded. Peak posterior cruciate forces occur near the lowest point of the squat and may reach 3.5x body-weight.

CONCLUSIONS

For anterior cruciate injuries, squats should be safer than isokinetic or isometric extension for quadriceps strengthening, though isokinetic or isometric flexion may safely be used for hamstrings strengthening. For posterior cruciate injuries, isokinetic extension at knee angles less than 70 degrees should be safe but isokinetic flexion and deep squats should be avoided until healing is well-advanced.

RELEVANCE

Good rehabilitation is vital for a successful outcome to cruciate ligament injuries. Knowledge of ligament forces can aid the physician in the design of improved rehabilitation protocols.

Prediction of antagonistic muscle forces using inverse dynamic optimization during flexion/extension of the knee

This paper examined the feasibility of using different optimization criteria in inverse dynamic optimization to predict antagonistic muscle forces and joint reaction forces during isokinetic flexion/extension and isometric extension exercises of the knee. Both quadriceps and hamstrings muscle groups were included in this study. The knee joint motion included flexion/extension, varus/valgus, and internal/external rotations. Four linear, nonlinear, and physiological optimization criteria were utilized in the optimization procedure. All optimization criteria adopted in this paper were shown to be able to predict antagonistic muscle contraction during flexion and extension of the knee. The predicted muscle forces were compared in temporal patterns with EMG activities (averaged data measured from five subjects). Joint reaction forces were predicted to be similar using all optimization criteria. In comparison with previous studies, these results suggested that the kinematic information involved in the inverse dynamic optimization plays an important role in prediction of the recruitment of antagonistic muscles rather than the selection of a particular optimization criterion. Therefore, it might be concluded that a properly formulated inverse dynamic optimization procedure should describe the knee joint rotation in three orthogonal planes.

Knee joint forces during isokinetic knee extensions: a case study

OBJECTIVE

To describe the procedures to obtain knee joint forces during isokinetic knee extensions and evaluate the patellar ligament force, quadriceps tendon force, patellofemoral and tibiofemoral joint forces at different speeds measured from a female subject.

DESIGN

A technical note with a case study.

BACKGROUND

Two previous studies examined knee joint forces during isokinetic knee extension using different techniques reported inconsistent findings. Also, the highest speed used in these two studies (180 degrees s(-1)) were much lower than the maximum speeds available in modern isokinetic dynamometers.

METHODS

The subject performed maximum effort isokinetic knee extensions at 16 different speeds ranged from 25 to 400 degrees s(-1). The gravitational and inertial effects were included in determining the resultant knee torque. Knee radiographs were used to determine the knee joint geometry. A combination of knee torque and geometric data was used to determine different knee joint forces.

RESULTS

All knee joint forces were found to decrease with increasing isokinetic speed. The tibiofemoral shears forces indicated that the anterior cruciate ligament was loaded throughout the range of motion.

CONCLUSIONS

The magnitudes of knee joint forces are largely depending on the knee torque values.

RELEVANCE

Isokinetic knee extensions are considered appropriate for the early part of the rehabilitation for patients with knee dysfunctions due to the lesser demand of coordination. However, to reduce the knee joint forces, submaximal efforts at lower speeds or maximal efforts at higher speeds are recommended.

Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises

PURPOSE

Although closed (CKCE) and open (OKCE) kinetic chain exercises are used in athletic training and clinical environments, few studies have compared knee joint biomechanics while these exercises are performed dynamically. The purpose of this study was to quantify knee forces and muscle activity in CKCE (squat and leg press) and OKCE (knee extension).

METHODS

Ten male subjects performed three repetitions of each exercise at their 12-repetition maximum. Kinematic, kinetic, and electromyographic data were calculated using video cameras (60 Hz), force transducers (960 Hz), and EMG (960 Hz). Mathematical muscle modeling and optimization techniques were employed to estimate internal muscle forces.

RESULTS

Overall, the squat generated approximately twice as much hamstring activity as the leg press and knee extensions. Quadriceps muscle activity was greatest in CKCE when the knee was near full flexion and in OKCE when the knee was near full extension. OKCE produced more rectus femoris activity while CKCE produced more vasti muscle activity. Tibiofemoral compressive force was greatest in CKCE near full flexion and in OKCE near full extension. Peak tension in the posterior cruciate ligament was approximately twice as great in CKCE, and increased with knee flexion. Tension in the anterior cruciate ligament was present only in OKCE, and occurred near full extension. Patellofemoral compressive force was greatest in CKCE near full flexion and in the mid-range of the knee extending phase in OKCE.

CONCLUSION

An understanding of these results can help in choosing appropriate exercises for rehabilitation and training.

Effect of combined axial compressive and anterior tibial loads on in situ forces in the anterior cruciate ligament: a porcine study

This study investigated the impact of a combination of axial compressive and anterior-posterior tibial loads on the in situ forces in the anterior cruciate ligament. An axial compressive load is believed to contribute to increased stability of the knee joint; however, its effect on in situ forces in the anterior cruciate ligament has not been clearly defined, to our knowledge. It was hypothesized that the application of an axial compressive load, when combined with an anterior tibial load, would result in larger in situ forces in the anterior cruciate ligament than those caused by an isolated anterior tibial load. With use of a porcine knee model, the results confirmed this hypothesis; the addition of a 200 N axial compressive load to a 100 N anterior tibial load increased knee stability by reducing anterior-posterior tibial translation and internal-external tibial rotation and also caused a significant increase in in situ forces in the anterior cruciate ligament (p < 0.05). Specifically, there was a 34% increase in the in situ force at 30 degrees of flexion, a 68% increase at 60 degrees of flexion, and an 84% increase at 90 degrees of flexion compared with those for an isolated anterior tibial load of 100 N. Additionally, there was a statistically significant increase of the in situ forces in the anterior cruciate ligament at 60 and 90 degrees as compared with those at 30 degrees. These results suggest that axial compressive loads on the knee may play a role in injury of the anterior cruciate ligament when the knee is flexed.

Electromyographic activity in expert downhill skiers using functional knee braces after anterior cruciate ligament injuries

We studied six expert downhill skiers who had sustained anterior cruciate ligament injuries and had different degrees of knee instability. The aim was to measure possible changes in electromyographic activity recorded from lower extremity muscles during downhill skiing in a slalom course without and with a custom-made brace applied to the injured knee. Surface electrodes were used with an eight-channel telemetric electromyographic system to collect recordings from the vastus medialis, biceps femoris, semimembranosus, semitendinosus, and gastrocnemius medialis muscles from both legs. Without the brace, the electromyographic activity level of all muscles increased during knee flexion. The biceps femoris muscle was the most activated and reached 50% to 75% of the maximal peak amplitude. With the brace, the electromyographic activity increased in midphase during the upward push for the weight transfer and the peak activity occurred closer to knee flexion in midphase. Also, the uninjured knee was influenced by the brace on the injured leg, a decrease in electromyographic activity was seen in midphase. Spearman's rank correlation revealed a significant correlation between an increase in biceps femoris activity of the injured leg and increasing knee instability. We suggest that the brace caused an increased afferent input from proprioceptors, resulting in an adaptation of motor control patterns secondarily modifying electromyographic activity and timing.

Passive knee muscle moment arms measured in vivo with MRI

OBJECTIVE: To determine moment arm lengths from seven knee muscles and the patellar tendon. The knee muscles were the biceps femoris, semitendinosus, semimembranosus, gracilis, sartorius, and the lateral and medial gastrocnemius muscles. DESIGN: The moment arms were calculated based on MRI measurements. BACKGROUND: Moment arm lengths of different muscles with respect to the joint centre of rotation (CR) or the centre of the contact point between joint surfaces are necessary basic data for biomechanical models predicting joint load. METHODS: Ten male and seven female subjects participated. Using a 1.5 Tesla magnetic resonance imaging system, 3-dimensional coordinates of relevant points were recorded from a 3-D volume reconstruction of the right knee at knee flexion angles of 0, 30 and 60 degrees. Muscular moment arms were calculated in both the sagittal and frontal planes. The recordings were all made during passive mode, which means that no muscular contraction was performed. RESULTS: All muscles except the lateral gastrocnemius showed statistically significant differences (P<0.05) of moment arm lengths between gender in the frontal plane. All muscles except biceps femoris and sartorius showed significant differences (P<0.05) of moment arm lengths between gender in the sagittal plane. Most muscles also showed a linear or quadratic trend of changing moment arms with varying knee angle. CONCLUSIONS: Our results indicate that for most biomechanical analyses involving knee muscles, gender- and angle-specific moment arms should be used.

Biomechanical model of the human knee evaluated by neuromuscular stimulation

A detailed model of the human knee was developed to predict shank motion induced by functional neuromuscular stimulation (FNS). A discrete-time model is used to characterize the relationship between stimulus parameters and muscle activation. A Hill-based model of the musculotendon actuator accounts for nonlinear static and dynamic properties of both muscle and tendon. Muscle fatigue and passive muscle viscosity are modeled in detail. Moment arms are computed from musculotendon paths of 13 actuators and from joint geometry. The model also takes nonlinear body-segmental dynamics into consideration. The simulated motion is visualized by graphic animation. Individual model parameters were identified by specific procedures such as anthropometric measurements, a passive pendulum test, and specific open-loop stimulation experiments. Model results were compared with experimental data obtained by stimulating the quadriceps muscle of paraplegic patients with surface electrodes. The knee moment, under isometric conditions, and the knee angle, under conditions of freely swinging shank, were measured. In view of the good correspondence obtained between model predictions and experimental data, we conclude that a biomechanical model of human motion induced by FNS can be used as a mathematical tool to support and accelerate the development of neural prostheses.

An isokinetic study of combined activity of the hip and knee extensors

The purpose of this study was twofold: to derive isokinetic concentric and eccentric normal strength values obtained during combined activity of the knee and hip extensors and to compare these values with those based on testing of knee extensors only. Fifteen men took part in the study. Combined extension was tested in the supine position with the knee and hip at an initial position of 95 degrees. Knee extension was tested in the seated position with the knee at the same initial position. The range of motion and angular velocities were equal in both configurations: 15 degrees and 8 degrees s(-1) and 15 degrees s(-1) respectively. The average peak force in the CKH mode was close to 10 Nm/kg bw and over 15 Nm/kg bw in the concentric and eccentric contractions respectively, whereas for the knee extensor mode the respective figures were approximately 8 Nm/kg bw and 10 Nm/kg bw. With respect to the same performance parameters, there were low and insignificant correlations between the two modes. RELEVANCE:--Isokinetic testing of knee extensors performance in what is commonly known as single-joint configuration is somewhat limited in its functional scope and, if applied wrongly, is potentially harmful in various dysfunctional states of the knee. On the other hand, multi-joint testing configuration, involving muscles of the hip as well as the knee, is possibly more functional and safe. To assess the muscle performance status of knee patients using the latter mode, data regarding what should be expected from normal individuals is essential. This paper supplements existing material concerning knee and hip extensors and looks into the relationship between the two dynamic contraction modes as well as the association between combined activity and knee extensors only. This association which was found to be very limited indicates that the two configurations reflect different muscle action paradigm and therefore may not be used interchangeably.

Muscular and tibiofemoral joint forces during isokinetic concentric knee extension

The purpose of this study was the examination of muscular and tibiofemoral forces during concentric isokinetic knee extension at angular velocities ranging from 30 to 210 deg s(-1), using a two-dimensional biomechanical model. Five males without knee joint injury history participated in the study. The maximum moment ranged from 226.2 Nm at 30 deg s(-1) to 166.4 Nm at 210 deg s(-1). The maximum muscular force ranged from 7.5 times body weight at 30 deg s(-1) to 5.7 at 210 deg s(-1). The compressive tibiofemoral force ranged from 7.5 times body weight at 30 deg s(-1) to 5.7 at 210 deg s(-1) and the shear tibiofemoral force ranged from 0.9 to 0.8 times body weight respectively. These results indicate that the forces developed during maximal isokinetic knee extension are significantly reduced relative to other powerful dynamic activities but are higher than joint forces during simple walking and cycling activities. Appropriate precautions and adjustment of the isokinetic protocol are required in the final phases of joint injury rehabilitation. RELEVANCE: Isokinetic dynamometry has widespread applications in rehabilitation and training of muscle function. It is therefore important to examine the joint and muscular forces under different conditions in order to alter rehabilitation and training programmes and prevent exercise-induced injuries.

A videofluoroscopy method for optical distortion correction and measurement of knee-joint kinematics

Image distortion in video and image intensifier X-ray systems requires appropriate distortion correction methods to obtain accurate biomechanical quantitative measurements for joint kinematics applications. This paper presents an algorithm for coordinate reconstruction and distortion correction using a modified polynomial method. This algorithm was used for the measurement of patellar tendon moment arm, tibial plateau-tibial axis angle and patellar tendon-tibial axis angle during knee extension using videofluoroscopy in vivo. These parameters allow the determination of a two-dimensional biomechanical model of the knee for the measurement of muscle and joint forces during dynamic activities. Five males without knee joint injury history participated in the study. The mean measurement error obtained using an image intensifier-video system was 0.246 +/- 0.111 mm over a 180-mm x 180-mm field of view. The mean maximum patellar tendon moment arm was 39.87 mm at 44.9 degrees of knee flexion. The patellar tendon-tibial plateau angle was 112.9 degrees at full extension and decreased linearly to 87.6 degrees at 90 degrees of knee flexion. The mean angle between the tibial plateau and the tibial long axis was 84.8 degrees. Applications of the method include motion analysis using video and X-ray fluoroscopy systems with non-linear distortion problems. RELEVANCE: Accurate measurement of anatomical parameters from videofluoroscopy systems is important for the determination of joint biomechanical models and measurement of muscular and joint forces.

Sagittal plane translation of the tibia in anterior cruciate ligament-deficient knees during commonly used rehabilitation exercises

It may be assumed that exercises that provoke high sagittal plane knee translations also induce high stresses on an anterior cruciate ligament substitute and, therefore, these exercises should be limited during the first months after reconstruction. In 18 patients with unilateral anterior cruciate ligament deficiency, sagittal plane knee translations were measured with a goniometer linkage system during common activities. The largest translations were found during low-speed isokinetic exercises. Further, isokinetic and isometric exercises on the Cybex-II dynamometer provoked in more than 40% of the patients larger translations on the injured than on the healthy knee. However, isometric exercises without distally applied load only provoked small translation. During bicycling, translations increased with increasing resistance similarly in both limbs. Except for walking downstairs, load-bearing exercises, such as sitting down and standing up from a chair and walking upstairs, only produced negligible amounts of tibial translation. In conclusion, during the early phase after anterior cruciate ligament reconstruction, activities such as bicycling and some weight-bearing exercises seem to be more recommendable than low-speed isokinetic exercises, isometric contractions at a low knee flexion angle with distally applied load or walking downstairs.

Cruciate ligament loading during isometric muscle contractions. A theoretical basis for rehabilitation

A model of the knee in the sagittal plane was used to investigate the ligament forces resulting when an external load applied to the tibia resisted either extension or flexion of the knee under increasing isometric quadriceps or hamstrings contractions, respectively. An elementary mechanical analysis showed which ligament, the anterior or posterior cruciate, was loaded at a given flexion angle and known line of action of the external load. Ligament force, as a proportion of the external load, was also calculated. The results serve as guidelines for the design of injury-specific physical therapy techniques for use after cruciate ligament reconstruction.

Kinematics of successful knee prostheses during weight-bearing: three-dimensional movements and positions of screw axes in the Tricon-M and Miller-Galante designs

Using roentgen stereophotogrammetric analysis we recorded the three-dimensional movements in six knees with implanted Tricon-M prostheses and ten knees with Miller-Galante prostheses as the patients ascended a platform. Fourteen patients with normal knees were used as controls. The two prosthetic designs displayed decreased internal tibial rotation and the Tricon-M increased valgus rotation. A central point on the tibial articular surface had a more lateral position in the Tricon-M design and a more distal one in the Miller-Galante design compared to normal knees. Increased posterior displacement with increasing flexion was observed in both designs. When the normal knees were extended at full weight-bearing the helical axes mainly shifted inclination in the frontal plane. In the prosthetic knees there was a tendency to anterior-posterior displacement of the axes as extension proceeded, especially in the Miller-Galante design. Translations along the helical axes were larger than normal in the Miller-Galante and smaller in the Tricon-M knees, reflecting differences in constraint of the two designs.

Anterior Cruciate Ligament Forces in Alpine Skiing

The purpose of this study was to estimate cruciate ligament forces in Alpine skiing during a movement that has been associated with anterior cruciate ligament (ACL) tears. Resultant knee joint forces and moments were obtained from two skiers during a World Cup Downhill race using an inverse dynamics approach and a 2-D bilaterally symmetric system model. It was found that ACL forces were typically small for both skiers throughout the movement analyzed because quadriceps forces prevented anterior displacement of the tibia relative to the femur at the knee joint angles observed. However, for about 10 ms, loading conditions in the knee joint of Subject 2 (who displayed poor form) were such that large ACL forces may have been present. These particular loading conditions were never observed in Subject 1, who displayed good form. Since neither of the skiers was injured, it is not possible to draw firm conclusions about isolated ACL tears in Alpine skiing from the data at hand.

Biomechanical considerations in patellofemoral joint rehabilitation

Patellofemoral joint biomechanics during leg press and leg extension exercises were compared in 20 normal subjects (10 men, 10 women) aged 18 to 45 years. Knee moment, patellofemoral joint reaction force, and patellofemoral joint stress were calculated for each subject at four knee flexion angles (0 degree, 30 degrees, 60 degrees, and 90 degrees) during leg press and leg extension exercises. All three parameters (knee moment, patellofemoral joint reaction force, and patellofemoral joint stress) were significantly greater in leg extension exercise than leg press exercise at 0 degree and 30 degrees of knee flexion (P < 0.001). At 60 degrees and 90 degrees of knee flexion, all three parameters were significantly greater in leg press exercise than leg extension exercise (P < 0.001). Patellofemoral joint stresses for leg press and leg extension exercises intersected at 48 degrees of knee flexion. This study demonstrates that patients with patellofemoral joint arthritis may tolerate rehabilitation with leg press exercise better than with leg extension exercise in functional ranges of motion because of lower patellofemoral joint stresses.

Ligament forces at the knee during isometric quadriceps contractions

A mathematical model of the knee in the sagittal plane was used to investigate the ligament forces resulting when a posteriorly directed external force, applied to the tibia, resists extension of the knee under increasing isometric quadriceps contractions. The model is based on simple geometric representations of the bones, ligaments and muscles at the knee. An elementary mechanical analysis was used to predict which ligament, the anterior or posterior cruciate, was loaded at a given flexion angle and known line of action of the external force. Ligament force, as a proportion of the external force, was calculated first assuming the ligaments to be represented by single, inextensible lines. Modelling the ligaments as continuous arrays of extensible fibres then showed that tibio-femoral translations and ligament forces increased non-linearly with increasing muscle forces and approached asymptotic values which depended on flexion angle. In most positions of the joint, the calculated asymptotic ligament force values were less than the reported ultimate strength of human ligament, despite quadriceps forces of over three times body weight. The possibility of these asymptotic values of ligament force may explain why, at certain flexion angles, large forces can be developed by the muscles at the knee without ligament rupture.

The patella thinning osteotomy. An experimental study of a new technique for reducing patellofemoral pressure

The authors describe an original procedure, the patella thinning osteotomy, as an alternative to advancement of the tibial tuberosity or patellectomy in cases of severe anterior knee pain. They present an experimental study on cadaveric knees prior to a clinical trial. This study on 13 knee specimens, using Fujifilm Prescale barosensitive film, shows that thinning of the patella by 7 mm diminishes to a significant degree the patellofemoral contact areas from 16.07% at 60 degrees of flexion to 27.90% at 30 degrees of flexion. Patellofemoral joint reacting forces, measured in 12 knees, also diminish in both medial and lateral surfaces at 30 degrees, 60 degrees and 90 degrees of flexion, the level of statistical significance being over 0.05, except for the lateral surface at 60 degrees of flexion. This technique decompresses the patellofemoral joint, and produces the biological effects found after other osteotomies.

Three-dimensional kinematics of the human knee during walking

Three-dimensional kinematics of the tibiofemoral joint were studied during normal walking. Target markers were fixed to tibia and femur by means of intra-cortical traction pins. Radiographs of the lower limb were obtained to compute the position of the target markers relative to internal anatomical structures. High-speed cine cameras were used to measure three-dimensional coordinates of the target markers in five subjects walking at a speed of 1.2 m s-1. Relative motion between tibia and femur was resolved according to a joint coordinate system (JCS). The measurements have identified that substantial angular and linear motions occur about and along each of the JCS axes during walking. The results do not, however, support the traditional view that the so-called 'screw home' mechanism of the knee joint operates during gait.

Abnormal kinematics of the artificial knee. Roentgen stereophotogrammetric analysis of 10 Miller-Galante and five New Jersey LCS knees

The in vivo kinematics of two types of unconstrained, posterior cruciate ligament retaining knee prostheses were analyzed 1 year postoperatively using roentgen stereophotogrammetric analysis. Ten knees had the Miller-Galante and five the New Jersey LCS design. The Miller-Galante knees displayed decreased adduction during active flexion when compared with normal knees. In both types of prostheses, there was decreased medial and increased proximal and posterior displacement. The abnormal kinematics probably reflect the design of the articular surfaces, the absence of the anterior cruciate ligament, and the dysfunction of the posterior cruciate ligament.

Anterior tibial translation during a maximum quadriceps contraction: is it clinically significant?

Quadriceps exercises are used sparingly in the early rehabilitation of ACL reconstructions because of concern about prematurely stretching the ACL graft. The aim of this study was to determine if a maximum isometric quadriceps contraction significantly translates the tibia anteriorly at 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 75 degrees of flexion. Secondly, the role of the ACL in knee stability was analyzed by comparing the amount of tibial translation in normal, ACL deficient, and reconstructed knees. Thirdly, the location in the motion arc where a quadriceps contraction produces anterior tibial translation was determined. Anterior tibial translation was measured using an arthrometer (KT-1000) during an 89 N and manual maximum translation applied to the knee at rest. The manual maximum translation test determines the magnitude of anterior tibial translation produced by a high anterior force applied directly to the proximal calf. These translations were compared to the tibial translation intrinsically induced by a quadriceps contraction. Testing was performed in normal (N = 22), ACL deficient (N = 10), and reconstructed (N = 10) knees. Anterior tibial translation produced by a maximum quadriceps contraction was measured at 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 75 degrees of flexion. The extension exercise resulted in less anterior tibial displacement than an 89 N drawer and half the translation produced by a manual maximum translation (P less than 0.001). Instrumented laxity testing produced greater anterior translation of the tibia than a maximum isometric quadriceps contraction. Anterior tibial translation was the same during maximum isometric knee extension in all tested knees.(ABSTRACT TRUNCATED AT 250 WORDS)

An interactive graphics-based model of the lower extremity to study orthopaedic surgical procedures

We have developed a model of the human lower extremity to study how surgical changes in musculoskeletal geometry and musculotendon parameters affect muscle force and its moment about the joints. The lines of action of 43 musculotendon actuators were defined based on their anatomical relationships to three-dimensional bone surface representations. A model for each actuator was formulated to compute its isometric force-length relation. The kinematics of the lower extremity were defined by modeling the hip, knee, ankle, subtalar, and metatarsophalangeal joints. Thus, the force and joint moment that each musculotendon actuator develops can be computed for any body position. The joint moments calculated with the model compare well with experimentally measured isometric joint moments. We developed a graphical interface to the model that allows the user to visualize the musculoskeletal geometry and to manipulate the model parameters to study the biomechanical consequences of orthopaedic surgical procedures. For example, tendon transfer and lengthening procedures can be simulated by adjusting the model parameters according to various surgical techniques. Results of the simulated surgeries can be analyzed quickly in terms of postsurgery muscle forces and other biomechanical variables. Just as interactive graphics have enhanced engineering design and analysis, we have found that graphics-based musculoskeletal models are effective tools for designing and analyzing surgical procedures.

Kinematics of active knee extension after tear of the anterior cruciate ligament

Three-dimensional movements of the knees in 13 patients with unilateral old tears of ACLs were studied during extension. Roentgen stereophotogrammetric methods were used to measure tibial movements in the injured and the intact knees. Reduced internal rotation and adduction were recorded at the end of extension on both sides. The injured knees displayed increased anterior and distal displacements of the tibial intercondylar eminence. Abnormal tibial displacements in our patients indicate that the absence of the ACL is not completely compensated for during active extension past 30 degrees; close to the extended position, the tibial movements tend to normalize.

Tibiofemoral joint forces during isokinetic knee extension

Using a Cybex II, eight healthy male subjects performed isokinetic knee extensions at two different speeds (30 and 180 deg/sec) and two different positions of the resistance pad (proximal and distal). A sagittal plane, biomechanical model was used for calculating the magnitude of the tibiofemoral joint compressive and shear forces. The magnitude of isokinetic knee extending moments was found to be significantly lower with the resistance pad placed proximally on the leg instead of distally. The tibiofemoral compressive force was of the same magnitude as the patellar tendon force, with a maximum of 6300 N or close to 9 times body weight (BW). The tibiofemoral shear force changed direction from being negative (tibia tends to move posteriorly in relation to femur) to a positive magnitude of about 700 N or close to 1 BW, indicating that high forces arise in the ACL when the knee is extended more than 60 degrees. The anteriorly directed shear force was lowered considerably by locating the resistance pad to a proximal position on the leg. This model may be used when it is desirable to control stress on the ACL, e.g., in the rehabilitative period after ACL repairs or reconstructions.

A planar model of the knee joint to characterize the knee extensor mechanism

A simple planar static model of the knee joint was developed to calculate effective moment arms for the quadriceps muscle. A pathway for the instantaneous center of rotation was chosen that gives realistic orientations of the femur relative to the tibia. Using the model, nonlinear force and moment equilibrium equations were solved at one degree increments for knee flexion angles from 0 (full extension) to 90 degrees, yielding patellar orientation, patellofemoral contact force and patellar ligament force and direction with respect to both the tibial insertion point and the tibiofemoral contact point. The computer-derived results from this two-dimensional model agree with results from more complex models developed previously from experimentally obtained data. Due to our model's simplicity, however, the operation of the patellar mechanism as a lever as well as a spacer is clearly illustrated. Specifically, the thickness of the patella was found to increase the effective moment arm significantly only at flexions below 35 degrees even though the actual moment arm exhibited an increase throughout the flexion range. Lengthening either the patella or the patellar ligament altered the force transmitted from the quadriceps to the patellar ligament, significantly increasing the effective moment arm at flexions greater than 25 degrees. We conclude that the levering action of the patella is an essential mechanism of knee joint operation at moderate to high flexion angles.

Knee and ankle joint forces during steps and jumps down from two different heights

Two healthy subjects were filmed on TV-video when performing 14 different steps and jumps from two different heights (0·20 m and 0·43 m) onto two Kistler force platforms that recorded the reaction forces. The ankle and knee load moments and joint forces were calculated using a sagittal plane semi-dynamic biomechanical model. Steps with the ball of the foot from the lower height induced a vertical ground reaction force (Fz) close to 1 body weight (bw) and around 2 bw from the greater height. From the greater height the knee moments for the majority of the step-downs studied were about 100 Nm, which gave knee joint compressive forces of 4-7 bw. The ankle was exposed to loads of similar magnitude but not so much influenced by step height. The reasons why patients with knee pain prefer performing backward step-downs are discussed.