Knee Joint Reaction Forces Research Articles

Knee joint anatomy predicts high-risk in vivo dynamic landing knee biomechanics

Background With knee morphology being a non-modifiable anterior cruciate ligament injury risk factor, its consideration within injury prevention models is limited. Knee anatomy, however, directly influences joint mechanics and the potential for injurious loads. With this in mind, we explored associations between key knee anatomical and three-dimensional biomechanical parameters exhibited during landings. We hypothesized that lateral and medial posterior tibial slopes and their ratio, and tibial plateau width, intercondylar distance and their ratio, were proportional to peak stance anterior knee joint reaction force, knee abduction and internal rotation angles. Methods Twenty recreationally active females (21.2 (1.7) years) had stance phase three-dimensional dominant limb knee biomechanics recorded during ten single leg land-and-cut tasks. Six anatomical indices were quantified for the same limb via a series of two dimensional (sagittal, transverse and coronal) magnetic resonance images. Linear stepwise regression analyses examined which of these anatomical factors were independently associated with each of the three mean subject-based peak knee biomechanical measures. Findings Lateral tibial slope was significantly ( P < 0.0001) correlated with peak anterior knee joint reaction force, explaining 60.9% of the variance. Both tibial plateau width:intercondylar distance ( P < 0.0001) and medial tibial slope:lateral tibial slope ( P < 0.001) ratios were significantly correlated with peak knee abduction angle, explaining 75.4% of the variance. The medial tibial slope:lateral tibial slope ratio was also significantly ( P < 0.001) correlated with peak knee internal rotation angle, explaining 49.2% of the variance. Interpretation Knee anatomy is directly associated with high-risk knee biomechanics exhibited during dynamic landings. Continued understanding of multifactorial contributions to the anterior cruciate ligament injury mechanism should dictate future injury screening and prevention efforts in order to successfully cater to individual joint vulnerabilities.

Differences in gait parameters between healthy subjects and persons with moderate and severe knee osteoarthritis: A result of altered walking speed?

Background While knee osteoarthritis has been shown to affect a multitude of kinematic, kinetic and temporo-spatial gait parameters, few investigations have examined the effect of increasing levels of radiographic osteoarthritis severity on these gait parameters. Fewer still have investigated the effect of walking speed on gait variables in persons with knee osteoarthritis. The objective of this study was to investigate the influence of walking speed on biomechanical variables associated with joint loading in persons with varying severities of medial compartment knee osteoarthritis. Methods Twenty-one persons with moderate osteoarthritis (Kellgren–Lawrence score 2–3) and 13 persons with severe osteoarthritis (Kellgren–Lawrence score of 4) participated. Twenty-two persons without knee pain or radiographic evidence of arthritis comprised a healthy control group. Sagittal plane kinetics, knee adduction moment, sagittal plane knee excursion, ground reaction forces and knee joint reaction forces were calculated from three-dimensional motion analysis at 1.0 m/s, self-selected and fastest tolerable walking speeds. Differences were analyzed using multivariate analysis of variance and multivariate analysis of covariance with speed as a covariate. Findings Persons with knee osteoarthritis showed significantly lower knee and ankle joint moments, ground reaction forces, knee reaction force and knee excursion when walking at freely chosen speeds. When differences in walking speed were accounted for in the analysis, the only difference found at all conditions was decreased knee joint excursion. Interpretation Compared to a healthy control group, persons with knee OA demonstrate differences in joint kinetics and kinematics. Except for knee excursion, these differences in gait parameters appear to be a result of slower freely chosen walking speeds rather than a result of disease progression.

The femur as a musculo-skeletal construct: A free boundary condition modelling approach

Previous finite element studies of the femur have made simplifications to varying extents with regard to the boundary conditions used during analysis. Fixed boundary conditions are generally applied to the distal femur when examining the proximal behaviour at the hip joint, while the same can be said for the proximal femur when examining the distal behaviour at the knee joint. While fixed boundary condition analyses have been validated against in vitro experiments it remains a matter of debate as to whether the numerical and experimental models are indicative of the in vivo situation. This study presents a finite element model in which the femur is treated as a complete musculo-skeletal construct, spanning between the hip and knee joints. Linear and non-linear implementations of a free boundary condition modelling approach are applied to the bone through the explicit inclusion of muscles and ligaments spanning both the hip joint and the knee joint. A non-linear force regulated, muscle strain based activation strategy was found to result in lower observed principal strains in the cortex of the femur, compared to a linear activation strategy. The non-linear implementation of the model in particular, was found to produce hip and knee joint reaction forces consistent with in vivo data from instrumented implants.

A method of calculating physiologically relevant joint reaction forces during forward dynamic simulations of movement from an existing knee model

In the commonly used SIMM software, which includes a complete musculoskeletal model of the lower limbs, the reaction forces at the knee are computed. These reaction forces represent the bone-on-bone contact forces and the soft tissue forces (e.g. ligaments) other than muscles acting at the joint. In the knee model integrated into this software, a patellotibial joint rather than a patellofemoral joint is defined, and a force acting along the direction of the patellar ligament is not included. Although this knee model results in valid kinematics and muscle moment arms, the reaction forces at the knee calculated do not represent physiologic knee joint reaction forces. Hence our objectives were to develop a method of calculating physiologic knee joint reaction forces using the knee model incorporated into the SIMM software and to demonstrate the differences in the forces returned by SIMM and the physiologic forces in an example. Our method converts the anatomically fictional patellotibial joint into a patellofemoral joint and computes the force in an inextensible patellar ligament. In our example, the rectus femoris was fully excited isometrically, with the knee and hip flexed to 90°. The resulting SIMM tibiofemoral joint reaction force was primarily shear, because the quadriceps force was applied to the tibia via the fictional patellotibial joint. In contrast the physiologic tibiofemoral joint reaction force was primarily compression, because the quadriceps force was applied through the patellar ligament. This result illustrates that the physiologic knee joint reaction forces are profoundly different than the forces returned by SIMM. However physiologic knee joint reaction forces can be computed with postprocessing of SIMM results.

Biomechanical Effects of Kneeling After Total Knee Arthroplasty

Kneeling following total knee arthroplasty can be a difficult task, impairing the activities of patients to varying degrees. Little is known about the biomechanical effects of kneeling following total knee replacement. The objective of this study was to quantify the effects of kneeling on patellofemoral joint contact areas and pressures, knee joint reaction force, and patellar kinematics. Total knee arthroplasties were performed on eight fresh-frozen cadaveric knees, and they were tested with use of a custom knee jig, which permits the simulation of physiologic quadriceps loading as well as the application of an anterior force to simulate kneeling. The knees were tested at flexion angles of 90 degrees , 105 degrees , 120 degrees , and 135 degrees with no anterior force (mimicking a squatting position) and with an anterior force application simulating double-stance kneeling and single-stance kneeling. Patellofemoral joint contact areas and pressures were measured with pressure-sensitive film, and the knee joint reaction force was measured with use of a six-degree-of-freedom load cell. Patellar kinematics were assessed with use of digital photographs tracking fixed markers on the patella. Compared with the condition without kneeling, both single-stance and double-stance kneeling demonstrated significant increases in patellofemoral contact area (p < 0.05) and pressure at all flexion angles (p < 0.05), with the exception of double-stance kneeling at 135 degrees of flexion. The resultant knee joint -reaction force increased with kneeling at all flexion angles. The compressive component of this force increased with kneeling for most conditions, while the lateral component of this force decreased significantly (p < 0.05) with kneeling only at 90 degrees , and the anterior component of this force increased significantly at all knee flexion angles (p < 0.05). Overall, kneeling had minimal changes on patellar tilt, with significant changes in patellar tilt seen only with kneeling at 120 degrees (p = 0.02 for double stance, and p = 0.03 for single stance). The findings of this study suggest that kneeling at a higher flexion angle (135 degrees ) after total knee arthroplasty has a smaller effect on patellofemoral joint contact area and pressure than kneeling at lower flexion angles (<or=120 degrees ).

Age-related neuromuscular function during drop jumps

Muscle- and movement-specific fascicle-tendon interaction affects the performance of the neuromuscular system. This interaction is unknown among elderly and consequently contributes to the lack of understanding the age-related problems on neuromuscular control. The present experiment studied the age specificity of fascicle-tendon interaction of the gastrocnemius medialis (GM) muscle in drop jump (DJ) exercises. Twelve young and thirteen elderly subjects performed maximal squat jumps and DJs with maximal rebound effort on a sledge apparatus. Ankle and knee joint angles, reaction force, and electromyography (EMG) from the soleus (Sol), GM, and tibialis anterior (TA) muscles were measured together with the GM fascicle length by ultrasonography. The results showed that the measured ankle joint stiffness (AJS) during the braking phase correlated positively with the rebound speed in both age groups and that both parameters were significantly lower in the elderly than in young subjects. In both groups, the AJS correlated positively with averaged EMG (aEMG) in Sol during the braking phase and was further associated with GM activation (r = 0.55, P < 0.01) and TA coactivation (TA/GM r = -0.4 P < 0.05) in the elderly subjects. In addition, compared with the young subjects, the elderly subjects showed significantly lower GM aEMG in the braking phase and higher aEMG in the push-off phase, indicating less utilization of tendinous tissue (TT) elasticity. These different activation patterns are in line with the mechanical behavior of GM showing significantly less fascicle shortening and relative TT stretching in the braking phase in the elderly than in the young subjects. These results suggest that age-specific muscle activation patterns as well as mechanical behaviors exist during DJs.

QUANTIFYING PLYOMETRIC INTENSITY VIA RATE OF FORCE DEVELOPMENT, KNEE JOINT, AND GROUND REACTION FORCES

Because the intensity of plyometric exercises usually is based simply upon anecdotal recommendations rather than empirical evidence, this study sought to quantify a variety of these exercises based on forces placed upon the knee. Six National Collegiate Athletic Association Division I athletes who routinely trained with plyometric exercises performed depth jumps from 46 and 61 cm, a pike jump, tuck jump, single-leg jump, counter- movement jump, squat jump, and a squat jump holding dumbbells equal to 30% of 1 repetition maximum (RM). Ground reaction forces obtained via an AMTI force plate and video analysis of markers placed on the left hip, knee, lateral malleolus, and fifth metatarsal were used to estimate rate of eccentric force development (E-RFD), peak ground reaction forces (GRF), ground reaction forces relative to body weight (GRF/BW), knee joint reaction forces (K-JRF), and knee joint reaction forces relative to body weight (K-JRF/BW) for each plyometric exercise. One-way repeated measures analysis of variance indicated that E-RFD, K-JRF, and K-JRF/BW were different across the conditions (p > 0.05), but peak GRF and GRF/BW were not (p > 0.05). Results indicate that there are quantitative differences between plyometric exercises in the rate of force development during landing and the forces placed on the knee, though peak GRF forces associated with landing may not differ.

Knee Moments and Joint Reaction Forces of the Judo Throw Uchimata

There is a popular opinion among the judo community that the throw uchimata creates more stress on the knee than other throws, although there is presently no empirical evidence to support this claim. PURPOSE: To measure reaction forces and muscle moments of the knee for the throw uchimata. METHODS: Four black belt throwers (tori) were filmed and analyzed using six cameras (60 Hz) and real-time motion analysis software (Vicon-Peak Performance Inc. Motus) electronically synchronized with an AMTI (Advanced Mechanical Technologies, Inc.) force plate. Inverse dynamic equations were integrated into the motion analysis system to calculate peak anterior, posterior, and vertical joint reaction forces and peak flexor and extensor moments of the knee. For comparative purposes, two similar throws were analyzed. Each subject performed five trials of the uchimata and harai-goshi throws with instructions to execute them with maximal effort without falling to the ground. In order to maintain accurate two-dimensional measurements within the global coordinate system, only trials with the supporting foot positioned along the anterior posterior axis of the force plate were accepted. Measurements were taken during the throwing phase, or when tori began their single leg support to the point when the faller hit the ground. RESULTS: A MANOVA with repeated measures (p≤0.05) found no significant difference between throws. CONCLUSIONS: Both throws created greater flexor moments compared to extensor moments indicating a greater importance to decelerate and stabilize the knee as opposed to actively accelerating it. The results, however, do not support the popular opinion that the throw uchimata creates more stress on the knee than other throws.Table

Quantifying Plyometric Intensity via Rate of Force Development, Knee Joint, and Ground Reaction Forces

Because the intensity of plyometric exercises usually is based simply upon anecdotal recommendations rather than empirical evidence, this study sought to quantify a variety of these exercises based on forces placed upon the knee. Six National Collegiate Athletic Association Division I athletes who routinely trained with plyometric exercises performed depth jumps from 46 and 61 cm, a pike jump, tuck jump, single-leg jump, countermovement jump, squat jump, and a squat jump holding dumbbells equal to 30% of 1 repetition maximum (RM). Ground reaction forces obtained via an AMTI force plate and video analysis of markers placed on the left hip, knee, lateral malleolus, and fifth metatarsal were used to estimate rate of eccentric force development (E-RFD), peak ground reaction forces (GRF), ground reaction forces relative to body weight (GRF/BW), knee joint reaction forces (K-JRF), and knee joint reaction forces relative to body weight (K-JRF/BW) for each plyometric exercise. One-way repeated measures analysis of variance indicated that E-RFD, K-JRF, and K-JRF/BW were different across the conditions (p < 0.05), but peak GRF and GRF/BW were not (p > 0.05). Results indicate that there are quantitative differences between plyometric exercises in the rate of force development during landing and the forces placed on the knee, though peak GRF forces associated with landing may not differ.

Comparison of the ACL and ACL graft forces before and after ACL reconstruction an in-vitro robotic investigation

Background Long-term follow-up studies have indi-cated that there is an increased incidence of arthrosis following anterior cruciate ligament (ACL) reconstruc-tion, suggesting that the reconstruction may not repro-duce intact ACL biomechanics. We studied not only the magnitude but also the orientation of the ACL and ACL graft forcesMethods 10 knee specimens were tested on a robotic testing system with the ACL intact, deficient, and recon-structed (using a bone-patella tendon-bone graft). The magnitude and orientation of the ACL and ACL graft forces were determined under an anterior tibial load of 130 N at full extension, and 15, 30, 60, and 90° of flexion. Orientation was described using elevation angle (the angle formed with the tibial plateau in the sagit-tal plane) and deviation angle (the angle formed with respect to the anteroposterior direction in the transverse plane)Results ACL reconstruction restored anterior tibial translation to within 2.6 mm of that of the intact knee under the 130-N anterior load. Average internal tibial rotation was reduced after ACL reconstruction at all flexion angles. The force vector of the ACL graft was significantly different from the ACL force vector. The average values of the elevation and deviation angles of the ACL graft forces were higher than that of the intact ACL at all flexion anglesInterpretation Contemporary single bundle ACL reconstruction restores anterior tibial translation under anterior tibial load with different forces (both magni-tude and orientation) in the graft compared to the intact ACL. Such graft function might alter knee kinematics in other degrees of freedom and could overly constrain the tibial rotation. An anatomic ACL reconstruction should reproduce the magnitude and orientation of the intact ACL force vector, so that the 6-degrees-of-freedom knee kinematics and joint reaction forces can be restored.

A quasi-static three-dimensional, mathematical, three-body segment model of the canine knee

A mathematical, three-dimensional, anatomically accurate model of the canine knee was created to determine the forces in the knee ligaments and the knee joint reaction forces during the stance phase of a slow walk. This quasi-static model considered both the tibio-femoral and patello-femoral articulations. The geometric and morphometric data of the hind limb were obtained from cadaver data. Muscle forces acting on the femur and the hip joint reaction force were determined by numerical optimization. Ligaments were modeled as non-linear-springs. Ligament material properties were obtained from the literature pertaining to the human knee. The model consists of-28 non-linear algebraic equations describing equilibrium of the femur and the patella, and geometric constraints. This system of equations was solved by a non-linear least-squares method. Results are presented for a knee with an intact cranial cruciate ligament (CCL) and for a knee with a ruptured CCL. Forces predicted to occur in the CCL by analysis of the model were found to be very similar to reported results of CCL forces measured in vivo in goats.

Knee joint reaction force during tibial diaphyseal lengthening: a study on a rabbit model

The in vivo passive knee joint reaction force was measured in a rabbit model of tibial diaphyseal lengthening. This was based on the assumption that limb lengthening creates soft tissue tension that compresses the joint surface and generates the joint contact force. A measurement method was developed that involved the distraction of the joint and the determination of the distraction force that just separates the joint surfaces. Sixteen immature (mean±SD age=9±0.6 weeks) New Zealand White rabbits underwent 30% (left) tibial diaphyseal lengthening at a rate of two 0.4 mm incremental lengthenings per day. The knee joint reaction force was measured at the end of lengthening (8 rabbits, mean±SD age=14±0.6 weeks) and five weeks after lengthening (8 rabbits, mean±SD age=19±0.7 weeks). An instrumented bilateral distractor and an extensometer were fixed cross the knee joint. The joint distraction force and distraction displacement were measured when the joint was distracted in steps and after the section of the Achilles tendon. The joint reaction force on the lengthened side was significantly higher than the control side at both time points (mean±SD 44.4±7.8 N v. 27.2±4.0 N at the end of lengthening, 44.3±S6.5 N v. 31.3±3.0 N at 5 weeks after lengthening). The contribution of the gastrocnemius to the joint reaction force on the lengthened side was also significantly higher than the control side at both time points (mean±SD 9.0±1.3 N v. 2.8±0.8 N at the end of lengthening, 5.3±1.4 N v. 2.7±0.5 N at 5 weeks after lengthening). There were significant knee and ankle joint contractures at the end of lengthening, as evidenced by decreased range of motion (mean±SD 27±8° and 36±13°, respectively), which remained 5 weeks after lengthening (mean±SD 26±6° and 35±8°, respectively). The gastrocnemius contributed about 20% of the joint reaction force, indicating that changes in the other intra- and extra-articular structures due to joint contracture may be more important in generating the joint reaction force.

Biomechanical Comparison of Two Lower Extremity Exercise Machines Used for Knee Injury Rehabilitation

2004 The goals of rehabilitation after an ACL reconstruction include improving cardiovascular and muscular fitness. Although stationary bicycles are commonly used to accomplish this task, recumbent stepping ergometers have been shown to achieve the same goals. Few data exist regarding the use of recumbent steppers by individuals who have ACL surgery. PURPOSE: To evaluate the knee joint reaction forces and lower extremity muscle activity during stepping and cycling. METHODS: Fourteen healthy individuals with no history of lower extremity injury (age: 22.9 ± 1.9 y, 173.6 ± 11.3 cm, 76.7 ± 13.2kg) and 10 individuals who had undergone ACL reconstruction in their right knees (age: 22.2 ± 4.1 y, 175.3 ± 7.6 cm, 73.0 ± 12.9 kg, 43 ± 32 months post-op) participated. Subjects were videotaped with two cameras as they performed moderate (RPE = 3) exercise on a stepper and a cycle. Four seat positions were utilized resulting in minimum knee flexion angles of 0° (full extension), 15°, 30°, and 45°. The right pedals of the stepper and bike were fitted with a load cell. Video (60Hz) and force data (900Hz) were synchronized and used to perform an inverse dynamics analysis. To assess the myoelectric activity of selected lower extremity muscles, six pairs of surface electrodes were attached to the right side of the body over the following muscles: vastus lateralis (VL), vastus medialis (VM), rectus femoris, biceps femoris, medial gastrocnemius, and soleus. RESULTS: Statistical analyses (ANOVA) revealed that proximal/distal forces were significantly decreased for the stepper compared to the cycle (p = .029) while medial/lateral forces increased (p<.001). When compared to the cycle, significantly reduced muscle activity was detected for the VL (p = .005) and VM (p = .001) for the stepper. Significant main effects (increased muscle activity with increasing knee angle) were found in the VM (p = .012) and VL (p = .058). CONCLUSION: Our results indicate that lower extremity biomechanics on the two machines tested are not affected by knee surgery status. The reduced compressive knee force, equal anterior shear force, and the similar muscle activity for 4 of the 6 lower extremity muscles tested, indicate that a recumbent stepper is a viable rehabilitation modality after ACL surgery. Supported by NuStep, Inc. (UPN#01061905)

Biomechanical Comparison of Two Lower Extremity Exercise Machines Used for Knee Injury Rehabilitation

2004 The goals of rehabilitation after an ACL reconstruction include improving cardiovascular and muscular fitness. Although stationary bicycles are commonly used to accomplish this task, recumbent stepping ergometers have been shown to achieve the same goals. Few data exist regarding the use of recumbent steppers by individuals who have ACL surgery. PURPOSE: To evaluate the knee joint reaction forces and lower extremity muscle activity during stepping and cycling. METHODS: Fourteen healthy individuals with no history of lower extremity injury (age: 22.9 ± 1.9 y, 173.6 ± 11.3 cm, 76.7 ± 13.2kg) and 10 individuals who had undergone ACL reconstruction in their right knees (age: 22.2 ± 4.1 y, 175.3 ± 7.6 cm, 73.0 ± 12.9 kg, 43 ± 32 months post-op) participated. Subjects were videotaped with two cameras as they performed moderate (RPE = 3) exercise on a stepper and a cycle. Four seat positions were utilized resulting in minimum knee flexion angles of 0° (full extension), 15°, 30°, and 45°. The right pedals of the stepper and bike were fitted with a load cell. Video (60Hz) and force data (900Hz) were synchronized and used to perform an inverse dynamics analysis. To assess the myoelectric activity of selected lower extremity muscles, six pairs of surface electrodes were attached to the right side of the body over the following muscles: vastus lateralis (VL), vastus medialis (VM), rectus femoris, biceps femoris, medial gastrocnemius, and soleus. RESULTS: Statistical analyses (ANOVA) revealed that proximal/distal forces were significantly decreased for the stepper compared to the cycle (p = .029) while medial/lateral forces increased (p<.001). When compared to the cycle, significantly reduced muscle activity was detected for the VL (p = .005) and VM (p = .001) for the stepper. Significant main effects (increased muscle activity with increasing knee angle) were found in the VM (p = .012) and VL (p = .058). CONCLUSION: Our results indicate that lower extremity biomechanics on the two machines tested are not affected by knee surgery status. The reduced compressive knee force, equal anterior shear force, and the similar muscle activity for 4 of the 6 lower extremity muscles tested, indicate that a recumbent stepper is a viable rehabilitation modality after ACL surgery. Supported by NuStep, Inc. (UPN#01061905)

Knee joint reaction force during tibial diaphyseal lengthening: a study on a rabbit model

The in vivo passive knee joint reaction force was measured in a rabbit model of tibial diaphyseal lengthening. This was based on the assumption that limb lengthening creates soft tissue tension that compresses the joint surface and generates the joint contact force. A measurement method was developed that involved the distraction of the joint and the determination of the distraction force that just separates the joint surfaces. Sixteen immature (mean±SD age=9±0.6 weeks) New Zealand White rabbits underwent 30% (left) tibial diaphyseal lengthening at a rate of two 0.4 mm incremental lengthenings per day. The knee joint reaction force was measured at the end of lengthening (8 rabbits, mean±SD age=14±0.6 weeks) and five weeks after lengthening (8 rabbits, mean±SD age=19±0.7 weeks). An instrumented bilateral distractor and an extensometer were fixed cross the knee joint. The joint distraction force and distraction displacement were measured when the joint was distracted in steps and after the section of the Achilles tendon. The joint reaction force on the lengthened side was significantly higher than the control side at both time points (mean±SD 44.4±7.8 N v. 27.2±4.0 N at the end of lengthening, 44.3±S6.5 N v. 31.3±3.0 N at 5 weeks after lengthening). The contribution of the gastrocnemius to the joint reaction force on the lengthened side was also significantly higher than the control side at both time points (mean±SD 9.0±1.3 N v. 2.8±0.8 N at the end of lengthening, 5.3±1.4 N v. 2.7±0.5 N at 5 weeks after lengthening). There were significant knee and ankle joint contractures at the end of lengthening, as evidenced by decreased range of motion (mean±SD 27±8° and 36±13°, respectively), which remained 5 weeks after lengthening (mean±SD 26±6° and 35±8°, respectively). The gastrocnemius contributed about 20% of the joint reaction force, indicating that changes in the other intra- and extra-articular structures due to joint contracture may be more important in generating the joint reaction force.

Biomechanical Analysis of the Canine Hind Limb: Calculation of Forces During Three-legged Stance

This paper presents a three-dimensional biomechanical model of the canine hind limb, and describes the process of determining the muscle forces and joint reaction forces and moments occurring in the hind limb during three-legged stance. The model was based on anatomical and morphometric data presented in a previous paper. Equations of equilibrium were formulated for the different components of the hind limb. Since the number of unknowns exceeded the number of equations, the problem was statically indeterminate.Two optimization techniques were applied to solve this statically indeterminate problem. The resultant hip-joint reaction force (acting on the acetabulum) predicted by these optimization methods ranged between 0.73 and 1.04 times body weight, and was directed dorsally, medially and caudally. The resultant knee-joint reaction force (acting on the femur) ranged between 1.05 and 1.08 times body weight, and was directed dorsally, laterally and cranially. The largest muscle forces predicted by the minimization of maximal muscle stress (MMMS) criterion were in the biceps femoris (0.24 times body weight), rectus femoris (0.15 times body weight), medial gluteal (0.18 times body weight),semi-membranosus (0.09 times body weight), the lateral and intermediate vastus (0.18 times body weight) and the medial vastus (0.17 times body weight). The largest muscle forces predicted by the minimization of the sum of muscle forces (MSMF) criterion were in the biceps femoris (0.29 times body weight), lateral and intermediate vastus (0.45 times body weight)), and the deep gluteal (0.16 times body weight).The magnitudes and directions of the forces in the joints of the canine hind limb, as well as in the muscles that surround these joints, provide a database needed for future biomechanical analyses of the physiology and pathophysiology of the canine hind limb.

Is lower limb muscle synchrony during landing affected by gender? Implications for variations in ACL injury rates

This study examined whether lower limb muscle synchrony during abrupt landings was affected by gender, thereby predisposing females to a higher incidence of non-contact anterior cruciate ligament (ACL) injuries than males. Seven males and 11 females landed in single-limb stance on a force platform after receiving a chest-height netball pass and decelerating abruptly. Ground reaction force and electromyographic data for rectus femoris, vastus lateralis, vastus medialis, semimembranosus (SM), biceps femoris, and gastrocnemius were sampled (1000 Hz) during landing. Subjects' sagittal plane motion was also filmed (200 Hz). Knee joint reaction forces and sagittal planar net moments of force were estimated using Newtonian equations of motion and inverse dynamics. Tibiofemoral shear forces ( F s) were obtained and muscle bursts temporally analysed with respect to initial foot–ground contact (IC) and peak F s times. Males displayed significantly delayed SM onset relative to IC (113±46 ms) compared to females (173±54 ms; p=0.03), and significantly delayed SM peak activity relative to peak F s (54±27 ms) compared to females (77±15 ms; p=0.03). Delayed SM activity during landing was suggested to allow peak muscle activity to better coincide with high anterior F s, thereby acting as an ACL synergist via increased joint compression and posterior tibial drawer. It was concluded that females displayed muscle synchrony less protective of the ACL than males, possibly increasing their susceptibility to non-contact ACL injuries.

Effects of walking poles on lower extremity gait mechanics

The purpose of this study was to determine whether walking with poles reduces loading to the lower extremity during level over ground walking. Three-dimensional gait analysis was conducted on 13 healthy adults who completed 10 walking trials using three different poling conditions (selected poles, poles back, and poles front) and without the use of poles (no poles). The inverse dynamics approach was used to calculate kinetic data via anthropometric, kinematic, and kinetic data. All walking with poles conditions increased walking speed (P = 0.0001-0.0004), stride length (P < 0.0001), and stance time (P < 0.0001) compared with the no poles condition. There also was a decrease in anterior-posterior GRF braking impulse (P = 0.0001), a decrease in average vertical GRF walking with poles (P < 0.0001-0.0023), and a decrease in vertical (compressive) knee joint reaction force (P < 0.0001-0.0041) compared with the no poles condition. At the knee, extensor impulse decreased a 7.3% between the no poles and selected poles conditions (P = 0.0083-0.0287) and 10.4% between the no poles and poles back conditions (P < 0.0001). The support moment was reduced between the no poles and poles back (P = 0.0197) and poles front (P = 0.0002) conditions. Ankle plantarflexor work (A2) was reduced in the poles-front condition (P = 0.0334), but no differences were detected in all other ankle, knee or hip power and work variables (P > 0.05). There were differences in kinetic variables between walking with and without poles. The use of walking poles enabled subjects to walk at a faster speed with reduced vertical ground reaction forces, vertical knee joint reaction forces, and reduction in the knee extensor angular impulse and support moment, depending on the poling condition used.

The relationship between ankle plantar flexor muscle moments and knee compressive forces in subjects with and without pain

Objective. The purpose of this study was to compare the compressive knee joint reaction force and ankle plantar flexor muscle moment during the terminal stance phase in symptomatic osteoarthritic and non-symptomatic subjects. Design. The study design was a comparative investigation of walking patterns. Background. Patients with knee osteoarthritic symptoms may employ altered gait patterns to reduce the loading of painful joints. Speculation is that decreased ankle plantar flexor moments in the terminal stance phase may be an attempt to minimize compressive knee joint reaction forces. Methods. Twenty community-dwelling men (52–83 years old), ten with knee osteoarthritis and ten non-symptomatic, were studied while walking across a walkway containing two force plates at a comfortable speed. Retroreflective markers were placed in accordance with the Helen Hayes marker system and recorded with six 120 Hz cameras. Three-dimensional kinematics and kinetics were computed. Results. Group means for gait velocity, peak ankle plantar flexor moment and compressive knee joint reaction force were significantly less for the osteoarthritic group relative to the non-symptomatic group. When accounting for the decreased velocity in the osteoarthritic group, however, no group differences were observed. There were significant correlations between all three gait parameters ( r>0.75), but peak ankle plantar flexor moment was the greatest predictor of compressive knee joint reaction force. Conclusions. While no group differences were found for compressive knee joint reaction forces when accounting for gait velocity, it appears that subjects with osteoarthritis utilize gait velocity as a mechanism to reduce compressive knee joint reaction forces. Relevance An understanding of compressive knee joint reaction forces is important to the understanding of the disabling effects of knee osteoarthritis on physical function and to the understanding of appropriate and safe interventions to improve not only global parameters (e.g., pain, gait velocity), but also to “re-program” the locomotor pattern to develop “normal” muscle moments without increasing compressive knee joint reaction forces to painful levels.

Osteoarthritis and elderly amputee gait.

The hypothesis that an increased load on the nonamputated leg of long-term prosthetic users leads to an increased risk of developing osteoarthritis was investigated using physical examinations and gait analysis. Based on the clinical results from an elderly group of experienced trans-tibial amputees and a similar control group of nonamputees, the amputee group experienced a significantly greater incidence of osteoarthritis (p < 0.05) in the knee of their nonamputated leg. The amputee group had consistently larger knee joint reaction forces, joint impulses, net joint moments, and net joint powers. Significantly higher results (p < 0.05) were found for amputee vertical impulse and net joint power during the double support phase of gait. These results support the hypothesis that elderly, trans-tibial amputees have a higher risk of developing osteoarthritis and experience larger forces at the knee of their nonamputated limb than people without lower extremity amputations.