A comparison of slow,uphill and fast,level walking on lower extremity biomechanics and tibiofemoral joint loading in obese and nonobese adults

We determined if slow, uphill walking (0.75 m/s, 6°) reduced tibiofemoral (TF) loading compared to faster, level walking (1.50 m/s) in obese and nonobese adults. We collected kinematic, kinetic, and electromyographic data as 9 moderately obese and 10 nonobese participants walked on a dual‐belt instrumented treadmill. We used OpenSim to scale a musculoskeletal model and calculate joint kinematics, kinetics, muscle forces, and TF forces. Compressive TF forces were greater in the obese adults during both speed/grade combinations. During level walking, obese participants walked with a straighter leg than nonobese participants, resulting in early stance vasti muscle forces that were similar in the obese and nonobese participants. Early stance peak compressive TF forces were reduced by 23% in obese (2,352 to 1,811 N) and 35% in nonobese (1,994 to 1,303 N) individuals during slow, uphill walking compared to brisk level walking. Late stance peak TF forces were similar across speeds/grades, but were greater in obese (～2,900 N) compared to nonobese (～1,700 N) individuals. Smaller early stance TF loads and loading rates suggest that slow, uphill walking may be appropriate exercise for obese individuals at risk for musculoskeletal pathology or pain. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:324–330, 2014.     

Evaluation of predicted knee‐joint muscle forces during gait using an instrumented knee implant

Musculoskeletal modeling and optimization theory are often used to determine muscle forces in vivo. However, convincing quantitative evaluation of these predictions has been limited to date. The present study evaluated model predictions of knee muscle forces during walking using in vivo measurements of joint contact loading acquired from an instrumented implant. Joint motion, ground reaction force, and tibial contact force data were recorded simultaneously from a single subject walking at slow, normal, and fast speeds. The body was modeled as an 8‐segment, 21‐degree‐of‐freedom articulated linkage, actuated by 58 muscles. Joint moments obtained from inverse dynamics were decomposed into leg‐muscle forces by solving an optimization problem that minimized the sum of the squares of the muscle activations. The predicted knee muscle forces were input into a 3D knee implant contact model to calculate tibial contact forces. Calculated and measured tibial contact forces were in good agreement for all three walking speeds. The average RMS errors for the medial, lateral, and total contact forces over the entire gait cycle and across all trials were 140 ± 40 N, 115 ± 32 N, and 183 ± 45 N, respectively. Muscle coordination predicted by the model was also consistent with EMG measurements reported for normal walking. The combined experimental and modeling approach used in this study provides a quantitative framework for evaluating model predictions of muscle forces in human movement. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1326–1331, 2009     

Modulating tibiofemoral contact force in the sheep hind limb via treadmill walking: Predictions from an opensim musculoskeletal model

Sheep are a predominant animal model used to study a variety of orthopedic conditions. Understanding and controlling the in‐vivo loading environment in the sheep hind limb is often necessary for investigations relating to bone and joint mechanics. The purpose of this study was to develop a musculoskeletal model of an adult sheep hind limb and investigate the effects of treadmill walking speed on muscle and joint contact forces. We constructed the skeletal geometry of the model from computed topography images. Dual‐energy x‐ray absorptiometry was utilized to establish the inertial properties of each model segment. Detailed dissection and tendon excursion experiments established the requisite muscle lines of actions. We used OpenSim and experimentally‐collected marker trajectories and ground reaction forces to quantify muscle and joint contact forces during treadmill walking at 0.25 m? s^?1 and 0.75 m? s^?1. Peak compressive and anterior–posterior tibiofemoral contact forces were 20% (0.38 BW, p = 0.008) and 37% (0.17 BW, p = 0.040) larger, respectively, at the moderate gait speed relative to the slower speed. Medial–lateral tibiofemoral contact forces were not significantly different. Adjusting treadmill speed appears to be a viable method to modulate compressive and anterior–posterior tibiofemoral contact forces in the sheep hind limb. The musculoskeletal model is freely‐available at www.SimTK.org . © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1128–1133, 2015.

     

Contributions of muscles, ligaments, and the ground-reaction force to tibiofemoral joint loading during normal gait.

The aim of this study was twofold: first, to determine which muscles and ligaments resist the adduction moment at the knee during normal walking; and second, to describe and explain the contributions of muscles, ligaments, and the ground reaction force to medial and lateral compartment loading. Muscle forces, ground reaction forces, and joint motions obtained from a dynamic optimization solution for normal walking were used as input to a three-dimensional model of the lower limb. A static equilibrium problem was solved at each instant of the gait cycle to determine tibiofemoral joint loading at the knee. Medial compartment loading was determined mainly by the orientation of the ground reaction force. Because this force vector passed medial to the knee, it applied an adduction moment about the joint during stance. In contrast, all of the force transmitted by the lateral compartment was due to muscle and ligament action. The muscles that contributed most to support and forward propulsion during normal walking (quadriceps and gastrocnemius) also contributed most to knee stability in the frontal plane. The knee ligaments, particularly those of the posterior lateral corner, provided stability to the knee at certain periods of the stance phase, when activity of the important stabilizing muscles was low.     

Pediatric obesity and walking duration increase medial tibiofemoral compartment contact forces

With the high prevalence of pediatric obesity there is a need for structured physical activity during childhood. However, altered tibiofemoral loading during physical activity in obese children likely contribute to their increased risk of orthopedic disorders of the knee. The goal of this study was to determine the effects of pediatric obesity and walking duration on medial and lateral tibiofemoral contact forces. We collected experimental biomechanics data during treadmill walking at 1 m?s^?1 for 20 min in 10 obese and 10 healthy‐weight 8–12 year‐olds. We created subject‐specific musculoskeletal models using radiographic measures of tibiofemoral alignment and centers‐of‐pressure, and predicted medial and lateral tibiofemoral contact forces at the beginning and end of each trial. Obesity and walking duration affected tibiofemoral loading. At the beginning of the trail, the average percent of the total load passing through the medial compartment during stance was 85% in the obese children and 63% in the healthy‐weight children; at the end of the trial, the medial distribution was 90% in the obese children and 72% in the healthy‐weight children. Medial compartment loading rates were 1.78 times greater in the obese participants. The medial compartment loading rate increased 17% in both groups at the end compared to the beginning of the trial (p = 0.001). We found a strong linear relationship between body‐fat percentage and the medial‐lateral load distribution (r² = 0.79). Altered tibiofemoral loading during walking in obese children may contribute to their increased risk of knee pain and pathology. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:97–105, 2016.

     

The effect of upper-limb motion on lower-limb muscle synchrony. Implications for anterior cruciate ligament injury

BACKGROUND: A high prevalence of rupture of the anterior cruciate ligament is associated with activities that incorporate both abrupt deceleration and catching a ball. In the present study, we examined whether the upper-limb motion involved in catching a ball affected the synchrony of the lower-limb muscles during tasks known to stress the anterior cruciate ligament-namely, abrupt decelerative landings. METHODS: Seven male and eleven female subjects decelerated abruptly to land in single-limb stance after catching a chest-height pass and after no catching. Ground-reaction force and electromyographic data for six lower-limb muscles were sampled while the subjects' landing technique was filmed. The joint-reaction forces and the sagittal planar net moments for the knee then were calculated to derive the tibiofemoral shear forces. The muscle onsets and peak muscle activities were temporally analyzed with respect to the time of initial foot-ground contact, the peak resultant ground-reaction force, and the peak tibiofemoral shear force. RESULTS: When catching a pass, the subjects demonstrated significantly (p < 0.05) earlier rectus femoris onset relative to the timing of the initial foot-ground contact and of the peak tibiofemoral shear force, and they showed delayed biceps femoris onset relative to the timing of the peak tibiofemoral shear force compared with the findings in the trials without catching. CONCLUSIONS: We concluded that catching a ball during an abrupt landing could increase the potential for an anterior cruciate ligament injury by limiting the time available for the hamstring muscles to generate posterior tibial-drawer force before the onset of the quadriceps-induced anterior tibial translation. Clinical Relevance: The integrity of the anterior cruciate ligament during landing relies on the proper coordination of the lower-limb muscles, particularly the quadriceps and the hamstrings. The present study demonstrated that motion of the upper-limbs may interfere with recruitment of these muscles, thereby predisposing the anterior cruciate ligament to injury.     

Rabbit knee joint biomechanics: motion analysis and modeling of forces during hopping.

Although the rabbit hindlimb has been commonly used as an experimental animal model for studies of osteoarthritis, bone growth and fracture healing, the in vivo biomechanics of the rabbit knee joint have not been quantified. The purpose of this study was to investigate the kinematic and kinetic patterns during hopping of the adult rabbit, and to develop a model to estimate the joint contact force distribution between the tibial plateaus. Force platform data and three-dimensional motion analysis using infrared markers mounted on intracortical bone pins were combined to calculate the knee and ankle joint intersegmental forces and moments. A statically determinate model was developed to predict muscle, ligament and tibiofemoral joint contact forces during the stance phase of hopping. Variations in hindlimb kinematics permitted the identification of two landing patterns, that could be distinguished by variations in the magnitude of the external knee abduction moment. During hopping, the prevalence of an external abduction moment led to the prediction of higher joint contact forces passing through the lateral compartment as compared to the medial compartment of the knee joint. These results represent critical data on the in vivo biomechanics of the rabbit knee joint, which allow for comparisons to both other experimental animal models and the human knee, and may provide further insight into the relationships between mechanical loading, osteoarthritis, bone growth, and fracture healing.     

Bi‐Cruciate Retaining Total Knee Arthroplasty Does Not Restore Native Tibiofemoral Articular Contact Kinematics During Gait

Bi‐cruciate retaining (BCR) total knee arthroplasty (TKA) design preserves both anterior and posterior cruciate ligaments with the potential to restore normal posterior femoral rollback and joint kinematics. Abnormal knee kinematics and “paradoxical” anterior femoral translation in conventional TKA designs have been suggested as potential causes of patient dissatisfaction. However, there is a paucity of data on the in vivo kinematics and articular contact behavior of BCR‐TKA. This study aimed to investigate in vivo kinematics, articular contact position, and pivot point location of the BCR‐TKA during gait. In vivo kinematics of 30 patients with unilateral BCR‐TKA during treadmill walking was determined using validated dual fluoroscopic imaging tracking technique. The BCR‐TKA exhibited less extension than the normal healthy knee between heel strike and 48% of gait cycle. Although the average external rotation trend observed for BCR TKA was similar to the normal healthy knee, the range of motion was not fully comparable. The lowest point of the medial condyle showed longer anteroposterior translation excursion than the lateral condyle, leading to a lateral‐pivoting pattern in 60% of BCR TKA patients during stance phase. BCR‐TKA demonstrated no statistical significant differences in anterior–posterior translation as well as varus rotation, when compared to normal healthy knees during the stance phase. However, sagittal plane motion and tibiofemoral articular contact characteristics including pivoting patterns were not fully restored in BCR TKA patients during gait, suggesting that BCR TKA does not restore native tibiofemoral articular contact kinematics. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1929–1937, 2019     

Patellofemoral joint contact forces during activities with high knee flexion

The patellofemoral (PF) joint plays an essential role in knee function, but little is known about the in vivo loading conditions at the joint. We hypothesized that the forces at the PF joint exceed the tibiofemoral (TF) forces during activities with high knee flexion. Motion analysis was performed in two patients with telemetric knee implants during walking, stair climbing, sit‐to‐stand, and squat. TF and PF forces were calculated using a musculoskeletal model, which was validated against the simultaneously measured in vivo TF forces, with mean errors of 10% and 21% for the two subjects. The in vivo peak TF forces of 2.9–3.4 bodyweight (BW) varied little across activities, while the peak PF forces showed significant variability, ranging from less than 1 BW during walking to more than 3 BW during high flexion activities, exceeding the TF forces. Together with previous in vivo measurements at the hip and knee, the PF forces determined here provide evidence that peak forces across these joints reach values of around 3 BW during high flexion activities, also suggesting that the in vivo loading conditions at the knee can only be fully understood if the forces at the TF and the PF joints are considered together. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:408–415, 2012     

Altered loading in the injured knee after ACL rupture

Articular loading is an important factor in the joint degenerative process for individuals with anterior cruciate ligament (ACL) rupture. Evaluation of loading for a population that exhibits neuromuscular compensation for injury requires an approach which can incorporate individual muscle activation strategies in its estimation of muscle forces. The purpose of this study was to evaluate knee joint contact forces for patients with ACL deficiency using an EMG‐driven modeling approach to estimate muscle forces. Thirty athletes with acute, unilateral ACL rupture underwent gait analysis after resolving range of motion, effusion, pain, and obvious gait impairments. Electromyography was recorded bilaterally from 14 lower extremity muscles and input to a musculoskeletal model for estimation of muscle forces and joint contact forces. Gait mechanics were consistent with previous reports for individuals with ACL‐deficiency. Our major finding was that joint loading was altered in the injured limb after acute ACL injury; patients walked with decreased contact force on their injured knee compared to their uninjured knee. Both medial and lateral compartment forces were reduced without a significant change in the distribution of tibiofemoral load between compartments. This is the first study to estimate medial and lateral compartment contact forces in patients with acute ACL rupture using an approach which is sensitive to individual muscle activation patterns. Further work is needed to determine whether this early decreased loading of the injured limb is involved in the development of osteoarthritis in these patients. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 458–464, 2013     

Evaluation of knee joint muscle forces and tissue stresses‐strains during gait in severe OA versus normal subjects

Osteoarthritis (OA) is the leading cause of pain and disability in the elderly with the knee being the most affected weight bearing joint. We used a musculoskeletal biomechanical model of the lower extremity including a detailed validated knee joint finite element model to compute lower extremity muscle forces and knee joint stresses‐strains during the stance phase of gait. The model was driven by gait data on OA patients, and results were compared with those of the same model driven by data on normal controls. Additional analyses were performed with altered cartilage‐menisci properties to evaluate the effects of deterioration during OA. In OA patients compared to normal subjects, muscle forces dropped at nearly all stance periods except mid‐stance. Force in the anterior cruciate ligament remained overall the same. Total contact forces‐stresses deceased by about 25%. Alterations in properties due to OA had negligible effects on muscle forces, but increased contact areas and cartilage strains and reduced contact pressures. Reductions in contact stresses and increases in tissue strains and transfer of load via menisci are partly due to the altered kinetics‐kinematics of gait and partly due to deterioration in cartilage‐menisci properties in OA patients. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:69–78, 2014.     

Musculoskeletal loading in the symptomatic and asymptomatic knees of middle‐aged osteoarthritis patients

This study quantified the contributions by muscles, gravity, and inertia to the tibiofemoral compartment forces in the symptomatic (SYM) and asymptomatic (ASYM) limbs of varus mal‐aligned medial knee osteoarthritis (OA) patients, and compared the results with healthy controls (CON). Muscle forces and tibiofemoral compartment loads were calculated using gait data from 39 OA patients and 15 controls aged 49 ± 7 years. Patients exhibited lower knee flexion angle, higher hip abduction, and knee adduction angles, lower internal knee flexion torque but higher external knee adduction moment. Muscle forces were highest in CON except hamstrings, which was highest in SYM. ASYM muscle forces were lowest for biceps femoris short head and gastrocnemius but otherwise intermediate between SYM and CON. In all subjects, vasti, hamstrings, gastrocnemius, soleus, gluteus medius, gluteus maximus, and gravity were the largest contributors to medial compartment force (MCF). Inertial contributions were negligible. Highest MCF was found in SYM throughout stance. Small increases in contributions from hamstrings, gluteus maximus, gastrocnemius, and gravity at the first peak; soleus and rectus femoris at the second peak; and soleus, gluteus maximus, gluteus medius, and gravity during mid‐stance summed to produce significantly higher total MCF. Compared to CON, the ASYM limb exhibited similar peak MCF but higher mid‐stance MCF. In patients, diminished non‐knee‐spanning muscle forces did not produce correspondingly diminished MCF contributions due to the influence of mal‐alignment. Our findings emphasize consideration of muscle function, lower‐limb alignment, and mid‐stance loads in developing interventions for OA, and inclusion of the asymptomatic limb in clinical assessments. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:321–330, 2017.

     

Contribution of tibiofemoral joint contact to net loads at the knee in gait

Inverse dynamics analysis is commonly used to estimate the net loads at a joint during human motion. Most lower‐limb models of movement represent the knee as a simple hinge joint when calculating muscle forces. This approach is limited because it neglects the contributions from tibiofemoral joint contact forces and may therefore lead to errors in estimated muscle forces. The aim of this study was to quantify the contributions of tibiofemoral joint contact loads to the net knee loads calculated from inverse dynamics for multiple subjects and multiple gait patterns. Tibiofemoral joint contact loads were measured in four subjects with instrumented implants as each subject walked at their preferred speed (normal gait) and performed prescribed gait modifications designed to treat medial knee osteoarthritis. Tibiofemoral contact loads contributed substantially to the net knee extension and knee adduction moments in normal gait with mean values of 16% and 54%, respectively. These findings suggest that knee‐contact kinematics and loads should be included in lower‐limb models of movement for more accurate determination of muscle forces. The results of this study may be used to guide the development of more realistic lower‐limb models that account for the effects of tibiofemoral joint contact at the knee. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1054–1060, 2015.     

Greater muscle co‐contraction results in increased tibiofemoral compressive forces in females who have undergone anterior cruciate ligament reconstruction

Individuals who have undergone ACL reconstruction (ACLR) have been shown to have a higher risk of developing knee osteoarthritis (OA). The elevated risk of knee OA may be associated with increased tibiofemoral compressive forces. The primary purpose of this study was to examine whether females with ACLR demonstrate greater tibiofemoral compressive forces, as well as greater muscle co‐contraction and decreased knee flexion during a single‐leg drop‐land task when compared to healthy females. Ten females with ACLR and 10 healthy females (control group) participated. Each participant underwent two data collection sessions: (1) MRI assessment and (2) biomechanical analysis (EMG, kinematics, and kinetics) during a single‐leg drop‐land task. Joint kinematics, EMG, and MRI‐measured muscle volumes and patella tendon orientation were used as input variables into a MRI‐based EMG‐driven knee model to quantify the peak tibiofemoral compressive forces during landing. Peak tibiofemoral compressive forces were significantly higher in the ACLR group when compared to the control group (97.3 ± 8.0 vs. 88.8 ± 9.8 N · kg^?1). The ACLR group also demonstrated significantly greater muscle co‐contraction as well as less knee flexion than the control group. Our findings support the premise that individuals with ACLR demonstrate increased tibiofemoral compression as well as greater muscle co‐contraction and decreased knee flexion during a drop‐land task. Future studies are needed to examine whether correcting abnormal neuromuscular strategies and reducing tibiofemoral compressive forces following ACLR can slow the progression of joint degeneration in this population. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:2007–2014, 2012     

Dynamic loading of the plantar aponeurosis in walking

BACKGROUND: The plantar aponeurosis is known to be a major contributor to arch support, but its role in transferring Achilles tendon loads to the forefoot remains poorly understood. The goal of this study was to increase our understanding of the function of the plantar aponeurosis during gait. We specifically examined the plantar aponeurosis force pattern and its relationship to Achilles tendon forces during simulations of the stance phase of gait in a cadaver model. METHODS: Walking simulations were performed with seven cadaver feet. The movements of the foot and the ground reaction forces during the stance phase were reproduced by prescribing the kinematics of the proximal part of the tibia and applying forces to the tendons of extrinsic foot muscles. A fiberoptic cable was passed through the plantar aponeurosis perpendicular to its loading axis, and raw fiberoptic transducer output, tendon forces applied by the experimental setup, and ground reaction forces were simultaneously recorded during each simulation. A post-experiment calibration related fiberoptic output to plantar aponeurosis force, and linear regression analysis was used to characterize the relationship between Achilles tendon force and plantar aponeurosis tension. RESULTS: Plantar aponeurosis forces gradually increased during stance and peaked in late stance. Maximum tension averaged 96% +/- 36% of body weight. There was a good correlation between plantar aponeurosis tension and Achilles tendon force (r = 0.76). CONCLUSIONS: The plantar aponeurosis transmits large forces between the hindfoot and forefoot during the stance phase of gait. The varying pattern of plantar aponeurosis force and its relationship to Achilles tendon force demonstrates the importance of analyzing the function of the plantar aponeurosis throughout the stance phase of the gait cycle rather than in a static standing position. Clinical Relevance: The plantar aponeurosis plays an important role in transmitting Achilles tendon forces to the forefoot in the latter part of the stance phase of walking. Surgical procedures that require the release of this structure may disturb this mechanism and thus compromise efficient propulsion.     

Analysis of body-device interface forces in the sagittal plane for patients wearing ankle-foot orthoses.

An ankle-foot orthosis (AFO) is employed principally to treat musculoskeletal disorders of the ankle and/or subtalar joints although, occasionally, it may be prescribed to provide stance phase control of the knee. In order to function satisfactorily, an AFO must apply appropriate forces to the lower leg in a manner which does not cause local tissue damage or discomfort. Equally the leg will apply forces to the AFO which it must be capable of withstanding without breakage or loss of function. Thus it is useful to know where the body-device interface forces act during walking and to be able to estimate their magnitudes. This is not well understood and has not been satisfactorily documented. This paper explains the force actions between the AFO and the leg, in the sagittal plane, where there is absence of muscle power. Furthermore, it explores the possibility of estimating the magnitudes of these forces. It is found that the forces are greatest when orthotic assistance is needed to compensate for plantar flexor insufficiency in late stance phase. On the other hand, where the AFO is used to support the foot, in the absence of dorsiflexion power in swing phase, the forces are relatively small. Understanding these force levels is relevant to the design of the AFO in terms of choice and use of materials and components.     

Anti‐gravity treadmills are effective in reducing knee forces

Lower body positive pressure (LBPP) treadmills permit significant unweighting of patients and have the potential to enhance recovery following lower limb surgery. We determined the efficacy of an LBPP treadmill in reducing knee forces in vivo. Subjects, implanted with custom electronic tibial prostheses to measure forces in the knee, were tested on a treadmill housed within a LBPP chamber. Tibiofemoral forces were monitored at treadmill speeds from 1.5 mph (0.67 m/s) to 4.5 mph (2.01 m/s), treadmill incline from ?10° to +10°, and four treadmill chamber pressure settings adjusted to decrease net treadmill reaction force from 100% to 25% of the subject's body weight (BW). The peak axial tibiofemoral force ranged from 5.1 times BW at a treadmill speed of 4.5 mph (2.01 m/s) and a pressure setting of 100% BW to 0.8 times BW at 1.5 mph (0.67 m/s) and a pressure setting of 25% BW. Peak knee forces were significantly correlated with walking speed and treadmill reaction force (R² = 0.77, p = 0.04). The LBPP treadmill might be an effective tool in the rehabilitation of patients following lower‐extremity surgery. The strong correlation between tibiofemoral force and walking speed and treadmill reaction forces allows for more precisely achieving the target knee forces desired during early rehabilitation. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 672–679, 2013     

Functional comparison of posterior cruciate-retained versus cruciate-sacrificed total knee arthroplasty

Gait of 11 patients with bilateral paired posterior cruciate-retaining and cruciate-sacrificing total knee arthroplasties (TKA) was studied preoperatively and two years postoperatively on walking and stair climbing. Five-year clinical and roentgenographic examinations were included in the study. Differences between the two prostheses were noted both in level walking and in stair climbing. On level walking, cruciate-sacrificed TKA had more flexion in loading response and increased flexion and varus moments with increased muscle activity of quadriceps and biceps femoris. Abnormal gaits common to both types of knee were decreased flexion in stance and decreased single-limb stance. Both knees had a stiff-legged gait during stance. On stairs, the cruciate-sacrificed TKA substituted soleus muscle activity for knee stability. The single-limb stance and range of motion were similar for both knees. In clinical terms, the cruciate-sacrificed TKA is less efficient and has greater medial loading and higher joint reaction forces that may affect durability of the prosthesis. The five-year knee scores, patient satisfaction, and roentgenographic examinations were equal for both sets of knees.     

Neuromechanical adaptations during a robotic powered exoskeleton assisted walking session

Objective: To evaluate gait parameters and neuromuscular profiles of exoskeleton-assisted walking under Max Assist condition during a single-session for; (i) able bodied (AB) individuals walking assisted with (EXO) and without (non-EXO) a powered exoskeleton, (ii) non-ambulatory SCI individuals walking assisted with a powered exoskeleton.

Design: Single-session.

Setting: Motion analysis laboratory.

Participants: Four AB individuals and four individuals with SCI.

Interventions: Powered lower extremity exoskeleton.

Outcome Measures: Temporal-spatial parameters, kinematics, walking velocity and electromyography data.

Results: AB individuals in exoskeleton showed greater stance time and a significant reduction in walking velocity (P < 0.05) compared to non-EXO walking. Interestingly, when the AB individuals voluntarily assisted the exoskeleton movements, they walked with an increased velocity and lowered stance time to resemble that of slow walking. For SCI individuals, mean percent stance time was higher and walking velocity was lower compared to all AB walking conditions (P < 0.05). There was muscle activation in several lower limb muscles for SCI group. For AB individuals, there were similarities among EXO and non-EXO walking conditions however there were differences in several lower limb EMGs for phasing of muscle activation.

Conclusion: The data suggests that our AB individuals experienced reduction in walking velocity and muscle activation amplitudes while walking in the exoskeleton and moreover with voluntary control there is a greater temporal-spatial response of the lower limbs. Also, there are neuromuscular phasic adaptions for both AB and SCI groups while walking in the exoskeleton that are inconsistent to non-EXO gait muscle activation.     

Tibiofemoral cartilage contact biomechanics in patients after reconstruction of a ruptured anterior cruciate ligament

We investigated the in vivo cartilage contact biomechanics of the tibiofemoral joint in patients after reconstruction of a ruptured anterior cruciate ligament (ACL). A dual fluoroscopic and MR imaging technique was used to investigate the cartilage contact biomechanics of the tibiofemoral joint during in vivo weight‐bearing flexion of the knee in eight patients 6 months following clinically successful reconstruction of an acute isolated ACL rupture. The location of tibiofemoral cartilage contact, size of the contact area, cartilage thickness at the contact area, and magnitude of the cartilage contact deformation of the ACL‐reconstructed knees were compared with those previously measured in intact (contralateral) knees and ACL‐deficient knees of the same subjects. Contact biomechanics of the tibiofemoral cartilage after ACL reconstruction were similar to those measured in intact knees. However, at lower flexion, the abnormal posterior and lateral shift of cartilage contact location to smaller regions of thinner tibial cartilage that has been described in ACL‐deficient knees persisted in ACL‐reconstructed knees, resulting in an increase of the magnitude of cartilage contact deformation at those flexion angles. Reconstruction of the ACL restored some of the in vivo cartilage contact biomechanics of the tibiofemoral joint to normal. Clinically, recovering anterior knee stability might be insufficient to prevent post‐operative cartilage degeneration due to lack of restoration of in vivo cartilage contact biomechanics. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1781–1788, 2012