The Effect of Surgical Approach and Hip Offset Reconstruction on Gait Biomechanics Following Total Hip Arthroplasty.

BACKGROUND: This study aimed to examine how hip offset (HO) and surgical approach affect gait biomechanics following total hip arthroplasty (THA). METHODS: There were 55 THA patients assigned to 3 groups based on surgical approach (ANT: anterior, LAT: lateral, or POS: posterior) and HO difference (large HO: >5 millimeters (mm), small HO; <5 mm, or normal; between +3 mm and -3 mm). Kinematics and kinetics were recorded using motion capture and force plate data. Group differences were assessed using statistical parametric mapping. RESULTS: The ANT group demonstrated more normal sagittal plane kinematics and kinetics. No frontal plane kinematic differences were found, but the LAT group displayed more normal frontal plane kinetics. The LAT group displayed a slower walking speed than the ANT group, and the LAT and POS groups used a shorter stride/step length than the control group. The large HO group showed fewer differences in sagittal plane kinematics and kinetics than the small HO and normal groups. No frontal plane kinematic differences were observed, but the normal group demonstrated more significant differences than the large HO and small HO groups. No significant differences were found between any of the HO patient groups. CONCLUSION: Anterior and lateral approaches led to more normal gait biomechanics in sagittal kinematics and frontal kinetics, respectively, but only the ANT group exhibited spatiotemporal gait parameters within normal ranges. Hip offset differences greater or less than 5 mm do not significantly change gait patterns. Surgical approach plays a greater role than HO reconstruction in producing more normal gait biomechanics following THA.

Muscle Activity and Biomechanics While Descending a Staircase After Total Knee Arthroplasty: A Study Comparing Different Posterior Stabilized and Medial Ball-and-Socket Designs.

BACKGROUND: Many patients report more difficulty when descending stairs compared to level walking after total knee arthroplasty (TKA). Different implant designs can affect knee biomechanics and muscle activity during gait, but their effect during stair descent is unclear. The purpose of this study was to evaluate knee biomechanics and muscle activations of quadriceps, hamstrings, and gastrocnemius muscles during a stair descent task in patients who underwent TKA with either a posterior stabilized (PS) or medial ball-and-socket (MBS) implant and to compare them to a group of healthy controls. METHODS: There were 28 TKA patients who were randomized to either an MBS (n = 14) or PS (n = 14) implant and were compared with 14 controls. Patients visited the biomechanics lab approximately 12 months after TKA, where knee biomechanics and muscle activity were measured as they descended a 3-step staircase. RESULTS: Compared to the MBS and control groups, the PS group descended the stairs with a reduced knee flexion angle and greater hamstring muscle activation throughout single limb support. Knee joint moments and power were similar between the MBS and PS groups, but neither reached the level of the control group. CONCLUSIONS: Lower knee flexion angles and increased hamstring muscle activity indicated that the PS group descended the stairs with a stiffer knee gait pattern than the MBS group. The MBS implant design may provide additional stability as patients require less muscle activity than the PS group.

Fatigue modifies hip and knee kinematics during single- and double-leg dynamic tasks: An investigation with female handball players.

This study investigated the effect of a handball-specific fatigue protocol on hip and knee kinematics. Twenty female handball athletes performed three trials of the single-leg landing (SLL), sidestep cutting manoeuvre (SCM), and drop vertical jump (DVJ) before and after the fatigue protocol. Knee and hip angle waveforms were compared using statistical parametric mapping (p < 0.05). During the SLL, the fatigue increased hip adduction (4-7% cycle) and knee abduction (4-9% and 25-27%). For the SCM, hip flexion was reduced under fatigue during 14-29% and 44-68% of the cycle. Similarly, the knee flexion decreased between 7-36% and 53-73%. Besides, during the fatigue state, the athletes reduced the hip abduction between 0-11% of the cycle and increased the knee abduction between 20-23%. During the DVJ task, when fatigued, the hip flexion decreased between 19-44% of the cycle and the knee flexion between 1-16% and 18-77%. The fatigue protocol altered the lower limb kinematics, decreasing knee and hip flexions during the SCM and DVJ and increasing the knee valgus during both single-leg landing tasks.

Cam FAI and Smaller Neck Angles Increase Subchondral Bone Stresses During Squatting: A Finite Element Analysis.

BACKGROUND: Individuals with a cam deformity and a decreased (varus) femoral neck-shaft angle may be predisposed to symptomatic femoroacetabular impingement (FAI). However, it is unclear what combined effects the cam deformity and neck angle have on acetabular cartilage and subchondral bone stresses during an impinging squat motion. We therefore used finite element analysis to examine the combined effects of cam morphology and femoral neck-shaft angle on acetabular cartilage and subchondral bone stresses during squatting, examining the differences in stress characteristics between symptomatic and asymptomatic individuals with cam deformities and individuals without cam deformities and no hip pain. QUESTIONS/PURPOSES: Using finite element analysis in this population, we asked: (1) What are the differences in acetabular cartilage stresses? (2) What are the differences in subchondral bone stresses? (3) What are the effects of high and low femoral neck-shaft angles on these stresses? METHODS: Six male participants were included to represent three groups (symptomatic cam, asymptomatic cam, control without cam deformity) with two participants per group, one with the highest femoral neck-shaft angle and one with the lowest (that is, most valgus and most varus neck angles, respectively). Each participant's finite element hip models were reconstructed from imaging data and assigned subject-specific bone material properties. Hip contact forces during squatting were determined and applied to the finite element models to examine maximum shear stresses in the acetabular cartilage and subchondral bone. RESULTS: Both groups with cam deformities experienced higher subchondral bone stresses than cartilage stresses. Both groups with cam deformities also had higher subchondral bone stresses (symptomatic with high and low femoral neck-shaft angle = 14.1 and 15.8 MPa, respectively; asymptomatic with high and low femoral neck-shaft angle = 10.9 and 13.0 MPa, respectively) compared with the control subjects (high and low femoral neck-shaft angle = 6.4 and 6.5 MPa, respectively). The symptomatic and asymptomatic participants with low femoral neck-shaft angles had the highest cartilage and subchondral bone stresses in their respective subgroups. The asymptomatic participant with low femoral neck-shaft angle (123°) demonstrated anterolateral subchondral bone stresses (13.0 MPa), similar to the symptomatic group. The control group also showed no differences between cartilage and subchondral bone stresses. CONCLUSIONS: The resultant subchondral bone stresses modeled here coincide with findings that acetabular subchondral bone is denser in hips with cam lesions. Future laboratory studies will expand the parametric finite element analyses, varying these anatomic and subchondral bone stiffness parameters to better understand the contributions to the pathomechanism of FAI. CLINICAL RELEVANCE: Individuals with a cam deformity and more varus neck orientation may experience elevated subchondral bone stresses, which may increase the risks of early clinical signs and degenerative processes associated with FAI, whereas individuals with cam morphology and normal-to-higher femoral neck-shaft angles may be at lesser risk of disease progression that would potentially require surgical intervention.

How Different Marker Sets Affect Joint Angles in Inverse Kinematics Framework.

The choice of marker set is a source of variability in motion analysis. Studies exist which assess the performance of marker sets when direct kinematics is used, but these results cannot be extrapolated to the inverse kinematic framework. Therefore, the purpose of this study was to examine the sensitivity of kinematic outcomes to inter-marker set variability in an inverse kinematic framework. The compared marker sets were plug-in-gait, University of Ottawa motion analysis model and a three-marker-cluster marker set. Walking trials of 12 participants were processed in opensim. The coefficient of multiple correlations was very good for sagittal (>0.99) and transverse (>0.92) plane angles, but worsened for the transverse plane (0.72). Absolute reliability indices are also provided for comparison among studies: minimum detectable change values ranged from 3 deg for the hip sagittal range of motion to 16.6 deg of the hip transverse range of motion. Ranges of motion of hip and knee abduction/adduction angles and hip and ankle rotations were significantly different among the three marker configurations (P < 0.001), with plug-in-gait producing larger ranges of motion. Although the same model was used for all the marker sets, the resulting minimum detectable changes were high and clinically relevant, which warns for caution when comparing studies that use different marker configurations, especially if they differ in the joint-defining markers.

Increased Hip Stresses Resulting From a Cam Deformity and Decreased Femoral Neck-Shaft Angle During Level Walking.

BACKGROUND: It is still unclear why many individuals with a cam morphology of the hip do not experience pain. It was recently reported that a decreased femoral neck-shaft angle may also be associated with hip symptoms. However, the effects that different femoral neck-shaft angles have on hip stresses in symptomatic and asymptomatic individuals with cam morphology remain unclear. QUESTIONS/PURPOSES: We examined the effects of the cam morphology and femoral neck-shaft angle on hip stresses during walking by asking: (1) Are there differences in hip stress characteristics among symptomatic patients with cam morphology, asymptomatic individuals with cam morphology, and individuals without cam morphology? (2) What are the effects of high and low femoral neck-shaft angles on hip stresses? METHODS: Six participants were selected, from a larger cohort, and their cam morphology and femoral neck-shaft angle parameters were measured from CT data. Two participants were included in one of three groups: (1) symptomatic with cam morphology; (2) asymptomatic with a cam morphology; and (3) asymptomatic control with no cam morphology with one participant having the highest femoral neck-shaft angle and the other participant having the lowest in each subgroup. Subject-specific finite element models were reconstructed and simulated during the stance phase, near pushoff, to examine maximum shear stresses on the acetabular cartilage and labrum. RESULTS: The symptomatic group with cam morphology indicated high peak stresses (6.3-9.5 MPa) compared with the asymptomatic (5.9-7.0 MPa) and control groups (3.8-4.0 MPa). Differences in femoral neck-shaft angle influenced both symptomatic and asymptomatic groups; participants with the lowest femoral neck-shaft angles had higher peak stresses in their respective subgroups. There were no differences among control models. CONCLUSIONS: Our study suggests that the hips of individuals with a cam morphology and varus femoral neck angle may be subjected to higher mechanical stresses than those with a normal femoral neck angle. CLINICAL RELEVANCE: Individuals with a cam morphology and decreased femoral neck-shaft angle are likely to experience severe hip stresses. Although asymptomatic participants with cam morphology had elevated stresses, a higher femoral neck-shaft angle was associated with lower stresses. Future research should examine larger amplitudes of motion to assess adverse subchondral bone stresses.

Does the Dual-Mobility Hip Prosthesis Produce Better Joint Kinematics During Extreme Hip Flexion Task?

BACKGROUND: Total hip arthroplasty (THA) using dual-mobility (DM) design permits larger hip range of motion. However, it is unclear how it benefits the patients during activities of daily living. The purpose was to compare kinematic variables of the operated limb between THA patients using either DM or single-bearing (SB) implants during a squat task. METHODS: Twenty-four THA patients were randomly assigned to either a DM or SB implant and matched to 12 healthy controls (CTRLs). They underwent 3-dimensional squat motion analysis before and 9 months after surgery. Sagittal and frontal plane angles of the pelvis and the hip were analyzed using statistical parametric mapping. Paired analyses compared presurgery and postsurgery squat depth. RESULTS: Peak sagittal pelvis angle of DM was closer to normal compared with that of SB. Both implant groups had similar hip angle patterns and magnitude but significantly lower than the CTRLs. SB reached a much large hip abduction compared with the other groups. Both surgical groups had significantly worst squat depth than the CTRLs. CONCLUSION: Neither THA implant groups were able to return pelvis and hip kinematics to the level of CTRLs. The deficit of DM implants at the pelvis combined with the poorer functional scores should caution clinicians to use this implant design in active patients. SB design causes a larger hip abduction to reach their maximum squat depth. Post-THA rehabilitation should focus on improving joint range of motion and strength.

Patient-specific anatomical and functional parameters provide new insights into the pathomechanism of cam FAI.

BACKGROUND: Femoroacetabular impingement (FAI) represents a constellation of anatomical and clinical features, but definitive diagnosis is often difficult. The high prevalence of cam deformity of the femoral head in the asymptomatic population as well as clinical factors leading to the onset of symptoms raises questions as to what other factors increase the risk of cartilage damage and hip pain. QUESTIONS/PURPOSES: The purpose was to identify any differences in anatomical parameters and squat kinematics among symptomatic, asymptomatic, and control individuals and if these parameters can determine individuals at risk of developing symptoms of cam FAI. METHODS: Forty-three participants (n = 43) were recruited and divided into three groups: symptomatic (12), asymptomatic (17), and control (14). Symptomatic participants presented a cam deformity (identified by an elevated alpha angle on CT images), pain symptoms, clinical signs, and were scheduled for surgery. The other recruited volunteers were blinded and unaware whether they had a cam deformity. After the CT data were assessed for an elevated alpha angle, participants with a cam deformity but who did not demonstrate any clinical signs or symptoms were considered asymptomatic, whereas participants without a cam deformity and without clinical signs or symptoms were considered healthy control subjects. For each participant, anatomical CT parameters (axial alpha angle, radial alpha angle, femoral head-neck offset, femoral neck-shaft angle, medial proximal femoral angle, femoral torsion, acetabular version) were evaluated. Functional squat parameters (maximal squat depth, pelvic range of motion) were determined using a motion capture system. A stepwise discriminant function analysis was used to determine which of the parameters were most suitable to classify each participant with their respective subgroup. RESULTS: The symptomatic group showed elevated alpha angles and lower femoral neck-shaft angles, whereas the asymptomatic group showed elevated alpha angles in comparison with the control group. The best discriminating parameters to determine symptoms were radial alpha angle, femoral neck-shaft angle, and pelvic range of motion (p < 0.001). CONCLUSIONS: In the presence of a cam deformity, indications of a decreased femoral neck-shaft angle and reduced pelvic range of motion can identify those at risk of symptomatic FAI.

Knee biomechanics variability before and after total knee arthroplasty: an equality of variance prospective study.

This study evaluated gait variability in patients before and after total knee arthroplasty (TKA) using the equality of variance method to determine where variability differences occur in the movement cycle. Twenty-eight patients underwent TKA with cruciate-sacrificed implants. Patients underwent motion analysis which measured knee biomechanics as they walked overground at their preferred pace before and 12 months after TKA. Equality of variance results were compared with 14 healthy controls of similar age. Before surgery, patients had reduced knee extension moment variability throughout the early stance phase (4-21% gait cycle, p < 0.05) compared to controls. Knee power variability was lower preoperatively compared to controls for most of the stance phase (0-13% and 17-60% gait cycle, p < 0.05). Sagittal knee moment and power variability further decreased following TKA. Knee extension moment variability was lower postoperatively throughout stance phase compared to preoperatively (4-22% and 36-60% gait cycle, p < 0.05) and compared to controls (4-30% and 45-60% gait cycle, p < 0.05). Knee power variability remained lower following TKA throughout stance phase compared to preoperatively (10-24% and 36-58% gait cycle, p < 0.05) and controls (3-60% gait cycle, p < 0.05). TKA patients may be less stable, and this may be in part due to an unresolved adaptation developed while awaiting TKA surgery and the cruciate sacrificing design of the implants utilized in this study.

On the prediction of tibiofemoral contact forces for healthy individuals and osteoarthritis patients during gait: a comparative study of regression methods.

Knee osteoarthritis (OA) is a public health problem affecting millions of people worldwide. The intensity of the tibiofemoral contact forces is related to cartilage degeneration, and so is the importance of quantifying joint loads during daily activities. Although simulation with musculoskeletal models has been used to calculate joint loads, it demands high-cost equipment and a very time-consuming process. This study aimed to evaluate consolidated machine learning algorithms to predict tibiofemoral forces during gait analysis of healthy individuals and knee OA patients. Also, we evaluated three different datasets to train each model, considering different combinations of primary kinematic and kinetic data, and post-processing data. We evaluated 14 patients with severe unilateral knee OA and 14 healthy individuals during 3-5 gait trials. Data were split into 70% and 30% of the samples as training and test data. Test data was independently evaluated considering a mixture of pathological and healthy individuals, and only OA and Control patients. The main results showed that accurate predictions of the tibiofemoral contact forces were achieved using machine learning methods and that the predictions were sensitive to changes in the input data as training. The present study provided insights into the most promising regressions methods to predict knee contact forces representing an important starting point for the broader application of biomechanical analysis in clinical environments.

Motion analysis, cartilage mechanics, and biology in femoroacetabular impingement: current understanding and areas of future research.

The effect and interplay of pathomorphology and joint kinematics is increasingly recognized as important in the study of femoroacetabular impingement (FAI). Hip joint kinematics consists of motion analysis at the macroscopic hip joint level. Although overall joint morphology and subject-specific kinematics are important, the cellular mechanobiology of cartilage and the biologic response to cartilage injury are poorly understood and require further study if surgeons are to understand how tissue damage actually occurs. A clearer understanding of these factors may provide the foundation for new treatments that could alter the joint injury associated with FAI. The purpose of this study group was to discuss the current evidence regarding the interaction of hip joint motion, cartilage mechanics, and cartilage biology with FAI and determine future priorities for research in these areas to expand the surgeon's ability to understand and manage this increasingly recognized clinical entity. Specific research needs were identified in four areas: motion analysis (how do muscle contributions to joint loading influence the disease process?), arthrokinematics (what happens at the joint level in vivo?), cartilage mechanics (how do cartilage cells respond to different mechanical stimuli?), and cartilage biology (need to identify biomarkers for cartilage degradation).

Does the anterior approach for THA provide closer-to-normal lower-limb motion?

The purpose of this study was to compare the muscle-sparing anterior approach for total hip arthroplasty to a traditional lateral approach using 3D motion analysis. Kinematics and kinetics of walking were obtained for 40 patients (20 anterior and 20 lateral) and 20 control participants. Participants were assessed six to twelve months postoperatively. It was hypothesized that the anterior group would have closer-to-normal range of motion, moments, and powers than the lateral group. Both surgical groups had gait anomalies, such as significantly lower peak hip abduction moments. It is therefore thought that other variables such as preoperative gait adaptations, trauma from the surgery, or postoperative protection mechanisms for avoiding loading the prosthesis might be more influential factors than surgical approach when determining function after surgery.

The biomechanics of vertical hopping: a review.

Repetitive vertical hopping is a simple and relatively controlled task useful for studying basic neuromuscular properties and tissue mechanics. However, several biomechanical and physiological factors are involved. This article provides an overview of muscle and tendon properties and how these interact during vertical hopping. Muscle properties discussed are force-velocity and force-length relationships, electromechanical delay, muscle fiber type, stretch induced contraction amplification, and muscle spindle afferent feedback. Tendon properties include storage and reuse of elastic energy, tendon stiffness, afferent information from Golgi tendon organs, and failure points. These muscle and tendon properties interact to generate vertical hopping force and power. In addition to these basic properties, there are other more complicated factors to consider when analyzing vertical hopping such as balance and coordination. A wealth of information can be gathered by studying vertical hopping. Caution should be taken, however, to prevent inappropriate conclusions being drawn about hop performance due to oversimplification.

Comparing three generic musculoskeletal models to estimate the tibiofemoral reaction forces during gait and sit-to-stand tasks.

The choice of musculoskeletal (MSK) model is crucial for performing MSK estimations to evaluate muscle demands and joint forces. This study compared two previously published generic MSK models and a modified model to estimate tibiofemoral reaction forces (TFRF) during gait, sit-to-stand, and stand-to-sit. The estimated tibiofemoral reaction forces were compared with an in vivo dataset from six patients using an instrumented knee prosthesis. A correlation and root mean square error (RMSE) in the time-series analysis and relative peak error (RPE) were evaluated. The results showed that the three MSK models were similar in estimating the vertical forces, with a large correlation, and RPE was found around 20 % during gait. The RMSE and the RPE indicated that the modified model had lower total and lateral compartment forces errors for sit-to-stand and stand-to-sit, showing the best performance. The shear forces for all tasks and models showed significant errors. Future MSK studies should consider these findings when researching functional tasks. The modified model was found to be more effective in estimating the vertical tibiofemoral joint reaction forces in tasks that impose greater demands on muscle forces and require high knee and hip flexion.

Gait variability between younger and older adults: An equality of variance analysis.

BACKGROUND: To estimate gait variability, several methods have been routinely used which provide a measure of global variability. A recent study introduced a group waveform variability method which provides a point-by-point measurement of data variance equality. This can identify where in the gait cycle the significant differences in variability exist. RESEARCH QUESTION: Do waveform differences exist in equality of variance and group means in lower limb biomechanical variables between healthy younger and older adults during a gait task? METHODS: Twenty healthy younger (19-44 years old, age=29.9(7.0) years, body mass index= 24.6(3.2)kg/m2, females= 10) and 20 healthy older (55-79 years old, age=63.6(5.5) years, body mass index= 25.9(2.7)kg/m2, females= 10) adults who were free from lower limb injuries and had no musculoskeletal or neurological disorders. Temporospatial outcomes, sagittal and frontal lower limb joint angles and moments, along with joint powers were examined as participants walked at a self-selected pace. Waveform patterns were normalized to the gait cycle and compared using equality of variance and statistical parametric mapping techniques. RESULTS: No difference in walking speed existed between the younger or older groups (P > .05). The older group had greater variability (P < .05) in sagittal hip angles, as well as greater frontal ankle angle and moment variability. The younger group had significantly greater mean (P < .05) ankle power generation prior to toe-off. SIGNIFICANCE: This study provided a baseline of temporal differences in variance between healthy younger and older individuals. Its findings warrant the use of the equality of variance test to compare temporal differences for a variety of populations and tasks. Older adults generally had more variability than the younger adults, with many differences occurring near the transition from double- to single-limb support. The statistical parametric mapping analysis showed that the older adults could not generate as much ankle power as the younger adults prior to toe-off.

Lower limb inter-joint coordination in individuals with osteoarthritis before and after a total knee arthroplasty.

BACKGROUND: Total knee arthroplasty is the most common treatment for severe knee osteoarthritis. Coordination and variability analyses are effective measures of the injury stage or rehabilitation process. This study compared the inter-joint coordination before and after arthroplasty, compared to controls. METHODS: Twenty-seven patients were evaluated before and 12 months after surgery, compared to 27 controls. Coordination and variability in the sagittal plane between the hip-knee and knee-ankle were calculated using vector coding and circular statistics. Coordination was categorized as in-phase, anti-phase, or distal or proximal joint-phase. The gait cycle was divided into sub-phases for the coordination, variability, and range of motion results. FINDINGS: Coordination and range of motion differed significantly between the patient groups and controls, while small differences between pre- and post-operative groups were also detected. The hip-knee showed a reduced in-phase frequency in the patient group compared to control during stance, particularly mid-stance: pre-operative 24.3% ± 33.9, post-operative 29.5 ± 29.7, and controls 70.7 ± 17.0. This difference was compensated for by increasing proximal-phase (hip) frequency in the patient groups. For knee-ankle coordination, the patient groups showed higher distal-phase (ankle) frequency during the early and mid-stance. Coordination variability was higher post-operatively during swing and terminal swing phases, compared to controls. INTERPRETATION: The results indicated reduced degrees of freedom for the knee during stance phase with a reduced capacity to move the knee and hip in opposing directions before and one year after surgery. The patient group after the surgery increased knee range of motion and coordination compared to pre-operative during swing phase.

Evaluation of Knee Kinematics and Moments during Active Deep Flexion Activity after Oxford Mobile-Bearing Medial UKA-A Two-Year Follow-Up Study.

Few studies have assessed knee range of motion (ROM) and moments of patients with mobile-bearing unicompartmental knee arthroplasty (MB UKA) during active deep flexion activities. We analyze knee kinematic and kinetic parameters during postoperative squatting-standing activity, aiming to evaluate the efficacy of MB UKA and postoperative rehabilitation progress. This was a clinical cohort study. We followed up with 37 patients diagnosed with medial knee osteoarthritis (OA) with primary UKA. After screening 31 patients were recruited to take gait tests. Squatting-standing activities were performed under the test of 10-camera motion analysis system and force plates preoperatively at different stages after UKA (12, 18, and 24 months). The average duration of follow-up was 24.4 months (from 22.8 to 26.7 months). Hip-knee-ankle angle improved significantly compared with pre-UKA as well as scores of American Knee Society Score, numeric rating scale, ORS, and Western Ontario and McMasters. University Osteoarthritis Index. About 83.6% (31/37) of follow-up patients completed squatting-standing activity independently. At 1-year follow-up, peak varus angle (20.6 ± 2.8 degrees), internal rotation angle (13.6 ± 1.8 degrees), extensor moment (1.44 ± 0.04N*m/kg), and internal rotator moment (0.02 ± 0.005N*m/kg) of UKA knees were inferior to contralateral knees. Peak adductor moment (0.76 ± 0.05N*m/kg) was superior to contralateral knees. At 2-year follow-up, peak flexion angle (125.0 ± 2.8 degrees) showed a growing trend meanwhile extensor (1.70 ± 0.03N*m/kg) and adductor (0.68 ± 0.06 N*m/kg) moment closely resembled those of the contralateral knee. MB UKA could alleviate the affected knee mainly in flexion-extension ROM and moment meanwhile did not affect the biomechanical indicators of healthy limbs. OA knees in the early postoperative period showed decreased extensor moment and increased adductor moment during active deep flexion activity. Better ROM and relatively more natural extensor and adductor moment of UKA knee with rehabilitation time increasing may predict ideal rehabilitation outcome in the medium or longer term.

A waveform test for variance inequality, with a comparison of ground reaction force during walking in younger vs. older adults.

Various methods have been suggested for estimating the variability in biomechanical variables during gait. However, all current measures of variability are performed on discrete measurements extracted from the kinematic or kinetic waveforms, which provide no temporal information on where differences in variability occur. This study used a variance equality test to compare temporal differences in group variance along the entire ground reaction force waveform. The variance equality test used an F-statistic whose critical value was determined using the random field theory function within the one-dimensional statistical parametric mapping package. Twenty healthy younger and twenty older adults were included in the study and completed gait analysis as they walked along a level walkway at a self-selected pace. Variance for each group was calculated and compared at each interval along the waveform to produce the F-value. The F-value was compared against a calculated F-critical value to determine where in the waveform significant differences in ground reaction force variance occurred. Results suggest that younger individuals may exhibit greater ground reaction force variance during heel contact in the vertical and posterior directions, and that older individuals may exhibit greater variability in the mediolateral direction at toe-off. This study was able to identify differences in ground reaction force variance within the gait cycle between younger and older adults. The findings of this study warrant the use of the function as a suitable method to compare variance along the entire waveform between two groups.

Comparing the Accuracy of Visual and Computerized Onset Detection Methods on Simulated Electromyography Signals with Varying Signal-to-Noise Ratios.

Electromyography (EMG) onsets determined by computerized detection methods have been compared against the onsets selected by experts through visual inspection. However, with this type of approach, the true onset remains unknown, making it impossible to determine if computerized detection methods are better than visual detection (VD) as they can only be as good as what the experts select. The use of simulated signals allows for all aspects of the signal to be precisely controlled, including the onset and the signal-to-noise ratio (SNR). This study compared three onset detection methods: approximated generalized likelihood ratio, double threshold (DT), and VD determined by eight trained individuals. The selected onset was compared against the true onset in simulated signals which varied in the SNR from 5 to 40 dB. For signals with 5 dB SNR, the VD method was significantly better, but for SNRs of 20 dB or greater, no differences existed between the VD and DT methods. The DT method is recommended as it can improve objectivity and reduce time of analysis when determining EMG onsets. Even for the best-quality signals (SNR of 40 dB), all the detection methods were off by 15-30 ms from the true onset and became progressively more inaccurate as the SNR decreased. Therefore, although all the detection methods provided similar results, they can be off by 50-80 ms from the true onset as the SNR decreases to 10 dB. Caution must be used when interpreting EMG onsets, especially on signals where the SNR is low or not reported at all.

Muscle and Hip Contact Forces in Asymptomatic Men With Cam Morphology During Deep Squat.

Cam morphology is defined as an aspherical femoral head-neck junction that causes abnormal contact of the acetabular rim with the anterior hip. Imaging confirmation of the cam morphology, associated with clinical signs and pain in the hip or groin, is characterized as femoroacetabular impingement (FAI) syndrome. Although some individuals with cam morphology do not experience any symptoms, sparse studies have been done on these individuals. Understanding the way asymptomatic individuals generate muscle forces may help us to better explain the progression of the degenerative FAI process and discover better ways in preventing the onset or worsening of symptoms. The purpose of this study was to compare the muscle and hip contact forces of asymptomatic cam morphology (ACM) and FAI syndrome men compared to cam-free healthy controls during a deep squat task. This prospective study compared 39 participants, with 13 in each group (ACM, FAI, and control). Five deep squatting trials were performed at a self-selected pace while joint trajectories and ground reaction forces were recorded. A generic model was scaled for each participant, and inverse kinematics and inverse dynamics calculated joint angles and moments, respectively. Muscle and hip contact forces were estimated using static optimization. All variables were time normalized in percentage by the total squat cycle and both muscle forces and hip contact forces were normalized by body weight. Statistical non-parametric mapping analyses were used to compare the groups. The ACM group showed increased pelvic tilt and hip flexion angles compared to the FAI group during the descent and ascent phases of the squat cycle. Muscle forces were greater in the ACM and control groups, compared to the FAI group for the psoas and semimembranosus muscles. Biceps femoris muscle force was lower in the ACM group compared to the FAI group. The FAI group had lower posterior hip contact force compared to both the control and ACM groups. Muscle contraction strategy was different in the FAI group compared to the ACM and control groups, which caused different muscle force applications during hip extension. These results rebut the concept that mobility restrictions are solely caused by the presence of the cam morphology and propose evidence that symptoms and muscle contraction strategy can be the origin of the mobility restriction in male patients with FAI.