Influence of graft type on sagittal plane knee biomechanics during stair ambulation following anterior cruciate ligament reconstruction

BackgroundBoth graft type and surgical technique for anterior cruciate ligament reconstruction can affect knee biomechanics. Several studies reported the influence of graft type, but few have controlled the surgical technique and fully investigated stair ambulation. This study aimed to compare knee biomechanics during stair ambulation between patients treated with hamstring tendon graft and those treated with patellar tendon graft when anterior medial portal technique was used to drill femoral tunnel.MethodsTwo groups of patients (patellar tendon, n = 18; hamstring tendon, n = 18) at average 12 months after reconstruction surgery were recruited to ascend and descend a customized staircase in a gait lab. Joint kinematics and kinetics were calculated for both operated and contralateral intact limbs based on kinematic analysis and inverse dynamics. The influence of graft type on knee flexion angle and moment was identified using one-way mixed (graft type and limb side) analysis of variance with post-hoc paired t-test.FindingsSignificant interaction between graft and limb was found for knee flexion and range of motion. Only the hamstring tendon group had significant kinematic deficits on the operated limb than the contralateral limb during stair ascent and descent. No significant interaction was found for knee flexion moment. Both graft groups had significant deficits in peak knee flexion moment on the operated side during stair ascent and descent.InterpretationWhile the choice of graft type does not affect the restoration of knee dynamic loading, patellar tendon graft better restores knee flexion-extension kinematics during stair ambulation.     

Biomechanical compensations of the trunk and lower extremities during stepping tasks after unilateral transtibial amputation

BackgroundLower extremity movement compensations following transtibial amputation are well-documented and are likely influenced by trunk posture and movement. However, the biomechanical compensations of the trunk and lower extremities, especially during high-demand tasks such as step ascent and descent, remain unclear.MethodsKinematic and kinetic data were collected during step ascent and descent tasks for three groups of individuals: diabetic/transtibial amputation, diabetic, and healthy. An ANCOVA was used to compare peak trunk, hip and knee joint angles and moments in the sagittal and frontal planes between groups. Paired t-tests were used to compare peak joint angles and moments between amputated and intact limbs of the diabetic/transtibial amputation group.FindingsDuring step ascent and descent, the transtibial amputation group exhibited greater trunk forward flexion and lateral flexion compared to the other two groups (P < 0.016), which resulted in greater low back moments and asymmetric loading patterns in the lower extremity joints. The diabetic group exhibited similar knee joint loading patterns compared to the amputation group (P < 0.016), during step descent.InterpretationThis study highlights the biomechanical compensations of the trunk and lower extremities in individuals with dysvascular transtibial amputation, by identifying low back, hip, and knee joint moment patterns unique to transtibial amputation during stepping tasks. In addition, the results suggest that some movement compensations may be confounded by the presence of diabetes and precede limb amputation. The increased and asymmetrical loading patterns identified may predispose individuals with transtibial amputation to the development of secondary pain conditions, such as low back pain or osteoarthritis.     

Trunk kinetic effort during step ascent and descent in patients with transtibial amputation using angular momentum separation

BackgroundPatients with transtibial amputation adopt trunk movement compensations that alter effort and increase the risk of developing low back pain. However, the effort required to achieve high-demand tasks, such as step ascent and descent, remains unknown.MethodsKinematics were collected during bilateral step ascent and descent tasks from two groups: 1) seven patients with unilateral transtibial amputation and 2) seven healthy control subjects. Trunk kinetic effort was quantified using translational and rotational segmental moments (time rate of change of segmental angular momentum). Peak moments during the loading period were compared across limbs and across groups.FindingsDuring step ascent, patients with transtibial amputation generated larger sagittal trunk translational moments when leading with the amputated limb compared to the intact limb (P = 0.01). The amputation group also generated larger trunk rotational moments in the frontal and transverse planes when leading with either limb compared to the healthy group (P = 0.01, P < 0.01, respectively). During step descent, the amputation group generated larger trunk translational and rotational moments in all three planes when leading with the intact limb compared to the healthy group (P < 0.017).InterpretationThis investigation identifies how differing trunk movement compensations, identified using the separation of angular momentum, require higher kinetic effort during stepping tasks in patients with transtibial amputation compared to healthy individuals. Compensations that produce identified increased and asymmetric trunk segmental moments, may increase the risk of the development of low back pain in patients with amputation.     

The use of a lateral wedge insole to reduce knee loading when ascending and descending stairs in medial knee osteoarthritis patients

Background

Stair climbing is a challenging task to the elderly being the task with the first complaint in patients with mild to moderate knee osteoarthritis. Stair climbing results in around six times more compressive load transmitted through the knee joint than walking on level ground. The purpose of this study was to assess whether lateral wedge insoles would reduce medial compartment knee loading when ascending and descending stairs in patients with medial knee osteoarthritis.

Methods

Eight patients with medial knee osteoarthritis were tested in random order with and without a pair of 5° off-the-shelf lateral wedge insoles for two separate activities (stair ascent and stair descent). Kinematic and kinetic data were collected for the lower extremity using a sixteen camera motion capture system and two force plates. Primary outcome measures were the external knee adduction moment and the knee adduction angular impulse.

Findings

During stair ascent and descent, lateral wedge insoles significantly (P < 0.05) reduced the 1st peak external knee adduction moment in early stance (ascent 6.8%, descent 8.4%), the trough in mid stance (ascent 13%, descent 10.7%), 2nd peak in the late stance (ascent 15%, descent 8.3%) and the knee adduction angular impulse compared to the control (standard shoe) with large effect sizes (0.75–0.95).

Interpretation

In this first study on stairs, lateral wedge insoles consistently reduced the overall magnitude of medial compartment loading during stair ascent and descent. Further research is needed to determine the relationship of this with clinical results when ascending and descending stairs with lateral wedge insoles.     

Interface pressure in transtibial socket during ascent and descent on stairs and its effect on patient satisfaction

BackgroundTranstibial amputees encounter stairs and steps during their daily activities. The excessive pressure between residual limb/socket may reduce the walking capability of transtibial prosthetic users during ascent and descent on stairs. The purposes of the research were to evaluate the interface pressure between Dermo (shuttle lock) and Seal-In X5 (prosthetic valve) interface systems during stair ascent and descent, and to determine their satisfaction effects on users.MethodsTen amputees with unilateral transtibial amputation participated in the study. Interface pressure was recorded with F-socket transducer (9811E) during stair ascent and descent at self-selected speed. Each participant filled in a questionnaire about satisfaction and problems encountered with the use of the two interface systems.FindingsThe resultant mean peak pressure (kPa) was significantly lower for the Dermo interface system compared to that of the Seal-In X5 interface system at the anterior, posterior and medial regions during stair ascent (63.14 vs. 80.14, 63.14 vs. 90.44, 49.21 vs. 66.04, respectively) and descent (67.11 vs. 80.41, 64.12 vs. 88.24, 47.33 vs. 65.11, respectively). Significant statistical difference existed between the two interface systems in terms of satisfaction and problems encountered (P < 0.05).InterpretationThe Dermo interface system caused less pressure within the prosthetic socket compared to the Seal-In X5 interface system during stair negotiation. The qualitative survey also showed that the prosthesis users experienced fewer problems and increased satisfaction with the Dermo interface system.     

Hip, knee, ankle kinematics and kinetics during stair ascent and descent in healthy young individuals

BACKGROUND: Few studies have reported the biomechanical aspects of stair climbing for this ergonomically demanding task. The purpose of this ethically approved study was to identify normal functional parameters of the lower limb during stair climbing and to compare the actions of stair ascent and descent in young healthy individuals. METHODS: Thirty-three young healthy subjects, (16 M, 17 F, range 18-39 years) participated in the study. The laboratory staircase consisted of four steps (rise height 18 cm, tread length 28.5 cm). Kinematic data were recorded using 3D motion analysis system. Temporal gait cycle data and ground reaction forces were recorded using a force platform. Kinetic data were standardized to body mass and height. FINDINGS: Paired-samples t tests showed significantly greater hip and knee angles (mean difference standard deviation (SD): hip 28.10 degrees (SD 4.08), knee 3.39 degrees (SD 7.20)) and hip and knee moments (hip 0.25 Nm/kg (SD 0.18), knee 0.17 Nm/kg (SD 0.15)) during stair ascent compared to descent. Significantly greater ankle dorsiflexion angles (9.90 degrees (SD 3.80)) and plantarflexion angles (8.78 degrees (SD 4.80)) were found during stair descent compared to ascent. Coefficient of variation (mean (SD)) in percentage between repeated tests varied for joint angles and moments, respectively (2.35% (SD 1.83)-17.53% (SD 13.62)) and (4.65% (SD 2.99)-40.73% (SD 24.77)). INTERPRETATION: Stair ascent was shown to be the more demanding biomechanical task when compared to stair descent for healthy young subjects. The findings from the current study provide baseline measures for pathological studies, theoretical joint modelling, and for mechanical joint simulators.     

Delayed onset of quadriceps activity and altered knee joint kinematics during stair stepping in individuals with knee osteoarthritis

OBJECTIVE: To determine if the electromyographic onset of vastus lateralis and kinematic knee joint motion in individuals with knee osteoarthritis (OA) differs from that of asymptomatic persons, during the task of stair stepping. DESIGN: Cross-sectional. SETTING: University laboratory in Australia. PARTICIPANTS: Twenty-five participants with symptomatic knee OA and 33 asymptomatic controls. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Surface electromyography to determine the onset of vastus lateralis activity. Two-dimensional kinematic analysis of sagittal plane knee motion during stance phase of stair ascent and descent. RESULTS: Participants with knee OA showed delayed onset of vastus lateralis activity during stair descent (P<.05) but not ascent. Both groups displayed a similar total range of knee motion. However, during stair descent, participants with OA had less knee flexion during early stance (P<.05) than controls. CONCLUSION: Individuals with knee OA display altered quadriceps function and knee joint kinematics during stair descent. These impairments may have implications for force attenuation across the knee joint and warrant future investigation.     

Lead limb loading during a single-step descent in persons with and without a transtibial amputation in the trailing limb

BackgroundDecreased mechanical work done by the trailing limb when descending a single-step could affect load development and increase injury risk on the leading limb. This study assessed the effect of trailing limb mechanics on the development of lead limb load during a step descent by examining individuals with unilateral transtibial amputations who are known to exhibit reduced work in the prosthetic limb.MethodsEight amputees and 10 able-bodied controls walked 5 m along the length of a raised platform, descended a single-step of 14 cm height, and continued walking. The intact limb of amputees led during descent. Kinematic and kinetic data were recorded using integrated motion capture and force platform system. Lead limb loading was assessed through vertical ground reaction force, and knee moments and joint reaction forces. Sagittal-plane joint work was calculated for the ankle, knee, and hip in both limbs.FindingsNo differences were found in lead limb loading despite differences in trail limb mechanics evidenced by amputees performing 58% less total work by the trailing (prosthetic) limb to lower the centre of mass (P = 0.004) and 111% less for propulsion (P < 0.001). Amputees descended the step significantly slower (P = 0.003) and performed significantly greater lead limb ankle work (P = 0.017). After accounting for speed differences, initial loading at the knee was significantly higher in the lead limb of amputees versus controls.InterpretationIncreasing lead limb work and reducing forward velocity may be effective compensatory strategies to limit lead limb loading during a step descent, in response to reduced trailing limb work.     

Effect of trunk inclination on lower limb joint and lumbar moments in able men during the stance phase of gait

Background

Though the effect of imposed trunk posture affects walking patterns little is known about the effect of natural orientation of the trunk on gait. The objectives of this study are to test if the lower limb joint and thoraco-lumbar moments are similar in subjects who maintain an average natural forward or backward trunk inclination during gait and verify if the lower limbs are equally affected.

Methods

Twenty-five young men were divided according to their natural backward or forward trunk inclination during level walking. Ankle, knee, hip and thoraco-lumbar moments were calculated by an inverse dynamic approach for the two limbs. A two-way ANOVA was performed on peak lower limb moments. A one-way ANOVA was performed on thoraco-lumbar peak moments.

Findings

There was a main effect for both trunk inclinations and lower limb sides but no interaction. For the forward leaners, the duration of hip extension moment was longer (P < 0.001) while the hip flexion moment was 1.3 times smaller (P < 0.001). Differences between the lower limb sides were noted in all joints but at push-off of the stance phase only. The two thoraco-lumbar extension moments were, respectively, 1.4 times higher for the forward leaners while the two flexion moments were approximately 1.4 times higher for the backward leaners.

Interpretations

The backward leaners propel themselves with a strong hip flexor activity at push-off while the forward leaners use their hip muscles throughout stance. These results support the idea that trunk inclinations and moment variations are associated with the type of walking patterns.     

Pre- and postoperative in silico biomechanics in individuals with cam morphology during stair tasks

BackgroundOsteochondroplasty for cam femoroacetabular impingement is a common treatment to improve hip function and prevent joint degeneration. The purpose was to compare in-silico hip biomechanics during stair tasks in pre- and postoperative patients matched with healthy controls.MethodsTen symptomatic cam femoroacetabular impingement patients performed stair ascent and descent pre- and 2 years postoperatively. Patients were age, and body-mass-index matched to controls. Full-body kinematics and kinetics were computed and, muscle and hip contact forces were estimated using musculoskeletal modeling and static optimization. Stance-phases were time-normalized and compared using statistical non-parametric mapping.FindingsPreoperatives showed lower hip abduction than controls during stairs ascent (76–100%, P = .007). Pre- and postoperative showed lower hip external rotation compared to controls on stair ascent (Pre-op vs controls: 71–100%, P = .005; Post-op vs controls: 72–100%, P = .01) and stair descent (Pre-op vs controls: 0–62%, P = .001; Post-op vs controls: 0–60%, P = .001). Postoperatives showed lower iliacus force compared to preoperative (1–3%, P = .012) and control (3–6%, P = .008), and higher gluteus maximus and piriformis forces compared to controls during stair descent. Lower postoperative anterior hip contact force (0–7%, P = .004) during descent, and superior (33–35%, P = .018) during ascent compared to controls were observed. Postoperative contact forces were medialized compared to preoperative (0–2%, P = .011) and controls (1–2%, P = .016).InterpretationForcing participants to adhere to standardized step length/rise minimized sagittal kinematic differences between conditions and groups. Persistent reduced hip external rotation postoperatively and minor muscle force adaptations led to reduced superior hip contact force during stair ascent and reduced anterior and more medialized contact forces during stair descent.     

Gait analysis after bi-compartmental knee replacement

Background

It is reported that a majority of the patients with knee osteoarthritis have cartilage degeneration in medial and patellofemoral compartments. A bi-compartmental knee replacement system was designed to treat osteoarthritis at medial and patellofemoral compartments. To date, there is very little information regarding the knee mechanics during gait after bi-compartmental knee replacement. The purpose of the study was to evaluate knee strength and mechanics during level walking after knee replacement.

Methods

Ten healthy control subjects and eight patients with unilateral bi-compartmental knee replacement participated in the study. Maximal isokinetic concentric knee extension strength was evaluated. 3D kinematic and kinetic analyses were conducted for level walking. Paired Student t-test was used to determine difference between surgical and non-involved limbs. One way MANOVA was used to determine difference between surgical and control groups.

Findings

The surgical knee exhibited less peak torque and initial abduction moment than both the non-involved and control limbs (P < 0.05). The non-involved limb had less knee extension at stance and greater knee extensor moment during push-off than both the surgical and control limbs (P < 0.05). No differences were found for other typical knee mechanics among the surgical, non-involved, and control limbs during walking (P > 0.05).

Interpretations

Patients with bi-compartmental knee replacement exhibited good frontal plane knee mechanics and were able to produce the same level of knee extensor moment as healthy control limbs during walking. While showing some compensatory patterns during walking, patients with bi-compartmental knee replacement largely exhibited normal gait patterns and knee mechanics.     

Knee joint moments during stair climbing of patients with anterior cruciate ligament deficiency

OBJECTIVE: To establish the gait adaptations of patients with anterior cruciate ligament deficiency during stair ascent. DESIGN: Joint kinematics and kinetics during stair climbing were measured in both knees of normal subjects and unilateral anterior cruciate ligament deficient patients. BACKGROUND: As there is limited research pertaining to activities other than level walking, the purpose of the current study was to elucidate the gait of patients with anterior cruciate ligament deficiency during stair climbing to determine the effects of the deficiency on knee joint motion and moments as compared with normal knee function. METHODS: A motion analysis system was used to measure and calculate kinematic and kinetic data for six normal subjects and nine patients with unilateral anterior cruciate ligament deficiency during stair ascent on a specially constructed staircase. Left and right leg data were analysed to reveal between-limb differences for each subject. RESULTS: Patients with anterior cruciate ligament deficiency displayed a significant (P < 0.05) reduction of up to 50% in peak knee flexion moments in their involved knee. In the present study where a step height of 15.5 cm was used, peak flexion moments in all subjects' limbs occurred at knee flexion angles of about 40 degrees during single limb support. CONCLUSION: The current study showed that most patients with an anterior cruciate deficient knee adapted their gait during stair ascent. RELEVANCE: As stair climbing is a common activity, its effect on gait is relevant to better understand appropriate treatment and management strategies of patients with anterior cruciate ligament deficient knees.     

Individual joint contributions to the total support moment during the sit-to-stand task differentiate mild and moderate knee osteoarthritis

BackgroundKnee osteoarthritis tends to modify the kinematics and kinetics of the sit-to-stand task. However, it is not clear whether the different degrees of knee osteoarthritis differentiate regarding these aspects. The objective was to identify if the trunk flexion, lower limb kinetics, total support moment, and individual joint contributions to the total support moment during the sit-to-stand task are different between patients with mild and moderate knee osteoarthritis.MethodsSixty-two participants were grouped as follows: moderate knee osteoarthritis (n = 16), mild knee osteoarthritis (n = 25), and controls (n = 21). The participants performed a sit-to-stand task, which was analyzed using a 3D-motion system and a force plate.FindingsThe three phases of the sit-to-stand task were analyzed. During Phase₁, the moderate osteoarthritis group decreased the total support moment (P = 0.012). During Phase₂, the moderate osteoarthritis group showed higher trunk flexion (P = 0.023) and lower internal hip and knee extension moments (P ≤ 0.001 and P ≤ 0.040, respectively) when compared to controls. Also in Phase₂, both the mild and moderate groups used lower total support moment (P = 0.019, and P ≤ 0.001, respectively). When compared to the controls and mild osteoarthritis group_, those with moderate osteoarthritis presented higher hip joint contribution to the total support moment (P ≤ 0.001 and P = 0.006, respectively) as well as lower knee joint contribution (P ≤ 0.003 and P = 0,013, respectively).InterpretationThose with moderate osteoarthritis showed modified sit-to-stand movement pattern. While in Phase₃ a higher contribution of the hip joint to the total support moment was observed, during previous phases the individuals were able to decrease the load on the knee without influencing the lower limb load distribution.     

The role of knee joint moments and knee impairments on self-reported knee pain during gait in patients with knee osteoarthritis

BackgroundThe association between high mechanical knee joint loading during gait with onset and progression of knee osteoarthritis has been extensively studied. However, less attention has been given to risk factors related to increased pain during gait. The purpose of this study was to evaluate knee joint moments and clinical characteristics that may be associated with gait-related knee pain in patients with knee osteoarthritis.MethodsSixty-seven participants with knee osteoarthritis were stratified into three groups of no pain (n = 18), mild pain (n = 27), or moderate/severe pain (n = 22) based on their self-reported symptoms during gait. All participants underwent three-dimensional gait analysis. Quadriceps strength, knee extension range of motion, radiographic knee alignment and self-reported measures of global pain and function were also quantified.FindingsThe moderate/severe pain group demonstrated worse global pain (P < 0.01) and physical function scores (P < 0.01) compared to the no pain and the mild pain groups. The moderate/severe pain group also walked with greater knee flexion moments during the midstance phase of gait compared to the no pain group (P = 0.02). Additionally, the moderate/severe pain group demonstrated greater varus knee malalignment (P = 0.009), which was associated with higher weight acceptance peak knee adduction moments (P = 0.003) and worse global pain (P = 0.003) and physical function scores (P = 0.006).InterpretationGreater knee flexion moment is present during the midstance phase of gait in patients with knee osteoarthritis and moderate/severe pain during gait. Additionally, greater varus malalignment may be a sign of increased global knee joint dysfunction that can influence many activities of daily living beyond gait.     

Dynamic stability during stair negotiation after total knee arthroplasty

BackgroundThe assessment of dynamic stability is crucial for the prevention of falls in the elderly and people with functional impairments. Evidence that total knee arthroplasty improves balance in patients with severe osteoarthritis is scarce and no information exists about how the surgery affects dynamic stability during stair negotiation.MethodsThis study aims to investigate if patients before and one year after surgery are less stable compared to asymptomatic controls. Seventeen control and twenty-seven patient participants with end-stage knee osteoarthritis that were scheduled to undergo unilateral total knee arthroplasty were recruited in this study. Participants' assessment was carried out by means of marker-based optical full-body motion capture with force platforms. The extrapolated Centre of mass and the margin of stability metrics were used to examine dynamic stability during stair ascent and descent.FindingsPatient participants, during both pre-operative and post-operative assessments, were equally balanced to the asymptomatic controls during stair gait (p > .188). Additionally, the patients' overall stability did not improve significantly one year after arthroplasty surgery (p > .252).InterpretationEven if pain from arthritis and fear of falling is decreased following surgery, our results indicate that stability in stair walking in not affected by osteoarthritis and total knee arthroplasty.Clinical trial registration number: NCT02422251.     

Diminished neuromuscular system adaptability following anterior cruciate ligament injury: Examination of knee muscle force variability and complexity

BackgroundAnterior cruciate ligament (ACL) injuries impair knee extensor and flexor force generation and may alter force variability. Fractal scaling exponents quantify signal complexity and reflect neuromuscular system adaptability. The purpose of this study was to evaluate force variability magnitudes and fractal scaling exponents in persons with ACL injuries.MethodsTwenty-four individuals with ACL injury (time from injury: 55 ± 66 days) and 25 uninjured controls completed 10-s isometric knee extension and flexion contractions on a dynamometer at 10%, 25%, 35%, and 50% of peak force. The middle 8-s of data were used to calculate coefficients of variation and fractal exponents. Injured and non-injured limbs as well as dominant and non-dominant limbs in the control group were compared with ANOVA (P < 0.05).FindingsPeak knee extensor and flexor forces were 19% and 10% lower in the injured limb of ACL-deficient participants (P = 0.014 and P = 0.036, respectively). Fractal scaling exponents of knee extensor force signals at 25% and 35% peak force in injured limbs were higher than in non-injured limbs (P = 0.008 and P = 0.027, respectively). The fractal scaling exponent of knee extensor force signals was greater in injured limbs of ACL-deficient participants than in dominant limbs of the control group at 35% peak force (P = 0.046). The magnitude of variability did not differ between limbs in ACL-deficient participants or between the injured and control groups.InterpretationAltered fractal exponents in knee extensor force signals represent sensorimotor and neuromuscular system deficits in individuals with ACL injury. Overall, fractal analysis identified both between-limb and between-group differences.     

Dynamic joint stiffness and co-contraction in subjects after total knee arthroplasty

Background

Although total knee arthroplasty reduces pain and improves function, patients continue to walk with asymmetrical movement patterns, that may affect muscle activation and joint loading patterns. The purpose of this study was to evaluate the specific biomechanical abnormalities that persist after total knee arthroplasty and examine the neuromuscular mechanisms that may contribute to these asymmetries.

Methods

Dynamic joint stiffness at the hip, knee and ankle, as well as co-contraction at the knee and ankle, were compared between the operated and non-operated limbs of 32 subjects who underwent total knee arthroplasty and 21 subjects without lower extremity impairment.

Findings

Subjects after total knee arthroplasty demonstrated higher dynamic joint stiffness in the operated knee compared to the non-operated knee (0.056 (0.023) Nm/kg/m/deg vs. 0.043 (0.016) Nm/kg/m/deg, P = 0.003) and the knees from a control group without lower extremity pathology (controls: 0.042 (0.015) Nm/kg/m/deg, P = 0.017). No differences were found between limbs or groups for dynamic joint stiffness at the hip or ankle. There was no relationship between dynamic joint stiffness at the knee and ankle and the amount of co-contraction between antagonistic muscles at those joints.

Interpretation

Patients after total knee arthroplasty walk with less knee joint excursion and greater knee stiffness, although no differences were found between groups for stiffness at the hip or ankle. Mechanisms other than co-contraction are likely the underlying cause of the altered knee mechanics. These findings are clinically relevant because the goal should be to create interventions to reduce these abnormalities and increase function.     

Decreased passive muscle stiffness of vastus medialis is associated with poorer quadriceps strength and knee function after anterior cruciate ligament reconstruction

BackgroundMuscle deficits of the quadriceps and hamstrings are common after anterior cruciate ligament reconstruction, and increase the risk of knee reinjury. Muscle stiffness is an important factor for dynamic joint stability. However, the changes in quadriceps and hamstring muscle stiffness and its influence after anterior cruciate ligament reconstruction remain unclear.MethodTwenty-five male subjects with anterior cruciate ligament reconstruction and twenty-one matched healthy subjects participated in this study. The passive muscle stiffness of the quadriceps and hamstrings was assessed by shear modulus using ultrasound shear wave elastography. The isokinetic muscle strengths of the quadriceps and hamstrings were tested. Knee function was evaluated by the International Knee Documentation Committee and Lysholm score. Muscle stiffness was compared between limbs via non-parametric tests. Correlation analysis was used to detect the relationship between muscle stiffness, isokinetic muscle strength and knee functional scores.FindingsThe involved limb exhibited significantly decreased shear modulus in the vastus medialis compared to the dominant limbs(z = −3.585;P = 0.001;ES = 1.13) and non-dominant limbs(z = −3.551;P = 0.002;ES = 1.24) of healthy controls. The shear modulus of ST was also significantly lower in the involved limb when compared with the contralateral limbs(z = −3.996;P < 0.001;ES = 1.33), dominant limbs(z = −4.477;P < 0.001;ES = 1.65) and non-dominant limbs(z = −4.234;P = 0.001;ES = 1.43) of healthy controls. The shear modulus of the vastus medialis was associated with quadriceps peak torque at 60°/s(r = 0.470; p < 0.001) and knee functional score(r = 0.459; p = 0.021).InterpretationThe passive muscle stiffness of the vastus medialis decreased after anterior cruciate ligament reconstruction, which is associated with poorer quadriceps strength and knee function. The effect of modulation of muscle stiffness on improving knee function warrants future investigation.     

Leg stiffness and electromyography of knee extensors/flexors: comparison between older and younger adults during stair descent

This study investigated differences in knee extensor/flexor electromyography (EMG), leg loading rate, and leg stiffness in older and younger men during stair descent. Sixteen older men (mean +/- standard deviation [SD] = 72 +/- 4.5 years) and sixteen younger men (mean +/- SD = 21.2 +/- 0.5 years) were recruited. The EMG signals were recorded from the rectus femoris and the biceps femoris, while an electrogoniometer measured knee joint angle changes, and a force platform recorded the ground reaction forces (GRFs). We calculated leg stiffness by dividing the first peak GRF by the corresponding leg displacement. We used the Student's t-test to examine group differences. Results showed that the older subjects had 78.6% higher preactivated EMG values in the knee extensor and 128% greater coactivity in the knee extensors/ flexors in the prelanding phase. At the impact phase, we observed leg stiffness to be 26.6% greater in the older than the younger subjects. The older subjects needed 94.6% more support time in performing push-off and also developed a compensatory strategy in stair descent, which altered the scaling of muscle preactivity and increased leg stiffness.