Pain inhibition-the unintended benefit of electrically elicited muscle strengthening contractions.

BACKGROUND: Neuromuscular electrical stimulation (NMES) is effective in muscle strengthening after orthopedic injury particularly when muscle activation failure is present, but the associated pain can be a barrier. Pain itself can produce a pain inhibitory response called Conditioned Pain Modulation (CPM). CPM is often used in research studies to assess the state of the pain processing system. However, the inhibitory response of CPM could make NMES more tolerable to patients and could improve functional outcomes in people with pain. This study compares the pain-inhibitory effect of NMES compared to volitional contractions and noxious electrical stimulation (NxES). METHODS: Healthy participants, 18-30 years of age experienced 3 conditions: 10 NMES contractions, 10 bursts of NxES on the patella, and 10 volitional contractions on the right knee. Pressure pain thresholds (PPT) were measured before and after each condition in both knees and the middle finger. Pain was reported on an 11-point VAS. Repeated measures ANOVAs with 2 factors: site and time were performed for each condition followed by post-hoc paired t-tests, with Bonferroni correction. RESULTS: Pain ratings were higher in the NxES condition compared to NMES (p = .000). No differences in PPTs prior to each condition were observed but PPTs were significantly higher in the right and left knees after the NMES contractions (p = .000, p = .013, respectively) and after the NxES (p = .006, P-.006, respectively). Pain during NMES and NxES did not correlate with pain inhibition (p > .05). Self-reported pain sensitivity correlated with pain during NxES. CONCLUSION: NxES and NMES produced higher PPTs in both knees but not in the finger, suggesting that the mechanisms responsible for the reduction in pain are located in the spinal cord and local tissues. Pain reduction was elicited during the NxES and NMES conditions regardless of the self-reported pain ratings. When NMES is used for muscle strengthening significant pain reduction can also occur, which is an unintended benefit of the intervention that could improve functional outcomes in patients.

Development of the Modified Four Square Step Test and its reliability and validity in people with stroke.

Adults with stroke have difficulty avoiding obstacles when walking, especially when a time constraint is imposed. The Four Square Step Test (FSST) evaluates dynamic balance by requiring individuals to step over canes in multiple directions while being timed, but many people with stroke are unable to complete it. The purposes of this study were to (1) modify the FSST by replacing the canes with tape so that more persons with stroke could successfully complete the test and (2) examine the reliability and validity of the modified version. Fifty-five subjects completed the Modified FSST (mFSST) by stepping over tape in all four directions while being timed. The mFSST resulted in significantly greater numbers of subjects completing the test than the FSST (39/55 [71%] and 33/55 [60%], respectively) (p < 0.04). The test-retest, intrarater, and interrater reliability of the mFSST were excellent (intraclass correlation coefficient ranges: 0.81-0.99). Construct and concurrent validity of the mFSST were also established. The minimal detectable change was 6.73 s. The mFSST, an ideal measure of dynamic balance, can identify progress in people with stroke in varied settings and can be completed by a wide range of people with stroke in approximately 5 min with the use of minimal equipment (tape, stop watch).

Individuals with medial knee osteoarthritis show neuromuscular adaptation when perturbed during walking despite functional and structural impairments.

Neuromuscular control relies on sensory feedback that influences responses to changing external demands, and the normal response is for movement and muscle activation patterns to adapt to repeated perturbations. People with knee osteoarthritis (OA) are known to have pain, quadriceps weakness, and neuromotor deficits that could affect adaption to external perturbations. The aim of this study was to analyze neuromotor adaptation during walking in people with knee OA (n = 38) and controls (n = 23). Disability, quadriceps strength, joint space width, malalignment, and proprioception were assessed. Kinematic and EMG data were collected during undisturbed walking and during perturbations that caused lateral translation of the foot at initial contact. Knee excursions and EMG magnitudes were analyzed. Subjects with OA walked with less knee motion and higher muscle activation and had greater pain, limitations in function, quadriceps weakness, and malalignment, but no difference was observed in proprioception. Both groups showed increased EMG and decreased knee motion in response to the first perturbation, followed by progressively decreased EMG activity and increased knee motion during midstance over the first five perturbations, but no group differences were observed. Over 30 trials, EMG levels returned to those of normal walking. The results illustrate that people with knee OA respond similarly to healthy individuals when exposed to challenging perturbations during functional weight-bearing activities despite structural, functional, and neuromotor impairments. Mechanisms underlying the adaptive response in people with knee OA need further study.

Quadriceps rate of force development affects gait and function in people with knee osteoarthritis.

OBJECTIVE: Quadriceps weakness exists in people with knee osteoarthritis (OA), but other muscle factors like rate of force development (RFD) may also be affected by knee OA. The purpose of this study was to determine if people with knee OA have deficits in quadriceps RFD, determine if quadriceps RFD would improve predicting knee joint power absorption and generation during free and fast walking, and determine if RFD would improve predicting functional outcomes. METHODS: 26 subjects with knee OA and 23 healthy control subjects performed maximal voluntary isometric strength (MVIC) and RFD measures of the quadriceps. Subjects also underwent a 3-D motion analysis of both self-selected free and self-selected fast walking speeds. Joint kinetics were calculated from inverse dynamics. RESULTS: RFD was not different by group (p = 0.763), however, the OA subjects generated the highest peak RFD at a lower % MVIC (p = 0.008). Controls walked significantly faster at both free and fast walking speeds (p = 0.001, p = 0.029). Knee angles at heel strike and peak knee extension were lower (p = 0.004, p = 0.027) in the OA group. During fast walking knee power generation was higher in controls (p = 0.028). MVIC and force of highest peak RFD predicted KOOS-ADL score in the OA subjects, but only MVIC predicted stair climbing time. CONCLUSIONS: The submaximal force at which peak RFD occurs plays a significant role in knee joint power as well as functional measures in the OA subjects, providing further evidence that factors other than maximal strength are also important in people with knee OA.

The structure of walking activity in people after stroke compared with older adults without disability: a cross-sectional study.

BACKGROUND: People with stroke have reduced walking activity. It is not known whether this deficit is due to a reduction in all aspects of walking activity or only in specific areas. Understanding specific walking activity deficits is necessary for the development of interventions that maximize improvements in activity after stroke. OBJECTIVE: The purpose of this study was to examine walking activity in people poststroke compared with older adults without disability. DESIGN: A cross-sectional study was conducted. METHODS: Fifty-four participants poststroke and 18 older adults without disability wore a step activity monitor for 3 days. The descriptors of walking activity calculated included steps per day (SPD), bouts per day (BPD), steps per bout (SPB), total time walking per day (TTW), percentage of time walking per day (PTW), and frequency of short, medium, and long walking bouts. RESULTS: Individuals classified as household and limited community ambulators (n=29) did not differ on any measure and were grouped (HHA-LCA group) for comparison with unlimited community ambulators (UCA group) (n=22) and with older adults without disability (n=14). The SPD, TTW, PTW, and BPD measurements were greatest in older adults and lowest in the HHA-LCA group. Seventy-two percent to 74% of all walking bouts were short, and this finding did not differ across groups. Walking in all categories (short, medium, and long) was lowest in the HHA-LCA group, greater in the UCA group, and greatest in older adults without disability. LIMITATIONS: Three days of walking activity were captured. CONCLUSIONS: The specific descriptors of walking activity presented provide insight into walking deficits after stroke that cannot be ascertained by looking at steps per day alone. The deficits that were revealed could be addressed through appropriate exercise prescription, underscoring the need to analyze the structure of walking activity.

EMG-driven modeling approach to muscle force and joint load estimations: case study in knee osteoarthritis.

It is important to know the magnitude and patterns of joint loading in people with knee osteoarthritis (OA), since altered loads are implicated in onset and progression of the disease. We used an EMG-driven forward dynamics model to estimate joint loads during walking in a subject with knee OA and a healthy control subject. Kinematic, kinetic, and surface EMG data were used to predict muscle forces using a Hill-type muscle model. The muscle forces were used to balance the frontal plane moment to obtain medial and lateral condylar loads. Loads were normalized to body weight (BWs) and the mean of three trials taken. The OA subject had greater medial and lower lateral loads compared to the control subject. Seventy-five to 80% of the total load was borne on the medial compartment in the control subject, compared to 90-95% in the OA subject. In fact, complete lateral unloading occurred during midstance for the OA subject. Loading for the healthy subject was consistent with the data from instrumented knee studies. In the future, the model can be used to analyze the impact of various interventions to reduce the loads on the medial compartment in people with knee OA.

Influence of systematic increases in treadmill walking speed on gait kinematics after stroke.

BACKGROUND: Fast treadmill training improves walking speed to a greater extent than training at a self-selected speed after stroke. It is unclear whether fast treadmill walking facilitates a more normal gait pattern after stroke, as has been suggested for treadmill training at self-selected speeds. Given the massed stepping practice that occurs during treadmill training, it is important for therapists to understand how the treadmill speed selected influences the gait pattern that is practiced on the treadmill. OBJECTIVE: The purpose of this study was to characterize the effect of systematic increases in treadmill speed on common gait deviations observed after stroke. DESIGN: A repeated-measures design was used. METHODS: Twenty patients with stroke walked on a treadmill at their self-selected walking speed, their fastest speed, and 2 speeds in between. Using a motion capture system, spatiotemporal gait parameters and kinematic gait compensations were measured. RESULTS: Significant improvements in paretic- and nonparetic-limb step length and in single- and double-limb support were found. Asymmetry of these measures improved only for step length. Significant improvements in paretic hip extension, trailing limb position, and knee flexion during swing also were found as speed increased. No increases in circumduction or hip hiking were found with increasing speed. Limitations Caution should be used when generalizing these results to survivors of a stroke with a self-selected walking speed of less than 0.4 m/s. This study did not address changes with speed during overground walking. CONCLUSIONS: Faster treadmill walking facilitates a more normal walking pattern after stroke, without concomitant increases in common gait compensations, such as circumduction. The improvements in gait deviations were observed with small increases in walking speed.

Combined effects of fast treadmill walking and functional electrical stimulation on post-stroke gait.

Gait dysfunctions are highly prevalent in individuals post-stroke and affect multiple lower extremity joints. Recent evidence suggests that treadmill walking at faster than self-selected speeds can help improve post-stroke gait impairments. Also, the combination of functional electrical stimulation (FES) and treadmill training has emerged as a promising post-stroke gait rehabilitation intervention. However, the differential effects of combining FES with treadmill walking at the fast versus a slower, self-selected speed have not been compared previously. In this study, we compared the immediate effects on gait while post-stroke individuals walked on a treadmill at their self-selected speed without FES (SS), at the SS speed with FES (SS-FES), at the fastest speed they are capable of attaining (FAST), and at the FAST speed with FES (FAST-FES). During SS-FES and FAST-FES, FES was delivered to paretic ankle plantarflexors during terminal stance and to paretic dorsiflexors during swing phase. Our results showed improvements in peak anterior ground reaction force (AGRF) and trailing limb angle during walking at FAST versus SS. FAST-FES versus SS-FES resulted in greater peak AGRF, trailing limb angle, and swing phase knee flexion. FAST-FES resulted in further increase in peak AGRF compared to FAST. We posit that the enhancement of multiple aspects of post-stroke gait during FAST-FES suggest that FAST-FES may have potential as a post-stroke gait rehabilitation intervention.

Gait Recovery in Healthy Subjects: Perturbations to the Knee Motion with a Smart Knee Brace.

Smart Knee Brace (SKB) is designed to provide controlled perturbations to the human knee during walking. A dynamic model of human walking is then used to evaluate the human applied joint torques to hypothesize how the human neuro-muscular system modulates the joint torques as a response to the perturbations caused on the gait. Our results show that the neuro-muscular response to perturbations can be reasonably well characterized by including the following features in the model: (i) normal gait in the absence of perturbation, (ii) corrective torque at a joint in response to the error at that joint and other joints, (iii) a characteristic time shift in the response. We believe that these parameters can be used to characterize subjects who are more prone to falling under gait perturbations.

Novel patterns of functional electrical stimulation have an immediate effect on dorsiflexor muscle function during gait for people poststroke.

BACKGROUND: Foot drop is a common gait impairment after stroke. Functional electrical stimulation (FES) of the ankle dorsiflexor muscles during the swing phase of gait can help correct foot drop. Compared with constant-frequency trains (CFTs), which typically are used during FES, novel stimulation patterns called variable-frequency trains (VFTs) have been shown to enhance isometric and nonisometric muscle performance. However, VFTs have never been used for FES during gait. OBJECTIVE: The purpose of this study was to compare knee and ankle kinematics during the swing phase of gait when FES was delivered to the ankle dorsiflexor muscles using VFTs versus CFTs. DESIGN: A repeated-measures design was used in this study. PARTICIPANTS: Thirteen individuals with hemiparesis following stroke (9 men, 4 women; age=46-72 years) participated in the study. METHODS: Participants completed 20- to 40-second bouts of walking at their self-selected walking speeds. Three walking conditions were compared: walking without FES, walking with dorsiflexor muscle FES using CFTs, and walking with dorsiflexor FES using VFTs. RESULTS: Functional electrical stimulation using both CFTs and VFTs improved ankle dorsiflexion angles during the swing phase of gait compared with walking without FES (X+/-SE=-2.9 degrees +/- 1.2 degrees). Greater ankle dorsiflexion in the swing phase was generated during walking with FES using VFTs (X+/-SE=2.1 degrees +/- 1.5 degrees) versus CFTs (X+/-SE=0.3+/-1.3 degrees). Surprisingly, dorsiflexor FES resulted in reduced knee flexion during the swing phase and reduced ankle plantar flexion at toe-off. CONCLUSIONS: The findings suggest that novel FES systems capable of delivering VFTs during gait can produce enhanced correction of foot drop compared with traditional FES systems that deliver CFTs. The results also suggest that the timing of delivery of FES during gait is critical and merits further investigation.

Functional electrical stimulation of ankle plantarflexor and dorsiflexor muscles: effects on poststroke gait.

BACKGROUND AND PURPOSE: Functional electrical stimulation (FES) is a popular poststroke gait rehabilitation intervention. Although stroke causes multijoint gait deficits, FES is commonly used only for the correction of swing-phase foot drop. Ankle plantarflexor muscles play an important role during gait. The aim of the current study was to test the immediate effects of delivering FES to both ankle plantarflexors and dorsiflexors on poststroke gait. METHODS: Gait analysis was performed as subjects (N=13) with chronic poststroke hemiparesis walked at their self-selected walking speeds during walking with and without FES. RESULTS: Compared with delivering FES to only the ankle dorsiflexor muscles during the swing phase, delivering FES to both the paretic ankle plantarflexors during terminal stance and dorsiflexors during the swing phase provided the advantage of greater swing-phase knee flexion, greater ankle plantarflexion angle at toe-off, and greater forward propulsion. Although FES of both the dorsiflexor and plantarflexor muscles improved swing-phase ankle dorsiflexion compared with noFES, the improvement was less than that observed by stimulating the dorsiflexors alone, suggesting the need to further optimize stimulation parameters and timing for the dorsiflexor muscles during gait. CONCLUSIONS: In contrast to the typical FES approach of stimulating ankle dorsiflexor muscles only during the swing phase, delivering FES to both the plantarflexor and dorsiflexor muscles can help to correct poststroke gait deficits at multiple joints (ankle and knee) during both the swing and stance phases of gait. Our study shows the feasibility and advantages of stimulating the ankle plantarflexors during FES for poststroke gait.

Influence of speed on walking economy poststroke.

BACKGROUND AND OBJECTIVE: Walking speed influences energy cost in healthy adults, but its influence when walking is impaired due to stroke is not clear. This study investigated the effect of manipulating walking speed on the energy economy of walking poststroke. METHODS: Sixteen persons with chronic stroke underwent a clinical examination, including several lower extremity impairment measures. consumption (VO(2)) was measured as they walked at their self-selected speed (Free), 20% slower (Slow), their fastest possible speed (Fastest), and 2 speeds between Free and Fastest speeds. VO(2) was normalized to body mass and speed, resulting in energy cost per meter walked (CW). RESULTS: A main effect for speed was observed (P = .00001), with faster than self-selected speeds showing greater relative economy as a whole. However, for 5 subjects with the fastest walking speeds (>1.2 m/s), there was a trend toward decreasing relative economy at speeds higher than self-selected speed (P = .18). There was a negative correlation between improvement in CW at the most economical speed and (a) Free speed (r = -.857; P < .0001) and (b) lower extremity Fugl-Meyer scores (r = -.653; P = .006). CONCLUSIONS: For those poststroke whose fastest walking speed after stroke is below 1.2 m/s, walking economy improves when speed is increased above the self-selected walking speed. The results suggest that for persons poststroke with very slow self-selected walking speeds, improvements in walking speed could be accompanied by improvements in walking economy if faster walking speeds can be attained through intervention.

Instability, laxity, and physical function in patients with medial knee osteoarthritis.

BACKGROUND AND PURPOSE: Studies have identified factors that contribute to functional limitations in people with knee osteoarthritis (OA), including quadriceps femoris muscle weakness, joint laxity, and reports of knee instability. However, little is known about the relationship among these factors or their relative influence on function. The purpose of this study was to investigate self-reported knee instability and its relationships with knee laxity and function in people with medial knee osteoarthritis (OA). PARTICIPANTS: Fifty-two individuals with medial knee OA participated in the study. METHODS: Each participant was classified into 1 of 3 groups based on reports of knee instability. Limb alignment, knee laxity, and quadriceps femoris muscle strength (force-generating capacity) were assessed. Function was measured with the Knee Injury and Osteoarthritis Outcome Score (KOOS) and a stair-climbing test (SCT). Group differences were detected with one-way analyses of variance, and relationships among variables were assessed with the Eta(2) statistic and hierarchical regression analysis. RESULTS: There were no differences in alignment, laxity, or strength among the 3 groups. Self-reported knee instability did not correlate with medial laxity, limb alignment, or quadriceps femoris muscle strength. Individuals reporting worse knee instability scored worse on all subsets of the KOOS. Self-reported knee instability scores significantly contributed to the prediction of all measures of function above that explained by quadriceps femoris muscle force, knee laxity, and alignment. Neither laxity nor alignment contributed to any measure of function. DISCUSSION AND CONCLUSION: Self-reported knee instability is a factor that is not directly associated with knee laxity and contributes to worse function. Further research is necessary to delineate the factors that contribute to self-reported knee instability and reduced function in this population.

Muscle stabilization strategies in people with medial knee osteoarthritis: the effect of instability.

The sensation of knee instability (shifting, buckling. and giving way) is common in people with medial knee osteoarthritis (OA). Its influence on knee stabilization strategies is unknown. This study investigated the influence of knee instability on muscle activation during walking when knee stability was challenged. Twenty people with medial knee OA participated and were grouped as OA Stable (OAS) (n = 10) and OA Unstable (OAU) (n = 10) based on self-reported knee instability during daily activities. Quadriceps strength, passive knee laxity, and varus alignment were assessed and related to knee instability and muscle cocontraction during walking when the support surface translated laterally. Few differences in knee joint kinematics between the groups were seen; however, there were pronounced differences in muscle activation. The OAU group used greater medial muscle cocontraction before, during, and following the lateral translation. Self-reported knee instability predicted medial muscle cocontraction, but medial laxity and limb alignment did not. The higher muscle cocontraction used by the OAU subjects appears to be an ineffective strategy to stabilize the knee. Instability and high cocontraction can be detrimental to joint integrity, and should be the focus of future research.

Age-related changes in strength, joint laxity, and walking patterns: are they related to knee osteoarthritis?

BACKGROUND AND PURPOSE: Aging is associated with musculoskeletal changes and altered walking patterns. These changes are common in people with knee osteoarthritis (OA) and may precipitate the development of OA. We examined age-related changes in musculoskeletal structures and walking patterns to better understand the relationship between aging and knee OA. METHODS: Forty-four individuals without OA (15 younger, 15 middle-aged, 14 older adults) and 15 individuals with medial knee OA participated. Knee laxity, quadriceps femoris muscle strength (force-generating capacity), and gait were assessed. RESULTS: Medial laxity was greater in the OA group, but there were no differences between the middle-aged and older control groups. Quadriceps femoris strength was less in the older control group and in the OA group. During the stance phase of walking, the OA group demonstrated less knee flexion and greater knee adduction, but there were no differences in knee motion among the control groups. During walking, the older control group exhibited greater quadriceps femoris muscle activity and the OA group used greater muscle co-contraction. DISCUSSION AND CONCLUSION: Although weaker, the older control group did not use truncated motion or higher co-contraction. The maintenance of movement patterns that were similar to the subjects in the young control group may have helped to prevent development of knee OA. Further investigation is warranted regarding age-related musculoskeletal changes and their influence on the development of knee OA.

Influences on knee movement strategies during walking in persons with medial knee osteoarthritis.

OBJECTIVE: To investigate the movement and muscle activation strategies during walking of individuals with medial knee osteoarthritis (OA) to determine the influence of quadriceps strength, medial knee laxity, limb alignment, and self-reported knee instability on knee motion. METHODS: Twenty-eight persons with medial knee OA and 26 control subjects participated. Quadriceps strength, medial knee laxity, and limb alignment were measured. Knee instability (I(KOS) score) was assessed with the Activities of Daily Living Scale of the Knee Outcome Survey. Knee motion and muscle activation patterns were measured with motion analysis. Group differences were detected with independent samples t-tests and predictive relationships were determined with linear and hierarchical regression analyses. RESULTS: Individuals with OA were weaker, had greater medial knee laxity, and had more varus alignment. The OA group used less knee motion and higher muscle co-contraction during weight acceptance and single-limb support. Quadriceps strength and I(KOS) score significantly strengthened the prediction of knee motion during weight acceptance and single-limb support, whereas limb alignment and medial laxity did not. CONCLUSION: The knee stiffening and higher muscle co-contraction used by the OA group may be detrimental to joint integrity. I(KOS) scores predicted knee motion after accounting for quadriceps strength, underscoring the importance of addressing knee instability with appropriate rehabilitation strategies in persons with medial knee OA in order to promote long-term joint integrity.

Effect of anatomic realignment on muscle function during gait in patients with medial compartment knee osteoarthritis.

OBJECTIVE: Individuals with medial compartment knee osteoarthritis (OA) and genu varum use different movement and muscle activation patterns to increase joint stability during gait. The purpose of this study was to ascertain whether opening-wedge high-tibial osteotomy (OW-HTO) corrected pathomechanical abnormalities associated with the progression of knee OA. METHODS: Fifteen patients diagnosed with medial knee OA and genu varum who were scheduled for OW-HTO were tested prior to and 1 year following OW-HTO. Fifteen age- and sex-matched controls were also tested. Frontal plane laxity was measured from stress radiographs. All participants underwent quadriceps strength testing with a burst superimposition technique and gait analysis with surface electromyography to calculate knee joint kinematics and kinetics and muscle co-contraction during the stance phase of gait. Participants rated their knee function and instability using a self-report questionnaire. RESULTS: Static alignment improved following the surgery. Medial laxity (P = 0.003) and instability (P = 0.002) significantly improved, and statistical reductions in the adduction moment resulted in lower levels of vastus medialis-medial gastrocnemius muscle co-contractions (P = 0.089). Despite improvements in global rating of knee function (P = 0.001), the OA group's ratings remained significantly lower than those of the healthy controls (P = 0.001). Quadriceps strength deficits and knee flexion impairments persisted. CONCLUSION: Persistent quadriceps weakness and impaired knee kinematics after realignment suggest that the movement strategy may perpetuate joint destruction and impede the long-term success of realignment. Rehabilitation should focus on quadriceps strength and improving joint mobility to improve the long-term function of individuals with medial knee OA.

Effects of the amount of valgus correction for medial compartment knee osteoarthritis on clinical outcome, knee kinetics and muscle co-contraction after opening wedge high tibial osteotomy.

The goal of opening wedge high tibial osteotomy (HTO) is to reduce excessive loading on the medial compartment of the knee by correcting varus deformity, thereby reducing pain and improving function. Although surgical outcome is reportedly poor in cases of under- or overcorrection, the recommended alignment varies. The aim of this study was to investigate the effect of the degree of frontal plane knee alignment following open wedge HTO surgery on muscle co-contraction, joint moments, and self-reported functional outcome. Sixteen patients with medial compartment osteoarthritis (OA), who were scheduled for an opening wedge osteotomy, were recruited for participation in the study. Data were collected using an optoeletric motion analysis system and varus and valgus angulations of the knee were measured, using standing, long cassette, radiographs of the lower extremities. Results showed that physical function improved significantly overall (p < 0.001). However, those subjects whose knee alignment was further away from the group's postoperative mean tended to improve less in their Knee Outcome Survey-Activities of Daily Living Scale (KOS-ADLS) scores than those closer to the mean (p = 0.07). They also had higher medial and lateral co-contractions and higher adduction moments one year after surgery (p

Stride-to-stride variability of knee motion in patients with knee osteoarthritis.

PURPOSE: Individuals with knee osteoarthritis (OA) experience pain, frontal plane joint laxity and instability. Co-contraction can control laxity and instability but may place constraints on the variability of the knee's motion during gait. Slight variation among gait cycles is normal, but reduced variability of joint motions could be detrimental. The purpose of this study was to quantify knee motion variability during gait and assess the influence of muscle activity, frontal plane laxity, and pain on knee movement variability in patients with medial knee OA. METHODS: Fifteen subjects with unilateral medial knee OA and 15 age and gender matched uninjured subjects underwent gait analysis, with electromyography to compute co-contraction. Stress radiographs were obtained for measuring frontal plane laxity. Knee motion variability was assessed from the phase angle (knee angle versus angular velocity) during early stance. RESULTS: Despite altered involved side knee kinematics and kinetics, individuals with knee OA showed involved side frontal plane variability which was not significantly different from the control group, but was significantly lower than the variability of the uninvolved knee's motion. Laxity and medial co-contraction influenced the amount of joint motion variability in the involved knee of the OA subjects. Pain did not influence variability. CONCLUSION: Patients with medial knee OA displayed altered involved knee kinematics and kinetics, although stride-to-stride variability of knee motion was unchanged. Evidence of excessive joint motion variability on the uninvolved side, however, may provide insight into the development of OA in the contralateral cognate joint.

Knee stabilization in patients with medial compartment knee osteoarthritis.

OBJECTIVE: Individuals with medial knee osteoarthritis (OA) experience knee laxity and instability. Strategies aimed at muscle stabilization may influence the long-term integrity of the joint. This study sought to determine how individuals with medial knee OA respond to a rapid valgus knee movement, to investigate the relationship between muscle-stabilization strategies and knee instability. METHODS: Twenty-one subjects with medial knee OA and genu varum and 19 control subjects were tested. Subjects stood with the test limb on a movable platform, comprising a plate that translated laterally to rapidly stress the knee's medial periarticular structures and create a potentially destabilizing sensation at the knee joint. Knee motion and muscle responses were recorded. Subjects rated the condition of their knee with a self-report questionnaire about knee instability during daily activities. RESULTS: Prior to plate movement, the OA subjects demonstrated more medial muscle co-contraction than did controls (P = 0.014). Following plate movement, the OA subjects shifted less weight off the test limb (P = 0.013) and had greater medial co-contraction (P = 0.037). OA subjects without knee instability had higher co-contraction of the vastus medialis medial hamstrings than did those who reported having instability that affected their daily activities (P = 0.038). More knee stability correlated positively with higher co-contraction of the vastus medialis medial hamstrings prior to plate movement (r = 0.459, P = 0.042). CONCLUSION: Individuals with medial knee OA attempt to stabilize the knee with greater co-contraction of the medial muscle in response to laxity that appears on the medial side of the joint only. This strategy presumably contributes to higher joint compression and could exacerbate joint destruction, and therefore needs to be altered to slow or stop the progression of the OA disease process.