Background: Gait abnormalities can influence surgical outcomes in people with severe knee osteoarthritis (OA) and thus a thorough understanding of gait abnormalities in these people prior to arthroplasty is important. Varus-valgus thrust is a characteristic linked to OA disease progression that has not yet been investigated in a cohort with severe knee OA awaiting knee arthroplasty. The aims of this study were to determine i) prevalence of varus and valgus thrust in a cohort with severe knee OA compared to an asymptomatic group, ii) whether the thrust magnitude differed between these groups iii) differences between varus and valgus thrusters within the OA cohort and iv) whether certain measures could predict thrust in the OA cohort. Methods: 40 patients with severe knee OA scheduled for primary TKR and 40 asymptomatic participants were recruited. Three-dimensional gait analysis was performed on all participants, with the primary biomechanical measures of interest being: varus and valgus thrust, knee adduction angle, peak KAM, and KAM impulse. Additionally, static knee alignment and quadriceps strength were assessed in the subgroup with knee OA. Findings: No difference was found in the prevalence of varus and valgus thrust between the severe OA and control groups (Pearson chi-square = 3.735, p value = 0.151). The OA varus thrust group had a significantly higher peak KAM (p=0.000), KAM impulse (p=0.001), static alignment (p=0.021), and lower quadriceps strength (p=0.041) than the valgus thrust group. Peak KAM and quadriceps strength were found to explain 34.9% of the variation in maximum thrust, such that an increase in KAM and a decrease in quadriceps strength were associated with an increase in maximum (varus) thrust. Interpretation: Few differences between the severe OA and control groups were seen, however dichotomizing the groups into varus and valgus cohorts revealed a number of biomechanical differences. Patients with severe OA are often treated as a homogenous cohort; however, by classifying which individuals have a varus or valgus thrust, we have identified a subset of patients with poorer biomechanics who could potentially be at a higher risk of a worse outcome after surgery.
Listed In: Biomechanics, Gait, Orthopedic Research

BACKROUND: Recent developments in modelling have made it easier to use muscle force predictions to augment clinical gait analysis and enhance clinical decision making. OpenSim claims to provide a straight forward, standardised pipeline (SimTrack) to predict muscle forces implemented in routine processing. This project aims to test SimTrack’s potential in the context of clinical gait analysis by developing a standardised protocol which compares predicted muscle forces with surface EMG at a range of walking speeds. METHODS: 10 healthy participants walked at 3 different speeds (comfortable, ±20%). Kinematics, kinetics and surface EMG of the lower limb were captured. Joint angles and ground reaction forces serve as inputs to predict muscle forces using computed muscle control (CMC) within SimTrack. Predicted muscle forces were compared with EMG to validate the model outputs. RESULTS: Agreement between force prediction and EMG varies between muscles. Some muscles show a general agreement and similar variation with walking speed, others show large unexpected differences between CMC outputs and observed EMG. DISCUSSION: These results suggest that this protocol is running in general. For most walking speeds, CMC muscle forces can be predicted within a timeframe appropriate for clinical purposes. However using the default settings, the model predictions do not agree with EMG measurements. Furthermore, during pilot testing of quicker walking speeds (up to +40%) CMC crashed due the chosen musculoskeletal model being too weak. These findings suggest the need of either different generic parameters or subject specific parameters to obtain valid results. Work is continuing to identify these.
Listed In: Biomechanics, Gait, Other

Knee pain is 1 of 5 leading causes of disability by altering lower-extremity muscle function and gait mechanics. While transcutaneous electrical nerve stimulation (TENS) mitigates deficits of muscle function due to pain, it is unclear whether TENS improves gait mechanics. Each of 15 participant (24±3yrs, 71±12kg, 178±7cm) was assigned to the TENS or matched placebo group (23±2yrs, 72±14kg, 177±9cm). Participants underwent 3 different experimental saline infusion sessions (hypertonic, isotonic, control) in a counterbalanced order, separated by 48-h. Hypertonic (5% NaCl) or isotonic (0.9% NaCl) saline was infused into the infrapatellar fat pad for 50-min. No infusion was administered to the control session. Participants and investigators were blinded to the saline solution. A 20-min TENS or placebo treatment was administered, which was blinded to participants. Gait kinematic data were collected using the high-speed video (240 Hz) and force-sending tandem treadmill (1200 Hz) at each time interval (baseline, infusion, treatment, post-treatment). Functional ANOVA (α=0.05) were used to evaluate difference between 2 groups (TENS, placebo) over time. Pairwise comparison functions with 95% confidence interval were plotted to determine specific difference. Hypertonic saline infusion (pain) resulted in increased (1) ankle dorsiflexion (38-75% of stance), (2) knee valgus (20-40%), (3) knee flexion (40-90%), (4) hip adduction (72-100%), (5) hip flexion (50-90%). However, there was no group x time interaction for all kinematics. Altered gait strategies due to pain may play a role in long-term compensation that could have consequences for the joint. TENS treatment, however, did not acutely reduce the deficits in aforementioned kinematic variables.

Listed In: Biomechanics, Gait, Neuroscience, Physical Therapy

Background: Patellofemoral pain (PFP) is a common condition seen in orthopedic practice. A commonly cited hypothesis as to the cause of PFP is increased patellofemoral joint (PFJ) stress secondary to abnormal lower extremity kinematics (ie. excessive hip internal rotation and knee valgus). However, the influence of these motions on PFJ contact mechanics is unknown. Purpose: To assess the influence of hip rotation and knee valgus on PFJ stress using finite element (FE) analysis. Methods: Patella cartilage stress profiles for a healthy participant were quantified utilizing a subject-specific FE model. Input parameters included: joint geometry, quadriceps muscle forces, and weight-bearing PFJ kinematics. Using a nonlinear FE solver, quasi-static loading simulations were performed to quantify patella cartilage stress during a static squatting maneuver (45° knee flexion). To simulate hip rotation (0-8°) and knee valgus (0-12°), the femur and tibia were rotated in the transverse and frontal plane respectively in 2° increments. Results: Increasing hip rotation resulted in a linear increase in patella cartilage stress. In contrast, increasing knee valgus resulted in a decrease in patella cartilage stress. The combination of hip rotation and knee valgus did not result in higher PFJ cartilage stress compared to isolated hip rotation. Conclusions: Patella cartilage stress appears to be influenced to a greater degree by hip internal rotation as opposed to knee valgus. Surprisingly, higher degrees of knee valgus resulted in decreased cartilage stress (in the absence of hip rotation). Our finding supports the premise that persons exhibiting excessive hip internal rotation may be pre-disposed to elevated patella cartilage stress.
Listed In: Biomechanics, Gait, Physical Therapy

Higher ACL injury frequencies have been reported on synthetic turfs compared to natural turfs. However, assessments of cleat stud type on lower extremity biomechanics worn on these surfaces are limited. The purpose of this study was to examine the knee biomechanics of a non-studded running shoe (RS), a football shoe with natural turf studs (NTS), and with synthetic turf studs (STS) during single-leg land-cut and 180°-cut tasks on synthetic turf. Fourteen recreational football players performed five trials of 180°-cut and land-cut tasks in the three shoe conditions on an infilled synthetic turf. Knee biomechanics were analyzed using a 2x3 (task x shoe) repeated measures ANOVA followed by post-hoc paired samples t-tests (p<0.05). For the 180° cut, 1st peak internal knee adduction moments were increased in RS and STS compared to NTS (Table) and in 1st peak knee extensor moments in RS compared NTS and STS. The peak negative knee extensor power was increased in RS compared to NTS and STS. The land-cut had significantly greater peak extensor moments, sagittal plane powers, and abduction angles, and significantly lower adduction moments compared to the 180°-cut. As expected, the land-cut movement involved increased power absorption, power generation, and extensor moment compared to the 180°-cut. However, shoe effects lie only in the 180°-cut. Decreased medial ground reaction force1, knee adduction and extensor moments in NTS suggest the knee may be in a safer environment using these studs during cutting maneuvers. Reduced knee adduction moments in NTS could have implications in non-contact ACL injury.
Listed In: Biomechanics, Gait, Sports Science